熔盐合成法制备Mo_2C纳米粉末的研究

以(NH_4)_2MoO_4和C_6H_(12)O_6作为前驱体,NaCl+KCl(摩尔比1:1)为原料,采用熔盐合成法在900℃制备了纳米片层状Mo2C粉末,利用X射线衍射分析(X-ray diffraction,XRD)、扫描电子显微镜观察(scanning electron microscopy,SEM)等方法研究了Mo_2C粉末物相结构和微观形貌的演变规律。实验结果表明:反应中相变过程是由MoO_3变成MoO_2再到产物Mo_2C的生成;Mo_2C由斜方晶型向六方晶型转变的温度出现在900~1000℃区间;提高合成温度和延长反应时间有利于加快反应进程,但过高的合成温度会导致晶粒显著长大。     

温度对碳热还原合成Ti(C,N)晶须的影响

以TiO2和碳黑为主要原料,NaCl为卤化剂,NiCl2粉作催化剂,N2为保护气氛,采用碳热还原法,在不同温度下合成Ti(C,N)晶须.用X-Ray衍射仪研究合成温度对样品的相组成的影响;采用扫描电镜观察样品的形貌,并检测粉末中的残留碳、氧含量.结果表明:合成温度对样品的相组成、形貌及游离碳和氧含量有重要影响.在1 200℃下主要发生TiO2与碳黑、氮气间的直接还原反应形成TiN,粉末中游离碳和氧含量分别为22.54%和19.82%,合成粉末由大量颗粒组成;温度升高至1 400℃时,粉末由Ti(C,N)和Ni两相组成,游离碳和氧含量分别降低至0.57%和0.38%,样品成为少量的颗粒与大量晶须组成的混合物,晶须长度在15～30 μm之间,直径约1 μm;晶须表面光滑.     

(Ti,W)(B,C,N)纳米晶粉末的合成

以偏钛酸、偏钨酸铵、木糖、硼酸为原料,采用"前驱体+碳热还原"法合成了(Ti,W)(B,C,N)纳米晶粉末。利用SEM、XRD等表征产物相组成和显微形貌,重点探讨了合成温度、保温时间对合成产物的影响。结果表明,合成温度、保温时间均对(Ti,W)(B,C,N)粉末合成有显著影响,随着合成温度的提高以及保温时间的延长,合成粉末晶粒尺寸呈明显长大趋势。在合成温度1 200℃,保温时间2h条件下成功合成了晶粒度约为21.3nm的(Ti,W)(B,C,N)纳米晶粉末。与传统的"普通球磨+碳热还原"法比较,"前驱体+碳热还原"法显著降低了合成温度,并具有原料成本低廉的优势。     

化学镀法制备Ni/TiH2复合粉末的显微组织及其Ni镀层的生长和作用机理

采用化学镀法对TiH2粉末表面镀Ni,制备Ni/TiH2复合粉末。通过X射线衍射(XRD)、扫描电镜(SEM)、能谱分析(EDS)及差热分析(DSC/TG)对Ni/TiH2复合粉末进行表征,探索Ni镀层的生长及作用机理,建立镀层在粉末表面的生长模型。结果表明:施镀温度为85℃时Ni/TiH2复合粉末表面Ni层包覆完整,镀层均匀致密,Ni层厚度约为1.0~2.0μm;施镀温度低于65℃时施镀几乎无法进行,而施镀温度高于95℃时,镀层很不均匀,且容易脱落;镀层的生长机制遵循奥斯特瓦尔德(Ostwald ripening)机制;与包覆前TiH2粉末相比,Ni/TiH2复合粉末的释氢反应开始温度由450℃上升至540℃。包覆层可降低TiH2粉末和熔融铝的温度梯度,从而推迟开始释氢的时间。     

