镁合金无铬化学转化膜的研究进展

综述了国内外镁合金无铬化学转化膜研究现状,通过分析不同转化液的配方、主要处理工艺及相应转化膜的组成、结构、形貌、膜层的耐蚀性能,指出现有无铬转化技术存在的不足,并展望了无铬化学转化膜的未来发展趋势.     

6063铝合金无铬有色化学转化工艺探讨

为了进一步提高6063铝合金表面无铬转化膜的性能以替代铬酸盐钝化膜,以钛盐为成膜主剂,钨酸盐为上色剂,多羟基有机酸钠为配位剂,在6063铝材表面进行无铬有色化学转化,采用铬酸盐点滴试验、电化学方法、中性盐雾试验及划格法对转化膜的耐蚀性、附着力进行了测试,并对转化液配方及成膜条件进行了优选,探讨了添加剂及工艺参数对膜层质量的影响。结果表明:较优转化液配方及成膜条件为2.0 g/L钛盐、0.3~0.5 g/L钨酸盐上色剂,0.5~0.7 g/L多羟基有机酸钠配位剂,25~30℃,pH值为3.2~3.6,转化时间为5~7 min;优化工艺可在6063铝合金表面获得均一的金黄色无铬转化膜,自腐蚀电流密度仅为基材的1/6;转化膜与聚酯漆膜的附着力与六价铬转化膜的相当;该工艺完全无铬、无毒。     

镁合金化学转化处理

综述了镁合金表面化学转化处理特别是无铬转化处理的现状、主要工艺以及在不同处理工艺下得到的转化膜的特性,重点介绍了铬酸盐转化膜,磷酸盐转化膜、重金属含氧酸化合物转化膜,稀土转化膜和有机化合物等工艺的具体研究状况,展望了镁合金化学转化膜的发展趋势,指出随着镁合金应用领域的拓宽和环保要求的提高,镁合金无铬化学转化处理的研究将越来越得到重视.     

汽车镁合金部件前处理与涂料配套性研究

研究了汽车镁合金部件经不同化学处理法获得的转化膜与涂料配套后的耐腐蚀性能.采用扫描电子显微镜(SEM)对镁合金部件化学转化膜的形貌进行观察.结果表明,镁合金部件经铬酸处理获得的转化膜与阴极电泳涂料配套耐盐雾腐蚀性能虽然比较好,但铬酸处理法工艺中使用的六价铬具有毒性,污染环境.镁合金部件采用磷酸盐一高锰酸盐处理、铁系磷化处理、非铬酸处理法获得的化学转化膜与溶荆型聚酯涂料、粉末涂料配套耐盐雾腐蚀性能优于或者与铬酸处理相当,均可替代铬酸处理,能够满足汽车镁合金部件涂装质量要求.     

国内外镁合金无铬转化技术研究规模及进展

为了促进环境友好型镁合金无铬转化技术的较快发展,调查了近10年镁合金表面该技术发表的论文及专利,对其处理种类及典型工艺作了简述,结合化学转化膜成膜机理和镁合金特点,提出有机转化膜有望成为镁合金表面无铬转化处理未来的发展方向。     

