块状菱镁矿煅烧过程动力学分析

发布时间：2018-04-18 06:55

  本文选题：块状菱镁矿 + 煅烧　； 参考：《辽宁科技大学》2015年硕士论文

【摘要】：重烧镁砂是镁质耐火原料的重要组成部分,研究块状菱镁矿在大型竖窑煅烧过程中,随温度、压力变化所发生的动力学行为,为设计大型重烧镁砂竖窑及制定生产工艺参数奠定重要基础。1.采用TG法分别对边长为20mm、30mm、40mm和50mm的立方体块状菱镁矿的热分解进行研究,结果表明:块度(L=20~50mm)与活化能的关系为:E=4.795×L+34.070(kJ·mol-1)。分解前期,Anti-ander方程控制的n=2的3D模型为最概然机理函数,动力学方程为:dα/dT=6.111×1010×β-1exp[(4.098-0.577×L)×T-1](1+α)2/3[(1+α)1/3-1]-1;分解中期,Avrami-Erofeev方程控制的n=3(Code:AE3)的随机成核和随后长大模型为最概然机理函数,动力学方程为:dα/dT=1.422×109×β-1exp[(4.098-0.577×L)×T-1](1-α)[-ln(1-α)]-2;分解后期,Avrami-Erofeev方程控制的n=3/2的随机成核和随后长大模型为最概然机理函数,动力学方程为:dα/dT=2.477×109×β-1exp[(4.098-0.577L)×T-1](1-α)[-ln(1-α)]-2。2.采用高温电炉对块状菱镁矿进行煅烧,研究了块状菱镁矿烧的烧结特性,结果表明:烧结初期母盐假相颗粒对烧结致密化行为有重要影响,温度在1150~1200℃时,假相颗粒的体积收缩,致其比表面积和颗粒配位数降低,致密化受到阻碍,出现缓滞现象。1000~1110℃时,Q=412.368 kJ·mol-1;1110~1230℃时,Q=473.990 kJ·mol-1;1230~1300℃时,Q=385.266 kJ·mol-1;烧结中期致密化系数由23.51%增加到71.24%,在液相的作用下烧结传质方式分别为流动传质和“溶解一沉淀”;烧结末期晶界快速移动,气孔“汇聚—排除”的速率和晶界向曲率中心的移动速率增加,方镁石晶粒长大。1600~1700℃时,晶界扩散是控制烧结致密化的主导机制,晶粒生长活化能为1.655×103kJ·mol-1,晶粒以结晶长大方式为主。1700~1800℃时,体积扩散是控制烧结致密化的主导机制,晶粒生长活化能为1.291×103kJ·mol-1,晶粒以聚晶长大方式为主。3.采用热压烧结法,模拟块状菱镁矿在压力作用下的烧结过程,结果表明:在匀速升温阶段,压力的增加,缩短了致密化时间,降低了试样致密化温度;在保温阶段,试样以塑性流动和扩散的方式致密化;在匀速降温阶段,压力越大,试样弹性模量越高,应力释放产生的弹性形变越大,相对密度降低速率越快。通过对试样的烧结过程和显微结构分析,自重压力为5MPa时的试样致密化程度和方镁石结晶度最高。
[Abstract]:Refired magnesite is an important part of magnesia refractory raw material. The dynamic behavior of block magnesite during calcination of large vertical kiln with temperature and pressure is studied.It lays an important foundation for designing large-scale heavy-fired magnesite shaft kiln and making production process parameters. 1.The thermal decomposition of cubic block magnesite with side length of 20 mm ~ 30 mm ~ 40 mm and 50mm is studied by TG method. The results show that the relation between the activation energy and the block size is 4.795 脳 L 34.070(kJ mol ~ (-1).The 3D model controlled by Anti-ander 's equation is the most probable mechanism function, and the kinetic equation is: 1 伪 2 / 3 [1 伪 1 / 1 / 3 1] -1 / 1, the random nucleation and subsequent growth model of Avrami-Erofeev equation controlled by the Avrami-Erofeev equation are the most probable mechanism functions, and the kinetic equation is:: d 伪 -dT 6.111 脳 1010 脳 尾 -1exp [4.098-0.577 脳 L) 脳 T ~ (-1) 脳 T ~ (-1)] -1.The random nucleation and subsequent growth model of Avrami-Erofeev equation control are the most probable mechanism functions.The kinetic equation is: 1. 422 脳 10 ~ 9 脳 10 ~ 9 脳 尾 -1exp [4.098-0.577 脳 T ~ (-1) 脳 T ~ (-1)] (-lnn ~ (1- 伪))] -2; the random nucleation and subsequent growth model controlled by the Avrami-Erofeev equation is the most probable mechanism function, and the kinetic equation is:: d 伪 / D _ (DT) 2.477 脳 109 脳 尾 -1exp [4.098-0.577L) 脳 T-1] 1- 伪) [-ln1- 伪] -2.2.The sintering characteristics of bulk magnesite were studied by means of high temperature electric furnace. The results showed that the initial sintering densification was affected by the pseudo phase particles of mother salt, and the sintering temperature was 1 150 ~ 1 200 鈩，

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