高温高压下无定形碳向金刚石结构转变的研究

碳素材料是合成金刚石的原料。人们对熔媒参与下,石墨向金刚石转变研究得最多,并对这一转变过程提出了不同的解释。本文以无定形碳为碳源,来探讨其向金刚石的转变过程。通常使用石墨而不用无定形碳作碳源来合成金刚石,其原因在于无定形碳不具备直接转变成金刚石所必须的结构。实验表明:无定形碳向金刚石转变必须经过石墨化。无定形碳的石墨化过程是:构成三维排列的石墨晶体结构和石墨晶粒的长大。     

金刚石与碳素材料

介绍了碳转变为金刚石机理,对溶剂说进行了充分地阐述.认为影响金刚石生长的决定因素是碳的分散、溶解速度.合理利用无定形碳高溶解速度的特点,无定形碳对金刚石生长是有利的.     

火焰法沉积金刚石薄膜的组织结构

用透射电镜（ＴＥＭ）对大气中火焰法沉积（ＣＦＤ）金刚石薄膜的组织结构进行了分析研究。结果表明，所沉积的金刚石晶体中（１１１）面上存在着大量层错及显微孪晶，在（１１１）面上晶粒边界处的位错密度较低，此外，在金刚石薄膜中还观察到存在于金刚石颗粒间的非金刚石型碳（Ｃ），即无定形碳及微晶石墨。     

聚晶用石墨发热体的煅烧温度对聚晶相对耐磨性的影响

本文通过对聚晶金刚石用石墨发热体煅烧后吸附及压缩性能的观测,对比了以煅烧和未煅烧石墨发热体合成聚晶金刚石的相对耐磨性,结果表明以煅烧后石墨发热体合成的聚晶金刚石的相对耐磨性比未煅烧者高几倍,最高相对磨耗比达10万以上,改善了聚晶金刚石的性能,同时也从一个侧面为制造合成聚晶金刚石专用石墨提供了依据。     

钨和钽丝碳化后的结构变化及其对金刚石成膜质量的影响

本文利用金相分析、Ｘ射线衍射等方法，对ＨＦＣＶＤ法沉积金刚石薄膜时使用的钨丝和钽丝在不同碳化条件下灯丝成分和结构变化作了分析研究，解释了碳化钽丝表面色泽金黄的原因，并在相同沉积条件下，比较了使用碳化和未碳化灯丝对生长金刚石薄膜的影响。结果表明，使用碳化灯丝生长的金刚石薄膜的石墨含量少，金刚石膜的质量和生长速度有所提高。     

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。     

金刚石纳米粉引晶方法制备金刚石薄膜方法

利用金刚石纳米粉引晶法和常规研磨方法分别在单晶硅衬底上制备金刚石薄膜,并采用扫描电镜、激光拉曼方法对所制备样品进行表征,通过SEM和拉曼谱分析,与研磨法生长金刚石薄膜相比,利用金刚石纳米粉引晶方法可以大大提高金刚石薄膜的成核速度,生长速率达到2μm/h以上。对相同碳源浓度下生长的金刚石薄膜样品的SEM和拉曼谱分析,采用引晶法生长的金刚石薄膜质量明显高于研磨法。     

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．     

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.     

放电电压对直流热阴极制备金刚石厚膜的影响

利用直流热阴极辉光放电方法制备出了高品质金刚石厚膜,生长速率达到20μm/h,生长厚度达到3mm.为了解其工作特性、优化沉积工艺,本文研究了放电电压对金刚石沉积速率和品质的影响.通过对扫描电镜、拉曼谱和XRD图谱分析得出,随着放电电压的增加,沉积速率呈下降趋势,电压在850～950V范围金刚石中石墨和非晶碳明显减少,晶粒均匀,表面晶向以(110)为主,金刚石薄膜的质量显著提高.     

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.     

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.     

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,     

Microstructures of metallic film and diamond growth from Fe-Ni-C system

The microstructures of metallic film surrounding diamond have been systemically studied using the transmission electron microscopy (TEM) and the atom force microscopy (AFM). The film can be divided into three layers (inner layer near diamond, external layer near graphite and middle layer). The graphite cannot be directly transformed into diamond in the film at HTHP; there exists a parallel relationship between (−111) of γ-(Fe,Ni) and (110) of Fe₃C in the inner layer; the sawtooth-like step morphology found by AFM on the film is similar to that of corresponding diamond surface. A new model for diamond growth at HPHT is proposed from the parallel relationship and sawtooth-like step morphology. It is believed that Fe₃C may be a transitional phase in the course of diamond growth, γ-(Fe,Ni) in the inner layer can absorb carbon atom groups with lamella structure from Fe₃C, and then the carbon groups stack on growing diamond.     

