Academic literature on the topic 'KCl solution concentration'

Abstract The environmental factors which may have influence on the Stress Corrosion Cracking (SCC) susceptibility of stainless steels are temperature of solution, dissolved oxygen, chloride ion concentration, pH, cation species and so on. In this study, the effect of high concentration brines on the SCC susceptibility of stainless steels has been investigated. Especially, the variation of pH and activity in high concentration brines has been closely studied for the fundamental aspects to determine the effect of the cation species on the variation of pH. The pH imaging sensor (Scanning Chemical Microscope -SCHEM which can measure the two-dimensional pH distribution) was applied to examine the local pH distribution in high concentration brines. It is elucidated that the pH in CaCl2 or MgCl2 solution is more variable than in NaCl or KCl solution due to their higher activity coefficient of proton and lower buffer powers. The local pH measured by SCHEM in the lower buffer power solution (i.e. CaCl2) is very variable with the addition of a small amount of proton. The SCC mechanism with the active path corrosion (APC) in high concentration brines can be proposed on the basis of the effect of the high activity coefficient of proton and low buffer power on the pH. It can be also proposed that the effect of the cation in brines due to its variability in pH on SCC sensitivity should be considered.

Abstract The corrosion properties of PBAT/LDH coating on mild steel substrate was investigated. Tafel tests and electrochemical impedance spectroscopy tests (EIS) was used to analyze the corrosion resistance of the coating on the mild steel substrates. The morphological characteristics of the coatings was done using the scanning vibrating electrode technique (SVET) and environmental scanning electron microscopy (ESEM). Buffered saline solution containing NaCl-0.138 M, KCl-0.0027 M at room temperature and pH of 7.4 was used as electrolyte in the 3 corrosion tests. The tafel results showed that least corrosion current density value of 0.315 (μA/cm2) was recorded for 50 % LDH concentration in PBAT. This suggests that 50 % LDH in PBAT was about 98.5 % more corrosion efficient than 1018 bare mild steel and 0.7 % more that the 65 % concentration. The EIS results showed a similar trend. The 65 % LDH concentration showed about 25 % greater impedance to current flow over the 50 % LDH concentration in both the nyquist and bode plots. The SVET results revealed that the greatest corrosion protection of the mild steel substrates was observed with 50 % and 65 % LDH coating. This proved that an increased concentration of LDH in PBAT could potentially improve the corrosion resistance of mild steel when in service in a phosphate buffered saline environment.

Abstract Hot corrosion is typically defined as the accelerated high temperature oxidation caused by a thin fused salt deposit in contact with the surface of a metallic material. When alloys used in air and land-base gas turbines experience hot corrosion, Na2SO4 is usually the dominant salt found in the deposit due to the thermodynamic stability of this compound in the presence of sodium and sulfur in an oxidizing gas. In an effort to study the hot corrosion of several Fe- and Ni-base commercial wrought alloys in a gas turbine environment, a burner rig test program was executed. The study was conducted at 900°C (1650°F) and incorporated various test durations and two fuel sulfur contents (0.4 and 1.0wt%). Also, a synthetic sea salt was injected into the combustion zone of the burner rig, thereby maintaining a specific concentration of the salt in the combustion gas. Tests with the injection of 0 parts per million (ppm), 5 ppm, or 50 ppm salt were conducted. The principal constituents of the solution were NaCl, MgCl2, Na2SO4, CaCl2, and KCl. In general, the Ni-base alloys tested exhibited superior hot corrosion resistance over the Fe-base alloys. When exposed to a 1000 hour test with the injection of 50 ppm salt, the Fe content of a Ni-22Cr-18Fe-9Mo alloy appeared to be detrimental to the hot corrosion resistance of this alloy when compared to a Ni-21Cr-9Mo alloy. The W content in a Ni-22Cr-14W alloy did not show a detrimental affect on the hot corrosion resistance of this material. Also, Fe-base alloys containing less than 25wt% Cr did not perform well in a 500 hour test burning fuel containing 1.0wt% sulfur and 50 ppm salt injected into the combustion zone. Reasons for the performance of the alloys are suggested to be the “quality” or protectiveness of the oxide scale grown on a given alloy, the composition of the oxide scale grown on a given alloy -- making the scale more or less susceptible to a synergistic hot corrosion attack, and/or the alloy composition in relation to its ability to resist attack by chloride salts.

