非等温动力学分析合成Gd_2O_2S∶Er的真空烧结过程

Non-isothermal Kinetic Analysis of the Vacuum Sintering Process of Synthetic Gd_2O_2S∶Er Phosphor

用不同升温速率下的热重(TG)和微分热重(DTG)技术研究固相反应法合成稀土掺杂硫氧化物(Gd_2O_2S∶Er)荧光粉的反应动力学,升温速率分别为5、10、15、20K/min。使用不同动力学分析方法对Gd_2O_2S∶Er的主要合成阶段进行动力学研究。用Kissinger和Flynn-Wall-Ozawa法计算得到了各合成过程的动力学参数。Coats-Redfern法用于确定最可能的反应机理函数。通过分析TG和DTG曲线,得出常压/真空条件下合成Gd_2O_2S∶Er荧光粉的过程可分为三个阶段:失水、单质S与Na2CO3反应、Na2Sx与Gd2O3反应。通过计算发现,在真空条件下反应的活化能较低,表明真空条件有利于Gd_2O_2S∶Er的生成。真空条件下Gd_2O_2S∶Er荧光粉的合成为随机成核和随后生长控制机理,机理函数为g(α)=[-ln(1-α)]n。第二步控制过程的n值为2/3,第三步控制过程的n值为1/2。

The Kinetic of synthetic of rare earth doped sulfur oxide(Gd2O2S∶Er)phosphors by solid state reaction method was investigated by thermogravimetric(TG)and differential thermogravimetric(DTG)techniques at different heating rates.The heating rates were 5,10,15 and 20 K/min,respectively.The main synthesis stage of Gd2O2S∶Er was studied by different kinetic analysis methods.The non-isothermal kinetic parameters of the formation process of Gd2O2S∶Er phosphor were evaluated from TG/DTG data by using Kissinger and Flynn-WallOzawa methods.The Coats-Redfern method was successfully applied to confirm the most probable reaction mechanism functions.The TG/DTG curves revealed three stages of the atmospheric/vacuum sintering process:dehydration,reaction of elemental sulfur with Na2CO3 and Na2 Sx reacted with Gd2 O3.It has been found by calculation that the activation energy of the reactions under vacuum was lower,indicating that the vacuum condition was beneficial to the formation of Gd2O2S∶Er.The reaction model,random nucleation and subsequent growth control mechanism,g(α)= [-ln(1-α)]n has been used to describe the vacuum sintering process of synthetic rare earth oxysulfide phosphor with n= 2/3 for the second step and n= 1/2 for the third step.