Investigation On The Preparation And Properties Of Aluminium Titanate Fibers And Modified Zirconia Fiber Composites

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.