Mixed Reactants Research Articles

Computational study of epoxy-amine reactions.

Density functional theory calculations were carried out for the title reactions. Ethylene oxide and methylamine were adopted as reactants. Amine clusters (dimer, trimer, tetramer, and pentamer) were considered, because the combination of one oxide and one amine molecule gave a large activation energy. An amine tetramer was found to react favorably with the oxide via various zwitterionic intermediates. A back-side S(N)2 nucleophilic attack of one amine and the subsequent proton relay up to the front side provide a stabilized reaction field. The amine-alcohol mixed reactant may react readily with the oxide, because the alcoholic O-H group is in contact with the oxide oxygen with the strong hydrogen-bond stabilization.

Efficient mixing and reactions within microfluidic channels using microbead-supported catalysts.

A strategy for efficiently mixing solutions and carrying out multistep catalytic reactions in microfluidic systems is described. The approach involves immobilizing catalysts on microbeads, placing the beads into well-defined microreactor zones, and then passing reactants through one or more of the reactor zones to yield products. The catalyst-modified beads effectively mix reactants and increase the effective surface area of the channel interior, both of which improve reaction velocities compared to open channels. This approach is demonstrated using two sequential reactions catalyzed by glucose oxidase and horseradish peroxidase. In addition to providing a general route to chemical synthesis within microfluidic systems, this design strategy may also be applicable to modeling reaction pathways within cells and to bio/chemical sensing applications.

A solid-polymer electrolyte direct methanol fuel cell with a mixed reactant and air anode

A comparison of the performance of a solid-polymer electrolyte direct methanol fuel cell (SPE-DMFC) with aqueous methanol and air mixed at the anode, and with only aqueous methanol is presented. The performance of the mixed methanol reactant and air fed anode SPE-DMFC is superior to the conventional methanol only fed anode SPE-DMFC. The experimental performance of the mixed-reactant anode SPE-DMFC are compared with results of a numerical modelling based on phenomenological transport equations for electrocatalyst layer, diffusion layer and the polymer electrolyte membrane.

Solution-Phase Synthesis of Mixed Amide Libraries by Simultaneous Addition of Functionalities (SPSAF) to a Diketopiperazine Tetracarboxylic Acid Scaffold Monitored by GC Analysis of Isobutyl Alcohol

A symmetric diketopiperazine scaffold 2 has been prepared in a very simple two-step procedure from L-aspartic acid dimethyl ester. This product (a tetracarboxylic acid equally protected at the two symmetric positions) has been employed as a template for the synthesis of mixed amide libraries in the solution phase using the SPSAF (simultaneous addition of functionalities) strategy. By judicious choice of the amines employed, it is possible to prepare parallel libraries containing hundreds of products using just a small number of different amines. We have also developed a simple method for monitoring the required conversion of the acid into amides based on an assay of the amount of iBuOH (determined by GC) formed during the coupling mediated by isobutyl chloroformate. We have observed that a conversion higher than 90% (iBuOH by GC) guarantees correct formation of the desired amides. This indirect method for assessing the conversion in a combinatorial reaction employing mixed reactants (SPSAF) can conveniently be used for the routine determination of libraries prepared in the solution phase. In a broader perspective, the present results contribute as a further step in the development of new and simple systems for monitoring the progress and evolution of combinatorial reactions

Preparation and ferroelectric properties of strontium barium bismuth tantalate ceramics

The preparation and ferroelectric properties of layered ferroelectric barium-doped SrBi2Ta2O9 were investigated in this study. Pure layered perovskites were successfully synthesized when the mixed reactants were heated up to 900°C. The formation of solid solutions of barium-doped SrBi2Ta2O9 were confirmed. The addition of barium cations was found to substantially improve the sinterability of SrBi2Ta2O9, and resulted in densified specimens at low sintering temperatures. The degree of c-axis preferred orientation of the sintered specimens also increased with the increase in the barium content in SrBi2Ta2O9. This variation in the c-axis orientation was related to the morphological change of the grains in barium-doped SrBi2Ta2O9. The barium-doped specimens exhibited well saturated P-E loops and high remanent polarization.

