HfC前驱体的合成及其裂解行为研究

以HfCl₄、乙酰丙酮、无水甲醇、对苯二酚为原料, 采用一锅法合成了HfC陶瓷前驱体, 通过前驱体裂解制备得到了HfC陶瓷粉体。采用XRD、FTIR、SEM/EDS、TEM、SAED等分析手段对裂解产物的组成、形貌和微观结构进行了分析和表征, 利用TG-DSC和TG-MS对前驱体的裂解行为进行了研究。结果表明: HfC前驱体在600℃左右开始陶瓷化, 在1300℃左右开始形成HfC陶瓷相, 在1500℃及以上完全转化为HfC陶瓷及自由碳。HfC陶瓷相具有单晶结构, 颗粒粒径在50~100 nm之间。HfC陶瓷相的形成基于前驱体在低温段裂解形成的HfO₂的碳热还原反应, 裂解过程中形成的自由碳抑制了HfC晶体的生长。     

一种碳前驱物热解反应的热力学和动力学研究

根据量子化学理论研究了碳前驱物CH3－Ar-CH2-NH2的热裂解机理,利用Gaussian98程序包听AM1法,用UHF计算对化合物五种可能的热裂解路径进行了热力学和动力计算,结果表明,碳前驱物CH3－Ar-CH2-NH2将首先发生生成自由基CH3－Ar-CH2和NH2．的热裂解主反应,活化能Ea=230.78kg/mol,而碳前驱物CH3－Ar-CH2-NH2的实验表观活化能Ea=206.78kg/mol.键能的计算值与实验值符合得比较好,通过分析优化的反应物及产物自由基的部分结构参数,了解了理论支持主反应原因,计算的产物自由基的空间构型表明主反应路径生成的产物自由基相互间若进行筒环缩合反应,获得得分子平面取向性很好的稠环芳烃产物。     

使用木糖醇合成纳米ZrB2粉末的研究

以正丙醇锆、乙酸、硼酸和木糖醇为原料, 采用溶胶-凝胶法, 通过碳热还原反应制备了纳米ZrB₂粉末。在反应体系中, 木糖醇既提供反应所需的碳, 又与硼酸形成了配位化合物。通过对凝胶前驱体粉末进行傅里叶红外光谱以及热重分析, 探讨了溶胶-凝胶反应过程对碳热还原反应温度以及凝胶陈化时间的影响。结果表明, 引入木糖醇促进了反应过程的进行, 湿凝胶无需陈化处理, 并且降低了碳热还原温度。当木糖醇与正丙醇锆的摩尔配比为1.4时, 使用未经陈化的凝胶前驱体, 经1450℃碳热还原即可获得平均直径约50 nm的等轴状ZrB₂纳米颗粒, 粉体氧含量为1.36wt%。     

二硼化锆陶瓷前驱体的制备与研究

介绍了一种二硼化锆陶瓷前驱体的制备方法.首先以氧氯化锆、邻羟基苯甲醇、乙酰丙酮为单体,在三乙胺作用下发生缩聚反应,合成出一种含锆聚合物.然后将该聚合物与硼酸在溶液中共混,除去溶剂后即得到二硼化锆陶瓷前驱体.用红外光谱、核磁共振和凝胶渗透色谱对含锆聚合物进行表征,用X射线衍射对二硼化锆陶瓷前驱体的配方及裂解温度进行优化分析.结果表明,所合成的含锆聚合物是一种以Zr-O-Zr为主链、乙酰丙酮与邻羟基苯甲醇配体为侧链的线性聚合物.该聚合物具有良好的溶解性,可与硼酸以1∶1.5的质量比在丙酮/乙醇溶液中共混,从而得到二硼化锆陶瓷前驱体.该前驱体在1400℃下的惰性气氛中裂解,可生成二硼化锆陶瓷粉末,其陶瓷转化率为30％左右.     

溶胶-凝胶燃烧合成法制备γ-LiAlO2

研究了以硝酸锂、硝酸铝和尿素为原料,用溶胶-凝胶燃烧合成法制备γ-LiAlO2粉体的工艺.采用热重分析(TG-DTA)、X射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)对反应前驱体、反应过程、燃烧产物进行了表征测试.分析了原料配比、溶胶前驱体pH值对反应产物特性的影响,并初步探讨了反应的历程.     

