中文版 English
Position:首页 > Papers > Spraying material

Synthesis of ZrB2 powder and preparation of ZrO2 matrix composites reinforced by ZrB2

Time:2013-12-17 08:45:40  From:CNKI  Author:Cao Xiaowei

ABSTRACT
As the ultra-high temperature ceramics (UHTCs), zirconium diboride (ZrB2) has been widely used in the structural ceramics with high temperature,refractory, abrasion resistant materials, electrode materials, composite materials, materials controlling of nuclear and other fields due to its high melting temperature and hardness, out standing thermal and electrical conductivities, excellent resistance to thermal shock and good capability of neutron controlling. It has become one of the most promising structure materials with high temperature. However, ZrB2 powder synthesized by the conventional method has large grain size and low activity, and is also difficult to be sintered; these weaknesses limit its application. Thus, it is necessary to develop the technology to obtain the high purity and the ultra-fine ZrB2 powders.
In this paper, ZrB2 powders have been synthesized by sol-gel method and microwave magnesiothermic process respectively. The influences of ratio of raw materials and preparation technology on phase composition, particle size and morphology of the synthesized powders were studied by XRD, SEM,EDS and TEM. The composite of ZrO2-ZrB2-MgO reinforced with the self-synthetic ZrB2 were prepared by microwave sintering and conventional pressureless sintering respectively. The effects of ratio of raw materials and sintering technology on bulk density, apparent porosity and mechanical properties were also researched. The experimental results show that:
1. ZrB2 powders have been synthesized with zirconium oxychloride (ZrOCl2•8H2O), boric acid, glucose as raw materials, citric acid as gelling agent at the resistance furnace in the argon atmosphere by sol-gel method. The ZrB2 content of the product is improved with the increasing of temperature,heating time, and boron content. When the raw materials with B:Zr=4:1 were heated at 1500℃ for 75 minutes, the ZrB2 content of the product can be increased to achive the maximum value of 94.7%.
2. ZrB2 nano-powders can be formed through sol-gel method followed by microwave magnesiothermic reduction processing. The relative intensity of the diffraction peak of ZrB2 reached to maximum in the condition when raw materials were heated by two steps: first in the power of 528W for 10 minutes and then in the power of 800W for 40 minutes.
3. ZrB2 powders have been synthesized from ZrO2, H3BO3, Mg within a short time by microwave heating. Magnesium content and heating time significantly affect the content of ZrB2 powders prepared. When materials with ZrO2:H3BO3:Mg=1:3:4 were heated in the power of 800W for 20 min,the relative content of ZrB2 reaches maximum. TEM results indicate that ZrB2 particles are existed as spherical with the average particle diameter 80nm. The particle size of ZrB2 was found to decrease with the addition of NaCl.
4. The ZrO2-ZrB2-MgO composite has been prepared by conventional pressureless sintering in reduction condition with the self-synthetic ZrB2 as reinforced phase and 15wt.%Y2O3 as sintering aids. When the raw materials with 80wt.%ZrO2 and 14wt.%ZrB2 are sintered at 1500℃ for 2h, the apparent porosity of composite reaches to a minimum value of 13.1%, and the bulk density is 5.4g/cm3. The optimized mechanical properties for microhardness,bending strength and fracture toughness are 10.3±0.2GPa, 347.2±9.1MPa,3.2±0.1MPa•m1/2 respectively.

KEY WORDS: ZrB2, ZrO2-ZrB2-MgO, sol-gel, microwave, mechanical properties


  本站文章未经允许不得转载;如欲转载请注明出处,北京桑尧科技开发有限公司网址:http://en.sunspraying.com/
 

Support
返回首页
Home page
发表评论 共有条评论
用户名: 密码:
验证码: 匿名发表
Information
Article
    无相关信息
Update
Hot