Densification and Transformation Mechanisms in Nitrogen Ceramics
Densification and Transformation Mechanisms in Nitrogen Ceramics
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氮陶瓷的致密化和转变机制
DOI：
10.1007/978-94-009-6851-6_18
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发表时间：
1983
期刊：
影响因子：
--
通讯作者：
K. Jack
中科院分区：
文献类型：
--
作者：
S. Hampshire;K. Jack
氮陶瓷的致密化通过液相烧结过程发生，这是由于形成氮氧化物液相，该氮氧化物液相促进收缩，同时发生从α-Si_3N_4到β-Si_3N_4或β ′-sialon的相变。致密化的动力学由Kingery的液相烧结模型来解释，并且在三个连续阶段中的每一个阶段期间的致密化量（i）颗粒重排;（ii）溶解-扩散-沉淀和（iii）固态相互作用取决于所使用的特定添加剂。在重排阶段（i）期间，MgO对致密化的贡献大于Y2 O3，因为形成了更大体积的较低粘度液体。阶段（ii）涉及α的溶解和β（或β ′）的形成，如果通过液体的扩散缓慢，则这可以在没有材料的主要输送的情况下发生（Si 3 N4.与Y2 O3），或者可能伴随着快速传输，因此致密化，如果缓慢的，速率决定过程是形成β（Si_3N_4 + MgO + Li_2O;从α到β（或β ′）转变的动力学证实了所提出的机制，并且不同添加剂的相似活化能对应于Si-β（或β ′）。N键能表明α − β是一种重构转变，需要溶剂和Si-N键的断裂。
Densification of nitrogen ceramics occurs by a process of liquid-phase sintering as a result of the formation of an oxynitride liquid phase that promotes shrinkage and at the same time the phase transformation from α-Si3N4to β-Si3N4or β’-sialon. The kinetics of densification are interpreted by Kingery’s model of liquid-phase sintering and the amount of densification during each of the three successive stages (i) particle rearrangement; (ii) solution-diffusion-precipitation and (iii) a solid-state interaction, depends on the particular additive used. The contribution to densification during the rearrangement stage (i) is greater with MgO than with Y2O3because a larger volume of lower viscosity liquid is formed. Stage (ii) involves the solution of a and formation of β (or β’) and this can occur without major transport of material if diffusion through the liquid is slow (Si3N4. with Y2O3) or may be accompanied by rapid transport and hence densification if the slow, rate-determining process is the formation of β (Si3N4with MgO and with Li2O; β’-sialon with MgO and Y2O3).The kinetics of the transformation from α to β(or β’) confirm the proposed mechanisms and similar activation energies for the different additives correspond with the Si-N bond energy suggesting that α − β is a reconstructive transformation requiring a solvent and the breaking of Si-N bonds.