第35卷第7期 2007年7月

硅 酸 盐 学 报

JOURNAL OF THE CHINESE CERAMIC SOCIETY

Vol. 35，No. 7 July，2007

硅粉粒径对反应烧结多孔氮化硅陶瓷介电性能的影响

徐 洁，朱冬梅，罗 发，周万城

(西北工业大学，凝固技术国家重点实验室，西安 710072)

摘 要：以硅粉为原料，添加质量分数为30%的成孔剂(苯甲酸)球形颗粒，反应烧结制备了气孔率为55%，具有球形宏观孔的低密度多孔氮化硅陶瓷。研究了硅粉粒径对反应烧结多孔氮化硅陶瓷介电性能的影响。结果表明：烧结后样品的介电常数ε′和介电损耗tanδ 随着初始硅粉粒径的减小都有明显的降低。平均颗粒尺寸为7 μm的硅粉制备的样品的ε′最小，约为2.5。原料硅粉的粒径变化将影响反应烧结的反应速率，从而影响反应烧结后样品的生成相和微观结构。随着平均颗粒尺寸的减小，反应烧结后Si3N4相含量增加，Si2ON2相和游离硅含量减少，气孔变小。

关键词：多孔氮化硅陶瓷；反应烧结；硅粉；粒径；介电性能

中图分类号：TQ174 文献标识：A 文章编号：0454–5648(2007)07–0848–04

EFFECT OF THE PARTICLE SIZE OF RAW SILICON POWDER ON THE DIELECTRIC PROPERTIES OF POROUS REACTION-BONDED SILICON NITRIDE CERAMICS

XU Jie，ZHU Dongmei，LUO Fa，ZHOU Wancheng

(State Key Laboratory of Solidification Processing，Northwestern Polytechnical University, Xi'an 710072, China)

Abstract: Low density silicon nitride with about 55% porosity and globed macropores was prepared by reaction-bonded raw silicon powder and adding 30% in mass pore-forming agent of benzoic acid ball-like particles. Effects of the particle size of raw silicon powder on the dielectric properties of reaction-bonded porous silicon nitride were investigated. The results clearly indicate that the specimens prepared with fine powders have lower dielectric constant ε′ and dielectric loss tanδ than that prepared using coarse pow-ders. The ε′ of the specimen prepared by the silicon powder with a minimum average particle size of 7 μm is the lowest, about 2.5. The change of the particle size of silicon powder will affect the rate of the reaction in the course of reaction sintering and the micro-structure and phase composition of specimen. More Si3N4 phase, less Si2ON2 phase and residual Si, smaller size of micropores will result after the decrease of average particle size of raw silicon powder.

Key words: porous silicon nitride ceramic; reaction-bonded; silicon powder; particle size; dielectric properties

Porous silicon nitride is one of the most promising ceramic materials for application in the radome because of its low relative dielectric constant (ε′=2.5—8), low dielectric loss (tanδ<3×10–3), good mechanical properties and high resistance to rain and sand erosion.

In the sintering process of reaction-bonded silicon nitride (RBSN), the reaction mechanism is very complex, because the chemical reaction and sintering occur con-currently, and that depend on the process condition, such as sintering temperature, gas pressure, gas composition and heating schedule.[1–6] The formation of RBSN can be expressed as follows: [7]

3Si(s)+2N2 →Si3N4(s) (1)

收稿日期：2007–01–08。 修改稿收到日期：2007–02–05。 基金项目：国家科学自然基金(90305016)资助项目。 第一作者：徐 洁(1980～)，女，博士研究生。 通讯作者：周万城(1954～)，男，教授。

ΔG0 2080+0.757T (2)

where ΔG0 (J/mol) is the change of the standard free energy of the reaction (1) and T is the absolute temperature of the reaction.

The results of thermodynamic calculation of the re-action show that the nitridation reaction between Si powder and nitrogen in making silicon nitride is exo-thermic and silicon can react with nitrogen in the stan-dard state in all physical conditions. Therefore, the ni-triding schedule must be controlled carefully in order to prevent the silicon from fusing.

The purpose of this work is to investigate the rela-tionship between the microstructure and dielectric properties

Received date: 2007–01–08. Approved date: 2007–02–05.

First author: XU Jie (1980—), female, postgraduate student for doctor degree. E-mail: fanglianmao@163.com

Correspondent author: ZHOU Wancheng (1954—), male, professor.