【作者】 刘伟；

【导师】 朱陆益；

【作者基本信息】 山东大学 ， 材料学， 2022， 硕士

【摘要】 国防工业和航空航天等尖端领域对热防护材料提出了迫切需求和巨大挑战。钇稳定氧化锆(YSZ)纤维具有高熔点、低导热、高强度、高化学稳定性等优点,在超高温隔热领域具有重要的研究意义和应用价值。作为一种高效热防护材料,在使用过程中常涉及到温度的急骤变化,造成材料内部较大的温度梯度和热应力,由此产生裂纹、剥落或崩损。热震稳定性是评价材料高温使用性能的关键指标,也是其热学和力学性能对热环境的综合体现,通常稳定性越高,使用性能越好。而纯YSZ纤维刚性制品的高温抗热震性能较差,易开裂甚至断裂,限制了其作为超高温隔热材料的应用。影响材料抗热震性的因素有热膨胀系数、热导率、力学强度、弹性模量等,其中热膨胀系数是主要因素。YSZ纤维制品的热膨胀系数较大,约10 × 10-6 K-1,而引入低热膨胀系数的第二相材料是调控抗热震性的一种简单有效的解决方案。在诸多氧化物材料中,钛酸铝(Al2TiO5)兼具耐高温和低热膨胀性能,有望用于改善YSZ纤维制品的抗热震性能。基于此,本文首先制备了 Al2TiO5纤维,系统研究了Al2TiO5纤维的形貌、结晶、热稳定性、热膨胀性和隔热性能;其次,将YSZ纤维与Al2TiO5纤维直接均匀混合制得YSZ-Al2TiO5(ZAT)纤维复合材料,详细测试了 ZAT纤维复合材料的形貌、热膨胀性、抗热震性、力学和隔热性能。主要研究内容如下:首先,以四氯化钛为钛源,无水氯化铝为铝源,分析了乙酰丙酮含量对钛-铝-乙酰丙酮聚合物(PAAT)前驱体的分子结构、成纤性及稳定性的影响,优选出用于制备A12TiO5纤维的前驱体。以PAAT为前驱体,利用静电纺丝技术制备了 PAAT前驱体纤维,研究了其形貌和结晶转变过程,热处理至1500℃获得了单相Al2TiO5纤维。该纤维在1000-1500℃的升降温循环中无分解和相变,具有优异的热稳定性。在200-1100℃,Al2TiO5纤维的平均热膨胀系数仅为1.02 × 10-6 K-1,展现出优异的低热膨胀性能。利用丁烷喷枪和红外热像仪测试了Al2TiO5纤维的隔热性能,当热面温度为1220℃时,经8 mm厚的Al2TiO5纤维可将冷面温度稳定在260℃,表现出优异的隔热性能。上述结果表明制备的Al2TiO5纤维兼具低膨胀系数和耐高温性能。在成功制备出PAAT前驱体和Al2TiO5纤维的基础上,采用三种实验方案探索制备ZAT纤维复合材料,分别为单组分静电纺丝法、多组分静电纺丝法以及两种纤维直接混合的方法。结果表明,前两种方法获得的纤维物相较为复杂,且存在物相变化;只有第三种方法可实现YSZ和Al2TiO5两相共存,即将YSZ纤维和Al2TiO5纤维短切后直接混合,模压后热处理至1500℃制得ZAT纤维复合材料。随着Al2TiO5纤维的增加,ZAT纤维复合材料的热膨胀系数逐渐减小,抗热震性能逐渐增强,强度逐渐提高,隔热性能先升高后降低。掺入8 wt%Al2TiO5的复合材料热膨胀系数为7.74 × 10-6 K-1,比YSZ样品降低了 26%左右(10.42 × 10-6 K-1)。YSZ样品经历一次1100℃至室温的水淬冲击后瞬间炸裂,而掺入8 wt%Al2TiO5的复合材料经历51次热冲击循环后仅轻微开裂,抗热震性明显改善。掺入8 wt%Al2TiO5的复合材料抗压强度为20.35 MPa,约为YSZ样品的18倍(1.14 MPa)。过量Al2TiO5纤维(≥ 8 wt%)使ZAT纤维复合材料密度大幅增加,导致隔热性能下降。因此,综合考虑ZAT纤维复合材料的热学及力学性能,8 wt%的Al2TiO5纤维掺入量为最佳配比。更多还原

