【作者】 孙振淋；

【导师】 周玉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2012， 博士

【摘要】 本文选用固态氨基甲酸铵作为氨源，以反应釜作为反应容器，采用溶剂热合成SiCNO陶瓷先驱体。先驱体经热解、球磨、热压烧结后，制备出无定形SiCNO陶瓷块体材料。采用X射线衍射、成分分析、FT-IR红外光谱分析、STA-IR-MS分析、XPS荧光光谱分析、扫描电镜、透射电镜和能谱等手段，研究了SiCNO先驱体合成机理、热解历程及其热稳定性；探讨了TiCxNy原位增强SiCNO块体材料的可行性；采用激光热导仪和高温热膨胀仪测试了热压烧结制得的块体材料热扩散系数和热膨胀系数。溶剂热合成SiCNO先驱体最大的优点是可以实现反应按化学计量比进行，简化了实验设备，提高了反应的安全性。首先将固态氨基甲酸铵和溶剂置入反应釜中，而后甲基乙烯基二氯硅烷(MS)与乙烯基三氯硅烷(TS)按照设定比例加入反应釜中，在70±10oC密闭情况下保温36小时后，即获得相应的SiCNO陶瓷先驱体。当摩尔比MS:TS大于3:2时，液相先驱体产率几乎不变；当摩尔比MS:TS小于3:2时，随着摩尔比值的进一步降低，液相先驱体产率表现出线性下降。乙烯基三氯硅烷自身含有三个Si-Cl键，氨解过程中表现出体缩聚的特征，甲基乙烯基二氯硅烷则表现出线缩聚特征。当两者在强力搅拌情况下，摩尔比MS:TS大于3:2时，乙烯基三氯硅烷自身不能相互接触，生成的先驱体由于缺乏体缩聚致使空间交联程度较低，先驱体以液相形式溶解于溶剂中。当MS:TS小于3:2时，过量的乙烯基三氯硅烷自身相互接触，发生体缩聚，产物四聚体由于空间交联程度增大从溶剂环己烷中脱溶，且随着乙烯基三氯硅烷相对含量的增加而液相先驱体呈现线性下降趋势。乙烯基三氯硅烷的相对含量对液相先驱体的陶瓷化产率影响较大，当摩尔比MS:TS大于3:2时，体缩聚使得液相先驱体的交联程度增大、热稳定增加，进而出现液相先驱体的陶瓷化产率随着乙烯基三氯硅烷相对含量的增加而增加的趋势；当摩尔比MS:TS小于3:2时，由于过量的四聚体以固相先驱体的形式得以析出，剩余的液相先驱体其成分基本一致，因此，液相先驱体的陶瓷化产率几乎没有变化。氨基甲酸铵在超过58oC时，分解产生的氨迅速与氯硅烷发生氨解反应，生成聚硅氮烷；与此同时，氨基甲酸铵分解的另一个产物二氧化碳与聚硅氮烷反应，生成聚硅氮烷氨基甲酸酯；在受热的情况下，聚硅氮烷氨基甲酸酯继续脱水，转化为硅异氰酸酯。作为一种新型的SiCNO陶瓷先驱体，硅异氰酸酯的热解过程与传统聚硅氮烷有一定的区别。硅异氰酸酯多为低聚物，300oC之前，由于其分子量较低，热解初期伴随有小分子量物质挥发的同时，一部分异氰酸酯官能团及大部分甲基和少量的乙烯基官能团发生断裂，先驱体失重达39wt.%。在陶瓷化转变过程中，未来得及断裂的异氰酸酯官能团，含有的共轭双键随着温度进一步升高，发生自身加成，使得剩余部分先驱体热稳定性大幅增加，而聚硅氮烷则主要靠原有价键的断裂与重新交联来提高其自身热稳定性。硅异氰酸酯热解至800oC时，先驱体基本完成有机—无机转变，1100oC时完成陶瓷化转变。无定形SiCN(M)块体陶瓷目前主要通过“温压烧结工艺”加以制备，由于诸多因素限制，该工艺制备的块体陶瓷尺寸小，不能满足实际需要。本文根据无定形SiCNO材料高温下表现出的粘流性，首次采用热压烧结工艺制备出50mm的无定形SiCNO块体材料，研究了烧结温度对块体材料的组织转变和性能影响。1500oC热压烧结后获得的无定形SiCNO块体材料，其力学性能基本上与文献报道相一致，无定形粉体在致密化过程中伴随着活性自由碳原子的扩散偏聚，这种碳偏聚区造成块体材料的弹性模量降低。当热压烧结温度超过1550oC后，无定形SiCNO开始分解，析出Si2N2O晶体相，块体材料在一定程度上获得增强增韧。本文探讨了金属钛粉原位增强SiCNO的可行性，钛加入后，在1500oC下热压烧结，钛借助活性自由碳原子，夺取SiCNO基体中的氮原子，原位生成具有TiN晶体结构的TiCxNy，同时，SiCNO基体中的氮原子被活性自由碳所替换。反应过程中钛原子向基体扩散，生成相TiCxNy密度大于钛，造成钛粉颗粒原位出现孔洞，并对复合材料的力学性能造成一定影响。当钛粉微量加入时，金属钛粉起到原位增强基体作用，随着钛粉加入量的增加，原位产生的孔洞也逐渐增加，除复合材料的弹性模量随之增加外，其弯曲强度和断裂韧性随之下降。无定形SiCNO块体材料表现出低的热膨胀系数和高的热导率，具有良好的抗热震性；其电导在10-2S·cm-1量级，表现出一定的半导体特性。大尺寸SiCNO块体陶瓷的成功制备，为该类材料的实际应用奠定了基础。更多还原

