摘要
将金属钇和镁接枝三甲基硅基取代聚硅氮烷先驱体中,先驱体在热解过程中就可以原位生成金属氮化物烧结助剂,烧结助剂含量可通过钇、镁的接枝量进行精准调控。热解陶瓷为高纯氮化硅陶瓷,碳元素含量低于0.1%(质量分数),氧元素含量低于1.6%。含烧结助剂的氮化硅陶瓷可直接低温烧结制备高纯多孔氮化硅陶瓷块体,相对密度可达到99.4%,具有良好的硬度和导热性能。原位生成烧结助剂避免了额外添加烧结助剂造成的杂质引入和混合不均匀的问题,在高纯陶瓷烧结领域具有独特的优势。
Introduction Uniform distribution in molecular level of ceramics could be achieved by polymer-derived method.Comparing to other methods,fewer crystal seeds existed in microstructure of polymer-derived ceramics,which made it more difficult to sinter.Up to now,few reports focused on the direct sintering of the polymer-derived ceramics.For silicon nitride sintering,the introduction of metal oxide additives caused defects in the lattice of silicon nitride because of oxygen atoms,which could affect the properties of the material.This work focused on the sintering behavior of polymer-derived ceramics and the issue of performance degradation caused by introducing oxygen elements in sintering additives.The metal elements were connected to the precursor molecule and formed the metal nitride sintering additives during pyrolysis process.The method could help to achieve the in-situ non-oxygen addition and uniformly mixing of sintering additives,and the followed low-temperature sintering could achieve the high-purity silicon nitride ceramics.Methods 4 mL of propylamine was added into a solution of trimethylsilyl chlorosilane monomer(14 g),yttrium chloride(0.14 g)and magnesium chloride(0.085 g)in pyridine(20 mL)at room temperature in N_(2) atmosphere.The mixture was warmed up to 120℃and stirred for 2 d.The mixture was then heated to 400℃for 4 h in N_(2) atmosphere and further heated to 1000℃with the rate of 10℃/min,finally the mixture were holding at 1000℃for 4 h and then cooled to room temperature naturally.A white silicon nitride powder SiN-1 was obtained.Silicon nitride powders SiN-2 and SiN-3 were prepared by the same method,in which 0.055 g magnesium chloride was added in SiN-2 and no magnesium chloride was added in sample SiN-3.Silicon nitride ceramics was prepared through spark plasma sintering of silicon nitride powders in 1450℃,45 MPa for 30 min.Before characterization of the silicon nitride ceramics,surface of it was pre-polished.Results and discussion Based on trimethylsilyl-substituted polysilazane precursors,the Y and Mg elements were successfully connected to N with the reaction of M-Cl to N-H and coordination.Through pyrolosis process,three kinds of ceramic powders SiN-1,SiN-2 and SiN-3 were obtained.The main component of these powders was silicon nitride,and content of C was below 0.1%,that of O was below 1.6%.As the content of metal decreased,there is a slight decrease in oxygen contents,being due to the high reactivity of metal nitrides.When treated at 1000℃,a large amount of amorphous silicon nitrides with small amount of magnesium nitrides via the dope of magnesium.Small amount of YSi_(3)N_(5) with Si_(3)N_(4) via the dope of yttrium.When ceramics were heated to 1500℃,amorphous silicon nitride began to crystallize,and sample SiN-3 only containedα-Si_(3)N_(4).As the amount of magnesium increased,the content ofβ-Si_(3)N_(4) crystal gradually increased.These results demonstrate that magnesium nitrides could promoted the transformation of amorphous Si_(3)N_(4) toβ-Si_(3)N_(4) crystalline,while yttrium nitrides activated the lattice of Si_(3)N_(4) crystal.Silicon nitride ceramics were prepared by spark plasma sintering when three types of silicon nitride ceramic powders acted as main raw materials,but only SiN-1 powders with the highest magnesium content could obtain pureβ-Si_(3)N_(4).The frame of the obtained ceramics was mainly composed of stacked rod-shapedβ-Si_(3)N_(4) crystals.These results prove that the pores in porous ceramics were mainly through-pores,and few closed-pores.The porous ceramics showed a hardness of 29.1 GPa,an elastic modulus of 229.1 GPa,which attributed to the speical porous structure.At 25℃,the ceramics possessed a thermal conductivity of 20.451(W/m·K),a specific heat capacity of 0.355 J/(g·K),a thermal diffusion coefficient of 18.169 mm^(2)/s,and an overall thermal expansion coefficient less than 4×10^(-6)/K in the range of room temperature to 1200℃.Due to the presence of pores,a significant decrease in thermal conductivity and thermal diffusion coefficient can be obtained,while the coefficient of thermal expansion remained relatively low.Conclusions Metal element Y and Mg were successfully connected to trimethylsilyl-substituted polysilazane precursors and contents could be adjusted as needed.Metal nitride sintering additives were in-situ generated during pyrolysis process and polymer-derived high-purity silicon nitride ceramics with sintering additives were prepared.This method could help to achieve both in-situ non-oxygen addition and molecular level uniform mixing of sintering additives in ceramic powders.Low-temperature sintering could help to achieve the silicon nitride ceramic powders which resulting in the obtained silicon nitride ceramics with good mechanical and thermal properties.
作者
李天昊
张健宁
何流
宋育杰
LI Tianhao;ZHANG Jianning;HE Liu;SONG Yujie(Qianwan Institute of CNITECH,Ningbo 315336,Zhejiang,China;Engineering Laboratory of Advanced Energy Materials,Ningbo Institute of Materials Technology&Engineering,Chinese Academy of Sciences,Ningbo 315201,Zhejiang,China;Advanced Energy Science and Technology Guangdong Laboratory,Huizhou 516029,Guangdong,China)
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2024年第9期2767-2772,共6页
Journal of The Chinese Ceramic Society
基金
国家重点研发计划(2021YFB3200500)
宁波3315计划(2018A-03-A)
先进能源科学与技术广东省实验室(HND20TDTHGC00)。
关键词
氮化硅
先驱体
烧结助剂
原位
多孔陶瓷
silicon nitride
precursor
sintering additive
in situ
porous
作者简介
第一作者:李天昊(1992-),男,博士,助理研究员;通信作者:宋育杰(1986-),男,博士,研究员。