干法纺丝制备二硼化锆陶瓷纤维及其表征

二硼化锆是一种很具潜力的超高温陶瓷材料。通过干法纺丝手段可以得到具有一定优良性能的二硼化锆纤维:以二硼化锆陶瓷制备中的液相前驱体转化技术为依据,采用八水合氧氯化锆、硼酸、蔗糖和柠檬酸为原料,并利用聚乙烯醇为纺丝助剂,制得二硼化锆前驱体纺丝液,然后利用干法纺丝制得前驱体纤维,通过高温烧结制得二硼化锆陶瓷纤维。仪器分析结果如下:通过同步热分析仪(TG-DSC)分析前驱体纤维在100℃~1400℃的失重情况,发现二硼化锆纤维在1200℃左右生成;采用X射线衍射(XRD)和X射线光电子能谱分析(XPS),发现陶瓷纤维中二硼化锆晶形完整且含量较高;通过陶瓷纤维的X射线能谱分析(EDS)及元素分析(EA),发现纤维产物的纯度也较高;另外,扫描电镜(SEM)、单丝强度测试和热失重(TG)分析结果表明:干法纺丝制得的陶瓷纤维表面光滑,强度较好,具有一定的耐高温性。     

沉淀-喷雾干燥法制备纳米晶碳化硅粉体

以廉价的水玻璃和炭黑为原料, 采用沉淀-喷雾干燥法制备反应前驱体, 经碳热还原合成碳化硅. 由于原料间混合均匀, 前驱体在1500℃下加热5h后就能实现完全反应. 对产物用XRD、IR、BET及SEM等进行了表征, 并对反应过程中温度、时间的影响进行了研究. 结果表明, 前驱体在1500℃下反应5h制得的产物为平均晶粒尺寸在37nm左右的β-SiC, 比表面积为12.4m²/g. 碳热还原过程中, 适当升高温度、缩短反应时间有利于得到高质量的SiC产物.     

混合锆类粉体对高模量碳纤维表面改性的研究

混合锆类粉体是含有锆元素的无机陶瓷材料。采用溶胶-凝胶法与碳热还原法制备得到了ZrO₂、ZrB₂、ZrC、ZrN混合锆类陶瓷粉体，并利用连续上浆工艺将其涂覆到碳纤维表面。采用X射线衍射仪对锆类粉体进行了结构与组分的分析。通过扫描电子显微镜、热重测试研究了混合锆类粉体的加入对碳纤维表面形貌、耐热性能的影响。结果表明，实验条件下制备混合锆类粉体的最佳原料配比是n(Zr)∶n(B)∶n(C)=1∶2.5∶12,粉体的最佳烧结温度为1600℃,此时粉体中ZrB₂含量相对最多；高模碳纤维经过10%粉体上浆改性后，碳纤维的起始氧化温度从675.1℃升高到了717.9℃,氧化反应的表观活化能从76.41kJ/mol升高到115.43kJ/mol。     

液相聚合物前驱体法制备高熵碳化物纳米粉体

高熵碳化物陶瓷是近年来发展的新型材料,由于具有高硬度、高模量和低热导率等优异性能而备受关注。液相聚合物前驱体法在陶瓷化过程中可以实现多元素的均匀分散,制备高熵陶瓷具有独特的优势,但是相关报道较少。本研究以金属醇盐为原料,通过可控水解缩合反应制备了金属醇盐共聚物溶液,加入碳源烯丙基酚醛(AN)后得到了澄清的粘稠液相高熵碳化物前驱体(PHEC),在真空下1800℃裂解2 h获得了(Ti, Zr, Hf, Ta)C高熵碳化物陶瓷纳米粉末。通过不同手段对前驱体和陶瓷粉体进行表征,结果表明:裂解温度低于800℃所获得的样品主要为t-ZrO₂及氧化物固溶体, 1000℃开始发生碳热还原反应形成碳化物固溶体,温度升高至1800℃后转化为高熵碳化物陶瓷;所得陶瓷粉末纯度高,元素分布均匀,颗粒尺寸一致,粒径～100 nm。制备的液相陶瓷前驱体具有高陶瓷产率(28.6 wt%)和低黏度(150 mPa·s)的特点,在极性溶剂中溶解性良好。所开发的液相前驱体法在制备高熵陶瓷纳米粉体、陶瓷纤维和陶瓷基复合材料领域具有重要应用价值。     

络合作用对Sol-gel法制备Er3+掺杂TiO2粉末光致发光特性影响

以钛酸正丁酯为前驱体，乙酰丙酮为络合剂，分别在室温和70℃进行对前驱体改性的络合反应，获得改性前驱体Ti（O-Bu）4-x（AcAc）x．以异丙醇为溶剂，采用溶胶-凝胶（sol-gel）法制备0．1—3．0mol％Er^3＋抖掺杂TiO2粉末．差热-热重（TG-DTA）分析结果表明，由室温络合改性前驱体制备的粉末，无定型到锐钛矿和锐钛矿到金红石的相变温度，较由70℃络合改性前驱体制备的粉末均升高40℃．X射线衍射（XRD）分析表明，700℃烧结，室温络合所得掺0．1-3．0mol％Er^3＋：TiO2粉末为单一锐钛矿结构，70℃络合所得粉末为锐钛矿和少量金红石的混合相结构．400-800℃烧结，两种络合所得粉末均获得中心波长为1．53μm的多峰结构光致发光（PL）谱．其中，700℃烧结的粉末PL强度最强．70℃络合较室温络合的粉末PL强度可提高3倍．     

