Papers by Keyword: Heavy Liquid Separation

Abstract: Hexagonal diamond is considered to be a metastable high-pressure phase of carbon. In previous ab-initio studies, elastic constants of hexagonal diamond were suggested to be higher than those of cubic diamond, which is the stiffest known material. However, the elastic constants of hexagonal diamond have not been investigated experimentally because the size of hexagonal diamond single crystal ever synthesized is not more than 0.5 μm. In this study, we synthesized hexagonal diamond with the size of more than 50 μm in order to measure the elastic constants accurately. Kish graphite powder was used as a starting material and a green compact of kish graphite and copper powder was fabricated as a target. The target was placed into a container made of stainless steel and shock-compressed by a copper projectile accelerated using a single stage powder gun with the velocity of approximately 800 m/s. The estimated shock pressure and temperature were 22 GPa and 1200 °C, respectively. After the shock compression, copper component of the target was dissolved in nitric acid for 24 hours and only carbon component was recovered. A clear (100) peak of hexagonal diamond was observed by a XRD result of the recovered carbon. No peak of cubic diamond was observed. Opaque particles including hexagonal diamond with the size of approximately 100 μm were separated from the graphite and SiO₂ contaminations using heavy-liquid separation method with sodium polytungstate aqueous solution.

Abstract: In this paper, static-pressure strength, toughness index (TI) and thermal-toughness index (TTI) of each sample have been analyzed on the basis of the experimental studies on the magnetic separation and heavy liquid separation of diamond abrasives. The results show that the magnetism of synthetic diamond abrasives has an obvious influence on their mechanical performances. With the increase of magnetism, synthetic diamond abrasive particles becomes darker and darker in appearance color, and have more bubbles, impurities and defects inside the particles, furthermore, their surface fineness observed under the microscope will be found worse. While, the static-pressure strength, the TI under the normal temperature and TTI all become lower and lower. But the influence on the static-pressure strength and the TI is smaller, however the influence on TTI is the greater. The specific gravity of synthetic diamond abrasives has little influence on their mechanical performances.

Abstract: In an abrasive tool the abrasive is the main part undertaking grinding work, thus, the grinding effects mainly depend on the types and properties of the abrasive. The strength and fracture property of the abrasive grain in a synthetic diamond abrasive tool have a direct influence on the operational performance of the tool. Generally, it is expected that the strength and protrusion height of the grain are as same as possible. The strength and fragmenting property of the abrasive grain hinge on its crystal shape and regularity and completeness, internal vice, impurity content and impurity distribution pattern. The abrasive grains must be sorted and classified to make their grain sizes and their properties consistent with each and all. In this paper, the author discusses the basic properties and related performances of synthetic diamond abrasives. Elementary discussion is made separately on improving the vibration sorting, introducing the magnetic separation, applying the heavy liquid separation, exploring the floatation technology and using the selective fragmentation principle. In addition, here are presented the basic methods for precise sorting of synthetic diamond abrasives and their general principles. Practices have proved these methods effective and feasible.