Abstract In order to evaluate the adaptability of hydroxyethane diphosphonic acid (HEDPA) as an environmentally benign alternative rust removal agent, a systematic investigation is being carried out. The effectiveness of HEDPA was thoroughly investigated as a function of acid concentration in the range 2-100 vol.% and at different temperatures in the temperature range 27 - 60°C. The results suggest that the acid HEDPA is very effective in the rust removal process. The rate of rust removal by HEDPA is strongly dependent on the acid concentration and the solution temperature. Once an optimum threshold is reached an increase in either the acid concentration and/or temperature has a negative effect on the reaction kinetics. While the rust was completely removed by the 2 vol.% HEDPA within 3 hours at 27°C, the rust removal was completed within 30 minutes of treatment at 60°C. Similarly, while, the complete rust removal by 2 vol.% HEDPA was noticed after 3 hours, 10 vol.% HEDPA required chemical treatment for 0.75 hours at 27°C. However, chemical treatment with as received 100 vol.% HEDPA did not dissolve even 20% of the rust after 6 hours and the rust removal at 60°C was <2 %. Chemical treatment of rusted steel samples with concentrated HEDPA solution (concentration range 5-100 vol.% HEDPA) has produced rust free steel samples with very rough surface topography. In addition, the chemical processing at higher temperatures (40 - 60°C) and higher HEDPA concentrations (5-100 vol.%) produced strong pungent smell and unpleasant cleaning environment. The most effective HEDPA concentration and temperature for the rust removal appears to be 2 - 4 vol.% and < 40°C respectively. The activation energy for the rust dissolution process also appears to increase with an increase in the acid concentration. However, it appears that the increase is not very significant for the concentrations in the range 2-4 vol% HEDPA (2 vol.% - activation energy 11 ± 1 kcal/mole; 3 vol.% - activation energy 12± 3 kcal/mole and 4 vol% - activation energy 14 ± 2 kcal/mole). The activation energies for rust dissolution by 5, 10 and 20 vol.% HEDPA were found to be 20, 28 and 32 kcal/mole respectively. Above, 20 vol% HEDPA concentrations, a semi-quantitative determined value for the activation energy is 2 ± 2 kcal/mole. Prolonged treatment of samples with HEDPA allows the deposition of the reaction products onto the cleaned sample surface. The reaction product contains a mixture of various higher order iron phosphates.

