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溶胶凝胶法制备连续氧化铝纤维的基础研究

发布时间:2019-06-22 15:21
【摘要】:氧化铝纤维是一种重要的无机氧化物陶瓷纤维,由于其优异的化学稳定性、结构稳定性和绝热性,已经被广泛地应用于高温绝热材料、高温反应中的催化剂担体、耐火材料以及树脂、金属和陶瓷基复合材料的增强材料。溶胶凝胶法是常用的制备氧化铝纤维的方法。本文采用溶胶凝胶法制备出有一定长度的氧化铝纤维,并对其基本过程开展了基础研究,为进一步制备连续氧化铝纤维奠定了基础。 以异丙醇铝(AIP)、硝酸铝(AN)和蒸馏水(H_2O)为基本原料,采用溶胶凝胶法,通过加热回流、蒸发浓缩得到可纺的氧化铝前驱凝胶。采用人工挑丝得到连续的凝胶纤维,经过后续的干燥和热处理过程得到长约20cm,直径20-30μm的α-氧化铝陶瓷纤维。 通过PH、粒度、FTIR、NMR等分析测试手段的跟踪检测,对溶胶凝胶过程中发生的化学反应及其相应的粒子结构的变化进行了研究。在溶胶凝胶过程中水解反应和聚合反应是同时存在的,前期以水解反应为主,后期则是聚合反应占据主导地位。在反应初期体系中粒子以八面体形式存在,随着反应的进行,四面体粒子开始出现,八面体与四面体的量均在增加;结构对称的低分子量粒子逐渐向低对称结构的高分子量粒子转变。随着浓缩的进行,溶胶粒子由线性大分子向网络结构转变。 采用单因素轮换法对前驱凝胶的合成工艺进行了优化。可纺凝胶合成的优化工艺参数为AIP/AN的摩尔比为3/1,O/AN摩尔比为100,乳酸用量为AIP与AN总量的4wt%,浓缩温度为80℃。采用该工艺合成得到的前驱凝胶可纺性好,固体含量较高。 对得到凝胶的组成结构研究表明:凝胶主要由Al、O、C、N和H元素组成,元素分布均匀。其中N主要以游离的NO3-的形式存在,C则以未完全水解的异丙醇基以及乳酸的形式存在,Al只与O相连接,以Al-O-Al的形式存在于凝胶结构中。凝胶主要以Al-O-Al或Al-OH-Al桥键结构为骨架,附带有残余的烷氧基,其中Al-O-Al在空间上以铝氧四面体(AlO4)和铝氧八面体(AlO6)结构的形式存在。 对凝胶的可纺性研究表明:凝胶可纺的必要结构条件是,凝胶由适度交联的高聚合度的线性大分子组成,并且没有因过分水解产生沉淀颗粒。得到可纺凝胶的溶胶PH范围为3.05-3.45;凝胶可纺性与粘度密切相关,其可纺的粘度范围为30-60Pa·s,在此范围内,凝胶纤维的直径随粘度的增大而增大。纤维成型受外界环境的温度和湿度影响,其中湿度对其影响较大。空气湿度在65%-75%的范围内,温度在25-30℃时,凝胶较易成纤,得到的凝胶纤维无色透明有光泽,表面光滑无明显缺陷,有一定的柔韧性,最长可达2-3m,其直径约为30-40μm。 凝胶纤维的干燥过程受到干燥环境的温度、湿度和压力的影响。水分的挥发速率随温度的增大、湿度的减小、压力的减小而增加。实验表明,当干燥温度在25℃-40℃,湿度为45%-65%的范围时,凝胶纤维的干燥效果较好同时生成的缺陷较少。 通过TG、DSC、MS、FTIR和XRD等手段研究了凝胶纤维的热处理过程。此过程可以分为三个阶段:第一阶段为室温到120℃,主要是由干燥后凝胶纤维中残余的自由水的挥发导致的。第二阶段为120℃到600℃,这一阶段失重呈直线下降的趋势,该阶段内体系发生比较剧烈的化学反应包括羟基分解、有机物分解及硝酸根分解所致,此阶段无机化过程基本完成。第三阶段为600℃到1200℃,此阶段失重几乎为零,纤维由无定型态向结晶态转变。 结晶动力学研究表明,γ-Al_2O_3结晶活化能为253.31KJ/mol,α-Al_2O_3结晶活化能为301.60KJ/mol。γ-Al_2O_3的结晶活化能随着结晶率的增大呈现逐步增加的趋势;α-Al_2O_3的结晶活化能随结晶率的增加变化不大,α-Al_2O_3的结晶过程比γ-Al_2O_3结晶过程简单。 为了得到直径细而均匀、表观缺陷少、结构致密、晶粒小而均匀且堆积紧密、孔洞率小的高性能氧化铝纤维,对热处理工艺进行了优化,确定以下热处理制度:以1℃/min从室温缓慢升温至600℃后保温2h,接着以10℃/min快速升温至1300℃,保温1h。另外加张烧成的纤维比未加张烧成的纤维更能维持纤维形状,而且表面缺陷较少。
[Abstract]:The alumina fiber is an important inorganic oxide ceramic fiber, which has been widely used in high-temperature heat-insulating material, catalyst supporter, refractory material and resin in high-temperature reaction due to its excellent chemical stability, structural stability and heat-insulating property. Reinforced materials of metal and ceramic-based composites. The sol-gel method is a commonly used method for preparing the alumina fiber. In this paper, the sol-gel method was used to prepare the alumina fiber with a certain length, and the basic research was carried out on the basic process, which laid the foundation for the further preparation of continuous alumina fiber. The spinnable alumina precursor was obtained by the method of sol-gel, by heating, refluxing and evaporating to obtain the spinnable alumina precursor by using the method of sol-gel method, such as aluminum isopropoxide (AIP), aluminum nitrate (AN) and distilled water (H _ 2O) as the basic raw material. The continuous gel fiber is obtained by using the artificial thread, and the following drying and heat treatment process is carried out to obtain the 1-alumina ceramic fiber with the length of about 20 cm