Academic literature on the topic 'Tough hydrogels'

ABSTRACTIn this paper, a facile and novel method was developed to fabricate high toughness and stiffness double network hydrogels made of ionical-linked natural hydrogel and synthetic hydrogel. The synthetic hydrogel network is formed firstly, and then the gel is soaked in the ionic solution to build second network to form double network hydrogel with high toughness and stiffness. Two different natural polymers, alginate and chitosan, are employed to build rigid and brittle network and poly(acrylamide) is used as soft network in double network hydrogel. The compressive strength of Calcium alginate/poly(acrylamide) double network hydrogels is increased twice than that of poly(acrylamide) single network hydrogels, and the Ca2+ ionically cross-linked alginate is the key to improve the compressive property of double network hydrogels as a sacrificial bond. However, the chitosan/poly(acrylamide) double network hydrogels exhibit no enhancement of compressive strength comparing to poly(acrylamide) single network hydrogels.

ABSTRACTTough and responsive hydrogels have recently attracted great research interests for potential applications in artifical muscles, soft robotics, and actuators, etc. This paper overviews our recent progresses in the design and synthesis of hydrogels with very high strength and toughness, and actuators based on these hydrogels. Inorganic nanospheres, nanorods, and nanosheets are exploited as multi-functional crosslinkers to adsorb or bond with hydrophilic chains, leading to hydrogels with very high strength, toughness, fatigue resistance, and/or self-healing. Introduction of functional groups including ionic monomers and amino groups results in hydrogels reponsive to pH, ionic strength and electric field. Besides, ionoprinting has been used to change local crosslink density based on reversible chelating/decomposition of metal ions with functional groups. This process is rapid and thus enables reversible and rapid actuation of hydrogel devices. Our studies will further aim to develop sophiscated devices by assembling hydrogel actuators.

This brief review attempts to summarize research advances in the mechanical toughness and structures of double-network (DN) hydrogels. The focus is to provide a critical and concise discussion on the toughening mechanisms, damage recoverability, stress relaxation, and biomedical applications of tough DN hydrogel systems. Both conventional DN hydrogel with two covalently cross-linked networks and novel DN systems consisting of physical and reversible cross-links are discussed and compared. Covalently cross-linked hydrogels are tough but damage-irreversible. Physically cross-linked hydrogels are damage-recoverable but exhibit mechanical instability, as reflected by stress relaxation tests. This remains one significant challenge to be addressed by future research studies to realize the load-sustaining applications proposed for tough hydrogels. With their special structure and superior mechanical properties, DN hydrogels have great potential for biomedical applications, and many DN systems are now fabricated with 3D printing techniques.

Macroscopic hydrogel fibers are highly desirable for smart textiles, but the fabrication of self-healable and super-tough covalent/physical double-network hydrogels is rarely reported. Herein, copolymers containing ketone groups were synthesized and prepared into a dynamic covalent hydrogel via acylhydrazone chemistry. Double-network hydrogels were constructed via the dynamic covalent crosslinking of copolymers and the supramolecular interactions of iota-carrageenan. Tensile tests on double-network and parental hydrogels revealed the successful construction of strong and tough hydrogels. The double-network hydrogel precursor was wet spun to obtain macroscopic fibers with controlled drawing ratios. The resultant fibers reached a high strength of 1.35 MPa or a large toughness of 1.22 MJ/m3. Highly efficient self-healing performances were observed in hydrogel fibers and their bulk specimens. Through the simultaneous healing of covalent and supramolecular networks under acidic and heated conditions, fibers achieved rapid and near-complete healing with 96% efficiency. Such self-healable and super-tough hydrogel fibers were applied as shape memory fibers for repetitive actuating in response to water, indicating their potential in intelligent fabrics.

