Free convection mass transfer at horizontal electrodes

The free convection mass-transfer behaviour of upward-facing horizontal surfaces has been investigated experimentally using an electrochemical technique involving the measurement of limiting currents for the deposition of copper on copper electrodes from acidified cupric sulphate solutions. The data are well correlated by the equations

Sh = 0·64(Sc . Gr)^0·25 for 3 × 10⁴ < ScGr < 2·5 × 10⁷ and

Sh = 0·16(Sc . Gr)^0·33 for 2·5 × 10⁷ < ScGr < 10¹². Electrode diameters varied between 0·1 and 12 cm and cupric sulphate concentrations between 0·01 and 0·3 M.

The data compare favourably with previous experimental results for the corresponding heat-transfer case.     

Upper and lower critical solution temperatures in polyethylene solutions

Upper and lower critical solution temperatures have been determined for solutions of polyethylene in n-butyl acetate and n-amyl acetate over the molecular weight range of M_η = 1·36 × 10⁴ to 17·5 × 10⁴. Polyethylene solution in n-butyl acetate displays a smaller miscibility region than that of the polyethylene/n-amyl acetate system, as indicated by the relative positions of their upper and lower critical solution temperatures. Contributions of the energy and the equation of state terms to the χ1 parameter have been examined by an application of the Patterson-Delmas corresponding state theory to the experimental results of the polyethylene solutions.     

ABSORPTION OF H2S INTO AQUEOUS METHYLDIETHANOLAMINE

The absorption of H₂S into aqueous methyldiethanolamine (MDEA) was studied experimentally over the temperature range 15 to 35°C and for MDEA concentrations from 10 to 25 wt% using a laminar liquid jet device and a stirred-cell absorber. The contact times ranged from 2 × 10^-3 to 1 × 10^-2 seconds for the jet absorber and from 6 to 38 seconds for the stirred-cell absorber. It was found that the absorption rate data for both devices could be modelled assuming an instantaneous reaction regime for the reaction between H₂S and MDEA. The experimental results were interpreted to give an estimate for the diffusion coefficient of MDEA in water. Diffusion coefficient results are consistent for the two apparatuses. A lower bound for the second-order rate constant for the reaction between H₂S and MDEA is estimated from the experimental data to be 1.4 × 10¹⁰cm³/g mole s at 25°C     

The Anisotropy of the Surface Tension of Polar Liquids: The Case of Liquid Crystals

The contact angle of the liquid crystal (LC) 4-phentyl, 4'-cyano biphenyl (5CB) on glass or polyethylene does not correspond to the value expected from its surface tension measured by the “du Nouy” method (29 × 10^-3 JM^-2). The value deduced from the Young-Dupre law is 40 × 10^-3 JM^-2.

Both these values have already been reported in the literature. Their apparent discrepancy is explained by the LC surface tension anisotropy. We show that 5CB as many other LCs orient perpendicular to the free surface but parallel to glass or polyethylene Thus both values of the surface tension correspond to two different molecular orientations.

The LC oriented perpendicularly has a surface tension of 29 × 10^-3 JM^-2 and 40 × 10^-3 JM when it lies parallel to the surface. We suggest that the anisotropy between the perpendicular and parallel state of LCs also exists between two perpendicular orientations. Furthermore, such anisotropy associated with any polar molecules explains the difference of the interfacial energy of similar polar or non polar (i.e., octanol-octane) compounds and water.     

MUCT工艺处理生活污水短程脱氮的实现及硝化菌群动态变化

采用连续流MUCT工艺处理实际生活污水,研究短程生物脱氮的实现,并采用实时荧光定量PCR方法(quantitative real time PCR,QPCR)分析全程脱氮向短程脱氮转变过程中氨氧化细菌(ammonia-oxidizing bacteria,AOB)和亚硝酸盐氧化菌(nitrite-oxidizing bacteria,NOB)的动态变化。通过降低溶解氧浓度为0.5mg·L^-1和缩短水力停留时间为6h,实现短程硝化,亚硝酸盐积累率达到90%。在短程硝化稳定运行阶段总氮去除率高达90%以上,远远大于全程阶段的74%。QPCR结果表明全程脱氮阶段水力停留时间的缩短使AOB细胞数呈现下降的趋势,NOB细胞总数稳定维持在10⁸cells·(g dried sludge)^-1。短程脱氮阶段,AOB细胞数小幅度上升,由3.17×10⁶cells·(g dried sludge)^-1增长到1.32×10⁷cells·(g dried sludge)^-1,同时AOB占全菌的比例也小幅度增长。NOB的细胞数在5.9×10⁷~1.78×10⁸cells·(g dried sludge)^-1之间波动。NOB占全菌的比例由1.44%下降到0.47%。因此,MUCT工艺处理实际生活污水的系统中NOB丰度降低及活性抑制是实现并维持短程生物脱氮的重要原因。短程脱氮运行期间由于控制低溶解氧浓度和短的水力停留时间,AOB丰度及相对含量没有显著增加,甚至下降,但不会影响氨氮和总氮的去除。     

