DISPERSION OF MATTER IN FLOW OF A BINGHAM PLASTIC IN A TUBE

The paper is concerned with the dispersion of a solute in a Bingham plastic fluid flowing in a pipe or a parallel plate channel. For pipe flow, the dispersion coefficient K₂ first increases with ξ₀ (the dimensionless radius of the plug flow region), reaches a maximum and then decreases. But in a channel flow, K₂ decreases monotonically with increasing ξ₀. Further K₂ for channel flow is found to be larger than that for pipe flow for all values of ξ₀ except 0.8≤ξ₀≤1.     

PRODUCTION OF SUB-MICROMETER SIZE O/W EMULSIONS USING A HIGH-PRESSURE WET-TYPE JET MILL

Emulsions composed of sub-micrometer size droplets were obtained by a high-pressure wet-type jet mill. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Droplet size distribution, Sauter mean diameter (d₃₂), geometric standard deviation of the droplet size distribution (σ_g), and emulsion viscosity (η_e) were investigated under the various combinations of process variables: dispersed phase volume fraction (Φ), dispersed phase viscosity (η_d), continuous phase viscosity (η_c), processing pressure, and number of passages through the wet-type jet mil. d₃₂ and σ_g were correlated with the process variables. For the entire experimental range, maximum droplet diameter was varied with d₃₂ in the range of 1.7-1.9-fold, and a correlation was proposed with K (=η_d/η_c) as a variable. Above a marginal value of d₃₂, at Φ ≥ 0.1, emulsions exhibited Newtonian behavior and could be described well by the Yaron and Gal-Or model. Below the marginal values, emulsions strongly depended on d₃₂ and exhibited a shear-thinning behavior. The relation between η_e and d₃₂ for such emulsions was modeled by use of particle Reynolds number.     

CHARACTERISTICS OF MICROMETER AND SUBMICROMETER SIZE O/W EMULSIONS PRODUCED BY RAMOND SUPERMIXER®

A novel motionless mixer named the Ramond Supermixer® (RSM®) was employed to produce O/W emulsions composed of micrometer and submicrometer-size droplets. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Pressure drop, droplet size distribution, Sauter mean diameter (d₃₂), and geometric standard deviation of the droplet size distribution (σ_g) were investigated under the various combinations of process variables; superficial liquid velocity, number of mixing units, number of passages through RSM®, dispersed phase viscosity (η_d), continuous phase viscosity (η_c), and dispersed phase volume fraction. Different modes of droplet size variations with process variables were obtained, with respect to micrometer- and submicrometer-size ranges, and theoretical explanations are forwarded. For the micrometer-size range, maximum droplet diameter (d_max) was proportional to d₃₂. For the submicrometer-size range, d_max varied with d₃₂ in the range of 1.53-2.19-fold, and a correlation is proposed with K (=η_d/η_c); d₃₂ and σ_g were well correlated with the process variables. Furthermore, a semi-empirical mechanistic model was developed for the formation of droplets obtained under inertial sub-range to interpret the effect of process variables.     

Correlation between equation of state and temperature and pressure dependence of self-diffusion coefficient of polymers and simple liquids

Correlation between the equation of state and the temperature dependence of the self-diffusion coefficient D for polymers such as polystyrene (PS) and polydimethyl siloxane (PDMS) and simple liquids such as argon, methane and benzene and the pressure dependence of D for oligomers such as dimethyl siloxane (DMS) and simple liquids such as cyclohexane and methanol has been examined based on the equation of state derived previously. The experimental data used were published by Antonietti et al. and McCall et al. for polymers, by McCall for linear dimethylsiloxanes and by Jonas et al. and Woolf et al. for simple liquids. The expression for D in this work is given by

where A₁(M) is a function of molecular weight M_w, C₁(T) and P₁(T) are functions of temperature and B₁, n₁ and m₁ are constants determined experimentally. For simple liquids, the values of n₁ obtained range from 0.3 to 1.2, with an average , and m₁ is in the range 0.5–1.2, with . For polymers, values of n₁ are in the range 2.5–7.0 for PS and 0.5–1.3 for PDMS and m₁ for DMS is in the range 0.8–1.0. The relation Dη/T = f(M) is found to be useful for simple liquids over a wide range of temperature including the critical region and for pressures up to ≈5 kbar

1 kbar = 100 MPa There is a close correlation between ln(D/T) and _p and β_T through ln(D/T)ln D_c−⁻¹_p−β⁻¹_T, where D_c is D at the critical temperature and _p and β_T are the thermal expansion coefficient and compressibility, respectively. The molecular weight dependence of D for polymers and simple liquids is discussed based on the experimental data and recent theory of Doi and Edwards. A new model for the mechanism of self-diffusion in the liquid state is proposed.     

