摘 要:根据差示扫描量热仪(DSC)测得的DSC曲线,对非等温动力学微分方程采用Achar-Brindley-Sharp-Wendworth法拟合实验数据,逻辑选择确定锆英砂碱熔分解反应的最可几微分机制函数。采用扫描电子显微镜(SEM)对锆英砂及碱熔分解产物的表面形貌进行分析。研究结果表明:锆英砂碱熔分解反应在分解深度为0.010.10范围内时,最可几微分机制函数为f(a)=(1-a)2,表观活化能和指前因子分别为245.42 k J·mol-1和1×1013.2s-1。当分解深度为0.280.66时,最可几微分机制函数转变为f(a)=3/2[(1-a)-1/3-1]-1,表观活化能和指前因子转变为163.90 k J·mol-1和1×107.1s-1。锆英砂碱熔分解反应最初先在锆英砂的外表面发生反应,为化学反应控速。随着碱熔分解反应的进行,锆英砂表面不断被产物层包裹,越来越厚的产物层对反应物质点扩散的阻碍作用增加,氢氧化钠的质点必须扩散到锆英砂颗粒内部进行反应。此时,反应阻力主要来源于扩散,反应机制转变为三维扩散,球形对称,扩散控制过程。
根据差示扫描量热仪(DSC)测得的DSC曲线,对非等温动力学微分方程采用Achar-Brindley-Sharp-Wendworth法拟合实验数据,逻辑选择确定锆英砂碱熔分解反应的最可几微分机制函数。采用扫描电子显微镜(SEM)对锆英砂及碱熔分解产物的表面形貌进行分析。研究结果表明:锆英砂碱熔分解反应在分解深度为0.01~0.10范围内时,最可几微分机制函数为f(a)=(1-a)2,表观活化能和指前因子分别为245.42 k J·mol~(-1)和1×10~(13.2)s-1。当分解深度为0.28~0.66时,最可几微分机制函数转变为f(a)=3/2[(1-a)~(-1/3)-1]~(-1),表观活化能和指前因子转变为163.90 k J·mol~(-1)和1×10~7.1s~(-1)。锆英砂碱熔分解反应最初先在锆英砂的外表面发生反应,为化学反应控速。随着碱熔分解反应的进行,锆英砂表面不断被产物层包裹,越来越厚的产物层对反应物质点扩散的阻碍作用增加,氢氧化钠的质点必须扩散到锆英砂颗粒内部进行反应。此时,反应阻力主要来源于扩散,反应机制转变为三维扩散,球形对称,扩散控制过程。
Mechanism Functions and Kinetics Parameters of Zircon Sand in Alkali Fusion Process
Bai Bin Chen Weidong Yan Shufang Yan Yantong Liu Fei Zhang Shujia
College of Materials Science and Engineering,Inner Mongolia University of Technology
Inner Mongolia Autonomous Region Boiler and Pressure Vessel Inspection and Research Institute
Abstract:
According to the curve of differential scanning calorimetry( DSC) test,the experimental data of non-isothermal kinetics differential equation was fitted by Achar-Brindley-Sharp-Wendworth method. The most probable text mechanism function differential of zircon logic alkali fusion decomposition was selected. The surface morphology of zircon sand and alkali fusion decomposition products were analyzed by scanning electron microscope( SEM). The results showed that the most probable mechanism function was f( a) =( 1- a)2and the apparent activation energy and pre-exponential factor were 245. 42 k J·mol~(-1)and 1 × 10~(13. 2)s~(-1),respectively,when zircon alkali fusion in the decomposition depth was in the range of 0. 01 ~ 0. 10. The most probable mechanism function into derivative was f( a) = 3 /2[( 1- a)~(- 1/3)- 1]~(-1) when the decomposition depth was in the range of 0. 28 ~ 0. 66. The apparent activation energy and pre-exponential factor were 163. 90 k J·mol- 1and 1 × 10~7. 1s~(-1),respectively. Zircon sand alkaline fusion decomposition reaction was initially reacted at the outer surface of the zircon sand,and the reaction rate was controlled by the chemical reaction of zircon sand and alkaline. The surface of zircon sand was covered by the product layer gradually and the thickness of the product layer increased with the reaction of alkali fusion decomposition reaction. The particles of sodium hydroxide must be diffused into the interior of the zircon sand particles to react further and the reaction resistance was mainly diffusion. The reaction mechanism was changed into three-dimensional diffusion with the spherical symmetric and the reaction rate was controlled by the diffusion process.
