Reaction kinetics of silicon etching in HF-K2Cr2O7-H2O solution

The reaction kinetics of silicon etching in HF-K₂Cr₂O₇-H₂O solution was studied experimentally. The etch rates were measured with varying HF and K₂Cr₂O₇ concentrations, agitation speed reaction temperature and time. The etch rates of n- and p-Si (100) were both similar. The etchec surfaces consisted mainly of silicon and showed a relatively smooth and planar morphology. At suffi ciently high HF concentration, the etch rate was increased with increasing K₂Cr₂O₇ concentratior due to the increase of hole formation on the silicon surface. However, at low HF concentration the etch rate maintains low value and increases very slowly because of insufficient hole concentratior for etching reaction. The apparent activation energy was about 7.8 kcal/g-mole, and the rate equatior for the silicon etching reaction in HF-K₂Cr₂O₇-H₂O solution was obtained as-r_Si = 600 exp(-3900/T) $$ - r_{Si} = 600{\text{ exp( - 3900/T) C}}_{{\text{K}}_{\text{2}} {\text{Cr}}_{\text{2}} {\text{O}}_{\text{7}} } ^{05} {\text{ C}}_{{\text{HF}}} ^3 $$ C_hk ³ at HF concentrations greater than 8 M.     

Effect of ultrasound on sulfuric acid-catalysed hydrolysis of starch

The influence of ultrasound on the hydrolysis of starch was investigated at moderate temperature range (90-100°C) and in the dilute sulfuric acid (1-5 wt%). Enhancements of the reaction rate by ultrasound was observed. The degree of the relative enhancement depended on the reaction temperature. The model reaction by maltose showed that the acid hydrolysis of glucosidic linkages was first order with respect to the substance concentration and the hydrogen ion concentration, respectively. And the activation energies of the control and the ultrasound-aided hydrolysis of maltose were 30.2 and 23.4 kcal/mol, respectively. Enhancement was thus expressed as the alleviation of activation energy by ultrasound irradiation.     

Transport phenomena in gas permeation through glassy polymer membranes with concentration-dependent sorption and diffusion parameters

The modified dual-mode mobility model for permeation of a gas in glassy polymer membranes was combined with the extended dual-mode sorption model to take account of the plasticization effect of sorbed gas molecules on both sorption and diffusion processes. The combined model was further simplified by the introduction of a concentration of the mobile gas species. However, the observed pressure dependence of mean permeability coefficients of carbon dioxide in methylmethacrylate-n-butyl acrylate copolymer and polymethylmethacrylate films at 30°c and also that of oxygen in a polycarbonate film at 50°C and 60°C showed that a plasticization action of sorbed gas species has an influence on the diffusion process rather than on the sorption process, that is, were simulated by the modified dual-mode mobility model combined with the conventional dual-mode sorption model.     

Critical Concentration of MgO for the Prevention of Abnormal Grain Growth in Alumina

The effects of MgO on sintering and grain growth of alumina in the absence of any other impurities as well as in the presence of various amounts of CaO were investigated using ultrapure (>99.999%) alumina and sintering at 1900°C for 1 h in a clean contamination-free condition. Critical concentrations of MgO required for the prevention of abnormal grain growth were linearly dependent on the CaO concentration. For a given concentration of CaO, at least the same amount of MgO has to be added to prevent abnormal grain growth. MgO addition alone to the ultrapure alumina enhanced both grain growth and densification kinetics during pressureless sintering. The beneficial effect of MgO doping could not be explained based on the solute drag (or pinning) model. It was more likely to be understood in terms of either a glass modification model or a solid–liquid interface modification model.     

Phase behaviours of polymer solutions in high pressure system

A modified generalized lattice-fluid (MGLF) model was developed to predict and describe phase behaviours of polymer solutions under high pressure condition. To consider the specific interaction between pure components, a new parameter, κ₁₁, was introduced into the generalized lattice-fluid (GLF) model. The proposed model was compared with a phase diagram predicted by the GLF model and experimental data for polymer solution systems (polystyrene/diethylether and polystyrene/acetone) showing lower critical solution temperature (LCST) at various pressures. The MGLF model predicted remarkably well the spinodal curve of a given polymer/solvent system.     

