特性爆炸纳米多晶金刚石及其新的理论技术(下)

文章对爆炸纳米多晶金刚石的结构形貌特性作了充分全面检测描述:X衍射曲线,Raman光谱曲线,X射线小角散射粒度测定,AFM,SEM,TEM电镜分析以及化学后处理后的各种成份含量分析。爆炸纳米多晶金刚石有三种颗粒形态:"晶核","原生聚晶颗粒"和"聚合聚晶颗粒"。"原生聚晶颗粒"呈球形由"晶核"集聚而成,但再不能用现代物理化学手段将其分离开来;"聚合聚晶颗粒"是由许多"原生聚晶颗粒"集聚而成的微米和亚微米级颗粒。"原生聚晶颗粒"的粒度是这种纳米多晶金刚石的特性显示,文中显示的"原生聚晶颗粒"粒度在50nm上下。开发了二种爆炸技术:成核爆炸技术和成核-聚合结合爆炸技术。由后者制作出的金刚石粉是最佳的抛光磨料,提出了有关爆炸纳米多晶金刚石的新理论。     

论爆炸多晶金刚石的特性与理论

文中叙述的“爆炸多晶金刚石”是特指冲击波通过石墨粉体使之相变的多晶金刚石.文中展示出这种晶体结构的形态和特异点.介绍了两种“击波聚晶”的爆炸装置:圆管收缩爆炸装置和平面打击爆炸装置.指出计算压力和温度力学模型的重要性,计算压力的“均相分布”理论不被实验所证实.粉体中的金属粉既起打击板的作用,又起降低卸载温度的冷却作用.提出作者的对提高飞片打击速度有实效的有关专利.作者发现在常压下爆炸时的飞片下气体受绝热压缩后的聚能效应.     

丙烯超临界聚合中原生晶特征

通过广角X射线衍射(WAXD)对由丙烯超临界聚合和传统本体淤浆法制得的等规聚丙烯原生结晶特征进行了研究,并讨论了聚合工艺、预聚温度、粒径、分子量等对原生晶特征的影响。结果表明,超临界聚合法制备的等规聚丙烯(SC-iPP)呈现出α和γ的混合晶型,而采用传统淤浆法制备的等规聚丙烯(C-iPP)只含有单一α晶型,这是因为超临界的高温高压状态,使得体系传热传质阻力较小,更有利于原生晶型的发展。此外,预聚温度、粒径、分子量等因素也对丙烯超临界聚合所制得的SC-iPP结晶特征有显著影响。     

纳米金刚石的发展及其应用前景

利用负氧平衡炸药,在密闭爆炸罐内爆炸所获得的纳米金刚石单晶微粒尺寸一般在5～10nm.而以石墨为原料,通过TNT RDX混合炸药爆炸所制得的则是由纳米量级金刚石所构成的多晶金刚石.这两种类型的金刚石各有特点,它们均兼有金刚石和纳米材料的双重特性.文章就其发展历程、制备技术、应用领域及其潜在前景等做了简要的阐述.     

纳米多晶柯石英的高温高压合成

利用国产铰链式六面顶压机,以高纯微米晶α-SiO_2为原料,在5GPa、1000℃条件下实现了微米晶α-SiO_2向柯石英多晶体的直接转变,合成出了纳米多晶柯石英块体,X射线衍射分析表明,该块体材料仅含柯石英单相。扫描电镜显示颗粒的平均尺寸为100nm左右。显微硬度为1406 MPa。     

纳米CL-20的制备、表征和粉碎机理研究（英文）

采用双向旋转研磨方法制备了纳米CL-20,用SEM、XRD及激光粒度分析仪测试了其形貌晶型及粒度分布,采用GJB 772A-97方法测试了其机械感度,分析了纳米CL-20的粉碎机理。结果表明,制备的CL-20为粒径100nm的半球形颗粒,且粒度分布较窄。纳米炸药晶型与微米炸药一致,均为ε型。与微米CL-20相比,纳米CL-20的摩擦感度、撞击感度、冲击波感度分别下降25.0%,116.2%和58.1%。     

