Use of boron carbonitride in devices for rapid analysis of slag oxidation

A new method has been developed for determining the degree of oxidation in a metallurgical slag. It is based on measuring the equilibrium oxygen partial pressure PO₂ with an electrochemical sensor. The basic component is a ceramic element containing boron carbonitride developed at the Institute of Problems of Materials Science, Academy of Sciences of the Ukraine. The rapid response enables one to monitor the state of the slag in the bath and to control the oxidation conditions and provide improved performance in refining steel with slag under various technological conditions.Institute of Problems of Materials Science, Academy of Sciences of the Ukraine, Kiev. Central Heavy Engineering Research Institute, Moscow. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 109–112, January–February, 1994.     

Stability of composite materials based on boron and silicon nitrides and carbides

Conclusions Tests on a number of refractory materials in molten borax with or without electrolysis have established that boron carbonitride exhibits the highest resistance to attack under these conditions. By employing boron carbonitride as lining material, it is possible to perform boronizing in a new, high-productivity electrolytic installation.Translated from Poroshkovaya Metallurgiya, No. 8 (68), pp. 60–65, August, 1968.     

Effect of porosity and grain size on the mechanical properties of hot-pressed boron carbide

Conclusions An investigation was carried out into the effect of porosity in the range 2–46% and grain size in the range (5–140)·10^–6 m on the mechanical properties of boron carbide. It is shown that the level of mechanical properties of boron carbide produced by hot pressing from powders synthesized from the elements is 1.5 times higher than that of boron carbide produced by other methods. Increasing the porosity of boron carbide to 46% decreases its strength by a factor of six or seven. Increasing the grain size to 140·10^–6 m has the same effect. An analysis is made of equations describing the dependence of the mechanical properties of boron carbide on porosity and grain size. The constants of these equations have been determined.Translated from Poroshkovaya Metallurgiya, No. 1(229), pp. 63–67, January, 1982.     

Abrasive power of titanium carbide and carbonitride

Conclusions In comparisons of the abrasive powers of powders it is necessary to consider their production technology. Only those results are comparable which have been obtained in grinding tests on the same material. In the choice of a powder as an abrasive it is necessary to know its dynamic abrasive power. The character of variation of this property enables optimum abrasive machining conditions to be determined. In the grinding of steels at pressure of up to 75 kN/m² titanium carbide and carbonitride (5 wt. % N) powders surpass electrocorundum in abrasive power during the first 300–500 sec of operation and give a better surface finish. They can therefore be successfully used as grinding powders and micropowders for the preparation of pastes intended for the abrasive machining of steels.Translated from Poroshkovaya Metallurgiya, No. 6(222), pp. 78–81, June, 1981.     

Catalytic synthesis of graphite-like boron nitride

It is well-known [1, 2] that lithium compounds have a strong effect on the process of formation of boron nitride by the carbothermal method from highly dispersed charges produced by the dissolution method. It is therefore interesting to examine the effect of these compounds on the formation and ordering of the structure of boron nitride in other methods of preparation.Investigations were carried out into the process of nitriding boron and a mixture of boric acid with soot in the presence of lithium compounds. Initial substances were amorphous boron with a purity of 98.6, boric acid of ChDA grade, grade 514 soot, grade ChDA lithium carbonate and hydroxyl, and dried nitrogen and ammonia. Charges were prepared by mixing the components by the dried method. The ratio of the boric acid and soot in the charges was constant (7:2), and the concentration of the addition was varied in the range from 1 to 58% (by mass). Nitriding was carried out in the temperature range 800–1500°C in a gas flow with an optimum speed of 2 litres/h. Temperature was measured with a platinum-platinum/rhodium thermocouple and regulated using an Sh-4501 device. Nitriding products were examined by chemical and x-ray analysis and also electron microscopy.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 91–96, May—June, 1996. Original article submitted May 23, 1994.     

Reaction of cubic boron nitride with titanium iodides

Conclusions The reaction of cubic boron nitride with the gaseous phase of titanium iodides (process duration 0.25–2.0 h, total pressure of titanium iodides 100 Pa) results in the preferential formation of TIN in the temperature range 900–1200°K and of titanium nitride and titanium diboride at 1200–1300°K.Translated from Poroshkovaya Metallurgiya, No. 10(262), pp. 57–59, October, 1984.     

High-temperature reaction of aluminum oxide with boron in vacuum

The reaction of aluminum oxide with boron in vacuum was studied over a wide range of temperatures. Analysis of the reaction products was carried out by chemical, x-ray diffraction, optical, and metallographic methods. The temperature dependence of the reaction was determined. A high boron phase of the composition AlB_18–31 is produced by the borothermic reduction of aluminum oxide. The crystalline phase possesses a hexagonal structure with the elementary cell parameters a = 1.097, c = 2.378 nm. Aluminum dodecaboride and diboride phases were not detected in the reaction products.Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Ukrainian State University of Food Technology, Kiev. T. Shevchenko National University, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 20–27, May–June, 1996. Original article submitted April 15, 1994.     

