Дисертації з теми "NiAl-Al2O3"
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1
Bihr, Jean-Claude. "Le Matériau composite NiAl-Al2O3." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1996. http://tel.archives-ouvertes.fr/tel-00149385.
Анотація:
Les industries aéronautiques tentent de mettre au point de nouvelles structures plus résistantes et surtout réutilisables en vue d'accélérer la conquête de l'espace. A cet effet, le matériau composite à matrice intermétallique NiAl renforcée par des fibres longues d'alumine semble prometteur et adapté à ces applications. Les travaux présentés concernent a la fois l' élaboration du composite par infiltration liquide sous pression de gaz et l'étude du couplage fibre-matrice (F/M), phénomène prépondérant qui gouverne les caractéristiques macroscopiques du matériau. Le couplage a été étudié par le biais de la microscopie électronique en transmission et de la spectroscopie de photo-électrons X ; une approche thermodynamique du couplage a ete obtenue au travers de l'étude de mouillabilite du renfort par la matrice. Ces différentes caractérisations des interfaces et interphases sont correlées les unes avec les autres pour permettre une compréhension globale des phénomenes de couplage a l'interface F/M.
2
Zhong, Yunlong [Verfasser]. "Interface Structure, Interface Properties and Tensile Properties of Single Crystalline Al2O3 Fiber Reinforced NiAl and IP75 Matrix Composites / Yunlong Zhong." Aachen : Shaker, 2008. http://d-nb.info/1164341332/34.
3
Troncy, Romain. "Synthesis and high-temperature behavior of self-restoring coatings." Thesis, La Rochelle, 2021. http://www.theses.fr/2021LAROS034.
Анотація:
La sélection des matériaux utilisés dans les parties chaudes des moteurs aéronautiques ou dans les centrales de production d’énergie est devenue un enjeu crucial au vu des impératifs écologiques et économiques. L’un des composants critiques de ces systèmes sont les aubes de turbine dont la tenue mécanique est assurée par la nature des substrats employés (aciers et superalliages à base nickel). Cependant, leur tenue environnementale nécessite l’application de revêtements protecteurs source d’Al capables de former de barrières d’oxyde (Al2O3) imperméables à l’attaque externe par oxydation et corrosion aux hautes températures. L’épuisement de l’Al pour former l’oxyde et par interdiffusion avec le substrat conduit inexorablement à la perte de protection. Ainsi, des structures spécifiques de revêtement telles les barrières de diffusion peuvent alors être mises en place pour augmenter la durée des vies des aubes au détriment de leurs propriétés mécaniques et de coûts élevés de fabrication et environnementaux. Durant cette étude, des nouvelles voies originales de synthèse des revêtements de diffusion d’aluminium « autorégénérants » ont été étudiées. Ces revêtements disposent d’une structure composite, avec une matrice de phases intermétallique (NixAly) renforcée par des microréservoirs constitués d’un cœur (NixAly) et d'une paroi en Al2O3 à travers laquelle l’Al du cœur peut ravitailler la matrice et maintenir une concentration globale en Al suffisamment élevée dans la matrice capable de former la couche externe protectrice d’Al2O3.Nos études démontrent que les réactions aluminothermiques entre du NiO et l’Al permettent de former un tel revêtement autorégénerant avec une barrière de diffusion à l’interface substrat/revêtement lorsque le Ni est initialement pré-oxydé à 1100°C pendant 2h. Néanmoins, aucun compromis n’a été trouvé pour former des revêtements sans NiO résiduel qui pourrait compromettre l’adhérence du revêtement au substrat. En revanche, une voie électrochimique permet d’incorporer de microparticules d’Al3Ni2 dans des électrodépots de Ni. A la suite d’un traitement d’aluminisation par barbotine, les microparticules préoxydées s’incorporent de manière homogène dans un revêtement de β-NiAl. Après traitement d’oxydation isotherme à 1000°C durant 48h, ce revêtement par voie électrodéposition + aluminisation présente une teneur en aluminium supérieure à 40 at%, ce qui est supérieur à un revêtement de diffusion absent de microréservoirs démontrant ainsi le caractère autorégénerant des nouveaux revêtementsThe selection of materials used in the hot parts of aeronautical turbines or in power plants has become a crucial issue in view of ecological and economic imperative. Turbine blades are amongst the most critical components. Their mechanical resistance is ensured by the substrate itself (steels and Ni alloys and superalloys). However, their low environmental resistance requires the application of protective coatings delivering Al to form oxide barriers blocking the external oxidative and corrosive attack. Upon exposure at high temperatures, Al depletes from the coating by oxidation to grow the oxide scale and by interdiffusion with the substrate’s elements resulting in the loss of protection. Some specific coating structures like the diffusion barriers have been investigated in the past but the overall mechanical properties are lowered and the fabrication and environmental costs are high. Therefore, a pioneering and original investigation has been conducted to synthesize “self-regenerating” aluminum diffusion coatings. These coatings are characterized by a composite structure whereby the matrix made of NixAly intermetallic phases is strengthened with microreservoirs made of NixAly core and an Al2O3 shell through which Al diffuses out to maintain the adequate Al concentration in the matrix, hence to stabilize the external protective Al2O3 scale.Our studies demonstrate that the aluminothermic reactions between NiO and Al lead to the formation of such a self-regenerating coating with an interdiffusion barrier at the coating/substrate interface whenever Ni is preoxidized at 1100°C for 2h beforehand. However, all the coatings sintered through this method possess residual NiO, which may compromise their adherence to the substrate. In contrast, the use of electrochemical methods allows to incorporate Al3Ni2 microparticles in the NI electrodeposits. With a subsequent slurry aluminizing treatment, the preoxidized particles incorporate homogeneously in a β-NiAl coating matrix. After exposure at 1100°C for 48h in air, the Al content in the self-regenerating coatings is greater than 40 at% as opposed to the micro-reservoirs-free aluminide coating allowing to demonstrate the self-regenerating property of these new coatings
4
Tyler, Samson. "Modelling the Effects of Element Doping and Temperature Cycling on the Fracture Toughness of β-NiAl / α-Al2O3 Interfaces in Gas Turbine Engines". Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23685.
Анотація:
This document describes work performed related to the determination of how elemental additions
affect the interfacial fracture toughness of thermal barrier coatings at the bond coat/thermally grown oxide interface in gas turbines. These turbines are exposed to cyclical thermal loading, therefore a simulation was designed to model this interface in a temperature cycle between 200 K and 1000 K that included oxide growth between 2 μm and 27 μm. The fracture toughness of this interface was then determined to elucidate the function of elemental additions. It was shown that minimal concentrations of atomic species, such as hafnium and yttrium cause notable increases in the toughness of the bond coat/thermally grown oxide interface, while other species, such as sulphur, can dramatically reduce the toughness. Furthermore, it was shown that, contrary to some empirical results, the addition of platinum has a negligible effect on the fracture toughness of this interface.
5
Shih-Kai, Weng, and 翁勢凱. "Wear Resistance of NiAl/Al2O3 Composites." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/17950341821774896099.
Анотація:
碩士國立臺灣大學
材料科學與工程學研究所
88
The objective of this work is to study the sliding wear behavior of NiAl/Al2O3 composites. The composites were prepared by hot-pressing in vacuum. The NiAl/Al2O3 composites were then brazed onto a AISI 1045 carbon steel in vacuum to enhance the heat relief produced during wear test. Dry pin-on-wheel wear test were conducted, SKD11 and diamond wheels are used as contact surface materials. The wear behavior and the work hardening on the surface were investigated. The result shows that the wear mechanisms against SKD11 wheel are dominated by abrasive and adhesive wear. The wear rates of composites are decreased with the increase of Al2O3 content; however, the friction force and mean reference temperature are increased with the increase of Al2O3 content. The wear mechanism against diamond wheel is dominated by abrasive wear, but there is no relationship with the increase of Al2O3 content. The wear rates of the composites containing 100~80 v% NiAl are low due to the block and blunt of the diamond wheel induced by the presence NiAl debris. The composites containing 60~40 v% NiAl have the poorest wear resistant because the pull-out of NiAl and Al2O3 particles. However, the wear rates of composites containing below 40 v% NiAl show no relationship with the NiAl content. It may be related to the pile-up of Al2O3 particles during wear. On the aspect of work hardening, the surface of pure NiAl is hardened by wearing against diamond or SKD11 wheels. A maximum degree of work hardening is produced against SKD11 wheel, and the degree of work hardening shows no clear trend with the increase of Al2O3 content in the NiAl/Al2O3 composites. The size of debris of the composite containing 20 v% Al2O3 content is the biggest. It’s primarily due to the composite has the highest toughness and strength.
