【作者】 赵文东；

【导师】 徐骏；

【作者基本信息】 北京有色金属研究总院 ， 材料科学与工程， 2010， 博士

【摘要】 人造金刚石作为天然金刚石的替代品,是一种用途广泛的极限性功能材料,其应用遍布工业、科技和国防等领域。因此,加强合成原材料和合成技术的研究,优化和改进现有的粉末触媒配方,开发低成本触媒,制备专门用途的人造金刚石磨料,极具战略意义。本文以铁基触媒配方研究为基础,深入研究了不同触媒成分、不同触媒与石墨配比对合成金刚石的影响规律,探讨了触媒在合成金刚石过程中的作用机理。并在此基础上设计出适合合成团粒结构金刚石(CSD)的新型低成本触媒配方,为此开展了以下研究：1)对Fe、Ni不同配比粉末触媒进行了合成金刚石实验,结果表明,随着触媒中Fe含量的增加,合成金刚石的最低条件和最佳条件均有所提高,金刚石生长V形区向右上方移动；金刚石的粒度峰值变粗,混合单产、静压强度、冲击韧性均有所降低；通过对触媒和石墨不同配比进行的金刚石合成实验表明；增加触媒用量可以提高合成金刚石单产。在综合考虑原材料成本、金刚石产量、质量等因素基础上,优化选择出Fe-30%Ni触媒、且与石墨配比为3：7的成分配比。并建立了触媒成分设计的基本原则。2)深入研究了在FeNi30中添加微量稀土元素对合成金刚石的影响,结果表明,稀土元素可有效降低触媒中结合氧含量,提高了粉末触媒的纯净度,在合成金刚石中对提高混合单产、增加粗颗粒比例、提高单粒度TI、TTI值,增加静压强度,降低磁化率值等都有不同程度的作用；通过优化实验,获得最佳稀土添加量为0.4%。3)根据触媒成分设计的基本原则,设计了不同成分的FeMn基触媒,并通过合成金刚石实验深入研究不同添加元素及含量对合成金刚石的影响规律,结果表明：单独使用FeMn触媒合成金刚石,在5.4～5.6GPa、1450～1600℃才能合成出金刚石,比FeNi触媒的合成条件高,且金刚石粒度较细,晶型较差；在FeMn触媒中加入5%的Ni或Co,合成压力、温度有所降低；添加稀土元素有助于金刚石晶形的改进；Ni含量保持15%不变,Mn含量由15%、20%、25%变化,金刚石的形核量逐渐增多,粒度变细,金刚石由灰绿色变成黑色,晶形变得不规则,Mn含量为25%时得到了团粒结构金刚石；Ni、Mn含量不变, Co含量增加,金刚石粒度变粗,晶形变好,混合单产增加,黑颜色金刚石变少,晶体透明度提高。4)针对市场对CSD金刚石不断增长的需求,利用FeMn基触媒的成本优势,开发出适合合成CSD金刚石的FeMn25Ni15触媒,并对合成工艺进行了深入研究,结果表明,采用新型FeMn触媒合成的CSD金刚石,性能指标达到使用要求,而成本显著低于目前使用的Ni70Mn30触媒。5)利用EDS能谱分析研究了金属包膜在金刚石合成过程中的作用,发现金属包膜在金刚石生长过程中起到向晶核输送碳源和向外排除杂质的作用,金属包膜破裂后,金刚石停止生长；对金属包膜的物相分析进一步表明室温下金属包膜的物相主要为Fe3C、(Fe,Ni)23C6以及γ-(Fe, Ni),石墨占的比例很少。因此,可以认为金刚石形核长大过程中存在着触媒粒子的熔聚现象。6)初步探讨了金刚石单晶生长所需碳的来源问题,利用现有热力学数据分析表明,金属包膜中金属碳化物(Fe3C)的分解降低了石墨转变为金刚石所要越过的势垒,因而更有利于形成金刚石；但是从Fe-C相图Fe3C的形成条件及Fe3C中碳转化成金刚石的数量等因素分析表明,在高温高压下Fe3C存在的可能性很小,用其作为金刚石合成的碳源在理论和实际应用中都缺乏依据。由于现有实验条件所限,金刚石转化碳源问题还需要进一步研究。更多还原

