Searching for Evidence of Hydride Formation on Corroding Magnesium

From the standpoint of power consumption the results of this investigation indicate that chromium plating baths should have a concentration of 4.5 molar CrO3 at 45° C. and 3.75 molar at 25° C. It is shown that for all practical purposes the increase of conductivity of chromic acid solutions is a linear function of the temperature, over the range of temperatures covered in plating work. It is shown that the addition of the sulfate ion has the effect of increasing the conductivity of the solution to a maximum when the sulfate ratio is approximately 50, which coincides with the sulfate ratio giving optimum cathode efficiency. Calculations of pH from conductivity data are in fair agreement with the values obtained by other investigators employing potential methods. The hydrogen and quinhydrone electrodes are definitely shown to give erroneous pH values in chromic acid solutions. Furthermore, the platinized‐platinum oxygen electrode is shown to be inaccurate in chromic acid solutions.

This study involved an experimental investigation into the improvement of mechanical properties of fiber-reinforced concrete (FRC) utilizing chemically treated polypropylene/polyethylene fibers. Four types of chemical surface treatments were examined: two types of chromic acid (Types B and C), potassium permanganate (PP), and hydrogen peroxide solutions. Untreated and treated fibers were added at 0.32% by volume of concrete and also at 0.50% for the best treatment technique. Compressive and flexural strength were measured to quantify improvement. It was found that there were no significant differences in compressive strength. Type B chromic acid solution was found to be the most effective technique in improving the flexural strength of FRC resulting in average increases of 8.9% and 17.6% for peak and residual strengths, respectively, compared to nontreated fibers. While not as effective as plasma treatments, further research may be warranted for chemical treatments. Surface wettability of the treated fibers was measured by contact angle with water. The contact angle was found to have no correlation to the toughness. The higher volume of fibers, both treated and nontreated gave higher residual strength and toughness; however, surface treatment did not significantly enhance mechanical properties.

Anodizing Al in chromic acid is a very useful surface finishing process for corrosion protection and nanoscale porous structure fabrication, whereas the self-ordering of porous anodic alumina (PAA) in chromic acid has never been found to date. Herein, we provide a self-ordered PAA film possessing numerous sub100-nm-scale characteristic bumps through anodizing in chromic acid at high temperature. Anodizing of high purity Al plates in a 0.3 M chromic acid solution at conventional low temperatures, such as 293 K, leads to the formation of a disordered PAA film, whereas anodizing at a high temperature of 348 K causes the self-ordering behavior of the pore structure. The PAA film grown in the initial stage possessed the highest regularity, and it decreased with anodizing time due to pore branching during anodizing. A highly ordered PAA film measuring approximately 340 nm in interpore distance can be fabricated by short-term, two-step anodizing in chromic acid at 348 K and 120 V. The ordered PAA film possesses a characteristic nanostructure consisting of hexagonally arranged 100-nm-scale pores and sub100-nm-scale disordered bumps on their pore walls without any electrolyte chromate anion.

BackgroundCervical fusion devices made by polyether ether ketone (PEEK) cause concomitant effects which decompress the spinal cord and nerve roots. Magnesium has good biocompatibility and bioactivity as a biodegradable orthopedic implant material; however, its fusion rate is low. In this paper, we aimed to improve interbody fusion rate of high-purity magnesium (HP-Mg) by coating it with fluoride.MethodsFluoride-coated HP-Mg (F-HP-Mg) cages were prepared, and HP-Mg cages served as controls. We tested hydrogen release in phosphate-buffered saline (PBS) and weight loss in chromic acid. Anterior cervical discectomy and bone graft fusion (ACDF) was performed at the C2-C3 segment on goats with F-HP-Mg and HP-Mg cages to evaluate fusion score.ResultsHydrogen release of F-HP-Mg cages was significantly lower than that of HP-Mg cages. Weight was significantly decreased in both types of cages after rinsing with chromic acid, while F-HP-Mg cages were more resistant to corrosion compared to HP-Mg cages. There were no significant differences in disc space height (DSH) and remaining cage volume between the two groups in computed tomography (CT) images of goat cervical spine, while cavities were found at postoperative 12 weeks and confirmed by histological staining. No complications were found, while serum aspartate aminotransaminase (AST) level was significantly higher in the HP-Mg group compared to the F-HP-Mg group. Fusion rate at 24 weeks after ACDF was significantly higher with F-HP-Mg cages.ConclusionsThe use of F-HP-Mg improved histological fusion in the cervical intervertebral space of goats compared to HP-Mg and showed good biosafety.

