基于等转化法及多元非线性拟合的高岭石非等温脱羟基动力学分析
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摘要
采用Netzsch STA409PC同步热分析仪研究了苏州高岭石(KW125)在30℃～1 200℃间的热分解过程。采用"Netzsch Thermokinetics software"软件对其脱羟基机理进行了非等温动力学研究。基于等转化法评价了反应活化能及反应进程的依存关系。基于多元非线性拟合确定了最可能反应机理及动力学参数。研究结果表明:苏州高岭石在30℃～1 200℃温度范围的热分解为脱羟基与相转变等两个阶段。其脱羟基(30℃～800℃)过程中活化能呈现三个变化:197.68 kJ/mol±12.95 kJ/mol→181.04 kJ/mol±18.98 kJ/mol→269.7 kJ/mol±14.64 kJ/mol。脱羟基反应遵循三步连续反应模型t:f,f;(D_3-F_n-F_n),一个三维扩散(D_3)反应,然后是两个n序列(F_n)反应。第一步,f(α)=3(1-α)~(2/3)/(2(1-(1-α)~(1/3)),E_1=185.27 kJ/mol,logA=10.83 s~(-1);第二步,f(α)=(1-α)~n,n=1.75,E_2=187.81 kJ/mol,logA=10.32 s~(-1);第三步,f(α)=(1-α)~n,n=4.4,E_3=262.70 kJ/mol,logA=13.26 s~(-1)。
The thermal decomposition of Suzhou kaolinite below 1 200 ℃was investigated by simultaneous thermal analyzer.Non-isothermal kinetic analysis was employed to study the dehydroxylation mechanism by using Netzsch Thermokinetics software.The dependence of activation energy on the reaction process was evaluated based on the isoconversional method,and the probable mechanism as well as the corresponding kinetic parameters was determined on the basis of multivariate non-linear regression program. It was showed that the thermal decomposition of Suzhou kaolinite was divided into two stages of dehydroxylation and phase transformation. During kaolinite dehydroxylation,three activation energy changes were recognized as 197.68→181.04→269.7 kJ/mol.The dehydroxylation reaction was controlled by three consecutive mechanisms t:f,f;(D_3-F_n-F_n),a three-dimensional diffusion(D_3 mode) reaction followed by two n-order(F_n mode) reactions. The first step was f(α)=(3(1-α)2/3/(2(1-(1-α)1/3)),E_1=185.27 kJ/mol, logA=10.83 s~(-1);the second step f(α)=(1-α)~n,n=1.75,E_2=187.81 kJ/mol,logA=10.32 s~(-1) and the third step was f(α)=(1-α)~n,n=4.4,E_3=262.70 kJ/mol,logA=13.26 s~(-1).
The thermal decomposition of Suzhou kaolinite below 1 200 ℃was investigated by simultaneous thermal analyzer.Non-isothermal kinetic analysis was employed to study the dehydroxylation mechanism by using Netzsch Thermokinetics software.The dependence of activation energy on the reaction process was evaluated based on the isoconversional method,and the probable mechanism as well as the corresponding kinetic parameters was determined on the basis of multivariate non-linear regression program. It was showed that the thermal decomposition of Suzhou kaolinite was divided into two stages of dehydroxylation and phase transformation. During kaolinite dehydroxylation,three activation energy changes were recognized as 197.68→181.04→269.7 kJ/mol.The dehydroxylation reaction was controlled by three consecutive mechanisms t:f,f;(D_3-F_n-F_n),a three-dimensional diffusion(D_3 mode) reaction followed by two n-order(F_n mode) reactions. The first step was f(α)=(3(1-α)2/3/(2(1-(1-α)1/3)),E_1=185.27 kJ/mol, logA=10.83 s~(-1);the second step f(α)=(1-α)~n,n=1.75,E_2=187.81 kJ/mol,logA=10.32 s~(-1) and the third step was f(α)=(1-α)~n,n=4.4,E_3=262.70 kJ/mol,logA=13.26 s~(-1).
引文
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[21] Voga G P,Coelho M G,De Lima G M,et al.Experimental and theoretical studies of the thermal behavior of titanium dioxide-SnO2 based composites [J].Journal of Physical Chemistry A,2011,115(13):2 719-26.
[22] Holt B J,Cutler I B,Wadsworth M E.Rate of Thermal Dehydration of Kaolinite in Vacuum [J].Journal of the American Ceramic Society,2006,45(3):133-6.
[23] Criado J M,Orteg A,Real C,et al.Re-examination of the kinetics of the thermal dehydroxylation of kaolinite [J].Clay Minerals,1984,19(1):653-61.