Hydrogels from biological sources are expected as potential structural biomaterials, but most of them are either soft or fragile. Here, a new strategy was developed to construct hydrogels that were both stiff and tough via the formation of the conjoined-network, which was distinct from improving homogeneity or incorporating energy dissipation mechanisms (double-network) approaches. Conjoined-network hydrogels stand for a class of hydrogels consisting of two or more networks that are connected by sharing interconnection points to collaborate and featured as follows: (i) All the composed networks had a similar or equal energy dissipation mechanism, and (ii) these networks were intertwined to effectively distribute stress in the whole system. As a specific example, a biogenic conjoined-network hydrogel was prepared by electrostatically cross-linking the chitosan-gelatin composite with multivalent sodium phytate. The combination of high compressive modulus and toughness was realized at the same time in the chitosan-gelatin-phytate system. Moreover, these physical hydrogels exhibited extraordinary self-recovery and fatigue resistance ability. Our results provide a general strategy for the design of biocompatible stiff and tough conjoined-network hydrogels due to a variety of potential cross-linking mechanisms available (e.g., electrostatic attraction, host-guest interaction, and hydrogen bonding).

In this review we highlight new developments in tough hydrogel materials in terms of their enhanced mechanical performance and their corresponding toughening mechanisms. These mechanically robust hydrogels have been developed over the past 10 years with many now showing mechanical properties comparable with those of natural tissues. By first reviewing the brittleness of conventional synthetic hydrogels, we introduce each new class of tough hydrogel: homogeneous gels, slip-link gels, double-network gels, nanocomposite gels and gels formed using poly-functional crosslinkers. In each case we provide a description of the fracture process that may be occurring. With the exception of double network gels where the enhanced toughness is quite well understood, these descriptions remain to be confirmed. We also introduce material property charts for conventional and tough synthetic hydrogels to illustrate the wide range of mechanical and swelling properties exhibited by these materials and to highlight links between these properties and the network topology. Finally, we provide some suggestions for further work particularly with regard to some unanswered questions and possible avenues for further enhancement of gel toughness.

Synthetic tough hydrogels have received attention because they could mimic the mechanical properties of natural hydrogels, such as muscle, ligament, tendon, and cartilage. Many recent studies suggest various approaches to enhance the mechanical properties of tough hydrogels. However, directly comparing each hydrogel property in different reports is challenging because various testing specimen shapes/sizes were employed, affecting the experimental mechanical property values. This study demonstrates how the specimen geometry—the lengths and width of the reduced section—of a tough double-network hydrogel causes differences in experimental tensile mechanical values. In particular, the elastic modulus was systemically compared using eleven specimens of different shapes and sizes that were tensile tested, including a rectangle, ASTM D412-C and D412-D, JIS K6251-7, and seven customized dumbbell shapes with various lengths and widths of the reduced section. Unlike the rectangular specimen, which showed an inconsistent measurement of mechanical properties due to a local load concentration near the grip, dumbbell-shaped specimens exhibited a stable fracture at the reduced section. The dumbbell-shaped specimen with a shorter gauge length resulted in a smaller elastic modulus. Moreover, a relationship between the specimen dimension and measured elastic modulus value was derived, which allowed for the prediction of the experimental elastic modulus of dumbbell-shaped tough hydrogels with different dimensions. This study conveys a message that reminds the apparent experimental dependence of specimen geometry on the stress-strain measurement and the need to standardize the measurement of of numerous tough hydrogels for a fair comparison.

Hydrogels are widely used in many commercial products including Jell-O, contact lenses, and superabsorbent diapers. In recent decades, hydrogels have been under intense development for biomedical applications, such as scaffolds in tissue engineering, carriers for drug delivery, and valves in microfluidic systems. But the scope is severely limited as conventional hydrogels are weak and brittle and are not very stretchable. This thesis investigates the approaches that enhance the mechanical properties of hydrogels and their structural applications. We discov¬ered a class of exceptionally stretchable and tough hydrogels made from poly-mers that form networks via ionic and covalent crosslinks. Although such a hydrogel contains ~90% water, it can be stretched beyond 20 times its initial length, and has a fracture energy of ~9000 J/m2. The combination of large stretchability, remarkable toughness, and recoverability of stiffness and toughness, along with easy synthesis makes this material much superior over existing hydrogels. Extreme stretchability and blunted crack tips of these hydrogels question the validity of traditional fracture testing methods. We re-examine a widely used pure shear test method to measure the fracture energy. With the experimental and simulation results, we conclude that the pure shear test method can be used to measure fracture energy of extremely stretchable materials. Even though polyacrylamide-alginate hydrogels have an extremely high toughness, it has a relatively low stiffness and strength. We improved the stiffness and strength by embedding fibers. Most hydrogels are brittle, allowing the fibers to cut through the hydrogel when the composite is loaded. But tough hydrogel composites do not fail by the fibers cutting the hydrogel; instead, it undergoes large deforming by fibers sliding through the matrix. Hydrogels were not considered as materials for structural applications. But with enhanced mechanical properties, they have opened up novel applications. This thesis aims to investigate the broader applications, well beyond those investigated so far. We show fiber reinforced tough hydrogels can dissipate a significant amount of energy at a tunable level of stress, making them suitable for energy absorbing applications such as inner layer of helmets. We develop inexpensive fire-retarding materials using tough hydrogels that provide superior protection from burn injuries. We also study hydrogels as actuators that can be used in soft robotics. Hydrogels contain mostly water and they freeze when the temperature drops below 00C and lose its functions. We demonstrate a new class of hydrogels that do not freeze and hydrogels that partially freeze below water freezing temperature. Partially freezing hydrogels are ideal for cooling applications such as gel packs and non-freezing hydrogels are useful in all the structural applications at low temperatures. This thesis will enable the use of inexpensive hydrogels in a new class of non-traditional structural applications where the mechanical behavior of the hydrogel is of prime importance.<br>Engineering and Applied Sciences - Engineering Sciences

