G. Bliznakov

On the borothermic preparation of titanium, zirconium and hafnium diborides

Abstract The formation of titanium, zirconium and hafnium diborides by reaction between metal dioxides and elemental boron in vacuum in the temperature range 1000 °–1750 °C has been investigated. It has been established that titanium diboride with a composition close to that of stoichiometric TiB2 is obtained after a heattreatment of the reactants at 1700 °C for I h; HfB2 is obtained after heat treatment at 1750 °C for 2 h. Experimental results show that higher temperatures are necessary for the preparation of stoichiometric ZrB2 by the borothermic method. The structure of HfB2, and its stability at boiling point and at room temperature in the presence of acids, mixtures of acids, mixtures of acids with oxidizing agents, and alkaline solutions has been studied.

On the borothermic preparation of some vanadium, niobium and tantalum borides

Abstract The formation of vanadium, niobium and tantalum diborides by the reactions of V2O3, Nb2O5 and Ta2O5 with elemental boron under vacuum in the temperature range 1000 °–1750 °C has been investigated. It has been established that niobium and tantalum diborides with a composition close to that of stoichiometric NbB2 and TaB2 are obtained after a heat treatment of the reactants at 1650 °C for 1 h. Borothermic reduction of V2O3 does not give a single-phase product but a mixture of VB2 and VB. A method for the chemical analysis of NbB2− and TaB2 samples has been proposed.

ON THE PREPARATION OF SOME CHROMIUM, MOLYBDENUM, AND TUNGSTEN BORIDES.

Abstract The formation of CrB2, Mo2B5 and W2B5 by the reactions of Cr2O3, MoO2 and WO2 with elemental boron in vacuum has been investigated. It has been established that the borothermic reduction of Cr2O3 is complete at temperatures above 1600°C, CrB2 containing CrB being obtained; the amount of CrB increases with increase in temperature. The reaction between MoO2 and B at low temperatures leads to a partial reduction of the dioxide to Mo2O3. Formation of Mo2B5 begins above 1200° C and at 1600°C the pure compound only is obtained. Mo2B5 has a defect structure. The optimum temperature for the borothermic preparation of W2B5 is also 1600°C. The product obtained displays a certain deficiency of boron. At low temperatures W2B-phase is obtained, while above 1600°C, monoboride, WB, is formed simultaneously with W2B5.

On the preparation of crystalline aluminium borides by a vapour deposition process

The possibility of the formation of crystalline aluminium borides rich in boron, by a vapour-deposition process has been investigated. The gas phase contained pure AlBr3, BCl3 and H2. Deposition on tungsten leads to a complex mixture of tungsten and aluminium borides. Crystals of C4AlB24 were deposited on a graphite surface at 1400°–1600°C, carbon being supplied at the beginning of the process by diffusion from the graphite. Subsequently, to make further crystal growth possible, a compound containing carbon was introduced into the gas phase; otherwise β-rhombohedral boron appears on the C4AlB24 crystals already formed. A binary compound of aluminium and boron (α-AlB12) has been prepared at temperatures above 1600°C.

ON THE PREPARATION AND SOME PHYSICAL PROPERTIES OF GADOLINIUM SESQUISULPHIDE AND GADOLINIUM MONOSULPHIDE.

Abstract The optimum conditions for the preparation of stoichiometric gadolinium sesquisulphide and gadolinium monosulphide according to the reactions Gd 2 O 3 +3 H 2 S = Gd 2 S 3 +3 H 2 O (1) and Gd 2 O 3 +2 Gd 2 S 3 + 3 C = 6 GdS +3 CO (2) have been investigated. It has been established that stoichiometric Gd 2 S 3 is obtained at temperatures above 750 °C. Gadolinium monosulphide was prepared by carrying out reaction (2) in vacuo in two stages : i.e. , the stoichiometric mixture of the three components was heat-treated at 1600 °C for 2–3 h, ground and pressed into pellets, then heat-treatment of the pellets was carried out at 1700 °C for 2 h. The magnetic susceptibilities of Gd 2 S 3 and GdS have been measured and the effective magnetic moments have been determined. The latter are close to the magnetic moment of the Gd 3+ ion which indicates the prevalence of ionic bonds in both sulphides. The dependence on temperature of the work function, ϑ, for cathodes of Gd 2 S 3 and GdS has been investigated. The conductivities of both sulphides have been determined theoretically; Gd 2 S 3 is deduced to possess a semiconducting, and GdS a metal, conductivity.

A study of the properties of carbide cutting plates with boride coatings

Abstract Boride coatings were obtained on various types of cutting plates of doped and undoped WC-Co alloys by thermal treatment using TiB 2 . The dependences of the coating hardness on temperature and on the duration of deposition were studied. The data obtained were compared with data on the hardness of cutting plates without coatings or with TiC and TiN coatings deposited by chemical vapour deposition (CVD). It was established that the hardness of the boride layers exceeds both the hardness of uncoated plates and the hardness of plates with CVD coatings. The microstructure of the coatings was investigated by optical and electron microscopy. Comparative studies of the wear resistance during steel cutting of boride-coated plates, of standard hard alloy plates and of CVD-coated standard plates were carried out. The boride-coated cutting plates showed the best wear resistance.

An investigation on the formation of metal-like compounds in the diffusion layer obtained during simultaneous multicomponent saturation of iron (Armco) with boron and zirconium☆

Abstract The structure, thickness and microhardness of the diffusion layer obtained during solid phase saturation of iron (Armco) with ZrB 2 using various activators were studied. Monoclinic ZrO 2 and Fe 2 B with zirconium doping were established by X-ray phase analysis. The diffusion mobilities of zirconium and boron, together with the increases in their amounts in the layer, were studied by X-ray microprobe analysis, emission spectrography and metallographic analysis. The grain size of the surface layer was established by scanning electron microscopy. The activation energy of the process was calculated. On the basis of thermodynamic calculations, a probable mechanism of formation of metal-like compounds in the diffusion layer in the presence of a given activator is proposed. It was established that during the heat treatment the system became heterogeneous and that transfer of the components took place with the participation of gaseous carriers and a liquid phase.

Modification of steel surfaces by thermal treatment in the presence of ZrB2 and KBF4

Abstract The preparation of coatings on some tool and carbon steels by treatment with ZrB2 and various activators was investigated. The phase composition and layer structure were studied. It was shown that increases in the amounts of carbon and some alloying elements in the steel hinder the diffusion of the transition metal into the matrix. The presence of zirconium in the surface zone results in the formation of phases with an enhanced hardness compared with that of iron borides. The treatment of steel surfaces with zirconium diboride and some activators by the contact method was shown to lead to complex boronization-zirconization.