Механохімічний синтез карбіду кобальту з використанням вуглецевих нанотрубок

Nanoscaled (about 15 nm of size) metastable carbide Co3C was synthesized in a high-energy planetary ball mill by mechanical alloying of a mixture of powder cobalt (75 at. %) and multiwalled carbon nanotubes (CNT, 25 at. %). Phase transformation takes place at reaction milling according to the reaction hcp-Co + CNT ® Co3C (reaction time is 120 - 220 min). The crystal structure of the Co3C carbide formed in the milling products was studied by X-ray diffraction method. It has revealed that the Co3C phase crystallizes in a Fe3C-type structure with a = 0.4982(3) nm, b = 0.6715(6) nm, c = 0.4457(7) nm, Pnma space group. The reliability factor RB is equal to 0.065 for 48 reflections presented at diffraction pattern. It is found that the crystal structure of the Co3C carbide obtained by reaction milling of the Co-CNT charge is significantly internally deformed (distortion degree of the CCo6 octahedron is 3.67 %) and contains the reduced interatomic Co-C distances (up to 0.188 nm). It was shown that the use of carbon nanotubes instead of graphite substantially reduces the duration of the Co3C carbide synthesis.Метастабільний нанорозмірний карбід Co3C зі структурою типу Fe3C вперше синтезовано механохімічним сплавленням в високоенергетичному планетарному млині шихти, що містить порошки кобальту та багатошарових вуглецевих нанотрубок. Докладно досліджено кристалічну структуру цього карбіду і показано, що механохімічна обробка веде до її суттєвої внутрішньої деформації, яка проявляється як в збільшенні ступеню деформації октаедру CCo6, так і в скороченні деяких Co-C міжатомних відстаней. Показано ефективність застосування вуглецевих нанотрубок замість графіту при механохімічному синтезі карбіду Co3C

Sintering of BN Based Composites with ZrC and Al under High Temperatures and Pressures

Abstract: The sintering of cubic boron nitride (cBN) based ceramic matrix materials with zirconium carbide and aluminum has been carried out under high pressures and temperatures. The performed study has revealed that the interaction between mixture components with the formation of a new phase, namely, zirconium diboride (ZrB2) occurs at sintering temperatures above 1750°C and an applied pressure of 7.7 GPa. A further increase in the sintering temperature leads to a growth in the volume ZrB2 content and reduces the microhardness and crack toughness of the studied materials. The flank wear of specimens under the conditions used for the processing of AISI316L stainless steel (vc = 300 m/min, t = 300 s) grows with an increase in the sintering temperature to attain the critical value VB = 325 µm, when the specimen sintered at temperature of 2300°C is used, and VB = 200 µm for the specimen sintered at 1750°C