焊铝合金用IGBT交流矩形波弧焊逆变器

本文介绍了新型开关元件ＩＧＢＴ管作为逆变开关元件的交流矩形波逆变器的原理。并通过实验证明，该电源具有良好的引弧和稳弧性能，在铝合金焊接方面具有较好的工艺性能。     

A new approach to the mechanism of chlorine evolution: Separate examination of the kinetic steps using ac impedance on a rotating thin ring electrode

In the absence of a bulk diffusion effect, it is shown for the first time that the impedance spectra for the chlorine evolution reaction on a rotating thin ring electrode comprise three consecutive semicircles in the capacitive half of the complex plane. The first (highest frequency) semicircle is due to the charge-transfer resistance for chloride discharge and the simultaneous chlorine adsorption coupled to the double-layer capacitance. The second semicircle (around 5 Hz) is due to the adsorption and desorption of a chlorine intermediate. The third (lowest frequency, around 0.5 Hz) semicircle is due to the relaxation of surface oxygen species. The impedance data allow the steps of the overall reaction to be examined individually. On a Pt surface the rate of chloride discharge and simultaneous chlorine adsorption (the admittance of the first semicircle) is first order with respect to chloride concentration and has a potential-dependence close to 58 mV/decade. The rate of the adsorption and desorption process (the admittance of the second semicircle) is second order with respect to chloride concentration, and has a potential dependence close to 30 mV/decade. The time constant for the adsorption/desorption processes is ca 20 ms, independent of electrode potential in the range studied. These features are consistent with a mechanism in which a faster discharge reaction (Cl⁻ Cl_ad + e) is followed by a slower surface combination reaction (2Cl_ad → Cl₂), but inconsistent with mechanisms in which ion + atom desorption is predominant, the initial chloride discharge is slow, or a unipositively charged chlorine species is involved.     

Structural and magnetic properties of Co1+ySnyFe2-2y-xCrxO4 ferrite system

The samples of the series Co_1+ySn_yFe_{2- 2y- x}Cr_xO₄ ferrites with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and y = 0.05, were prepared by the usual double sintering ceramic technique. The single- phase spinel structure of the samples was confirmed by using X- ray diffractometry technique. The lattice parameter ’a’ with an accuracy of ± 0.002 Å were determined using Bragg peaks of XRD pattern. The lattice parameter ’a’ decreases with concentration, x, which is due to the difference in the ionic radii of Cr³⁺ and Fe³⁺ ions. The X- ray intensity calculations were carried out in order to determine the possible cation distribution amongst tetrahedral (A) and octahedral [B] sites. The X- ray intensity calculations show Cr³⁺ ions occupying B site. The saturation magnetization, σ_s, and magneton number, n_B (the saturation magnetization per formula unit), measured at 300 K determined from high field hysteresis loop technique decrease with increase in concentration, x, suggesting a decrease in ferrimagnetic behaviour. Thermal variation of low field a.c. susceptibility measurements from room temperature to about 800 K exhibits almost normal ferrimagnetic behaviour and the Curie temperature, T_C determined from a.c. susceptibility data decreases with increase in x.

     

Latchkey children and susceptibility to peer pressure: An ecological analysis.

Data on adolescents' after-school experiences and their susceptibility to peer pressure were derived from surveys administered to a heterogeneous sample of 865 adolescents in Grades 5–9. Consistent with the findings of previous studies, the results show that Ss who reported home after school were not significantly different from those who were supervised by their parents at home during after-school hours. However, when a 2nd sample of latchkey children (n?=?594) was studied to include greater variation in after-school experiences, Ss who were more removed from adult supervision were found to be more susceptible to peer pressure to engage in antisocial activity. Ss who were home alone were less susceptible to peer pressure than are those who were at a friend's house after school, and those who were at a friend's house, in turn, were less susceptible than were those who describe themselves as "hanging out." Moreover, latchkey Ss whose parents knew their whereabouts and those who had been raised authoritatively were less susceptible to peer influence than were their peers, even if their afternoons were spent in contexts in which adult supervision was lax and susceptibility to peer pressure was generally high. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

渗铝304不锈钢不同实验方法的SCC敏感性评价

采用恒载荷试验方法及慢应变速率试验(SSRT)方法研究了渗铝304奥氏体不锈钢在沸腾42％MgCl2溶液中的应力腐蚀破裂(SCC)性能，分析了渗铝不锈钢SCC机理，讨论了不同试验方法对渗铝不锈钢SCC敏感性评价的影响．试验表明：渗铝处理可明显提高304钢抗SCC性能，其机理为渗铝层的环境遮断作用及对基体的电化学保护作用．两种方法在评价各种渗铝钢材料SCC性能方面有统一性：恒载荷试验中SCC敏感性指标σth高的材料，SSRT中SCC敏感性指标δi也相对较高．但两种方法中渗铝试样的断口形态表现出差异：恒载荷试验为穿晶型SCC断口，而SSRT无SCC断口特征，为韧性断口。     

Low frequency ac conduction and dielectric relaxation behavior of solution grown and uniaxially stretched poly(vinylidene fluoride) films

