【作者】 陈静；

【导师】 贾全利；

【作者基本信息】 郑州大学 ， 材料科学与工程， 2025， 硕士

【摘要】 超高温多孔陶瓷材料具有高熔点、优异的抗氧化/烧蚀性能和物理化学稳定性、低体积密度、高气孔率和低导热系数等特性,有望成为再入式高超声速飞行器热防护系统中的新型隔热材料。超高温多孔材料现有的制备方法存在成本高、工艺复杂、易引入杂质等问题,限制了其的应用。为此,本文采用硼/碳热还原复制模板法,以ZrO₂/B₄C/C、ZrO₂/B₄C/C/Si和ZrO₂/B₄C/C/SiC为原料,原位制备了ZrB₂-ZrC、ZrB₂-ZrC-SiC多孔陶瓷。结果如下:（1）首先,在真空下采用硼/碳热还原法制备ZrB₂-ZrC粉体,选取反应物ZrO₂:B₄C:C摩尔比为3:1:6时,在1700 ^oC下可合成ZrB₂-30vol%ZrC复合粉体,并通过调整ZrO₂和C的摩尔比合成不同ZrC含量（30～50 vol%）的复合粉体。此外,分别选取反应物ZrO₂:B₄C:Si:C摩尔比为3:1:0.5:6.5和反应物ZrO₂:B₄C:SiC:C摩尔比为3:1:0.5:6时,在1600 ^oC下可合成ZrB₂-ZrC-10vol%SiC粉体。在此基础上分别通过调整Si/C比（0.75/6.75、1/7）和SiC含量（0.75、1）合成不同SiC含量（15 vol%、20 vol%）的ZrB₂-ZrC-SiC复合粉体。（2）在上述基础上,采用硼/碳热还原复制模板法原位制备ZrB₂-ZrC多孔陶瓷,研究了不同ZrC含量对其性能的影响。结果表明:当合成ZrC含量为30vol%时,ZrB₂-ZrC多孔陶瓷具有较小的导热系数(4.61 W·m^-1K^-1);通过改变烧成温度和原料ZrO₂粒度可调控多孔陶瓷的显微结构和性能,可制得气孔率为63.55%～70.01%,线收缩率为2.58%～11.07%,耐压强度为0.80～7.65 MPa和导热系数为2.22～6.81 W·m^-1K^-1的多孔ZrB₂-ZrC陶瓷。其成孔机理为气体协同模板造孔,其中B₄C和C均为还原剂和造孔剂,反应释放的CO气体也为造孔剂;反应中ZrB₂颗粒的生长过程以ZrO₂颗粒为模板,受固-固（ZrO₂、B₄C、C）和固-液-固（ZrO₂、B₂O₃、C）两种生长机制协同作用,而ZrC颗粒的形成受固-固（ZrO₂、C）反应机制支配。（3）为提高ZrB₂-ZrC多孔陶瓷的强度,在ZrC含量为30 vol%的基础上引入SiC（Si与C原位生成或直接加入SiC）原位制备了ZrB₂-ZrC-SiC多孔陶瓷。结果表明:ZrB₂-ZrC-SiC多孔陶瓷的耐压强度均高于ZrB₂-ZrC多孔陶瓷,但随SiC含量增加,气孔率和耐压强度均降低。当改变ZrO₂粒度时,SiC的引入方式对多孔陶瓷的体积密度、气孔率影响趋势相反,这是因为原位生成的SiC抑制了烧结致密化,使材料结构更加疏松,而直接添加SiC通过填充效应促进了颗粒间的结合,使材料结构较为致密。其成孔机理均由硼碳热反应中释放的CO气体作为造孔剂,但不同SiC引入方式对其微观结构和孔隙分布的影响存在差异。本工作以低成本的ZrO₂、B₄C、C、Si、SiC为原料,通过改变ZrC和SiC的含量、烧成温度和ZrO₂粒度,采用硼/碳热还原复制模板法原位制备了气孔率高、耐压强度较高和导热系数低的多孔ZrB₂-ZrC和ZrB₂-ZrC-SiC复相陶瓷。更多还原