The glass temperature of polymer blends

The entropy theory of glasses is used to derive the glass temperature, T_g, of a binary polymer blend in terms of the glass temperatures of the two substituents. The formula is T_g = B₁T_g1 + B₂T_g2, where B_i is the fraction of flexible bonds of substituent i. A bond is flexible if rotation about it changes the shape of the molecule. Bonds in side groups as well as in the backbone are to be counted. This formula assumes that the free volume, taken here to be the volume fraction of empty lattice sites, is the same for each of the three materials. It has no parameters. The above equation expressed in weight fractions, W_i, is (T_g − T_g1)W₁(γ₁/ω₁) + (T_g − T_g2)W₂(γ₂/ω₂) = 0, where ω_i is the weight of a monomer unit and gg_i is the number of flexible bonds per monomer unit. A more general treatment is given. One variation of the more general treatment which expresses the properties of the blend in purely additive terms gives T_g = B₁T_g1 + B₂T_g2 + KB₁B₂(T_g1 − T_g2)(V₀₁ − V₀₂), where V_0i are the free volume fractions of the homopolymers at their glass temperatures and K is a constant. The added term is usually small. The most general form of the equation requires the energy of interaction between the two unlike molecules, which can be estimated by volume measurements on the blend.     

三元体系NH4Cl+MgCl2+H2O 323.2 K相平衡研究

采用等温溶解平衡法开展了323.2 K时三元体系NH₄Cl+MgCl₂+H₂O的相平衡研究,测定了平衡固液相组成及密度,并绘制了该三元体系相图。研究发现：该体系323.2 K时有复盐NH₄Cl·MgCl₂·6H₂O生成,相图包含2个共饱点（F₁、F₂）、3条单变量曲线（AF₁、F₁F₂、F₂B）、3个结晶区（NH₄Cl、MgCl₂·6H₂O、NH₄Cl·MgCl₂·6H₂O）。对比该体系273.2、298.2、323.2 K时的相图可知：随着温度升高,NH₄Cl和MgCl₂·6H₂O结晶区变小,NH₄Cl·MgCl₂·6H₂O结晶区变大,同时NH₄Cl·MgCl₂·6H₂O由不相称复盐转变为相称复盐,对应的不相称共饱点转变为相称共饱点。     

The quadratic electrooptic effect and estimation of antipolarization in ADP

The quadratic electrooptic coefficients g₁₁₁₁ and g₂₂₁₁ have been measured interferometrically in ADP at room temperature. In addition, ‖g₁₁₁₁-g₂₂₁₁‖ was determined by a dynamic polarimetric technique at the same temperature. Both experiments yield values for g₁₁₁₁-g₂₂₁₁ at 21 C and λ = 0.633 μm with an average of (-5.9±0.5)×10^-20 m²/V². An estimate is made, using this value, of the spontaneous antipolarization appearing in the antiferroelectric phase of ADP. This antipolarization is found to be comparable in magnitude with the spontaneous polarizations observed in ferroelectrics belonging to the KDP family of crystals.     

Effect of ammonium polyacrylate on rheology of anatase TiO2 nanoparticles dispersed in silicon alkoxide sols

Ammonium polyacrylate (NH₄PA) was introduced into powdered mixtures consisting of anatase-structured TiO₂ nanoparticles and silicon alkoxide precursors at the sol level, and the rheological behavior of the mixtures was examined under various solid loadings (φ=0.05–0.13 in volumetric ratios), shear rates (  s⁻¹) and NH₄PA concentrations. The alkoxide precursors were mixtures of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄), ethyl alcohol (C₂H₅OH), H₂O and HCl in a constant [H₂O]/[TEOS] ratio of 11. The nanoparticle–sol mixtures generally exhibited a pseudoplastic flow behavior over the shear-rate regime examined. The NH₄PA appeared to serve as an effective surfactant which facilitates the suspension flow by reducing the flow resistance at low NH₄PA concentrations. At φ=0.10, a viscosity reduction ca. 85% was found at  s⁻¹ when the NH₄PA concentration was held at 2.5 wt.% of the solids. As the NH₄PA exceeded a critical level, e.g., [NH₄PA]≥3.0 wt.%, the NH₄PA acted as a catalyst which quickly turned the TiO₂–silica sol mixtures (φ=0.10) into a gelled structure, resulted in a pronounced increase of mixture viscosity. The maximum solids concentration (φ_m) of the mixtures was experimentally determined from a derivative of relative viscosity, i.e., (1−η_r^−1/2)–φ dependence. The estimated φ_m increased from 0.127 to 0.165 when NH₄PA of 0.5 wt.% was introduced into the TiO₂–silica sol mixtures.     

