不同前驱体制备硅/石墨相氮化碳材料用于锂离子电池

分别以尿素、硫脲、三聚氰胺为前聚体,采用热缩聚法在550℃下制备了3种石墨相氮化碳,与硅粉复合后合成Si@C_3N_4-u、Si@C_3N_4-t、Si@C_3N_4-m 3种材料。通过SEM、TEM、XRD、XPS、FT-IR、BET等测试方法表征了3种原材料和复合材料的形貌及晶体结构,并采用恒流充放电、循环伏安、交流阻抗等测试了复合电极的电化学性能。结果表明,以硫脲为前聚体合成的氮化碳有着更加合适的片层以及多孔结构,C_3N_4-t上残留的含S基团还能与硅颗粒能形成氢键,部分硅可以进入片层之间以及大的孔洞中,从而缓解了硅的体积效应,使电极的电化学稳定性有所提高。以硫脲为前聚体合成的氮化碳与硅复合后的材料在500 mA/g的电流密度下,充放电循环200次后,容量可以保持在971.7 mAh/g。     

硫掺杂氮化碳微球的制备及其光催化还原性能

以含硫单体三聚硫氰酸为合成原料之一,低温溶剂热法合成硫掺杂氮化碳材料(CNS)。利用XRD、FT-IR、SEM、XPS等技术对催化剂进行了表征。通过对Cr(Ⅵ)的还原去除和光解水制氢性能测试,研究了CNS的光催化还原性能。结果表明,硫元素主要取代氮化碳分子中晶格氮形成C—S键。随着聚合反应时间的延长,所得产物中硫含量升高。催化剂具有显著的可见光吸收,随着聚合时间的延长,吸收带边红移,可扩展至约700nm。与直接煅烧法制备的氮化碳相比,在可见光照下,CNS对Cr(Ⅵ)具有显著增强的还原去除性。同时,CNS催化剂具有明显的光解水制氢性能。机理分析表明,光生电子和·O2-是CNS光催化还原Cr(Ⅵ)的主要活性物种。     

碳热还原含MgAl_2O_4尖晶石相氧化铝粉末的研究

研究了碳热还原氮化含MgAl2O4相氧化铝的反应过程．结果表明：碳热还原含MgAl2O4相的氧化铝；与引入氧化镁外加剂一样，可以在低温（＜1600℃）下制备尖晶石型氮氧化铝。不同的MgAl2O4尖晶石相含量对反应过程的影响不同，引入量的增加，有利于氮氧化铝相的生成；反应温度的提高，加速了还原氮化反应的过程．不同条件下所制备的氮氧化铝具有不同的晶格常数．     

几种碳源对碳热还原氮化法制备Ti(C,N)粉末的影响

以纳米TiO2和不同碳源为原料,采用碳热还原氮化法,制备了Ti(C,N)粉末.通过X射线衍射分析、热分析、扫描电镜、化学成分分析等手段研究了TiO2碳热还原氮化过程的反应机理和不同碳源对制备碳氮化钛粉末的影响.结果表明,在TiO2碳热还原氮化过程中,前期主要为TiO2/C固-固反应,后期CO参与的气-固反应变为主要反应...     

碳热还原含MgAl2O4尖晶石相氧化铝粉末的研究

研究了碳热还原氮化含ＭｇＡｌ２Ｏ４相氧化铝的反应过程，结果表明：碳热还原含ＭｇＡｌ２Ｏ４相的氧化铝，与引入氧化镁外加剂一样，可以在低温下制备尖晶石型氮氧化铝，不同的ＭｇＡｌ２Ｏ４尖晶石相含量对反应过程的影响不同，引入量的增加，有利于氮氧化铝相的生成；反应温度的提高，加速了还原氮化反应的过程，不同条件下所制备的氮氧化铝具有不同的晶格常数。     

AlN-SiC复合超细粉制备技术的研究进展

综述了国内外AlN-SiC复合超细粉制备方法的研究进展，着重阐述了化学合成法，包括溶胶-凝胶法，碳热还原氮化法、自蔓延高温合成法及化学气相沉积法（CVD）等的研究状况，并对不同制备工艺的优缺点进行了评述，结合本实验室的研究成果，认为原位化学反应合成工艺是今后制备AlN-SiC复合超细粉的发展趋势，并介绍了该领域的最新发展动态。     

AlN陶瓷粉末制备方法特点和进展

本文就国内外AlN粉开合成的研究情况,综述了直接氮化法、Al2O3碳热还原法、自蔓延高温合成法、等离子体法、气溶胶法等主要的几种AlN粉末制备方法的特点和研究进展,分析了制备AlN粉末的主要发展方向。     

