PDF《博士学位论文公示材料》

10 ) 在优选工艺参数条件下制备的氮化锰球的体积密度与氮含量的关系为:,其中 单位为 kg・ m-3 ,氮含量范围为 0-8%,其孔隙率与氮含量的关系为: . (11)为存在温度梯度的锰球氮化反应过程建立了一种可解算的动力学模型.该模型中氮化反应 遵循未反应核收缩模型,反应速度为内扩散控速方程.锰球的几何体被简化成嵌套的球壳模型,球壳 厚度为锰粉直径,球壳内按照体积密度分布一定数目的锰粉颗粒.氮化反应放出的热量通过辐射和热 传导的方式从球心向外传导至锰球外表面.利用有限差分的原理,每个时间步内,每个壳层都进行反 应速度、反应热量、壳层间热量传递计算,从而循环计算锰球氮化反应的过程.该动力学模型很好地 计算了锰粉粒度、氮气压力和氮化温度对氮化反应过程的影响,且能计算出锰球球心温度随时间的变 化而出现峰值. (12)设计了新的氮化锰生产工艺,物料经过预抽真空升温,当炉温达到 700℃时破真空通氮气, 继续升温到 900℃,恒温保压 0.5 MPa 氮化

1 小时,降温过程采取保压并控制降温速率(1℃?min-1 ). 与新工艺匹配,设计了新的压力氮化炉,包含相互配合的反应罐和压力电热炉,具有如下特点:a)采―3― 用两个氮化炉切换,实现了氮化铁合金的连续生产;

b)采用热交换系统,充分利用物料余热,加快冷 却速度;

c)采用物料两面加热的方法,增大了单批物料的加入量;

d)整体结构设计巧妙,整个技术 方案占地面积小,成本较低. ―4― 论文摘要(英文) The use of manganese nitridegradually increases with the deepening and popularity of understanding and utilization of nitride ferroalloy. Relevant fundamental researches and process developments of manganese nitride have practical significance and application values. There are a lot of shortages for the domestic manganese nitride process, which result inunstable nitrogen content of product, longer nitriding time and higher energy consumption. At the same time, relevant research results could not be directly applied to the nitriding process of Mn pellets limited topowdery materials used. Therefore, it is necessary to carry out the research of pressurizednitriding process of manganese pellets. Nitriding reaction of Mn pellets was investigated with the self-made air-proofed nitriding system under different preparation conditions (Mn particle size, pelletizing pressure and binder content) and procedure parameters (nitrogen pressure, nitriding time and cooling process). The changes of powder density, manganese granule volume density and granule porosity were also investigated before and after the nitriding process. A coupling model and new production process were developed for the nitriding of Mn pellets. The conclusions of the research are as follows: (1) The optimized process parameters for manganese pellet nitriding are 10-16 mesh of particle size,

354 MPa of pelletizing pressure, 2% of sodium silicate solution, 900℃ of initial temperature and

1 h of temperature holding time. (2) Based on the optimized process parameters, with the decrease of particle size from 10-16 mesh to 60-80 mesh, the maximum temperature increment at the pellet center (?Tmax) increases from 147℃ to 233℃, the time for temperature of pellet center reaching peak (tp) shifts from 164s to 101s, and the conversion ratio at

1 h is enhanced from 90.81% to 93.64%. (3) Based on the optimized process parameters, with increasing pelletizing pressure from