Microwave Combustion Synthesis and Sintering of Intermetallics and Alloys

The high melting points and high-temperature stability of many intermetallics=alloys make them useful for high-temperature applications, especially for corrosion and oxidation resistance. Some intermetallics ®nd applications in wear components and oxidation barriers as well as reinforcing phases in many metallurgical systems, including superalloys. Intermetallics and alloys have been prepared by a variety of methods including casting, mechanical alloying, gas atomization, sintering, combustion synthesis, etc. In the combustion synthesis process (also called self-propagating high-temperature synthesis), two or several mixed reactants react exothermically in a self-sustaining manner, to form products due to the large difference in free energy and enthalpy between the product and reactants [1, 2]. In the conventional combustion process, reactants are ignited in a resistance furnace or by a hot ®lament or laser. The novelty of the present method is the use of microwave energy to initiate the combustion reaction between metals to form intermetallic compounds or alloys. Investigations in the area of microwave combustion synthesis previously were successful only for ceramics and composites [3]. A second novelty of this method is the sintering of metal±metal systems using microwaves. Microwave sintering of white ceramics with marginal success has been studied for two decades (see reviews in [4, 5]). Recently, in our laboratories, it was used in a new con®guration for sintering to essentially theoretical density translucency and even transparency of a wide range of ceramics: alumina, mullite, spinel, etc. [6, 7]. The earlier disputed question ` Is there microwave effect?'' has been de®nitively answered not only in the radically enhanced (one to two orders of magnitude) kinetics of sintering but the totally different reaction pathways for reactions such as BaCO3 ‡ TiO2 ! BaTiO3 ‡ CO2. So far, there have been no reports of metal±metal chemical reaction processes or sintering through solid-state or liquid-state diffusion using microwave energy, possibly because metals invariably cause plasma discharges within a microwave cavity and are therefore unsuitable for microwave synthesis and sintering. It was recently demonstrated in this laboratory [8], however, that a wide variety of compacted metal powders and ordinary commercial powder metal compacts can couple effectively with microwave ®elds and be synthesized or sintered at least as well as or better than conventional heating. This letter reports on the use of this new method for the preparation of intermetallics and alloys by combustion synthesis and sintering using microwave energy. Microwave heating is fundamentally different from conventional heating because all the energy is directed at the workpiece, as is also the case in laser processing. In microwave processes, the heat is generated internally through material±microwave interaction instead of originating from an externalheating source. This internal volumetric heating results in an energy diffusion that is reverse to the direction of those observed in conventional heating. As noted, the large body of work existing on microwave processing of polymer and ceramic materials has been summarized elsewhere [4, 5] but will be repeated here. For metal processing, as expected, there is almost no work. Even ®nely powdered metals do not couple well with microwave energy at room temperature. Walkievwicz et al. [9] reported that 25 g samples of powder of a half-dozen metals (Al, Co, Fe, etc.) exposed for 1 h in a 2.45 GHz cavity reached temperatures of 120±770 8C and showed no sintering. One US patent [10] refers to composites of metals and oxides being sintered in microwaves. We have demonstrated that microwave coupling ef®ciency of metals is greatly increased by increasing the temperature of the sample. This can be achieved by starting with a hybrid method in which an external susceptor is used to trigger the reaction, but we established that exactly the same result can also be achieved in a pure microwave system but with slower heating rates. Once the material is heated to a ` critical'' temperature, enhanced microwave absorption becomes suf®cient to cause self-heating, and the susceptors can be removed. As the temperature of material increases, the absorption of microwave energy by the material also increases. Extensive work on commercial powder metal samples [8] has established the experimental feasibility of sintering virtually all powder metal compacts. Our focus was on intermetallic synthesis and sintering. Stoichiometric and nonstoichiometric mixtures of metal powders in systems Ti±Al, Ni±Al, Fe±Al, Nb±Al, Ta±Al, Ge±Al, Cu±Al, Co±Al, Mo±Al, W±Al, Pt±Al, Pd±Al, Sb±Al, Zr±Al, Cr± Al, Nb±Ge, Ti±Ni, Ti±Co, Ti±Fe, Cu±Ti, Cu±Zn, Fe±Ni, Ni±Mg, Ni±Zr, Ti±Cu±Al, Cu±Zn±Al, Nb±Ti±Al, Nb±V±Al, Nb±Zr±Al, Ta±Al±Fe, Ni±

