Periodic Nucleation of Calcium Phosphate in a Stirred Biocatalytic Reaction

Highly ordered superstructures composed of inorganic nanoparticles appear in natural and synthetic systems, however the mechanisms of non‐equilibrium self‐organization that may be involved are still poorly understood. Herein, we performed a kinetic investigation of the precipitation of calcium phosphate using a process widely found in microorganisms: the hydrolysis of urea by enzyme urease. With high initial ratio of calcium ion to phosphate, periodic precipitation was obtained accompanied by pH oscillations in a well‐stirred, closed reactor. We propose that an internal pH‐regulated change in the concentration of phosphate ion is the driving force for periodicity. A simple model involving the biocatalytic reaction network coupled with burst nucleation of nanoparticles above a critical supersaturation reproduced key features of the experiments. These findings may provide insight to the self‐organization of nanoparticles in biomineralization and improve design strategies of biomaterials for medical applications.     

Phase States of Europium Selenites in Aqueous Medium and in Thermal Analysis

The solubility isotherm of the system Eu₂O₃-SeO₂-H₂O was studied at 100°C. Certain amounts of the obtained selenites (normal and acid) were subjected to thermal analysis. The intermediate phases were isolated and chemical and X-ray phase analysis was made. The scheme of thermal decomposition was determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimation of Critical Temperature of Thermal Explosion for Nitrosubstituted Azetidines Using Non-isothermal DSC

Based on reasonable hypothesis, two general expressions and their six derived formulae for estimating the critical temperature (T_b) of thermal explosion for energetic materials (EM) were derived from the Semenov's thermal explosion theory and eight non‐isothermal kinetic equations. We can easily obtain the values of the initial temperature (T_0i) at which DSC curve deviates from the baseline of the non‐isothermal DSC curve of EM, the onset temperature (T_ei), the exothermic decomposition reaction kinetic parameters and the values of T₀₀ and T_e0 from the equation T_{0i or ei}=T_{00 or e0}+a₁β_i+a₂β_i²+···+a_L?2β_i^L?2, i=1, 2, ;···, L and then calculate the values of T_b by the six derived formulae. The T_b values for seven nitrosubstituted azetidines, 3,3‐dinitroazetidinium nitrate ( 1 ), 3,3‐dinitroazetidinium picrate ( 2 ), 3,3‐dinitroazetidinium‐3‐nitro‐1,2,4‐triazol‐5‐onate ( 3 ), 1,3‐bis(3′,3′‐dinitroazetidine group)‐2,2‐dinitropropane ( 4 ), 1‐(2′,2′,2′‐trinitroethyl)‐3,3‐dinitroazetidine ( 5 ), 3,3‐dinitroazetidinium perchlorate ( 6 ) and 1‐(3′,3′‐dinitroazetidineyl)‐2,2‐dinitropropane ( 7 ), obtained with the six derived formulae are agreeable to each other, whose differences are within 1.5%. The results indicate that the heat‐resistance stability of the seven nitrosubstituted azetidines decreases in the order 6 > 7 > 5 > 4 > 3 > 2 > 1 .     

Estimation of Critical Temperature of Thermal Explosion for Trinitromethyl Explosives by Non-isothermal DSC

Two general expressions and their six derived formulae for estimating the critical temperature(Tb) of thermal explosion for energetic materials(EMs) were derived from the Semenov’s thermal explosion theory and eight non-isothermal kinetic equations via reasonable hypothesis. We can easily obtain the values of the initial temperature(T0i) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of EMs, the onset temperature(Tei), the exothermic decomposition reaction kinetic parameters and the values of T00 and Te0 from the equation T0i or ei=T00 or e0+α1βi+α2βi2+···+αL–2βiL–2, i=1, 2, ···, L and then calculate the values of Tb by means of the six derived formulae. The results obtained with the six derived calculating methods for six trinitromethyl explosives: bis(2,2,2- trinitroethyl-N-nitro) ethylene diamine(BTNEDA), 2,2,2-trinitroethyl-4,4,4-trinitrobutyrate(TNETB), bis(2,2,2- trinitroethyl) formal(BNTF), bis(2,2,2-trinitroethyl-nitramine)(BTNNA), 2,2,2-trinitroethyl-2,2,2-trinitroethyl-N- nitroamino acetate(TNTNNA) and tetrakis [2,2,2-trinitroethyl] orthoester(TTNOE) agree well with each other.     

