Papers by Author: You Jin Zheng

Abstract: In this paper, AlN ceramics doped with additive Sm₂O₃ has been synthesized by HPHT method. Furthermore, we have studied the impact of Sm2O3 on sintering AlN ceramic. The results show that the relative density of AlN ceramics increased at first, but decreased later with increasing Sm₂O₃. Compared with pressureless sintering, the time required to complete sintering AlN ceramic was shorter, and the sintering temperature was lower. And the growth model of AlN ceramics was pointed out and the proper explanation of its related phenomena were given in detail.

Abstract: In this paper, a new dopant of P₃N₅ (phosphorus nitride) was doped into the diamond growth cell to grow diamond crystals by temperature gradient growth method (TGM) under high pressure and high temperature (HPHT). The experiments were performed at a fixed pressure of about 6.0 GPa and temperatures of 1600-1650 K. The gained diamond crystals were characterized by infrared (IR) absorption spectroscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. IR measurements demonstrated that, nitrogen atom was indeed doped into diamond crystals, and the diamond crystals with perfect shape containing nitrogen concentration ranging from 461 atomic parts per million (ppm) to 2186 atomic ppm were successfully synthesized. Nitrogen atoms present in diamond crystal were predominantly in isolated form accompanied by a small amount of nitrogen pairs. Micro-Raman spectra implied that crystalline quality deteriorated with nitrogen concentration gradually increased in diamond-growing environment. The XPS spectra revealed that only a few of phosphorus impurities about tens of ppm level were incorporated into a diamond crystal which was heavily doped with P₃N₅. This study will promote the application of doping diamonds in micro-electronics field and other fields.

Abstract: Boron doped diamond (BDD) films were deposited on porous Ti substrates by direct current plasma chemical vapor deposition (DC-PCVD) system. For improve adhesion between diamond and porous Ti, and shorten diamond nucleation period, appropriate pretreatments were carried out. Micro diamond particles were mechanical embedded in the holes of porous Ti substrates and then nanodiamond powders were seeded on substrates by ultrasound sonication prior to deposition. The samples were examined by scanning electron microscopy (SEM), micro-Raman spectroscopy, and cyclic voltammetry. It was found that BDD films covered the whole porous Ti substrate surface, and exhibited the good electrochemical property.

Abstract: In this study we report on the synthesis and characterization of thermally stable polycrystalline diamond (PCD) using Ni-based alloys catalyst as a sintering aid and the B-doped diamond powder in the infiltrating way. The samples were treated at 5.6 GPa and 1200–1480 °C for 10 min in China-type cubic high pressure apparatus. Scanning electron microscopy showed significant intergrowth of the diamond particles sintered in the presence of Ni-based alloy. X-ray diffraction showed the phase change of the samples sintered at the different temperature. Differential thermal analysis (DTA) and thermogravimetric analysis (TG) showed the sample was significantly more heat-resisting compared to conventional PCD. The results showed that the appropriate conditions of thermally stable PCD sintered were 5.6GPa and 1200–1480 °C.

Abstract: The DC plasma chemical vapor deposition (DC-PCVD) method was a promising technique to fabricate CVD diamond coatings in industry, because it has many good properties, such as high grown rate of diamond films, big grown area, high qualities, and cost effective. In the present work, we synthesized diamond films on cemented carbide (YG6) substrates, and studied the different nitric acid aqueous solution treatment durations influence on diamond nucleation stage. The results indicated that well-chosen nitric acid aqueous solution treatment durations should be selected. For too short treatment times, the residual Co will promote the carbon transform from diamond metastable phase into graphite stable phase. On the other side, too long treatment times will consume too much Co, which will lead to the shortage of cohesive body, and finally the crackers in the bulk propagated and peeled off with the diamond films well grown on WC grains.

Abstract: In this paper, industrial diamonds using FeNi powder catalyst with additive La2O3 has been synthesized by HPHT method. Optical microscope, XRD and SEM were utilized for observation and detection. The influences of additive La2O3 on the synthesis have been investigated from several aspects such as the diamond-forming conditions, the composition of synthesized sample and inclusions in diamond, and the morphology character of diamonds etc. The results indicate that There is a new compound LaO, LaFeO3, Fe3C and Fe3O4 in the sample., and related phenomena were given in detail in this paper.

Abstract: Synthesis of Ⅱa industrial diamond with high quality at high temperature and high pressure (HTHP) was examined in this paper and Ⅱa industrial diamonds were synthesized successfully. The experimental results show that the lowest synthesis pressure of diamond changed significantly which goes down firstly, and then up with the increasing of Ti content. It is discovered by optical microscopy that the color of synthesizing diamond in nitrogen getter system is lighter than that in raw catalyst power system and most crystals are hexahedrons & octahedrons. The experiment results measured by IR analysis shows that nitrogen content in synthesizing diamond in nitrogen getter system is significantly lower than that in the raw catalyst power system. Surface morphology of diamond synthesized in two different systems is investigated by the aid of SEM.

Abstract: High-density AlN ceramics were fabricated under high pressure, in a cubic anvil high-pressure and high-temperature apparatus. This work provided that the method is capable of producing high-density AlN ceramics at a sintering temperature as low as 1300°C in a relatively short sintering time. And the growth model of AlN ceramics was pointed out and the proper explanation of its related phenomena were given in detail in this paper.