CHROMIUM carbide – nickel CHROMIUM powder Cr3C2-25wt. NiCr was plasma sprayed by a water-stabilized system WSP® . A series of experiments with variable feeding distance was carried out. Basic characterization of coatings was done by XRD, SEM and light microscopy plus image analysis. Microhardness was measured on polished cross sections. The main focus of investigation was on resistances against wear in dry as well as wet conditions. The appropriate tests were performed with set-ups based on ASTM G65 and G75, respectively. The influence of spray parameters onto coating wear performance was observed. The results of mechanical tests are discussed in connection with changes in the character of the coating’ s microstructure. The results show that for obtaining the best possible Cr3C2-25NiCr coating with WSP® process, from the viewpoint of wear resistance, medium feeding distance is desired and its decrease or increase leads to certain worsening of studied properties.

The role of conductive polymers was studied in removing CHROMIUM from CHROMIUM plating industry waste water and the results were compared with different absorbents. The results indicated that polyaniline has the desirable effect in CHROMIUM ion removal with 59.6%, but polypyrrole has removing effect of 8.2% in similar conditions. The role of conductive polymer composite in CHROMIUM removal was studied and the results show that the percentage of CHROMIUM removal has increased in conductive polymer composite with poly (vinyl alcohol). In case of a composite of polyaniline and quartz, the CHROMIUM removal percentage from waste water decreased in comparison to polyaniline without quartz but with polypyrrole and quartz composite, the CHROMIUM removal percentage from waste water increased in comparison to polypyrrole without quartz.

This investigation seeks to reduce the environmental impact of the tanning process by recovering Ca and Cr from tannery waste solution. The treatment process reduces both the amount of Cr discharged to the environment and the amount of raw Cr extracted from natural resources. The procedure was based on the selective separation of Ca ions from the waste solution as Ca oxalate, prior to the recovery of Cr as the hydroxide precipitate at pH 6.5. The dried Cr hydroxide cake was then subjected to heating (heating rate 0.5oC min-1) at different temperatures up to 500oC to produce Cr oxide nanoparticles. The physicochemical characteristics of the nanoparticles were investigated using X-ray diffraction, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, surface area measurement and thermal analysis. Results revealed that heating of the treated Cr hydroxide at 300oC yielded amorphous Cr oxide, while with heating at 400oC, the Cr oxide started to crystallize to hexavalent, trivalent and divalent Cr species. At 500oC, a pure phase consisting of trivalent Cr oxide nanoparticles was formed that contained traces of hexavalent Cr. A mechanism for the formation of the different forms of Cr oxide was proposed and confirmed by XRD.

Background and Aim: High chipping rates of the veneering porcelain in zirconia ceramic restorations have been reported in many clinical studies. However, information on the bonding behavior of veneering porcelain to zirconia and lithium disilicate frameworks is limited. The purpose of this study was to evaluate the bonding strength of porcelain veneering to zirconia, lithium disilicate, nickel-CHROMIUM (Ni-Cr) and cobalt-CHROMIUM (Co-Cr) alloys. Materials and Methods: In this in vitro experimental study, core specimens were fabricated with 12 mm height and 11 mm diameter, and veneering specimens were fabricated with 7 mm height and 5 mm diameter according to the manufacturer’ s instructions in four groups (n=12) as follows: Group I: Ni-Cr alloy, group II: Co-Cr alloy, group III: lithium disilicate, and group IV: zirconia. The shear bond strength (SBS) test was performed in all samples with a universal testing machine with a crosshead speed of 0. 5 mm/min. The fractured samples were examined under a stereomicroscope (×10) to determine the mode of failure. The results were analyzed by one-way ANOVA (P<0. 05). Results: Maximum SBS was recorded in group IV (zirconia; 34. 6 MPa) followed by groups II (Co-Cr; 30. 66 MPa), I (Ni-Cr; 30. 58 MPa), and III (lithium disilicate; 20. 05 MPa). One-way ANOVA revealed no significant difference between the study groups (P=0. 174). Conclusion: The SBS of porcelain veneering to zirconia, lithium disilicate, Ni-Cr, and Co-Cr alloys was not significantly different.

Pollution of water due to presence of certain heavy metal ions is a severe socio-environmental problem caused by the discharge of industrial wastewater. In view of their toxicity, non-biodegradebility and persistent nature, their removal becomes an absolute necessary. CHROMIUM is one of the major pollutants in the environment and is frequently present in wastewaters from various industrial units. Several conventional physical and chemical treatment techniques may be used for the removal of CHROMIUM. However, such processes are not only expensive and highly energy intensive, but also lead to production of harmful by-products and end-products, the ultimate disposal of which again causes secondary pollution. Hence, the potential application of microorganisms as biosorbent for the removal of CHROMIUM has been recognized as an alternative to the existing conventional physico-chemical methods. The aim of the present study is to review the removal of CHROMIUM from aqueous solution using various materials of agricultural and biological origin , which have been studied as potential CHROMIUM biosorbent (plant leaves, saw dust, sugar cane bagassa, sugar beet pulp, maize cob and rice hulls). Also reported cases on CHROMIUM removal from aqueous solution by using fungal, algal and bacterial biomass under the growing, resting and dead conditions in batch as well as in continuous bioreactors are reviewed.

Cr (VI) as an extremely soluble and highly toxic ion is present in effluents of industries and imposes severe health-related problems. The current study aimed to provide information on Cr (VI) adsorption potential of fire clay as an abundant, cost-effective and untried material. Batch adsorption trials of Cr (VI) were performed to investigate the effects of pH, contact time, initial metal ion concentration and the adsorbent dosage. Langmuir, Freundlich and Dubinin–Radushkevich isotherm models were used to evaluate the equilibrium data at 20°C and regression coefficients were derived. Moreover, adsorption kinetics was analyzed using the pseudo-first-order and the pseudo-second-order kinetic models. Maximum CHROMIUM removal was found at pH 2.0. A kinetic study yielded an optimum equilibrium time of 90 minutes with an adsorbent dose of 2.5 g/50 mL. Results suggested that the equilibrium adsorption described by the Freundlich model. The kinetic data of the sorption showed that the pseudo second-order equation was the more appropriate. The results of the study indicated that fire clay was not a suitable adsorbent for Cr (IV). Apart from relatively long equilibrium time, the efficiency was not satisfactory. Therefore, searching for better alternative and/or modify such adsorbent is necessary in this area.

CHROMIUM contaminants emanating from industrial activities pose a significant threat to human’s well-being. CHROMIUM (III) and CHROMIUM (VI) are the forms in which they are commonly encountered, of which the trivalent form is relatively benign. Hence, biological reduction of hexavalent CHROMIUM has been widely explored by researchers, yielding fruitful outcomes, opening up exciting avenues and also throwing up new challenges. This article attempts to review this area of research. Microbes, especially bacteria capable of CHROMIUM (VI) reduction, belonging to a heterogeneous group have been isolated from contaminated sites. They exhibit plasmid-mediated chromate resistance and the reduction is enzymatically mediated. Reduction studies have been carried out with free and immobilized enzymes as well as whole cells. Experiments have been carried out in specifically designed bioreactors operated in batch and continuous modes. Although significant progress has been made, much needs to be done for its successful in situ application as the organism may not withstand the CHROMIUM concentration or may be impeded by the presence of other toxicants. With molecular engineering, it may be possible to derive strains with improved performance even under stressful field conditions.