Combination of overall reaction rate with Gibbs energy minimization

A method to calculate multi-component chemical reaction mixtures as a sequence of time-dependent, intermediate thermochemical states is presented. The method combines the overall reaction kinetics with thermodynamic Gibbs energy minimization. The overall reaction is assumed to proceed according to the Arrhenius rate law. During the time-course of the reaction, the temperature and composition of the reaction mixture are calculated by a thermodynamic subroutine, which minimizes the Gibbs energy of the system. The extent of the overall reaction is algorithmically constrained in the Gibbs energy minimization procedure. During the sequential calculation, the kinetic condition is removed by finite differences. The temperature of each intermediate state is reached by an iterative procedure, which takes into account the heat transfer between the system and its surroundings and the enthalpy changes due to the chemical reactions. Thus, the method allows for the effect of temperature on the reaction kinetics as the reaction evolves. The chemical species present in each intermediate state are virtually independent and there is a chemical potential assigned to each of these species. The gradual chemical change in the thermodynamic system proceeds from the initial state of mixed reactants to the final state of product mixture. Both stationary and transient phenomena may be calculated. The method has been applied to some well-known industrial multi-component reaction systems and a fair agreement between the calculated and measured values has been obtained. The application of the thermochemical algorithm in reaction calorimetry is discussed.

Synthesis and characterisation of monomeric and dimeric 2-substituted η3-bonded butadienyl complexes of molybdenum(II)

Addition of excess thiol RSH ( R = Et, nPr, iPr, nBu or iBu ) to solutions of [MoCl(CO) 2( η 3-CH 2C(COCl)C=CH 2)(phen)] ( 1) (phen = 1,10-phenanthroline) gave good yields of the complexes [MoCl(CO) 2( η 3-CH 2C(COSR)C=CH 2)(phen)], containing a 2-substituted butadienyl ligand. On reaction of 1 with 1,2-ethanedithiol in 2:1 molar ratio under basic conditions, dimeric complexes were obtained containing two metal centres bridged by a pair of 2-substituted butadienyl groups linked by the dithiol unit. Analogous dimeric complexes containing linked amido η 3-butadienyl groups were isolated from a similar 2:1 reaction of 1 and diamines RHN(CH 2) 2NHR (R  H or Me). However, reactions involving 1 and mixed bifunctional reactants HA(CH 2) 2BH (A = NH, B = O, S or A = O, B = S) under the same conditions gave monomeric complexes exclusively, the less electronegative atom of the donor pair remaining unreacted.

Ignition and Flame Propagation in Methane-Air Multi-Stratified Vortical Flow Field

Abstract The objective of this study is to analyze the flame propagation under the interaction between fluid mechanics and chemical kinetics in a counter shear layer. First, a large-scale Kelvin-Helmholtz instability is triggered by initially-imposed linear perturbations to form a multi-stratified vortical layer. Second, mixed reactants in such a stratified vortex are ignited by local energy addition where flame propagation under the effect of instability is observed. Three different ignition locations are selected to examine combustion efficiency. The ignition in a vortex core shows a 1.7 times C02 productivity in comparison with the ignition in a braid region: The most advantageous ignition position for C02 productivity is the vortex core region where the mixture strength is high and the flammable mixture spreads rapidly. Once formed, a wrinkled diffusion flame propagates through the multi-stratified mixture, destroying the initially existing vortical structure. In addition, a Lewis number analysis in t...