YMnO_3纳米颗粒的制备与表征

采用改进的丙烯酰胺聚合凝胶法制备YMnO3纳米颗粒。通过加入丙烯酰胺使Y和Mn的无机盐水溶液成胶,在溶液成胶过程中,丙烯酰胺聚合形成高分子网络骨架,为粒子提供生长的空间。利用X射线衍射、热重分析、差示扫描量热分析及红外光谱等多种手段研究干凝胶的热分解及YMnO3的形成过程,结果表明:在800℃煅烧可获得高纯的YMnO3粉体,比固相反应法合成YMnO3降低了近300℃。扫描电镜观察显示:制得的YMnO3粉体的粒度分布均匀,颗粒呈类球形。磁滞回线测量结果表明:YMnO3纳米颗粒在室温具有微弱的铁磁性,这是其陶瓷样品所不具有的。     

热稳定金刚石聚晶的制备及表征

在高温高压条件下(5.6GPa,1200℃～1480℃),以舍硼金刚石微粉为原料,镍基合金为烧结助剂,采用熔渗法成功制备了热稳定金刚石聚晶(Thermally stable PCD).通过X射线衍射(XRD)和扫描电镜(SEM),研究了烧结温度对热稳定金刚石聚晶的物相成分、微观组织形貌的影响;并与普通金刚石聚晶进行了差热(DTA)、热重(TG)的对比分析测试,结合X射线光电子能谱(XPS)测试结果给出了相应解释.实验结果表明:在压强为5.6GPa条件下,温度在1300℃～1450℃区间内,才能实现热稳定PCD的烧结;此时形成的热稳定PCD的耐热性和抗氧化性相比普通PCD均有较大幅度提高.     

纳米硫酸钡晶种法制备亚微米硫酸钡的工艺研究

使用硫酸钠、氯化钡和纳米硫酸钡晶种为原料,制备得到了亚微米级硫酸钡产品。通过使用扫描电子显微镜、激光粒度仪等分析手段,系统研究了工艺条件对于产品硫酸钡颗粒的形貌、粒径及粒度分布的影响。实验结果表明:随着反应物浓度的增大,产物硫酸钡粒子的粒径逐渐减小,且粒度分布逐渐变窄;两种反应物同时加入的加料方式所得产品粒径较大且粒度分布较宽;反应温度的升高也会导致产物颗粒粒径增大、粒度分布变宽。将0.5 mol/L氯化钡溶液滴加入含有纳米硫酸钡晶种的0.5 mol/L硫酸钠溶液中,保持反应温度为40℃,可以得到粒径为260 nm左右的硫酸钡颗粒。     

河南第一条纳米金刚石生产线的建立

河南是中国静态高压高温-触媒法生产单晶金刚石的第一大省.河南联合磨料磨具有限公司在外聘技术专家的帮助参与下,用常规的爆炸法(或爆轰产物法)制备出了纳米多晶(或单晶)金刚石,填补了河南省没有纳米金刚石生产的空白.纳米多晶金刚石的产业化已由中科院力学研究所于1993年实现.为使业内人士对纳米金刚石及其下游产品的发展历史真相有所了解,文章特将国内纳米金刚石生产线的建立和纳米多晶金刚石研发简史,纳米金刚石抛光液和抛光膜的研制与应用现状做一简要的阐述.     

Synthesis of Fine-Grained Polycrystalline Diamond Compact and Its Microstructure

Sintering of a fine-grained polycrystalline diamond compact with grains less than 1 μm in size was successfully carried out by making a laminate on a WC/Co powder compact under sintering conditions of 5.8 GPa and 1430° to 1480°C for 30 min, in which small amounts of poly(ethylene glycol) and fine powder of cubic boron nitride were added to the starting diamond powder. The former played the role of preventing agglomeration of the diamond powder and the latter of suppressing abnormal grain growth during sintering. Microstructural observation of the polycrystalline diamond showed that in the regions near the WC/Co layer a comparatively large amount of Co metal was present between diamond grains, but in other regions the amount of Co decreased, and the diamond grains were seen to be bonded strongly. The Vickers hardness of the polycrystalline diamond was 55 ± 5 GPa with 19.6 N load.     