The oil and gas industry can be considered one of the main industrial fields in corrosion inhibitor usage. In this aggressive environment, dissolved CO2poses as an intensifying component. The study and synthesis of new materials that can mitigate corrosion rates in such an aggressive environment is a constant scientific effort. Nanomaterials research can be considered a fast-growing field with many applications [1]. Specifically for corrosion inhibitor studies, materials that present a 2D or 0D structure, such as graphene oxide and carbon dots, respectively, may offer excellent inhibition capabilities given their increased surface area in comparison to other molecules [2,3,4]. Carbon dots (CD) are a new class of carbon-based nanomaterials that presents as promising in different applications such as imaging, sensing, and catalytic processes [5]. Having a characteristic size of less than 10 nm and properties such as biocompatibility and low toxicity, this class of nanomaterial has been studied extensively in different scientific fields in the past few years. Due to their properties mentioned above, coupled with a relatively easy synthesis route and versatility in possible doping materials, they can be a potential candidate for corrosion inhibitors [6]. Thus, the present work aims to evaluate the corrosion inhibition efficiency (η%) of sulfur/nitrogen-doped carbon dots in a CO2-saturated 3.5% NaCl solution. The inhibition effect was evaluated by electrochemical impedance spectroscopy (EIS), linear potentiodynamic polarization, and weight loss measurements. Nano molecules were synthesized via thermal processing using citric acid (C₆H₈O₇) and thiourea (CH4N2S) as precursors, which resulted in Nitrogen/Sulfur co-doped carbon dots (NS-CD). All electrochemical procedures were performed in a 100 ml electrolyte cell and followed by 15 minutes of deaeration with N2, 15 minutes of CO2saturation, and 1 h of Open Circuit Potential monitoring. Analyses were carried out using a potentiostat/galvanostat model PGSTAT30 (Autolab, Metrohm-Eco Chemie) and a standard three-electrode cell: 1) work electrode: Mild Steel AISI 1018. 2) platinum counter electrode. 3) Ag/AgCl sat—KCl reference electrode. The metallic samples were cut and mounted in epoxy resin to allow a 1 cm2exposed surface area and then prepared for the electrochemical tests, which consisted of sanding from 220 grit up to 600, rinsed in distilled water, reagent grade ethanol and dried with hot air. Weight loss measurements were carried out with metallic rods with approximately 10 cm2of surface area. After 1 hour of CO2saturation, samples remained exposed for 48 hours, and through the weight difference, the corrosion rate was estimated, and the effect of inhibition addition was evaluated. Figure 1shows the polarization curves obtained for AISI 1018 alloy with and without inhibitor addition. Results show that both anodic and cathodic branches were influenced by the presence of the nano molecules, which suggests a mixed-type inhibition effect with adsorption of NS-CD molecules in the metallic surface acting as a physical barrier and mitigating degradation reactions [7]. The increase of carbon dot concentration resulted in a downward shift of the curves towards lower current densities. At approximately 200 mV of overpotential, a rapid rise of current density can be seen for all concentrations studied, which was not present for the blank samples and can be attributed to desorption processes. Corrosion Potential (Ecorr) shifted to more anodic values after inhibitor addition, and the shift was proportional to the inhibitor concentration added, up to a maximum of 70 mV at 90 ppm. Tafel analysis was performed to estimate corrosion current density (icorr) and inhibition efficiency (η%). Table 1shows the data obtained for Ecorr, icorr, and η%. As expected, the inhibition efficiency increases with NS-CD addition, reaching 93% at 90 ppm, which is an excellent inhibition effect. Figure 2shows the Nyquist plots obtained from EIS analyses. A distinct capacitive response can be observed for all conditions studied as highly deformed semi-circles. The diameter of said semi-circles can be related to the sample's Polarization resistance (Rp), where higher Rp values translate to lower corrosion rates [8]. At the low-frequency region, a small inductive loop was observed. This inductive behavior can be attributed to adsorption processes at the sample surface [9,10]. Results demonstrate that as the concentration rises from 35 to 90 ppm, the diameter of the semicircle increases; therefore, Rp values are higher than the blank results. Table 2shows the EIS parameters obtained, Rp and η%. At a maximum concentration of 90 ppm, the Rp reached 1kΩ.cm2with an efficiency value of 81%. The effect of immersion time in the EIS analyses was also investigated. Figure 3shows the calculated RP values after addition of 90 ppm of NS-CD with increasing immersion time, up to 7 hours. It can be seen that, initially the polarization resistance rose with longer immersion periods, up until 4 hours of exposure, where it stabilized at approximately 5 kΩ.cm2which gives an estimated η% of 97%. Weight loss results are shown in Table 2. Corrosion Rate and η% were estimated for AISI 1018 alloy with and without inhibitor addition. All concentrations studied led to a decrease in corrosion rate. Furthermore, the inhibition efficiency increases with NS-CD concentration up to 86% at 90 ppm. Optical microscopy was used to visually inspect the samples surface after exposure with and without NS-CD addition. Figure 4shows the optical micrographs obtained. In the blank sample, after 24 hours of exposure, a severely degraded surface can be observed with a heavy indication of general corrosion. On the other hand, after 90 ppm NS-CD addition, the sample surface remained protected to a degree, with a much less severe degradation aspect to be observed, which once more points to the inhibition effect of the nanoparticles synthesized. In summary, sulfur/nitrogen-doped carbon dots displayed an efficient corrosion inhibition behavior for a very aggressive medium, pointing to its potential usage in the oil and gas industry.

Abstract The effect of NaCl concentration (non-ideality) was investigated on the solubility of FeCO3 layer. After a layer of FeCO3 was formed on a gold coated crystal, NaCl was incrementally added into the solution and the mass change of the FeCO3 layer was measured with an Electrochemical Quartz Crystal Microbalance (EQCM). It was found that the mass of the precipitated FeCO3 layer did not change with increasing NaCl concentration even though the saturation value of FeCO3 (SFeCO3.) was far below 1 and dissolution of FeCO3 was expected. It was hypothesized that the calculation of SFeCO3 was incorrect due to inaccurate equations for dissociation equilibrium constants or solubility product constant (Ksp). Therefore, the equations for dissociation equilibrium constants taken from Oddo & Tomson 1982 and the Ksp equation borrowed from Sun et al. 2009 were revisited. New equations were proposed for carbonic acid first dissociation equilibrium constant (Kca) and Ksp. Kca=387.6×10−(6.527−1.594×10−3Tf+8.52×10−6Tf2−3.07×10−5P−0.7173I0.5)Ksp=10−(58.98+0.041377TK+2.1963TK−24.5724logTK−1.5223I0.5+0.5594I) The predicted pH and SFeCO3 values at low pressures over a temperature range of 30°C to 80°C and an ionic strength range of 0 to 4.95 M were in good agreement with the experimental results. The new equations could justify the observations for the effect of NaCl concentration on FeCO3 solubility.

