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[en] Homogeneous mixtures of boron and silicon with compositions ranging from 0 to 14.3 at.% Si were reacted at 1600⁰C in an argon atmosphere. X-ray powder patterns of these samples revealed only two regions in this composition range. From 0 to 5.6 at.% Si a regular variation of the cell parameters of β-rhombohedral boron is observed that corresponds to a single-phase solid solution of silicon in boron. In the range 5.6-14.3 at.% Si a two-phase alloy occurs, consisting of a mixture of SiB₆ and silicon-saturated boron solid solution. Micrographic examinations and microprobe analysis of metallographic sections of bulk zone-melted B-Si alloys support these conclusions. Density measurements performed on bulk samples with silicon contents varying from 0 to 5.6 at.% indicate that, unlike many other impurities, silicon could dissolve by substitution in β-rhombohedral boron. (Auth.)

[en] The purification of boron by electron beam melting and chemical vapour deposition from BI₃ was investigated. The analytical results obtained by spark source mass spectrography are compared and discussed. (Auth.)

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[en] The synthesis, purification and thermal decomposition of boron triiodide have been investigated as a method for preparing high purity boron. Using spark source mass spectrography for the analyses of bulk samples, the purity of boron is studied as a function of the purification treatments applied to BI₃ prior to its decomposition. Bisublimation,recrystallization and, to a higher degree, zone refining of BI₃ result in a noticeable decrease in the levels of almost all impurities except carbon and oxygen. The lowest contamination levels attained are 200 and 470 wt. ppm for carbon and oxygen, respectively, and a total content of 150 wt. ppm for the other main impurities. Whereas the latter value could be reduced by improved zone refining of BI₃, lower levels of carbon and oxygen appear very difficult to obtain. (Auth.)

[en] Chemical interaction was investigated experimentally between solid mild steel and liquid Mg-Mn alloys at 1000 K. In half-saturated Mg-Mn melts (0.6-0.7 at.% Mn), a transition zone with a gradient in Mn concentration consisting of an inner layer of αFe(Mn) and an outer one of γ(Fe, Mn) grows at a slow rate by solid state diffusion. When the Mg-Mn melt is fully saturated in Mn (1.3 at.%), a continuous reaction layer of βMn(Fe) with an Mn content ranging from 65 to 93 at.% is rapidly formed at the steel surface. Growth of this layer proceeds by solid state diffusion of Fe and Mn atoms according to a parabolic law e²=kt, with k=2.4x10^-12 m² s^-1. The effects of silicon dissolved as impurity in the melt and of carbon dissolved in Fe base substrate are pointed out

[en] Various features of the synthesis, analysis and crystal growth of single-phase boron-rich B-Si alloys were studied. Polycrystalline samples were prepared by sintering powdered mixtures of boron and silicon at 1600⁰C. Coherent pellets resistant to thermal stress were obtained for all compositions in the range 0 - 5.6 at.% Si, the density being about 70% of the theoretical value. However, dense polycrystalline B-Si ingots were obtained by zone melting at about 2000⁰C using a modified Verneuil process, but the maximum silicon content for homogeneous samples was 4 at.% and these melted specimens were very brittle. Chemical vapour deposition from a gaseous mixture of BBr₃ and SiBr₄ was also investigated from a thermodynamic point of view: the calculated results were compared with the experimental data obtained by previous authors. The homogeneity of the B-Si alloys was characterized by non-destructive electron microprobe analysis of silicon using SiB₆ single crystals as standards. The average silicon content was determined by UV spectrophotometric titration after chemical treatment of the samples, i.e. after conversion into chlorides, hydrolysis and preparation of the α-Si(Mo₁₂O₄₀) complex. The growth of B-Si solid solution single crystals was attempted both in the solid state by diffusion of silicon into a boron single crystal and from the liquid phase by zone melting. The latter technique gave the best results: under specific conditions the spontaneous growth of 0.2-1 cm³ B-Si single crystals containing up to 3 at.% Si was achieved. (Auth.)

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[en] During a wider study of the correlation between the purity and the physical properties of β rhombohedral boron, Knoop hardness and room resistivity measurements were performed on samples prepared by different methods (chemical vapour deposition (CVD) and fusion) and precisely analysed with a spark source mass spectrometer. The authors systematically measured the hardness (taking into account the surface state, the load, the anisotropy and the grain size) to determine small hardness variations within the range of 10%. Hardness HK₂₀₀ (kg mm^-2) increases regularly with the impurity content C (ppm) according to the equation HK₂₀₀=0.015lambdaC + 2320 where lambda = 1 for the molten samples and lambda = 6.2 for the CVD samples; the different slopes are probably due to a different impurity distribution: the logarithm of the room resistivity rho (MΩ cm) increases linearly with the purity according to the equation log₁₀rho=(0.6 - 1.1)x10^-4 C for samples of grain size 5 - 500 μm; the Knoop hardness and resistivity are anisotropic in single crystals. (Auth.)