【Abstract】 Synthetic Diamond, as a substitute for natural diamond, is a versatile functional material and applied in many fields including the industrial, scientific and defense fields. As a result, it is of great strategic significance to enhance research on synthetic technology and synthesis of raw materials, optimize and improve existing powder catalyst formulations, develop low-cost catalysts, and prepare special-purpose synthetic diamond abrasives.In this paper, based on the research on iron-based catalyst, the rule of influence for synthetic diamond by the different composition of catalyst and different ratio between catalyst and graphite has been studied deeply, and also the mechanism of catalyst in the process of synthesizing diamond has been discussed. Based on above the research, new low-cost catalyst formula suitable for synthesizing granular structure diamond (CSD) has been designed out and the followed study has been carried out as a result:1) Carrying out Synthesis experiments using powdered catalyst with different ratio of Fe and Ni. The results show that, As the Fe content in catalyst is increasing, the lowest and the best synthesizing conditions are improved somewhat, and diamond V-shaped growth area moves to the upper right; diamond particle’s crest value is thicker, the mixed yield per unit, static strength and impact toughness all decrease; the tests on the different ratios of catalyst and graphite have shown:increasing the usage of catalyst can enhance yield per unit. Considering the elements such as the cost of raw materials, diamond production and quality, the best effect can be gained by selecting the content of 70% Fe and 30% Ni and with the 3:7 ratio of catalyst and graphite, and the basic principle for designing catalyst composition has also been established.2) Studying deeply the effect on the synthesizing diamond by adding rare earth elements in FeNi30. It shows As followed:rare earth elements can increase effectively oxygen bonding content in catalyst, enhance the purity of powdered catalyst, and exert varying effect on increasing the mixed yield per unit, the proportion of coarse particles, TI and TTI value of single grain, static strength increases, and the magnetic susceptibility; optimized tests show that the best addition of rare earth is 0.4%.3) According to the basic principle for designing catalyst composition, FeMn-based catalysts with different composition have been designed, and by synthesizing diamond tests, it is studied on the rules which different adding elements and contents effect diamond synthesis, and the result shows that:by using FeMn-based catalyst only, diamond can be synthesized on 5.4～5.6GPa and 1450～1600℃, the synthetic conditions is more strictly than that in FeNi-based catalysts, and diamond particle size is less fine, and its crystal form is poorer; when 5% Ni or Co is added into the FeMn catalyst, the synthesizing pressure and temperature can be reduced more or less; adding rare earth elements contributes to the improvement of diamond crystal; when Ni content of 15% remains invariable, and Mn content varies from 15%,20% to 25%, diamond nucleation increases gradually, the particle size becomes thinner, the diamond color varies from gray-green to black, and crystal shape becomes irregular, and when Mn content is 25% the aggregate structure of diamond can been produced; when Ni and Mn contents keep invariable and Co content increases, the particle size becomes coarse, grain shape becomes better, mixed yield increases, black diamond decreases, and crystal transparency increases.4) Aimed at the increasing needs of market for CSD diamond, by advantage of cost of FeMn-based catalyst, the FeMn25Ni15 catalyst suitable for CSD diamond has been developed, and synthetic technics have also been studied deeply, the result shows that:the performance evaluation of CSD diamond synthesized by FeMn-based catalyst can meet the useful requirements and the cost is significantly lower than that of Ni70Mn30 catalyst which is currently used.5) EDS energy spectrum analysis is used to study the effect of metal envelope in the process of synthesizing diamond, and it is found that metal envelope exerts the effect of transporting carbon source and eliminating impurity to outside in the progress of diamond’s growing, and after metal envelope breaks down, diamond will stop growing; the analysis for the phase of metal envelope further shows that the metal envelope’s phase mainly consists of Fe3C, (Fe,Ni)23C6, andγ-(Fe,Ni), and the graphite content is very small. Therefore, it can be considered that catalyst grain agglomerating exists in the process of the diamond nucleation.6) Discussing initiatively the problem of source of carbon needed during the progress of diamond’s growing; and the analysis on current thermodynamic data shows that, the decomposition of metal carbide(Fe3C) in metal envelope reduces the energy barrier during the progress of transforming graphite into diamond, and it benefits more the diamond’s formation; however, through analyzing such elements as the formation conditions of Fe3C in Fe-C Phase diagram and the quantity of diamonds transformed from carbon in Fe3C, the result shows that it has little possibility for Fe3C to exist under high temperature and high pressure, and lacks base in theory and in real application for Fe3C to be used as carbon source during the process of synthesizing diamond. Due to limited test’s conditions, it needs further study on carbon sources of diamond.更多还原