Gas hydrates are crystalline compounds formed by inclusion of small gas molecules into a lattice constructed by water. Development of a mathematical model for qualitive quantitative description of hydrate crystal growth rate is the basic aim of this work. The difference between the temperature of crystal surface and that of the liquid bulk is employed as driving force of crystal growth. Parameters of model for hydrate formation from methane and ethane are calculated and it was shown that the heat transfer model combined with distribution of growing particles is capable of describing the experimental data.

Even purified enzyme preparations are often heterogeneous. For example, preparations of aspartate aminotransferase or cytochrome oxidase can consist of several different forms of the enzyme. For this reason we consider how different the kinetics of the reactions catalysed by a mixture of forms of an enzyme must be to provide some indication of the characteristics of the species present. Based on the standard Michaelis- Menten model, we show that if the Michaelis constants (Km) of two isoforms differ by a factor of at least 20 the steady-state kinetics can be used to characterise the mixture.However, even if heterogeneity is reflected in the kinetic data, the proportions of the different forms of the enzyme cannot be estimated from the kinetic data alone.Consequently, the heterogeneity of enzyme preparations is rarely reflected in measurements of their steady-state kinetics unless the species present have significantly different kinetic properties. This has two implications: (1) it is difficult, but not impossible, to detect molecular heterogeneity using kinetic data and (2) even when it is possible, a considerable quantity of high quality data is required.

The rate of Zn desorption from soil surfaces into soil solution is a dynamic factor that regulates it continuous supply to growing plants. To ascertain the pattern of Zn desorption and the effective soil characteristics, the kinetics of Zn desorption from 20 selected soils of Iran by diethylentriaminepentaacetic acid (DTPA) were investigated. Eight kinetic models were evaluated to describe the rate of desorption of soil Zn by DTPA, which was rapid initially but gradually declined with time. The simple Elovich, the parabolic double diffusion and the two constant rate equations adequately described Zn desorption from soils. Rate constants for the parabolic double diffusion equation (K1 and K2), the two constants (a and ab), and parabolic diffusion (Kd) were closely correlated with soil pH, calcium carbonate equivalent, Olsen-P and DTPA-Mn, which are the soil characteristics that affect solubility, desorption and diffusion of Zn in soils. Rate constant for the simple Elovich equation (bs) was correlated with Olsen-P and rate constant for two-constant equation (b) was correlated with CEC, organic carbon and FC. The ratio of initial Zn desorption (rapid desorption) to total Zn desorption of soils decreased significantly with increase in calcium carbonate equivalent of soils.

n this study, the kinetics of nanocrystallization of amorphous Finemet alloys is investigated under nonisothermal condition. In order to estimate kinetic parameters, differential scanning calorimetric analyses of the amorphous samples were performed at various heating rates. These results show that the crystallization of the α Fe phase starts at around 450 ̊ C. X-ray diffraction pattern samples confirm these results. According to the XRD results, the crystallite size of the sample annealed at 450 ̊ C and 550 ̊ C were 12 nm and 19 nm, respectively. The variable activation energy of crystallization was calculated, based on differential scanning calorimetric results and according to Vyazovkin advanced isoconversional method. Results show that, the activation energy is variable as a function of transformed fraction and increases from 290 to 390 kJ mol-1. Variation of activation energy confirms the complexity of the nanocrystallization process. Numerical reconstruction of the reaction model using experimental data showed that nanocrystallization mechanism could not be described with a single theoretical model. But it is closer to three dimensional phase boundary reaction mechanism. Rrounded and isotropic crystallites observed on the TEM images confirmed these results.

Zinc hydrosulfite is produced by slurry reaction between sulfur dioxide and zinc powder. This reaction is the first step of sodium hydrosulfite production in zinc powder processing. In this paper through performing a series of experiments, zinc hydrosulfite production rate is obtained as a function of 502 flow rate,  temperature and specific area of zinc powder. In addition. Equations for predicting the end-point of the reaction and the decomposition rate of zinc hydrosulfite after that end-point are proposed. Finally, a time dependent flow rate equation is suggested to predict the maximum yield.

Three mathematical methods called non-linear, linear and four -point were used to simulate the rate of corrosion reactions. The most appropriate method was shown to be the first; because it is capable of simultaneous calculation of both the tafel slope and the corrosion current density ; irrespective of what interval is chosen for the electric potential. In order to obtain a best fit between the empirical and the empirical and the theoretical data, utilization was made of the least square technique with exponential polynomials and the polarization equation i =icorr.[exp (aDe) - exp (-bDe)].The simulation program, called CKS, is capable of accurate evaluation of the corrosion parameters, with a relatively high speed.