超分子自组装法制备氮化碳聚合物光催化剂

利用光催化技术将低密度的太阳能转化为高密度的化学能或直接降解有机污染物,是解决能源短缺和环境污染等问题的理想途径。氮化碳是近期发展出来的一类聚合物半导体新型光催化剂,在分解水制氢、污染物降解、二氧化碳还原、选择性有机合成等研究方面有着重要科学意义和应用前景。前驱物超分子自组装法是制备高效纳米氮化碳光催化剂的重要合成方法之一。通过分子间的弱相互作用力,如三聚氰胺与三嗪衍生物之间的氢键相互作用,形成有序的超分子组装体,再进一步焙烧热聚合可制备氮化碳纳米材料。通过控制自组装过程的反应参数和条件,可以有效地调控氮化碳的组成、形貌、能带结构、光学性能、光生载流子分离效率,从而提高氮化碳的光催化性能。综述了超分子自组装法合成氮化碳光催化剂的最新研究进展,总结了系列纳米结构氮化碳光催化剂的研究工作,包括共聚合改性氮化碳、非金属掺杂氮化碳、金属掺杂氮化碳、金属氧化物-氮化碳复合物、氮化碳异质结以及高结晶度氮化碳光催化剂等。同时阐述了超分子自组装法对氮化碳的组成、结构和光催化性能的调控作用,并就该研究领域未来发展进行了展望。     

动态真空条件下快速合成β-SiC的研究

以淀粉(经85℃糊化)为碳源,正硅酸乙酯(TEOS)为硅源,通过溶胶-凝胶法制备了淀粉-SiO2混合凝胶,将混合干凝胶在动态真空条件下进行碳热还原制备碳化硅(SiC).用TGA、XRD、SEM及N2低温物理吸附等手段对淀粉-SiO2混合凝胶和碳热还原产物进行表征.结果表明,在950℃动态真空条件下即可合成出晶粒尺寸约为50nm,结晶度较高的β-SiC.     

湿化学法合成纳米AlN粉末

采用醇盐水解工艺结合碳热氮化还原法进行纳米Al N粉末的制备。以异丙醇铝、果糖、无水乙醇为原料,制备出透明的凝胶,干燥后得到分子水平混合的前驱体,在1 450℃经碳热氮化还原法制备出单相Al N纳米粉末。系统研究了前躯体形成机制,以及碳热氮化还原的温度和时间、C/Al摩尔比、凝胶温度等因素对合成粉体的影响。采用XRD、TG-DSC和SEM对合成产物的特性进行了分析和表征。通过优化工艺,制得类球形的Al N粉末颗粒,其颗粒大小为30~90 nm。     

工艺参数对淤泥沙合成O′-Sialon-SiC-Fe3Si粉的影响

以天然的可再生资源淤泥沙为主要原料,以固体废弃物金属矿尾矿为调剂料,利用炭黑作还原剂,采用碳热还原氮化法合成了O′-Sialon-SiC-Fe3Si粉。用X射线衍射法测定了产物相组成及相对含量,研究了合成温度和恒温时间对反应过程的影响。结果表明,合成温度对O′-Sialon-SiC-Fe3Si粉体的合成过程影响显著,随着合成温度的升高,产物中O′-Sialon相含量增大,1500℃时O′-Sialon相含量最大,是最佳的合成温度。恒温时间对产物相组成的影响不十分显著,但较长的恒温时间可以使还原氮化反应进行得更充分,恒温6h的试样中O′-Sialon相含量达到了83%,是较理想的恒温时间。合成过程中SiO的挥发导致试样较大的质量损失,且随着合成温度的升高和恒温时间的延长而增大。     

Preparation of nano-TiN powders by Ni-catalysed carbothermal reduction nitridation

TiN nanoparticles were prepared at 900–1100 °C by Ni-catalysed carbothermal reduction nitridation from sol-gel using tetrabutyl titanate, citric acid monohydrate and nickel chloride hexahydrate as starting materials. The catalytic effects of nickel on the carbothermal reduction nitridation of xerogels were investigated. Ni has a crucial promoting effect on the carbothermal reduction reaction of the xerogels and visibly enhanced carbothermal reduction and nitridation reactions. The dry gel with 5% NiCl₂ was added to obtain nano-TiN at 900 °C. The transmission electron microscopy analysis and Materials Studio simulation results showed that the facilitating effect of Ni on carbothermal reduction nitridation reaction was ascribed to the provision of heterogeneous nucleation sites for amorphous titania, promoting crystallisation and adsorption of N₂, resulting in its smooth dissociation into highly active N atoms and consequently enhancing the carbothermal reduction nitridation.     

