高温高压下石墨变金刚石的结构转化机理

本文从容观事物内部矛盾的斗争及其在特定条件下可以相互转化这一基本观点出发,从分析石墨、金刚石和触媒物质三者的结构和原子间的相互作用入手,提出了一个高温高压下石墨变金刚石的结构转化机理。 本文认为,在一定条件下,石墨中碳原子的sp~2π杂化状态可以转化为sp~3杂化状态,从而使石墨变成金刚石。这就是石墨具有在一定条件下可以转变成金刚石的内在矛盾性,也是结构转化机理的理论基础。由此出发,说明在一定条件下,石墨既可以通过溶解扩散过程,又可以通过直接转变过程转变成金刚石,并给出了在无触媒及有触媒作用的情况下,石墨转化为金刚石的微观机理图象。提出了如何选择触媒与石墨的指导原则。同时还提出了一个在目前生产金刚石常用的合成方法中,如何进一步提高晶粒度和强度的途径。     

合成金刚石用触媒合金的组织结构

研究了Ｎｉ７０Ｍｎ２５Ｃｏ５触媒合金合成金刚石前后的组织结构。结果表明，合成金刚石前，触媒合金是冷加工纤维组织，单相奥氏体合金；合成金刚石后，触媒合金的组织为铸态，合金中存在奥氏体相、金刚石相、石墨相和碳化物Ｍ３Ｃ相。     

触媒静压法合成金刚石的机理问题

对太原市晋阳金刚石厂触媒静压法合成金刚石的专用石墨、触媒和合成产物进行了观测。看到有的金刚石生长在石墨中,也有的金刚石生长在触媒上。依照扫描电镜的形貌观察,我们认为,此种材料和工艺生产的金刚石,其形成机理是“直接转化说”、“溶剂说”二者都符合。文章的最后还提出了我们的工艺改进意见。     

“单含硼”和“双含硼”黑金刚石合成的比较

我们将样品按两种不同的原料匹配方式(含硼触媒合金与不含硼石墨,简称“单含硼”;含硼触媒合金与含硼石墨,简称“双含硼”),分半对称地组装在同一高温高压反应腔中,研究了硼不同的含量和原子分布情况对高温高压合成含硼黑金刚石的影响。实验结果表明,“双含硼”方式得到的金刚石与“单含硼”相比不仅平均单产高,而且粗颗粒度比也高;硼原子可以增加金刚石单晶体的长大速度,因此可能缩短大颗粒单晶的合成时间,在高温范围内,“双含硼”方式得到的金刚石单晶有着增强抗氧化性能的趋势。     

铁基粉末触媒合成金刚石

本文利用六种铁基粉末触媒（FeNiNa,n=0,1,2,3,d,5X。代表Fe在触媒中的含量,Xn〉xn-1）在国产六面顶压机上进行了金刚石单晶的合成实验,研究了高温高压条件下（～6GPa,～1600℃）,铁基粉末触媒随铁含量的改变,石墨碳—铁基触媒体系合成金刚石条件的变化规律以及金刚石单晶的生长特性,利用穆斯堡尔谱对金刚石中铁元素形成的包裹体进行了检测．结果表明,随着铁基粉末触媒中铁含量的增加,合成金刚石的压力和温度条件逐渐增高,金刚石生长的“V形区”上移,同时得出了铁基粉末触媒适合高温区（110）和（111）面生长以及金刚石中铁元素以FeNi和FeyC形式存在的结论．     

类泡沫触媒合成金刚石的工艺特征

对触媒形状的变化关系与表面问题进行了研究．在制备类泡沫触媒的基础上，总结了类泡沫触媒在国产六面顶压机上合成金刚石的基本工艺规律，并对类泡沫触媒在六面顶压机上合成金刚石的适用范围进行了分析、确定．结果表明，增加石墨与触媒的接触面积或反应面积，是提高合成金刚石转化率的一条重要途径．     

超硬纳米类金刚石膜的结构特点及其形成机制的探讨

研究了超硬碳膜的力学性质、波谱性质及结构性质 ,指出有一种无氢类金刚石膜是由石墨碎片、布基葱和金刚石晶粒以新型的共价键组成的网架结构 ,具有良好的力学性能 .由于石墨碎片中的π键变形 ,石墨碎片和布基葱边缘的不饱和悬键与金刚石晶粒周围的悬键结合成新型的共价键 .金刚石晶粒只能由激发态碳原子在非平衡重组过程中产生 ,而石墨碎片既可以在碳原子重组过程中产生 ,也可以在蒸发石墨过程中产生 .     