Synthesis and properties of single phase diamond ceramics

We report on the synthesis of single phase diamond ceramics and its microstructural and physical characterization. The most relevant physical properties are listed and are compared to natural diamond. The ceramic solid has been fabricated from chemically treated micro crystalline diamond powder, where oxy-functional groups have been attached to the surface. The special surface treatment is considered essential to achieve direct atomic bonding between adjacent grains.The hot isostatic pressing method (HIP) has been applied for materials processing that pertains to the stability region of the related carbon phase diagram. No further additives have been used for preparation. Transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and Raman spectroscopy have been used for the micro structural analysis. The achievable density is close to that of natural diamond, revealing porosity values of <3%. The micro structural analyses indicated the presence of small amounts of isolated diamond micro crystals, embedded into a matrix of polycrystalline diamond with a very small grain size. The grains are much smaller than the originally used micro crystalline source material, indicating crystal break-up and atomic rebonding during the sintering process. Also traces of sp²-hybridized carbon have been identified, located primarily at grain boundaries. Fracture of the material appears mostly transgranular. Relevant physical properties as thermal and electrical conductivity, hardness and Young's modulus approach those of natural diamond.     

CVD金刚石薄膜技术发展现状及展望(下)

简要描述了CVD金刚石薄膜技术的发展历程。介绍了纳米特别是超纳米金刚石膜、CVD金刚石大单晶的技术特点及其应用。超纳米金刚石膜在MEMS(微机电系统)、电化学和生物医学上的应用和CVD金刚石大单晶是当前的研究热点。简言之,金刚石的发展向着更大或者更小的方向深入进行,即"非大即小"。     

Determination of crystal size distributions in alumina ceramics by a novel X‐ray diffraction procedure

A novel X‐ray diffraction based method is presented, capable of determining volume‐based crystal size distribution (CSD) of polycrystalline materials and crystalline powders with unprecedented sampling statistics; the method is named fast X‐ray diffraction crystal size distribution analysis (FXD‐CSD). FXD‐CSD can be performed with standard laboratory X‐ray diffractometers equipped with a position sensitive detector and uses a software package written in Python for the data analysis. FXD‐CSD is a destruction‐free and generally applicable method to establish CSDs of polycrystalline materials as well as powders for sizes well below 1 μm up to about 100 μm; it even allows for studies of samples enclosed in complex environments, e.g., for in situ measurements in a furnace or in a pressure cell. To show the capability of the method the microstructural evolution of four alumina substrates with different time‐spans of sintering (4, 8, 16, and 24 hour at 1600°C) is investigated via FXD‐CSD and SEM imaging. The corresponding CSDs and average grain sizes are determined, results obtained by FXD‐CSD and the line‐intersection methods are compared and clear evidence for the presence of abnormal grain growth (AGG) during sintering is shown. From three tested probability density functions (PDF) describing the CSDs a log‐normal PDF fits best to the volume based CSDs; the method provides size distributions with unprecedented precision opening the way to a systematic and meaningful comparison between theoretically predicted and observed CSDs.     

Habits of Grains in Dense Polycrystalline Solids

We show here that the boundaries of individual grains in dense polycrystals prefer certain crystallographic habit planes, almost as if they were independent of the neighboring crystals. In MgO, SrTiO₃, MgAl₂O₄, TiO₂, and aluminum, the specific habit planes within the polycrystal correspond to the same planes that dominate the external growth forms and equilibrium shapes of isolated crystals of the same phase. The observations decrease the apparent complexity of interfacial networks and suggest that the mechanisms of solid-state grain growth may be analogous to conventional crystal growth. The results also indicate that a model for grain-boundary energy and structure based on grain surface relationships is more appropriate than the widely accepted models based on lattice orientation relationships.     