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 82-87).<br>In nature, robust interfacial adhesion plays crucial roles in maintaining integration and functionality of various physiological structures including tendon and cartilage to bones and epidermis to dermis in mammalian skins. For instance, the bonding of tendon and cartilage to bone is extremely tough (e.g., interfacial toughness ~800 Jm-2 ), yet such tough interfaces have not been achieved between synthetic hydrogels and various types engineering solids including rigid nonporous solids and elastomers. In this study, we report a strategy to design extremely robust interfacial bonding of synthetic hydrogeis containing 90 % water to various types of rigid engineering solids, precious metals and commonly-used elastomers. The design strategy is to anchor the long-chain polymer networks of tough hydrogels covalently to various solid surfaces, which can be achieved by diverse surface chemical treatments. We discuss the mechanism behind the proposed design strategy to further understand the tough wet adhesion of hydrogels in engineering and biological situations. We also demonstrate multiple novel applications of robust hydrogel-solid hybrids for both rigid engineering solids and elastomers. We discuss details of such new class of applications and their potential usefulness in diverse fields.<br>by Hyunwoo Yuk.<br>S.M.

Dissertação de Mestrado Integrado em Engenharia Biomédica apresentada à Faculdade de Ciências e Tecnologia<br>Bioelectronic devices have an important role in the healthcare. Examples of application include monitoring heart signals, brain signals and neuromuscular electrostimulation. However, the existing setups for signals transmission and acquisition are bulky and populated with many wires and many electrodes that should be placed individually. The overall system is not conformable to the body, nor comfortable. It is desired to employ e-skin or e-textile patches with printed electrical interconnects that replace wires, and integrated electrodes that eliminates the need for individual placement of electrodes.This dissertation focuses on the synthesis and characterization of Hydrogel electrodes that can be easily integrated into an e-textile patch. Hydrogels, being mainly composed by water, are excellent options to interface with the human epidermis. Other required characteristics of these hydrogel that makes them appropriate for this purpose include being conductive, conformable to the skin, inherent adhesiveness, stretchability, and biocompatibility. Moreover, these electrodes are expected to present low electrode to skin impedance. In addition, we target to address the well-known problem of the hydrogels, i.e. loss of water in a short time, that is against the desired long-term use of the e-textile patch. Transparency is as well a desired property, mainly due to the aesthetics, but not a critical parameter. Previous work has successfully addressed the development of hydrogels with some of the mentioned characteristics, including toughness and adhesiveness. However, a combination of all these properties has not been reported. During this work a Polyacrylamide type hydrogel with the desired properties is synthesized and characterized. Furthermore, two methods for its integration on textile (e-textile patch) are developed. To develop such hydrogel electrode, a method based on the presence of a double solvent (water and glycerol) in the fabrication of the hydrogel solution is used. The addition of glycerol improved the mechanical properties of the hydrogel as well as its adhesiveness and its water retaining abilities, preventing the hydrogel from fast drying.To characterize the developed hydrogel, firstly mechanical properties were evaluated including tensile, compression and adhesion properties. Moreover, a careful impedance analysis of the hydrogel electrodes was carried out and compared against several electrodes of common use (Ag/AgCl, Stainless Steel, Gold CuP, and AG625 commercial Hydrogel electrodes). In addition, Electrocardiography signals were acquired with the same electrodes, to evaluate the Signal to Noise Ratio (SNR) of each electrode type. Lastly a toxicity analysis and a dehydration test were performed to the hydrogel.The results obtained were very satisfying. The hydrogel revealed low Young Modulus, high stretchability and high adhesion force comparable with the recent works in the literature. The impedance analysis revealed a better skin-impedance of the developed hydrogel when compared to all other types of the electrodes, and as well a higher SNR. Dehydration analysis revealed a very slow rate of water loss in the presence of glycerol on the hydrogel network, remaining soft and adhesive even after 15 days, while the hydrogel without the glycerol, lost 50\% of its weight in water, in the first day. Regarding the toxicity analysis, no trace of acrylamide monomer was detected in the sample. The method for textile integration was successfully developed, and demonstrated in a case study in which a wearable e-textile headband was successfully used for acquisition of brain signals. Overall, this work is a step toward realization of conformable and comfortable wearable e-textile , with direct application in bioelectronics.