金属表面植酸转化膜研究进展

化学转化膜技术是金属物件表面处理中应用较为广泛的一项技术,可使金属物件得到较好的防护,可用于金属防腐、耐磨、减摩、涂装底层,其应用涉及汽车制造、家电以及五金构件加工等诸多行业。化学转化膜技术作为最常用的金属表面预处理技术,因工艺简单、效果显著、沉淀均匀、成本低且膜的厚度易控制等优势而受到越来越多的关注。传统的铬酸盐和磷酸盐转化处理方法会对环境产生持久性危害,因而已逐步被绿色环保的方法取代。目前,金属表面绿色前处理技术的开发和应用已成为该领域十分重要的研究方向。经过十几年的努力,研究人员相继开发了各类环境友好型转化膜。本文针对无铬化学转化膜,从锆盐、钛盐、钒盐、钼酸盐、锡酸盐、铌盐和稀土元素类转化膜等的制备工艺、防腐蚀效果等方面阐述了无铬化学转化膜的研究进展。虽然,无铬转化新技术有一定的实践应用,但作为防腐蚀技术而言,单一使用该技术的效果并不理想,还需要与其他方法相结合并加以改进。本文重点分析了植酸转化膜的沉积机理、影响因素及改进技术发展。植酸是从植物中提取的无毒天然有机大分子,分子中含有能够与金属离子发生螯合作用的六个磷酸基,每个磷酸基中又有两个羟基和四个氧原子,可在较宽的pH值范围内与大多数二价及以上的金属离子螯合形成稳定的配合物。植酸作为金属表面化学转化膜成膜材料在金属腐蚀与防护领域的应用越来越广泛。大量研究结果表明,金属在植酸处理液中通过电化学反应,使金属表面的金属离子与植酸分子发生螯合作用,沉积形成植酸化学转化膜。植酸化学转化膜的研究涉及多种金属如镁合金、钢、铁等。本文通过分析植酸转化膜的制备过程,总结了影响转化膜表面形貌和耐蚀性的三个主要因素,即植酸的浓度、处理液的pH值和处理时间;同时还归纳了单一植酸转化膜存在的不足,如膜层表面存在微小裂纹、膜层较薄、耐蚀时间较短、耐腐蚀效果不佳等。研究表明,提高植酸转化膜保护效率的途径有碱预处理、热后处理及与金属离子协同等改进技术,以及同其他转化膜复合、同其他物质复合等复合方法。此外,还展望了植酸在金属表面转化处理的发展前景。     

铝合金表面化学转化技术的研究进展

随着环保要求的不断提高,传统的含铬化学转化膜已不能满足工业生产的要求,开发新型无铬环保的铝合金转化处理技术,已成为研究热点。研究表明,以新型无机盐和稀土为成膜物质的化学转化膜具有优良的表面防护能力。综述了当前新型化学转化技术的研究现状,介绍了无机和稀土转化膜的研究进展,分析了转化膜的性能特点,指出了当前化学转化处理技术存在的问题,展望了化学转化技术的发展趋势,明确了无机盐及稀土的用量对转化膜性能的影响、转化液中辅助物质对转化膜的影响是今后研究的方向。     

添加Co(Ⅱ)和硅溶胶的热镀锌铝合金层三价铬钝化膜的抗腐蚀性能

为进一步提高热镀锌铝钢三价铬钝化膜的耐蚀性,分别或同时向三价铬钝化液中加入Co(Ⅱ)、硅溶胶进行钝化,通过中性盐雾试验、极化曲线测试及形貌观察、成分分析,考察了硅溶胶、Co(Ⅱ)盐对三价铬磷酸盐钝化膜耐蚀性的影响,考察两者的协同效应.结果表明:硅溶胶和Co(Ⅱ)盐的加入均能有效提高三价铬钝化膜的耐蚀性,两者同时添加时转化膜耐蚀性更好;硅溶胶的加入对钝化膜起到了很好的填充作用,少量Co(Ⅱ)盐使膜层表面晶格歪曲,抑制活性点的过度生长,可防止尖刺生成;同时添加Co(Ⅱ)和硅溶胶的三价铬钝化液所得的钝化膜中磷酸锌、磷酸铝生成时伴随磷酸铬和磷酸钴生成,二氧化硅在最外层,后期填充形成外表层,表层同时有一定量的磷酸锌.     

铝合金表面锆盐转化膜的制备及其性能

为提高铝合金涂膜的结合力及耐蚀性,在铝合金表面制备了锆盐转化膜.通过盐雾试验、电化学试验、膜微观结构与涂膜结合力测试,研究了锆盐转化膜的耐蚀性与漆膜的结合力,并与通用的铬酸盐转化膜和无铬转化膜进行对比.结果表明:锆盐转化膜120 h盐雾试验的耐蚀等级达8级,在3.5%NaCl溶液中铝合金的自腐蚀电位明显正移,腐蚀电流密度大大降低;转化膜层均匀多孔,含有Al,O,Zr和Mg元素,且与漆膜结合力良好.     