[24] Ptácˇek P,Kubátová D,Havlica J,et al.Isothermal kinetic analysis of the thermal decomposition of kaolinite:The thermogravimetric study [J].Thermochimica Acta,2010,204(1-2):222-7.
[2] Celis K,Van Driessche I,Mouton R,et al.Kinetics of Consecutive Reactions in the Solid State:Thermal Decomposition of Oxalates [J].Key Engineering Materials,2002,206-213(1):807-10.
[3] Flynn J H.Thermal analysis kinetics-past,present and future [J].Thermochimica Acta,1992,203(2):519-26.
[4] Vyazovkin S,Burnham A K,Criado J M,et al.ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data [J].Thermochimica Acta,2011,520(1-2):1-19.
[5] Flynn J H.A general differential technique for the determination of parameters for d(α)/dt=f(α)A exp (-E/RT) [J].Journal of Thermal Analysis and Calorimetry,1991,37(2):293-305.
[6] Ozawa T.Kinetic analysis by repeated temperature scanning.Part 1.Theory and methods [J].Thermochimica Acta,2000,356(1-2):173-80.
[7] 李艳春.热分析动力学在含能材料中的应用 [D].南京;南京理工大学,2010.
[8] Zhang X-H,He C,Wang L,et al.Non-isothermal kinetic analysis of thermal decomposition of the Ca-bentonite from Santai,China [J].Mineralogy and Petrology,2015,109(3):319-27.
[9] 曹秀华.高岭石的改性与应用研究 [D].2003.
[10] 张实,张惠芬.高岭石的热稳定性和热处理产物的DTA IR和EPR研究 [J].矿物岩石,1992(2):28-33.
[11] Franco F,Cruz M D R.Thermal behaviour of dickite-dimethylsulfoxide intercalation complex [J].Journal of Thermal Analysis and Calorimetry,2003,73(1):151-65.
[12] Mackenzie K J D,Meinhold R H,Brown I.W.M,et al.The formation of mullite from kaolinite under various reaction atmospheres [J].Journal of the European Ceramic Society,1996,16(2):115-9.
[13] Mackenzie K J D,Brown I W M,Meinhold R H,et al.Outstanding Problems in the Kaolinite-Mullite Reaction Sequence Investigated by 29Si and 27Al Solid-state Nuclear Magnetic Resonance:I,Metakaolinite [J].Journal of the American Ceramic Society,2010,68(6):293-7.
[14] Ortega A,Macías M,Gotor F J.The Multistep Nature of the Kaolinite Dehydroxylation:Kinetics and Mechanism [J].Journal of the American Ceramic Society,2010,93(1):197-203.
[15] Brindley G W,Sharp J H,Patterso J H.Kinetics and mechanism of dehydroxylation processes.I.Temperature and vapor pressure dependence of dehydroxylation of kaolinite [J].American Mineralogist,1967,52(1-2):201-12.
[16] Ptácˇek P,?oukal F,Opravil T,et al.The non-isothermal kinetics analysis of the thermal decomposition of kaolinite by Effluent Gas Analysis technique [J].Powder Technology,2010,203(2):272-6.
[17] Ptácˇek P,Kubatova D,Havlica J,et al.The non-isothermal kinetics analysis of the thermal decomposition of kaolinite by thermogravimetric analysis [J].Powder Technology,2010,204(2-3):222-7.
[18] Nahdi K,Llewellyn P,Rouquérol F,et al.Controlled Rate Thermal Analysis of kaolinite dehydroxylation:effect of water vapour pressure on the mechanism [J].Thermochimica Acta,2002,390(1):123-32.
[19] 姚林波,高振敏.苏州高岭石的热变过程研究 [J].矿物学报,2007,27(3):255-61.
[20] Chakraborty A K.Phase Transformation of Kaolinite Clay[M].Springer India,2014.
[21] Voga G P,Coelho M G,De Lima G M,et al.Experimental and theoretical studies of the thermal behavior of titanium dioxide-SnO2 based composites [J].Journal of Physical Chemistry A,2011,115(13):2 719-26.
[22] Holt B J,Cutler I B,Wadsworth M E.Rate of Thermal Dehydration of Kaolinite in Vacuum [J].Journal of the American Ceramic Society,2006,45(3):133-6.
[23] Criado J M,Orteg A,Real C,et al.Re-examination of the kinetics of the thermal dehydroxylation of kaolinite [J].Clay Minerals,1984,19(1):653-61.
[24] Ptácˇek P,Kubátová D,Havlica J,et al.Isothermal kinetic analysis of the thermal decomposition of kaolinite:The thermogravimetric study [J].Thermochimica Acta,2010,204(1-2):222-7.
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