Papers by Keyword: Synthetic Diamond

Abstract: The aim of this paper was to determine the influence of the mechanical and thermal parameters of the matrix materials on their retentive properties. The term ‘matrix retention’ denotes the capacity of a metallic matrix material to retain diamond particles at the surface of a diamond tool during working. The bonding is obtained during cooling after the hot pressing process. Proper mechanical bonding depends on elastic and plastic properties of the matrix. The model of a diamond particle embedded in a metallic matrix was created using Abaqus software. The analysis has indicated the mechanical parameters that are responsible for the retention of diamond particles in a matrix.

Abstract: Inside the indirect heating chamber, raw material itself is not being electrified nor giving out heat. Instead, heat is offered by some heater outside and transferred inside to heat the raw material indirectly. Gradient of pressure parallels to as well as matches with that of temperature, which solves the mismatch between these two elements inside the high-pressure chamber. Meanwhile, both electrical resistance and temperature remain unchanged when raw material reacts. What described above realizes uniformity and stability of pressure and temperature. During the process of synthesizing diamond, we employ the technology of two-parameter dynamic matching of pressure and temperature. In this way, attached load increases gradually while attached power decreases little by little to keep pressure and temperature in the rich diamond crystal growth area and allow them to move in a restricted area in direction of identical quality line. As a result, pressure and temperature can match dynamically and diamond crystal can grow steadily and continuously in a long time period to produce high-quality product, per unit output reaches as much as 580cts, 60% of which are of high grade.

Abstract: Crystal defects in a large diamond crystal synthesized by high pressure and high temperature (HPHT) method were investigated by synchrotron radiation topography. Five bundles of dislocations were observed in the specimen. Two bundles of the dislocations are in the <100> direction and three of the others are extended at <110>. The Burgers vectors of the dislocations are different within the same bundle as the extinction hinted. The dislocations in <100> direction possess higher energy than the dislocations in <110> and {111}, so they are in the metastable state. The <100> dislocations has not been found in natural diamond yet. The reason of that was the great difference of the growth rate of synthetic and natural diamonds.

Abstract: The synthesis of diamond crystal from powder mixture of graphite and catalyst alloy is a well known process but it is limited to relatively small crystal dimensions due to the size of the conventional compression chambers. In this work the design and construction of a novel high pressure multi-anvil device with a parallelepiped shaped compression chamber is presented. The design allows the length of the chamber to be limited only by the working space of the press equipment. A four horizontal anvils device was constructed for a specific 2500 ton press with a 600mm working space. The efficiency of this construction was tested in diamond crystal synthesis.

Abstract: Diamond crystals were synthesized at 4.5GPa and 1300°C in a Ni-Mn-C system with and without Fe doping. The reactive mixture was prepared with 50 wt% graphite and 50 wt% Ni-Mn followed by doping of 2 to 5wt% of pure iron. The synthesis was performed inside an anvil type high pressure device. After extraction and purification, the paramagnetic properties of the diamond crystals were evaluated by specific techniques at room temperature. It was found that the diamond synthesized with different iron content exhibit different paramagnetic properties. The data obtained by infrared spectroscopy and electron spin resonance (ESR) spectroscopy are coincident for radiation defects and different for nitrogen centers. The spectra of the electron spin resonance exhibited broad lines produced by residual impurities of Fe compounds together with catalyst alloy and were accompanied by a distortion of the spectrum of paramagnetic nitrogen in the form of a tilt of the ESR spectra with respect to the zero line.

Abstract: t is well recognized that a catalyst agent is essential to synthesize diamond at high pressure and high temperature. The catalyst agent also acts as a carbon solvent and affects the properties of the final product. This is a consequence of its direct influence on the growth of diamonds crystals. The control of the growth, which is required to achieve a high quality level, is still a question open to discussion. In this work, an industrial diamond powder was synthesized from graphite using Ni-Mn as catalyst alloy added with up to 5% of iron. The synthesis was carried out at 4.5GPa and 1300°C for 10 minutes in high pressure device with central concavity. The analysis of the cubic-shaped diamond surface topography suggests that the formation of defects on the {111} faces is most likely a consequence of a complex growth process that influences the crystal productivity and morphology.

Abstract: As a harmful impurity, Pyrophyllite must be remove in synthetic diamond purification process. It commonly use chemical method. A trial research is made on the removing of pyrophyllite impurity in synthetic diamond by physical method. As a result, after synthetic diamond materials containing pyrophyllite are selectively interground in the ball grinding machine, the pyrophyllite is effectively broken and removed from the coarse – medium grade diamond only by physical method, but diamond quality is not affected.

Abstract: This paper introduces the mechanical construction, operation principle, performance characteristics and the using result of physical impurities removing and purification technology of the kneading mixer, which is specially developed and particularly suitable for disintegrating and refining of synthetic diamond electrolysis residue. In order to avoid the slipping of materials in the tank and impacting the effect, non-slip kneading bar is especially equipped in the tank; the main shaft of helical mixing blade is driven by motor drive variable-speed system (speed control system), the mechanical strength is adjustable; running cycle is automatically controlled and adjustable, and the impact of human factors is excluded. Industrial tests and production applications show that the design of the machine achieves the desired results.

Abstract: Transmission Electron Microscope (TEM) and Different Scanning Calorimetry (DSC) Methods Were Used to Investigate the Diamonds Grown with Different Boron Content Alloy Catalysts under High-Pressure High-Temperature (HPHT). Experimental Results Demonstrated the Microstructure and Composition of Boride Compounds in Synthetic Diamond, such as (FeNi)₂₃(CB)₆ ,(Fe, Ni)₃(C,B), (Fe,Ni)B and B₄C, Whose Formation Process Was Analyzed. the Thermal Stability of Diamond Depends on Boron Concentration in Catalyst According to DSC Studies. we Analyzed the Reason of Diamond Oxidation.The Work Offers Valuable Information for Improving the Thermal Stability of Synthetic Diamond Crystals by Adjusting Boron Content in the Fe-Ni Based Catalyst.

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.