Interpenetrating polymer networks of poly(dimethylsiloxane): 1. Preparation and characterization

Model networks of ,ω-dihydroxy-poly(dimethylsiloxane) (PDMS) were prepared by tetrafunctional crosslinking agent tetraethyl orthosilicate (TEOS) and the catalyst stannous 2-ethylhexanoate. Hydroxylterminated chains of PDMS having molecular weights 15 × 10³ and 75 × 10³ g mol⁻¹ were used in the crosslinking reaction. Bimodal networks were obtained from a 50% (w/w) mixture of PDMS chains with M_n = 15 × 10³ and 75 × 10³ g mol⁻¹. A sequential interpenetrating network of these PDMS chains was also prepared. Physical properties of the elastomers were determined by stress-strain tests, swelling and extraction experiments, and differential scanning calorimetry measurements.     

Ferroelectric Pb5-xBix (Ge.Si)3-xBxO11 single crystals as a material for IR radiation detectors

The coupled substitution of Bi³⁺ for Pb₂₊ and B³⁺ for Ge⁴⁺ was successfully achieved in ferroelectric Pb₅Ge₃O₁₁. Large single crystals of optical quality were grown from the melt. Deterioration of the crystal quality could not be observed within a period of two years under ambient conditions. The dielectric permittivity ε_r, electric conductivity p and pyroelectric coefficient γ are investigated as a function of temperature. The room temperature data (εr = 43, γ = 2.4·10^-4Cm^-2 K^-1, p = 7·10⁷ Ω, volume specific heat s = 2·10⁶ Jm^-3K^-1) show the usefulness of Pb_5-xBi_xGe_3-xB_xO₁₁ around x = 0.1 as a material for pyroelectric thermal detectors operating at room temperature. Also the difficulty of producing lead germanate silicate mixed crystals in the size and quality needed for vidicon applications is overcome by additional replacement of some Pb and Ge by Bi and B.     

Mass transfer by free convection at horizontal electrodes

Limiting currents were measured in an unstirred cell at horizontal cathodes facing upward. Electrolyte composition ranged from 0·01 to 0·7 M CuSO₄ in 1·5 M H₂SO₄. Cathode sizes varied from 0.1–30 by 10 cm, and the free height above the electrode from 1–16 cm. Limiting currents for deposition of copper ranged from 0·68–129 mA/cm². For electrode width larger than 20 mm the data is well represented by the general correlation

Nu′ = 0.19 (Sc. Gr) , where Nu′, Sc, and Gr are the Nusselt number for mass transfer, the Schmidt, and Grashof numbers, respectively. The experimental range used in the correlation included 10⁸ < (Sc. Gr) < 1·4 × 10¹² The results indicate that the boundary layer is turbulent, as it is in the case of the analogous heat-transfer model.     

TRANSITION TO ANNULAR FLOW IN TWO-PHASE, TWO-COMPONENT VERTICAL FLOW: EXAMINATION OF CORRELATIONS

The available empirical, semi-empirical and analytical correlations and flow pattern maps for predicting the transition to annular flow in upward, two-phase, gas-liquid flow in a vertical tube were tested against a large set of experimental data. These experimental data were taken on the same rig through an observation section (i.d. = 11.7 mm, L = 30.5 cm), preceded by a heated test section ( L/D≃ 52) and a calming length (L/D = 130), all having the same inside diameter as that of the observation section. The total range of variables covered by these data is: 2≤Re_SL≤ 1.3 × 10⁵, 5.6 ≤Pr_L≤ 7000, 0.01 V_SG/V_SL ≤ 7900, 2 × 10^-4≤ρ_G/ρ_Ls0.01, and 19.7 × 10^-3≤ σ ≤72× 10^-3N/m. In total, fifteen correlations and flow-pattern maps were tested with eight liquid-gas combinations covering a very wide range of fluid properties and mass flow rates of both phases. Using the Kutateladze number as the criterion for the transition appears to provide an excellent separation particularly when a lower value than 3.1, as suggested in the model of Taitel et al. (1980) is used (between 1.5 and 2.0). Also using the Weisman and Kang (1981) correlation, the Wallis parameter and the void fraction criteria of Mishima and Ishii (1984) were quite successful in correlating the data.     