Reburial of fossil organic carbon in marine sediments

Marine sediments act as the ultimate sink for organic carbon, sequestering otherwise rapidly cycling carbon for geologic timescales. Sedimentary organic carbon burial appears to be controlled by oxygen exposure time in situ, and much research has focused on understanding the mechanisms of preservation of organic carbon. In this context, combustion-derived black carbon has received attention as a form of refractory organic carbon that may be preferentially preserved in soils and sediments. However, little is understood about the environmental roles, transport and distribution of black carbon. Here we apply isotopic analyses to graphitic black carbon samples isolated from pre-industrial marine and terrestrial sediments. We find that this material is terrestrially derived and almost entirely depleted of radiocarbon, suggesting that it is graphite weathered from rocks, rather than a combustion product. The widespread presence of fossil graphitic black carbon in sediments has therefore probably led to significant overestimates of burial of combustion-derived black carbon in marine sediments. It could be responsible for biasing radiocarbon dating of sedimentary organic carbon, and also reveals a closed loop in the carbon cycle. Depending on its susceptibility to oxidation, this recycled carbon may be locked away from the biologically mediated carbon cycle for many geologic cycles.     

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 ...     

锂离子电池碳负极中边缘碳及表面碳原子含量的理论计算

通过理论分析与计算得到边缘碳及表面碳原子含量的表达式。分析了石墨微晶结构与成键特征,研究了石墨微晶中边缘碳原子与基平面碳原子的电化学特性。结果表明:边缘碳原子比基平面碳原子更易于与其他原子或基团形成较为稳固的联接,电化学反应活性较高;在首次充电过程中,边缘碳原子附近电解质的分解与SEI膜成膜反应速度较快,有利于形成联接较为紧密的SEI膜;建立了紧密堆砌的正六棱柱颗粒模型,推导出理想石墨中边缘碳原子及表面碳原子含量与微晶参数、颗粒尺寸之间的关系式。通过引入适当因子,修正了实际石墨颗粒与理想石墨在结构、形貌、孔隙率等方面的差别,得到的表达式可适用于石墨、无定形碳及改性碳等多种碳材料碳原子含量的计算。     

膨胀石墨与炭黑协同补强天然橡胶复合材料的性能研究

采用强氧化法制备插层石墨(GIC),用微波辐射处理插层石墨制备膨胀石墨(EG)。结果表明,膨胀石墨表面较天然鳞片石墨粗糙,内部空隙增大,结构疏松;且表面有机官能团增多,结晶度下降。用机械共混法制备膨胀石墨/炭黑/天然橡胶复合材料,添加膨胀石墨后,填料在复合材料中分散性改善,复合材料的100%、300%定伸强度明显提升,Payne效应减弱,加工性能提升;但复合材料动态损耗因子增大,滞后效应明显。     

纳米炭黑对镉胁迫下黑麦草种子萌发和幼苗生长的影响

采用水培方法,分别进行了镉胁迫、纳米炭黑与镉共同作用下黑麦草种子的萌发实验,并应用电感耦合等离子体质谱(ICP-MS)对黑麦草幼苗体内的镉含量进行测定。镉溶液浓度低于50 mg/L时对发芽率和发芽指数表现为促进作用,而镉溶液浓度高于50 mg/L则为抑制作用。对幼苗的根长、芽长和种子的活力指数表现为典型的Hormesis效应,在溶液镉浓度为5 mg/L时促进作用最为明显。添加定量纳米炭黑后,在较低镉浓度下(≤10 mg/L)可明显提高黑麦草种子的发芽力,其他种子萌发指标均高于未加入纳米炭黑的各项处理组,且趋势相同。ICP-MS测定结果显示,幼苗体内镉含量随镉浓度增加而增加,在溶液镉浓度小于100 mg/L时,添加纳米炭黑的处理组幼苗体内镉含量低于未添加纳米炭黑的处理组,这说明纳米炭黑对镉有一定的钝化作用,可阻碍幼苗对镉的吸收,降低体内镉含量。     

爆轰过程中游离碳的状态研究

目的 研究高密度负氧平衡炸药爆轰过程中游离碳的状态。方法 结合爆轰合成纳米金刚石数值结果以及对固相爆轰产物的实验研究,对爆轰过程中游离碳的状态进行讨论。用具有明确物理意义和纯石墨,金刚石,超微金刚石和类液碳的状态方程对多种炸药的爆速进行计算。结果与结论 用超微金刚石和类液碳的状态方程比用纯石墨和金刚石的状态方程预报的炸药爆轰参数更接近实验值,证明高密度负氧平衡炸药爆轰时ＣＪ点上游离碳主要是以液态或