臭氧复合钼酸铵促进剂对金属铝磷化的影响

利用臭氧的强氧化性和环境友好性,研究将其用作铝材磷化过程中的氧化促进剂。采用SEM、极化曲线等测试手段,确定了磷化液的最佳配比为：ρ(Zn²⁺)=5.0 g/L、ρ(PO^3-₄)=20 g/L、ρ(F^-)=1.5 g/L、ρ(钼酸铵)=1.0 g/L、ρ（臭氧）=0.5~0.9 mg/L,pH控制在3.5~3.7。在此条件下加入臭氧复合钼酸铵促进剂,制得磷化膜的主要成分为Zn₃(PO₄)₂•4H₂O,并含少量锌,膜质量可达4.95 g/m²。在质量分数为3％的氯化钠溶液中测定磷化膜的电极化曲线,其腐蚀电位相对于其他条件下形成的磷化膜发生正移,腐蚀电流密度仅为3.0 μA/cm²,说明磷化膜的耐腐蚀性能好。     

低温磷化促进剂的研究

研究了甲醛、乙醛对磷化膜性能的影响及其他磷化促进剂的协同作用和最佳配合用量，并考察了乙醛和NaNO2协同的低温成膜性。探讨了稀土复合促进剂的协同作用。     

低温锌系磷化促进剂研究

针对锌系中温磷化技术的缺点，研制出一种低温锌系磷化促进剂。实验结果表明，将甲醛与氯酸盐进行混合而制成的复合促进利，在磷化温度为30～40℃，磷化时间为10min的条件下，可以获得性能良好的磷化膜。     

臭氧在橡胶促进剂废水处理中的应用研究

研究了用臭氧预处理橡胶促进剂废水的方法和效果,并通过改变pH、填料和助荆等条件以确定最佳反应工况,结果表明,臭氧在处理该种废水时COD的去除率在20%以上,在调节pH至8～9且投加大理石填料和助剂的情况下,COD的去除率可达44%,大大降低了后续生物处理的有机负荷,提高了可生物氧化性.     

电化学方法在常温磷化中的应用研究

对新型磷化方法——电化学磷化进行了探究,采用对工件外加电压的方法对磷化过程进行加速,并获得了优良的磷化效果,证明电化学方法确实有利于磷化过程。通过磷化膜外观评分、磷化膜膜重、硫酸铜点滴时间、3%NaCl浸渍时间4种参数对磷化效果进行评定,初步确定了电化学磷化最佳参数值为:在20℃下,电流密度为7.80~9.00 A/dm2,平均磷化时间为3.8 min,磷化综合评价M值为16.0~17.1。     

常温铁系磷化工艺探究

通过对常温铁系磷化工艺的研究,探讨溶液组成与工艺参数对磷化膜性能的影响,分析了磷化膜性能检测、溶液的测试与调整、故障原因与处理对策。常温铁系磷化工艺具有操作温度范围宽、成膜均匀、操作简便的特点,有利于节约成本,改善劳动环境,是极具有开发价值的新型磷化发展方向。     

车身磷化膜发黄、发蓝的原因探讨

磷化是汽车前处理的一个关键工序,磷化膜的质量对车身电泳漆膜的质量影响较大。根据现场积累的经验,探讨了生产中磷化膜常见的发蓝、发黄缺陷的产生原因及解决方法。     

铝材磷化及铬磷化处理

0前言磷化及铬磷化工艺多用于铝材涂装底层,磷化膜及铬磷化膜具有膜层厚、孔隙率高、与烤漆及涂料结合良好等特点。随着铝材在机械工业、家电及交通运输业中的应用越来越广泛,铝材磷化及铬磷化工艺被日益重视。1铝材磷化处理铝材磷化可以选用铁系磷化或锌系磷化。使用     

稀土在磷化技术中的应用

磷化工艺是金属的表面处理的重要方法之一,稀土的引入使之得到了进一步的发展。本文从磷化工艺流程出发,综述了稀土在磷化前处理,作为磷化添加荆、促进剂、磷化后处理中的应用以及促进成膜机制的研究进展及现状,并展望该技术的发展前景。     