石墨中渗钴的实验研究

本文报道作者用 CoCl_2·6H_2O 溶液浸泡石墨片渗钴使钴元素在高温高压前进入石墨的实验结果.实验用扫描电镜、x 射线能谱及透射电镜观察,证明钴已渗入到石墨片中.用该石墨片合成的金刚石产量和粒度比都有明显改善.从而验证了石墨在触媒作用下向金刚石转化的机理.     

金刚石表面的金属化

用真空蒸镀法在金刚石镀覆Ｔｉ层，并经扩散处理使金刚石表面形成ＴｉＣ膜，实现了金刚石表面的金属化，Ｘ射线衍射分析证实了ＴｉＣ的存在，利用ＸＰＳ定量分析验证了在金刚石表面碳原子与钛镀层之间的反应模型，经表面金属化的金刚石烧结体的力学性能测试表明，金刚石与粉末合金界面上的结合得到增强。     

活性碳,碳黑,石墨与金刚石晶种的生长

介绍了活性碳、碳黑与石墨在过剩压驱动下金刚石晶种的生长．对两种无定形碳以及石墨在触媒中的分散溶解输运与再结晶进行了观察，对活性碳、碳黑在金刚石晶种生长中的机理作了探索性的讨论．三种碳片上的晶种均有明显长大，无定形碳作晶种生长的碳源是可行的     

Study on growth of coarse grains of diamond with high quality under HPHT

The growth of coarse grains of diamond was observed with graphite as carbon source and Fe₈₀Ni₂₀ alloy powder as catalyst at HPHT in a China-type SPD 6×1670T cubic high-pressure apparatus with highly exact control system. To synthesize coarse grains of diamond crystal with high quality, advanced indirect heat assembly, powder catalyst technology and catalyst with optimal granularity were used. Especially the nucleation of diamond and the growth rate were strictly controlled by the optimized synthesis craft. At last, diamond crystals (about 0.85 mm) in the perfect hex-octahedron shape were successfully synthesized at ~5.4 GPa and ~1360℃ in 60 min. The characteristic of crystal growth with powder catalyst technology under HPHT was discussed. The results and techniques might be useful for production of coarse grains of diamond.     

Mechanism of diamond-to-graphite transformation at diamond-stable conditions

The diamond-to-graphite transformation at diamond-stable conditions is studied by temperature gradient method （TGM） under high pressure and high temperature （HPHT）, although it is unreasonable from the view of thermodynamic considerations. It is found that, at diamond-stable conditions, for example, at 5.5 GPa and 1550 K, with fine diamond grits as carbon source and NiMnCo alloy as metal solvent assisted, not only large diamond crystals, but metastable regrown graphite crystals would be grown by layer growth mechanism, and the abundance of carbon source in the higher temperature region is indispensable for the presence of metastable regrown graphite crystals. From this transformation, it is concluded that, with metal solvent assisted, although the mechanism of crystal growth could be understood by the macro-mechanism of solubility difference between diamond and graphite in metal solvents, from the point of micro-mechanism, the minimum growth units for diamond or graphite crystals should be at atomic level and unrelated to the kinds of carbon source （diamond or graphite）, which could be accumulated free-selectively on the graphite with Sp2Tr or diamond crystals with sp3 bond structure.     

Analysis of the carbon source for diamond crystal growth

The lattice constants of diamond and graphite at high pressure and high temperature （HPHT） were calculated on the basis of linear expansion coefficient and elastic constant. According to the empirical electron theory of solids and molecules （EET）, the valence electron structures （VESs） of diamond, graphite crystal and their common planes were calculated. The relationship between diamond and graphite structure was analyzed based on the boundary condition of the improved Thomas-Fermi-Dirac theory by Cheng （TFDC）. It was found that the electron densities of common planes in graphite were not continuous with those of planes in diamond at the first order of approximation. The results show that during the course of diamond single crystal growth at HPHT with metal catalyst, the carbon sources forming diamond structure do not come from the graphite structure directly. The diamond growth mechanism was discussed from the viewpoint of valence electron structure.     