6
TSAI, CHEN-HUNG, and 蔡政宏. "Mechanical properties of Al2O3/NiAl composite." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/71565420473299278700.
Анотація:
碩士國立臺灣大學
機械工程學系
85
Structural ceramic (also named Engineering ceramic) is a newly developedmaterial. Compared with metal for structure, it demonstrates manyexcellent physical and mechanical properties. Such as low density, lowcoefficient of expansion,low heat transfer coefficient, high Young'smodulus, high hardness, high compress strength, and good corrosion, oxidization,and creep resistance. Howrver, extreme brittleness is the primany obstacleto its application in engineering. Alumina is the typical material of ceramic. It is execellent for its high srengthand good ability to resist corrosion and oxidization. However,alumina alsopossess the weakness of low toughness.By adding reinforcement, its strengthand toughness can be improved. For example, the fracturetoughness can be increased by adding the metallic reinforcement. However, theoxidization resistance and the property of low density will be sacrificed.Therefore, it will be a target for researchers to choose areinforcement that will improve the weaknesses of the material and keep itselementary properties at the same time. Owing to its low density,easy to conduct heat, and excellent oxidization resistance,NiAl is chosen as a reinforcement in this study. To make a sample, we add NiAl particleinto alumina matrix evenly, from the mixed powder into the initial sample bydie-pressing method, and then sinter it in argon atmosphere at 1500℃. After sintering and milling, we proceed the following experiments: phase identificatinoby X-ray, measurement of mechanical and physical properties (including density,flexural strength, and fracture toughness)in room temperature, strength and toughnessof the samples after oxidization, and properties of the composite after thermalshock. By observing the microstructure of the samples, We tempt to find out thecauses that effect strength and toughness of the composit. Because of the complexity of making ceramic materials and time consumingprocess, we try to use the remaining material with other materials glued toboth ends to reduced the processing time and procedure.Thus, we can reusethe material and conduct the experiments repeatedly. Meanwhile, we comparethe data with that we got from experiment by standard sample. key words：fracture toughness, NiAl metallic compound ,methanical properties,
7
Chen, Yi-Ren, and 陳怡仁. "Preparation and oxidation behavior of NiAL/Al2O3 composites." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/47330474327285717727.
Анотація:
碩士國立成功大學
材料科學(工程)學系
86
NiAl介金屬化合物與其他超合金相比較，具有低密度、高融點、高強度 以及較佳的抗氧化性等優點，因此成為航太工業上深具潛力的結構材料。 前人曾利用粉末預先氧化方法與控制晶粒大小的方法製成NiAl/Al2O3複合 材料，該複合材料具有優於NiAl者的機械性質與高溫強度。為繼續瞭解 NiAl材料及NiAl/Al2O3複合材料在高溫時的氧化行為，本研究利用前述二 種方法製成NiAl/Al2O3複合材料，檢討預先氧化的溫度和晶粒的尺寸對於 該材料在1000℃/24h長時間高溫氧化的影響。 本研究主要以熱重分析儀 （Thermogravimetric analyzer，TGA）進行實驗，以檢測試樣在高溫氧 化時之重量增加量與增重的速率，來評定該試樣的抗氧化性質是否良好。 實驗結果顯示，NiAl/Al2O3複合材料的高溫氧化行為可分為二階段進行： 氧化開始後的十小時間，NiAl/Al2O3複合材料表面形成氧化膜的速率（即 熱重曲線的斜率）較快，十小時以後的第二階段，因氧化膜逐漸長成緻密 的保護膜使得氧化速率減緩。NiAl粉末經過適當的預先氧化而製成的 NiAl/Al2O3複合材料，其氧化速率低於NiAl材料。在本實驗中，經過分級 為7mm的NiAl粉末，再以650℃/2h預先氧化後，形成的NiAl/Al2O3燒結體 有最佳的抗氧化性。 另一方面，由於NiAl的價格較為昂貴，為降低製作 NiAl/Al2O3複合材料的成本，吾人亦嘗試以較為廉價的Ni、Al元素粉末與 強化用的Al2O3粉末為起始原料，利用反應燒結的方式來合成NiAl/Al2O3 複合材料。此實驗是藉由製程條件的改變，以尋求一個最佳的反應燒結製 程。實驗結果顯示，以2atm的Ar氣氛、15℃/min昇溫速度進行反應燒結， 所得的NiAl/Al2O3燒結體之形狀與緻密性，會比在真空下、以5℃/min昇 溫速率進行反應燒結的燒結體來的好。 然而，以反應燒結製成的最佳 NiAl/Al2O3燒結體，其相對密度僅有89.8％，導致其機械性質與抗氧化性 並不好，甚至遠低於以預先氧化法製成的緻密燒結體的性質。 Compared with other superalloys, Nickel aluminide compound (NiAl) has many advantages such as low density, high melting point, high strength, and excellentoxidation resistance. Therefore, NiAl is the most potential material for application in aerospace industry. Some works have been done by using of the methods of powder pre-oxidation and controlling grain sizes to prepare NiAl/Al2O3 composites, which have better mechanical properties and elevated temperature strength than that of NiAl. To understand continuous the monolithicof NiAl and understand the oxidation behavior of NiAl/Al2O3 composites at high temperatures, two methods prescribed above are used to produce the monolithic NiAl and NiAl/Al2O3 composites. Then, the effects of pre-oxidation and controlsof grain size on the oxidation behavior of monolithic NiAl and NiAl/Al2O3 composites at 1000℃ for 24h are investigate. The thermogravimetric analyzer is used to determined the weight gain and the oxidation rate of NiAl/Al2 O3 composites. The results show that two stages can beobserved in the oxidation behavior of NiAl/Al2O3 composites. In the first stage of initial ten hours, oxides formed on the surface of NiAl/Al2O3 composites increases with oxidation time. In the second stage, the oxidation rate becomes slower as result of formation of the dense protective layer. The oxidation rate of the NiAl/Al2O3 composites is lower than that of NiAl. In this study, the NiAl/Al2O3 composite prepared from 7 micrometer NiAl powder and pre-oxidized at 650℃/2h has the best oxidation resistance. On the other hand, for reducing the production cost, the syntheses NiAl/Al2O3 composites with cheaper Ni, Al and Al2O3 powders by the reactive sintering method are investigated in this study. The result shows that the shape and density of the reactive sintered NiAl/Al2O3 composite synthesized in 2 atm Ar atmosphere and in a heating rate 15℃/ min. to 1450℃ is better than that composites synthesized in vacuum and in a heating rate of 5℃/min. to 1400℃. However, the relative density of the best reactive-sintered NiAl/Al2O3 composites is only 89.8%, which makes the mechanical and the oxidation properties decrease.Key Words: NiAl, NiAl/Al2O3 composites, oxidation, synthesis
8
YANG, Shyh-Chyi, and 楊士奇. "High Temperature Mechanical Properties of NiAl/Al2O3 Composites." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/64590805629751039863.
