Synthesis and Thermal Oxidation Stability of Nanocrystalline Niobium Diboride

Inorganic Materials - A method has been developed for the synthesis of nanocrystalline NbB2 powder with an average particle size of 65 nm. The material has been prepared by reacting Nb and...     

Iodine-Assisted Solid-State Synthesis and Characterization of Nanocrystalline Zirconium Diboride Nanosheets

A solid-state route was developed to prepare zirconium diboride nanosheets with the dimension of about 500 nm and thickness of about 20 nm from zirconium dioxide, iodine and sodium borohydride at 700°C in an autoclave reactor. The obtained ZrB₂ product was investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The obtained product was also studied by thermogravimetric analysis. It had good thermal stability and oxidation resistance below 400°C in air. Furthermore, the possible formation mechanism of ZrB₂ was also discussed.     

TiB_2粉料的还原合成与酸洗纯化研究

用SHS还原合成法合成了TiB2 混合粉料 ,并通过酸洗处理获得了高纯TiB2 粉料。研究了合成过程和酸洗条件对TiB2 纯度的影响 ,对合成粉料酸洗过程进行了热力学分析。试验结果表明 ,TiO2 B2 O3 Mg三元系统的化学反应由两部分组成 ,第一部分由金属Mg还原出B和Ti单体 ,第二部分由这两种单体化合反应生成TiB2 。TiB2 粉料的纯度主要取决于酸洗条件。提高盐酸浓度、增加酸过量和延长酸洗时间可以提高TiB2 粉料的纯度 ,而升高酸洗温度还可以大大加快酸洗速度。     

Material Properties of Titanium Diboride

The physical, mechanical, and thermal properties of polycrystalline TiB₂ are examined with an emphasis on the significant dependence of the properties on the density and grain size of the material specimens. Using trend analysis, property relations, and interpolation methods, a coherent set of trend values for the properties of polycrystalline TiB₂ is determined for a mass fraction of TiB₂ ⩾ 98 %, a density of (4.5±0.1) g/cm³, and a mean grain size of (9±1) µm.     

Elastic-Stiffness Coefficients of Titanium Diboride

Using resonance ultrasound spectroscopy, we measured the monocrystal elastic-stiffness coefficients, the Voigt C_ij, of TiB₂. With hexagonal symmetry, TiB₂ exhibits five independent C_ij: C₁₁, C₃₃, C₄₄, C₁₂, C₁₃. Using Voigt-Reuss-Hill averaging, we converted these monocrystal values to quasiisotropic (polycrystal) elastic stiffnesses. Briefly, we comment on effects of voids. From the C_ij, we calculated the Debye characteristic temperature, the Grüneisen parameter, and various sound velocities. Our study resolves the enormous differences between two previous reports of TiB₂’s C_ij.     

An Investigation of Titanium Nitride Prepared by a DC Arc Plasma Jet

The properties of a titanium nitride film prepared by a DC arc plasma jet were investigated by microscopic observations, composition analysis, and hardness measurements. Scanning electron microscopy showed that the film was composed of three phases, designated the A, B, and C regions from the outer surface. The existence of three regions was also supported by composition analysis and hardness measurements on the cross section. XRD patterns showed the presence of -TiN in the A region. In the B region, a number of voids were observed, which have never been reported in previous papers. These were made up from specific crystallographic surfaces. The C region also had a few voids which were somewhat different from those in the B region. In the matrix, an acicular texture was found and identified as -Ti solid solution by XRD. The cross section of the film changed the color determined by the nitrogen content.     

TiB2基复合材料的研究进展

TiB2具有良好的物理化学性能,应用前景广阔,但是陶瓷材料所固有的脆性和很高的烧结温度限制了TiB2材料的广泛使用.为了制得有实用价值的材料,对TiB2陶瓷复合材料、TiB2金属陶瓷进行了大量研究,并研制出了多种先进制备技术.综合评述了近年来国内外对TiB2陶瓷复合材料、TiB2金属陶瓷的研究进展,并简述了制备二硼化钛复合材料的先进制备技术.最后,讨论了TiB2基复合材料今后的研究方向.     

TiB2陶瓷活化烧结及制备技术

TiB2材料具有高熔点、高硬度、耐磨、耐腐蚀、抗氧化以及导电性好和导热性好等优点,是一种具有广泛应用前景的新型陶瓷材料.但是其极强的共价键晶体结构和较低的自扩散系数,使得其很难获得致密的陶瓷材料.主要从添加助烧剂和烧结技术两方面介绍了TiB2陶瓷活化烧结方法的研究进展,并分析了该技术促进材料烧结致密化的机制,同时介绍了热压烧结和放电等离子(SPS)烧结技术.     

Intrinsically Ductile Failure in a Nanocrystalline Beta Titanium Alloy

A nanocrystalline bcc Ti_67.4Nb_24.6Zr₅Sn₃ alloy is shown to fracture in an intrinsically ductile manner with exceptionally large dimples (up to 10 µm) which are two orders of magnitude greater than the grain size (≈ 40 nm). This large plasticity length scale is attributed to a combination of low shear modulus (≈ 27 GPa), high Poisson's ratio (≈ 0.4) and ultrahigh strength (UTS ≈ 1.1 GPa), close to the ideal shear stress, which facilitates ideal shear deformation to promote transgranular shear.     

