The growth kinetics and properties of potentiodynamically formed thin oxide films on aluminium in citric acid solutions

The growth kinetics and properties of potentiodynamically formed thin oxide films on Al were investigated in 0.05 M citric acid solutions of different pH (5, 6 and 7) by means of potentiodynamic polarization and a.c. electrochemical impedance spectroscopy (EIS) measurements. Al showed passive behaviour within the pH range that was examined. The potentiodynamic growth of the oxide film on Al takes place due to ionic conductivity under the influence of the high electric field. Characteristic kinetic oxide film growth parameters such as the high-field growth exponential law constants (A and B), ionic conductivity through the oxide film, field strength and half barrier width have been calculated. Impedance measurements were used to determine the parameters related to the characteristic sizes and properties of oxide film. The capacitive response of the impedance spectrum was related to the thickness and dielectric properties of the barrier oxide film. The oxide film resistance values were very high, indicating that the oxide films formed under potentiodynamic conditions are highly uniform in thickness and very resistant. The anodic behaviour of Al in the citric solutions under potentiodynamic conditions were characterized by the rapid growth of the oxide film which diminished the influence of relaxation processes on the growth kinetics and structural characteristics of the aluminium/anodic oxide film/electrolyte system.     

柠檬酸对Ni-P合金化学镀沉积速度和镀层性能的影响

研究了柠檬酸浓度对乙酸盐缓冲体系Ni-P合金化学镀沉积速度、镀层含磷量及其耐蚀性与结构的影响，并对镀层在镀态下和经热处理后的耐蚀性与结构进行了比较。结果表明，随柠檬酸浓度的增加，沉积速度先增加后l牵低，而镀层中磷含量则先降低后增加；镀态时高磷合金为非晶态结构且具有较好的耐蚀性，中磷合金则为非晶 微晶结构，耐蚀性较低，而所有镀层经350℃热处理1h后，结构都转变为晶态，且耐蚀性明显提高。     

柠檬酸及其盐在金属防护中的应用研究现状

综述了柠檬酸及其盐作为缓蚀剂,电镀和化学镀镀液添加剂及其在金属防护膜中的应用状况.认为柠檬酸与其他缓蚀剂的缓蚀协同性研究是柠檬酸型缓蚀剂开发的重点,柠檬酸型配位剂是替代氰化物等有毒镀液添加剂的理想选择,在稀土等无铬转化膜中添加柠檬酸盐是改进稀土转化膜耐蚀性研究的一个方向.     

柠檬酸改性原位晶化催化剂的性能及传质扩散行为研究

采用不同浓度的柠檬酸溶液对原位晶化催化剂进行了改性脱铝研究,利用XRD、荧光衍射、氮气吸附、吡啶红外吸附等表征手段对脱铝后的催化剂进行了分析表征,分析表征结果表明柠檬酸能显著调变催化剂孔结构,有效改变中强酸和总酸量。ACE的反应评价结果表明,采用柠檬酸改性后催化剂的裂化能力显著增强,转化率提高3.23%（质量分数）以上、油浆收率降低1.13%（质量分数）以上、液化气质量分数增加2.7%以上、柴油质量分数降低1.94%以上、焦炭选择性变好。说明柠檬酸改性可显著提高原位晶化催化剂酸性位可接近性,从而改善反应选择性,柠檬酸质量分数为0.5%时具有最佳的反应结果。以菲为探针分子测试的催化剂穿透曲线验证了这一点。     

The inhibitive action of dimethyltin dichloride towards the corrosion of aluminium in hydrochloric acid and sodium hydroxide solutions

The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of dimethyltin dichloride as corrosion inhibitor has been studied using hydrogen evolution and thermometric methods. The two methods gave consistent results. The higher inhibition efficiency of this compound in acidic than in alkaline media may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive. The adsorption of this compound was found to obey Frumkin adsorption isotherm.     

柠檬酸工业废水强化镉污染土壤的电化学法修复

通过批量解吸附实验和电化学修复实验,研究利用柠檬酸工业废水作为电化学修复的增效剂从高缓冲容量的天然土壤中去除镉的可行性。批量实验结果表明,当加入柠檬酸工业废水时,85%以上的镉能在土壤pH≤5.0的条件下从土壤中溶解到溶液中;在pH5.0～8.0范围内镉的解吸附率比用去离子水增加20%～45%。电化学修复实验结果表明,与相同pH值的HNO₃相比,该废水作为电极溶液可使镉在土壤中发生明显迁移;在距离阳极0～4 cm及8～10 cm处土壤镉含量由282 mg·kg^-1降低至167～200 mg·kg^-1,而在距阳极4～8 cm处土壤镉含量升高至约400 mg·kg^-1。经过514 h的电化学修复,约84.7%的镉可以从土壤中去除,其中约94.6%从土壤中去除的镉富集在阴极溶液中。可见柠檬酸工业废水是一种非常有前景的重金属污染土壤电化学修复增效剂。     