Diamond synthesis from a system of chromium-carbide and Ni70Mn25Co5 alloy

In order to ascertain the mechanism of interaction between carbide and metallic catalyst and formation of diamond under high pressure and high temperature, and find a new method to synthesize diamond with special properties, it is necessary to investigate the reaction behavior of different carbides and metallic solvent_catalysts under high pressure and high temperature. A system of Cr-3C-2 powder and Ni 70Mn 25Co 5 alloy in weight ratio of 1∶6 was treated under 6 0 GPa and 1 500℃ for 20, 30 or 60 min respectively. X_ray diffraction of the samples indicated the Cr 3C 2 decomposed partially after high pressure and temperature treatment, and Cr 7C 3, Cr and diamond formed respectively. There was not any trace of graphite in the samples. The result suggested that the separated carbon atoms could form diamond directly without conversion process of graphite into diamond. The observation of SEI, WDX and EDX also showed that diamond crystals were synthesized in the system, which have perfect surfaces and shapes, with the average grain size of about 40 μm. The properties of the crystals are being investigated.     

大面积CVD金刚石膜的热铁板抛光

研制成功国内第1台大面积CVD金刚石膜热铁板抛光机,它可以在10^-3pa真空条件下,加热到1100℃;抛光台可以在0－10r/min间实现无级调速,一次完成3片φ110mm的金刚石膜的抛光,金刚石膜在980℃,2h抛光的结果表明该装置有良好的抛光效果。金刚石膜在980℃抛光不同时间的Raman谱表明,金刚石热铁板抛光是金刚石石墨化和C原子不断扩散的过程。     

Effects of carbon diffusing field in alloy solvent on the growth of tower-shape diamond single crystal

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 ...     

人工合成金刚石技术比较

静压法是当前工业合成金刚石的主要的合成手段,合成工业用金刚石主要采用静压法中的静压触媒法,合成宝石级金刚石主要采用静压晶种触媒法生产,通过静压法中的直接变换法,纯净的多晶石墨棒可以在短时间内转化为多晶金刚石,二十世纪八十年代还出现了一种在低压下生长金刚石的新方法——化学气相沉积法(CVD),目前只能用于制备金刚石薄膜,本文通过总结比较各种金刚石合成技术,提出了利用激光控制金刚石生长的设想,使用这种方法将提高金刚石的质量,     

触媒合金中的C，N，B对合成金刚石性能的影响

为进一步提高人造金刚石的质量和产量．通过实验研究了触媒合金中的Ｃ，Ｎ，Ｂ对合成人造金刚石的粒度、晶形、单产、抗压强度以及热稳定性的影响．实验结果可供实际生产中参考．     

Fe-Ni-C粉末触媒体系金刚石的合成与表征

利用FeNi粉末触媒在六面顶压机上进行工业金刚石单晶的合成与表征. 结果表明: 在Fe-Ni-C体系合成了优质的六面体、 六-八面体及八面体金刚石单晶; 金刚石{111}晶面的生长属于二维层状生长机制; 金刚石中的包裹体主要由FeNi合金组成.     

电镀晶种法合成金刚石单晶实验研究

目的寻求一种合成金刚石大单晶的有效方法。方法采用在金刚石单晶上面电镀一层金属镍膜作为触媒,镀有镍膜的金刚石晶种被规则地放在石墨片上预先刻好的洞中,每两个洞之间保持相等的间距,然后与其他石墨片交替组装在高温高压下进行实验合成。结果实验结果表明,在合成压力、温度和时间分别~5.8 GPa、~1 460℃和14 min的条件下,合成后的单晶尺寸约是原晶种的3倍。与传统的合成工艺相比较,合成后的金刚石单晶具有较好的形貌与质量。结论采用电镀晶种法合成对高品级金刚石大单晶的合成具有一定参考意义。