A refined model for ozone mass transfer in a semibatch stirred vessel

The mathematical model proposed by Anselmi et al. (1984) for a semibatch stirred gas‐liquid contactor is refined to describe the mass transfer of ozone absorption and decomposition in aqueous solution with the decomposition rate expression of general reaction orders (not necessarily integers). Three system equations are employed to describe the ozone concentrations in the bulk liquid (C_ALb), the hold‐up gas (C_AGi), and the outlet gas in the free volume above the liquid surface (C_AGe), respectively. The effect of ozone decomposition on the mass transfer, which is reflected by the enhancement factor (E_r) defined as the ratio of mass absorbed per unit area in time t with chemical reaction (r) to that without chemical reaction or of the purely physical absorption, is considered in the refined model. Furthermore, the refined model also takes into account the variation of E_r with C_ALb, which changes with time during the course of gas‐liquid contacting. Thus this analysis extends the applicability of the model of Anselmi et al. (1984) and is of special importance for ozone mass transfer in the cases of basic solutions and of low mass transfer coefficients, in which the effect of decomposition on absorption is significant, and in the system with variable liquid phase ozone concentration.     

Self-organized nano-scale multilayer coating on SiC fibers obtained by phosphating

Ceramic matrix composites (CMC) combine refractory and structural properties, with a damage-tolerant behavior ensured by an interphase material, usually deposited on fibers. Unfortunately, surface deposition does not prevent contacts between fibers, which are responsible for the premature collective failure of fiber clusters and therefore for limited lifetime. Recently, a workaround has been proposed by transforming the surface of the fibers itself into a continuous monolayer coating. Here we describe an SiC fiber etching process by phosphoric acid vapors at atmospheric pressure and intermediate temperature (600–700?°C), leading to an in situ multilayer transformation into a (carbon/silicophosphate)_n coating, n ranging from unity to tens and layers thickness from 100 to 300?nm. The carbon layers are micro/mesoporous carbide-derived carbon (CDC) tubes with micrometric radii. This one-step etching process gives opportunity to create layered materials containing CDC even on complex geometries such as fabrics.     

Kinetic Study of Ozone Decay in Homogeneous Phosphate-Buffered Medium

The ozone decomposition reaction is analyzed in a homogeneous reactor through in-situ measurement of the ozone depletion. The experiments were carried out at pHs between 1 to 11 in H₂PO₄^?/HPO₄^2– buffers at constant ionic strength (0.1 M) and between 5 and 35 °C. A kinetic model for ozone decomposition is proposed considering the existence of two chemical subsystems, one accounting for direct ozone decomposition leading to hydrogen peroxide and the second one accounting for the reaction between the hydrogen peroxide with the ozone to give different radical species. The model explains the apparent reaction order respect of the ozone for the entire pH interval. The decomposition kinetics at pH 4.5, 6.1, and 9.0 is analyzed at different ionic strength and the results suggest that the phosphate ions do not act as a hydroxyl radical scavenger in the ozone decomposition mechanism.     

Decomposition of Dissolved Ozone in the Presence of Activated Carbon: An Experimental Study

In aqueous solutions molecular ozone (O₃) decomposes rapidly into secondary radical or ionic species such as (OH^o,, , …). This decomposition is enhanced by many factors, essentially the pH, the temperature, and the organic or inorganic compounds in the solution. The aim of this work is to study the effect of the addition of granular activated carbon on the rate of ozone decomposition in aqueous solutions containing promoter (P) and inhibitor (Q) mixtures. The activated carbon used is laboratory produced from olive stones. We found that the rate of decomposition of ozone in these conditions is described by a pseudo-first-order kinetic: . Experimental results show that adding 15 mg/L of the olive stones activated carbon (OSAC) enhances the rate constant of the P and Q controlled chain depletion by about a factor of two. We found that the decomposition increases linearly with the solid concentration (W): and that the kinetics are enhanced when the activated carbon specific area increases. We also conclude that the preozonation of the OSAC has no effect on its activity. We note that the temperature has a significant effect on the ozone decomposition rate even in the presence of OSAC. The value of the activation energy in the presence of the OSAC is lower than that obtained in homogeneous decomposition.     

