NH4F对Li3N-hBN体系中合成CBN晶体的影响

本文研究了在Li3N—hBN体系中加入不同量的NH4F后，对CBN晶体的合成的影响。结果表明，加入NH4F后，合成压力降低了约20％。分析以NH4F和Li3N混合粉末为原料的实验结果后推测：在高温高压条件下NH4F首先会分解为NH3和HF,HF进一步和Li3N反应生成更加稳定的LiF和NH3，其化学反应式可以写成：3NH4F＋Li3N=3LiF＋4NH3，这一过程通过X光衍射分析实验产物得到证实。为了考察LiF在合成立方氮化硼过程中的作用，我们用Li3N和NH4F反应所制得的LiF单独作触媒，在LiF—hBN体系中进行了CBN晶体的合成实验，结果表明在上述压力温度条件下，没有CBN晶体生成，即LiF不宜单独做触媒。尽管在NH4F与Li3N反应消中耗了Li3N—hBN体系中的作为触媒的Li3N，但是，合成压力仍有较大幅度的降低，表明少量氨的存在，使CBN晶体的形成更加容易。

Effect of NH4F additions on growth of CBN crystal in the Li3N-hBN system

In this paper,the effect of NH4F additions on growth of CBN crystal was investigated.The results showed that the pressure for synthesising CBN crystal was reduced by 20% after NH4F was addited.By analyzing the results of the experiments with NH4F and Li3N as raw materials,we considered that,firstly,NH4F would be decomposed into NH3 and HF under HPHT,then the much stabilized LiF was created by the reaction 3NH4 Li3N=3LiF 4NH3.This was proved by analyzing XRD patterns of the products.In order to confirm the effect of LiF additions on growth of CBN crystal,the experiment was repeated when LiF which was made by reacting Li3N and NH4F under HPHT was the single catalyzer under the same HPHT conditions,but CBN crystals were not found,namely LiF was not equal as the single catalyzer.Although Li3N was consumed partly,synthesis pressure decrease showed CBN formation become easy when a small amount of NH3 existed in the Li3N-hBN system.