Heat and Mass Transfer in a Tank Reactor Stirred by Gaseous Jets

A spherical tank reactor stirred by gaseous jets has been developed in order to study the activity and selectivity of a catalytic or a reactive solid. In the present work, mass and heat transfer from a sphere suspended in the reactor are studied.The mass transfer study was carried out by using naphthalene spheres of different diameters and varying the air flow rate. A correlation of the experimental results is developed and compared with those in the literature.A heat transfer study from a heated sphere was also carried out. The natural convection effect on the experimental results is analyzed and these are correlated in terms of the effective Reynolds number.     

Conservation Laws for Chemical Reactions with Arbitrary Kinetics in a Partially Stirred Reactor

Russian Journal of General Chemistry - One of the difficulties encountered in solving direct and inverse chemical kinetics problems is the complexity of studying multidimensional systems of...     

DSC Research on Critical Temperature in Thermal Explosion Synthesis Reaction Ti+3Al→TiAl3

The critical furnace chamber temperature (T′_ign) of the thermal explosion synthesis reaction Ti+3Al→TiAl₃ is studied by isothermal and non-isothermal DSC. The reaction product is characterized by using the X-ray powder diffraction. The value of T′_ign is between 740 and 745°C obtained from the isothermal DSC observations, and 729°C obtained from non-isothermal DSC curves. It shows that these two values have a good consistency. With the help of the apparent activation energy of the reaction obtained by Friedman method and the value of T′_ign0 by the multiple linear regression of the T′_igns at different heating rates (β), the critical temperature (T _b) of thermal explosion for Ti–75at%Al mixture is estimated to be 785°C. This revised version was published online in August 2006 with corrections to the Cover Date.     

热爆合成三铝化钛复杂反应动力学的差示扫描量热法

用Friedman法研究了非等温DSC条件下热爆合成反应Ti 3Al→TiAl3的复杂反应动力学。根据表观激活能（Ea）随转化率（α）的变化关系，识别出该反应至少包含3个Ea值分别为109、175和89kJ/mol的子过程。通过与Ti-Al二元系的反应和互扩散激活能的比较，提出了可能的复杂反应动力学机制。     

Modeling of the Permeate Flux during Microfiltration of BSA-Adsorbed Microspheres in a Stirred Cell

A study on the variation of the permeate flux was performed in a stirred cell charged with microspheres, to investigate the effects of the stirrer speeds (300, 400, and 600 rpm) and the BSA concentration (0.1, 0.2, 0.4, and 0.8 g/L) under constant pressure. The permeate flux increased over time before the saturation point, but it began to decrease after that point. An increase of the BSA concentration and the stirrer speed resulted in the rapid increase of the permeate flux. This is contrary to the observation of the conventional filtration experiments using a stirred cell. A resistance-in-series model was employed for the modeling of the permeate flux. The cake resistance (R(c), induced by the concentration polarization of microspheres) and the fouling resistance (R(f), induced by the adsorption of BSA inside the membrane pore) must be considered simultaneously for the modeling. These modeling results were in good agreement with the experimental data. These can be applied to the special system considering both R(c) and R(f) as well as the general filtration systems using a stirred cell. Copyright 2000 Academic Press.     

Temperature Dynamics and Start-up of a Continuous Flow Stirred Tank Polymerisation Reactor

Experimental results have been obtained for the potassium persulphate initiated polymerisation of acrylamide in a continuous flow stirred tank reactor. Variables investigated included monomer and initiator concentrations and feed inlet temperature and flowrate. Results were compared with a theoretical model and satisfactory agreement obtained for steady state temperature and conversion. During the start-up period, during which temperature measurements only were made, comparison with theory showed that the induction periods observed experimentally under certain conditions were not predicted. Allowance for heat transfer from the reactor to the surroundings has been shown to be important.     

