Showing 6 results for Chromium
A. Ataie1,, S. Heshmati-Manesh1,, S. Sheibani1,, G. R. Khayati,y. Firozbakht,
Volume 5, Issue 1 (3-2008)
Abstract
Abstract: In this paper solid state reduction of high carbon ferrochromium-chromite composite
pellets in the temperature range of 900-1350°C was investigated. A two stage reduction
mechanism is proposed. The first stage is likely to be controlled by the chemical reaction with
activation energy of 127.2kJ/mol. In the second stage, solid state diffusion of carbon through the
reaction product layer is suggested to be rate controlling. The activation energy of this stage was
calculated to be 93.1kJ/mol. The reduction process was found to be favored by high temperatures
as well as high vacuum. The results also show that pre-milling of initial mixture has a negative
effect on the reduction degree.
H. Aghajani, M. Soltanieh, F. Mahboubi, S. Rastegari and Kh. A. Nekouee,
Volume 6, Issue 1 (3-2009)
Abstract
Abstract: Formation of a hybrid coating by the use of plasma nitriding and hard chromium electroplating on the
surface of H11 hot work tool steel was investigated. Firstly, specimens were plasma nitrided at a temperature of 550
°C for 5 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. Secondly, electroplating was carried out in a solution
containing 250 g/L chromic acid and 2.5 g/L sulphuric acid for 1 hour at 60 °C temperature and 60 A/dm2 current
density. Thirdly, specimens were plasma nitrided at a temperature of 550 °C for 5 and 10 hours in an atmosphere of
25 vol. % H2: 75 vol. % N2. The obtained coatings have been compared in terms of composition and hardness. The
compositions of the coatings have been studied by X-ray diffraction analysis. The surface morphology and elemental
analysis was examined by using scanning electron microscopy. The improvement in hardness distribution after third
step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the
formed phases in the hybrid coating were determined to be CrN+Cr2N+Cr+Fe2-3N+Fe4N.
A. Azizi, S. Z. Shafaei, M. Noaparast, M. Karamoozian,
Volume 10, Issue 4 (12-2013)
Abstract
This paper was aimed to address the modeling and optimization of factors affecting the corrosive wear of low alloy and high carbon chromium steel balls. Response surface methodology, central composite design (CCD) was employed to assess the main and interactive effects of the parameters and also to model and minimize the corrosive wear of the steels. The second-order polynomial regression model was proposed for relationship between the corrosion rates and relevant investigated parameters. Model fitted to results indicated that the linear effects of all of factors, interactive effect of pH and grinding time and the quadratic effects of pH and balls charge weight, were statistically significant in corrosive wear of low alloy steel balls. The significant parameters in the corrosive wear of high carbon chromium steel balls were the linear effects of all factors, the interactions effect of solid concentration, mill speed, mill throughout, grinding time, and the quadratic effects of pH and solid content. Also, the results showed that within the range of parameters studied, the corrosion rate of 78.38 and 40.76 could be obtained for low alloy and high carbon chromium steel balls, respectively.
N. Ghanbarpourabdoli, Sh. Raygan, H. Abdizadeh,
Volume 13, Issue 4 (12-2016)
Abstract
In this study, the adsorption of hexavalent chromium and zinc ions from the solution is investigated by raw red mud and mechanical-chemical activated red mud along with the possibility of selective reclamation of these ions from the solution. The mechanical-chemical activation of red mud was done by employing high-energy milling and subsequent acid treatment with HNO3. Raw red mud (RRM) and mechanical-chemical activated red mud (MCARM) adsorbents were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) methods. In order to determine the suitable adsorption conditions, effects of pH of the solution, amount of adsorption, temperature, and time of adsorption were investigated. It was found that the optimum pH for the adsorption of hexavalent chromium and zinc ions by MCARM adsorbent was 2 and 6, respectively. According to these pH values, MCARM had the ability to separately adsorb more than 95 and 79% of hexavalent chromium and zinc ions from the solution, respectively. Experimental results were in good agreement with Langmuir and Freundlich isotherms. By considering the kinetic models of adsorption, the kinetics of the adsorption of both ions followed the pseudo-second-order reaction model. It was also determined that almost 25.8 and 61.8% of the hexavalent chromium and zinc ions adsorbed in MCARM could be recovered
V. Dave, R. Kotian, P. Madhyastha, K. Boaz, P. Rao, B.p. Charitha,
Volume 16, Issue 4 (12-2019)
Abstract
The aim of the present study is to assess the hardness, corrosion, and cytotoxicity of a commercially available cobalt-chromium (Co-Cr) alloy before and after simulated heat treatments at porcelain firing temperature. Five Co-Cr samples were fabricated using lost wax casting procedure. Heat treatments were carried out at 650°C, 750°C, 850°C, and 950°C. Vickers hardness was measured for as-cast and heat treated samples. The corrosion test was carried out separately in 0.1 N NaCl, 1% citric acid and artificial saliva at room temperature using potentiodynamic polarization technique. Gingival tissue biopsy of patients was taken and cultured to measure the cell viability by MTT colorimetric assay. Lowest hardness was observed at 650°C. 0.1 N NaCl and 1% citric acid corrosion medium showed a similar trend of corrosion rate. The least corrosion rate was found in artificial saliva. Firing temperature has an impact on the physical, chemical and biological properties of Co-Cr alloy in long-term clinical use.
Rabah Bobaaya, Omar Allaoui, Mokhtar Djendel, Samir Benaniba,
Volume 18, Issue 3 (9-2021)
Abstract
Coatings based on chromium borides and chromium carbides are commonly employed in applications requiring mechanical performance, such as high hardness and low friction coefficient, as well as corrosion resistance. In this work, we made layers of chromium borides and chromium carbides on the surface of low carbon steel through some specific treatments. For chromium borides, the boriding treatment in a solid medium at 900 °C for 4 hours followed by chromium electroplating on the steel surface and finally the application of annealing treatment at temperatures at 950 °C for 1 and 2 hours. For chromium carbides, the cementation in a solid medium followed by electroplating of chromium on the surface and finally the application of annealing treatment at temperatures between 500 and 1100 °C for 1 hour. The obtained results show that, in the first case, boron diffusion and chromium deposition lead to chromium borides on the treated surface. Similarly, for the second case, the cemented layer and the chromium deposited on the surface combine to form chromium carbides on the treated surface after annealing. The characteristics of the chromium borides and chromium carbides obtained are very similar to those of chromium borides and chromium carbides obtained by other processes.