Анотація:
碩士國立成功大學
材料科學(工程)學系
85
NiAl介金屬化合物具有高熔點、高楊氏係數、低密度及高抗氧化的特 性，使其在航太工業之高溫應用上，足以取代傳統的鎳基及鈦基超合金而 成為深具發展潛力的材料。但是，NiAl亦有室溫脆性及高溫強度不足的缺 點。為改善NiAl的性能，以往的研究中有以預先氧化法將Al2O3添加於 NiAl中，而提升了NiAl的室溫機械性質。甚至藉由控制NiAl基材的晶粒尺 寸，更進一步提升此NiAl/Al2O3複材的機械性質。為進一步瞭解此NiAl/ Al2O3複合材之高溫機械性質，本實驗吾人繼續採用預先氧化法，先調製 出NiAl/Al2O3粉末再將之熱壓燒結緻密後，分別以壓縮測試法及單邊缺口 誶法(SENB)檢討了NiAl/Al2O3複合燒結體的高溫壓縮強度與韌性。 實 驗結果顯示：含有16.5 vol%Al2O3之NiAl/Al2O3複合燒結體在600, 800及1000 K的0.2%應變量之壓縮應力值分別為867, 678及366 MPa，而僅 含微量3.4vol%Al2O3的試樣其相同測試條件下之壓縮應力值分別為621, 629, 304 MPa。即Al2O3含量愈多，其高溫壓縮強度愈強。由壓縮應力與 溫度關係圖可知：藉由夾頭速率的提升(由0.01 mm/min提升10倍至0.1mm/ min)或Al2O3含量的增加(由3.4vol%增至16.5vol%)，NiAl/Al2O3複合材的 脆韌轉換溫度(BDTT)提升了50~100 K。 利用SENB法以三點抗折方式量 測高溫破斷韌性的結果顯示：各試樣的破壞韌性值皆隨測試溫度之升高而 增加。NiAl /3.4 vol%Al2O3試樣在1000 K時具有本研究中最高的破壞韌 性值26.4 MPa.m1/2，而NiAl/16.5 vol%Al2O3試樣會因較多的Al2O3抑制 了NiAl的延展性，使其在1000 K時的破壞韌性值減為18.8 MPa.m1/2。 Nickel aluminide intermetallic compound (NiAl) has high melting point, high strength , low density and excellent oxidation properties. It is possible to substitute for traditional Ni-based and Ti-based superalloys and is considered as the most potential high temperature material for applications in aerospace industry. However, the major drawback of NiAl is a lack of room temperature ductility and low creep resistance. NiAl/Al2O3powders can be prepared by preoxidizing the NiAl powder. The mechanical properties of hot pressed NiAl/Al2O3 composites at room temperature is better than NiAl compound. By controlling the grain size of NiAl matrix, the mechanical properties of NiAl/Al2O3 composites were also enhanced. In this study the high temperature strength and toughness were investigated by compressive testing and SENB method. The results show the compressive strength of hot pressed NiAl/Al2O3 composites containing 16.5 vol% Al2O3 is 867, 678, 366 MPa at 0.2% compressive strain at 600, 800, 1000 K individually. The compressive strengthof samples without preoxidation is 621, 629, 304 MPa. The high temperature compressive strength increased with incressing the content of Al2O3. The brittle to ductile transition temperature of NiAl increased by increasing thecross head rate from 0.01 to 0.1 mm/min or the content of Al2O3 from 3.4 to 16.5 vol% Al2O3. All fracture toughness measurement were done in four point bending with SENB method from 600 ~1100 K. The results show that KIC values of all samplesincreased with testing temperature increased. The NiAl/3.4vol%Al2O3 compositesshow the maximum fracture toughness of 26.4 MPa．m1/2 at 1000 K in this study. However, the KIC value of NiAl/16.5vol% Al2O3 composites is only 18.8 MPa．m1/2.
9
Hsu, Hsin-Chung, and 許信忠. "Growth of C60 thin-film on Al2O3/NiAl(100) and Au-Pt bimetallic clusters on Al2O3/NiAl(100) exposed to methanol." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/53861004915873516283.
Анотація:
碩士國立中央大學
物理研究所
100
We present a scanning tunneling microscopy study of C60 films grown on Al2O3/NiAl(100) under ultrahigh vacuum conditions. The C60 islands formed on the crystalline Al2O3 have rectangular shapes whereas those on the amorphous area have irregular shapes, resembling those on NiAl(100). The long side of the C60 rectangular islands was along the direction of protrusions, which are along two directions ([001] and [010] of NiAl(100)) and perpendicular to each other.. Increasing the C60 coverage, layer-by-layer grown was found to dominate the growth. On the grown C60 films, the boundary defects caused by mismatch of C60 islands were identified. Annealing to 400 K, C60 film was still stable but became rougher; increasing the temperature to 500 K or higher, C60 film became unstable and a lot of C60 desorbed. The Au-Pt bimetallic clusters at varied coverages on Al2O3/NiAl(100) were exposed to methanol 1 L. The morphological change is not recognized. Annealing to the sample up to 170 K, coalescence and dissociation of the bimetallic clusters are not observed.
10
Gu, Don-Lin, and 古東林. "Microstructure and Mechanical Properties of the NiAl/Al2O3 composites." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/06479379492601697733.
Анотація:
碩士國立成功大學
材料科學及工程學系
87
The intermetallic compound NiAl has potentials as a high temperature structural material because of its high melting point, low density, and excellent oxidation resistance. However, some disadvantages of NiAl which needs solving are brittleness at room temperature and low creep resistance. To improve the mechanical properties of NiAl, adding second phase to from intermetallic matrix composites is a practicable direction . It has been reported on "Pre-Oxidation Method", which shows NiAl/Al2O3 composites have better room temperature mechanical properties than that of NiAl. So it is worth studying further. In this study, as received NiAl powder and oxidized NiAl/Al2O3 powder were dry ball milled for a long time, and then hot-pressed in vacuum. The effects of ball milling on the NiAl/Al2O3 composite powder and the microstructures and mechanical properties of the hot pressed NiAl/Al2O3 composites were investigated. The results of the experiment show that both as received NiAl powder and pre-oxidized NiAl/Al2O3 powder oxidizes, refines, and strains after ball milling , and their particle size distributions are bimodal distributions. α-Al2O3 disperses in the grain boundary and within the grain of the NiAl/Al2O3 composites. As the ball milling time increases, NiAl/Al2O3 composites show refinement of grain size and increase in the content of α-Al2O3. Fracture mode of NiAl/Al2O3 transforms from intergranular mode to transgraular mode as the content of α-Al2O3 increases, and it benefits to increase the room temperature mechanical properties of NiAl/Al2O3 composites.
11
Chiang, Chao-I., and 江昭毅. "Patterning Co Nanoclusters on Thin Film Al2O3/NiAl(100)." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/3fx4vp.
Анотація:
碩士國立中央大學
物理研究所
94
We observe uniform and sizable Co nanoclustres grown by vapour deposition are highly aligned by protrusion structures of the crystalline Al2O3, which are grown on NiAl(100) substrate. Through thermal treatments, we can control the crystalline Al2O3 films and consequently pattern the Co nanoclusters into quasi-lattice or linear, T-shape and rectangular cluster chains with various lengths as well as widths, from single values to multiples of the cluster’s diameter. Thermal stability tests show the patterns are robust as they are sustained even when the Co nanoclusters are flashed to 750 K. Moreover, the patterns can be further refined by using STM tips. The results imply potential applications in both fundamental and applied researches for electronic and magnetic nanodevices as well as catalysis. Experiments were done in an UHV chamber with a base pressure lower than 10-9 torr and results were displayed by scanning tunneling microscopy (STM). In this thesis, we will give a literature survey first to show previous experiments about the nanoclusters. It also shows the known knowledge of NiAl(100) and Al2O3 films. Then, experimental equipments and experimental procedure will be presented. Finally, we will discuss the experimental results which include each step of the experiments displayed by STM.
12
Wang, Cheng-Ting, та 汪政廷. "Probing the structures underneath the surface of θ-Al2O3/NiAl(100) and Au-Pt bimetallic clusters supported on the θ-Al2O3/NiAl(100)". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/23837018575989242979.
Анотація:
碩士國立中央大學
物理研究所
98
We have probed the structures beneath the surface of thin film θ-Al2O3/NiAl(100) and Au-Pt bimetallic clusters on θ-Al2O3/NiAl(100) with a scanning tunneling microscope (STM). With different settings, electrons tunnel from tip to different oxide layers and show the morphology of the structures beneath the surface. It is understood by the related energy level and the unoccupied states of the sample. On θ-Al2O3/NiAl(100), Au and Pt atoms are sequentially vapor deposited at 300 K. The ratio for the later deposited metal joining existing clusters depends on the coverage. In the presence of 0.06 ML Pt on θ-Al2O3/NiAl(100) surface, the ratio for the later deposited Au joining the existing clusters is decreased from 43 % to 21 %. Most of the Au atoms form new pure clusters; in contrast, the ratio is increased on 0.22 ML Pt/θ-Al2O3/NiAl(100) surface from 52 % to 71 %. For Pt/Au/θ-Al2O3/NiAl(100), the ratio for the later deposited Pt (0.17 ML) joining existing Au clusters (0.13 ML) is 58 %. After annealing to 450 K, the coverage decreases from 1 ML to 0.3 ML. After annealing to 700 K, the coverage is 0.2 ML. Most of the metals diffuse to the substrate.
13
Lin, Cheng-shun, and 林正勛. "Using RHEED、LEED and AES to investigate the growing situation and geometric structure of Al2O3 on NiAl(100) and Co on Al2O3/NiAl(100)." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/b58r27.