<br>Os dispositivos de bioelectrónica têm um papel bastante importante na saúde. Alguns exemplos destas aplicações, incluem monitorização de sinais cardíacos, sinais cerebrais e electroestimulação. No entanto, os sistemas existentes para transmissão e aquisição de sinais, são volumosos e requerem o uso de uma grande quantidade de fios e elétrodos, os quais devem ser colocados individualmente. Estes sistemas não se conformam ao corpo e apresentam um certo nível de desconforto. De modo a superar as desvantagens apresentadas, o desenvolvimento de e-skin e e-textiles está a ser vastamente investigado. Com estas opções é possível obter as interconexões elétricas impressas no substrato (polimérico ou de tecido) que substituem os fios das aplicações comuns, e os elétrodos são integrados nos próprios sistemas, eliminando a necessidade de colocar individualmente cada elétrodo.Esta dissertação centra-se na síntese e caracterização de elétrodos de hidrogel que podem ser facilmente integrados num sistema e-Textile. Hidrogéis, sendo maioritariamente constituídos por água, são excelentes opções para fazer interface com a epiderme. Outras características que são desejadas para estes hidrogéis, tornando-os apropriados para esta finalidade incluem ser condutor, conformável à pele, adesividade inerente, ser extensível, e biocompatível. Além disso, é também necessário que estes elétrodos apresentem baixa impedância entre a pele e o elétrodo. Além disso, esta tese tem ainda o objetivo de superar a comum desvantagem apresentada pelos hidrogéis: a perda rápida de água num curto espaço de tempo; de modo a ir de encontro ao que é requerido para uma aplicação de um e-textile de longo prazo. A transparência é também uma propriedade desejada, principalmente devido à estética, no entanto, este não é considerado um parâmetro crítico. Pesquisas anteriores abordaram, com sucesso, o desenvolvimento de hidrogéis com algumas das características mencionadas, incluindo resistência mecânica e adesividade. No entanto, a combinação de todas estas propriedades na simples formulação de um hidrogel, bem como a sua integração num e-textile patch ainda não foi relatada.Durante este trabalho um hidrogel de Poli-Acrilamida e Poli-Ácido Acrilico com as propriedades já mencionadas é sintetizado e caracterizado. Além disso, dois métodos para a integração do mesmo num e-textile são desenvolvidos. Para desenvolver tal elétrodo de hidrogel, um método baseado na presença de um solvente duplo (água e glicerol) durante a fabricação da solução de hidrogel é utilizado. A adição de glicerol na rede do hidrogel, melhora as suas propriedades mecânicas, bem como sua adesividade e a habilidade de retenção de água, impedindo o hidrogel de desidratar rapidamente.De modo a caracterizar o hidrogel desenvolvido, inicialmente foram avaliadas propriedades mecânicas, incluindo propriedades de tensão, compressão e adesão. Além disso, foi realizada uma análise cuidadosa da impedância de vários elétrodos, inclusive os elétrodos desenvolvidos, de modo a estes serem comparados com elétrodos comerciais e atualmente em utilização. Sendo assim, para além dos elétrodos desenvolvidos foram testados os elétrodos de Ag/AgCl, de aço inoxidável, gold cup, e elétrodos comerciais de hidrogel (AG625). Foram ainda adquiridos sinais de eletrocardiografia com os mesmos elétrodos, para avaliar a relação sinal/ruído (SNR) de cada tipo de elétrodo. Última uma análise da toxicidade e um teste da desidratação foram executados ao Hydrogel.Os resultados obtidos foram muito satisfatórios. O hidrogel revelou baixo Módulo de Young, uma extensibilidade e tenacidade elevada, tal como boas propriedades de adesão quando comparado com trabalhos anteriores. A análise da impedância revelou uma melhor impedância entre o elétrodo e a pele para o caso do hidrogel desenvolvido tal como um SNR mais elevado. A análise de desidratação revelou uma taxa bastante lenta de perda de água na presença de glicerol, permanecendo macio e adesivo mesmo após 15 dias, enquanto o hidrogel sem o glicerol, perdeu cerca de 50\% do seu peso em água evaporada, apenas no primeiro dia. Em relação à análise de toxicidade, não foi detetado nenhum vestígio de monómeros tóxicos.O método para a integração dos elétrodos de hidrogel em tecido (e-textil) foi desenvolvido com sucesso, e demonstrado num case-study, onde foi desenvolvida uma wearable headband fabricada a partir desse mesmo método. Este dispositivo desenvolvido foi usado com sucesso para a aquisição de sinais de eletroencefalografia. Em conclusão, este trabalho é um passo mais longe em direção ao fabrico de wearable e-textil, que se adapta e conforma ao corpo humano, com aplicação direta na bioelectrónica.<br>Outro - Add.Additive: Reference Nr. 59563 - cofinanciado pelo Fundo Europeu de Desenvolvimento Regional (FEDER), através do Programa Operacional Competitividade e Internacionalização (POCI-01-0247-FEDER-024533).<br>Outro - CMU-Portugal - Project Stretchtronics (Nr. CMUP-ERI/TIC/0021/2014) funded by the national funds of the Foundation of Science and Technology of Portugal.<br>Outro - Dermotronics: Reference: 31784 - Fundos Europeus Estruturais e de Investimento (FEEI) - Programa Operacional Regional do Centro e por fundos nacionais através da Fundação para a Ciência e a Tecnologia (FCT)