Atomic layer deposition growth of zirconium doped In2O3 films

Zirconium doped indium oxide thin films were deposited by the atomic layer deposition technique at 500 °C using InCl₃, ZrCl₄ and water as precursors. The films were characterised by X-ray diffraction, energy dispersive X-ray analysis and by optical and electrical measurements. The films had polycrystalline In₂O₃ structure. High transparency and resistivity of 3.7×10⁻⁴ Ω cm were obtained.     

以炭黑为还原剂制备硅酸锆晶须的研究

以无水四氯化锆为锆源, 正硅酸乙酯(TEOS)为硅源, 氟化锂为矿化剂, 乙醇为溶剂, 炭黑为还原剂, 采用非水解溶胶-凝胶法在700 ℃制备得到硅酸锆晶须, 借助TG-DTA、XRD和TEM等测试手段研究了炭黑加入方式及用量对硅酸锆合成与形貌的影响。结果表明: 炭黑以悬浮液形式加入有助于硅酸锆的一维择优生长; 炭黑用量为6wt%时能获得直径为30~90 nm, 长径比为6~15, 沿[001]方向择优生长的硅酸锆晶须。炭黑与氧反应形成二氧化碳和一氧化碳, 炭黑加入方式及用量能够调控反应体系的氧分压。降低氧分压有利于形成更多的气相SiF₄, 这是促进ZrSiO₄一维定向生长的基础, 但氧分压过低又妨碍ZrSiO₄晶体的合成。因此, 适当氧分压有利于ZrSiO₄晶须的 生长。     

Mass flow limitations in reactive sputtering

Reactive sputtering may be accomplished by mixing the inert gas argon with some reactive gas during sputtering. To form ZrN, sputtered zirconium atoms must react with nitrogen. At a specific deposition rate, a certain number F_N0 of nitrogen atoms must arrive at the substrate. This requirement is fulfilled at the partial pressure P_N = P_N0. The minimum partial pressure P_N0 to obtain a nitride is often detected by a sharp decrease in sputtering rate at a specific N₂ partial pressure. However, during reactive sputtering of for example ZrN we found that the value of P_N0 was strongly dependent on the total gas throughout in the vacuum system. An increase in total gas throughput causes a decrease in the value of P_N0.

The decrease in sputtering rate has indirectly been measured by optical emission spectroscopy from the sputtering plasma.     

Electrochemical behaviour of surface zirconium oxides in the presence of some electroactive species

The open circuit potential, capacitance and resistance techniques were used to investigate the behaviour of two types of surface zirconium oxides in pure 0.5 N H₂SO₄ and in the presence of additives of K₂CrO₄, KI, FeSO₄ and HCOOH.

The air-formed preimmersion oxide film grows in all solutions following a logarithmic rate law. Depending on the nature of the additive the oxide grows directly by oxidation of the surface by the oxidizing additive (K₂CrO₄) or indirectly by mediating the oxidation by atmospheric oxygen in the presence of reducing additives.

Anodically formed zirconium oxide films dissolve in all solutions. The results of impedance measurements indicate that adsorption of HCOOH activates the oxide surface owing, possibly, to its hydrophilic nature while iodide adsorption diminishes the reactivity of active sites (probably oxygen vacanies) where the dissolution process is initiated.     

Effect of preparation conditions on properties of atomic layer deposited TiO2 films in Mo–TiO2–Al stacks

TiO₂ films were grown by atomic layer deposition on Mo electrodes in order to elucidate the dominating conductance mechanism and its dependence on the growth chemistry. TiCl₄ and Ti(OC₂H₅)₄ served as titanium precursors, and H₂O or H₂O₂ as oxygen precursors. The films grown at lower temperatures were amorphous. With increasing growth temperatures the crystallization first started in the TiCl₄–H₂O process. The films grown in this process were clearly leakier compared to the films grown from Ti(OC₂H₅)₄ and H₂O and from Ti(OC₂H₅)₄ and H₂O₂. In the Ti(OC₂H₅)₄-based processes, the application of H₂O₂ instead of H₂O resulted in the films with considerably lowered conductivity, although structural differences in these films were insignificant. Space–charge-limited currents were prevailing in all our amorphous Mo–TiO₂–Al packages. Measurements at different temperatures suggested quite high trap densities likely due to the presence of impurities and structural disorder, while the strong differences in conductivity seemed to be due to different densities of gap states.     