Анотація:
碩士國立中央大學
物理研究所
94
The growth and structures of aluminum oxides on NiAl(100) have been investigated by RHEED(reflection high energy diffraction) ,complemented by LEED (low energy electron diffraction) ,AES (Auger electron spectroscopy) and STM (scanning tunneling microscopy). Crystalline θ-Al2O3 phase grows through gas-phase oxidation on the NiAl(100) substrate with its a and b-axes parallel to [0-10] and [001] direction of the substrate,respectively,forming a (2 × 1) unit cell.Whilst,three-dimensional nano-sized NiAl(100) protrusions and Al2O3,NiAl (011)clusters were found to co-exit at the surface,evidenced by extraordinary transmission spots superposed to the substrate reflection rods in the RHEED patterns,particularly,the NiAl (011) clusters develop with their (011) plane parallel to the NiAl(100) surface,and [100] axis parallel to the [0-10] direction of the substrate.STM observation combined with information from AES and TPD (temperature programmed desorption) suggest the formation of these 3D structures is closely associated with partial decomposition of the crystalline oxide during annealing.On the other hand,smoother (2×1) oxide islands with thickness close to a complete monolayer of θ-Al2O3 can be formed on NiAl(100) by electro-oxidation,in contrast with the large crystalline films formed by gas-oxidation. Moreover,the Co nanoclusters grown from vapour deposition on thin film Al2O3/NiAl(100) have been studied by reflection high energy electron diffraction (RHEED),scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES).The results show that the annealed Co nanoclusters,with mean diameters of 2.4 ,3.4 ,5.8 nm and heights of 0.7 ,1.5 ,1.5 nm respectively,are highly crystalline.Structural analysis based on the RHEED patterns indicate that these Co clusters,although with different sizes,have an fcc phase and grow with their (001) facet parallel to the NiAl(100).It is optimal growth for the Co clusters,as the Co fcc (001) facet is to match better with the rectangular oxygen mesh of the oxide surface even though there is an appreciable lattice mismatch.The lattice constant of the Co clusters is consequently expanded by 4-5 ％ in comparison with that of fcc Co bulk,in order to match better with the oxide surface and minimize the interface strain.The preferential formation of the Co fcc phase is also driven by such significant interfacial interaction and perhaps a relatively smaller surface free energy of the Co-fcc clusters.
14
Chang, Shu-Yu, and 張書瑜. "The thermal shock and wear resistance of Al2O3/NiAl composites." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/70295656063318883261.
Анотація:
碩士國立臺灣大學
材料科學與工程學研究所
86
Abstract The main objective of this work is to study the thermal shock resistance and wear property of Al2O3/NiAl composites prepared by hot press sintering in vacuum. Thermal cycles are performed between room temperature and 600℃/800℃ respectively by rapid quenching. The results show that the thermal shock resistance of 40Al2O3/60NiAl composite is inferior to the composites with less Al2O3 content in general. A decrease in hardness is readily appreciable for the composite with 40vol.% Al2O3 after RT/800℃thermal cycles. This is attributed to the defects accumulation. In addition, crack emanating from the hardness indentation is anisotropic in nature. It propagates fav The results of the ring-on-disk wear test under fixed load (223N) and sliding rate (0.71m/s) at room temperature show that the wear rate of Al2O3/NiAl composites decreases with increasing volume fraction of Al2O3. On the otherhand, the high alumina brick used as disk in this test shows the opposite way. However, the weight loss in both Al2O3/NiAl composites and Al2 O3 brick decreases at 300℃. For Al2O3/NiAl composites, the wear mechanisms are dominated by abrasive and adhesive wear. However, wear performed at high temperature and high load show a tribochemical reaction involved. It is evidenced by presence of NiO from X-ray analysis. Pin-on-wheel wear test show that the wear resistance of Al2O3/ NiAl composites increases with increasing volume fraction of Al2 O3, and enhanced by load increase. The major wear mechanisms of Al2O3/NiAl composites are thought to be abrasion and adhesion.
15
Lin, I.-Chiao, and 林逸樵. "The process, microstructure and mechanical properties of Al2O3/ NiAl composites." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/47192508698647106732.
Анотація:
碩士國立臺灣大學
材料科學與工程學研究所
85
Both the nickel aluminide intermetallics and the alumina are potential structural materials in high temperature applications. However, nickel aluminide exhibits a lack of ductility at low temperatures and poor strength at high temperatures, and the inherited brittleness of alumina are seen to limit the applications as a single material. To combine the physical and mechanical advantages of nickel aluminide and alumina?T瀗 Al2 O3/NiAl and Al2O3/NiAl(Fe) composites system is developed in this study. In this work, started from the powder preparation by changing the attrition time to various sintering work such as hot press sintering in vacuum and vacuum sintering, are used to prepare the Al2O3/NiAl and Al2O3/NiAl(Fe) intermetallics matrix composites (IMC). The microstructures and the mechanical properties of the composites are evaluated and presented. Besides, the grinding effects by different grinding wheel on the mechanical property are also studied. The results show that different attrition time on mixing NiAl powder had no effect on it's change in particle size. But when alumina was added more than 10Vol.%, the particle size became smaller than that of pure NiAl and NiAl(Fe). Neverthe less when the alumina content farther increased, it also produced no effect on changing the particle size. Therefore, in these two composite systems, their particle size are not sensitive to the attrition time and alumina content. A dense Al2O3/NiAl or Al2O3/NiAl(Fe) composite can be produced by hot press sintering in vacuum. By vacuum sintering, however, the composites suffer a deficiency in densification. For those Al2O3/NiAl and Al2O3/NiAl(Fe) composites prepared by hot press sintering in vacuum, the hardness, flexural strength and fracture toughness are increased as alumina are added. Furthermore, the addition of 0.25 at.% Fe into NiAl, the prepared composites demonstrate a great improvement on the mechanical properties. But the composites prepared by vacuum sintering, their flexural strength and fracture toughness are lower than the composites prepared by hot press sintering in vacuum, It is belived primarily due to low sintering density in these composites.The mechanical properties of the composites are greatly influenced by the surface condition of specimens. In this study, different grinding wheel materials with different grif size are used to prepared composites. It indicate finer grif size diamond grinding wheel (#600) produce the best surface finishing than that prepared by coarse diamond grinding wheel (#325) and other Al2O3 grinding wheel. Accordingly, the flexural strength and fracture toughness respond in the same way as surface finishing. However. composites prepared by the alumina grinding wheel of coarser grit size of 120 mesh, its surface roughness are finer than the test bars prepared by the diamond grinding wheel of grit size 140 mesh,but the flexural strength and fracture toughness deteriorated greatly than the composites prepared by the diamond grinding wheel with grit size 140 mesh.It's primarily due to the less induced defects on or under specimens surface by alumina grinding.
16
Lin, Yi-Qiao, and 林逸樵. "The process, microstructure and mechanical properties of Al2O3/ NiAl composites." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/53725752610182600198.
17
Chou, Weng-Bing, and 周文彬. "The Processing, Microstructure and Mechanical Properties of NiAl/Al2O3 Composites." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/03586935982083037333.
18
Liu, Tien-Jui, and 劉添瑞. "The study of NiAl/Al2O3 composites on microstructure and mechanical properties." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/60809780736947302656.
19
Hung, Hsu Sheng, and 洪旭昇. "Study of In-situ Formation Techanique on Al2O3-NiAl Composite Powders." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/51091686014785905655.
20
Shiu, Hung-wei, and 許紘瑋. "Catalytic properties of Au nanoclusters supported on Al2O3/NiAl (100) surface." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/82083431818454577809.
Анотація:
碩士國立中央大學
物理研究所
95
We have studied the adsorption and decomposition of methanol on well-defined supported Au nanoclusters as a model catalyst by using synchrotron-based high-resolution photoemission spectroscopy (PES). Au nanoclusters are deposited on well-ordered Al2O3 film grown on NiAl (100) through vapor deposition in the ultrahigh vacuum conditions (＜3 x 10-10 torr) at 300 K, 450 K, and 570 K. Gold nanoclusters are studied by using both PES and scanning tunneling microscopy (STM). Form STM images, Au atoms nucleated on crystalline Al2O3 films as nanoclusters and the average size of Au nanoclusters is slightly increased at the deposition temperature of 450 K. However, at 570 K deposition temperature sudden change in the average size of Au nanoclusters is observed, which is probably due to higher diffusion coefficient. To study methanol decomposition, methanol was adsorbed on Au/Al2O3/NiAl (100) at 120 K and subsequently annealed to different temperatures. In our annealing experiment we observe that the methanol C1s peak shifts toward lower binding energy with annealing temperature, which indicates more than one intermediate C-species before it decomposes to CO. We also found the activity for methanol decomposition is highly dependent on the structure of supported Au catalyst. After annealing to 310 K, a sudden shift for C1s peaks may imply that C-O scission and reforming to another hydrocarbon species.