纳米(Ti,50W)C固溶体粉末的制备研究

采用前驱体与真空碳热还原相结合的方法制备出(Ti,50W)C固溶体粉末,并利用XRD、SEM和FESEM研究了合成温度和保温时间等工艺参数对(Ti,50W)C固溶体粉末微观形貌和相组成的影响。实验结果表明:在合成温度1 100℃、保温时间2.0h条件下能制备出粉末粒径小于100nm的(Ti,50W)C固溶体粉末。与传统工业制备方法相比,本法制备的(Ti,50W)C固溶体粉末所需合成温度更低,原料成本也更低廉。     

(In_(1-x)Fe_x)_2O_3粉末的制备及红外性能研究

采用固相合成法,以In2O3和Fe2O3为原料合成了(In1-xFex)2O3粉末样品,并研究了Fe掺杂浓度和焙烧温度对(In1-xFex)2O3粉末结构和红外性能的影响。结果表明:当Fe掺杂浓度为x=0.05,焙烧温度为900℃时,所制备(In1-xFex)2O3粉末中Fe元素能很好地固溶到In2O3晶格中;随着Fe掺杂浓度的增加,(In1-xFex)2O3粉末的晶粒尺寸呈现先减小后增大的趋势,但In2O3的晶体结构基本不变,为典型的立方晶系方铁锰矿结构;掺杂Fe后的(In1-xFex)2O3粉末在400~4 000cm-1的红外波段内存在较强的吸收峰。     

喷雾干燥-煅烧制备钨钴氧化物粉末的反应机理

以偏钨酸铵(AMT)、醋酸钴Co(CH3COO)2·4H2O、有机碳为原料,通过喷雾干燥得到前驱体粉末,然后在氮气氛下煅烧制备钨钴氧化物复合粉末;并对AMT、醋酸钴及前驱体粉末进行TG-DSC-DTA分析,用XPS对钨钴氧化物粉末进行价态分析,以X射线衍射对钨钴氧化物粉末进行物相分析,用SEM对粉末进行形貌分析。结果表明:煅烧温度550℃、氮气流量6.5 m3/h、煅烧时间20 min制备的钨钴氧化物粉末粒度为10~125μm,平均粒度为50μm,产物为裂解碳、WO3、Co3O4。此温度可避免AMT分解生成的WO3在水蒸气作用下生成钨水化物WO2(OH)2;避免WO2(OH)2在H2作用下还原成W粉;及避免W粉沉积在早先被还原的W核上使W粉颗粒长大。     

“前驱体+真空碳热还原”法制备超细Mo_2C粉末的研究

利用"前驱体+真空碳热还原"法制备了超细Mo_2C粉末,采用XRD、FESEM等表征手段研究配碳量、合成温度以及保温时间对Mo_2C粉末微观形貌和物相组成的影响。结果表明:在配碳量为150%(质量分数)、合成温度1 150℃、保温2.0 h条件下制备的超细Mo_2C粉末,粒径约为100~500 nm。     

Mo和Si混合粉末烧结合成MoSi2工艺的研究

通过差热分析（DTA）和X射线衍射分析手段．探讨了Mo和Si混合粉末烧结合成MoSi2过程中．烧结温度和时间对相生成的影响，指出了Mo和Si混合粉末烧结合成MoSi2的起始温度和合理工艺．     

V2O5碳热还原合成碳化钒粉末的反应过程

为了实现小批量连续化制备碳化钒粉末,以工业级V2O5和纳米炭黑为原料,利用碳热还原法,在常压下碳管炉中得到了V8C7。通过X射线衍射仪(XRD)、扫描电镜(SEM),分析了合成过程。结果表明:在较低的温度下,纳米炭黑将V2O5还原为VO2;随着合成温度的升高,还原为更低价的V2O3,但没有VO生成;接着发生碳化反应,生成VC1-x、V8C7,合成的各阶段相互重叠;在合成过程中,试样的显微组织因物相不同而有所不同,生成的钒氧化物为炭黑附着的颗粒状大团聚体,VC1-x粉末颗粒呈类球形,但大小不均匀;随着温度升高,合成的最终产物V8C7粉末颗粒呈球形或类球形,大小均匀,粒度为1μm左右;还原碳化过程中,产生的气体有CO、CO2。     

