| As well known, cubic boron nitride (cBN) is widely used in the region of mechanics, thermology, optics and electronics. Due to its unique physical and chemical property such as its hardness next to diamond, thermal stability (up to 1300℃) as well as the chemical inertness to ferrous metals and its alloy etc, cBN is extensively used in machine industry. Also, cubic boron nitride, the simplestⅢ-Ⅴcompound with a large band gap up to 6.3 eV, is an interesting material as electronic material. It can be both p type and n type semiconductor by doping Be and S, Si respectively, and UV light emission from a p-n junction has been observed. These characteristics make cBN a very promising material for application in high-temperature microelectronic as well as optoelectronic devices. Whether as the superhard materials or as the semiconductor, cBN crystal must possess excellent property. So the synthesis method of cBN crystal is always studied by researchers. Since the cBN was synthesized in 1966, our country has made great progress in growth technology of cBN. However, growth technology of cBN in china is still laggard than developed country. Thus, in recent years, we devoted the basic investigation of cBN crystal all along.Based on the solvent theory of cBN synthesis, we studied the growth of cBN crystal under high pressure and high temperature using the six-cell apparatus. We systemically investigated the assembly for cBN synthesis and technology using Mg and Li3N as catalyst. Also, based on this, we farther studied the effect of hBN property and B additions on the synthesis of cBN crystal.Firstly,we introduced the thin-flake assembly mode for cBN synthesis. The assembly mode influenced the temperature and pressure distributing in the sample chamber, which ultimately affected the quality of synthesized crystals. In this paper the effect of assembly mode on the cBN synthesis was studied. The results indicated that cBN nucleation most located at the interface between the two flakes and the dominant crystal shape of cBN is octahedral thick flake when the flake assembly mode was used with the mixed powder of the catalyst and hBN. The reason was as follow. The mixture powder of catalyst and hBN would be pre-pressured into flakes for synthesis. In this process, the density of the mixed powder at the surface is higher than that inside, because the thickness of flake resulted in bad conductivity of pressure. The high density of the mixed powder was also in favor of the conductivity of the temperature and the pressure. These all made cBN growth at the interface easy. It was concluded that the thinner the flake was, the more symmetrical and higher the density of the flake was. So it was preferred to the high density of hBN and thin flake assembly mode to improve the cBN yield.Secondly, we studied the effect of hBN property on cBN synthesis using hBN ball-malled with different time and Li3N as starting materials. The conclusion was as follow.(1) The crystallinity of hBN dereased with increasing ball milling time.(2) The results of Raman specctrocpy showed that the strongest peak of 1365cm-1, the characteristic peak of hBN, only shifted a little, which demonstrated sp2- hexagonal structure of B-N layer in these hBN did not change.(3) The temperature and pressure for cBN synthesis shifted the higher region with the crystallinity of hBN decreasing.(4) XPS was used to evaluate the atomic concentration of various elements at the surface of hBN with different ball-milling time. The results indicated there was not only the bond of B-N but also that of B-O, and the amount of the latter increased with the ball-milling time increasing.(5) The ball-milled hBN was changed not only the crystallinity but also other property. The granularity of hBN was diminished after ball milling, and the activeness of surface increased. As a result, hBN was easy to be oxidated during the process of assembly, and B2O3 layer grew on the surface of hBN.(6) B2O3 reacted with Li3N and then formed Li3BO3 layer, which blocked the reaction between hBN and Li3N. So it resulted in restraining cBN synthesis.Thirdly, using Mg as catalyst, we synthesized cBN with B additions and the effect of that on cBN synthesis showed as follow.(1) The conversion of cBN crystals changed little with B additions. The reason was that B reacted Mg to form MgB2. MgB2 was also the main catalyst for cBN synthesis, and it possessed high capacity to make hBN convert cBN under proper temperature and pressue.(2) Whether adding B or not, the color of cBN crystals was black, and their morphology was integrity. The surface was coarse, and many inclusions in the synthesized cBN crystal.(3) There were many inclusions in the synthesized cBN crystals such as MgO,MgB2,Mg3N. Because of the Mg ion with different valence coexisting in cBN crystals, it resulted in making cBN crystal black.Lastly,the effet of B additions on the growth of cBN crystals was investigated, and we got the conclusion as follow.(1) The conversion rate of cBN was decreased with increasing the content of additive boron.(2) There were two growth mechanisms for cBN formation in the hBN-Li3N-B system: dissolution- recrystallization and chemical reaction process, and the dissolution- recrystallization process was dominant.(3) With adding B addtions, the color and morphology of cBN crystals changed from yellow truncated thick plank into black ortahedral or sphere-like.(4) We used X-ray diffraction to analyse the impurities in cBN crystals,and no impurity phase was detected. Raman spectroscopy showed that boron entered into the synthesized black cBN crystals, which made color and mophology of cBN crystals change.(5) Boron entered into the synthesized black cBN crystals through the way of substituting N vacancy on {111} facet.(6) The residual stress in the synthesized cBN crystals, which was calculated by the results of Raman spectroscopy, decreased markedly with increasing the content of additive boron. So the black cBN crystals were favorable for industrial application.
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