Search academic texts

Information × Registration Number 0213U000351, 0110U001986 , R & D reports Title Phase equilibria and the synthesis of superhard phases in the Al-B-C and Mg-Zn-B-C systems at high pressures in a wide range of temperatures popup.stage_title Head Turkevich V. Z.; Bochechka O. O., Registration Date 01-02-2013 Organization V.Bakul Institute for Superhard Materials popup.description2 Phase formation in the ternary Al-B-C at high pressures (up to 7.7 GPa) and temperatures (up to 2200 ° C) was studied. It was found that the interaction between the components in the subsystem Сdia AlВ12 (AlB2) with the formation of new phases at the interfaces starts at temperatures above 1500 ° C. This interaction is most active at temperatures T > 1700°С. At a pressure of 7.7 GPa aluminum diboride decomposes to AlВ12 and aluminum at a temperature above 2200 оС. Liquid aluminum reacts with the diamond to form a compound Al8B41С7, which is localized at the interphases in the form of nanoprecipitations. Based on published data and experimental results obtained in this work the phase diagram of the Al-B-C at 7.7 GPa was charted by thermodynamic calculation. According to this diagram carbide Al4C3, which is harmful to the polycrystalline material, is not formed during sintering in subsystems AlВ12-В4С and AlВ12-Сdia. Superhard ceramics, which has the best ratio of hardness (45-50 GPa) and fracture toughness (4.7-5 МПа?м1/2) was obtained by sintering AlВ12 and diamond. It was found that alloy, which consists of phase Mg, Zn, and electronic connections Mg51Zn20, MgZn2, is formed as result of effect of temperatures of 1250 °C and a pressure of 3 GPa on mixture Mg-Zn-B. Above phases form plate-grain. Amorphous boron is between these grains. The result of interactions in the system Mg-Zn-В-C at a temperature above 1700 °C and a pressure of more than 7 GPa is the synthesis of diamond, the decay of electronic connections Mg51Zn20, and the formation of MgZn2. В4С and MgВ2С2 are formed at high concentrations of boron. MgO is formed due to the presence in the mixture of oxygen impurity. It has been shown that the electrical resistivity of the synthesized diamond powder is reduced from 10^6 to 80 Ohm*cm with increasing amounts of boron from 0.007 to 1.00 % (atom) in the mixture of Mg-Zn-B-C. A further increase of boron in the charge does not reduce the resistivity. Sintering of the specified diamond powder leads to a further reduction of the resistivity of 8-10. It was found that the concentration of boron atoms in the diamond lattice is of (6.5-8.7)*10^18 cm^-3 at a concentration of boron in the growth system of 0.17 % (atom). Increasing the concentration of boron in the growth system does not lead to a significant change in the concentration of boron atoms in the lattice of the synthesized diamond. It was developed a synthesis method of diamond of high thermal stability category due to the formation during synthesis in the system Mg-Zn-B-C together with a diamond the boron compounds, which are close to the diamond on the bulk modulus and coefficient of thermal expansion. When entering these compounds in diamond crystals as inclusions they do not cause significant residual tensile stresses. Product Description popup.authors Ільницька Г. Д. Білявина Н. М. Бочечка О. О. Виноградов С. О. Гаврилова В. С. Колабиліна Т. В. Куцай О. М. Луцак Е. М. Назарчук С. М. Олєйник Г. С. Осіпов О. С. Петасюк Г. А. Романко Л. О. Свирид К. А. Старик С. П. Стратійчук Д. А. Ткач В. М. Тонкошкура М. О. Туркевич В. З. Чернієнко О. І. popup.nrat_date 2020-04-02 Close