The Crystal Shape,Impurity,Defect And Color Of Synthetic Diamond And The Influence On The Parameters Characterizing Diamond Quality

During the production process of synthetic diamonds, sorting and checking of them play key roles for stabilizing and increasing their quality. Some famous domestic and overseas companies plough massive manpower, material resource, and money into developing the technologies of quality evaluating and performance checking, which are regarded by these companies as the trump to compete with their rivals. In this paper, we systematically investigated the diamonds from three aspects: crystal shape, impurity and defect, and color. Furthermore, based on the experiments, the relationship was analyzed between these three aspects and the diamond's important characteristic parameter TTI. Through analyzing the crystal shapes of synthetic diamond, we know that its basic crystal shapes are hexahedron and octahedron from which other crystal shapes can be deduced, such as angle-cutting hexahedron, angle-cutting octahedron, and cubo-octahedron. The reasons for forming these crystal shapes are owing to the growing rules of diamond as well as the temperature field and pressure field in which it grows. The diamond has different nucleation rules and growing states at different position in the V shape section formed by temperature and pressure. For the diamond produced by slice catalyst technique, in the comparatively regular single crystals, square crystals take a large proportion, while round crystals takes a little and cubo-octahedron crystals are hardly to see. In the comparatively irregular single crystals, the crystals with potholes on the surface take a large proportion, while the missharpen and needlelike ones take a little. For the diamond produced by powder catalyst technique, in the comparatively regular single crystals, round crystals take a considerable proportion and the square ones are only a little less than them, while the perfect cubo-octahedron crystals with symmetrical hexagon and triangle (111) faces take a little. In the comparatively irregular single crystals, the crystals with potholes on the surface take a large proportion, while the missharpen and needlelike ones take a little. Scanned by DiaInspect image analyzing system, the parameters FC and FE can reflect the integrity degree of the diamond crystals. Thedifference of crystal shapes can affect the value of TTI directly. Along with the increase of TTI, the roundness factor (FC) and the ellipticity factor (FE) drop linearly. According to the spectra analysis of the diamonds produced by our company, Ni takes the largest proportion of the impurities in the diamond produced by slice catalyst technique, Mn takes the second largest proportion, and Co takes the third. Mn, Ni, Co as a whole takes 99.84%. The diamonds produced by powder catalyst technique contains much Fe and Ni impurities, which as a whole takes 97.88% of all the impurities, while others take a little. Experiments show that for the diamond with more impurities and defects which is calcined under 1100℃,lots of dark spots appear inside it and the crystal color darkens. For the diamond with less impurities and defects which is calcined under 1100℃, only small mount of dark spots appear and the crystal color doesn't change obviously. Scanning analysis of DiaInspect system shows that the crystal's transparency T, rises linearly with the increase of TTI. The value of T reflects how much light gets through the diamond. Impurities and defects in the diamond can absorb and scatter somelight, so the more the impurities and defects are, the fewer the value of T is, and as a result, the fewer the value of TTI is. Nitrogen impurities can largely affect the diamond's color, as it can form all kinds of color centers in it. Scanning analysis of the diamond's color by DiaInspect system shows that for the diamonds of the same size, along with the increase of TTI (i.e. with the increase of the diamond grade), the values of R/G, R/B, and G/B increase linearly. The larger the values of R/G, R/B, and G/B are, the more yellow its color is. That is to say, in the diamonds of the same size, the larger the TTI value is, the more yellow its color is. After studying the relationship between diamond's crystal shape, impurities and defects, and color with the characteristic parameters of its properties, we established a sorting technique of high grade roundness diamonds, a shape-treatment technique of intermediate and low grade diamonds, and a new checking technique of finished products of diamonds, and, also, we stabilized the quality of diamonds and have made favorable economic benefits.