Synthesis Of Several Transition Metal Phosphate Functional Materials And Kinetic Study Of Their Thermal Decomposition

As a kind of very important inorganic function materials, transition metal phosphate can be used for ion exchange, absorption, separation, ionic conductivity, heterogeneous catalyst, fertilizers, magnetic and optical devices, fire retardants and pigments which have good anticorrosion properties. Solid-state reaction is of good selectivity, high output and simplicity, so, this preparation technique is become more and more used extensively in synthesis of inorganic function solid materials. Research progress of the transition metal phosphate and solid-state reaction were summarized in the first chapter. Kinetic analysis of thermal decomposition can have either a practical or theoretical application. And choosing a reliable method plays an impotant role in kinetic analysis of thermal decomposition. The calculations are reliable only when sound kinetic analysis methods, which are showed in the first chapter, are used. Besides, the works about this paper and meaning of this research were demonstrated in the first chapter.The prism-shaped single phase LiZnPO4·H2O was directly synthesized via solid-state reaction at room temperature using LiH2PO4·H2O, ZnSO4·7H2O and Na2CO3as raw materials. XRD analysis showed that LiZnPO4·H2O was a compound with orthorhombic structure. The single phase KZn2(PO4)(HPO4) was synthesized via solid-state reaction at80℃using K3PO4·3H2O, K2HPO4·3H2O and ZnSO4·7H2O as raw materials. Besides, the layered single phase NH4CoPO4·H2O and magnesium zinc phosphate hydrate whose chemical formula was determined as MgZn2(PO4)2·4H2O with ICP-AES and XRD, the single phase NH4ZnPO4-ABW(Ⅱ) and (NH4)2Ce(PO4)2·H2O were prepared via solid-state reaction at60℃.The model-fitting and model-free methods were used to study non-isothermal kinetics of the thermal decomposition reaction of LiZnPO4·H2O, and reliable of this two methods was tested by comparison between their calculated results. Based on the iterative iso-conversional procedure, the average values of the activation energy associated with the thermal dehydration of LiZnPO4·H2O, was determined to be86.59kJ mol-1. Dehydration of the crystal water molecule of LiZnPO4·H2O is single-step reaction that is controlled by contracting cylinder mechanism. The pre-exponential factor A was obtained on the basis of Ea and g(a). Besides, some thermodynamic functions (△S≠,△H≠,△G≠) of the transition state complex of the dehydration reaction of LiZnPO4·H2O were determined. The apparent activation energy Ea associated with the thermal decomposition reaction of KZn2(PO4)(HPO4) was estimated with seven comparative isoconversional procedures. The average value of the apparent activation energy Ea was determined to be411.57kJ mol-1. The thermal decomposition of KZn2(PO4)(HPO4) is a single-step kinetic process and can be described by a unique kinetic triplet [Ea, A, g(a)]. Linear and comparison methods were used to define the most probable reaction mechanism g(a) of the thermal decomposition reaction. The value of pre-exponential factor A was obtained on the basis of Ea and g(a). Besides, some thermodynamic functions (△S≠,△H≠,△G≠) of the transition state complex were also calculated.Based on the iterative isoconversional calculation procedure, the values of activation energy Eα associated with the thermal decomposition stages of NH4CoPO4·H2O and (NH4)2Ce(PO4)2·H2O were obtained, which demonstrate that the three thermal decomposition stages of NH4CoPO4·H2O and the first thermal decomposition stage of (NH4)2Ce(PO4)2·H2O are all single-step kinetic process and can be adequately described by unique kinetic triplets; However, the second stage of the thermal decomposition of (NH4)2Ce(PO4)2·H2O is a kinetically complex process. The most probable reaction mechanisms of the single-step stages were estimated by comparisons between experimental plots and modeled plots. The values of pre-exponential factor A of the single-step stages were obtained on the basis of Ea and the reaction mechanisms, when some thermodynamic functions (△S≠,△H≠,△C≠) of the transition state complexes of the single-step decomposition reaction were calculated.The values of activation energy Eα associated with the thermal decomposition reaction of NH4ZnPO4-ABW(Ⅱ) as well as the two thermal decomposition stages of MgZn2(PO4)2·4H2O were obtained by using the advanced isoconversional calculation procedure, which demonstrate that the two stages of MgZn2(PO4)2·4H2O and the region1of NH4ZnPO4-ABW(Ⅱ) are all a single-step kinetic process and can be adequately described by unique kinetic triplets; but, the region2of NH4ZnPO4-ABW(Ⅱ) is a kinetically complex process. The most probable reaction mechanisms of the single-step processes were estimated by comparisons between experimental plots and modeled results. The values of pre-exponential factor A of the single-step stages were obtained on the basis of Eα and g(a).In this paper, different kinetically complex processes were researched by using two methods:the distributed activation energy model (DAEM) and the nonlinear model-fitting method were applied to study the region2of the thermal decomposition reaction of NH4ZnPO4-ABW(Ⅱ) and the second stage of the thermal decomposition reaction of (NH4)2Ce(PO4)2·H2O in which kinetically complex processes took place, respectively.The (NH4)2Ce(PO4)2·H2O synthesized by using solid-state reaction at low-heating temperature and H2SO4were mixed to obtain H+/(NH4)2Ce(PO4)2·H2O. The synthesis of isobutyl acetate was carried out with H+/(NH4)2Ce(PO4)2·H2O as catalyst, and uniform experimental design as well as data mining technology was applied to the catalytic experiments, in which the effect of the reaction time, the molar ratio of acid to alcohol and the amount of catalyst on the conversion yield of esterification were studied. When the amonnt of isobutyl alcohol was0.10mol, under the optimal reaction conditions, i.e. reaction time of330min,2.2of molar ratio of acid to alcohol and1.4g of catalyst, the conversion yield of esterification was95.36%.