21
Wang, Chau-jian, and 王朝建. "Alloying of Au-Pt nanoclusters on thin film Al2O3/NiAl(100)." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/wq49jk.
Анотація:
碩士國立中央大學
物理研究所
97
We have studied the adsorption and decomposition of methanol on well-defined supported Pt nanoclusters as a model catalyst and the alloying of Au-Pt nanoclusters on thin film Al2O3/NiAl(100) by using synchrotron-based high-resolution photoemission spectroscopy (PES). Pt nanoclusters are deposited on well-ordered Al2O3 film grown on NiAl (100) through vapor deposition in the ultrahigh vacuum conditions (＜3 x 10-10 torr) at 300 K. By using PES we find that the electron structure of Pt doesn’t change with Pt coverage. On annealing to 450 K the oxidized Pt form on the surface. To study methanol decomposition, methanol was adsorbed on Pt/Al2O3/NiAl (100) at 120 K and subsequent annealed to different temperatures. In our annealing experiment, the C1s peak shifts towards higher binding energy with increasing temperature, which is probably due to that the hydrocarbon-species (CHx) adsorb on Pt nanoclusters, and the hydrocarbon-species (CHx) formed at the surface at 300 K. According to the PES results, we observe evident shift for the Au-4f because of the electron transfer from Pt to Au when Au-Pt alloy formed. During the annealing procedure, the intensity of alloy decrease because of the Pt diffuse or oxidization. There are change in intensity of Pt, pure Au, and alloy signals when adsorbing methanol on (annealed) alloy cluster, which is probably due to a specific ratio of Pt to Au in alloy cluster when adsorbed methanol.
22
Ho, Jiun-Yu, and 何峻宇. "Adsorbate-induced restructuring in Au-Pt bimetallic nanoclusters on Al2O3/NiAl(100." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/66767767643519087512.
Анотація:
碩士國立中央大學
物理研究所
99
We have studied the adsorbate-induced restructuring of Au-Pt bimetallic nanoclusters on the well-defined θ-Al2O3/NiAl(100) by using synchrotron-based high-resolution photoemission spectroscopy (PES). The Au-Pt bimetallic clusters were vapor deposited on ordered thin film Al2O3 at 300 K. Upon adsorption of adsorbates, such as methanol, ethanol and cyclohexene, the Au atoms aggregate at the surface of clusters. However, we find that the CO from methanol (and/or ethanol) decomposition remains on the surface and block the aggregation of Au atoms. After annealing to 650 - 800 K, the metallic Pt become oxidized Pt and the surface of clusters is coated with alumina materials; some Au are exposed at the surface. Adsorbing the hydroxyl group (-OH) such as CH3OH and C2H5OH, the annealed Au-Pt bimetallic undergo dramatic changes in chemical state—oxidized Pt is reduced to metallic Pt, and thus Pt alloys with Au again. In contrast, no substantial alternation was found in the oxidized bimetallic clusters exposed to C6H10 which had only (CHn-) group.
23
Lee, Chien-wei, та 李建緯. "The Growth of Self-Assembled Docosanoic Acid Monolayers on θ-Al2O3 / NiAl(100)". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/43523338813741843981.
Анотація:
碩士國立中央大學
物理研究所
99
The formation of docosanoic acid (CH3(CH2)20COOH) self-assembled monolayers (SAMs) and their stability were investigated by atomic force microscopy (AFM). The growth begins with the formation of single-layer islands by exposing the sample to solution of docosanoic acid. In an initial growth stage, new islands form through nucleation and the island density increases. As adsorption continues, the heights of nucleated islands (single-layer islands) increase from 1 – 2 nm to 2 – 3 nm. This observation suggests that the densely packed islands form, so the deformation or tilting induced by AFM tip is not apparently. Finally, the individual islands coalesce decreasing the island density. We annealed the sample to the temperature ranging from 40 – 70 ℃ for varied times and placed the sample in solution to measure the stability of the docosanoic acid SAMs. In the annealing experiments, the density of bilayer islands decreased dramatically after the annealing, but the single-layer islands do not desorb. This difference is attributed to the different bonding strength at the interface: the first layer molecules are chemically bonded to the oxide; the upper layer in the bilayer islands and the bilayer islands adsorbed on the single islands are physically bonded to the lower molecular layer. The single-layer islands were randomly distributed on the surface at the beginning, and became aligned along the oxide strips after the annealing - the annealing facilitates the diffusion of the islands on the surface. In the agitated alcohol solution most single-layer films on the surface desorb but the single-layer islands are less affected, indicating disparate stabilities for these two structures. In addition, the docosanoic acid SAMs are not stable in water; they desorb continuously in water. We attribute this desorption kinetics to the competition of the hydrophobic interactions of tails and affinities between head groups and surface. Finally, we demonstrate an atypical behavior of this molecule: after annealing the bilayer islands, they formed great closed-loop lines consisting of single-layer islands. The height of these lines ranges primarily from 2 – 3 nm, and the average width is in the range of 50 – 90 nm, 2 – 3 times the diameter of a single-layer island prior to coalescence.
24
Ten, Ming-Han, and 田明翰. "STM and PES studies of metal nano-clusters on thin film Al2O3/ NiAl (100)." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/p5fy9q.
Анотація:
碩士國立中央大學
物理研究所
97
We have studied the Au nano-clusters on the well defined support by using scanning tunneling microscopy (STM) and Pt nano-clusters by using synchrotron-based high-resolution photoemission spectroscopy (PES). The nano-clusters were vapor deposited on the well-ordered Al2O3 grown on NiAl (100) in the ultrahigh vacuum environment at 300 K, 450 K, and 570 K (600K for Pt). The STM images show that the Au nano-clusters form two-dimensional (2D) clusters at small coverage. At the elevated sample prepare temperature, the quasi-2D (height of 1 – 2 atomic layers) and greater three–dimensional clusters coexist. We studied Pt nano-clusters on the well-ordered Al2O3 by using PES. The Pt 4f binding energy (BE) shifts to higher values with the sample temperature. This implies that the Pt clusters are oxidized at the higher sample temperature. The methanol was adsorbed on Pt clusters at 120 K and subsequently annealed to different temperatures. The methanol decomposes to hydrocarbon at sample temperature of annealing to 380 K. The amount of adsorption methanol was decreased with the increasing contamination.
25
Hsiao, Kai-Jen, та 蕭凱仁. "STM and RHEED Studies of Vanadium Nanoclusters Grown on the θ-Al2O3/NiAl(100)". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/3u8y4n.
Анотація:
碩士國立中央大學
物理學系
106
Reactivity and selectivity of supported metal clusters in catalytic processes can be varied by controlling the cluster size. The size effect is thus centered in the studies of the nanocluster’s catalytic properties. To reveal origin of the size effect, a knowledge of the atomic structures of the nanoclusters is essential. The present work is devoted to controlling the size and resolving the structures at atomic level of vanadium (V) nanoclusters supported by ordered θ-Al_2 O_3 thin film grown on NiAl(100). We investigated the growth and thermal stability of V nanocluster grown on deposition of V vapor onto thin film θ-Al_2 O_3/NiAl(100) at 300 K, under ultrahigh vacuum conditions and with scanning tunneling microscope (STM) and reflection high energy electron diffraction (RHEED).The size of the V clusters increased with coverage: the mean diameter increased from 1.56 nm up to 2.07 nm, and the mean height from 0.46 nm to 0.66 nm at 300k. At low coverage (< 0.88 ML), the island density and average size of clusters increases with the coverage; at larger coverages (> 0.88 ML), the diameter does not change while the height increases significantly, accompanied with a slightly increase of cluster density. V nanoclusters become smaller after annealing to 450 K. With the temperature increasing to 570 K and 700 K, V atoms form larger clusters. The V clusters are structurally ordered, having a bcc phase, with their (110) plane parallel to the Al2O3(100) surface, and with [001] axes parallel to [0-10] direction of the Al2O3(100) (V(110)[001]//Al2O3(100)[0-10]). The lattice constant increases with the coverage and decreases with the annealing temperature.
26
Wen, Wen-Hua, and 溫文華. "Atomic Structures and Electro-catalytic Properties of Pt Nanoclusters on Thin Film Al2O3/NiAl(100)." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/79424594509890548453.
