High-quality type-Ib tower-shape diamond single crystals were synthesized in cubic anvil high pressure apparatus (SPD-6×1200) at 5.4 GPa and 1250-1450°C. The (100) face of seed crystal was used as the growth face, and FeNiMnCo alloy was used as the solvent/catalyst. Two kinds of carbon diffusing fields (type-B and type-G) were simulated by finite element method (FEM). Using the two kinds of carbon diffusing fields, many diamond single crystals were synthesized. The effects of carbon diffusing fields on the crystal quality and β value (the ratio of height to diameter of diamond crystal) were studied. The results show that using type-B diffusing field, considerable inclusions appeared in tower-shape diamond crystals with high β values; however, using type- G diffusing field, inclusions were reduced markedly in high β values tower-shape diamond crystals, and the crystal, up to 0.6 carat in weight and 5.3 mm in size, was synthesized. Experimental phenomena were explained well with the help of the FEM.
High quality grown polycrystalline diamond compact (PDC) with low residual stress was prepared using the infiltration method with nickel based alloys as the solvent under high temperature and high pressure (HPHT). Scanning electron microscopy (SEM) was used to observe the micro morphology of the diamond layer and the diamond/WC substrate interface. It was found that dense and interlaced microstructure with diamond-diamond (D-D) direct bonding formed in the diamond layer of PDC. Micro-Raman spectroscopy was used to measure the Raman shift of diamonds in the polycrystalline diamond (PCD) layer and the residual stress was calculated based on the Raman shift of diamonds. Experimental results show that the residual stress of PCD layer is compressive stress, and the range of the residual stress is from 0.075 to 0.250 GPa in the whole PCD layer, much lower than that of other reports (up to 1.400 GPa). Moreover, the distribution of the residual stress from the diamond surface layer to the inner cross-section is homogeneous.
JIA HongSheng, MA HongAn, GUO Wei & JIA XiaoPeng* National Laboratory of Superhard Materials, Jilin University, Changchun 130012, China
Polycrystalline diamond compacts (PDC) were synthesized using diamond powder of average crystal size 3-20 μm by the Ni 70 Mn 25 Co 5 alloy infiltration technique at high temperature and high pressure (HPHT).The surface residual stress of polycrystalline diamond (PCD) layer was measured using micro-Raman spectroscopy with hydrostatic stress model and X-ray diffraction (XRD).Measurements of the stress levels of PCDs show that the residual compressive stresses range from 0.12 to 0.22 GPa,which increase with the crystal size of diamond.Scanning electron microscopy (SEM) was used to observe the morphology of initial diamond grains and PCD cross-section.The results indicate that PCD has a dense and interlaced microstructure with diamond-diamond (D-D) direct bonding.And the smaller the crystal size of diamond,the better the growth of diamond direct bonding and the smaller the binder metal between diamond boundaries will be.
In this paper,we investigate diamond crystallization in Fe-Ni-C with an aluminum additive and the capability of aluminum for converting graphite to diamond in a series of experiments at 4.9-5.5 GPa and 1240-1500°C.Our experimental results show that the growth habits of diamond crystal have been significantly influenced by the addition of aluminum as a catalyst.The crystal color changes from yellow to nearly colorless.The morphology of the synthesized diamond crystals gradually changes from cubic-octahedron to octahedron in the Fe-Ni-C systems with increasing aluminum additive.The lowest synthesis conditions fell first and then rose with increasing aluminum.We found a suitable addition of aluminum is very effective in lowering the synthesis conditions while an excessive aluminum additive may have a suppressive effect on the diamond nucleation.
High quality type-Ib tower-shape gem-diamond crystals in carats grade were synthesized in cubic anvil high pressure apparatus (SPD-6×1200) at 5.4 GPa and 1250-1450°C. The relationship between the growth time and the weight of growth diamond has been gained. The faces of {110} and {113} were found in the synthetic diamond crystals frequently. We found that the relative growth rate of {113} face was descending with the increase of growth temperature, and that of {110} face had no obvious change with the increase of the growth temperatures and the growth time. In the work, the crystal defects were studied carefully, and the reasons for the appearance of the defects were also obtained. Some diamond crystals have been polished into the anvil of DAC (Diamond Anvil Cell) and the diamond jewelry. Compared with natural diamond crystal, synthetic diamond crystal has the merits such as small grinding quantity, low cost, etc., so it can be widely used in super high pressure field and gemstone industry.
XIAO HongYu JIA XiaoPeng MA HongAn LI ShangSheng LI Yong ZHAO Ming
In this paper,we report on the influence of annealing treatment on as-grown Ib-type diamond crystal under high pressure and high temperature in a china-type cubic anvil high-pressure apparatus.Experiments are carried out at a pressure of 7.0 GPa and temperatures ranging from 1700 C to 1900 C for 1 h.Annealing treatment of the diamond crystal shows that the aggregation rate constant of nitrogen atoms in the as-grown Ib-type diamond crystal strongly depends on diamond morphology and annealing temperature.The aggregation rate constant of nitrogen remarkably increases with the increase of annealing temperature and its value in octahedral diamond is much higher than that in cubic diamond annealed at the same temperature.The colour of octahedral diamond crystal is obviously reduced from yellow to nearly colorless after annealing treatment for 1 h at 1900 C,which is induced by nitrogen aggregation in a diamond lattice.The extent of nitrogen aggregation in an annealed diamond could approach approximately 98% indicated from the infrared absorption spectra.The micro-Raman spectrum reveals that the annealing treatment can improve the crystalline quality of Ib-type diamond characterized by a half width at full maximum at first order Raman peak,and therefore the annealed diamond crystals exhibit nearly the same properties as the natural IaA-type diamond stones of high quality in the Raman measurements.
Diamond crystals with low nitrogen concentration were synthesized from the Fe-Ni-C system with Ti additive at high pressure and high temperature (HPHT) in a china-type cubic high pressure apparatus (CHPA). The synthesis pressure range was 4.8-5.2 GPa, and the temperature range was 1420-1600 K. The lowest synthesis pressure for diamond fell first and then rose with the increase of Ti additive. The color, shape, surface morphology and nitrogen impurity concentration of the synthesized diamond crystals were characterized using optical microscopy (OM), scanning electron microscopy (SEM) and micro Fourier transform infrared (FTIR) spectrometry. The results show that the Ti additive has significant effects on color, growth rate, crystal shape, surface morphology and nitrogen impurity con- centration of the synthesized diamond crystals. The color of diamond crystals synthesized without Ti additive is yellow, while that with Ti additive becomes light and nearly colorless. The growth rate without Ti additive is higher than that with Ti additive. The crystal shapes of as-grown diamond crystals vary with the increase of Ti additive. The {111} crystal faces become dominant and some {311} crystal faces appear with the increase of Ti additive. The concentration of nitrogen impurity in diamond crystals without Ti additive is higher than that with Ti additive.
HAN Wei JIA XiaoPeng JIA HongSheng HU MeiHua HUANG HaiLiang LIU XiaoBing MA HongAn
Type Ib diamonds were grown by the temperature gradient method (TGM) at 5.5 GPa and 1500-1560 K in a china-type cubic anvil high pressure apparatus using Ni70Mn25Co5 alloy as solvent/catalyst. The concentration of nitrogen (CN) in type Ib diamonds synthesized at different synthesis temperatures was measured by a Fourier transform infrared (FTIR) spectrometer. The dependence of CN in diamond on synthesis temperature was studied. For the type Ib diamonds synthesized using Ni70Mn25Co5 as catalyst, its CN decreases along with the increase of synthesis temperature.