In recent years, hydrogen technology has been at the forefront of environmental discussions to meet increasingly tough climate protection goals and particularly low emissions targets in the transportation sector. Like any major change, a transition to hydrogen energy faced challenges in many countries, which caused several problems in the growth of the hydrogen share of the total energy supply portfolio. In 2018, Hydrogen Law (Hylaw) was introduced, which removes the legal barriers to the deployment of fuel cells and hydrogen applications. It is a flagship project aimed at boosting the market uptake of hydrogen and fuel cell technologies providing market developers with a clear view of the applicable regulations while calling policymakers' attention to legal barriers to be removed. This chapter introduces a consistent framework for the Hylaw regulations that makes is a clear and precise statement and an interconnection between law and energy management policies.

Temperature responsive hydrogel has attracted considerable attention as an outstanding material for creating a variety of reconfigurable structures. As a well-known temperature responsive hydrogel, poly(N-isopropylacrylamide) (PNIPAAm) has been widely used in various applications. Here, we report high resolution 3D micro fabrication of PNIPAAm structures using projection micro-stereolithography (PμSL). We also show the controllability of degree of swelling and transition temperature of 3D printed PNIPAAm structures by controlling process parameters of PμSL. In addition, we demonstrate improvement of mechanical properties of PNIPAAm by introducing ionic crosslinks into 3D printed PNIPAAm structures to form ionically and covalently crosslinked hybrid networks.

Hydrogenation reactor, a typical equipment in petrochemical industry, usually works in tough condition, such as high temperature, high pressure, with hydrogen gas as medium. 2.25Cr-1Mo is widely used as reactor material. However, with the increase of operating condition, a better material is needed. At present, 2.25Cr-1Mo-0.25V is proved having a better mechanical property in high temperature than that of 2.25Cr-1Mo. Hence, it is very important to study the hydrogen impact on 2.25Cr1Mo0.25V. This paper aims to study the relationship between H atom and metal crystal from microscopic view. Based on the first-principles calculation, the convergence analysis of parameters, the adsorption of H atom on Fe, V and their surfaces have been discussed. The results show that the parameter values of simple crystal surface (110) are less than surface (100), such as energy cutoff, k-point sampling, especially the number of slab layers. Tetrahedral-site is the stable site when H atom exists in bbc Fe, V lattice. And quasi three-ford site is the stable status when atomic H absorption on Fe(110) and V(110).