Анотація:
碩士國立中央大學
物理研究所
95
The Pt nanoclusters grown from vapour deposition on thin film Al2O3/NiAl(100) have been studied by reflection high energy electron diffraction (RHEED), scanning tunnelling microscopy (STM), and Auger electron spectroscopy (AES). The results show that the Pt nanoclusters (with a mean diameter of 2.25 nm and height of 0.4 nm) are highly crystalline and their structures and phases are significantly affected by the oxide substrate. Structural analysis based on the RHEED patterns indicates that Pt clusters, although with different sizes, have an fcc phase and grow with their (001) facets parallel to the NiAl(100) surface, and with [110] axis along the [0-10] direction of the bulk NiAl(100). It is an optimal growth as the Pt fcc (001) facets match better with the rectangular oxygen mesh of the oxide surface. The lattice constant of the Pt clusters is expanded by about 5 % (4.12 Å) relative to that of fcc bulk Pt (3.92Å), as the Pt fcc (001) plane has better lattice match with the oxide surface. The electro-catalytic properties of the Pt/Al2O3/NiAl(100) electrode for methanol oxidation and its kinetic characterization were investigated by cyclic voltammetry (CV), RHEED, AES and scanning electron microscopy (SEM). We observed excellent electro-catalytic activity. The Pt nanoclusters have been sintered under the CV conditions. The result exhibits that the aggregated size of Pt nanoclusters is ca. 15~30nm in diameter. The structures of the aggregated Pt nanoclusters have also an fcc phase but have their (111) plane randomly oriented with respect to the oxide surface.
27
Wu, Yu-Cheng, and 武昱成. "Decomposition of methanol on vanadium nanoclusters supported by graphene/Ru(0001) and Al2O3/NiAl(100)." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/f2at56.
Анотація:
碩士國立中央大學
物理學系
106
The catalytic decomposition of methanol (CH3OH) is extensively investigated because the principal reaction is applied in direct methanol fuel cells (DMFC), which offer a prospect of efficient conversion of methanol to electricity, and because it can serve as a source of hydrogen. As the performance of DMFC or the production of hydrogen is governed largely by the catalyzed reaction, a knowledge of the detailed reaction kinetics and a correlation between reactivity and structure of the catalysts are desirable. To respond to the demand, we investigated the adsorption and reaction of methanol-d4 (CD3OD) on vanadium (V) nanocluster supported on graphene grown on Ru(0001) single crystal and θ-Al2O3/NiAl(100), under ultrahigh vacuum conditions and with infrared reflection absorption spectroscopy and temperature programmed desorption. TPD results shows the distinct desorption of HD, D2 and methane from the surface around 400 K; there is no any CO desorption feature was found indicating CO bond scission along with dehydrogenation. The IRAS results show the C-O bond scission of methanol-d4 or methoxy start around 180 K. From TPD and IRAS results we have two different guess for the methanola-d4 reaction route on the V/Al2O3/NiAl(100). First, on the V surface the O-D bond scission happen and as the temperature reach to 180 K the C-O bond scission of methoxy takes place. The other guess is O-D bond scission after the C-O bond scission, thereafter; all the products dehydrogenated further to atomic oxygen, deuterium and carbon then diffused into V nanoclusters or substrate. For methanol-d4 on the V nanoclusters/graphene/Ru(0001), the TPD spectra show desorption of methanol-d4 only. Further, the vibration of CD3 from the IRAS spectra has a red shift reveal the C-O bond scission of methanol-d4. It seems that methanol-d4 decomposes on the V nanoclusters while all the products diffuse into the substrate.
28
Chao, Chen-sheng, and 趙振盛. "Methanol Decomposition on Pt Nanoparticles supported by Al2O3/NiAl(100):A combined IRAS and TPD study." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/05446266090226580118.
Анотація:
碩士國立中央大學
物理研究所
100
Methanol decomposition on Pt nanoparticles supported by Al2O3/NiAl(100) as a model system is studied by IRAS and TPD. The Pt nanoparticles are grown from vapor deposition. Two channels of methanol decomposition are revealed: dehydrogenation and C-O bond scission. The adsorbed methanol are dehydrogenated to CO first at low-coordinated Pt sites, at 150 K on Pt(100) clusters and 200 K on Pt(111) clusters, whereas both terrace and low-coordinated Pt sites are reactive toward the dehydrogenation, despite of the cluster size. The produced CO per surface Pt on the clusters are 2 - 6 times more than those on the single-crystal counterparts. Additionally, the co-adsorbed atomic hydrogen from dehydrogenated methanol prevent CO from dissociating further to elemental carbon. In the alternative reaction channel, the C-O bond break to form intermediate CH3; the CH3 combine with the atomic hydrogen above 300 K to form methane, rather than dehydrogenating to other hydrocarbons. The C-O bond scission channel exhibits evident dependence on the lattice constant of the clusters: the reaction probability declines when the lattice constant decreases with the cluster size or coverage. The CO blocking experiments suggest that not only the atop sites but also the bridge and/or hollow sites are reactive toward the two reaction channels. The two reaction channels are also observed for methanol adsorbed on oxidized Pt (Pt2+) nanoclusters. The oxidized Pt clusters grown at 300 K and annealed to 650 K are partially encapsulated by the alumina, and only 30 % bare Pt remain (low-coordinated Pt). The dehydrogenation to CO starts at 150 K, resembling that on the pristine Pt clusters, but the produced CO per surface Pt on the oxidized clusters are only 50 % of those on the pristine Pt clusters. In contrast, the oxidation of Pt has little effect on the C-O bond scission: the produced methane per surface Pt are similar on both oxidized and pristine clusters. Moreover, CO dissociation is enhanced on the oxidized low-coordinated Pt, which occurs above 200 K, significantly lower than that on the pristine low-coordinated Pt (500 K).
29
HSU, PO-WEI, and 徐柏瑋. "RHEED Studies on Structures of Rh and Rh-Au Bimetallic Nanoclusters on Thin Film Al2O3/NiAl." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/64348118120285547710.
Анотація:
碩士國立中央大學
物理學系
101
The Rh, Au and Rh-Au bimetallic nanoclusters grown from vapor deposition on thin film θ-Al2O3/NiAl(100) have been studied by reflection high energy electron diffraction (RHEED). The results show that the Rh and Rh-Au bimetallic nanoclusters are highly crystalline and their structures and lattice constant are significantly affected by the oxide substrate. Structural analysis based on the RHEED patterns indicates that Rh and Rh-Au bimetallic nanoclusters have a fcc phase and grow with their (001) facets parallel to the θ-Al2O3(100) surface, and with [110] axis along the [010] direction of the θ-Al2O3(100). It is an optimal growth as the fcc (001) facets match better with the oxide surface. The lattice constant of the Rh nanoclusters (3.90 – 4.04 Å) is expanded relative to that of fcc bulk Rh (3.80 Å). The lattice constant decreases with the coverages and annealing temperature. Annealing the Rh nanoclusters at coverage higher than 1.9 ML to the temperature higher than 800 K leads to the ordered intensity modulation spots. The modulation spots imply the substrate become rough. The Al2O3 and the NiAl are structurally modified by Rh nanoclusters. Nevertheless, the reciprocal lattice spots of Rh nanoclusters are still observed in the RHEED patterns, indicating some of Rh nanoclusters remain on the substrate. The Au nanoclusters grown onto the oxide surface are structurally ordered, having a fcc phase and growing with their facets either (111) or (001) parallel to the Al2O3(100) surface at room temperature. The lattice constant of the Au nanoclusters is expanded by about 3 % (4.2 Å) relative to that of fcc bulk Au (4.08 Å). After annealing above 730 K, the Au nanoclusters grow in a preferred orientation, Au(001)[110]||Al2O3(100)[010]. The diffraction pattern becomes fainter at higher annealing temperature (900 K), as some of Au diffuses into the substrate. The structure of the bimetallic nanoclusters is identical to that of the Rh nanoclusters. The lattice constant of the bimetallic nanoclusters is closer to that of the pure Rh nanocluster, rather than that of the pure iv Au nanoclusters. The structure of Rh-Au bimetallic nanoclusters is thus dominated by Rh. Annealing the sample above 800 K, the RHEED patterns show modulation spots but no obvious diffraction spots from the bimetallic nanoclusters. The Al2O3 and the NiAl are structurally modified by Rh-Au bimetallic nanoclusters. There are just few bimetallic nanoclusters remaining on the substrate, so no obvious diffraction spots from the bimetallic nanoclusters are exhibited.
30
Wu, Ming-che, and 吳明哲. "Characteristics of brazing Al2O3/NiAl composites to medium carbon steel and their applications on turning tool." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/13783763017081723359.
