【作者】 陈宁；

【导师】 高祀建； 霍冀川；

【作者基本信息】 中国建筑材料科学研究总院 ， 材料学， 2014， 博士

【摘要】 高温透波材料是高速、超高速飞行器通信系统的保障，也是高速精确制导飞行器发展的关键材料之一。随着飞行器飞行速度和使用环境的不断升级，要求高温透波材料具有更加优良的力、电综合性能以及更长的寿命，但目前尚未获得一种耐热一透波一承载综合性能十分理想的透波材料。面对当前为数不多的高温透波材料品种，开展低成本高性能磷酸铬铝基透波复合材料的研究具有重要意义。磷酸铬铝具有低介电、化学稳定、耐高温的特点，但力学性能低，易吸潮，普遍采用硅质纤维增强与防潮涂层相结合的方式改进。然而硅质纤维增强磷酸盐材料由于纤维本身耐温能力和加热后磷酸铬铝对纤维的侵蚀限制了该系列材料的使用温度范围。纵观磷酸盐基复合材料研究现状，开展颗粒、晶须增强磷酸铬铝陶瓷基复合材料的研究是降低磷酸铬铝吸潮率、提高其使用温度的有效方法之一。众多陶瓷材料中，莫来石是少数和磷酸铬铝有良好化学相容性、热匹配特性的材料，并具有较低的介电常数和较高的耐温性能。因此为更好利用磷酸铬铝良好的耐高温、低介电性能，论文结合莫来石与磷酸铬铝的优点，提出了一种新的磷酸铬铝复合材料体系和增强工艺，即：原位生长莫来石颗粒、晶须增强磷酸铬铝复相陶瓷体系，并对其高温介电性能进行初步理论预测，以期为高温透波材料的发展提供更多的参考。本文研究主要结果有：1.磷酸铬铝基体热性质研究表明，160~900基体为无定型聚合结构，900~1300将分别发生析晶和分解，1300~1600由含铬的正磷酸铝构成，介电常数随物相变化而变化。经1300以上热处理，介电常数趋于稳定，吸潮率<0.02wt%。2.获得了室温抗弯强度157.45MPa、1000抗弯强度143.78MPa、断裂韧性4.08MPa·m1/2、介电常数<3.8、损耗<0.05(8~12GHz)、显微硬度550Hv、抗热震临界温差<200的原位生长莫来石颗粒增强磷酸铬铝复相陶瓷。控制高温莫来石化时原料晶型状态是制备无开裂莫来石/磷酸铬铝复合材料的关键；莫来石/磷酸铬铝体系热力学研究表明，二者反应标准吉布斯自由能随温度升高非线性降低，且磷酸铬铝具有更低的反应标准吉布斯自由能；莫来石生长满足莫来石化动力学模型，1500达到最大反应速率，材料致密化受游离SiO2含量控制；体系属晶界增强型复相陶瓷，TEM显示二者无明显晶界相；莫来石晶粒对磷酸铬铝晶界有明显钉扎作用；热膨胀系数差异导致残余应力诱发裂纹偏转、分叉以及莫来石晶粒阻挡、拔出是主要的增强、增韧行为。3.获得了室温抗弯强度135.60MPa、1000抗弯强度121.71MPa、断裂韧性4.52MPa·m1/2、介电常数<3.6、损耗<0.05(8~12GHz)、显微硬度400Hv、抗热震临界温差300的原位生长莫来石晶须增强磷酸铬铝复相陶瓷。原位生长晶须有效改善了莫来石颗粒增强磷酸铬铝复相陶瓷抗热震及介电性能；采用晶须引发剂内加法更适合本体系制备工艺；TEM显示原位生长莫来石晶须表面具有台阶状特点，使复合界面增加了机械锁合几率；莫来石晶须/磷酸铬铝复合界面结合属弱结合，复合材料最终通过晶须桥联、拔出、裂纹偏转机制达到增强、增韧目的。4.原位生长莫来石增强磷酸铬铝复相陶瓷体系具有较好的宽频透波能力，8~12GHz范围内电磁波透过率均大于60%，设计厚度为7mm时，透过率达到最佳状态(>80%)；高温介电初步建模结果显示，磷酸铝介电常数、损耗随温度升高至1000K时迅速增加，与“P-O”键相对高的离子性有关；莫来石介电常数、损耗随温度升高至800K时迅速增加，高温介电损耗主要由氧空位贡献，故控制莫来石晶体氧空位数是降低其高温介电损耗的手段之一；最终实验结果表明，复杂晶体化学键理论在多元化合物高温介电模型中的应用是可行的。更多还原