Production of microcellular foam plastics by supercritical carbon dioxide

The production of microcellular plastic was studied in the polymethyl metacrylate (PMMA)-supercritical carbon dioxide and polycarbonate (PC)-supercritical carbon dioxide systems. The test pieces of PMMA and PC were put into a saturation vessel of which temperature and pressure were kept constant. Supercritical carbon dioxide at temperature between 303K and 393K and pressure between 100 bar and 250 bar was used as a foaming agent. After saturation of carbon dioxide, the pressure was quickly released to atmospheric pressure. The samples were immediately taken out from the vessel and heated in an oil bath. The fractured part of the sample was used for microstructure analysis with SEM. The effect of the saturation temperature, pressure of sorption and the foaming time on the cell mean size and cell density of the foam was investigated by considering the solubility of carbon dioxide in PMMA and PC. The foam morphologies of the foamed plastics were affected by solubility of carbon dioxide, which was directly related to saturation temperature and pressure. The cell density increased and, consequently, the cell size decreased with the solubility of carbon dioxide. The foaming time can be used a controlling factor to obtain the desired foam structure and the volume expansion ratio.     

Hydriding properties of Mg–xNi alloys with different microstructures

The hydriding properties of Mg–xNi (x = 13.5, 23.5 and 33.5 wt%) alloys with different microstructures produced by various processing routes were evaluated in this study. The hydrogen storage capacity and kinetics of hydriding of Mg–xNi alloys were strongly dependent on their microstructures. The capacity and kinetics of hydriding were larger and faster when the average size of the hydriding phase was smaller and the volume fraction of the phase boundary was larger.     

Synthesis and characterization of TRITON™ X‐based surfactants with carboxylic or amino groups in the oxyethylene chain end

This paper describes the synthesis and characterization of a series of TRITON™ X‐based surfactants with a predominantly alkyl phenol ethoxylate (APE) backbone and carboxylic or amino chain ends. Three carboxylic acid‐containing TRITON X (or APE)‐derivatives, [OPE2‐COOH], [OPE5‐COOH], and [OPE10‐COOH], were prepared from commercially available octyl phenol ethoxylate (OPE) of different oxyethylene units (i.e., n = 2, 5, and 10) and ethyl bromoacetate via a simple etherification reaction followed by saponification. Two amine‐containing TRITON X ‐derivatives, [NPE10‐NH₂] and [NPE10‐imidazole], were prepared based on modifications of mesylate of nonyl phenol ethoxylate (NPE) of 10 oxyethylene units reacted with ammonia and imidazole, respectively. Depending on their composition and chain length of oxyethylene units used in the reaction, the surfactants show different thermal degradation behaviors. The carboxylic acid‐containing surfactants give no char at high temperatures under air condition. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 162–170, 2007     

Growth mechanism of monodispersed TiO2 fine particles by the hydrolysis of Ti(OC2H5)4

In order to investigate the growth mechanism of TiO₂, the monodispersed TiO₂ fine particles were prepared by hydrolysis of Ti(OC₂H₅)₄ using the seed preparation method. Although it was impossible to grow TiO₂ particles to more than 1 μm with conventional liquid phase reaction method, we obtained monodispersed T1O₂ fine particles of up to 2.5 urn. Nielsen’s chronomal analysis and Overbeek’s theory were applied to clarify the particle growth mechanism. The particle growth mechanism was found out as a first-order polynuclear layer growth mechanism and the growth rate constant, k_P was about 6.45X10^-6 cm/s.     

New method for evaluating the kinetic constant of thermal protection materials

Thermal protection material (TPM) is used to protect rocket structures from extreme conditions created by the hot exhaust of the rocket. Designing TPM is an important step in the rocket design process. Considering that an increase in the system weight decreases the overall performance of a rocket, the amount of TPM is carefully determined during the design process. Therefore, the precise properties of TPM guarantee an accurate thermal analysis and the successful design of the rocket. Among the many properties of TPM, the kinetic constant and activation energy, which govern the thermochemical reaction of the TPM, are the most important. Thus, an experiment to measure the kinetic constant and activation energy is conducted as part of this research. A theoretical approach to deduce the properties from measured data is discussed, and a method to apply the theory to experimental data, termed the R² method, is developed. Compared to a previous method which was difficult to apply, the R² method reduces unclear selections of the reaction time and does not require intervention by an interpreter. The properties deduced by the R² method show good agreement with the other method despite the limited number of experimental results.