Study on Agglomeration and Densification Behaviors of Gadolinium-Doped Ceria Ceramics

By synthesizing reactive powders via a self-sustaining combustion synthesis, the glycine-nitrate process, the gadolinium-doped celia （GDC） with the chemical formula Ce0.8Gd0.2O1.9 was prepared. The resultant powders were dispersed with the terpineol as the dispersant through different methods such as ball milling and high-shear dispersing. Coagulation factor （CF） was used to mark the degree of agglomeration on the nano-scale GDC in this work. The effect of agglomeration on the densification behavior at different sintering temperatures was investigated. The studies indicated that agglomeration retarded the densification at the sintering stage. The powders with better dispersion exhibited a higher sintered density at the same temperature. After effective dispersion treatment, GDC could be fully densified at the sintering temperature of 1300 ℃. The densification temperature was significantly lower than those reported previously. The high sintering kinetics of the ceramics was obtained based on the agglomeration control.     

Magnesium-thermic synthesis of molybdenum carbide in ion melts

The physicochemical aspects of the synthesis of the powders of molybdenum carbide by the magnesium-thermic reduction of its oxide in melts of lithium, sodium, and potassium carbonates are considered. The thermodynamic evaluation of reactions based on the synthesis is given. The influence of the melt temperature on the granulometric characteristics of the carbides is revealed. It is shown that the powders with the largest specific surface are formed in the melt of lithium carbonate (Mo₂C of 7.96 m²/g) at 750°C.     

层状可加工陶瓷Ti3SiC2自蔓延高温合成反应机理的研究

采用燃烧波淬熄法,以Ti粉、Si粉和C粉为原料研究了层状可加工陶瓷Ti3SiC2在自蔓延高温合成(SHS)中的反应机理.淬熄试样中保留未反应区、反应区和已反应区,用扫描电子显微镜观察燃烧反应中显微组织的转变过程,用能谱仪分析各微区的成分变化,并通过差热分析(DSC-TGA)和XRD分析考察了从600℃到1500℃ Ti-C-Si系统的反应合成过程和相形成规律.结果表明:层状可加工陶瓷Ti3SiC2自蔓延高温合成的机理为溶解-析出机制,Ti粉与Si粉的固态扩散导致低熔点Ti-Si溶液形成,Ti、Si、C粉粒逐渐向Ti-Si溶液中溶解,当溶液中的Ti、Si、C浓度饱和时,从中析出TiC、SiC颗粒,最后形成最终产物Ti3SiC2.     

Fabrication of metal matrix composites of

Fine fibrous titanium carbide (TiC) was processed through the self-propagating high-temperature synthesis (SHS) method and employed to fabricate aluminum matrix composites. Two consol-idation methods were investigated: (1) combustion synthesis of TiC fiber/Al composites directly using titanium powders and carbon fibers ignited simultaneously with varying amounts of the matrix metal powder and (2) combustion synthesis of TiC using titanium powders and carbon fibers followed by consolidation into different amounts of the metal matrix powder, Al,via hot isostatic pressing (HIP). In the former method, when the amount of the Al in the matrix was increased, the maximum temperature obtained by the combustion reaction decreased and the propagation of the synthesis reactions became difficult to maintain. Preheating was required for the mixture of reactants with more than approximately 5 mole pct aluminum matrix powders in order to ignite and maintain the propagation rate. Microstructural analysis of the products from the Al/C/Ti reaction without preheating shows that small amounts of an aluminum carbide phase (AI4C3) are present. In the second method, following separation of the individual fibers in the TiC product, dense composites containing the SHS products were obtained by HIP of a mixture of the TiC fibers and Al powders. No ternary phase was formed during this procedure. Formerly Graduate Research Assistant, Department of Chemical Engineering, Michigan Technological University, is with Particle Technology, Inc., Hanover, MD 21076. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

A two-stage approach of manufacturing FeAl40 iron aluminides by self-propagating synthesis and pressureless sintering