Secondary electron emission from CVD diamond films

Secondary electron emission from boron doped diamond polycrystalline membranes (hole concentration 5×10¹⁸ cm⁻³), prepared by microwave plasma assisted CVD, was investigated in both the reflection and transmission configurations. The model of secondary electrons behavior taking into account the distribution and diffusion mechanism of secondary electrons is proposed to explain the yield dependencies on primary electron energy in both configurations. The model predicts the SEE yield K=19 at the primary electron energy E₀ close to 1 keV for reflection configuration and K=3–7 at E₀=15–30 keV for transmission configuration for polycrystalline films used in the study. Experimental measurements of the SEE yield vs. primary electron energy (18 at E₀=950 eV for the reflection scheme and 3.5–4 at E₀=25 keV for the transmission one) are found to accord well with the theoretical results. Estimations, which were made using the model, show that SEE yield in transmission configuration can be increased up to 60 for the primary electron energy of about 10 keV. Since such high yields in transmission scheme may be obtained in monocrystalline membrane, another approach using porous polycrystalline diamond membranes is considered. Porous diamond membranes having SEE yield in transmission scheme of more than 10 at the primary electron energy E₀=1 keV were fabricated.     

Die abhängigkeit der Ah-Kapazität von Leclanché-trockenbatterien von der Zellenbelastung und Zellengeometrie

An attempt is made to show that a definite relation exists between the ampere-hours capacity of Leclanché cells, their discharge current strength and their cell geometry which is satisfactorily represented by the formula

Ah = Ah_max{1 - exp [-K₀(4πhRa)^1/2]}

Résumé

On essaye de démontrer qu'une relation simple existe entre la capacité en Ah d'éléments Lechlanché et du courant de décharge ainsi que de la géométrie de la cellule, qui est représentée d'une manière satisfaisante par la formule

Ah = Ah_max{1 - exp [-K₀(4πhRa)^1/2]}     

Low-temperature sintering of 0.85CaWO4–0.15LaNbO4 ceramics

Microwave dielectric properties of 0.85CaWO₄–0.15LaNbO₄ (CWLN) ceramics were investigated as a function of H₃BO₃, Li₂CO₃ content and sintering temperature. With the co-addition of 3.0 wt.% H₃BO₃–1.0 wt.% Li₂CO₃, the sintering temperature could be effectively reduced from 1150 °C for pure CWLN ceramics to 900 °C without any degradation of dielectric properties. These results are due to the enhancement of the sinterability of CWLN by liquid phase sintering. For the specimens with H₃BO₃–Li₂CO₃ sintered at 900 °C for 3 h, the dielectric constant (K) did not changed remarkably. However, the quality factor (Qf) and the temperature coefficient of resonant frequency (TCF) increased up to y = 1.0 of 3.0 wt.% H₃BO₃–y wt.% Li₂CO₃, and then decreased due to the formation of the secondary phases. Typically, K of 11.8, Qf of 45,200 GHz and TCF of −23.1 ppm/°C were obtained for the specimens of CWLN with 3.0 wt.% H₃BO₃–1.0 wt.% Li₂CO₃ sintered at 900 °C for 3 h.     

Grain growth in TiO2-added ZnO–Bi2O3–CoO–MnO ceramics prepared by chemical processing

The effect of TiO₂ on the grain growth of the ZnO–Bi₂O₃–CoO–MnO ceramic system prepared by chemical coprecipitation, was studied between 1150 and 1300 °C in air. Bi₂O₃ melts during firing, and then TiO₂ dissolves into Bi₂O₃-rich liquid. TiO₂ initially reacts with Bi₂O₃ to form Bi₄Ti₃O₁₂. Above ≈1050 °C, Bi₄Ti₃O₁₂ reacts with ZnO to form Zn₂TiO₄ spinel phase. The kinetic study of grain growth carried out using the expression Gⁿ–G_oⁿ=K_o·t·exp(−Q/RT) gave grain exponent (n) value as 6 and the apparent activation energy (Q) as 226.46 kJ/mol. 1.00 mol% TiO₂ addition increased the grain growth exponent value from 6 to 7 and apparent activation energy with 1.00 mol% TiO₂ addition was found to be 197.10 kJ/mol. The ZnO grain size gradually increases with increasing TiO₂ content. Addition of TiO₂ may increase the reactivity of the Bi₂O₃-rich liquid towards the ZnO grain, thus affecting the ZnO grain growth.     

