Chromium

Weld cladding is a process for producing surfaces with good corrosion resistant properties by means of depositing/laying of stainless steels on low-carbon steel components with an objective of achieving maximum economy and enhanced life. The aim of the work presented here was to investigate the effect of auxiliary preheating of the solid filler wire in mechanized gas metal arc welding (GMAW) process (by using a specially designed torch to preheat the filler wire independently, before its emergence from the torch) on the quality of the as-welded single layer stainless steel overlays. External preheating of the filler wire resulted in greater contribution of arc energy by resistive heating due to which significant drop in the main welding current values and hence low dilution levels were observed. Metallurgical aspects of the as welded overlays such as chemistry, ferrite content, and modes of solidification were studied to evaluate their suitability for service and it was found that claddings obtained through the preheating arrangement, besides higher ferrite content, possessed higher content of chromium, nickel, and molybdenum and lower content of carbon as compared to conventional GMAW claddings, thereby giving overlays with superior mechanical and corrosion resistance properties. The findings of this study not only establish the technical superiority of the new process, but also, owing to its productivity-enhanced features, justify its use for low-cost surfacing applications.

Background and Objectives: In recent years, concerns about the long-term effects of heavy metals as one of the main environmental pollutants has increased. These metals have adverse effects on human health, which include growth retardation, cancer, damage to the nervous and heart system. Mainly heavy metals discharge into environment from industrial and urban sewage. There are the different methods to reduce water pollution and removal of heavy metals from water.There are the different methods to reduce water pollution and removal of heavy metals from water that one of them is adsorption by using organic and inorganic absorbers. In this study, the use of nanoclay (Cloisite Na+) for adsorption of chromium form Single- and two- component solution (competitive) was investigated.
Materials and Methods: this study was conducted in scale laboratory conditions and batch system by changing the factors that affect the absorption process such as pH (2-10), contact time (5-1440 minutes), adsorbent dose (1- 5 and 2 gr/L) and adsorbate concentration (1-100 mg/ L). Then in solution of single and two elements systems, experimental data were investigated with absorption isotherms of Freundlich, Langmuir and Sips.
Results: Results showed that the optimum pH values for adsorption of chromium were 6 and 7 for single-element and two elements systems, respectively. Also, in single and two-element systems, the maximum removal efficiency was obtained (82% and 59.2%). Effect of contact time on the adsorption process showed that equilibrium time of removal of Cr (VI) by nanoclay (Cloisite Na+) is 180 min in single element systems and 240 min in two-element systems. Optimum dosage of adsorbent for absorption of chromium ions from single and two element solution with a concentration of 10 ppm is 5 and 20 g/L, respectively. Comparison of the Freundlich, Langmuir and Sips isotherms showed that the Sips model for single element system was described data of adsorption better than other models with R2 (0.9977) and RMSE (0.1751). Also in two-element system, Freundlich model with R2 (0.9721) and RMSE (0.2831), is better fit with data of adsorption.
Conclusion: Due to the presence of heavy metals in various industries wastewater and their effects on adsorption of each other by the different adsorbent, it is necessary for getting real results in the process of adsorption Notice to this matter. The results of this study also showed that the absorption presses of chromium from solutions of single element or combination of elements with the same adsorbent are completely different.

There is accumulating evidence that the metabolism of several trace elements is altered in diabetes mellitus and that these nutrients might have specific roles in the pathogenesis and progress of this disease. The aim of present study was to compare the level of essential ...

The aim of this study was to investigate the seasonal and spatial variations in surface water quality at the mid-Black Sea coast of Turkey. The samples were collected from ten monitoring stations including rivers and sea water during the years from 2007 to 2008. The samples were analyzed for 25 parameters: total carbon, total inorganic carbon, total organic carbon, chromium, cadmium, copper, lead, iron, nickel, manganese, phenol, surfactants, ammonium, nitrite and nitrate-nitrogen, total phosphorus, adsorbable organic halogen, sulfate, hardness, dissolved oxygen, pH, temperature, total dissolved solids, electrical conductivity, and salinity. Multivariate statistical techniques, cluster analysis (CA) and factor analysis/principal component analysis (FA/PCA), were applied to analyze the similarities among the sampling sites to identify the source apportionment of pollution parameters in surface waters. The results indicate that seven factors for river water explained 82.24% of the variance. In seawater, seven factors account for 89.65% of the total variance. Varifactors obtained from factor analysis indicate that the parameters responsible for water quality variations are mainly related to organic pollution (municipal effluents), inorganic pollution (industrial effluents and waste disposal areas), nutrients (agricultural runoff), and dissolved salts (soil leaching and runoff process).

Oinofyta region was originally rural. After a series of ministerial and presidential decisions that facilitated the establishment of industries and allowed the disposal of sewage in the river Asopos, Oinofyta turned into industrial region with environmental pollution by heavy metals, mainly. This paper aims to outline the problem of heavy metal environmental pollution of drinking-water in Oinofyta and brief recording existing heavy metals measurements found in domestic literature and through responsible authorities. According to municipality data in 1996 Cr +6  concentrations equal to 54 μg/L was measured. In 2003, 4 Cr measurements were from 50.3 to 54.9 μg/L. Exceeding the As limit was observed in the years
2004 and 2008, while for Pb in the year 2003. According
to the study of IGME in 35 samples Cr +6  concentrations
above 10 μg/L were detected (the higher concentration
was 156 μg/L). Moreover, elevated Ni, As and Pb concentrations were observed in locations across the bed of the river and areas of Oinofyta, Schimatari and Avlona. Finally, according to a study of the Geology Department of the University of Athens there were found Cr and As concentrations exceeding limit. In conclusion, increased heavy metals concentrations are likely to be the result of industrial pollution with an adverse effect on public health.

Lake Orta (N. Italy) was severely polluted from 1927 by an effluent from a rayon factory, which discharged great amounts of ammonium nitrogen and copper into the lake. In the mid nineteen fifties, some plating factories also started dumping chromium and aluminum. As a result of ammonium oxidation, the lake became very acid and the concentration of metals in the waters reached very high values. Phytoplankton, zooplankton and fish disappeared suddenly from the lake which was by 1930 classified as “sterile”. Later on, about the fifties, a small population of Cyclops abyssorum re-colonised the lake together with some rotifers, in particular Hexarthra fennica. In mid eighties following the introduction of anti-pollution legislation, ammonium loads were greatly reduced and Daphnia obtusa was recorded. The lake waters however were still very acid, prompting the proposal of the Istituto Italiano di Idro-biologia to lime the lake with calcium carbonate to neutralise the excess acidity and re...

This paper is concerned with whether the micro-scale abrasive test is suitable for studying non-flat surfaces. A new micro-scale abrasion test has been developed to do studies on cylindrical shapes. A complete procedure to determine the intrinsic wear resistance of coatings is presented and discussed. The new method allows the direct characterization of small cylindrical parts, such as pins, bolts, shafts, etc. The method developed is used to study the abrasion resistance of W–Si–N sputtered coatings and electroplated chromium films.

In this work, the adsorption of chromium(VI) was studied on activated carbon prepared from Tamarind wood with zinc chloride activation. Adsorption studies were conducted in the range of 10–50mg/l initial chromium(VI) concentration and at temperature in the range of 10–50°C. The experimental data were analyzed by the Freundlich isotherm and the Langmuir isotherm. Equilibrium data fitted well with the Langmuir