cBN合成块断口形貌观察及XRD分层表征

以Li3N为触媒,采用静态高压法合成了大颗粒立方氮化硼单晶.以扫描电镜(SEM)观察了快冷后的的立方氮化硼(cBN)合成块的断口形貌,并利用X射线衍仪(XRD)对cBN晶体附近的物质分层进行了表征.扫描结果显示,cBN处于熔融状物质的包裹之中,并在cBN的裸表面发现了生长台阶及近似熔入台阶中的颗粒状物质；XRD分层表征结果表明,cBN晶体表面分层界面中检测出含有中间相Li3BN2和cBN小颗粒.由此推断,高温高压下Li3N可以与hBN发生共熔反应并转变为中间相Li3BN2；根据分层表征结果可推测,在适量中间相Li3BN2存在的区域cBN小颗粒更易于聚集并通过不断消耗扩散到大颗粒cBN晶体表面的cBN小颗粒的方式不断长大.

Fracture Morphology and XRD Layered Characterization of cBN Cake

Cubic boron nitride single crystals of large particle were synthesized by static high pressure method,using Li3N as catalyst.The fracture morphology of the quickly cooled cBN cake was observed by SEM.The layered components distributing near large cBN particles were characterized by XRD.The results of SEM indicate that there are growth steps which small particles approximately melt into on the surface of naked cBN which is wrapped by melted materials;The results of XRD layered characterization shows that mesophase Li3BN2 and small cBN particles were detected in the region of the stratified interfaces on the surface of cBN crystals.It could be duced that the whole Li3N will be transformed into mesophase Li3BN2 by co-melting reaction with hBN under high pressure and high temperature;the small cBN particles were easy to aggregate and grow up by absorption of small cBN particles which diffuse to large cBN particles’ surface in region of proper mesophase Li3BN2 according to the results of layered characterization.