Abstract The transient current response, using a scribing technique in a 0.01 M H2SO4-0.01M KCl solution, has been measured in three alloys of Fe-Cr-Ni system: Fe-25%Cr-25%Ni (25Cr/25Ni), Fe-15.5%Cr-10.7%Ni (16Cr/11Ni) and Fe-7.5%Cr-18%Ni (8Cr/18Ni), where the concentrations are in weight percents. Three different grain sizes (in the range from 170 to 440 μm) were produced in these alloys by annealing at 1100°C for different times. The effects of grain sizes, presence of two microconstituents in the microstructure, chemical composition of the alloys and the impact force of the stylus on the scratch current density (or maximum current) have been compared in this paper.

Abstract This paper presents an overview of stress corrosion cracking (SCC) in low-pressure (LP) turbine discs through 1993. Disc cracking experience in power plants and pertinent results of research programs are summarized. Analyses of field experiences and laboratory studies conducted in the United Kingdom, the United States, and other countries showed that stress corrosion cracking of LP turbine disc steels can occur in pure condensed steam or pure water, as well as in known cracking environments, such as hot hydroxide solutions. It has been established that stress corrosion crack initiation in LP turbine disc steels exposed to high-purity water environments typical of those found in nuclear power plants depends upon seven factors: the presence of a liquid phase; the oxygen concentration of the liquid phase (or the electrode potential corresponding to the oxygen concentration); the yield strength of the steel used in discs; the disc temperature; tensile stress level; crevices and localized corrosion within crevices; and a combination of tensile stress and a flaw of size and shape sufficient to produce a Kl value greater than Klscc, i.e., greater than about 7.2 MPa√m (6.6 ksi√in.). In general, susceptibility of discs to crack initiation increases with increasing oxygen concentration, steel yield strength, and disc temperature. Crack initiation is much more likely to occur on creviced surfaces, as are present at disc keyways, bores, and rim attachments, and the likelihood of cracking decreases when the clearance between two surfaces is greater than about 0.04 mm (0.001 in.). Crack initiation has been found to be independent of disc steel composition, inclusions, and pitting, although cracks may be initiated at pits formed on steel surfaces at inclusions. While stress corrosion crack initiation depends upon the several factors listed above, the growth rate of stress corrosion cracks in LP turbine disc steels exposed to high-purity water and steam environments depends upon only three factors: the presence of a liquid phase; disc yield strength; and disc temperature. Importantly, stress corrosion crack growth rates in LP turbine disc steels are essentially independent of tensile stress level and stress intensity. Increases in both yield strength and temperature result in increased crack growth rate.

Quantum-chemical simulation of interaction between guanosines molecules in water solution shows possibility of existing hydrogen bonds between NH2 and C=O groups of one molecule and atom O of 3'-ОН and atom H of 2'-ОН groups of other molecule, respectively. It was found that stability of hydrogel increased with the increasing of guanosine concentration in the solution but little depends on the KCl concentration.

Abstract The present work in nanofluids is focusing into using the electro-kinetic phenomenal occurring around nanoparticles immersed in a base fluid as a method to stabilize a nanofluid and enhance its thermal conductivity. The electro-kinetic physic establishes, that when an electrolyte solution is in contact with a solid, an electric double layer (EDL) is produced on the solid surface. Due to the high concentration of ions with the same charge around of the particle surface, “it is possible to stabilize a nanofluid by the action of an electro repulsive force caused by ions over the nanoparticle surface and enhance its thermal conductivity as the concentration of the solutions increases”. The nanofluid samples were prepared by the two-step method and a continuous ultrasonication. 1wt% and 3wt% concentration (mass fraction) of Titanium oxide, Anatase (TiO2) nanoparticles, is added in an electrolyte solution (base fluid) made of different concentration of Potassium Chloride (KCl), and deionized water. The pH of the base fluid is maintained constant adding HEPES as a buffering agent. To measure the different level of stability for the nanofluid we used the thermal conductivity enhancement of the base fluid by nanoparticles. The experimental results under controlled temperature condition show that an electrolyte solution with nanoparticles after 20 days of preparation, presents a higher thermal conductivity with respect to the base fluid with an improvement rate ranging from 0.43±0.12% to 0.72±0.12% for 1wt%, and 2.15±0.17% to 3.03±0.21% for 3wt% of nanoparticles added respectively. The higher improvement shows sign of a major level of homogeneity of the nanofluid, and this behavior seems to be directly proportional to the KCl concentration.