Synthesis of Vanadium Nitride by a One Step Method

Vanadium nitrides were prepared via one step method of carbothermal reduction and nitridation of vanadium trioxide. Thermalgravimetric analysis （TGA） and X-ray diffraction were used to determine the reaction paths of vanadium carbide, namely the following sequential reaction： V2O3→V8C7 in higher temperature stage, the rule of vanadium nitride synthesized was established, and defined conditions of temperature for the production of the carbides and nitrides were determined. Vanadium oxycarbide may consist in the front process of carbothermal reduction of vanadium trioxide. In one step method for vanadium nitride by carbothermal reduction and nitridation of vanadium trioxide, the nitridation process is simultaneous with the carbothermal reduction. A one-step mechanism of the carbothermal reduction with simultaneous nitridation leaded to a lower terminal temperature in nitridation process for vanadium nitride produced, compared with that of carbothermal reduction process without nitridation. The grain size and shape of vanadium nitride were uniform, and had the shape of a cube. The one step method combined vacuum carborization and nitridation （namely two step method） into one process. It simplified the technological process and decreased the costs.     

碳化硼抗弹陶瓷的制备方法及应用

碳化硼陶瓷具有高硬度、高熔点和低密度的特点,是优异的结构陶瓷,在民用、宇航和军事等领域都得到了重要应用。本文中综述了碳化硼结构陶瓷的优异性能和制备新方法,重点介绍了自蔓延高温合成法(SHS),碳管炉、电弧炉碳热还原法,激光化学气相反应法,溶胶-凝胶碳热还原法等合成碳化硼粉末的主要方法以及碳化硼成型和烧结的常用方法,简述了碳化硼抗弹陶瓷材料的发展应用和研究现状。     

Influence of yttrium dopant on the synthesis of ultrafine AlN powders by CRN route from a sol–gel low temperature combustion precursor

Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al₂O₃, C and Y₂O₃ prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO₃, Al₃Y₅O₁₂ and Al₂Y₄O₉, which formed a liquid at about 1400 °C and promoted the transformation of Al₂O₃ to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150 °C, and Al₂O₃ transformed to AlN completely at 1450 °C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450 °C were 150–300 nm.     

A study on the synthesis and characterisation of nanocrystalline transition metal oxynitrides

A different processing route to bimetallic oxynitrides has been developed using oxide precursors generated from coprecipitation of ethanolic solutions of the relevant metal chlorides. The nitridation of the mixed-metal precursors yields nanocrystalline oxynitrides. Representative group 5–group 6 transition metal oxynitrides, M_1?xM′_x(O,N) (M = Nb, Ta; M′ = Mo, W) have been prepared and characterised by powder X-ray diffraction (PXD), scanning electron microscopy with energy dispersive analysis by X-rays (SEM/EDAX), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), BET surface area measurements and SQUID magnetometry. The mixed-metal oxynitrides form rock salt structures (a ～4.3 Å) with disordered distributions of both cations and anions. The purity, particle size and surface area of materials are significantly dependent on nitridation temperature.     

球磨促进碳热还原反应合成氮化铝研究

研究了高能球磨氧化铝和细化和机械力化学作用及球磨对碳热还原反应合成氮化铝（ＡｌＮ）的影响。结果表明：经高能球磨细化后的氧化铝（Ａｌ２Ｏ３）,相对于原始粉末,反应生成的ＡｌＮ 较大提高,且随着球磨时间增加,ＡｌＮ生成量增大。用灰色关联分析方法比较了几种球磨效应对碳热还原反应的作用,发现粉末的晶粒尺雨与反应的关联度最大,表明球磨晶粒细化作用是球磨促进碳热还原反应的最主要原因。     

Sintering behaviour of silicon nitride powders produced by carbothermal reduction and nitridation

In this study, the sintering behaviour of silicon nitride (Si₃N₄) powders (having in situ form sintering aids/self-sintering additives) produced directly by the carbothermal reduction and nitridation (CRN) process is reported. The sintering of as-synthesised α-phase Si₃N₄ powders was studied, and the results were compared with a commercial powder. The α-Si₃N₄ powders, as-received contains magnesium, yttrium or lithium–yttrium-based oxides that were shaped with cold isostatic pressing and tape casting techniques. The compacts and tape casted samples are then pressureless-sintered at 1650–1750 °C for up to 2 h. After sintering, the density and the amount of β-phase formation were examined in relation to the sintering temperature and time. The highest density value of 3.20 g cm^?3 was obtained after only 30 min of pressureless sintering (at 1700 °C) of Si₃N₄ powders produced by CRN from silica initially containing 5 wt.% Y₂O₃. Silicon nitride powders produced by the CRN process performed similarly or even better than results from the pressureless sintering process compared with the commercial one.