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The modeling of nitrogen mass transport in CoCr alloys 全文
2016
Petraitiene, A., Aleksandras Stulginskis Univ., Akademija, Kauno reg. (Lithuania). Centre of Mathematics, Physics and Information Technologies
The modeling of nitrogen mass transport in CoCr alloys 全文
2016
Petraitiene, A., Aleksandras Stulginskis Univ., Akademija, Kauno reg. (Lithuania). Centre of Mathematics, Physics and Information Technologies
The kinetics of plasma nitriding of CoCr alloy below temperatures of nitrides formation and mechanisms of nitrogen penetration are analyzed by proposed kinetic modeling in this article. Proposed nitrogen diffusion model is based on the trapping – detrapping (TD) model and developed taking into account the effect of the concentration dependent diffusivity of nitrogen, nitrogen adsorption on the surface of alloy and surface swelling process. The model indicates the influence of chromium atoms to nitrogen atoms diffusivity. The model consists of time and depth dependent diffusion, which is described by a partial differential equation, and it is solved by using Crank – Nicolson finite difference method. By fitting of experimental nitrogen depth profiles, it is shown that nitrogen diffusion coefficient varies with nitrogen concentration according to Einstein-Smoluchowski relation. Nitrogen depth profiles in plasma nitrided medical grade CoCr alloy (ISO 5831 – 12) at T = 400 °C for 1, 4 and 20 hours calculated on the basis of this model are in good agreement with experimental nitrogen profiles. Furthermore, the swelling process is showed and analysed, derived the dependency of swelling rate on nitriding duration – the swelling rate is inversely proportional to the square root of nitriding duration. The obtained diffusion coefficient value and the swelling process rates satisfy the experimental data form Ref. The derived model explains physical processes during plasma nitriding and allows obtaining nitrogen depth profiles for any requisite nitriding duration.
显示更多 [+] 显示较少 [-]The Modeling of Nitrogen Mass Transport in CoCr Alloys 全文
2016
Petraitienė, Akvilė
The kinetics of plasma nitriding of CoCr alloy below temperatures of nitrides formation and mechanisms of nitrogen penetration are analyzed by proposed kinetic modeling in this article. Proposed nitrogen diffusion model is based on the trapping – detrapping (TD) model and developed taking into account the effect of the concentration dependent diffusivity of nitrogen, nitrogen adsorption on the surface of alloy and surface swelling process. The model indicates the influence of chromium atoms to nitrogen atoms diffusivity. The model consists of time and depth dependent diffusion, which is described by a partial differential equation, and it is solved by using Crank – Nicolson finite difference method. By fitting of experimental nitrogen depth profiles, it is shown that nitrogen diffusion coefficient varies with nitrogen concentration according to Einstein-Smoluchowski relation. Nitrogen depth profiles in plasma nitrided medical grade CoCr alloy (ISO 5831 – 12) at T = 400 °C for 1, 4 and 20 hours calculated on the basis of this model are in good agreement with experimental nitrogen profiles. Furthermore, the swelling process is showed and analyzed, derived the dependency of swelling rate on nitriding duration – the swelling rate is inversely proportional to the square root of nitriding duration. The obtained diffusion coefficient value and the swelling process rates satisfy the experimental data form Ref. The derived model explains physical processes during plasma nitriding and allows obtaining nitrogen depth profiles for any requisite nitriding duration.
显示更多 [+] 显示较少 [-]Mineral composition, nitrogen distribution of goat’s milk produced under Algerian steppe condition across lactation stage 全文
2024
Chenouf, Amel | Yabrir, Benalia | Khirani, Ali | Boukerch, Amina | Hakem, Ahcen | Houali, Karim
Goat milk constitutes a well-priced source of minerals and proteins for a large rural population, particularly those living in the mountains and whose access to state-subsidized milk is very limited. This study aims at assessing the mineral composition and nitrogen distribution of goat milk produced by the Algerian Arabia breed and estimating how lactation stage affects these elements. Thirteen individual Arabia goat milks were collected and analysed three times during the lactation period (early, mid, and late). Minerals were analysed by atomic absorption spectrometry and nitrogen fractions using the Kjeldahl method. The findings of the research showed that casein, whey, and milk protein content had respective mean values of 2.95, 0.74, and 3.54 g 100 mlE−1, respectively. The highest levels of minerals were found for calcium (537 μg mlE−1), and sodium (336 μg mlE−1). The average trace mineral concentration was between 1.78 μg mlE−1 (Fe) and 0.007 μg mlE−1 (Cs). Heavy metal concentrations were assessed to be 0.057 μg mlE−1 for Pb and 0.009 μg mlE−1 for Cd. An important effect of stage of lactation (p < 0.05) was observed on only K, Fe, and Na mineral components, whereas nitrogen distribution was not affected. As the lactation period progressed, the variation of these components was not constant and fluctuated across lactation stages.
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