Influence of Edible Films upon the Moisture Loss and Microstructure of Dietetic Sucrose-Free Sponge Cakes during Storage

The kinetics of changes in the bound water content in dietetic sucrose-free sponge cakes (DC) during storage was investigated. The effect of edible films of polymyxan, pectin, xanthan, and carboxymethylcellulose upon this kinetics was also investigated. The quantitative changes in both states of water (slightly bound water and strongly bound water) were registered by combined dynamic analysis (thermogravimetry analysis, TGA, and differential thermal analysis, DTA). The moisture changes in DC crumb were analyzed by drying out to constant mass. The rate constants were determined according the equation q = q_oe^-kt. The values of rate constants 'k', in day^-1, concerning the different edible films were as follows: for crumb moisture is (8.00 ≤ k ≤ 12.47) × 10^-3, for bound water is (3.07 ≤ k_w ≤ 6.26) × 10^-2, for slightly bound water is (4.22 ≤ k₁ ≤ 8.49) × 10^-2 and for strongly bound water is (2.02 ≤ k₂ ≤ 5.62) × 10^-2 as compared to 18.53 × 10^-3, 7.16 × 10^-2, 9.04 × 10^-2, and 5.36 × 10^-2 in the uncovered DC, respectively. The best water-retaining effect in respect to crumb moisture during storage was ascertained in the use of polymyxan and xanthan films. The lowest rate constant values for bound water and its two states were measured for DC covered with pectin. The relation between the kinetics of both bound water states during storage and ageing of the crumb of DC covered with different edible films and the crumb microstructure was represented. By means of scanning electron microscope was read the smallest change in crumb microstructure of pectin-covered DC on the sixth day of storage.     

Magnetic-field dependence of the soft-mode frequency in KTaO3 AT 20K

The change in the soft-mode frequency in single-crystal KTaO₃ with magnetic field was measured at 20.1K via dielectric measurements using the Lyddane-Sachs-Teller relation. At 10T, the change in the soft-mode frequency is ∼-0.2%. Converted to shifts in the Curie temperature with magnetic field, the data indicate that T₀(H)-T₀(0) ∼ 5×10^-4H² + 7.5×10^-6H⁴ (H in Tesla). These data are consistent with recent neutron measurements on SrTiO₃ and dielectric measurements on BaTiO₃.     

刚玉型复合氧化物催化剂Cr1.3Fe0.7O3上二氯甲烷催化燃烧

通过溶胶-凝胶法合成一系列具有刚玉结构的Cr_(1.3)Fe_(0.7)O_3复合氧化物,在二氯甲烷催化燃烧反应中进行活性评价。结果表明,复合氧化物比单金属氧化物CrO_x和FeO_x具有更高的催化活性,其催化活性与氧化物的表面酸性和可还原性密切相关,二者在反应中协同作用。与高温焙烧样品相比,低温焙烧的Cr_(1.3)Fe_(0.7)O_3催化剂具有更高的比表面积、表面酸性和可还原性,催化性能更优。以表面酸性位数量为基础计算的催化剂转化频率(TOF)表明,各Cr_(1.3)Fe_(0.7)O_3催化剂活性相近(300℃时约2.3×10~(-3) s~(-1)～2.8×10~(-3) s~(-1)),表面酸性位上发生二氯甲烷分子吸附及C-Cl键断裂,是反应活性位。300℃时Cr~(6+)的TOF为9.3×10~(-3) s~(-1),Cr~(3+)的TOF为0.59×10~(-3) s~(-1),Cr~(6+)物种比Cr~(3+)物种具有更高的活性。     

Dilute solution properties of carboxymethylchitins in high ionic-strength solvent

