• 主题
高级搜索  >
历史搜索 清空历史
首页> 外文学位 >Fabrication of mullite-bonded porous SiC ceramics from multilayer-coated SiC particles through sol-gel and in-situ polymerization techniques.
【24h】

Fabrication of mullite-bonded porous SiC ceramics from multilayer-coated SiC particles through sol-gel and in-situ polymerization techniques.

机译：通过溶胶-凝胶和原位聚合技术从多层涂覆的SiC颗粒制备莫来石键合多孔SiC陶瓷。

获取原文
获取原文并翻译 | 示例
页面导航
  • 摘要
  • 著录项
  • 相似文献
  • 相关主题

摘要

In this work, mullite-bonded porous silicon carbide (SiC) ceramics were prepared via a reaction bonding technique with the assistance of a sol-gel technique or in-situ polymerization as well as a combination of these techniques. In a typical procedure, SiC particles were first coated by alumina using calcined powder and alumina sol via a sol-gel technique followed by drying and passing through a screen. Subsequently, they were coated with the desired amount of polyethylene via an in-situ polymerization technique in a slurry phase reactor using a Ziegler-Natta catalyst. Afterward, the coated powders were dried again and passed through a screen before being pressed into a rectangular mold to make a green body. During the heating process, the polyethylene was burnt out to form pores at a temperature of about 500°C. Increasing the temperature above 800°C led to the partial oxidation of SiC particles to silica. At higher temperatures (above 1400°C) derived silica reacted with alumina to form mullite, which bonds SiC particles together. The porous SiC specimens were characterized with various techniques.;The first part of the project was devoted to investigating the oxidation of SiC particles using a Thermogravimetric analysis (TGA) apparatus. The effects of particle size (micro and nano) and oxidation temperature (910°C--1010°C) as well as the initial mass of SiC particles in TGA on the oxidation behaviour of SiC powders were evaluated. To illustrate the oxidation rate of SiC in the packed bed state, a new kinetic model, which takes into account all of the diffusion steps (bulk, inter and intra particle diffusion) and surface oxidation rate, was proposed. Furthermore, the oxidation of SiC particles was analyzed by the X-ray Diffraction (XRD) technique.;The effect of different alumina sources (calcined Al2O 3, alumina sol or a combination of the two) on the mechanical, physical, and crystalline structure of mullite-bonded porous SiC ceramics was studied in the second part of the project. Alumina sol was synthesized by the hydrolysis of Aluminum isopropoxide using the Yoldas method. Alumina sol was homogenous and had a needle-like shape with a thickness of 2--3 nm. Crystalline changes during the heating process of alumina sol were studied using XRD. In addition, Fourier transform infrared (FTIR) spectroscopy was performed to identify the functional groups on the alumina sol surface as a function of temperature.;In the third part of the project, the feasibility of the in-situ polymerization technique was investigated to fabricate porous SiC ceramics. In this part, the mixture of SiC and calcined alumina powders were coated by polyethylene via in-situ polymerizing referred to as the polymerization compounding process in a slurry phase. The polymerization was conducted under very moderate operational conditions using the Ziegler-Natta catalyst system. Differential scanning calorimetry (DSC) and TGA analysis and morphological studies (SEM and TEM) revealed the presence of a high density of polyethylene on the surface of SiC and alumina powders. The amount of polymer was controlled by the polymerization reaction time. Most parts of particles were coated by a thin