工艺参数对铝合金稀土转化膜微观形貌的影响研究

采用稀土盐Ce（NO3）3与氧化剂KMnO4作为无铬化学转化液的主要成分，在6063铝合金表面制备了耐腐蚀稀土转化膜，利用正交试验法与单因素实验法对转化膜处理溶液浓度、溶液温度与pH值以及时间等工艺参数进行了优化，利用SEM微观分析法，并对稀土转化膜的表面形貌进行了研究，并分析了处理工艺参数对转化膜微现形貌与耐腐蚀性能的影响。     

Modification of spin coating method and its application to grow thin films of cobalt ferrite

Spin coating method has been modified to widen its scope for applications. The film deposition assembly is suitably designed. With this modification, it is possible to use common inorganic chemicals in the form of their aqueous solutions as starting materials to grow thin films of binary/ternary oxides. This method is applied to grow thin films of cobalt ferrite. The structure, morphology and magnetic properties of thin films of cobalt ferrite have been determined by using X-ray diffraction, Scanning electron microscopy and vibrating sample magnetometer respectively. The results show that the present technique is useful to deposit thin films of cobalt ferrite, which are qualitatively comparable to the films grown by other wet chemical techniques.     

Recycling cobalt from spent lithium ion battery

Spent lithium ion battery is a useful resource of cobalt. In this paper, cobalt was recovered by a chemical process based upon the analysis of the structure and composition of the lithium ion battery. X-ray diffraction results show that cobalt oxalate and cobaltous sulfate have been obtained in two different processes. Compared with the cobaltous oxalate process, the cobaltous sulfate process was characterized by less chemical substance input and a cobalt recovery rate of as much as 88%. A combination of these two processes in the recycling industry may win in the aspects of compact process and high recovery rate.     

Synthesis and characterization of different nanostructures of cobalt phosphate

In this research, different nanostructures of cobalt phosphate were successfully prepared. Flowerlike cobalt phosphate and platelike ammonium cobalt phosphate were made by coprecipitation method without any use of surfactant or capping agent as structure directors. Reverse micelle route in water/CTAB/n-hexanol microemulsion system was used to synthesize cobalt phosphate nanoparticles. The synthesized nanostructures were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), chemical analysis, and BET. The SEM images showed that the flowerlike nanostructure is an arrangement of cobalt phosphate plates. TEM images revealed that the nanoparticles are spherical with the diameter of 30-50 nm. The purity of cobalt phosphate nanoparticles was confirmed by chemical analysis. Finally, the possible mechanisms which can describe the formation of these nanostructures were discussed.     

Cobalt modified solid superacid assisted electrochemical reaction of toluene with methanol

The electrochemical catalytic reaction of toluene with methanol, assisted with a pair of porous graphite plate electrodes, catalyzed by solid superacid of cobalt modification catalyst with chemical conversion higher than 81%, was described and investigated by UV-vis spectrum, scan electron microscopy (SEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS). A possible free radical reaction mechanism was proposed. It may be concluded that a simply and feasible electrochemical catalytic coupling oxidation reaction at room temperature and air pressure may be possible.     

Application of NiCo2O4 as a catalyst in the conversion of p-nitrophenol to p-aminophenol

Transition metal containing spinel structure type oxides exhibit characteristic structural, electrical, magnetic and catalytic properties. Present work investigated a novel application of nickel and cobalt containing spinel oxide (NiCo₂O₄) in the conversion of p-nitrophenol to p-aminophenol. The oxide compound was synthesized by citrate gel method and characterized by powder X-ray diffraction method and scanning electron microscopy. The conversion process involved room temperature hydrogenation of p-nitrophenol by aqueous sodium borohydride. Powder nickel cobalt oxide was used as a catalyst. The reduction of p-nitrophenol has been monitored by UV-VIS and IR spectroscopic analysis. Complete conversion of the nitro compound to amino compound was achieved within a minute.     

Growth of carbon nanotubes on nanoporous titania templates

This work reports the synthesis of multiwalled carbon nanotubes (MWCNTs) on nanoporous titanium dioxide (TiO2) templates. TiO2 nanotubular templates for MWCNTs are produced by anodization of titanium followed by pulsed electrodeposition (PED) of cobalt inside the TiO2 nanotubes. Cobalt acts as a catalyst for the growth of MWCNTs using chemical vapor deposition (CVD) technique. The cobalt catalyst initiates the growth of well graphitized MWCNTs inside the titania pores as well as beyond the titania pores. These materials have been characterized by SEM, EDS, GXRD, XPS, TEM, and ED techniques. The MWCNTs were about 10 mu in length and 80-120 nm in diameter.     