【Abstract】 SiCNO precursor was synthesized with solid ammonium carbamate asammonia resourse via solov-thermal route. The SiCNO bulk ceramics were preparedby hot press sintering after the precurosr were pyrolyzed and billed. The synthesisand pyrolys mechanisms of SiCNO precursor as well as the thermal stability werestudied by XRD, elemental analysis, FT-IR, STA-IR-MS, XPS, SEM, TEM and EDS.In-Situ TiCxNycrystal reinforcing amorphous SiCNO ceramic bulks were alsodiscussed. The coefficient of thermal diffusion as well as the thermal expansion andthe electrical conductivity of SiCNO ceramic bulks were measured.One of benefits from solvo-thermal route synthesizing SiCNO precursor wasthat the reaction can be forced to occur according to chemical stoichiometric ratios.In addition, the experiments were simplified and the safty improved largely. Solidammonium carbamate and solvent were first put into autoclave, then methyl vinyldichlorosilane (MS) and vinyl triclorosilicane were dropped into the autoclaveaccording to the designed chemical mole ratios. After heating36h at70±10oC inclosed circumstance, SiCNO precursors were finally obtained.When mole ratios of MS to TS were above1.5, the liquid precursor yields werealmost the same. At the mole ratios below1.5, the liquid precursor yields would bedropped with a decrease in mole ratio. For the reason of three Si-Cl groups in TS,the ammonolysis of TS behaved body poly-condensation, however, the ammonolysisof MS behaved linear poly-condensation.Under stronger agitation, TS can not touchitself and the final precursors were liquid for the absence of body poly-condensationwhen mole ratios of TS: MS were above3:2. On the contrary, when the ratios werebelow3:2, SiCNO precursors began to precipitate in solid state from the solvent forthe massive TS touched itself, the body poly-condenstation led to an increase incross-linking and the precursor with big molecular weight was produced. With anincrease in TS content, it was showed there was a linear decreasing tendency for theyield of SiCNO liquid precursor.The content of TS had an important effect on the ceramic yield for SiCNOliquid precursor. When mole ratios of MS to TS were above1.5, the ceramic yieldsof SiCNO precursors were improved with an increase in TS content. However, whenthe mole ratios were below1.5, the chance of excessive TS fragment contactingitself was increased. Once they were connected with themselves rather than DS,solid precursor precipited. So the composition of liquid precursors was much as thesame. It was almost the same for the ceramic yields of liquid precursors.At temperatures over58oC, ammonium carbamate will decomose into ammonia and carbon dioxide. After ammonia reacted with chlorosilane quickly,carbon dioxide could react with polysilazane and polysilane ammonium carbamatebe produced. When it was heated, a dehydration occured and siloxane isocyanatewas obtained.There were many differences between traditional polysilazane and siloxaneisocyanate. Siloxane isocyanate was lower polymer. For low molecular, largenumbers of small molecurlars, isocyanate and methyl as well as part of vinyl groupswere evaporated during pyrolysis.During pyrolysis, the self polycondensation of isocyanate groups occurred witha further increase in temperature. The higher molecular made the thermal stability ofthe polymer improved. A transformation of organic—inorganic was finished at800oC and SiCNO ceramic could be obtained after being pyrolyzed at1100oC.Amorphous SiCN(M) ceramic bulks can be obtained by “warm press” sintering.However, only small size of parts was prepared by this process. According to lowviscosity of SiCN materials at high teperature, this work tried to use hot-presssintering and prepared amorphous SiCNO ceramic bulks with a diameter of50mm.The effect of sintering temperature on structure and properites was studied. Whenthe sintering temerpature was at1500oC, the mechanical properties of SiCNOceramic bulks were in accordance with the related literature except elastic modulus.Free carbon precipitating from the matrix and clusting were observed by SEM andresposible for the low elastic modulus. At sintering temperature above1500oC,Si2N2O crystal phase was observed by TEM.Titanium was filled into SiCNO and In-situ TiCxNyreiforcing SiCNO ceramicbulk was prepared. With the aid of active free carbon, titanium atom deprivednitrogen atom from the amorphous SiCNO matrix and TiCxNywas produced. Freecarbon atom substituted the deprived nitrogen atom. As titanium atom diffusedtowards amorphous matrix, the macro holes were produced, which had an effect onthe composite mechanical properties. When a bit of titanium was filled, themechanical properties were improved largely. With an increase in titanium content,the bending strength and fracture toughness were decreased, but the elastic moduluswas increased for the production of high elastic modulus phase TiCxNy.Amorphous SiCNO ceramic bulks expressed low coefficient of thermalexpansion, high thermal conductivity and high electrical conductivity (102S·cm-1).The successful preparation of amorphous SiCNO ceramic bulks with large scalemade the practical applicaiton possible for the other related materials.更多还原