Rapidly Synthesis of Nanocrystalline Diamond Films by Helicon Wave Plasma

正A new technique of the synthesis of Nanocrystalline Diamond(NCD)Films by helicon wave plasma(HWP)chemical vapor deposition at room temperature was reported.The growth morphology and the roughness of NCD samples was characterized using filed emission scanning electron microscopy(SEM-SU8010)and atom force microscopy(AFM),respectively.The results show the growth rate of the film was very fast,about 833nm/min.Typical G,D bands     

NaCl加入量对自蔓延高温燃烧合成法大规模制备的超细二硼化钛粉体性能的影响

以TiO2、B2O3、Mg粉为原料,引入稀释剂NaCl,通过自蔓延高温燃烧合成法宏量制备了亚微米TiB2粉体,并对其进行了SEM(扫描电镜)、EDS(能谱)、XRD(X射线衍射)和粒度分析.用原子吸收光谱测定了浸出产物TiB2粉体中杂质Mg,O的含量.结果表明:稀释剂加入量对样品形貌、粒度、物相有明显影响.随着NaCl含量的增加,制备的TiB2粉体的平均颗粒尺寸从496nm降低到268nm.产物浸出前主要由MgO,NaCl,TiB2和少量Mg3B2O6组成;浸出后前两相消失,产物为TiB2和少量Mg3B2O6.当原料中NaCl加入量k=0.5,1.0,1.5,2.0mol时,浸出产物中Mg3B2O6杂质含量极少,产品纯度均超过98％.稀释剂可以降低颗粒尺寸,提高产物纯度.采用此种自蔓延高温燃烧合成法可以大规模制备超细TiB2粉体.     

Flow Visualization in a Rotating-Arc Plasma Jet

Knowledge of the gas flow pattern in a plasma jet exhaust is important in relation to heat transfer and gas temperature estimation. The extreme conditions within the jet, however, have hitherto encouraged the use of water cooled probes for flow measurements to the exclusion of quicker and more convenient optical methods.

An optical system has been developed to indicate gas velocities throughout the volume of a transparent water jacket enclosing the exhaust gas by means of particle track photography. The difficulties caused by the size of the test space and the high gas luminosity are overcome by using a bi-focal lens system to utilize a photographic flash bulb source efficiently.     

电弧等离子体法裂解甲烷制备碳纳米管

利用电弧等离子体法以Co2O3为催化剂裂解甲烷制备得到了碳纳米管.所得固相产物进行了扫描电镜(SEM)和高分辨透射电镜(HRTEM)分析表征.结果表明:固相产物中形成的碳纳米管纯度较高,直径在50～90nm之间,并发现了一种特殊的管壁厚度不均,呈厚-薄-厚形态的碳纳米管.     

Anisotropies in Carbon Nanotube Synthesis by the Hydrogen Arc Plasma Jet Method

Single-wall carbon nanotubes were prepared under hydrogen gas atmosphere with a DC arc discharge maintained between the tip of a sharpened graphite cathode and an anode formed by a catalytic mixture of graphite, FeS, Ni, Fe and Co compressed powders. The cathode is placed with an inclination with respect to the anode, so that the plasma jet of the discharge is deviated towards the empty space of the growth chamber. Samples were classified and analyzed according to their type and growth positions relative to the direction of the plasma jet flow. Characterization of the samples was performed with mass spectrometry, Raman spectroscopy and transmission electron microscopy. A subtle variation is found in the properties of the nanotubes obtained in different locations due to the directionality of the plasma jet flow. Observed differences in sample properties may be qualitatively understood in terms of accepted mechanisms of SWNT growth.     

Jet Formation in Plasma Sprayers

Optospectroscopic studies of plasma jets in powder sprayers have been made. It has been shown that the jet of the PlasmaTechnik AG sprayer is a periodically pulsating formation similar to that generated by the twojet plasma torch. A scheme of a plasmasonic reactor for treatment and synthesis of gaseous and condensed materials is proposed.     

碳纳米管-TiB2陶瓷基复合材料的制备与性能研究

研究了用热压烧结(HP)方法制备TiB2-xwt%CNTs-5wt%Ni(x=0.1、0.3、0.5、1、4)复合材料的工艺条件、力学性能和微观结构.用XRD研究了其相组成,用SEM观察了复合材料的断口形貌和裂纹扩展.研究表明碳纳米管的加入使复合材料的硬度、弯曲强度和断裂韧性得到明显的提高,并且在碳纳米管含量为0.5wt%左右时,复合材料的硬度达到20.5GPa,弯曲强度为496MPa,断裂韧性达7.25MPa·m1/2;断口形貌分析表明碳纳米管主要分布于TiB2颗粒的晶界处,复合材料的增韧机制主要是碳纳米管的拔出机制和桥联机制.     

Microwave Plasma Sintering of Nanocrystalline Alumina

Sintering of nanocrystalline alumina by microwave plasma has been studied. The relative density,microhardness of the samples with different grain sizes by microwave plasma and other sintering techniques have been compared     

纳米氧化铝粉体的绿色合成及其物相转变控制研究

以氯化铝、碳酸钠为原料,采用直接沉淀法,并于500～1,200℃煅烧,制备纳米Al2O3粉体。然后用TiO2、BaO对纳米Al2O3粉体掺杂,控制其物相转变过程。通过X射线衍射仪、差式扫描量热仪和透射电子显微镜分析纯净和掺杂后的纳米Al2O3的物相转变过程。结果表明,直接沉淀法所得水合Al2O3,经500℃煅烧后可转变为纳米活性Al2O3,粒径约为10 nm;纯净和掺杂Al2O3样品经1,200℃煅烧2 h后均为纳米粉体,其粒径为40～50 nm;在较高温度下,掺杂氧化钡对Al2O3的物相转变具有强烈抑制作用,粉体直至1,200℃仍未转变为结晶良好的α-Al2O3物相;而氧化钛则对其物相转变有显著促进作用,在1,000℃时粉体的主要物相即为α-Al2O3,1,100℃之后粉体已完全转变为α-Al2O3。