Polymer-Mediated Synthesis of Fine-Sized Cobalt Particles

A novel method to synthesize monodisperse, fine-sized cobalt particles (average particle size 200 nm) by a polymer matrix (not commonly known for chemical chelation)-mediated sodium borohydride reduction of cobalt chloride has been demonstrated and discussed. As against the conventional concept of using a supramolecule as a growth Poisson during the crystallization of inorganic salt from solution, the present procedure adopts the path very similar to biomineralization. The polymer matrix chelates the cobalt ions by a combined process of physical entrapment and chemical chelation. The process leads to a controlled nucleation and ordered growth of cobalt salt in polymer matrix. Orderly grown cobalt salt on reduction yields monodisperse cobalt particles having uniform size and morphology.     

Magnetic behavior of cobalt oxide films prepared by pulsed liquid injection chemical vapor deposition from a metal-organic precursor

Thin films of cobalt oxide were prepared by the pulsed liquid injection chemical vapor deposition technique from metal-organic precursor. By using a β-diketonate complex of cobalt, namely cobalt (II) acetylacetonate (Co(acac)₂) as the precursor, oxygen as the reactant and argon as the carrier gas, cobalt oxide films 100 nm in thick were deposited onto Si (100) substrates at 650 °C in about 40 min. According to the characterization by X-ray diffraction and atomic force microscopy, smooth and polycrystalline films, consisting exclusively of the Co₃O₄ phase, were deposited. Magnetic properties, such as saturation magnetization, the remanence, the coercivity, the squareness ratio and the switching field distribution, were extracted from the hysteresis loop. Cobalt oxide films with coercivities of 6.61 mT, squareness ratio of 0.2607 and saturation magnetization of 12.17 nA m², corresponding to a soft magnetic material, were achieved.     

A study on N2O catalytic decomposition over Co/MgO catalysts

Different oxide supported cobalt catalysts were prepared by co-precipitation method and tested for the decomposition of nitrous oxide. Co/MgO with cobalt loading of 15% showed the best activity and a 100% N(2)O conversion was obtained at temperatures higher than 700 K. The active phase of cobalt species in Co/MgO catalysts was Co(3)O(4) highly dispersed in the matrices of MgO, based on XRD and XPS results as well as the kinetic analysis. The existence of NO, O(2) and H(2)O in reaction system showed different negative effects on N(2)O decomposition. Nevertheless, a 100% N(2)O conversion could be achieved at 800 K under simulated conditions of tail gas from nitric acid plant. Moreover, Co/MgO catalyst exhibited quite good durability and no obvious activity loss was observed in the 100 h stability test.     

Metal chalcogenide-oxide composite coatings prepared by spray pyrolysis

The spray pyrolysis technique has been employed to deposit composite coatings of chalcogenides of cadmium, zinc, lead and cobalt with oxides of aluminium, tin, lead, zinc and cobalt. Widely varying microstructural, electronic, optical and chemical properties have been obtained for such layers by monitoring the oxide composition, its spatial distribution and profile along the thickness. The large area chalcogenide-oxide composite films prepared by this technique are eminently suited for photovoltaic energy conversion, photothermal energy conversion and voltage-dependent resistor (Varistor) applications.In this paper we report our studies on co-pyrolytically deposited CdS:Al₂O₃ and CdS:SnO₂ layers and their application to improved thin film solar cells. Each of the oxides is insoluble in CdS and is segregated at the grain boundaries in the deposited films. Small amounts (less than 10%) of oxide in CdS are found to reduce its grain size negligibly and to make the film more compact, hard, adherent and less susceptible to chemical attack. The altered microstructure modifies the surface topography of the CdS film from a pebble-like roughness to an improved void-free serpentine texture. Segregated oxide in CdS does not affect the optical band gap of the films, although the composites exhibit enhanced diffuse optical scattering.Large area CdS films with a gradient profile of oxide have been utilized to fabricate thin film CdS/Cu₂S solar cells. The growth (length and distribution) of Cu₂S fingers and/or curtains deep into the top CdS layers during the topotaxial conversion reaction of chemiplating is controlled by the presence of oxide along the grain boundaries. This has not only resulted in improved interface topography for better carrier collection and reduced shunt losses but has also enabled us to decrease drastically the CdS film thickness necessary for the solar cells. Furthermore, the subsequent degradation of the junction via the well-known mechanism of the loss of copper from the Cu₂S layer by diffusion into CdS is expected to be considerably reduced by the presence of the oxide gradient in the CdS layer.