メタン‐空気多重成層渦混合領域における点火及び火炎形成過程の物理

The objective of this study is to analyze the flame propagation under the interaction between fluid mechanics and chemical kinetics in a counter shear layer. First, a large-scale Kelvin-Helmholtz instability is triggered by initially-imposed linear perturbations to form a multi-stratified vortical layer. Second, mixed reactants due to such a stratified vortex are ignited where flame propagation under the effect of instability growth is observed. Three different ignition points are selected to examine combustion efficiency. The ignition point selected in a vortex core shows 1.7 times CO2 productivity in comparison with the ignition in a braid region: The most advantageous ignition point for CO2 productivity is the vortex core region where the mixture strength is high and the flammable mixture spreads rapidly. Once formed, a wrinkled diffusion flame propagates through the multi-stratified mixture, destroying the initially existing vortical structure. In the flamepassed region, the flame extinguishes due to dilution effect by products. In addition, Le number analysis in the vicinity of propagating flame shows flame instability and local extinction.

Synthesis of silica glass using solventless sol-gel process

Silica glass was synthesized form TEOS and deionized water using sol-gel process. To introduce the physicochemical effects of ultrasonic waves, an ultrasonic homogenizer was used to mix reactants instead of adding cosolvents. 2-step method was chosen to separate hydrolysis reaction and condensation reaction, and thus to control the microstructure of wet gels. Wet gels were dried in 5–8 hours without cracks using supercritical drying with ethanol at 300°C and 10.34 MPa. Aerogels thus obtained have hydrophobic surfaces due to the reesterification reactions during supercritical drying. Aerogels were sintered in a tube furnace in the changing atmosphere from N2 through O2 to He. Sudden volume change was started at 1050°C and sintering was completed at 1100°C as expected. Large pores of aerogels allowed fast sintering in 16 and a half hours. Incomplete extraction in supercritical drying step produced crystals during sintering.

反応性ガス圧燃焼合成による高密度複合材料の作成

Self-propagating high-temperature synthesis (SHS), also called as combustion synthesis, has advantages such as energy efficiency, simplicity, high reaction temperature and productivity.The TiAl-based composite materials containing TiB2 and Ti2AlN were combusion-synthesised within few seconds from the mixed reactants of Ti+(0.7-0.95)Al+(0.05-0.50)B under nitrogen gas atmosphere of 30-100atm. The combustion temperature exceeded the melting points of TiAl and Ti2AlN, and hence most parts of the composite was fused due to high reaction heat. The molten product was isostatically pressed by surrounding nitrogen gas. The products solidified were fully dense without cracks, which consist of homogeneous grains of -10μm due to rapid cooling after the SHS reaction. The use of pressurized reactive gas such as nitrogen was found to be very effective for simultaneous synthesis and consolidation of nitride ceramics-dispersed TiAl intermetallic compound.

Neutron radiography study in Tsinghua University : Mo Da-Wei; Liu Yi-Si; Guo Zhi-Ping; An Fu-Liu; Zhang Ghao-Zong; Miao Qi-Tian neutron radiography, proceedings of the second world conference, Paris (France), 16–20 Jun. 1986. pp. 87–94. D. Reidel Publishing Company

In vitro to in vivo extrapolation (IVIVE), an approach for hepatic clearance (CLH) prediction used worldwide, remains controversial due to systematic underprediction. Among the various probable factors, the original assumption of the hepatic mathematical model (i.e., the well-stirred model, WSM) may become problematic, leading to the underestimation of drug CLH. Having a similar prerequisite that the well-stirred conditions are homogenous with perfectly mixed reactants, but using a different driving concentration, the modified well-stirred model (MWSM) stands apart from the WSM. However, we believe that both models should coexist so that the entire well-stirred scenario can be completely illustrated. Consequently, we collected published data from the literature and employed a logistic regression method to differentiate the optimal timing of use between WSM and MWSM in drug CLH prediction. Generally, variances adopted in the regression, including partition coefficient (logP), fraction unbound (fu), volumes of distribution at steady-state (Vss), and mean residence time (MRT), corresponded to our assumption when protein-facilitated uptake was considered. Furthermore, a new empirical approach was introduced to allow practical use of the MWSM. The results showed that this model could provide a more precise prediction compared to previous empirical approaches. Therefore, these preliminary results not only delineated a more detailed structure and mechanism of MWSM but also highlighted its necessity and potential.