Effect of lithium on structure formation of graphite-like boron nitride with carbothermal synthesis

Formation of a graphite-like boron nitride structure during carbothermal analysis in the presence of lithium compounds in a stream of nitrogen or ammonia is studied by electron microscopy, x-ray, and chemical methods. A marked reduction in the formation temperature for graphite-like boron nitride with a highly ordered structure is observed and chemical aspects of the process are discussed.Institute of Problems of Materials Science, National Academy of Sciencesof the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 1–8, July–August, 1994.     

Elastic constants and elasticity moduli of cubic and wurtzitic boron nitride

Elasticity moduli and elastic constants for sphaleritic and wurtzitic boron nitride are calculated and determined by experiment. Numerical values are given for single crystals of these materials and polycrystals of hexanite-R, elbor-R, belbor, kiborite, and other superhard materials. An approach is suggested for combining hot pressing at ultrahigh pressures and a pulsed ultrasonic technique which may be used to determine the elasticity modulus and elastic constants of the majority of refractory compounds which are difficult to determine by other techniques.Institute of Materials Science, Ukrainian Academy of Sciences, Kiev. Institute of Metal Physics, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7/8(380), pp. 92–99, July–August, 1995.     

Structural special features and infrared spectra of absorption of ultradisperse boron nitride

Conclusions The ultradisperse powders of boron nitride with the mean particle size of 5.3–66 nm showed marked anisotropic deformation of the crystal lattice as a result of the structural stresses which are caused by the dimensional factor and are distributed nonuniformly through the volume of the particle.The turbostratic strain leads mainly to weakening of the interlayer bonds and shifts the maximum of the band of the interplanar oscillations to lower frequency by 17 cm^–1 for the specimen with a dispersion of 5.3 nm. In addition to this, the turbostratic strain causes asymmetric widening of the band of the intraplanar oscillations in the short-wave wing of the curve and displaces the maximum of this band by 20 cm^–1 to the short-wave range (for the specimen with a dispersion of 5.3 nm).Examination by the IR spectral method showed that the interatomic bonds shorten on the average by 10^–4 nm within the limits of the flat lattices. The investigations revealed the regular nature of the removal of the strain of the crystal lattice from the ultradisperse boron nitride during vacuum heat treatment accompanied by sintering of the powder.Translated from Poroshkovaya Metallurgiya, No. 1(301), pp. 85–91, January, 1988.     

Structural studies of ceramics based on detonation-wave-treated graphite-like boron nitride

The formation of a structure during pressureless sintering of graphite-like boron nitride (BN) powders pretreated in detonation waves was studied. The treated powders contained 10–12% wurtzite BN phase and 2–3% sphalerite phase. During sintering at just 1200 °C a reverse transformation from dense BN phases to graphite-like phases and primary recrystallization of highly fragmented BN_g occur as a result of the pretreatment. Accretive recrystallization of BN_g begins at 1500 °C and at T=1700–1950 °C platy grains with a size of 1–3 µm are formed in the developed surface. At 1700 °C the density of the specimens reach 0.95 of the theoretical value. The specimens produced at 1950 °C have a higher compressive strength and radiation resistance than do those made without pretreatment.Deceased.Institute of Materials Science, Ukrainian Academy of Science, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 75–80, May–June, 1995.     

Effect of boron on the thermal conductivity and thermal expansion of titanium

Conclusions Additions of boron substantially increase the thermal conductivity of titanium. A linear relationship is observed between the thermal conductivity of titanium-boron alloys and their boron content. It must be emphasized, however, that the rise in the thermal conductivity of these alloys cannot be ascribed solely to the formation of TiB₂ phase. The coefficient of linear expansion of titanium linearly decreases with rise in boron content up to a temperature of 500°C. Above this temperature, a more complex relationship is observed.Translated from Poroshkovaya Metallurgiya, No. 8 (92), pp. 78–82, August, 1970.     

Investigation of the heat resistance and thermal stability of micaceous ceramic materials with additions of boron nitride

Conclusions On the basis of complex investigations it has been established that Brand UMB-5KT materials, having a high heat resistance and satisfactory thermal stability, can be recommended for use in the flowthrough parts of high-head compressors, with a temperature of the gas flow equal to 600–700°C, and in certain types of turbines with a working temperature up to 950–1000°C.It has been established that the requirements for densified materials are most fully satisfied by Brand UMB-5KT material with 4–8% boron nitride.Special graphite K70/30-3 and aluminum-asbestos-graphite layers have sufficient heat resistance only up to 500°C, and cannot be recommended for long-term operation at higher temperatures.Deceased.Translated from Poroshkovaya Metallurgiya, No. 9 (81), pp. 80–86, September, 1969.     