The visible light induced photocatalytic activity of tungsten trioxide powders

The preparation, characterization and photoreactivity of tungsten trioxide powders are presented. Tungsten trioxide powders were prepared by air annealing of various W precursors. The effects of W precursor type and pretreatment conditions on the physical properties, and photocatalytic performance of the obtained WO₃ powders were examined. The photooxidation of water to oxygen and protons in the presence of reducible additives Ce⁴⁺, using the luminous and near IR illumination was used as a test reaction to evaluate the activity of the powders. Increasing annealing temperatures gave materials with a high degree of crystallinity and red-shifted the onset of light absorption. The light absorption of the obtained powders in the long wavelength region versus the type of the W precursor increased in the order: H₂WO₄<(NH₄)₆W₁₂O₃₉<(NH₄)₁₀W₁₂O₄₁. The level of crystallinity of the obtained powders increased in the order: (NH₄)₁₀W₁₂O₄₁≈(NH₄)₆W₁₂O₃₉2WO₄. The activity of the WO₃ powders depended on the type of W precursor used, annealing conditions, and the physico-chemical characteristics of the resulting powders. The activity according to the types of the W precursor increased in the order: (NH₄)₁₀W₁₂O₄₁<(NH₄)₆W₁₂O₃₉2WO₄. The activity as a function of annealing temperature and duration of W precursors goes through a maximum at 700–800°C and 4–8 h, respectively. Increasing the specific surface area of WO₃ powders, did not alter the activity significantly. Addition of 0.1–1% Pt and RuO₂ as co-catalysts improved the initial rates and long-term activity by about 1.3–1.5 times. Small amounts of hydrogen were also produced from photochemical reactions involving the photoexcitation of Ce³⁺.     

Crystal structures of fully dehydrated fully Sr-exchanged zeolite X and of its ammonia sorption complex

The crystal structures of fully dehydrated Sr₄₆–X [Sr₄₆Si₁₀₀Al₉₂O₃₈₄; a=25.214(7) Å] and of its ammonia sorption complex, Sr₄₆–X·102NH₃ [Sr₄₆Si₁₀₀Al₉₂O₃₈₄·102NH₃; a=25.127(7) Å], have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd at 21(1)°C. The Sr₄₆–X crystal was prepared by ion exchange in a flowing stream of aqueous 0.05 M Sr(ClO₄)₂ for 5 days followed by dehydration at 360°C and 2×10⁻⁶ Torr for 2 days. To prepare the ammonia sorption complex, another dehydrated Sr₄₆–X crystal was exposed to 230 Torr of zeolitically dried ammonia gas for 1 h followed by evacuation for 12 h at 21(1)°C and 5×10⁻⁴ Torr. The structures were refined to the final error indices, R₁=0.043 and R_w=0.039 with 466 reflections, and R₁=0.049 and R_w=0.044 with 382 reflections, for which I>3σ(I). In dehydrated Sr₄₆–X, all Sr²⁺ ions are located at two crystallographic sites. 16 Sr²⁺ ions are at the centers of the double six-rings, filling that site (site I, Sr–O=2.592(6) Å). The remaining 30 Sr²⁺ ions are in the supercage (site II); each extends 0.56 Å into the supercage from the plane of its three nearest oxygen atoms (Sr–O=2.469(6) Å). In the structure of Sr₄₆–X·102NH₃, the Sr²⁺ ions are located at three crystallographic sites: 12 are found at site I [Sr–O=2.652(10) Å]; four in the sodalite units (site I′) each coordinated to three framework oxygen atoms at 2.654(9) Å and also to three ammonia molecules at 2.76(8) Å. The remaining 30 Sr²⁺ ions lie at site II. Each extends 1.12 Å into the supercage where it coordinates to three framework oxygen atoms at 2.584(7) Å and also to three ammonia molecules at 2.774(24) Å.     