Effect of WC particle size on the microstructure and mechanical properties of Ni–Co coarse grain cemented carbide

The effect of different WC grain size additions on the microstructure and grain distribution of Ni–Co coarse crystalline cemented carbide was studied. And then the effect of grain distribution on the mechanical properties of cemented carbide was discussed. The effect of WC grain size on the grain size and coherency of cemented carbide was analyzed by microstructure. And the distribution of grains in the microstructure was investigated by the truncation method. The addition of fine (1.1–1.4 μm), medium (2.3–2.7 μm), and coarse WC (5.6–6.0 μm) particles can increase the nucleation rate of WC grains in the bonded phase. And the higher grain growth driving force can produce the theoretical limitation of nucleation and inhibit the coarsening of WC grains to a certain extent. The WC grain size has an insignificant effect on the frequency of the occurrence of super-coarse grains in coarse crystalline cemented carbide. The average grain size and super coarse grains in microstructure gradually decrease, which promotes the improvement of transverse rupture strength. The increase of the adjacent degree and the decrease of the mean free path reduce which is beneficial to the improvement of the corrosion resistance of the alloy. The best overall performance of the alloy is achieved when fine-grained WC is added.     

A study on the conduction path in undoped polycrystalline diamond films

The conduction path in as-grown undoped diamond films deposited by chemical vapor deposition has been investigated by employing impedance spectroscopy, electroplating and electroetching. The thickness- and direction-dependencies of electrical resistivity did not agree with the previously known surface conduction model. The Cu electroplating and Ag electroetching results showed that the current path followed the grain boundaries within the diamond films. The Cu electroplating of diamond film with an insulating surface layer also showed that the grain boundaries within the films were the main conduction path in undoped polycrystalline films.     

Nucleation and Growth of Diamond in Detonation Products

Diamond particles were produced from a mixture of graphite and explosive powders using a detonation method. Morphologically, the products were a crystalline, twisted, ribbonlike particle and a curled, ribbonlike particle in an amorphous-like state. Analyses of electron diffraction patterns and high-resolution electron microscope images provided evidence that the crystalline, ribbonlike diamond developed due to crystallization of the amorphous-like diamond formed by condensation of gaseous carbon generated from the explosive in the release process; the microcrystallite size at an early stage of the crystallization process was about 1 to 2 nm.     

Microtexture of c‐Axis‐Oriented Polycrystalline Lanthanum Silicate Oxyapatite Formed by Reactive Diffusion

We annealed the La₂SiO₅/La₂Si₂O₇ diffusion couple at 1873 K for 25 h to prepare the grain‐oriented lanthanum silicate oxyapatite (LSO) polycrystal at the interfacial contact boundary. The polycrystalline LSO was characterized using optical microscopy, transmission electron microscopy, scanning electron microscopy, and X‐ray diffractometry (XRD). The external shape line information on individual crystal grains were extracted from the backscattered electron image on the section surface of the polycrystal. We collected the electron backscatter diffraction patterns and XRD patterns to determine, respectively, the crystallographic orientations of individual grains and orientation degrees of the LSO polycrystal. The reaction area was in the form of a layer parallel to the original contact boundary, and consequently categorized, based on the differences in grain size distribution and orientation degree, into three distinct regions. The innermost region with the layer thickness of 30 μm was composed mainly of the rounded and relatively small crystal grains with the size less than ~16 μm in diameter. Furthermore, this region showed the lowest orientation degree among the three regions. On the other hand, the LSO grains on both sides of this region were much larger in size and prismatic in morphology; the LSO crystals were elongated along the c‐axis, and built up of faces {001}, {304}, and {100}. The individual crystal grains were aligned almost along their c‐axes, with their a‐axis directions being randomly distributed around the common c‐axis. The differences in microtexture among the three regions would be induced by the distinct growth behaviors of LSO crystals.     

Bi:YIG纳米薄膜的磁光特性

用射频磁控溅射和快速退火方法制备了纳米量级的Bi:YIG薄膜,研究了薄膜的磁光特性.当晶粒尺寸从150 nm降到80 nm时,透射率和Faraday角的值分别从75%和3.6°变成了80%和4.0°.结果表明:高的透射率和大Faraday角可以在晶粒尺寸为纳米量级的薄膜中共存.