Oxidation Kinetics of Zirconium Carbide at Relatively Low Temperatures

The isothermal oxidation of ZrC powders was carried out at relatively low temperatures of 380° to 550°C at oxygen pressures of 1.3, 2.6, and 7.9 kPa under a static total pressure of 39.5 kPa, achieved by mixing with argon, using an electromicrobalance. The oxidation kinetics are described by the diffusion-controlled Jander's equation, following rapid oxidation in the early stage. Two activation energies were obtained: 138 kJ · mol⁻¹ below about 470°C and 180 kJ · mol⁻¹ above that temperature. The high- and low-temperature oxidation mechanisms are discussed in connection with the crystallization of cubic ZrO₂, accompanied by the generation of cracks, as well as the formation of carbon in the hexagonal diamond form in the product phase.     

A review of the minerals industry in Zimbabwe

A brief history is presented of the minerals industry from ancient to modern times and the importance of the industry to the Zimbabwean economy is indicated.To illustrate progress being made in the mordern industry three new projects have been selected from the areas of diamond, copper and platinum production as examples of current developments and indicators of the potential for the minerals industry in Zimbabwe. Some aspects of social and political factors involved in this development are discussed.     

碳源扩散不均一性对宝石级金刚石单晶生长的影响

高温高压温度梯度法生长优质宝石级金刚石单晶过程中,晶体生长主要由碳源在触媒中的扩散过程决定。本研究通过有限元对碳源对触媒的扩散过程进行了简单模拟,结果发现,受温度梯度法特定组装结构影响,实际晶体在生长过程中,由高温端扩散下来的碳源在触媒中的分布是相当不均匀的。对晶体生长来说,这种碳源扩散不均一性会直接影响晶体的生长过程。在籽晶粒度超过2mm时,晶体中心部位出现较多包裹体,或者生长表面无法生长愈合。     

EBSD – orientation analysis of monocrystalline diamonds used for diamond metal composites – Influence of sample preparation

This paper focuses on a new field of application for the EBSD‐technique. Generally, EBSD‐mappings are performed on different metal alloys used for quality assurance and to get information about the microstructure regarding grain orientation, grain size and distribution. In contrast, the orientation determination of monocrystalline diamond grains with an EBSD system is not a conventional method. Thus, this work describes the EBSD testing sequence in detail and illustrates the preparation of orientation data for a statistical design. Furthermore, dependencies of the sample preparation, alignment to the detector, and the analyzed position on the diamond on the quality of the Kikuchi‐patterns, respectively on the indexing rates, have been scrutinized. Finally, the orientation obtained of each tested diamond sample has been utilized in a statistical design to show a direct influence of the crystal orientation on the wear behavior of the diamond grains.     

Electrodeposition of tungsten and molybdenum carbide onto the surfaces of disperse dielectric and semiconductor materials

The systems suitable for a high‐temperature electrochemical synthesis on the surfaces of diamond, boron nitride, and silicon and boron carbides were selected on the basis of the thermodynamic analysis of the reactions of dielectrics and semiconductors with ionic melts and the study of their electrochemical behavior. Electroplating of the grains of dielectrics and semiconductors with molybdenum carbide favors the increase in their breaking load and wettability and in the efficiency of tools. Thermodynamic calculations showed that the most energy favorable process for boron nitride is its oxidation to gaseous nitrogen and boron metaborate or oxide. A compound of an element of group VI and carbon will be presumably reduced to this element in the pure state or to its oxide of an intermediate oxidation state. The most energy favorable process for silicon and boron carbides will be their oxidation to a metasilicate (metaborate) or silicon (boron) oxide. A compound of an element of group VI will be also presumably reduced to the elements in the pure state or in the form of an intermediate oxide.     

Nanocarbon Allotropes—Graphene and Nanocrystalline Diamond—Promote Cell Proliferation

Two profoundly different carbon allotropes – nanocrystalline diamond and graphene – are of considerable interest from the viewpoint of a wide range of biomedical applications including implant coating, drug and gene delivery, cancer therapy, and biosensing. Osteoblast adhesion and proliferation on nanocrystalline diamond and graphene are compared under various conditions such as differences in wettability, topography, and the presence or absence of protein interlayers between cells and the substrate. The materials are characterized in detail by means of scanning electron microscopy, atomic force microscopy, photoelectron spectroscopy, Raman spectroscopy, and contact angle measurements. In vitro experiments have revealed a significantly higher degree of cell proliferation on graphene than on nanocrystalline diamond and a tissue culture polystyrene control material. Proliferation is promoted, in particular, by hydrophobic graphene with a large number of nanoscale wrinkles independent of the presence of a protein interlayer, i.e., substrate fouling is not a problematic issue in this respect. Nanowrinkled hydrophobic graphene, thus, exhibits superior characteristics for those biomedical applications where high cell proliferation is required under differing conditions.