Анотація:
碩士國立臺灣大學
材料科學與工程學研究所
88
Abstract Al2O3/NiAl composites, which prepared by hot press sintering, with excellent mechanical properties can be reproduced in this study. Al2O3/NiAl composites can be brazed with SAE 1045 successfully by active filler metal in vacuum furnace. Regarding to the interface characteristic of the braze joint in this study, the Al2O3 content of the composites affects the diffusion behavior of titanium in the joining interface. Thus, the microstructure of the interface becomes different as the Al2O3 content of the composites changes. The composites composition and the brazing temperature affect the interface microstructure. The composites composition is the major effect on the interface microstructure. Regarding to the fracture behavior of the braze joint in this study, the microstructure of the joining interface affects the fracture mode. When the NiAl content of the composite more then 60 vol.%, fracture occurs adjacent to the interface of SAE1045 substrate and the filler metal. The fracture surface contains mainly Ag-riched phase and Cu-riched phase. Ag-riched phase plays the dominant role on the fracture. However, when the NiAl content of the composite less than 60 vol.%, fracture occurs adjacent to the interface of the filler metal and the composite. The fracture surface contains mainly NiAl、Al2O3 and Ag-riched phase. Regarding to the shear strength of the braze joint in this study, shear strength is relative to the composites composition and the fracture mode. The shear strength of fracture modeⅠ is greater than that of fracture modeⅡ and has the average shear strength of 250 MPa between NiAl 60 vol.% and 100 vol.% composites braze joint. The shear strength of fracture modeⅢ is greater than that of fracture modeⅡ. Because the filler metal overflows around the composites, this overflow filler metal deflects the crack. So most fracture joints are fracture modeⅡ. The average shear strength of fracture modeⅢ is 300 MPa. The average shear strength of total braze joints is 200 MPa. Using active filler metal(Ticusil®) and various Al2O3/NiAl composites as thermal expansion buffer, NiAl can be brazed to Al2O3 in a joint successfully. Al2O3/NiAl composite was used as a turning tool to evaluate its feasibility in some important engineering metallic materials. Single turning operation was performed on those materials, including Al, Cu, brass, cast iron, steel and stainless steel. Preliminary study shows composite with 60vol% or 40 vol% NiAl can be used in turning operation without major difficulty. The general wear was found in operation on brass and cast iron. Feeding depth is more sensitive to wear than that of distance traveled. However, for tough copper, ultralow carbon steel and stainless steel, a chipped-off zone near the side cutting edge is generally seen. This is attributed to the poor back rack angle preparation as evidenced by a hindered continuous chip flow, particularly in stainless steel. “Red hot” overheating can sometimes be observed during operations, but it does no harm in composites. This specific high temperature stability feature in Al2O3/NiAl composites is proved in study. Key words﹕Al2O3/NiAl composites、active filler metal、brazing、interface、microstructure、joining shear strength、turning tool、turning、back rack angle
31
Huang, Jie-Yung, and 黃絜詠. "Nanowires from Aligned One-dimensional Arrays of Co Nanoclusters on Al2O3 Grown on Vicinal NiAl Surfaces." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/335szf.
Анотація:
碩士國立中央大學
物理研究所
96
We present a simple, self-organized approach for synthesis of arrays of supported metal nanowires. By oxidizing NiAl surfaces vicinal to the (100) plane titled along the crystallographic direction [010], we produce ordered θ-Al2O3 thin-films exhibiting highly uniform protrusion stripes which propagate uniquely in crystallographic direction [001] of the NiAl and attain length of micrometer-scale. These protrusions are preferential nucleation centres for vapor-deposited metal; the nanoclusters grown from vapor-deposited metal are thus aligned and form one-dimensional arrays along the [001] direction. The Co cluster arrays form readily nanowires with a width as small as 3 nm and length up to micrometers.
32
Adelt, Maik [Verfasser]. "Untersuchungen zur Plasmonenanregung von Silber- und Goldteilchen auf Al2O3/NiAl(110) mittels Kathodolumineszenz / vorgelegt von Maik Adelt." 2000. http://d-nb.info/959565582/34.
33
Hung, Ting-Chieh, and 洪碇傑. "Methanol Decomposition on Rh Nanoclusters supported by Al2O3/NiAl(100)：A combined IRAS, TPD and PES study." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/j9s37e.
Анотація:
碩士國立中央大學
物理學系
102
Methanol decomposition on Rh nanoclusters supported by Al2O3/NiAl(100) as a model system is studied by IRAS, TPD and PES. The study contained two parts: surface structures of Rh clusters probe with CO and methanol decomposition on Rh nanoclusters. The Rh nanoclusters are grown from vapor deposition. The IRAS spectra with CO as a probe show that the CO adsorbed on on-top site of Rh nanoclusters; no other site such as bridge or hollow site have been detected. The CO TPD spectra show that CO desorbed with two distinct peaks, one at 430 K, which is observed for CO on Rh single crystal results and the other at about 360 K, which is observed for CO on small Rh clusters. The PES spectra show that the CO dissociation rate ranges between 21 and 55 %, depending on the coverage and hence the size of the clusters. For the clusters annealed to 700 K, the IRAS spectra show the same CO absorption band but the CO TPD spectra show the proportion of low temperature desorption increases. We argue that the desorption temperature depends on the cluster size. Adsorbed methanol was dehydrogenated on the nanoclusters. The dehydrogenation to CO began below 200 K, and some of the CO formed from the dehydrogenated methanol dissociated into atomic carbon. Our PES results confirm that about 21 - 55 % of molecularly adsorbed CO dissociates into atomic carbon, depending on the size of the clusters. The produced CO desorbed above 300 K and D2 from methanol-d4 above 200 K; no intermediate species were detected in the dehydrogenation process. The PES results show the ratio of methanol dissociating into atomic C is about 43.1 ± 2.0 %. This result suggests that the probability of methanol decomposed into CO is about 86.9 ± 4.5 %. Annealing the sample to 700 K does not result in oxidation of the Rh clusters. The ratio of CO TPD desorption intensities from dehydrogenated methanol and molecularly adsorbed CO on the annealed Rh clusters is greater than that on the pristine Rh clusters. For 1 ML Rh, the ratio increases from 47.2 ± 1 % to 54.4 ± 10 %, and for 4 ML Rh, the ratio increases from 39.9 ± 10 % to 77.9 ± 10 %. The fraction of monolayer methanol undergoing dehydrogenation on the annealed Rh clusters is also greater than that on the pristine Rh clusters. On the annealed 4 ML Rh, the fraction of methanol undergoing dehydrogenation increased to 83.9 % (from 64.9 %), consistent with the result of CO ratio.
34
Li, Yu-da, and 李昱達. "Methanol decomposition on Au-Pt bimetallic nanoclusters supported by Al2O3/NiAl(100): A combined IRAS and TPD study." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/79077603082467063374.
Анотація:
碩士國立中央大學
物理學系
101
We investigate the surface structures of Au-Pt bimetallic clusters by probe molecule CO and IRAS and TPD. Au and Pt deposited sequentially from vapor onto thin-film Al2O3/NiAl(100) at 300 K form preferentially Au-Pt intermixed bimetallic nanoclusters, despite the order of the metal deposition. For the deposition of Pt followed by Au, the deposited Au atoms prefer to decorate the edges of Pt clusters (low coordination sites) and aggregates with the following deposited Au; the 2 ML Au deposited cover only a small portion of the Pt cluster surface. For the reverse order of deposition, the deposited Pt atoms have no preferential sites and cover the Au cluster easily, but there are still few isolated Au atoms on the surface. The enhancement of infrared absorption for CO on Au sites of Au-Pt bimetallic cluster was observed. The effect indicates that the cluster surface consists of both Au and Pt atoms and the surface Au is not only coordinated to Pt but is also preferentially low coordinated. Methanol decomposition on Au-Pt bimetallic nanoclusters supported by Al2O3/NiAl(100) is studied by IRAS and TPD. Two decomposition channels are observed for methanol adsorbed on Au-Pt bimetallic nanoclusters: dehydrogenation to CO and C-O bond scission. The produced CO and D2 from methanol dehydrogenation increased in proportion to the Pt sites on the surface of Au-Pt bimetallic clusters, but the varied Pt sites of the surface change little probability of C-O bond scission. Comparing the desorption of molecularly adsorbed CO to CO from methanol decomposition on Au-Pt bimetallic clusters, we found that the produced CO amounts to about 70 - 80 % of CO saturating the clusters, smaller than that (above 90 %) on pure Pt clusters. It indicates that the productivity, number of CO produced per surface Pt sites, is smaller than that on pure Pt clusters. The pre-adsorbed CO can not prohibit entirely the dehydrogenation and the C-O bond scission of methanol, but decrease the probability of these reactions. The unblocked sites, such as bridge and hollow sites, are still reactive. The effect of alloying Pt with Au to reduce the effect CO poison is insignificant; the probability of methanol decomposition on CO-poisoned Au-Pt bimetallic clusters is similar to that on CO-poisoned pure Pt clusters.