Hirudin, a protein composed of 65 or 66 amino acid, is a newly risen anticoagulant agent and has been considered as the most potent thrombin inhibitor. Hirudin can block the active site of thrombin by means of its carboxylic acid reaction with the active regime of thrombin, and becomes a tightly bound complex, and thus controls the formation of thrombus. Hirudin was covalently immobilized onto the water-soluble carbodiimide preactivated and chromic acid oxidized PE surface. Surface chemistry analysis indicated that a certain amount of carboxylic acid groups was generated on the polyethylene surface after oxidation with chromic acid solution. The amount of carboxylic acid functional group increased with the oxidation time. In addition, polyethylene surface was etched by chromic acid solution, and a rougher surface was created. The morphology of oxidized polyethylene surface was similar to each other among the samples with oxidation time from 1 to 8 min. ESCA results indicated the number of hirudin molecules immobilized was constant at the reaction time studied. In vitro platelet adhesion assay indicated the number of adhered platelets on the oxidized polyethylene surface increased significantly after oxidation. In contrast, surface with hirudin immobilization showed a reduction in adhered platelet density than the chromic acid oxidized counterpart due to the decrease of platelet-activating capability by the hirudin-thrombin complex and the differences in the adsorbed protein composition.

0·07 M (1 per cent.), 0·17 M (2·5 per cent.), and 0·34 M (5 per cent.) solutions of analytical-grade potassium dichromate have pH values of 4·10, 4·05, and 3·85 respectively. The values for corresponding solutions of chromic acid are 1·20, 0·85, and 0·70. The oxidation potential for potassium dichromate is 0·76 V, and for chromic acid, 1·10 V. During fixation for 18–20 hours at room temperature, with either reagent, there is a small decrease in hydrogen-ion concentration but no appreciable change in oxidation potential. During postchroming for 48 hours at 37° C., there is a further decrease in hydrogen-ion concentration, but only in the case of chromic acid is there a decrease in oxidation potential. The morphological features of the fixed cells are determined almost entirely by the fixing reagent. Postchroming can influence staining properties. There are two characteristic fixation ‘pictures’ depending upon the pH of the reagent: (1) with chromic acid and the more acidic dichromates (barium, calcium, mercuric, or silver) there is destruction of the mitochondria and disorganization of the cytoplasm and nuclear contents, resisted only by the nucleolus, and (2) with potassium dichromate and the other less acidic dichromates (ammonium, lithium, or sodium), the mitochondria, cytoplasm, and nucleus are well fixed. With various tissues from mice, the transition between the two types occurs around pH 3·4–3·8. The chemical mechanism of cytological fixation by anionic chromium reagents remains to be elucidated. Oxidative reactions do occur. Probably more important are ionic interactions and complex formations, often with associated precipitation, involving various tissue constituents and the several chromium ions.

Chromic acid dealumination of zeolites

Hydrogen gas could provide attractive options as ideal fuel for a world, in which environmental friendly and economically sustainable manner. Microalgae have the ability to bio-synthesis hydrogen gas. Algal H2 does do not generate any toxic or polluting bi-products and could potentially offer value-added products derived from algal biomass. In this work, the feasibility of coupling sulfur deprivation and light on hydrogen production by Chlamydomonas sp grown in photobioreactor was investigated. The cells growth, hydrogen production, total carbohydrate and chlorophyll content were determined. The results showed that, under optimum condition, algae cells were required 168 hr (7days) to reach the late logarithmic phase (the algal dry weight 4.11 g/L). Whereas the algae cells were needed about 18~22 days to reach this value (3.55 g/ L) when grow in optimum medium. The concentration of Chlorophyll (5.65%) and carbohydrate (39.46%) were accumulated in algae cells grow in S-deprives medium coupled with dark condition over that did in algae cells cultured in optimum medium. After about a 24 h of cultivation, photo-production of H2 was observed for C. sp either in absence or presence of sulfate. But under sulfur deprivation coupled with dark condition, higher H2 gas was obtained after 16 hr (7 several days) of incubation period. In new design photobioreactors (PhBRs), after 18 days of cultivation, the volume of H2 gas in was found to be 450 ml in cells grow in sulfur-deprived culture). This value was 360 ml in cells grow under optimal condition.

Background: Biohydrogen production from organic wastes is one of the most promising alternatives for sustainable, green energy production. Dark fermentative biohydrogen production is a complicated anaerobic process in the absence of sunlight. Objectives: The current study investigated the enrichment of biohydrogen-producing bacteria from anaerobic mixed culture by acid and alkaline pretreatment. Methods: Anaerobic sludge was extracted from a full-scale anaerobic sludge digester. In order to remove large particles and debris, the sludge was sieved and subjected to acid and alkaline pretreatment. Four strong acids including HCl, HNO3, H2SO4, and H3PO4 was used for acid pretreatment and tow mineral bases including NaOH and KOH for alkaline pretreatment. The pretreated sludge was fed to glass containers with a working volume of 400 mL and headspace of 100 mL. Results: HCl and H2SO4 as acid pretreatment agents produced more biohydrogen than the other agents. In case of HCl pretreatment, the volume of H2 gas was 133.6 mL, followed by H2SO4 (80.6 mL), KOH (72.5 mL), HNO3 (70.1 mL), H3PO4 (68.7 mL), and NaOH (59.8 mL). In the pretreatment methods, the solution pH and alkalinity were in the ranges of 4.8 to 6.9 and 2,400 to 3,800 mg/L, respectively. Conclusions: According to the results, pretreatment methods with acids, especially HCl, could be used for the enrichment of biohydrogen-producing bacteria from mixed cultures.