Summary Unstable supply of renewable energy arises with the inevitable seasonal dependency, which contradicts with periodic energy demand. As hydrogen shows high energy density and mobility, yet low solubility and residual saturation, underground hydrogen storage (UHS) becomes a promising solution of scalable energy storage to rebalance demand and supply. Depleted gas reservoirs (DGR) are one of the most appropriate options for UHS because of the integrity of their caprock and storage system. In this study, we developed a numerical model based on TOUGH+RGB simulator (code) to simulate the flow and thermal transport during UHS in reservoirs such as DGR. Given the different transport and thermodynamic properties of hydrogen, different Equation-of-State (EOS) for modeling the phase behavior of hydrogen-included mixtures are calibrated with literature (lab) data, and further are coupled with the simulator. This benefits our numerical experiments to exam various cushion gas pre-injection strategies for pressure maintenance, boundary conditions, and potential hydrogen leakage into caprock. Hence, we can comprehensively assess the seasonal gas recovery factor of hydrogen stored in DGR. The calculated density of hydrogen-methane mixture based on GERG-2008 EOS and Soave-Redlich-Kwong (SRK) EOS is in perfect agreement with experimental data, while that from Peng-Robinson EOS is not quite consistent. Due to the accuracy and efficiency, SRK EOS is employed in our simulator. Hydrogen injection-idle-withdrawal operation is simulated in a synthetic heterogeneous anticline DGR. Due to gravity segregation, we observe that hydrogen displaces pre-existing methane and resides at the top of the storage zone. When the caprock permeability ranges from 10(-5) to 10(-3) mD, only 0.05% of the injected hydrogen at maximum leaks into the caprock. Besides, an open boundary condition connecting with the storage zone helps the pressure maintenance in the storage and lowers the leakage, since with a close boundary condition the leakage rises to 0.35%. Further, about 1% of injected hydrogen is dissolved into the aqueous phase. Those results demonstrate that UHS in DGR has become a feasible choice. Nevertheless, only about 75% amount of hydrogen can be withdrawn if the bottom-hole pressure of producing well is 2MPa below the reservoir pressure. Therefore, cushion gas is necessary for the UHS project to increase hydrogen recovery. This work provides an in-depth investigation of various physics important to UHS, including EOS, hydrogen transport, capillary pressure, mixing, and dissolution. We quantitatively evaluated the hydrogen loss problem, including leakage to caprock, dissolved in water, and mixing with other gas molecules, which is the first-of-its-kind analysis in literature to the authors’ best knowledge. The modeling study is useful for the feasibility analysis of hydrogen storage in the depleted gas reservoir.

Gas generation and gas transport phenomena occur in geological repositories of radioactive waste. This has been extensively studied over the past ten years, usually within the framework of international projects (MEGAS, PROGRESS, etc.). These studies indicate that the production of hydrogen by anaerobic corrosion of metals is the most important source for gas generation. Laboratory and in situ experiments carried out at SCK•CEN indicate that, in the presence of Boom Clay (the reference geologic formation for deep disposal studies in Belgium), carbon steel suffers generalised corrosion estimated conservatively at 1 μm y−1. Simulations with the finite difference multi-phase flow code TOUGH2 were carried out in an attempt to quantify the effects of hydrogen gas generation on desaturation of initially saturated concrete components of the disposal gallery and the concomitant expulsion of cementitious pore-water into the surrounding host formation. Several simulation cases were considered and addressed differences in initial water saturation degree of concrete, hydrogen gas generation rate, and material porosity. Several conceptual models have been developed to better understand the phenomena at work in the transport of gas in the cementitious engineered barriers and Boom Clay. Multi-phase flow modelling was found to be helpful to get insight into the phenomenology of coupled water-gas flow in the cementitious engineered barriers. However, modeling the discontinuous variation in the conductivity of the clay relative to the gas (creation of preferential pathways) requires incorporation of geomechanical processes in conventional models based on the laws of two-phase flow.