35
Zhenhe, Liao, та 廖振和. "A STM Study of Growth of Rh and Rh-Au Bimetallic Nanoclusters on the θ-Al2O3/NiAl(100)". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/u938re.
Анотація:
碩士國立中央大學
物理學系
101
Rh and Rh-Au bimetallic nanoclusters formed through vapor deposition on the thin film Al2O3/NiAl(100) are studied by scanning tunneling microscope (STM). We investigate the growth behaviors of Rh and Rh-Au bimetallic clusters at 300 K and the effect of thermal treatments. In the studies of pure Rh clusters formed at 300 K, at low coverage (< 0.51 ML), the cluster density increases with the coverage, more noticeable than the increase of average size; at larger coverages (> 0.51 ML), the cluster density changes little while the diameter increases significantly, accompanied by a slightly increase of height. Rh clusters prefer to form 3D structures even at very low coverage (0.04 ML) and low temperature (150 K). In the studies of annealed Rh clusters formed at 300 K, for high coverages (> 1.35 ML), Rh clusters reduce to smaller ones to form an energetically more favored structure on annealing to 430 K, accompanied by increased cluster density, and then form larger clusters with lower density at 570 K; the size increases and the density decreases further at 800 K. Oswald ripening is responsible for the increase of average size and the decrease of cluster density above 570 K. The Rh-Au bimetallic clusters are formed by sequential deposition of Au and Rh on the Al2O3/NiAl(100) at 300 K. For the deposition of Au and then Rh, the deposited Rh not only joins the existing Au clusters but also forms new Rh clusters on the oxide surface; for the reverse order of deposition, all the deposited Au were incorporated in the existing Rh clusters. In the studies of thermal stability of the Rh-Au bimetallic clusters, more Au in the bimetallic clusters, more the coverage decreases (both Au and Rh) with the temperature. Both thermal-induced features of Au and Rh are exhibited. When initial amount of Rh is great (> 1 ML), the cluster density increase at 430 K, showing the feature of pure Rh clusters. For the sample with high Au-to-Rh ratio annealed above 700 K, the morphology of bimetallic clusters is similar to the pure Au clusters: broad and bimodal-like distributions of size are observed.
36
Lee, Hsuan, and 李璿. "Methanol Decomposition on Au-Rh Bimetallic Nanoclusters supported by Al2O3/NiAl(100): A combined IRAS and TPD study." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/4526t2.
Анотація:
碩士國立中央大學
物理學系
104
We probe the surface structure and composition of Au-Rh bimetallic nanoclusters on thin-film Al2O3/NiAl(100) at 300K with molecular CO, temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). For the deposition of Au onto Rh nanoclusters, the numbers of Rh sites decrease linearly with Au deposition. For the metal deposition in the reverse order, Au segregates at the surface and then forms Rh core – Au shell structure. The infrared absorption for CO on Au sites was significantly enhanced with Au deposition. We observed that no CO induces structural change for Au-Rh bimetallic nanoclusters during the CO desorption whereas CO adsorbed on Au sites suppresses the IR absorption of CO on Rh sites, despite the order of the metal deposition. For the investigation of thermal stability, we discovered that in the bimetallic clusters, the Au atoms preferentially covered Rh core at 450 K but both Au and Rh attenuated significantly at 700 K. The decomposition of methanol proceeded through dehydrogenation, primarily on Rh sites of Au-Rh bimetallic nanoclusters. The reactivity of methanol decomposition dramatically decreases for the bimetallic clusters formed by small coverages of Au ( 0.5 ML) deposited onto Rh clusters of large size (1.0 ML) because the Au atoms prefer to occupy the low-coordinated sites of Rh clusters. Nevertheless, the activation energy of methanol decomposition on the bimetallic clusters changes insignificantly. The reactivity of methanol decomposition to CO on small Rh clusters (0.25 ML) does not be change with Au deposition because all the Au atoms occupy the low coordinated Rh sites. The reactivity of methanol decomposition on the bimetallic clusters formed by Rh deposited onto Au clusters gradually attenuates with Rh deposition. The revolution of the reactivity with following Rh deposition is similar to that with Rh deposited on pure Rh clusters.
37
Yen, Hong-Yu, and 顏宏聿. "Magnetic Properties of Self-Aligned Fe, Mn Nanoparticles and Fe Capped Mn Nanoparticles on Nanostructured Template Al2O3/NiAl(100)." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/03932475087497124774.
Анотація:
碩士國立臺灣大學
物理研究所
95
Interest in magnetic nanoparticles has increased in the recent years due to the industrial applications such as the ultra-high density storage device and the fundamental interest in finite size effect. By naturally grown stripe structures with ~ 4 nm interdistance on the Al2O3 layer, Fe and Mn nanoparticles were prepared by self assembling. The surface morphology and magnetic properties were characterized by STM and MOKE, respectively. The 9~33 ML Fe and 0.1~16.9 ML Mn nanoparticles both reveal that the separation of particles decreases with increasing coverage. [1 ML is defined as the surface atom density: 1.54 × 10^15 at./cm2 on Cu(100).] The Fe nanoparticles are magnetic isotropic until 23 ML, and the twostep hysteresis loops of 23, 33 ML are ascribed to the uniaxial anisotropies with the higher order term along the stripe directions, which is supported by the Stoner-Wohlfarth simulation. Mn nanoparticles are proven to be non-ferromagnetic at 0.1~8.5 ML and there is no exchange bias with Fe capped on 3.4~16.9 ML Mn at our lowest accessible temperature ~ 130 K. For 17.6 ML Fe capped n ML Mn (n= 3.4~16.9), the drastic reduction of magnetic moments and the enhancement of coercivity were found at RT (room temperature), while at LT (150 K), the coercivity decreases unusually. The increasing roughness with increasing coverage of Mn and Fe-Mn interdiffusion account for the RT observations, and the temperature dependent reversed domain nucleation and domain wall pinning may be responsible for the LT behaviors.
38
Yen, Hong-Yu. "Magnetic Properties of Self-Aligned Fe, Mn Nanoparticles and Fe Capped Mn Nanoparticles on Nanostructured Template Al2O3/NiAl(100)." 2007. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-0307200715140000.
39
Hsia, Ching-Lun, та 夏敬倫. "A First-Principles Study of Adsorption of an Au Atom and Dimer on a θ-Al2O3/NiAl(100) Surface". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/uq7tk4.
Анотація:
碩士國立中央大學
物理學系
101
We constructed θ-Al2O3/NiAl(100) models with varied thickness (1 – 5 layers) of Al2O3 slabs on NiAl(100) slabs. We calculated the adsorption and cohesive energies for Aun clusters (n = 1 or 2) in various initial configurations and at various sites on the oxide surface. The most stable configuration for a single Au atom adsorbed on θ-Al2O3/NiAl(100) surface is the Au atom bound to the Al atom at the middle of the flat area. For an Au dimers adsorbed on θ-Al2O3/NiAl(100) surface, two kinds of stable configurations are indicated: on 2-layer, 4-layer and 5-layer θ-Al2O3 on NiAl(100), the dimer adsorbs preferentially with one Au bonded to a surface O and the other dangling, whereas on 1-layer and 3-layer θ-Al2O3 slabs, the dimer lies on the surfaces with the Au-Au bond along [010] direction and with the two Au atoms bound to the Al atoms. The adsorption energies of Au atom on NiAl-supported alumina surfaces are greater than that on pure alumina surface. These thickness-dependent adsorption properties of Au adsorbed on θ-Al2O3/NiAl(100) are discussed in four origins: (1) structural relaxation, (2) work function reduction, (3) charge transfer, and (4) density of state (DOS) shift. The structural relaxation of every layer of alumina slabs all contribute to adsorption energy. The most significant contribution is from the relaxation of the surface layer. The structural relaxation plays an important role in the adsorption energy but cannot account for all the adsorption properties. The reduction of work function of NiAl-supported alumina surface enhances the charge transfer from substrate to Au atom and dimer, and the charge transfer increases the interaction between substrate and the Aun adsorbate. The reduction of the band gap and the left-shift of DOS of Au adsorbate is another reason to cause the enhancement of adsorption energy.