单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,#,Overview of silicon nitride ceramics,Name:000001,Major:Chemical technology,Contents,1,、,Properties of silicon nitride,2,、,Crystal structures,3,、,Synthesis methods,4,、,Sintering methods,5,、,Actual application,Properties of silicon nitride,Si,3,N,4,is one of the most important structure ceramics because it possesses a combination of,advanced properties,.Such as:,However the,fracture behaviour,of Si,3,N,4,ceramic is considered to be the major obstacle for its wider use as a structural material.,Properties of Si,3,N,4,ceramics,Good wear,Flexural strength,Corrosive resistance,Creep resistance,Fracture resistance,High hardness,Thermal shock resistance,Properties of Si,3,N,4,ceramics,Crystal structures of Si,3,N,4,ceramics,Silicon nitride exists in two major crystalline forms:,-,and,-phase.,（,fig.1,）,Both phases have a hexagonal crystal structure.,-Si,3,N,4,is the,low,temperature modification and,-Si,3,N,4,is the,high,temperature modification.,（,fig.2,）,More than 1400-1800,phase,transform,into,phase.,Crystal structures of Si,3,N,4,ceramics,Fig.1:Crystal structures of a,-Si,3,N,4,and b,-Si,3,N,4,a=7.7541(4),c=5.6217(4),a=7.6044(2),c=2.9075(1),Fig.2 XRD patterns of the samples sintered at different temperature holding for 60 min,Synthesis methods of Si,3,N,4,ceramics,1,、,Carbothermic process,2,、,Silicon powder direct nitridation method,3,、,Self-propagating high temperature synthesis method(SHS),4,、,Chemical Vapor Deposition,（,CVD,）,Sintering methods,Hotisostatic-pressing,(HIP),pressure-less sintering,(PLS),Hot pressing(HP),Reaction sintering,(RS),Sintering aids(,烧结添加剂）,Si,3,N,4,is one of the typical,covalent bonded,solids.Its self-diffusion coefficients is very low.,Sintering aids,are always needed to bring down the grain boundary of Si,3,N,4,and to increase diffusivity.,Reduce the sintering temperature,pressure and sintering time.,MgO,、,Y,2,O,3,、,Al,2,O,3,Actual application,One of the earliest uses of Si,3,N,4,was in the Si,3,N,4,-bonded refractory brick for blast furnaces in the 1950.,Owing to the brittle nature of Si,3,N,4,over the years,there has been a continuous interest in exploring a variety of approaches for,enhancing,its fracture toughness and reliability.,Thanks to,advanced properties,of the Si,3,N,4,it has been widely used in many fields,for example:,Metallurgy,industry,Metal cutting,Construction of,motors,Nuclear,fusion reactors,Semiconductor,technology,Aviation,Biomaterial,.,Thanks,!,