Contact reaction of Kh20N80 alloy with boron nitride

Conclusions A study was made of the causes of the contact reaction between Kh20N80 alloy and boron nitride during the sintering of composite compacts in various environments at temperatures of 1170–1330°C. It was established that the contact reaction between Kh20N80 alloy and boron nitride occurs in the following stages:partial dissociation of the boron nitride, with the evolution of free nitrogen, which then reacts with the chromium;reaction of boron with the nickel and chromium, with the formation of boride phases;enrichment of the nickel-base solid solution in chromium and the appearance of a chromium-base solid solution.In sintering in various gaseous environments the temperature at which partial melting begins during the contact reaction falls in the order argon (1330°C) > hydrogen and cracked ammonia (1250°C) > vacuum (1170°C).A 20% Cr-80% Ni alloy - Translator.Translated from Poroshkovaya Metallurgiya, No. 5(161), pp. 31–39, May, 1976.     

Effect of the different crystal structures of boron nitride on its high-temperature stability in oxygen

Conclusions The crystal structure of boron nitride has a pronounced effect on its high-temperature stability in oxygen. The least oxidation resistance is exhibited by wurtzite-type boron nitride, which is due to its extremely defective structure, and the highest oxidation resistance by cubic boron nitride, which has a perfect crystal structure. The oxidation of all three modifications of boron nitride is accompanied by the formation of boric anhydride, elemental nitrogen, and nitrogen dioxide. The observed intense evolution of nitrogen dioxide from BN_g is apparently linked with differences in electronic structure between this boron nitride form and the diamondlike modifications (BN_s and BN_w). The amount of nitrogen dioxide liberated from each modification is a maximum at a temperature of 1100°C.Translated from Poroshkovaya Metallurgiya, No. 7(223), pp. 83–86, July, 1981.     

Structure and properties of powders of some composite materials based on wurtzite boron nitride

Conclusions Addition of titanium carbide and zinc or aluminum oxide to a granulating blend of wurtzite boron nitride produces a low-strength sintered mass which disintegrates easily along the BN granule boundaries under mechanical action, ensuring the production of granules of a given grain size.Individual particles of composite material based on wurtzite boron nitride obtained with admixtures of zinc oxide are characterized by good compressive strength.Translated from Poroshkovaya Metallurgiya, No. 6(270), pp. 81–85, June, 1985.     

Austenite recrystallization and carbonitride precipitation in niobium microalloyed steels

The response of austenite to thermomechanical treatment is investigated in two series of niobium microalloyed steels. Optical and electron metallographic techniques were used to follow the austenite recrystallization and carbonitride precipitation reactions in these steels. The first series of steels contained a constant level of 0.05Nb, with carbon levels varying from 0.008 to 0.25 pct. It was found that a lower carbon concentration results in faster austenite recrystallization, due to a smaller carbonitride supersaturation, which leads to a reduced precipitate nucleation rate. The second series of steels was designed with a constant carbonitride supersaturation, by simultaneously varying the Nb and C concentrations while maintaining a constant solubility product. In these steels, the recrystallization kinetics increase as the volume fraction of Nb(C, N) is reduced and/or as the precipitate coarsening rate is increased. The volume fraction of carbonitrides increases as the Nb: (C+12/14 N) ratio approaches the stoichiometric ratio of approximately 8:1. The precipitate coarsening rate was shown to increase with increasing amounts of niobium remaining in solution in the austenite (i. e., “excess” Nb after precipitation). As expected, recrystallization proceeds more slowly at lower temperatures and after a reduced amount of deformation. An experiment to determine whether Nb atoms dissolved in the austenite could exert a significant solute-drag effect on the recrystallization reaction indicated that 0.20Nb in solution could reduce the rate of recrystallization compared to a Nb-free C-Mn steel. However, this solute effect was smaller than the retarding effect which 0.01Nb can have when it is precipitated in the form of carbonitrides on the austenite substructure after rolling.     

Dependence of the Structure of Sintered Boron Carbonitride on the Defect Level in the Starting BN Powder

We have carried out a comparative x-ray analysis of boron nitride powders with different degrees of ordering and sintered specimens of boron carbonitride based on such powders. We have established that an indicator of sintering activity for the boron carbonitride specimens is the rate of formation of the r-BN phase, the content of which depends on the degree of ordering of the starting BN powder. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 100–107, May–June, 2005.     

Crystallization of comminuted boron powders

Conclusions An x-ray diffraction investigation has established that, irrespective of their degree of amorphization, comminuted boron powders crystallize after melting in the rhombohedral structure, i.e., revert to their original crystalline state.Translated from Poroshkovaya Metallurgiya, No. 4 (148), pp. 83–87, April, 1975.     

Preparation of technical zirconium diboride by the carbothermic reduction of mixtures of zirconium and boron oxides

Conclusions A study was made of the preparation of technical zirconium diboride by the reduction of mixtures of zirconium and boron oxides with carbon under industrial conditions. It is shown that the optimum conditions for the preparation of zirconium diboride by the carbothermic method are established when a charge having the composition ZrO₂+1.2 B₂O₃+5 C (i.e., with a 20% excess of boric anhydride over the stoichiometric composition) is reduced at 2000°C in a hydrogen or converted gas atmosphere. The resultant ZrB₂ contains 18–19% B (compared with the theoretical boron content of 19.25%) and not more than 0.8% C.Translated from Poroshkovaya Metallurgiya, No. 11 (131), pp. 80–84, November, 1973.