A. Jerez

Generalization of the kissinger equation for several kinetic models

In this work, a generalization of the Kissinger equation was extended to several solid-state kinetic models, and the expressions for the correction term were also deduced from the algebraic equations of the differential (f(α)) and integral (g(α)) functions.

A modification to the Freeman and Carroll method for the analysis of the kinetics of non-isothermal processes

An analysis of the mathematical treatment employed in the Freeman and Carroll method has showed the existence of large errors in the determination of the order of the kinetic equation. A modification is proposed which allows that this error to be reduced.

Synthesis and magnetic properties of crystalline CrVO4

Crystalline CrVO/sub 4/ was prepared by solid state reaction from Cr/sub 2/O/sub 3/ and V/sub 2/O/sub 5/ at 723 K. Their crystallographic parameters, and atomic positions were refined by the powder X-Ray method and their i.r. absorption bands were assigned. Magnetic properties were discussed on the basis of a 1D model.

The monoclinic perovskite La2LiSbO6. A rietveld refinement of neutron powder diffraction data

Abstract The crystal structure of La 2 LiSbO 6 has been refined by neutron diffraction at 295 K.This compound adopts a distorted perovskite structure with an ordered distribution of Li and Sb atoms in B-sites and the La atoms are located in A-sites. The tilting of (Sb, Li)O 6 octahedra is responsible of the irregular coordination in the LaO 8 polyhedra. The bond valence calculations for metal atoms are in agreement with the experimental bond distances.

Kinetic studies by DSC on the thermal decomposition of calcium oxalate

Abstract In the present paper, we have studied the kinetics of the thermal decomposition of calcium oxalate monohydrate, using a new method of kinetic study employing data obtained from differential scanning calorimetry, as previously proposed by us. Initial products and those obtained following decomposition have been identified by infrared spectroscopy and X-ray powder diffraction. A comparison between the results obtained in this paper and those reported in the literature has also been made.

A method for the kinetic analysis of nonisothermal decomposition reactions of solids

Abstract A new method, which allows the determination of the mechanism of a decomposition reaction of solids and leads to reliable kinetic parameters, is proposed. The test of the validity of the method is performed with seven simulated TG and DTG curves.

Synthesis, characterization and magnetic properties of some LnBO3 (Ln ≡ Pr, Sm, Eu AND Yb) compounds

Abstract The aim of this work is to complete a study previously initiated by us on the synthesis, characterization and magnetic properties of the lanthanide orthoborates. The different LnBO 3 compounds were obtained by mixing metal hydroxides Ln(OH) 3 and orthoboric acid B(OH) 3 in stoichiometric amounts at low temperatures between 873 and 973 K and at pressures of between 10 −4 and 10 −5 mmHg. This method had been previously successfully applied to the isolation of the other lanthanide orthoborates. The characterization of these materials was carried out by X-ray powder diffraction and IR spectrometry. The magnetic susceptibilities of these compounds were measured in the temperature range 4.2–300 K. The susceptibilities of PrBO 3 and YbBO 3 obey the Curie-Weiss law from 300 to 30 K, but deviations from this law occur at lower temperatures. The temperature dependences of the magnetic susceptibilities of SmBO 3 and EuBO 3 were also studied.

Synthesis, structure determination and magnetic susceptibilities of the oxides Ln3Li5Sb2O12 (Ln ≠ Pr, Nd, Sm)

Abstract The oxides Ln 3 Li 6 Sb 2 O 12 (Ln≠Pr, Nd, Sm) were prepared in air by heating a mixture of Ln 2 O 3 , LiNO 3 and Sb 2 O 3 in the temperature range 1023–1243 K. Lattice parameters as well as atomic coordinates in the space group 12,3 (Z≠8) are established from X-ray powder diffraction data by the Rietveld method. Magnetic susceptibilities from 4.2 to 300 K follow a Curie-Weiss law above 50 K (Ln≠Pr) or 70 K (Ln≠Nd). This is attributed to the splitting of the ground state associated with the Ln 3+ ions by the influence of the crystal field. The magnetic moments, 3.54 and 3.61 μ D for praseodymium and neodymium respectively, agree with those calculated by Hunds formula. The Sm 3+ behaviour can be explained by taking into account that the splitting of the multiplets is not too large compared to kT. The magnetic moment observed at room temperature for this cation is 1.6 μ B .

Synthesis and structure determination of a new phase in the La2O3Li2OSb2O5 system

Abstract The new phase La3Li5Sb2O12, isostructural with the Nb(V) and Ta(V) compounds of the same stoichiometry, has been isolated and characterized. The crystal structure is refined from X-ray powder diffraction data by Rietvelds method. The unit cell is cubic (space group I213, Z = 8) with a = 12.8460(5) A and the final reability factors are: RP = 14.35, Rb = 8.93.

Application of a new method to the kinetic study of the thermal decarbonylation of sodium oxalate

Abstract The application of a new method for studying the kinetic parameters of the thermal decarbonylation of sodium oxalate in dinitrogen using differential scanning calorimetry is described. The activation energy and the pre-exponential Arrhenius factor for the loss of carbon monoxide are calculated from the DSC curves and the reaction order and mechanism are also determined. A comparison is made between the results obtained using the proposed method and those reported in the literature.