Studies of thermal decomposition kinetics and temperature dependence of thermodynamic functions of the new precursor LiNiPO4·3H2O for the synthesis of olivine LiNiPO4

Abstract

The olivine LiNiPO 4 was synthesized via the calcination of the new precursor LiNiPO 4 Á3H 2 O at 600°C. The precursor was obtained from low-temperature (50°C) wet chemical reaction. The results from XRD, FTIR, AAS/ AES and TG/DTG/DTA techniques confirmed the formula of the title compounds. The SEM results indicated the morphologies of the hydrate precursor as thin plate particles and the calcined product as small bead particles. The BET surface area of the final calcined product at 600°C is much higher (5.807 m 2 g -1 ) than that reported in the literature (0.25 m 2 g -1 ). The kinetic triplet [activation energy, E, pre-exponential factor, A, and the most probable mechanism function, g(a)] and the thermodynamic functions of activated complexes (DS = , DH = and DG = ) for the dehydration step of LiNiPO 4 Á3H 2 O were determined and discussed. The mechanism of the dehydration process is the single-step A 3/2 (assumed random nucleation and its subsequent growth). New information, namely the isobaric molar heat capacity, experimental entropy, enthalpy and Gibbs energy changes as function of temperature (K) of LiNiPO 4 Á3H 2 O and LiNiPO 4 , was evaluated from the DSC data by third-order polynomial fitting and reported for the first time. The calculated corresponding thermodynamic functions from kinetic parameters are compared and discussed.

An experimentally validated numerical model of interface advance of the lithium sulfate monohydrate dehydration reaction

“…The geometric models, widely used in the kinetic analysis of thermal decomposition reactions [20][21][22][23][24][25], are based upon the processes of nucleation and growth of product nuclei by interface advance. It was suggested that more reliable data can be obtained from the kinetic study of single crystals compared to powdery samples [1].…”

Thermal stability and non‐isothermal kinetics of poly(ethyl cyanoacrylate) nanofibers

“…The general equation 30,46,47 describing this theory is given as follows: where е = 27 183 is the Neper number; χ is the transition factor, which represents unity for monomolecular reactions; k B is the Boltzmann constant; h is the Planck constant; and T p is the peak temperature of the DTG curves at various heating rates. Taking into account that: the thermodynamic functions Δ S ≠ , Δ H ≠ and Δ G ≠ , which well characterize the decomposition process, may be calculated 44,48,49 . Then, the changes in the entropy and enthalpy may be calculated according to the formulae: and The change in the Gibbs free energy Δ G ≠ for the activated complex formation from the reagent can be calculated using the well‐known thermodynamic equation: The values of Δ S ≠ , Δ H ≠ and Δ G ≠ were calculated at T = T p since this temperature characterizes the highest rate of the process, and therefore it is an important parameter.…”

Size-controllable synthesis of lithium niobate nanocrystals using modified Pechini polymeric precursor method

“…In this process, the polymerization of the complex is stimulated by heating the transparent solution and a uniform resin in which metal ions are homogeneously dispersed at molecular level, which ultimately results in the formation of LN [12,13] or other lithium metal oxide [14] nanoparticles with outstanding chemical uniformity. Furthermore, it is pertinent to mention that the lack of Li loss is ensured by the use of low-temperature methods resulting in the control of chemical composition of the product [15,16]. Other advantages of the Pechini method include the possibility to work in aqueous solutions in which starting materials can be solved easily.…”