layer of polyethylene and polymer. The porous SiC ceramics, which were fabricated by these treated particles showed higher mechanical and physical properties compared to the samples made without any treatment. The relative intensity of mullite was higher compared to the samples prepared by the traditional process. The effects of the sintering temperature, forming pressure and polymer content were also studied on the physical and mechanical properties of the final product.;In the last phase of this research work, the focus of the investigation was to take advantage of both the sol-gel processing and in-situ polymerization method to develop a new process to manufacture mullite-bonded porous SiC ceramic with enhanced mechanical and physical properties. Therefore, first the SiC particles and alumina nano powders were mixed in alumina sol to adjust the alumina weight to 35 wt%. Then, the desired amount of catalyst, which depends on the total surface area of the particles, was grafted onto the surface of the powders under an inert atmosphere. Consequently, the polymerization started from the surface of the substrate. The treated powders were characterized by SEM, XPS and TGA. In addition, the amount of pore-former was determined by TGA analysis. Porous SiC ceramics, which were fabricated by the novel process, consist of mullite, SiC, cristobalite and a small amount of alumina and TiO 2 as a result of reaction of TiCl4 with air. Furthermore, the effect of the sintering temperatures (1500°C, 1550°C and 1600°C) on the crystalline structure of the porous samples was investigated. Furthermore, it was proposed that converting TiCl4 to TiO2 acted as the sintering additive to form mullite at a lower sintering temperature. (Abstract shortened by UMI.).
机译：在这项工作中，借助于反应结合技术借助于溶胶-凝胶技术或原位聚合以及这些技术的组合来制备莫来石结合的多孔碳化硅（SiC）陶瓷。在典型的程序中，首先使用煅烧粉末和氧化铝溶胶通过溶胶-凝胶技术用氧化铝涂覆SiC颗粒，然后干燥并通过筛网。随后，在淤浆相反应器中使用齐格勒-纳塔催化剂，通过原位聚合技术将它们涂覆所需量的聚乙烯。然后，将涂覆的粉末再次干燥并通过筛网，然后压入矩形模具中以制成生坯。在加热过程中，聚乙烯在约500℃的温度下被烧成孔。将温度提高到800°C以上会导致SiC颗粒部分氧化为二氧化硅。在更高的温度（高于1400°C）下，衍生的二氧化硅与氧化铝反应形成莫来石，从而将SiC颗粒粘合在一起。用各种技术对多孔SiC样品进行了表征。该项目的第一部分致力于使用热重分析（TGA）设备研究SiC颗粒的氧化。评估了粒度（微米和纳米）和氧化温度（910°C--1010°C）以及TGA中SiC颗粒的初始质量对SiC粉末氧化行为的影响。为了说明填充床状态下SiC的氧化速率，提出了一种新的动力学模型，该模型考虑了所有扩散步骤（本体，粒子间和粒子内部的扩散）和表面氧化速率。此外，通过X射线衍射（XRD）技术分析了SiC颗粒的氧化。;不同氧化铝源（煅烧Al2O 3，氧化铝溶胶或二者的组合）对机械，物理和晶体结构的影响该项目的第二部分研究了莫来石键合多孔SiC陶瓷的制备。使用Yoldas方法通过异丙醇铝的水解来合成氧化铝溶胶。氧化铝溶胶是均匀的并且具有2--3nm的厚度的针状形状。使用XRD研究了氧化铝溶胶加热过程中的结晶变化。此外，还进行了傅立叶变换红外光谱（FTIR）鉴定氧化铝溶胶表面上的官能团与温度的关系。在项目的第三部分中，研究了原位聚合技术在制造中的可行性。多孔SiC陶瓷。在此部分中，通过原位聚合（称为淤浆相中的聚合配混工艺），用聚乙烯涂覆SiC和煅烧氧化铝粉末的混合物。使用齐格勒-纳塔催化剂体系在非常适中的操作条件下进行聚合。差示扫描量热法（DSC）和TGA分析以及形态学研究（SEM和TEM）揭示了SiC和氧化铝粉末表面上存在高密度聚乙烯。聚合物的量由聚合反应时间控制。大部分颗粒被聚乙烯和聚合物的薄层所覆盖。与未经处理的样品相比，由这些处理过的颗粒制成的多孔SiC陶瓷具有更高的机械和物理性能。与通过传统方法制备的样品相比，莫来石的相对强度更高。还研究了烧结温度，成型压力和聚合物含量对最终产品的物理和机械性能的影响。；在本研究工作的最后阶段，研究的重点是利用溶胶-凝胶处理和原位聚合方法，以开发一种新的工艺来制造具有增强的机械和物理性能的莫来石键合多孔SiC陶瓷。因此，首先将SiC颗粒和氧化铝纳米粉末在氧化铝溶胶中混合以将氧化铝重量调节至35重量％。然后，在惰性气氛下将所需量的催化剂（其取决于颗粒的总表面积）接枝到粉末的表面上。因此，聚合从基材的表面开始。通过SEM，XPS和TGA对处理的粉末进行表征。另外，通过TGA分析确定成孔剂的量。 TiCl4与空气反应的结果是，用新颖的方法制造的多孔SiC陶瓷由莫来石，SiC，方石英和少量的氧化铝和TiO 2组成。此外，研究了烧结温度（1500℃，1550℃和1600℃）对多孔样品的晶体结构的影响。此外提出在较低的烧结温度下将TiCl 4转化为TiO 2作为烧结添加剂形成莫来石。 （摘要由UMI缩短。）。

著录项

  • 作者

    Ebrahimpour, Omid.;

  • 作者单位

    Ecole Polytechnique, Montreal (Canada).;

  • 授予单位 Ecole Polytechnique, Montreal (Canada).;
  • 学科 Engineering Chemical.;Engineering Materials Science.;Chemistry Polymer.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 203 p.
  • 总页数 203
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱：kefu@zhangqiaokeyan.com

京公网安备：11010802029741号 ICP备案号：京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有

  • 客服微信

  • 服务号