Background:Due to depletion of fossil fuel reserves, global warming, and the need for energy efficiency, the new energy resource is required. For this purpose, hydrogen can be considered as clean and efficient energy carrier. In this study, biohydrogen production from physical pretreated mixed culture was investigated.Materials and Methods:In this study, the optimal conditions for physical pretreatment of mixed culture were investigated for the enrichment of hydrogen-producing bacteria (HPB). Three individual pretreatment processes, including thermal, ultraviolet (UV) radiation, and ultrasonication (US) were conducted in batch tests. The batch tests were carried out via 500 mL glass flasks with working volume 400 mL. Glucose was used as sole substrate, and other essential nutrient and trace elements were added. To agitation of substrate with HPB inoculum, the magnet stirrer was used at 60 rpm.Results:The results showed the production of H2 gas could be increased by appropriate pretreatment methods including thermal pretreatment at 100°C. At 100°C as a pretreatment, the volume of H2 gas was 112.25 mL and followed by US (97.46 mL), UV (89.11 mL), 80°C (72.72 mL), 90°C (53.95 mL), and 70°C (26.01 mL). In the pretreatment methods, the solution pH and effluent soluble chemical oxygen demand was 6.3–6.7 and 5100–8300 mg/L, respectively.Conclusions:The Gompertz model depicts that all R2 values were more than 0.93, indicating that the fitted curves were best fitted with the experimental points.

CHROMIUM Composition and properties of cathodic film in deposition. In a solution of chromic acid on the surface of a chromium cathode there may be a film of various kind. Cathodic films of a primary type arise in electrolysis of chromic acid in the presence of SO42− ions, have a macroscopic character, are more or less easily dissolved in the electrolyte without current, and facilitate reduction by chromic acid to metallic chromium. Oxide films (those of second(ary) type) are formed in electrolysis of chromic acid without sulphate ions, or without current through action of chromic acid on the surface of the cathode metal, have a microscopic character, are not dissolved in the electrolyte, and their presence does not facilitate reduction by chromic acid. It was found that the composition of the cathode films of the first type markedly changes with change in the composition of the solution and electrolysis conditions. Increase in current density and concentration of sulphuric acid, and also reduced concentration of chromic acid, increase the relative concentration of trivalent chromium and sulphate ions in the film. A connection was found between composition and strength (stability) of the cathodic films, on the one hand, and the rate of deposition of metallic chromium on the other. (Four references.)—Z. A. Solov'yeva et al., Zh. prikl. Khim., 1962, (8), 1806–1811.

Corrosion behavior of arc sprayed Al–Zn–Si–RE coatings on mild steel in 3.5 wt% NaCl solution

Experimental investigation of pool boiling heat transfer and critical heat flux of nanostructured surfaces

En el presente trabajo se desarrolla experimentalmente el proceso de cromado duro sobre probetas de acero AISI A36. El trabajo incluye el desarrollo del proceso de cromo duro a nivel de laboratorio para brindar un procedimiento simplificado en la aplicación industrial. La electrodeposición es el principio fundamental de depósito del cromo duro, mediante la aplicación de un diferencial de potencial eléctrico, sobre el acero A36 sumergido en un baño electrolítico de ácido crómico, se deposita una capa de cromo entre 30-80 micrómetros. El depósito de cromo se logra mediante la combinación de variables; tales como: concentración de la solución electrolítica de ácido crómico, material base, ánodos, densidad de corriente, temperatura de la solución y tiempo. De las anteriores, el tiempo y la densidad de corriente son los parámetros de trabajo que serán manipulados mientras los otros permanecerán constantes. Un modelo simplificado lineal derivado de la ley de electro-deposición de Faraday es desarrollado. Se presenta la variación del espesor de material depositado, microdureza y agrietamiento del depósito de cromo duro según la combinación de parámetros de tiempo y densidad de corriente empleados. El espesor del Cr depositado es medido gravimétricamente y microscópicamente. Los resultados obtenidos al combinar dichos parámetros muestran una estabilización de valores de dureza dentro del rango de 66 a 70 HRC. Esta investigación estudia y analiza las posibles causas que influencian la dureza relacionada al número de grietas superficiales, tiempo y densidad de corriente en el proceso de cromado duro.

The aim of this study was to gain an understanding on the collective cellular effects of magnesium (Mg) corrosion products on the behaviour of cells responsible for bone formation and remodelling. The response of mesenchymal stem cells (MSCs) and osteoclast cells to both soluble (Mg ions) and insoluble (granule) corrosion products were recapitulated in vitro by controlling the concentration of the corrosion products. Clearance of corrosion granules by MSCs was also inspected by TEM analysis at sub-cellular level. The effect of Mg corrosion products varied depending on the state of differentiation of cells, concentration and length of exposure. The presence of the corrosion products significantly altered the cells’ metabolic and proliferative activities, which further affected cell fusion/differentiation. While cells tolerated higher than physiological range of Mg concentration (16 mM), concentrations below 10 mM were beneficial for cell growth. Furthermore, MSCs were shown to contribute to the clearance of intercellular corrosion granules, whilst high concentrations of corrosion products negatively impacted on osteoclast progenitor cell number and mature osteoclast cell function.