A two-stage sintering process was successfully used to sinter FeAl to densification levels of just above 95% at a temperature of 1300°C. In the first stage, mixed iron and aluminium powders were synthesised at 750°C via self-propagating high-temperature synthesis (SHS) to form brittle and porous Fe₂Al₅. Then the pellets were crushed and milled to various sizes and mixed with iron powders in the nominal composition of FeAl40 and pressurelessly sintered at a higher temperature to obtain a higher densification by taking advantage of the less violent exothermic reaction of Fe₂Al₅ and Fe. The intermediate and end products in SHS and sintering were characterised by SEM/EDX and XRD. The porosity level of the final FeAl40 product was controlled by the heating rate and powder size, which was also strongly influenced by the temperature, holding time and the ratio of the two powders.     

Calcium hydride synthesis of Ti–Nb-based alloy powders

The metallothermic (calcium hydride) synthesis of Ti–Nb alloy powders alloyed with tantalum and zirconium is experimentally studied under various conditions. Chemical, X-ray diffraction, and metallographic analyses of the synthesized products show that initial oxides are completely reduced and a homogeneous β-Ti-based alloy powder forms under the optimum synthesis conditions at a temperature of 1200°C. At a lower synthesis temperature, the end products have a high oxygen content. The experimental results are used to plot the thermokinetic dependences o formation of a bcc solid solution at various times of isothermal holding of Ti–22Nb–6Ta and Ti–22Nb–6Zr (at %) alloys. The physicochemical and technological properties of the Ti–22Nb–6Ta and Ti–22Nb–6Zr alloy powders synthesized by calcium hydride reduction under the optimum conditions are determined.     

Synthesis and characterization of porous Fe–25 wt.% Al alloy with controllable pore structure

Porous Fe–25 wt.% Al alloy is synthesized by reactive synthesis with Fe and Al powders as the raw materials. Various processing parameters such as the final sintering temperature, pressure during cold pressing, and powder size are investigated to control the pore structure of the alloy. It has been shown that the optimal final sintering temperature is around 950–1050°C. When the pressure is higher than 110 MPa, the variation of the pore structure is mainly caused by the change of the pore nature in the as-pressed compact. In addition, the pore structure of porous Fe–25 wt.% Al alloys depends on the size of the raw powders and the weight fraction of different-sized raw powders.     

TiH2对TiB2自蔓延高温合成过程的影响

采用纯Ｔｉ粉或氢化钛粉、Ａｌ粉及Ｂ粉混合后进行整体加热，使其发生自蔓延高温反应，合成了ＴｉＢ２粉末。研究了氢化钛粉及合成温度对ＴｉＢ２合成反应过程的影响，探讨了ＴｉＢ２粒子的形成机理。     

Hard Alloy WC – 24% Ni Obtained in the Solid Phase from Ultrafine WC, NiO, and C Powders. Part 1. Density and Structure of Specimens

We have studied the density and structure of specimens of the alloy WC – 24 mass% Ni, obtained by combining into one step the processes of synthesis of the metallic phase and compaction of the ultrafine mixture of WC – Ni powders by high-energy pressing and sintering. We have established that reduction of nickel monoxide by carbon occurs at temperatures of 650-750°C and does not affect the shrinkage process which in the case of sintering begins only at a temperature of 1050°C. High-energy pressing of briquettes sintered at the indicated temperature reduces their porosity from 30-25% down to 8-4%. Specimens of porosity <1% can be obtained by pressing at 1150°C or 1050°C in the case of triple pressing. Raising the temperature at which the briquettes are heated is accompanied by enlargement of the pores together with a decrease in the total porosity, but at temperatures of 1300°C (sintering) and 1250°C (pressing), the pore dimensions are sharply reduced. The high density of the specimens pressed at low temperature does not provide low electrical resistance, which suggests the presence of weakly connected boundaries. When the specimens are sintered and pressed in the solid phase, we observe the growth of tungsten carbide particles. It is most rapid at 1150-1250°C, while at 1050°C the particle growth process slows down. Reduction of the metal oxide when the powders are heated promotes formation of structure in the higher temperature range.