纳米增韧NiFe2O4陶瓷惰性阳极烧结行为与性能的研究

采用粉末冶金法制备NiFe₂O₄纳米粉增韧NiFe₂O₄陶瓷铝电解惰性阳极, 研究了NiFe₂O₄纳米粉添加量对NiFe₂O₄陶瓷惰性阳极烧结行为和材料性能的影响。通过线收缩和SEM对NiFe₂O₄陶瓷的烧结性能和显微结果进行分析。研究结果表明: 随着NiFe₂O₄纳米粉添加量的增加, 烧结收缩程度逐渐增大, 烧结致密化开始温度和烧结初期活化能逐渐降低, 添加量为40%时试样从900℃开始大幅度收缩, 烧结初期表观活化能下降到291.43 kJ/mol。NiFe₂O₄陶瓷惰性阳极的体积密度、抗弯强度和断裂韧性随NiFe₂O₄纳米粉添加量的增加均呈现先上升后下降的变化趋势, 气孔率和静态腐蚀率呈先下降后上升的趋势, 均在30%达到极值, 断裂韧性达到最大值3.12 MPa•m^1/2, 是未添加纳米粉试样的2.14倍。NiFe₂O₄纳米粉的添加能够明显增强晶界结合强度, 降低陶瓷材料气孔率, 从而提高断裂表面能实现增韧作用。     

Si3N4-ZrO2-La2O3系统反应合成ZrN及相图构建

本工作研究了Si₃N₄-ZrO₂-La₂O₃三元系统的相关系, 采用X射线衍射仪分析了物相组成。结果表明, 在1500 ℃/1 h/N₂气氛条件下固相反应, 生成了ZrN和La_4.67Si₃O₁₃、La₅Si₃NO₁₂、La₄Si₂N₂O₇、LaSiNO₂、La₂Zr₂O₇等镧盐化合物的共存相。由于生成的氮化锆和硅酸镧等化合物不在Si₃N₄-ZrO₂-La₂O₃三元系统内, 需引入SiO₂测定SiO₂-La₂O₃-ZrO₂三元分系统相图, 进而扩大成Si₃N₄-ZrO₂-La₂O₃-SiO₂-ZrN五元系统, 本工作绘制并提出了此五元系统相图, 且提出了1570 ℃时SiO₂-La₂O₃-ZrO₂三元分系统实验相图。此外, 验证了La₂O₃在Si₃N₄-ZrO₂-La₂O₃三元系统反应中促进Si₃N₄-ZrO₂取代反应生成ZrN的作用。     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Preparation and properties of radiofrequency sputtered X-ray amorphous films in the system SiO2–ZrO2

Amorphous films in the system SiO₂–ZrO₂ were prepared by radiofrequency sputtering method and their density, refractive index, elastic constants, and thermal expansion coefficient were measured. All of the physical properties had a similar compositional dependence; that is, they increased, but not proportionally, with increasing ZrO₂ content. The coordination states of cations in these amorphous films were estimated by the compositional dependence of volume and molar refractivity. The coordination state of silicon ions in the amorphous films did not change, but the coordination number of zirconium ions changed from 8 to 6, depending on ZrO₂ content. These results indicate that, in amorphous films in the system SiO₂–ZrO₂, the change of the coordination state of zirconium ions in the amorphous films has an important effect on the properties.     

凝胶陈化对ZrB2粉末制备的影响

以正丙醇锆、硼酸、醋酸和D-果糖为原料, 采用溶胶-凝胶法, 结合高温碳热还原反应制备得到了长柱状单相ZrB₂粉末。反应体系中, D-果糖不仅提供碳热还原反应的碳源, 同时作为化学修饰剂, 起到抑制正丙醇锆快速水解的作用。通过对比未陈化和陈化的凝胶制备得到的产物, 探讨了陈化过程对于ZrB₂粉末制备的影响。结果表明, 凝胶陈化有利于ZrO₂向ZrB₂的完全转化。当起始原料满足n(B)/n(Zr) = 3.5~4, n(C)/n(Zr)= 7时, 采用室温陈化7 d的凝胶在1550℃保温2 h可获得长度为4~7 μm, 横截面等效直径约为1 μm, 长径比约为4~7, 比表面积为2.53 m²/g, D₅₀ = 6.46 μm的单相长柱状ZrB₂粉末。