Determining the Conditions of Preliminary Mixing in Stirred Vessels

The results of experimental and theoretical studies of the influence exerted by stirring on a chemical reaction are presented. A parameter is proposed for evaluating this influence. The values of this parameter at which the state of preliminary mixing of reactants is achieved are determined.     

Estimation of the Critical Temperature of Thermal Explosion for the Highly Nitrated Nitrocellulose Using Non-isothermal DSC

Two methods for estimating the critical temperature (T_b) of thermal explosion for the highly nitrated nitrocellulose (HNNC) are derived from the Semenov's thermal explosion theory and two non-isothermal kinetic equations, d/dt=Af()e^–E/RT and d/dt=Af()[1+E/(RT)(1–T_o/T)]e^–E/RT, using reasonable hypotheses. We can easily obtain the values of the thermal decomposition activation energy (E), the onset temperature (T_e) and the initial temperature (T_o) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of HNNC, and then calculate the critical temperature (T_b) of thermal explosion by the two derived formulae. The results obtained with the two methods for HNNC are in agreement to each other.This revised version was published online in November 2005 with corrections to the Cover Date.     

Vinyl Chloride Peroxide Explosion in a Vinyl Chloride Recovery Plant

The formation of polymer peroxides by the addition of oxygen to unsaturated organic compounds was described for the first time by Staudinger, taking 1,l-diphenyl ethylene peroxide as an example [1]. In the meantime, numerous other polyperoxides have become known, among them the peroxides of acrylonitrile [2], dimethyl butadiene [3], chloroprene 141, methyl methacrylate 51, styrene 161, vinyl acetate [5], and vinyl chloride [7-10]. Because of the great significance of the aforementioned compounds as monomers in the production of plastic materials, the investigations centered on the influence of oxygen on the polymerization behavior of the monomers and on the properties of the polymers.     

原油乳状液破乳的动态法研究

The stability of different crude oil emulsions from ASP flooding production well is studied by the method of a stirred tank. The demulsifying of crude-oil emulsion by different demulsifying agents is discussed. The breakage of the crude oil emulsions from the well PO11 by the different types and concentrations of the emulsifying agents is also discussed. The breaking mechanism of the demulsifying agent is described microscopically.     

Addition of Sulphur to Graphene Nanoflakes Using Thermal Plasma for Oxygen Reduction Reaction in Alkaline Medium

A batch process is developed to generate sulphur functionalized graphene nanoflakes (S-GNFs), corresponding to nanoparticles of stacked graphene. The growth and functionalization of the catalysts are done in a single thermal plasma reactor. The GNFs are first grown through the decomposition of methane in the thermal plasma volume followed by homogeneous nucleation of the nanoparticles in the well-controlled recombining plasma stream allowing the 2-dimensional evolution of the nanoparticle morphology. The precursor feeding conditions are then changed to liquid carbon disulphide in order to generate sulphur-based functional groups on the nanoparticles. The plasma conditions and carbon disulphide injection are varied, and samples with tuneable amount of sulphur between 4 and 28 at% are obtained. The functional groups generated include polythiophene polymer partly covering the GNFs, sulphur functionalities implemented directly on the graphitic structure, and traces of orthorhombic sulphur. The S-GNFs exhibit higher electrocatalytic activity toward the oxygen reduction reaction in alkaline medium for the samples containing the highest amounts of sulphur.     

Thermal Conductivity and Thermal Diffusivity Anisotropy in a Liquid Crystal

Thermal conductivity (k) and thermal diffusivity (D) of the 9CB liquid crystal have been simultaneously determined by a photopyroelectric (PPE) technique in the temperature range from 308 K to 332 K where two different phase transitions occur. The measurements have been performed on oriented samples and the k and D anisotropy has been studied. The behaviour of the macroscopic order parameter vs. temperature has been determined and the order of the phase transitions checked. This revised version was published online in July 2006 with corrections to the Cover Date.