柠檬酸酐的合成与表征

以无水柠檬酸和乙酸酐为原料合成柠檬酸酐,通过单因素试验利用滴定法考察投料摩尔比、反应温度以及溶剂用量对反应转化率和收率的影响。结果表明:反应温度为52℃,n(乙酸酐)∶n(无水柠檬酸)=1.2∶1,n(乙酸)∶n(无水柠檬酸)=1.0∶1,反应时间为1.5 h时,柠檬酸酐收率达88.8%。利用红外光谱、核磁共振氢谱和质谱表征了合成产物,证明其为五元环状柠檬酸酐。     

柠檬酸生产新工艺的研究

研究了热再生树脂性能及其在柠檬酸提纯中的应用，提出了柠檬酸生产新工艺，解决了现行工艺中存在的生产成本高、周期长、环境污染等问题。新工艺仅在原料成本方面就比现行工艺降低２０％以上     

Effect of curing on the corrosion protective properties of thin organosilane films on aluminium

Film properties and corrosion protection given by thin organosilane films (bis-1,2-(triethoxysilyl)ethane: BTSE) on aluminium were investigated as a function of curing. The thickness was determined using spectroscopic ellipsometry (SE). Impedance spectra, modelled by an electrical equivalent circuit, show three time constants. The variation of the elements in these three time constants as a function of the immersion time in a NaCl solution indicate the structure of the film after curing. It can be concluded that the barrier properties of the organosilane films are influenced more by the curing temperature than by the curing time.     

柠檬酸清洁生产新工艺

简要介绍我国柠檬酸的生产现状，针对国内提取工艺普遍存在的“三废”问题综述了国内外清洁生产工艺的最新进展。     

Properties of starch‐based blend films using citric acid as additive. II

Starch/polyvinyl alcohol (PVA) blend films were prepared by using corn starch, polyvinyl alcohol (PVA), glycerol (GL), and citric acid (CA) as additives and glutaraldehyde (GLU) as crosslinking agent for the mixing process. The additives, drying temperature, and the influence of crosslinker of films on the properties of the films were investigated. The mechanical properties, tensile strength (TS), elongation at break (% E), degree of swelling (DS), and solubility (S) of starch/PVA blend film were examined adding GL and CA as additives. At all measurement results, except for DS, the film adding CA was better than GL because hydrogen bonding at the presence of CA with hydroxyl group and carboxyl group increased the inter/intramolecular interaction between starch, PVA, and additives. CA improves the properties of starch/PVA blend film compared with GL. TS, % E, DS, and S of film adding GLU as crosslinking agent were examined. With increasing GLU contents, TS increases but % E, DS, and S value of GL‐added and CA‐added films decrease. When the film was dried at low temperature, the physical properties of the films were clearly improved because the hydrogen bonding was activated at low temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2554–2560, 2006     

Evaluation of some machining processes as adherend surface treatments in bonding aluminium

—This paper reports detailed studies on some machining processes used as adherend surface preparation methods. The two conventional treatments of sand blasting and chromic-sulphuric acid etching were also studied to compare their relative merits in making strong bonds. The nature of the adherend surface produced by these processes was examined by electron microscopy and surface profile records to determine its significance in the bonding process. Aluminium alloy 2014 (untempered) was used as the adherend material and a heat-curing, two-part structural epoxy as the adhesive. It was observed that different treatments render different bond strengths, and that variation of some process parameters in each treatment influences the joint strength with the same adhesive-adherend system. The surface profile records and electron micrographs of the treated adherends give an indication of the relative bond strengths which occur after the joints are formed. Some machining processes such as shaping, milling, and turning seem superior to the sand blasting treatment. However, chromic-sulphuric acid etching produces the highest joint strengths.     