In modern industrial gas turbines swirling flow is widely used for stabilizing flames at the transition from the burner to the combustor. In premixed combustion systems using highly reactive fuels, flashback due to combustion induced vortex breakdown (CIVB) has been observed frequently when swirl was present. This paper focuses on the effect of low swirl intensities on the flashback propensity and the predominant flashback mechanisms in a hydrogen-air tube burner. An existing test rig with a vertical quartz tube and a generic swirl generator has been used. At the tube exit the flame was stabilized in the free atmosphere. The turbulent flashback limits were measured for hydrogen-air mixtures at atmospheric conditions over a broad range of equivalence ratios for both non-swirling and swirling flow. The upstream flame propagation during flashback was observed through the OH*-chemiluminescence captured by two synchronized intensified high-speed cameras in a 90° arrangement, both looking at the flame from the side. In addition to that, a high-speed particle image velocimetry (PIV) system was used to insert a horizontal laser sheet into the vertical tube in order to investigate the propagation path of the leading flame tip through a time series of Mie-scattering images from the bottom. As expected, it turned out that the flame always flashes back along the wall boundary layer for non-swirling flow. For swirling flow it could be shown that again only boundary layer flashback takes place for equivalence ratios lower than ϕ≈0.75. In this rather lean region, the resistance against flashback is improved compared to non-swirling flow due to higher wall velocity gradients. For higher equivalence ratios, flashback is initiated through CIVB. That is, the flame enters the tube on the burner centerline until its tail gets in touch with the burner walls. Subsequently, there is a shift in flashback mechanism and the flame propagates further upstream along the wall boundary layer. For the given setup and these near-stoichiometric mixture compositions, this resulted in a significantly increased flashback propensity when compared with non-swirling flames. The present studies showed that imposing low swirl upon the burner flow can improve the resistance against boundary layer flashback for low and moderate equivalence ratios, whereas the change to the CIVB mechanism deteriorates the performance for high equivalence ratios.

The challenges associated with the welding of high-strength pipeline steels, such as X-80 and X100, are well established. While there are many filler metals that provide either adequate strength or good impact toughness, it is difficult to find products that provide both. Add to that the need for all-position welding and high deposition rates, and the options become almost non-existent. Several years ago, Hobart® Filler Metals began working on a line of flux-cored arc welding (FCAW) consumables that are unique in the welding industry. The products have a basic slag system, but do not operate like traditional EXXXT-5 electrodes. Traditional T-5 electrodes have a low-melting, fluid slag, which makes welding out-of-position especially difficult. They also have a high level of calcium fluoride, which affects the stability of the arc and causes weld spatter. While the weld metal mechanical properties and crack-resistance are excellent, the welder appeal and ease-of-use tend to be sorely lacking in most EXXXT-5 electrodes. The new approach utilizes aluminum for deoxidation, which has the added benefit of very clean weld deposits. The composition has been carefully optimized with appropriate levels of carbon, silicon, nickel and manganese. Alternative fluorine sources are used in place of calcium fluoride, which results in very good welder appeal and all-positional capabilities, including vertical down. The novel use of aluminum in a gas shielded process results in very low oxygen, nitrogen and sulfur content, providing exceptionally clean, tough weld deposits. Although the new products have been produced over a range of strength levels, the primary emphasis of this paper is on E691T5-GC (E101T5-GC) and E831T5-GC (E121T5-GC) electrodes. Testing shows that tensile strength levels ranging from 700–880 MPa (100–128 ksi) can be achieved, with toughness levels of 120 J at −60°C (90 ft-lbs at −76°F) or better. The highly basic slag, combined with low weld metal hydrogen (less than 4 ml/100 gm), provides excellent resistance to cracking. The product can be used in all positions, including vertically down, making it an especially appealing choice for welding high-strength pipe.

