理论模拟在本征高介电聚酰亚胺分子设计中的应用

本文研究了10种含羰基/砜基聚酰亚胺的分子链聚集特性和介电常数,同时,基于密度泛函理论(DFT)及分子动力学理论(MD),计算了理论密度、自由体积分数、极化率密度以及偶极矩密度等微观参数。结果表明:部分结晶的聚酰亚胺体系具有相对较高的理论密度和较低的自由体积分数,理论计算结果与实测结果相吻合。相比较于极化率密度,使用与取向极化高度相关的偶极矩密度在kHz频率范围内的测试中可以更加准确地预测聚酰亚胺介电常数与分子结构的关系。

表面氧含量对高纯硅粉高温氮化行为的影响

研究了表面氧含量对高纯硅原料在氮氢气氛下直接氮化行为的影响,并合成高α相氮化硅。研究结果表明,硅粉在氮氢气氛下1 350℃保温3h,氮化产物中α-Si_3N_4含量随原料氧含量的增加呈先增加后减少的趋势,当硅原料表面氧含量为3.91%时,氮化产物中α-Si_3N_4含量可达97%以上,残留硅含量低于1%,产物中部氧含量为1.71%,在此环境下硅粉氮化主要以化学气相沉积的方式进行,产物形貌以杆状α-Si_3N_4晶须为主。硅原料表面氧含量低于4.38%时,氮化产物α-Si_3N_4含量均在95%以上,另有少量的β-Si_3N_4和残留硅,XRD测试精度范围内无氮氧化硅相存在。当硅原料氧含量高于5.61%时,产物中则出现氮氧化硅,随着原料氧含量增加,氮氧化硅含量明显上升。当硅原料氧含量低于5.61%时,残留硅含量随氧含量增加明显减少,说明原料中氧的增加可以显著加快氮化速率,降低氮化产物中残留硅的含量。

Combustion synthesis of fine TiFe series alloy powder by magnesothermic reduction of ilmenite

Fine TiFe series alloy powder was fabricated by magnesothermic reduction of ilmenite as main raw material.Adiabatic temperature of the FeTiO_(3)-Mg system was studied through thermodynamic analysis.Meanwhile,the characteristics of TiFe series alloy were described by XRD,SEM and grading analysis.It is shown that combustion synthesis of the FeTiO_(3)-Mg system can carry out due to its strong exothermic reaction through adiabatic temperature calculate.Ultrafine TiFe series alloy powder after leached for 5 h has reasonable phases and morphology with the particle distribution of 0.2 to 1μm.It indicates that in-situ magnesothermic reduction of natural ilmenite is a feasible way to fabricate ultrafine powder with a relatively lower cost.