氧化硅微粉的相变和熔融行为

Phase Transformation and Melting Behavior of Silica Fumes

借助于X射线荧光仪、场发射扫描电子显微镜、能谱仪、X射线衍射仪和激光粒度仪研究了3种不同产地的氧化硅微粉在常温和800～1200℃热处理3h后的形貌、粒径分布、相变和熔融行为。常温下3种氧化硅微粉均为粒径小于1μm的圆球,可分辨的圆球粒径为30～50nm,部分小球黏附在大球表面。圆球粒径大小不同,粒径大于1μm的多为团聚体。所有氧化硅微粉热处理至800℃都为非晶态,至900℃热处理后开始方石英化,1 200℃热处理后生成鳞石英。800℃热处理后,部分氧化硅微粉出现轻微黏结现象,随温度升高出现变形和熔融软化,在1 200℃热处理3 h后,所有氧化硅微粉均呈熔融状。不同氧化硅微粉的相变和熔融行为与粒径分布和Na2O、K2O的含量有关,含ZrO2的氧化硅微粉经900℃热处理3h后出现t-ZrO2,温度继续升高后未观察到进一步相变。

The morphology, particle size distribution, phase transformation, and melting behaviors of three kinds of silica fumes at room temperature and heated at 800-1 200 ℃ for 3 h were investigated by X-ray fluorescence spectrometry, field emission scanning electron microscope, energy dispersive spectrometry, X-ray diffractometer （XRD） and laser particle size analysis, respectively. At room temperature, they are spherical particles with the size of 〈 1 μm, which contain some smaller distinguished spheres in the range of 30-50 nm. The smaller spheres are adhered onto the surface of larger particles. The particles with the size of 〉 1 μm are mostly the agglomerates. The analysis by XRD revealed that silica in all the samples appeared amorphous when heated it 800 ℃, and then be- came cristobalite and tridymite after heated at 900 ℃ and 1 200 ℃, respectively. The cohering phenomenon occurred when heated at 800 ℃, and then the deformation and softening phenomena took place with the further increase of temperature. All the samples melted after heated at 1 200 ℃ for 3 h. The phase transformation and melting behaviors of the different silica fumes were related to the parti- cle size distribution and the Na2O and K2O content. Tetragonal zirconia appeared in the ZrO2 containing silica fume after heated at 900 ℃ for 3 h, and thereafter there existed no further phase transformation when heated at a higher temperature.