The measurements of ac conductivity [σ_m(ω)], dielectric constant [?′(ω)] and loss [?″(ω)] have been performed on solution grown (thickness ∼85 μm) and uniaxially stretched (thickness ∼25, 45 and 80 μm) films of poly(vinylidene fluoride) (PVDF) in the frequency range 0.1 kHz-10 MHz and in the temperature range 77-400 K. The σ_m(ω) can be described by the relation σ(ω) = Aω^s, where s is close to unity and decreases with increase in temperature. Three relaxations, observed in the present investigation, have been designated as the α_c-, the α_a- and the β-relaxations appearing from high temperature side to the low temperature side. The α_c-relaxation could not be observed in the case of uniaxially stretched poly(vinylidene fluoride) films. The α_c- and α_a-relaxations are associated with the molecular motions in the crystalline regions and micro-Brownian motion in the amorphous regions of the main polymer chain, respectively, whereas the β-relaxation is attributed to the rotation of side group dipoles or to the local oscillations of the frozen main polymer chain.     

Dielectric properties of SBR vulcanizates loaded with HAF carbon black and BaTiO3 ceramics

The influence of HAF carbon black and BaTiO₃ ceramic powder contents in SBR vulcanizates on the dielectric constant (ε′) at different frequencies and at fixed temperature of 303 K is studied well in this article. The temperature dependence of the ac conductivity (σ_ac) was also studied. ε′ appreciably decreases as frequency increased for both filled and unfilled SBR vulcanizates. At each frequency, ε′ gradually decreased with BaTiO₃ loading, but its change at any fixed frequency with BaTiO₃ filler loading is not uniform. For HAF group ε′ (at loading ≥ 40 phr), drops rapidly with frequency. Meanwhile, it increased appreciably beyond a certain HAF filler loading (≈ 20 phr). Experimental values of the dielectric constant of both BaTiO₃ and HAF contents were compared with those calculated by using Tsangaris, Clausius and Bruggman models. Tsangaris model with simple modifications was applied and a fairly good agreement was obtained. The HAF particles or aggregates was found to take the shape of oblate ellipsoids with the minor axes parallel to the applied frequency as detected from the decreasing behavior of the depolarizing factor (Y) with HAF contents. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2227–2234, 2007     

丁腈胶乳的加氢反应

采用水合肼/过氧化氢氧化还原体系，以硼酸为催化剂，在常压下进行丁腈胶乳的氢化反应，研究了过氧化氢加入方式，硼酸和水合肼用量，反应温度及反应时间对丁腈胶乳加氢度的影响。结果表明，过氧化氢连续滴加再附加室温条件，氢化反应效果最好。当硼酸用量为2.64mmol，水合肼用量为95.2mmol，过氧化氮用量为79.3mmol。在60℃，6h下，丁腈胶乳的加氢度可达到90%以上。     

Tween-60+Span-80/异戊醇/环己烷微乳液法制备纳米Fe3O4

采用W/O型Tween-60 Span-80/异戊醇/环己烷微乳液作为"微反应器"合成纳米磁性Fe3O4粒子。研究结果表明纳米Fe3O4粒子磁化率均随着反应温度、pH、铁离子的浓度比例ω(=[Fe2 ]/[Fe3 ])的增大先增大后减小;最优的制备条件为反应温度30℃、ω=1.2:2、pH=11。最优条件下制备的纳米Fe3O4粒子AFM图片表明所得纳米Fe3O4为均匀分散的球形微粒,平均粒径为70nm。     

Assessment of a redox alkaline/iron-chelate absorption process for the removal of dilute hydrogen sulfide in air emissions

The oxidative absorption of hydrogen sulfide (H₂S) into a solution of ferric chelate of trans-1,2- diaminocyclohexanetetraacetate (CDTA) was studied in a counter-current laboratory column randomly packed with 15 mm plastic Ralu rings. The present investigation takes concern about the Kraft pulping situation where dilute H₂S concentrations are omnipresent in large-volume gas effluents. A fractional two-level factorial approach was instigated to determine the significance of six operating variables, namely the solution's alkalinity (pH; 8.5-10.5), the liquid mass flow rate (L;1.73-), the solution's ionic strength (I_C;0.01-), the gas mass flow rate (G;0.19-), the inlet H₂S concentration (C_H2S,0;70-430 ppm) and the initial ferric CDTA concentration (C_Fe,0;100 -). Initially, a Plackett-Burman design matrix of seven duplicated experiments revealed that pH is the leading factor controlling the H₂S conversion rate while the ionic strength and ferric CDTA concentration effects remained negligible within the factorial domain. Surface response analysis based on 11 duplicated factorial experiments plus 10 central composite trials revealed that the H₂S conversion significantly increases with liquid flow rate but decreases with growing H₂S load up. Further examination about the influence of ferric CDTA on H₂S absorption rate was set up over a broader concentration range (C_Fe,0;0- at pH of 9.5 and 10.5. It showed good potential at as H₂S conversion increased by a significant 25% for both pH values in comparison to pure alkaline solutions containing no ferric CDTA.