保温时间对原位生成Si3N4结合MgO-C耐火材料的性能影响

 以电熔镁砂、Si粉和鳞片石墨为主要原料,木质磺酸钙溶液(1.25g/mL)为结合剂,采用两段保温烧结工艺氮气气氛下低温段1350℃保温2h和高温段1450℃分别保温2、3和4h烧成MgO-C材料.研究了保温时间对MgO-C材料物相组成、显微结构形貌以及常规物理性能的影响.结果表明,当保温时间从2h增长到3h时,试样中的物相组成以及原位生成的α-Si₃N₄和SiC晶须尺寸无明显变化,随着保温时间继续增加到4h,Si单质相消失,晶须尺寸出现明显增长.常规物理性能方面,随着保温时间的增加,试样内部CO_(g)、SiO_(g)生成量不断增加,显气孔率不断增大,体积密度和耐压强度不断下降.

Effects of Keeping Warm Time on the Properties of In-situ Synthesis Si3N4 Bonded MgO-C Refractory

MgO-C refractory was prepared by taking high quality fused magnesia, silicon powder, and flake graphite as raw materials, liquid calcium lignosulfonate with the concentration of 1.25g/mL was used as the binder. Then the samples were sintered under N₂ atmosphere via two-stage sintered process that a low-temperature stage is with 1350℃ for 2h and a high-temperature stage is with 1450℃ for 2h, 3h, and 4h, respectively. The effects of keeping warm time on phase compositions, microstructure, and conventional physical properties of MgO-C refractory are investigated. The phase composition of fired samples is analyzed by X-Ray diffraction. The microstructure is analyzed by scanning electron microscope. The conventional physical property is characterized by apparent porosity, bulk density, and compression. The results show that there are no evidently differences on the phase compositions and the size of SiC and α-Si₃N₄ whisker formed through the in-situ formation with the increase of keeping warm time from 2h to 3h. With the increase of keeping warm time to 4h, the silicon phase disappeared and the sizes of SiC and α-Si₃N₄ whisker have obviously increased. For the conventional physical performances, with the increase of keeping warm time from 2h to 4h, the formation of CO_(g) and SiO_(g) is increasing, which lead to a increase of apparent porosity and a decrease of bulk density and compression strength.