【Abstract】 Ultra-high temperature porous ceramic materials possess outstanding characteristics such as high melting point,oxidation/ablation resistance,physical and chemical stability,low bulk density,high porosity,and low thermal conductivity.These properties make them promising candidates for new thermal protection materials in re-entry hypersonic vehicles.The existing fabrication methods for ultra-high temperature porous materials suffer from high costs,complex processes,and susceptibility to impurity introduction,which restrict their application.To address these issues,this study applied the boro/carbothermal reduction template replication method to in situ prepare porous ZrB₂-ZrC and ZrB₂-ZrC-SiC ceramics in reaction systems of ZrO₂/B₄C/C,ZrO₂/B₄C/C/Si,and ZrO₂/B₄C/C/SiC.The results are as follows:（1）Firstly,ZrB₂-ZrC composite powders were synthesized under vacuum using the boro/carbothermal reduction method.When the molar ratio of ZrO₂:B₄C:C was set to 3:1:6,ZrB₂-30vol%ZrC composite powders was obtained at 1700 ^oC.Additionally,by adjusting the molar ratio of ZrO₂ to C,composite powders with different ZrC contents（30～50 vol%）were synthesized.In addition,when the molar ratios of reactants ZrO₂:B₄C:Si:C=3:1:0.5:6.5 or the molar ratios of reactants ZrO₂:B₄C:SiC:C=3:1:0.5:6,ZrB₂-ZrC-10vol%SiC powders were successfully synthesized at 1600 ^oC.Based on this,by modifying the Si/C ratio（0.75/6.75,1/7）or the SiC content（0.75,1）,ZrB₂-ZrC-SiC composite powders with varying SiC contents（15～20vol%）were prepared.（2）Based on the above studies,porous ZrB₂-ZrC ceramics were in situ synthesized using the boro/carbothermal reduction template replication method,and the effect of varying ZrC content on their properties was systematically investigated.The results indicated that when the ZrC content was 30 vol%,the porous ZrB₂-ZrC ceramics exhibited a relatively low thermal conductivity of 4.61 W·m^-1K^-1.By adjusting the sintering temperature and the particle size of ZrO₂,the microstructure and properties of the porous ceramics could be tuned.As a result,porous ZrB2-ZrC ceramics with porosity ranging from 63.55%to 70.01%,linear shrinkage from 2.58%to 11.07%,compressive strength from 0.80 MPa to 7.65 MPa,and thermal conductivity from 2.22W·m^-1K^-1 to 6.81 W·m^-1K^-1 were successfully fabricated.The pore formation mechanism was attributed to gas-assisted template porosity generation,where both B₄C and C acted as reducing agents and pore-forming agents,while the CO gas released during the reaction also acted as a pore-forming agent.During the reaction,the growth of ZrB₂ particles was templated by ZrO₂ particles and was governed by the synergistic effects of solid-solid（ZrO₂,B₄C,C）and solid-liquid-solid（ZrO₂,B₂O₃,C）growth mechanisms,the formation of ZrC particles was primarily dictated by the solid-solid reaction between ZrO₂ and C.（3）To enhance the strength of porous ZrB₂-ZrC ceramics,porous ZrB₂-ZrC-SiC ceramics were in situ synthesized based on the 30 vol%ZrC system by employing different SiC introduction methods,either through the in situ reaction of Siand C or by directly adding SiC.The results demonstrated that the compressive strength of the porous ZrB₂-ZrC-SiC ceramics was consistently higher than that of the porous ZrB₂-ZrC ceramics.However,with increasing SiC content,both porosity and compressive strength exhibited a decreasing trend.Additionally,when the particle size of ZrO₂ was varied,the impact of SiC introduction methods on bulk density and porosity showed opposite trends.This was attributed to the fact that in situ-generated SiC inhibited sintering densification,resulting in a more porous structure,whereas directly added SiC facilitated particle bonding through a filling effect,leading to a denser microstructure.The pore formation mechanism was driven by CO gas released during reaction,acting as a pore-forming agent.Nevertheless,different SiC introduction methods resulted in variations in the microstructure and pore distribution.This work used low-cost ZrO₂,B₄C,C,Siand SiC as raw materials.By adjusting the content of ZrC and SiC,sintering temperature,and raw ZrO₂ particle size,porous ZrB₂-ZrC and ZrB₂-ZrC-SiC composite ceramics with high porosity,relatively high compressive strength,and low thermal conductivity were in-situ prepared using the boro/carbothermal reduction replication template method.更多还原