Kinetics of the dissolution of silica in aqueous sodium hydroxide solutions at high pressure and temperature

The kinetic of the reaction of sand with aqueous NaOH corresponding to the ratio SiO₂/Na₂O = 2 was studied in a pressure vessel at 220°C and 2.7 MPa. Since the kinetic curves could not be obtained directly from the experimental data, a new method is proposed to plot the entire kinetic graph from experimental data. An analytical expression of the type α = A [1 -exp(-Bt)] describes the system perfectly. The constants A and B were calculated for a silica sample having a narrow granulometric distribution (range i.e. 300–315 μm). The value of A is found to be almost constant, between 0.95 to 0.99 and B ranges from 0.03 to 0.14 when [OH-] increases from 0.5 to 12.5 mol/L. The kinetic order with respect to OH^? is equal to 0.470 + 0.013 and the kinetic constant at 220°C is 3.933 × 10^?6 g/m².s.     

Interfacial Reaction Kinetics between Silver and Ceramic-Filled Glass Substrate

Interfacial reaction kinetics between Ag and ceramic-filled glass (CFG) substrate, containing borosilicate glass, high-silica glass, and alumina, has been investigated at 850°–925°C in different atmospheres. No chemical reaction at the interface of Ag/CFG is found when firing takes place in N₂ or N₂+ 1% H₂. Fired in air, however, an interfacial reaction zone is formed at the interface of Ag/CFG with Ag⁺ ion diffusing from silver and Al³⁺ ion dissolving from CFG, and both ions are always coupled together in the reaction zone. Microstructural and chemical analyses show that the reaction zone consists of two distinct layers; one is homogeneous, and the other, heterogeneous. The homogeneous layer, which is adjacent to Ag, is uniform in microstructure with a composition rich in Ag⁺ and Al³⁺. The heterogeneous layer is not uniform in microstructure with Si-rich and Ag–Al-rich phases. The reaction zone moves toward CFG with time, forming a heterogeneous layer first and then converting into a homogenous layer when diffusion of Ag⁺ ion into the CFG becomes significant. The growth kinetics for the homogeneous layer follows a linear rate equation, whereas the heterogeneous layer, a parabolic rate equation. Activation analyses suggest that the formation of the homogeneous layer is controlled by the combination of breakage and formation of M–O bonds, but the heterogeneous layer, by the diffusion of Ag⁺ ion in the BSG.     

Synthesis and Sintering of Large Batches of Barium Zirconate Nanopowders

The acrylamide gelification process is a fast, inexpensive, reproducible, and easily scaled up chemical method for obtaining nanopowders of BaZrO₃ that can be used for sintering crucibles and many electronic applications. This method enables the production of 100 g of high-purity powders in one run, using simple laboratory equipment and low-cost raw materials. The gelification process, synthesis temperature, and gas conditions required for obtaining high-quality powders were the subjects of the present study. Fine powders were sintered to full density at 1450°C, making the fabrication of BaZrO₃ crucibles possible for many laboratories.     

Modeling adaptation of breast cancer treatment decision protocols in the <Emphasis Type="SmallCaps">Kasimir</Emphasis> project

Medical decision protocols constitute theories for health-care decision making that are applicable for “standard” medical cases but have to be adapted for the other cases. This holds in particular for the breast cancer treatment protocol studied in the Kasimir research project. Protocol adaptations can be seen as knowledge-intensive case-based decision support processes. Some examples of adaptations that have been performed by oncologists are presented in this paper. Several issues are then identified that need to be addressed while trying to model such processes, namely: the complexity of adaptations, the lack of relevant information about the patient, the necessity to take into account the applicability and the consequences of a decision, the closeness to decision thresholds, and the necessity to consider some patients according to different viewpoints. As handling these issues requires some additional knowledge, which has to be acquired, different methods are presented that perform adaptation knowledge acquisition either from experts, or in a semi-automatic manner. A discussion and a conclusion end the paper.     

Effect of surfactants and biomass on the gas/liquid mass transfer in an aqueous‐silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove VOCs from gaseous effluents

BACKGROUND: The two‐phase partitioning bioreactor (TPPB) has become a new strategy for waste gas treatment. However, the impact of biomass and surfactants on gas/liquid (G/L) mass transfer needs to be better evaluated because the effects on the mass transfer coefficient K_L and the interfacial area a, respectively, remains misunderstood. RESULTS: This study showed that, first, the surfactant extract produced by Rhodococcus erythropolis reduced the surface hydrophobicity of the biomass. Secondly, an optimal concentration appeared to exist for both components, respectively 0.5 g L^?1 and 0.7 g L^?1 for biomass (B) and surfactant extract (SE) when the global mass transfer coefficient (K_La) of oxygen was measured in a silicone oil/water TPPB. However, the combination of B and SE was found to induce a negative synergism. In particular, SE improved the interfacial area a by increasing the bubble diameter, while B reduced it as soon as a concentration of 1 g L^?1 was exceeded. In contrast, the SE acted negatively on the K_L, while B improved it overall. CONCLUSION: Better consideration is needed of the effect of biotic components in order to understand the phenomenon of G/L mass transfer in a TPPB. The behaviour of biomass growth and surfactants may strongly influence the mathematical models proposed in the literature. Copyright © 2009 Society of Chemical Industry     

Study of self-stratifying compositions

Paint applied as a single layer, and its spontaneous separation to form a primer and a top coat, is one of the newest concepts of the effective and economical application of two layers in one step. The influence of the molecular weight of epoxy oligomer and acrylic polymer and their ratio on self-stratification was investigated. The degree of stratification depending on molecular weight and their mutual ratio was determined using ATR-FTIR spectroscopy, differential scanning calorimetry, microscopy techniques, adhesion tests, and surface tension measurements. Phase separation and self-stratification of two-component homogenous mixtures were followed using FTIR technique and surface tension measurements. As a result of these investigations, optimal oligomeric/polymeric composition was selected. The obtained coating system showed good mechanical properties, gloss, and interlayer adhesion.     

AN ENERGY ANALYSIS OF BELT POLISHING PROCESS AND ITS APPLICATIONS TO TIME CYCLE AND TRACKING EFFECTS

Belt polishing is a fine machining process widely used to improve surface texture and to increase wear resistance and fatigue life. Despite the basics of this manufacturing process are not yet well understood, the cycle-time and the belt oscillations frequency are considered as fundamental process variables. In this article, their effects on the surface characterization and on the form aspects are investigated in connection with the principal physical mechanisms activated during the superfinishing operations (cutting, ploughing and sliding). With this aim, an energy approach of the belt polishing process, coupled with SEM observations of the abrasive belt, is introduced. Two belt polishing energetic regimes are identified and then discussed.