Electrochemical behaviour of aluminium in the presence of EDTA-containing chloride solutions

The electrochemical behaviour of pure aluminium in an EDTA-containing chloride solution was investigated using potentiodynamic and potentiostatic electrochemical techniques and electrochemical impedance spectroscopy. A pronounced EDTA-induced anodic dissolution was observed in alkaline solutions, but the presence of EDTA in solution had little activating effect on the passivation properties at pH values close to 4.0. This was attributed to the relative stability of the Al(EDTA)^– complex formed at the different pH values. This EDTA-induced activation had no deleterious effect on pitting attack, in fact, higher breakdown potentials were observed in the presence of EDTA. This was attributed to the buffering action of EDTA, which inhibited the attainment of a critical pit solution composition. But, in the presence of molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorption of EDTA species during the dissolution process, which in turn, form a large capacitive network, with capacitance values of the order of 3 mF cm^–2 in the low frequency region.     

柠檬酸工业废水处理现状

我国是世界上最大的柠檬酸生产和出口国,但柠檬酸生产工艺的固有特点,使其生产过程中产生大量高浓度废水,成为环境的严重污染源,而目前由于投资、技术、运行成本等原因,该行业三废基本处于任意排放状态,严重污染周围环境,因此,废水治理已成为我国柠檬酸行业的当务之急。作者分析了柠檬酸废水的来源及水质特性,综述了生物法、光合细菌法、乳状液膜法等方法在柠檬酸废水处理中的应用,并介绍了中和废水的回用技术。     

柠檬酸硬脂酸单甘脂的合成研究

通过对柠檬酸硬脂酸单甘脂的合成研究 ,确定了以乙酸为催化剂兼溶剂 ,柠檬酸与硬脂酸单甘脂进行酯化反应的最佳工艺路线。结果表明 ,在此工艺路线下的最佳工艺条件为 :柠檬酸与硬脂酸单甘脂的摩尔比为 2∶1,乙酸用量为 10 0 % (以硬脂酸单甘脂质量计 ) ,反应温度为 12 0℃ ,酯化反应时间 3h ,真空度为 0 9MPa。该产品可作为食品乳化剂 ,在食品工业中有广泛的应用前景     

三氟甲磺酸催化合成柠檬酸酯

利用一种新型高效绿色催化剂三氟甲磺酸(CF3SO3H)合成绿色增塑剂柠檬酸三丁酯,结果表明该催化剂用量少(占柠檬酸的0.1%),反应时间短(5 h)。研究了该催化剂合成乙酰柠檬酸酯的一体化工艺,实现了无须精制柠檬酸三丁酯,直接从柠檬酸出发制得乙酰柠檬酸三丁酯,产率高(两步87.1%),纯度高(99.1%),大幅简化了生产工艺和成本且环保,适合工业化。同时,研究了CF3SO3H催化合成丙酰、丁酰柠檬酸酯类产品的一体化工艺。     

柠檬酸废水处理的研究进展

我国是世界上最大的柠檬酸生产和出口国，但柠檬酸生产工艺的固有特点使其生产过程中产生大量高浓度废水，成为环境的严重污染源，因此，废水治理已成为我国柠檬酸行业的当务之急。介绍了几种柠檬酸废水的处理工艺，如生产饲料酵母法，上流式厌氧污泥床（UASB）工艺，活性污泥法，光合细菌法，乳状液膜法及综合处理法，并对不同方法的原理和工艺流程作了简要的比较。     

电站锅炉的柠檬酸清洗

大港电厂采用柠檬酸作清洗剂对锅炉进行了化学清洗,清洗效果不错,设备表面清洗干净,形成了钢灰色的钝化膜,监视片腐蚀速率低,圆满完成了清洗任务。     

Copolymer of acrylonitrile/acrylic acid solid surface film dendrigrafted with citric acid

BACKGROUND: The aim of the present work was to improve the properties of acrylic polymer, which is a major fibre‐forming polymer. Acrylonitrile/acrylic acid copolymer, P(AN/AA), was chosen for this purpose and it was intended to study the condition for the formation of hydroxyl groups through the formation of hyperbranched polymers. RESULTS: The synthesis of a dendritic polymer of citric acid (CA) in the solid phase on a P(AN/AA) core is described. The product was analysed using the elemental analysis technique and ¹H NMR. Dendritic molecules were grown by a reaction between the carboxylic acid of acrylic acid and hydroxyl group of CA activated by dicyclohexylcarbodiimide. Products were analysed using Fourier transform infrared and NMR spectroscopy. CONCLUSION: The formation of CA dendrigraft on P(AN/AA) films in a heterogeneous system is possible. The percentage conversion of the copolymer reaction with CA was calculated based on the NMR results. The percentage conversion showed a gradual reduction with an increase in step numbers. The contact angle of water on the films was affected by the percentage conversion of the reactions. A calculation scheme is presented to show that the low degree of conversion leads to an increase in hydrophobic groups. Copyright © 2008 Society of Chemical Industry