“…It is reported that not only would it be possible to thermally decompose APR to rhenium oxides and then reduce it to rhenium powder (Equations 2 and 3), but also rhenium can be produced by oxidation of APR to rhenium heptoxide and its reduction by hydrogen (Equations 4 and 5). There are several methods which have been published based on these theories but there are still some aspects that have to be concerned (Goncharov et al 1999;Leonharot et al 2001;Li et al 2001;Hu et al 2003;Leonhardt et al 2003;Jurewicz and Guo 2005).…”
Section: Introductionmentioning
confidence: 99%
“…There are several methods which have been published based on these theories but there are still some aspects that have to be concerned (Goncharov et al. 1999; Leonharot et al. 2001; Li et al.…”
Ammonium perrhenate (APR) is an intermediate product in rhenium extraction process, by which it is possible to produce rhenium powder. The main purpose of this research is to investigate the behaviour of APR in different atmospheres as a part of reduction process. In this research, differential thermal analysis and thermo gravimetric analysis are used to peruse the APR behaviour in nitrogen, argon and hydrogen atmospheres. Also for further validation, X-ray diffraction analysis and the scanning electron microscopy were used. The results indicate that APR behaves almost the same in the argon and nitrogen atmospheres. In these conditions, APR decomposes to rhenium oxides during thermal decomposition. However, APR in hydrogen reductive atmosphere is reduced to pure rhenium powder without any reactions. SEM images showed that hydrogen reduced APR had a spherical morphology, but on the other hand the directly reduced rhenium powder in hydrogen atmosphere showed flake morphology.
“…It is reported that not only would it be possible to thermally decompose APR to rhenium oxides and then reduce it to rhenium powder (Equations 2 and 3), but also rhenium can be produced by oxidation of APR to rhenium heptoxide and its reduction by hydrogen (Equations 4 and 5). There are several methods which have been published based on these theories but there are still some aspects that have to be concerned (Goncharov et al 1999;Leonharot et al 2001;Li et al 2001;Hu et al 2003;Leonhardt et al 2003;Jurewicz and Guo 2005).…”
Section: Introductionmentioning
confidence: 99%
“…There are several methods which have been published based on these theories but there are still some aspects that have to be concerned (Goncharov et al. 1999; Leonharot et al. 2001; Li et al.…”
Ammonium perrhenate (APR) is an intermediate product in rhenium extraction process, by which it is possible to produce rhenium powder. The main purpose of this research is to investigate the behaviour of APR in different atmospheres as a part of reduction process. In this research, differential thermal analysis and thermo gravimetric analysis are used to peruse the APR behaviour in nitrogen, argon and hydrogen atmospheres. Also for further validation, X-ray diffraction analysis and the scanning electron microscopy were used. The results indicate that APR behaves almost the same in the argon and nitrogen atmospheres. In these conditions, APR decomposes to rhenium oxides during thermal decomposition. However, APR in hydrogen reductive atmosphere is reduced to pure rhenium powder without any reactions. SEM images showed that hydrogen reduced APR had a spherical morphology, but on the other hand the directly reduced rhenium powder in hydrogen atmosphere showed flake morphology.
“…Part II had a preferred orientation in α -Ta (110) direction, with small peaks also observed at 2 θ = 68 and 73° corresponding to ß -Ta. Such a mixture of phases has been encountered in low-pressure CVD [16,17] depending on deposition conditions. Figure 3 XRD patterns of Parts I and II of the Ta coating and α -Ta.…”
Section: Resultsmentioning
confidence: 99%
“…CVD–Ta precursors can be classified as organic (e.g. Ta(NEt 2 ) 3 , Ta(NEt 2 ) 4 [15], and Ta(CO) 5 ) or as halides [16]. The organic cases can leave behind impurities [15].…”
Section: Introductionmentioning
confidence: 99%
“…Part II had a preferred orientation in α-Ta (110) direction, with small peaks also observed at 2θ = 68 and 73°corresponding to ß-Ta. Such a mixture of phases has been encountered in low-pressure CVD[16,17] depending on deposition conditions.The coating orientation resulting from CVD depends strongly on operating conditions, such as adsorption[21] and concentration of reaction and byproducts[22]. Along the flow direction, increasing concentration of HF caused surface active sites on the crystal planes to be more adsorbed by HF than by H 2 (This is because the heat of adsorption of HF = 3680 J/mol [Equation(3)] is more than the heat of adsorption of H 2 = 840J/mol[20]).…”
Tantalum coating for bio-medical applications is prepared by atmospheric pressure chemical vapour deposition in a TaF 5 -H 2 system on the inner wall of a stainless steel tube. The concentration of hydrogen fluoride (HF) has a significant effect on the morphology and crystallographic orientation of the tantalum coating. As the HF concentration increases, the tantalum coating gradually becomes smooth from roughness. The rougher part and the smoother part of tantalum coating reveal ( 200) and ( 110) preferred orientation, respectively. Simultaneously, the kinetic equation containing HF concentration has been developed. The calculated results from the equation show a good correspondence with the experimental results. The performance of tantalum coating with distinct morphologies on the effect of osseointegration was studied by implanting samples in vivo. The coating with a rougher surface was more osteoattractive than the one with a smoother surface.
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