【Abstract】 The defense industry and aerospace and other cutting-edge fields present urgent needs and great challenges for thermal protection materials.Yttria-stabilized zirconia(YSZ)fibers are endowed with a high melting point,low thermal conductivity,considerable mechanical strength,and high chemical resistance stability,making them have important research significance and application value in the field of ultra-high temperature thermal insulation.As promising thermal protection materials,they often involve rapid fluctuation of temperature changes in the application process,resulting in large temperature gradients and thermal stresses within the materials,which cause the products to crack,spall,or crumble.Thermal shock stability is a key indicator to evaluate the usability of the material at high temperatures and a comprehensive reflection of its thermal and mechanical properties.Generally,the higher the stability,the better the usage performance.However,the high-temperature thermal shock resistance of pure YSZ rigid fiber products is unsatisfactory.They will easily crack and destroy under repeated thermal cycling,which limits their application as ultra-high temperature insulation material.The factors affecting the thermal shock resistance of materials include thermal expansion coefficient,thermal conductivity,mechanical strength,and elastic modulus,among which the thermal expansion coefficient is the main factor.The thermal expansion coefficient of YSZ fiber products is about 10 × 10-6 K-1.Incorporating a second-phase material with a low thermal expansion coefficient into the matrix is expected to be a simple and effective way to regulate the thermal shock resistance.Among many oxide materials,aluminum titanate(Al2TiO5),which has both high-temperature resistance and low thermal expansion,is suitable for improving the thermal shock resistance of YSZ fiber products.Hence,Al2TiO5 fibers were firstly prepared in the present study,and the morphology,crystallization,thermal stability,thermal expansion,and thermal insulation properties of Al2TiO5 fibers were systematically investigated.Secondly,YSZ-Al2TiO5(ZAT)fiber composites were prepared by directly mixing YSZ fibers and Al2TiO5 fibers.The morphology,thermal expansion,thermal shock resistance,mechanical properties,and thermal insulation performance of ZAT fiber composites were examined in detail.The main research contents are as follows:First,the effects of acetylacetone on the molecular structure,fiber formation,and stability of titanium-aluminum-acetylacetonate polymer(PAAT)precursors were analyzed using TiCl4 as the titanium source and AlCl3 as the aluminum source,and the precursors were preferably selected for the preparation of Al2TiO5 fibers.PAAT fibers were prepared by electrospinning technique using PAAT as the precursor.The morphology,crystallization,and phase transition were investigated,and single-phase Al2TiO5 fibers were obtained by heat treatment at 1500℃.The fibers had no decomposition and phase transformation during the temperature-rising and falling cycles at 1000-1500℃,indicating excellent thermal stability.At 200-1100 ℃,the average thermal expansion coefficient of Al2TiO5 fibers was only 1.02 × 10-6 K-1,exhibiting excellent low thermal expansion properties.The thermal insulation performance of the Al2TiO5 fibers was tested by using a butane blowtorch and infrared camera.When the hot surface temperature was 1220 ℃,the cold surface temperature of 8 mm thick Al2TiO5 fibers was only 260℃,showing excellent thermal insulation performance.The results showed that the prepared Al2TiO5 fibers had both low thermal expansion coefficient and high-temperature resistance.Based on the successful preparation of PAAT precursors and Al2TiO5 fibers,ZAT fiber composites were prepared by using three methods:monocomponent electrospinning method,bicomponent electrospinning method,and direct mixing of the two fibers,respectively.The experimental results showed that the phases of the fibers obtained by the first two methods were more complex.Only the third method could achieve the coexistence of YSZ and Al2TiO5 phases,i.e.,YSZ fibers and Al2TiO5 fibers were directly mixed,followed by heat-treated to 1500℃after molding to prepare ZAT fiber composites.With the increase of Al2TiO5 fibers,the thermal expansion coefficient of ZAT fiber composites gradually decreased,the thermal shock resistance gradually increased,the strength gradually increased,and the thermal insulation performance first increased and then decreased.The thermal expansion coefficient of ZAT fiber composites doped with 8 wt%Al2TiO5 fibers was measured to be 7.74 × 10-6 K-1,which was about 26%lower than that of the YSZ samples(10.42 × 10-6 K-1).The YSZ samples burst immediately after only one water quenching shock between 1100℃ and room temperature,while ZAT composites doped with 8 wt%Al2TiO5 only slightly cracked after undergoing 51 thermal shock cycles,and the thermal shock resistance was significantly improved.The compressive strength of ZAT composites doped with 8 wt%Al2TiO5 was 20.35 MPa,which was 18 times higher than that of the YSZ fiber samples(1.14 MPa).The excessive Al2TiO5 fiber content(≥ 8 wt%)increased the density of ZAT composites,resulting in a decline in thermal insulation performance.With comprehensive consideration of the thermal and mechanical properties of ZAT fiber composites,8 wt%Al2TiO5 fiber content was the optimum proportion.更多还原