Ba2+、MoO42-掺杂对NaCaPO4：Eu3+荧光粉发光性能的影响研究

为提高红色荧光粉的发光强度和色纯度,以硝酸钙、硝酸钠、硝酸铕、磷酸二氢铵、钼酸铵、硝酸钡为原料,采用高温固相法合成了NaCa_1-xPO₄：xEu³⁺、NaCa_1-x（PO₄）_1-y（MoO₄）_y：xEu³⁺、NaCa_1-x-zPO₄：xEu³⁺,zBa²⁺系列红色荧光粉。探讨了Eu³⁺单掺杂和Eu³⁺/MoO₄^2-、Eu³⁺/Ba²⁺共掺杂对荧光粉发光性能的影响。用X射线衍射（XRD）、荧光分光光度计、色坐标等对荧光粉的结构进行表征。研究结果表明：掺杂Eu³⁺、MoO₄^2-、Ba²⁺后NaCaPO₄晶系没有发生变化,但是晶胞参数发生了变化,说明Eu³⁺、MoO₄^2-、Ba²⁺进入NaCaPO₄晶格中。在393 nm紫外光激发下,荧光粉发射光谱图出现两个Eu³⁺比较强的特征发射峰,分别属于Eu³⁺的⁵D₀→⁷F₁和⁵D₀→⁷F₂跃迁。与单掺杂16%Eu³⁺荧光粉相比,共掺杂16%Eu³⁺/3%MoO₄^2-或16%Eu³⁺/6%Ba²⁺荧光粉的发射光谱中⁵D₀→⁷F₂跃迁产生的发射峰强度均高于单掺杂16%Eu³⁺荧光粉的发射峰强度,其⁵D₀→⁷F₂与⁵D₀→⁷F₁发射光强度之比（R）分别为1.76（R_Mo）和1.28（R_Ba）,都大于单掺杂16%Eu³⁺荧光粉的R_Eu（0.99）,共掺杂Eu³⁺/MoO₄^2-荧光粉的色纯度比单掺杂Eu³⁺和共掺杂Eu³⁺/Ba²⁺荧光粉的色纯度更好。     

Kinetics of the selective catalytic reduction of NO by NH3 on a Cu-faujasite catalyst

The kinetics of the selective catalytic reduction (SCR) of NO by NH₃ in the presence of O₂ has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<T_R<513 K, 2503 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O₂, and essentially 0 with respect to NH₃. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH₃ was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) Cu^I is oxidized by O₂ to “Cu^II-oxo”, (ii) “Cu^II-oxo” reacts with NO to yield “Cu^II-N_xO_y”, and (iii) finally “Cu^II-N_xO_y” is reduced by NH₃ to give N₂, H₂O, and the regeneration of Cu^I (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that Cu^I or “Cu^II-oxo” species constitute the rate-determining active center.     

The breaking strength of imperfect (real) polymer fibers

The thermodynamic fusion theory of strength of perfect polymer fibers of finite molecular weight is extended to include imperfect (i.e. real) fibers of incomplete crystallinity and orientation. Approximate equations for failure strength, strain, and work of failure are derived by extracting from the real visco-elastic fiber an equivalent reversible component suitable for thermodynamic analysis. This is facilitated by an explicit relationship between fiber breaking stress, σ_*, and breaking strain, _*, which is shown to be σ_*=0.632K_* (K=modulus) for constant strain-rate deformations. It is shown that fiber breaking time is equivalent to the fiber visco-elastic mechanical relaxation time. Experimental data shows that the activation energy of rupture of polyethylene fibers is not the activation energy of covalent bond rupture. Instead it agrees with the activation energy expected of crystal melting in accordance with the fusion theory of rupture. The activation volume of the polyethylene fibers also agrees with the value expected from this theory.     

Walden product, ion-solvent interactions and solvent structure in water-rich mixtures ionic conductances in water-sulfolane, water-acetonitrile and water-dimethylsulfoxide

Conductance measurements are reported for several salts in binary aqueous mixtures containing up to 60 mole % sulfolane, 20 mole % acetonitrile and 20 mole % dimethylsulfoxide. The variations of R = (λ^±₀η₀)_s/(λ^±₀η₀)_w with solvent composition have been compared with those observed in other water-rich mixtures. Alkali cations show R values greater than one with maxima in all the solvent mixtures. This behaviour has been discussed in terms of “sorting”, “averaging” and “steric” effects. Contrary to what happens to alkali cations, halide ions show R values greater or lesser than one according to whether the organic solvent respectively increases or decreases water structure. On these bases we suggest that conductometric behaviour of the halide ions may be indicative of the effect of the cosolvent on the water structure in water-rich mixtures and that DMSO is a water structure breaker.     

Comparison of parameters calculated from the BET and Freundlich isotherms obtained by nitrogen adsorption on activated carbons: A new method for calculating the specific surface area

The empirical linear relationship between the BET surface area S_BET and the Freundlich constant K_F, calculated from nitrogen adsorption isotherms of activated carbons, S_BET = a₀K_F is mathematically demonstrated. This correlation exists in the relative pressure domain in which the BET equation is valid, whatever the value of c for the BET equation and for values of the Freundlich exponent, , between 0 and 0.2. This study allows to determine the correlation factor a₀ = 1/a with . From this result, a new expression, depending of and K_F, can be deduced for calculating the specific surface area.