and the diameter of 20-30 & mu; m The chemical reaction and the corresponding particle structure in the sol-gel process are carried out by the trace detection of the analytical and analytical methods such as PH, particle size, FTIR, NMR and the like. In the process of sol-gel, the hydrolysis reaction and the polymerization reaction are the same, in the prophase, the hydrolysis reaction is the main and the latter is the main part of the polymerization reaction. In that initial system of the reaction, the particle are present in an octahedral form, and as the reaction proceeds, the amount of the octahedral and the tetrahedra is increase, and the structure-symmetric low-molecular-weight particles gradually move toward the high-molecular-weight particles of the low-symmetric structure. Subtransformation. As the concentration progresses, the sol particles are bound to the network by linear macromolecules. Method for synthesizing precursor gel by single factor rotation method the optimized process parameters of the spinnable gel synthesis are that the molar ratio of the AIP/ AN to the AIP/ AN is 3/1, the molar ratio of the O/ AN is 100, the amount of the lactic acid is 4 wt% of the total amount of AIP and the AN, the concentration temperature The obtained precursor gel prepared by the process has good spinnability, The composition structure of the obtained gel shows that the gel is mainly composed of Al, O, C, N and H elements. In which N is present mainly in the form of free NO3-, C is present in the form of non-fully hydrolyzed isopropyl alcohol and lactic acid, and Al is only connected to the O and deposited in the form of Al-O-Al. in that gel structure, the gel is mainly composed of an Al-O-Al or Al-OH-Al bridge bond structure as a framework, and a residual alkoxy group is attached, wherein Al-O-Al is in a space in an aluminum-oxygen tetrahedron (AlO4) and an aluminum-oxygen octahedron (AlO6), in the form of a structure, the spinnability of the gel shows that the gel can be spun by the necessary structural condition that the gel is composed of a moderately cross-linked linear macromolecule with a high degree of polymerization, The sol PH range of the spinnable gel is 3.05-3.45, the spinnability of the gel is closely related to the viscosity, the spinnability of the sol can be in the range of 30-60 Pa 路 s, and the diameter of the gel fiber in this range the fiber formation is influenced by the temperature and the humidity of the external environment, The air humidity is in the range of 65-75%, the temperature is 25-30 DEG C, the gel is more easily formed, the obtained gel fiber is colorless and transparent, and up to 2-3 m, the diameter of which can be up to 2-3 m, the drying process of the gel fibers is subjected to a drying environment, The effect of temperature, humidity, and pressure. The rate of evaporation of water increases with temperature and humidity. The experiment shows that when the drying temperature is in the range of 25 鈩,

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