The hydrodynamic characteristics in aqueous solution at ionic strength I=0.2  of carboxymethylchitins of different degrees of chemical substitution have been determined. Experimental values varied over the following ranges: the translational diffusion coefficient (at 25.0°C), 1.1<10⁷×D<2.9 cm² s⁻¹; the sedimentation coefficient, 2.4<s<5.0 S; the Gralen coefficient (sedimentation concentration-dependence parameter), 130<k_s<680 mL g⁻¹; the intrinsic viscosity, 130<[η]<550 mL g⁻¹. Combination of s with D using the Svedberg equation yielded ‘sedimentation–diffusion' molecular weights in the range 40 000<M<240 000 g mol⁻¹. The corresponding Mark–Houwink–Kuhn–Sakurada (MHKS) relationships between the molecular weight and s, D and [η] were: [η]=5.58×10⁻³ M^0.94; D=1.87×10⁻⁴ M^−0.60; s=4.10×10⁻¹⁵ M^0.39. The equilibrium rigidity and hydrodynamic diameter of the carboxymethylchitin polymer chain is also investigated on the basis of wormlike coil theory without excluded volume effects. The significance of the Gralen k_s values for these substances is discussed.     

基于邻二氮菲-Fe2+的间接显色光度法检测片剂中的卡托普利

卡托普利还原Fe³⁺,Fe²⁺与邻二氮杂菲显色物在510 nm处有最大吸收,吸光度(A)与卡托普利浓度有相关性。结果表明,卡托普利浓度(c)在1×10^-6~1×10^-4 mol/L范围内与A呈良好的线性关系:y=0.006 4c+0.005 5,相关系数(r)=0.997 6,检测限为9.37×10^-7 mol/L。该方法用于片剂卡托普利测定,结果满意。     

Fe(Ⅱ)活化过硫酸盐氧化破解剩余污泥

采用 Fe(Ⅱ)活化过硫酸盐,产生强氧化性硫酸根自由基(SO₄^-·),以污泥释放的溶解性COD(SCOD)、相对疏水性(RH)和污泥比阻(SRF)为表征,考察了SO₄^-·氧化破解剩余污泥强化脱水的影响因素,并解析了机理。结果表明:当初始pH为4.5,n(S₂O₈^2-)=2.2 mmol·(g VSS)^-1,n(Fe²⁺)=1.32 mmol·(g VSS)^-1,常温下反应3 h后,SCOD由66.5 mg·L^-1增加到472.3 mg·L^-1,RH由26.9%升高到41.1%,SRF由24.9×10⁸ S²·g^-1降低至4.5×10⁸ S²·g^-1;在此基础上利用响应面法,根据Box-Benhnken中心组合试验设计,以SRF为响应指标,优化条件为pH 4.27,n(S₂O₈^2-)=2.6 mmol·(g VSS)^-1,n(Fe²⁺)=1.59 mmol·(g VSS)^-1时,SRF为3.8×10⁸ S²·g^-1,泥饼含水率为72.7%。镜检发现,破解后污泥变为颗粒碎片状;傅里叶红外光谱显示污泥表面官能团对应的特征吸收峰强度有一定程度的减弱;热重分析表明无明显物理吸附水失重区。证实了在SO₄^-·作用下,污泥菌胶团结构破坏,溶胞释放了有机物,使表观疏水性更强,与水结合力明显减弱,脱水性得到了较大提高,有利于污泥减量化应用。     

Reverse thermopolarization effects in dielectrics

The reverse thermopolarization effect in dielectrics manifested by a appearance of a temperature difference δ between the opposite sides of charging and discharging capacitors was observed. A capacitor of PbMg_1/3Nb_2/3O₃ (PMN) crystals was charged by applying an electric field of E = 10⁶V/m with a time constant. ≃ 10^-5s. The temperature difference δ amounted ≃ 10^-4K at 293 K. The thermal and electric field dependencies of this effect were investigated too. The analysis of the generalized Peltier effect at the boundary of two arbitrary materials shows that the experimental results can be considered as a “dielectric Peltier effect”.     