【Abstract】 High temperature wave-transparent materials are the protections of high-speed,ultra high-speed aircraft communication systems, and one of the key materials forhigh-speed precision-guided aircraft. With the escalation of flight speed and serviceenvironment, high temperature wave-transparent materials have been required formore excellent mechanical property, dielectric property and longer life. However,researchers have not found an ideal wave-transparent material with goodcomprehensive performance of heat resistance, transmission efficiency and bearingcapacity yet. Given that there are few varieties of present products, it is significant tocarry out a low-cost, high-performance aluminum-chrome phosphates compositesresearch.Aluminum-chrome phosphates have low dielectric constant, good chemicalstability and high melting point, but also have low mechanical property and highmoisture-absorb. Therefore researchers usually adopt combination way of siliceousfiber-reinforced and moisture-proof coatings to improve. However, the servicetemperature of siliceous fiber reinforced aluminum-chrome phosphates compositesare limited by low temperature resistance of siliceous fiber and the erosion after beingheated. Throughout the current state of phosphate-based composites research,utilizing particles and whiskers reinforced aluminum-chrome phosphates ceramicmatrix composites is one of the best ways to decrease moisture absorption rate and toimprove high temperature service capacity. But few ceramic particles and whiskerscan match the chemical and thermal compatibility of aluminum-chrome phosphates,and mullite is one of them, which also has a low dielectric constant and hightemperature performance. Thus, new aluminum-chrome phosphates composite systemand enhance process have been proposed namely in-situ mullite particles andwhiskers reinforced aluminum-chrome phosphates multiphase ceramics system, onbasis of the good chemical and thermal compatibility between aluminum-chromephosphates and mullite, and the insufficient heat resistant ability of siliceousfiber-reinforced composites. Meanwhile preliminary theoretical prediction of its hightemperature dielectric property has been taken in order to provide more reference forthe development of high-temperature wave-transparent materials.The indications of the study are as follows：1. Thermal properties study of aluminum-chrome phosphates matrix showed that,the matrix was amorphous polymeric structure in160~900, and then crystallizedand decomposed successively in900~1300, finally, constituted by final productsAlPO4and Cr2O3in1300~1600. Thermal transformation of matrix from160to1600lead to a fluctuant dielectric constant, but finally stabled after heatingabove1300, which moisture absorption rate <0.002wt%.2. Obtained an in-situ mullite particles reinforced aluminum-chrome phosphatesmatrix multiphase ceramics, which normal temperature flexural strength,1000flexural strength, fracture toughness, dielectric constant, loss tangent, Vickers hardness and critical thermal shock temperature difference are157.45MPa,143.78MPa,4.08MPa·m1/2,<3.8,<0.05(8~12GHz),550Hv and <200. Controlingraw materials crystal forms at mullitization temperature is the key step to prepare acracking-free composite. Thermodynamics analysis of this system shows that: bothstandard Gibbs free energy nonlinear reduced with temperature rise, whilealuminum-chrome phosphates has a lower, mullite reaction met the mullitizationkinetics model with maximum rate at1500, matrix densification controlled by freeSiO2. System is grain boundary enhanced multiphase ceramics and TEM displayed noobvious boundary between the two phases. Mullite had obviously pinning effect formatrix grain boundaries. Both particles were incorporated to improve the strength andtoughness by residual stress induced crack deflection, crack branching and grain’spull-out.3. Obtained an in-situ mullite whiskers reinforced aluminum-chrome phosphatesmatrix multiphase ceramics, which normal temperature flexural strength,1000flexural strength, fracture toughness, dielectric constant, loss tangent, Vickershardness and critical thermal shock temperature difference are135.60MPa,121.71MPa,4.52MPa·m1/2,<3.6,<0.05(8~12GHz),400Hv and300. Mullitewhiskers improved thermal shock and dielectric properties of particle reinforcedaluminum-chrome phosphates system. Internal adding whiskers trigger is moresuitable for this system. In-situ mullite whisker had a stepped surface increasing theinterface mechanical locking probability. Both whisker and matrix were incorporatedto improve the strength and toughness by whisker bridging, pull out and crackdeflection to achieve enhanced toughening purpose.4. In-situ mullite reinforced aluminum-chrome phosphates multiphase ceramicshas a better broadband wave transmittance and transmission efficiency more than60%in the range of8~12GHz. Transmittance is optimal when thickness is7mm. Hightemperature dielectric modeling results show that, aluminum phosphate dielectricconstant increased rapidly when temperature raise to1000K because of the relativelyhigh iconicity of "P-O" bond. Mullite dielectric constant and loss tangent increasedrapidly when temperature raise to800K, which is duo to the contribution of oxygenvacancies, thus control the number of mullite oxygen vacancies is one of the means toreduce its high temperature dielectric loss.Chemical bond theory of complex crystalsis feasible for multiple compounds dielectric simulation.更多还原