Kinetics of Heterogeneous Catalytic Ozone Decomposition in Water on an Activated Carbon

Ozone decomposition in water in the presence of an activated carbon has been studied. Variables investigated were agitation speed, carbon particle size, temperature and pH. In all cases, the presence of activated carbon improved the ozone decomposition rate. Between pH 2 and 7 the ozone decomposition rate due to both the homogeneous and heterogeneous mechanisms hardly varied while a significant increase was noticed with increasing pH. A kinetic study based on a Langmuir-Hinselwood type mechanism for the heterogeneous surface reaction was undertaken. According to this mechanism the heterogeneous ozone decomposition kinetics can be simplified to follow a first order process. Fit of experimental results to the kinetic equations derived from the mechanism allowed for the determination of the apparent first order rate constants of the ozone surface heterogeneous reaction and adsorption equilibrium constants.     

The influence of the water heater in dental chairs on the ozone concentration in the water used

Water heaters in dental chairs serve to heat water to about body temperature in order to make it more comfortable for the patient. This leads to a reduction in ozone concentration of 40–50%, as shown in laboratory experiments and also at dental chairs. In the event that evidence is found of positive biological effects in oral surgery on using relatively high ozone concentrations in water (5–10 μg/ml) then water heaters should not be used.     

Mass transfer characteristics and overall mass transfer coefficient in the ozone contactor

The overall mass transfer coefficient k_La,F in the flow characteristics was determined by the measurement of the diffusivity of ozone, density of aqueous solution, and viscosity. However, the measured values k_La,F in the range of 0.0096–0.0622 min^-1 show large changes in hydraulic retention time, and the dissolved ozone concentration C_L,F presented under 0.1 mg/l is lower than the dissolved ozone observed. The overall mass transfer coefficient k_La,M in the ozone decomposition was determined by measurement of the equilibrium dissolved ozone, overall decomposition rate constant, and overall Henry’s law constant. The measured values k_La,M are in the range of 0.0441–0.0749 min^-1, and they present small changes depending on the hydraulic retention time. Furthermore, the measured dissolved ozone concentration C_L,M presents a larger value than the C_L,F. Then, the k_La,M is selected as an input overall mass transfer coefficient to predict the dissolved ozone requirement in the ozone contactor.     

Experimental Aspects of Mechanistic Studies on Aqueous Ozone Decomposition in Alkaline Solution

Ozone decomposition in aqueous solution was studied by the stopped - flow method over the pH 10.4 - 13.2 range at 25 ± 0.1 °C and I = 0.5 M NaClO₄. At 260 nm the molar absorptivity of aqueous ozone was determined to be 3135 ± 22 M^?1cm^?1. It was shown that various experimental factors may significantly alter the course of the reaction. Even small amounts of H₂O₂ absorbed by the plastic parts of the stopped-flow instrumént can affect the kinetic features of the reaction for an extended period of time. Under strictly controlled experimental conditions sufficiently reproducible data could be obtained for the decomposition. The data were evaluated by comparing experimental and simulated kinetic traces. A detailed kinetic model was developed which is able to predict the decay and life-time of ozone as well as the formation and decomposition of the ozonide ion radical (O₃ ^?) over the pH 10.4 - 13.2 range.     

A New Device for the Measurement of Ozone in the Gas Phase

This paper presents a new device for the dosage of ozone in the gas phase. This device measures the concentration of ozone according to the isothermal differential pressure procedure. In principle, this procedure achieves a totally physical ozone measurement without requiring calibration using a chemical method. A comparison is made between the physical results and chemical results obtained by the iodometric standard method (IOA, 1987). There is satisfactory agreement between the two series of measurements in the range of ozone concentration where the chemical method is applicable (with a standard error of estimate of 4.4%).The method and the device are perfectly reliable based upon the strict measurements of temperature and pressure and a convenient choice of constitutive materials.