表2 本文分析中所用的动力学函数Table 2 Kinetic functions used for this analysis 下载原图
表2 本文分析中所用的动力学函数Table 2 Kinetic functions used for this analysis
表3 用DSC测定的锆英砂碱熔分解反应的a,d H/dt值a and d H/dt value of zircon sand decomposition Table 3reaction determined by DSC 下载原图
表3 用DSC测定的锆英砂碱熔分解反应的a,d H/dt值a and d H/dt value of zircon sand decomposition Table 3reaction determined by DSC
要明确最可几机制函数,必须同时满足相关系数r>0.9900,80 k J·mol-1<E<250 k J·mol-1,7<lg(A/s-1)<30,Q<0.02。经计算发现,锆英砂碱熔分解反应的整个过程并不符合表2中的任何一个函数,而是分段符合两个不同的微分机制函数。满足条件的微分机制函数及动力学参数如表4和5所示。
表4是符合上述条件的分解深度为0.01~0.10范围内的锆英砂碱熔分解反应微分机制函数及动力学参数。从表4中可以看出第27号函数的相关系数r最大,剩余方差Q最小。因此,逻辑上可以判断f(a)=(1-a)2就是锆英砂碱熔分解反应分解深度在0.01~0.10内的最可几微分机制函数。由图1中的线性拟合可以得出E为245.42 k J·mol-1,A为1×1013.2s-1。
表4 反应深度为0.01~0.10时锆英砂分解反应微分机制函数及动力学参数Differential mechanism function and kinetic pa-Table 4rameters for zircon decomposition reaction with reaction depth of 0.01~0.10 下载原图
表4 反应深度为0.01~0.10时锆英砂分解反应微分机制函数及动力学参数Differential mechanism function and kinetic pa-Table 4rameters for zircon decomposition reaction with reaction depth of 0.01~0.10
表5 反应深度为0.28~0.66时锆英砂分解反应微分机制函数及动力学参数Differential mechanism function and kinetic pa-Table 5rameters for zircon decomposition reaction with reaction depth of 0.28~0.66 下载原图
表5 反应深度为0.28~0.66时锆英砂分解反应微分机制函数及动力学参数Differential mechanism function and kinetic pa-Table 5rameters for zircon decomposition reaction with reaction depth of 0.28~0.66
随着锆英砂碱熔分解反应的继续进行,当分解深度为0.28~0.66时,符合条件的锆英砂碱熔分解反应微分机制函数及动力学参数如表5所示。其中,第35号函数对应的Q最小,r最大。逻辑上可以确定f(a)=3/2[(1-a)-1/3-1]-1(金斯特格林方程)就是该分解深度内锆英砂碱熔分解反应的最可几微分机制函数。由图2中的线性拟合可以得出E为163.90 k J·mol-1,A为1×107.1s-1。
图3 锆英砂及碱熔分解产物的表面形貌Fig.3 SEM images of zircon sand and decomposition products of alkaline fusion reaction
图4 锆英砂碱熔分解反应体系的DSC曲线Fig.4 DSC curve of zircon sand decomposing reaction system
4 结论
1.锆英砂碱熔分解反应在分解深度为0.01~0.10时,最可几微分机制函数为f(a)=(1-a)2,表观活化能和指前因子分别为245.42 k J·mol-1和1×1013.2s-1;当分解深度为0.28~0.66时,最可几微分机制函数转变为f(a)=3/2[(1-a)-1/3-1]-1,表观活化能和指前因子转变为163.90k J·mol-1和1×107.1s-1。