ABSORPTION OF CARBON DIOXIDE WITH A FREELY FALLING AQUEOUS SODIUM HYDROXIDE SOLUTION DROP

Measurements for the rates of absorption of carbon dioxide from carbon dioxide-air mixtures with a water and an aqueous sodium hydroxide solution drop falling freely were made for Fourier number Fo = 1.53 · 10^-5 — 9.83 × 10^-5, initial concentration of aqueous sodium hydroxide solution C_BO — 0.05 — 0,4 mol/1 and feed gas concentration of carbon dioxide y = 0.05 — 1.0. Observed dimensionless rates of absorption were compared with the theoretical values by the present model and gave a good agreement with theory. The effect of drop diameter on the enhancement factor, which is a measure of the effect of chemical reaction on the rates of absorption of carbon dioxide with a freely falling alkaline solution drop, were also discussed by using numerical simulation     

（C5H7N2O2）4（SiMo12O40）的合成、结构及催化氧化碘离子研究

采用常规水溶液法合成了一种新型的有机-无机杂化多金属氧酸盐（C₅H₇N₂O₂）₄（SiMo₁₂O₄₀）（简称SiMo-12）。采用红外光谱（IR）、热重分析（TG）、单晶和粉末X射线衍射（XRD）、元素分析等对SiMo-12进行了表征。以过氧化氢为氧化剂,运用SiMo-12催化碘离子氧化,考察了催化剂用量、氧化剂用量、pH、温度等因素对反应速率的影响。结果表明：该化合物属三斜晶系,P-1空间群,晶胞参数a=1.097 58（4） nm、b=1.144 88（4） nm、c=1.252 66（4） nm、α=64.665（1）°、β=64.804（1）°、γ=83.441（1）°、V=1.282 89（8） nm³、Z=1、R=0.034 0、wR₂=0.079 9。化合物由4个1-咪唑乙酸和一个经典的Keggin型[SiMo₁₂O₄₀]^4-单元组成,有机配体和多金属氧酸阴离子之间通过静电作用、质子转移以及氢键作用沿x轴形成一维链,链与链之间相互平行形成平行于xy面的二维层,层与层之间再通过氢键连接而得到三维网状结构。SiMo-12在催化碘离子氧化中表现出较为优异的催化活性,在c（SiMo-12）=2.0×10^-4 mol/L、c（过氧化氢）=2.0×10^-3 mol/L、pH=1.4、50 ℃条件下反应速率达到2.641 6×10^-5 mol/（L·s）,比未加催化剂时的反应速率提高了1 565倍。     

Al2O3含量对PbO-CaO-B2O3-SiO2系玻璃析晶行为与烧结性能的影响

PbO-CaO-B₂O₃-SiO₂系玻璃粉体是耐高过载低温共烧陶瓷(LTCC)生瓷带的主要组成部分。玻璃粉体的析晶行为影响烧结性能,进而决定基板的使用性能。本文研究了Al₂O₃含量对PbO-CaO-B₂O₃-SiO₂系玻璃析晶行为与烧结性能的影响。结果表明:向PbO-CaO-B₂O₃-SiO₂系玻璃中引入Al₂O₃可抑制玻璃析晶,防止高膨胀晶相的析出,并提高玻璃烧结密度;不含Al₂O₃的PbO-CaO-B₂O₃-SiO₂玻璃粉体析晶峰温度为862 ℃,烧结过程中析出方石英晶相,20~200 ℃的平均线膨胀系数高达260.8×10^-7 ℃^-1;引入2.1%(质量分数)Al₂O₃可显著抑制玻璃析晶,700 ℃烧结后膨胀系数降低至72.9×10^-7 ℃^-1,介电常数显著增大,由6.30提高至7.02。     

驱油用化学法丙烯酰胺的杂质控制

丙烯酰胺作为驱油用聚丙烯酰胺的主要合成原料,其质量直接影响高品质聚合物的生产。利用超高分子量聚丙烯酰胺合成技术,研究化学法丙烯酰胺中杂质对聚合反应和聚丙烯酰胺产品质量的影响,总结杂质的影响规律,确定杂质影响的临界量。结果表明,当化学法丙烯酰胺中杂质浓度超过某临界量后会加快聚合反应速度,降低聚合物分子量;杂质含量应控制为Cu~(2+)≤0.1×10~(-6)、丙烯腈≤30×10~(-6)、羟基丙腈≤300×10~(-6)、氮基三丙酰胺≤120×10~(-6)、Fe~(3+)≤0.2×10~(-6)。研究离子交换树脂在不同精制路线下的除杂效果,结果表明,离子交换树脂对Cu~(2+)去除效果明显,且强酸强碱型树脂精制效果优于弱酸弱碱型树脂,阳离子、阴离子和混合树脂串联精制路线得到的丙烯酰胺产品电导率更低,活性更高。