Borothermic reduction

An intimate mixture of the starting materials is pelleted and placed in a crucible and heated to 1500-2000°C under vacuum or in a vented furnace, i. Borothermic Reduction of a Metal Oxide. 

The borothermic reduction of a metal oxide is easiest when there is no formation of dodecaboride. The boric oxide is volatile and is completely eliminated > 1500°C under vacuum. 

Borothermic reduction of oxides enhanced by electron-beam bombardment. Light lanthanide borides have been prepared from the oxides according to a reaction such as the following one (Latini et al. 2002) ... 

Borothermic reduction was confirmed at a lower temperature, and the carbothermic reduction occurred at a higher temperature (33), which favors the production of high-purity powders. TiB2 and ZrBj powders were also synthesized by mechanochemical treatment of titania and zirconia powders with amorphous boron followed by a relatively low-temperature annealing (1100°C) (34). The occurrence of polymorphic transformations has been observed with milling time for both systems, together with a decrease upon annealing of the temperature of the boro-... 

P Millet, T Hwang. Preparation of TiB2 and ZrB2. Influence of a mechanochemical treatment on the borothermic reduction of titania and zirconia. J Mater Sci 31 351, 1996. 

Structural and physical properties of solid solutions Ce Sm B were studied by Aivazov et al. (1980) on a series of samples prepared by borothermal reduction of the mixed oxides at 1700°C in vacuum. X-ray and chemical analysis revealed a continuous solid solubility of SmBj, to CeB i, CaB -type, Pm3m (table 4). Magnetic susceptibilities (80-1000 K 3, 5, 10 kOe) revealed Sm-ions to be present in different valence states. Hall emf, electrical conductivity and thermo-emf were also measured on specimens obtained by hotpressing at 1900-2000°C, 500 kg/cm in vacuum. 

Raman spectra of the hexaboride solid solution EUj Gdi ,B5 have been measured by Ishii et al. (1976). Samples were prepared by borothermal reduction of oxide mixtures. Lattice parameters obtained from powder X-ray methods confirmed the... 

The existence of a continuous series of solid solutions Lai tEUjB6, CaB -type, Pm3m, was confirmed by Aivazov et al. (1979), who used various physico-chemical methods. Samples were synthesized by borothermal reduction of the corresponding oxides (1900-2000°C). On the basis of the electrophysical properties a supposition is made on an increase of the ionic component in the Me-B bond when Eu is substituted for La. Boron and metal defects were determined from density and lattice parameter measurements (small negative deviation from Vegard s rule). Their X-ray results essentially agree with the data by Mercurio et al. (1974). 

The nature of the exchange interaction in solid solutions La,Eu,, B6 was investigated by Mercurio et al. (1979). Samples were prepared by borothermal reduction of mixed oxides at 1550°C in high vacuum (X-ray and chemical analysis). No lattice parameter data were given. 

Aivazov et al. (1979) investigated phase equilibria and magnetic properties within the section LaB -SmEg. Alloys were prepared by borothermal reduction at 1700°C in vacuum ... 

Tarascon et al. (1980) independently studied the valence transition of Sm as well as the temperature dependence of the Sm oxidation state in Sm, La tB6 solid solutions, CaBg-type, Pm3m. Samples were prepared by borothermal reduction of the mixed oxides under vacuum and high temperatures. The exact values of x have been... 

A continuous solid solution (Y, La)B6 with CaB -type of structure, Pm3m, was found from specimens b), but a restricted solid solution appears from alloys a), due to the different melting behavior of YBj (incongruent) and LaBg (congruent), which results in a nearly complete fractional crystallization of the two hexaborides. At variance with the results obtained by Bondarenko et al. (1966) on samples prepared by borothermal reduction, lattice parameters of specimens b) closely obey Vegard s rule and are shown in fig. 36 including superconductivity data. 

Tarascon et al. (1980) investigated the valence transition of Sm in the hexaboride solid solutions Sm, M B (M = Yb, Sr +, La ", Y, Th +). Samples were prepared by borothermal reduction of the mixed oxides under vacuum and high temperatures. The exact values of x have been determined by x-ray fluorescence analysis and checked by density measurements. Density measurements. X-ray and chemical analysis of SmB indicate an atomic ratio B/Sm x 6. From X-ray absorption measurements at the L, edge at 300 K the Sm + Sm + atomic ratio was obtained as a function of x. (The L,n absorption spectrum of Eu + in EuB was used as reference.) Y + substitution of Sm decreases the average Sm valence towards Sm in accordance with estimations of the average Sm valence in the hexaborides (Sm, Sm +), M B from lattice parameter measurements, fig. 34c. Lattice parameters of Sm +B a = 4.186, and Sm + Bg a = 4.115, were derived from interpolations of neighboring divalent and trivalent rare earth hexaborides. 

A sample with composition Y, 585, prepared by borothermal reduction of the... 

Superconductivity in hexaboride solid solutions Yi ,Yb tB5 (x < 0.3) was studied by Hiebl and Sienko (1980) on samples prepared by borothermal reduction of the... 

Kasaya et al. (1983) investigated the mixed valency behaviour of Tm in the concentrational section Ybj. Tm Bg by means of susceptibility measurements and Ln, absorption spectroscopy. Due to the thermodynamic instability of TmB a rather limited solid solubility is observed for 0 < x < 0.5. Lattice parameters show a negative deviation from Vegard s rule. Samples were prepared by borothermal reduction of the mixed oxides in vacuum and exact values of x were derived from X-ray fluorescence analysis. 

A powder with good characteristics (high purity, good homogeneity, fine particle size, narrow particle size distribution, absence of hard agglomerates) is a must to get the desired properties and microstructure in the final component and thus synthesis of high quality powder is extremely important. Powders of ZrB and HfB are synthesized by (a) reaction between elements (Brochu et al., 2008 Tamburini et al., 2008) (b) borothermic reduction of metal oxide (Peshev et al., 1968), (c) boron carbide reduction of metal oxide in presence of carbon (Sonber et al, 2010 2011) (d) carbothermic reduction of metal oxide and B Oj (Fahrenholtz et al., 2007) (e) Metallothermic reduction of metal oxide and B Oj (Setoudeh et al., 2006 Kobayashi et al., 1993),(f) molten salt electrolysis (Frazer et al.,1975) (g) solution based techniques (Yan et al., 2006) and (h) s3mthesis from polymer precursors (Suetal., 1991). 

Borothermic reduction of metal oxide No carbon contamination Elemental boron is expensive Loss of boron... 

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