Selective molecular oxygen oxidation of thio ethers to sulfoxides catalyzed by cerium(IV)

The selective molecular oxygen conversion of thioethers to sulfoxides is catalyzed by ceric ammonium nitrate (CAN) with rate enhancements that are at least three orders of magnitude greater than the uncatalyzed autoxidation of thioethers. Mechanistic studies (including spectroscopic, labeling, uptake, mixed reactant, and autocatalysis studies) of this novel reaction reveal that both atoms of dioxygen are incorporated into product sulfoxide, that a novel oxygen-driven Ce(IV)Ce(III) redox cycle gives rise to the catalysis, and that molecular oxygen efficiently traps a sulfur-centered radial cation of the thioether (produced by Ce(IV) oxidation of thioether) to yield the oxygenated radical cation R/sub 2/S/sup +/OO/sup ./, which, it is proposed, reoxidizes Ce(III) to Ce(IV). The zwitterionic R/sub 2/S/sup +/OO/sup -/ intermediate (persulfoxide) reacts with thioether to yield two sulfoxide product molecules.

High-pressure self-combustion sintering of SiC from fine mixed powders of silicon and carbon

A dense β-SiC sintered body was fabricated using a new process, high-pressure self-combustion sintering (HPCS). By using this process, SiC can be simultaneously synthesized and sintered directly from mixed reactants of silicon and carbon without any sintering aids by initiating the exothermic reaction under high pressure. The conversion ratio to SiC was improved over 99% and the mean grain diameter in the compact could be reduced below 1μm when submicron fine powders of silicon and carbon were used as starting elements. The relative density, Vickers microhardness and fracture toughness were 92-93% of theoretical, 27GN/m2 and 4.5MN/m3/2 respectively.

Self-propagating high-temperature synthesis of the SiC

Self-propagating high-temperature synthesis (SHS), also called combustion synthesis, is useful for fabricating numerous ceramics. In the case of SiC, heat released from the exothermic reaction is not sufficient to completely convert the mixed reactants of constituent elements into SiC in the usual nonadiabatic experimental system. This disadvantage could be overcome by a new ignition process called, the “direct passing method of electric current.” By using this method, stoichiometric fine SiC powder could be obtained rapidly and efficiently with low electric power. This paper also involves the effect of particle size of Si and C initial reactant powders on conversion efficiency into SiC and also on particle size of SiC powder fabricated by this method.

Spectrometric rapid sampling/mixing system for analytical/clinical methods

A rapid sampling/mixing system has been designed which conforms to certain criteria necessary for its use as a clinical analyser. These include low solution volume (<100μl) for each determination on a sample, rapid cycle time (<2 sec to take an aliquot, mix and transfer reactants to an observation cell), good precision (reproducibility better than 0.2%), and ready automation (requiring only two electronic signals to perform a complete cycle). This device has been incorporated into an automated spectrophotometer to be used for a variety of clinical methods. Equilibrium methods for the determination of calcium and albumin are presented that require measurement times of only 6 and 7 sec, respectively. A reaction-rate procedure for total protein is presented that requires only 3 sec per sample. Precisions obtained with these procedures are typically better than 1% in the normal serum range. Results on samples from hospital patients are compared with values obtained on an SMA 12/60 instrument.

A stopped-flow dual-wavelength spectrophotometer suitable for the study of respiratory chains

The requirements for a dual-wavelength stopped-flow spectrophotometer to be suitable for studying limited quantities of respiratory-chain preparations are described. They can be met by a design using mainly commercially available components. The constructed apparatus has a dead-time of approx. 2.6 ms, a mixing ratio of 17:1, and a minimal requirement for 0.5 ml of mixed reactants per flow.