The Republic of South Africa is currently developing the Pebble Bed Modular Reactor (PBMR); an advanced, fourth-generation reactor that incorporates inherent safety features, which require no human intervention and which provide an unprecedented level of nuclear safety. In addition to electrical power generation, the reactor is uniquely suited for a variety of non-traditional nuclear applications including oil sands extraction, desalination, and hydrogen production. A state-of-the-art digital Protection System for the PBMR is currently being developed in conjunction with Westinghouse Electric Company (WEC). The Protection System provides for: • reactor shutdown using two different reactor trip methodologies (dropping of the control rods and insertion of Small Absorber Spheres (SASs) which are composed of boron carbide); • post-event monitoring; and • manual reactor shutdown, which is independent of software-based systems. The reactor shutdown and post-event instrumentation monitoring components of the Protection System are being implemented utilizing the WEC ‘Common Q’ platform, which is comprised of ‘commercially dedicated’ Programmable Logic Controllers (PLCs), colour-graphic Flat Panel Displays (FPDs) with integral touch screens, and high-speed data communication links. High reliability and availability are achieved through component redundancy, continuous automatic self-testing which is run online in a background mode, and implementation of a multi-channel system design which is tolerant to failures. The Protection System is also designed to support periodic surveillance testing through a suite of built-in computer-aided test facilities that are accessible via an FPD interface. These allow various system surveillance requirements to be readily performed in a convenient and systematic manner. This paper discusses the following topics with regard to the PBMR Protection System: development strategy, functional requirements, selection of applicable Codes and Standards, key design specifications, architectural configuration, design and implementation challenges, and unique opportunities that are provided by this type of Protection System.

“Microstamping” is one of patterning techniques [1] developed to deliver thousands of samples in parallel onto a surface for use in biosensors and medical diagnostics and the inexpensive production of micropatterned arrays of active proteins is of interest. Successful print of these protein island arrays includes conformal contact between an inked patterned stamp and the surface of a substrate and the full control over the amount and distribution of protein solution transferred from the impregnated stamps. In most common design, stamper is made of a solid material and proper inking method is required. Martin et al [2] have created a microstamper constructed by forming the hydrogel in sequence within the narrow ends of machine-pulled capillary tubes. This paper studies the protein-filling (inking)/stamping/printing process by numerical computations for a proposed Array-Stamper Chip with embedded microchannels. (Fig. 1) The array chip consists of thousands of microchannels with their own stampers to deliver thousands of fixed size/shape liquid samples to a bottom chip by capillary force simultaneously. The transfer process and physics are analyzed by solving first principle equations, i.e. conservation laws of mass, momentum. Due to the symmetry design of the array chip, the analysis is performed for a representative stamp only (Fig. 1b). Stable and robust numerical approaches as volume-of-Fluid (VOF) method [3] for two phase homogenous flow model and the interface tracking technique in cooperation with Continuum Surface tension Force (CSF) Model [4] are employed to determine the shape of liquid/gas interface as well as the fluid flowing pattern. Figure 2 shows the entire protein transfer during stamping/printing process, the Stamper Chip is moved toward/touch/away bio reaction chip starting at a distance of 50 μm away. The process consists of (a) The liquid fluid forms a meniscus and tends to reach out at the tip of the microchannel from the Stamping Chip (Fig. 2a), (b) The droplet meniscus is formed and the Stamper Chip starts to be moved toward the bottom chip (Fig. 2b), (c) The Stamper Chip is touched down and then is pulled up from the Bio-Reaction Chip, the liquid flows horizontally via the horizontal microchannels (Fig. 2c) and reaches the bottom chip, (d) part of the liquid is pushed upward and formed a small waist (Fig. 2d), (e) The Stamper Chip is moved further upwards with liquid slug of narrower waist (Fig. 2e), and (f) Stamper Chip is back to the original position with part of liquid broken at some point and left on the Bio-reaction Chip successfully. The controlling of the spot size left on bio-chip can be manipulated by physical properties of the filling protein, the inner/outer diameter of the microchannel, moving speed of the Stamper Chip, and the hydrophilic nature of the outer edge surface of the stamper. Two sets of physical properties are employed for computations (1) protein of low concentration with physical properties as water (2) 2mg/ml BSA concentration according to Fig. 3. Degree of hydrophilic nature with different liquid/gas/solid contact angle on stamper edge surface AB and the stamping speed do play significant role on the printing spot formation and size as shown in Table 1. Figure 4 shows that the size of printing size decreases with outer diameter of the microchannel. The detailed flowing process illustrate that the formations of the printing spot are resulted from forces interactions between the capillary flow formation process and stamper moving speed. In summary, numerical simulations not only give the suggestions for the array-stamper design with precise control of printing spot but also provide the physics and detailed information of the spot formation.