Guerold S. Bobrovnitchii

Some properties of diamonds synthesized in the new Mg–Ni–C system

Diamonds obtained in the Mg–C system were found to exhibit semi-conducting properties and cubic morphology. In these cases, strict synthesis processing parameters are required (8.0–8.5 GPa and 1800–2100 °C). The present work aims to study the mechanical and electrical properties of diamonds in the new Mg–Ni–C system. The new system has the advantage of allowing the reduction of synthesis parameters. The Mg–Ni alloy was initially produced by the preparation (4.0 GPa/1300 °C) of a Mg and Ni powders mixture. Diamond synthesis was conducted (5.5–7.7 GPa and 1250–1700 °C) with compositions varying between 15 at% Mg+85 at% Ni, and 85 at% Mg+15 at% Ni. Semi-conducting diamond was obtained with granulometry ranging from 40 to 250 μm. Some crystals displayed a cubic morphology. The best results were obtained for pressures ranging from 6.5 to 7.7 GPa, and temperatures ranging from 1550 °C to 1700 °C.

Propriedades mecânicas e termomecânicas de compósitos com partículas de diamante dispersas em matriz epoxídica modificada na razão resina/endurecedor

The mechanical properties of composites with dispersed diamond particles in epoxy matrix cured with different proportions of hardener to monomer ratio, characterized by the resin/hardener ratio (phr) were studied. An investigation on the thermo-mechanical behavior of these composites was also carried out by dynamical mechanical analysis (DMA). In the present work a complete evaluation of the mechanical properties was carried in a wide interval of phr associated with possible technological applications. Composites with up to 30 wt. % of diamond particles dispersed in type DGEBA/TETA epoxy matrix were fabricated with phr ratios varying from 7 to 21. For all investigated conditions, the composite strength decreased with the amount of incorporated diamond. Matrices with phr above the stoichiometric 13 were associated with composites with better mechanical performance. The DMA results showed that the storage modulus increases with the amount of diamond particles incorporated in the composite. The values obtained for the delta tangent, allowed an evaluation of possible mechanisms that contribute to the thermal mechanical performance of these composites.

SiC Infiltred Diamond Composites

Polycrystalline SiC-diamond composites have been fabricated by high pressure and high temperature, HPHT, sintering using a Si infiltration method. However, infiltration of liquid silicon around the diamond particles results not only in SiC but also in free silicon, which causes deterioration of the composite properties. In this work, a novel sintering procedure was developed to avoid the formation of free silicon in the composite structure. A disc composed of a mixture of graphite and silicon was first press-molded at room temperature. The disc was then placed above the diamond powder inside a high pressure chamber used for the HPHT sintering process. This arrangement permitted to preferentially form liquid Si in a C solution, which infiltrates in between the diamond particles. Using this procedure, free silicon formation is inhibited and the SiC-diamond composite forms a rigid structure with improved properties.

Nanoparticles Consolidation Mechanism at High Pressure and High Temperature in Diamond-B-Si-Cu System

The synthesis of advanced materials with superior performance and properties is of growing scientific and technological interest. In particular, significant achievements have been attained in the synthesis of nanocomposites associated with superhard materials. This work investigates nanostructured composites obtained by high pressure and high temperature sintering of synthetic diamond combined with boron, silicon and copper. Diamond powder was mixed with B, Si and Cu, also in the form of powder. The mixture was then submitted to high energy wet milling until a nanopowder was formed. Sintering of this resulting nanopowder was carried out at 5.6 GPa of pressure and 1300°C. X-ray diffraction and scanning electron microscopy analysis revealed the formation of new phases in a well consolidated nanostructure with relatively high density.

Efeito da adição de zinco sobre o rendimento do processo de síntese de diamantes em condições de altas pressões e altas temperaturas

In the present work zinc was introduced in the reactive mixture composed by Ni-Mn and graphite. The main objective of the zinc impregnation was to control the diamond nucleation process and crystal growth of particles. The results indicated that the zinc addition promotes a significant diamond yield by synthesis cycle, around 40%. Additionally, the diamond powder obtained has a high friability.

A influência de tratamento térmico complementar sobre a resistência ao desgaste de pastilha de nitreto cúbico de boro

Os compositos a base de nitreto cubico de boro (cBN) atualmente se destacam na usinagem de metais e ligas de dureza elevada, podendo substituir a retifica. A efetividade de utilizacao dos compositos de cNB depende, em geral, do estudo da tenacidade do inserto. A obtencao de pastilhas de cBN, realiza-se sob altas pressoes ate 8 GPa e temperaturas de ate 2000oC. Em condicoes nao hidrostaticas, as tensoes internas tem valores significantes, diminuindo a vida util da ferramenta. Para aumentar a tenacidade e a eficiencia de uso foi proposto o tratamento termico complementar em condicoes de vacuo sob temperaturas de ate 1000oC e tempo de 1hora. As pastilhas de cBN foram sinterizadas a pressao de 7,7 GPa e temperatura de 1600oC. A composicao da pastilha utilizada foi de 65%p de cBN e 35%p de ligante. Para determinacao de nivel de desgaste durante usinagem foi utilizado aco 4140 com dureza de 56-58HRc. Comparando a efetividade de usinagem das pastilhas de cBN obtidas com o composito Elbor®, pode ser notado que o tratamento termico complementar aumentou a capacidade de usinagem da pastilha de cBN em 40%.

The role of the ‘graphitation degree’ on the high pressure-high temperature diamond synthesis

Abstract The influence of the ‘graphitation degree’ on the formation of diamond in an anvil type high pressure was studied using different types of graphites. The ‘graphitation degree’ was measured by a new parameter PHP, related to the percentage of hexagonal perfection. Results have shown that in samples, which presented PHP ‘graphitation degree’ below 50% no diamond was formed. This suggested that a minimum ‘graphitation degree’ should be attained in order to have a successful synthesis for diamond production.