Preparation and Characterization of Amorphous Layer on Aluminum Alloy Formed by Plasma Electrolytic Deposition (PED)

PLASMA Electrolytic Deposition(PED)is a relativelynew technology to form ceramic layers on somenon-ferrous metal and their alloys such as aluminum,magnesium and titanium'1'21.By apply high electricalpotential between the work-piece and another counterelectrode in certain electrolysis,the breakdown of thepassive film or the gas envelope surrounding theworkpiece lead to electrical discharge in the interfacebetween the workpiece surface and the electrolysis.Ceramic layers and/or diffusion lay…     

Study of the corrosion inhibition effect of sodium silicate on AZ91D magnesium alloy

The poor corrosion resistance of magnesium alloys is a major impediment to their applications in many fields. In this paper, sodium silicate as a corrosion inhibitor is studied on the inhibition effect of AZ91D magnesium alloy. From the results of the corrosion tests, sodium silicate could effectively improve the corrosion resistance of alloy at the optimum concentration 10 mmol/L, while the pH value range from 10.5 to 12.5 is preferable. The corrosion inhibition mechanism of the protective layers is also discussed. These results can provide a guide for the protection of magnesium alloy in the cooling water systems, etc.     

熔模精铸型壳强化技术研究与应用

介绍了一种新型的型壳强化技术,系统研究了强化剂的配比和工艺控制方案,解决了水玻璃型壳高温强度低的难题,实现型壳减层工艺的大批量生产应用.结果表明,通过强化剂的应用,撒石英砂的水玻璃型壳高温强度达到了11 MPa,达到了全硅溶胶的水平.     

The performance of a waterborne zinc-rich coating from sodium silicate solution catalyzed by ammonium acetate

Through general property tests, rheological measurements, SEM observations and weight changes after immersion, electrochemical methods and water vapor transmission tests, a waterborne zinc-rich coating from sodium silicate solution catalyzed by ammonium acetate was characterized. Results showed that the formula catalyzed by ammonium acetate overcame the poor water resistance of other non-catalyzed coatings, while binding the zinc powder in the film. The zinc-rich film had the basic features required for a zinc-rich primer to be useful and was electrochemically cathodically protective during tests. The acetate anion from ammonium acetate resulted not only in little early corrosion while catalyzing the formation of zinc silicate before cure but also stronger corrosion protection during the immersion test on the cured film. The velocity of water vapor transmission and the amount of acetate anions present decreased with time until a stable value was achieved after approximately 6 days.     

混合粘结剂-水玻璃复合型壳精密铸造新工艺

混合粘结剂采用硅酸乙酯水解液、硅溶胶以及活性剂酒精混合而成。混合粘结剂用于型壳的1～3层，而加固层采用水玻璃粘结剂。采用混合粘结剂制壳的优点是，不用氨气化学硬化，而型壳干燥比硅溶胶快，层间干燥时间通常不超过1h。混合粘结剂的的应用，缩短了制壳生产周期，提高了精铸件的质量，改善了劳动条件，减少了环境污染，大幅度降低了生产成本。     

Effect of sodium silicate pretreatment on phosphate layer: Morphology and corrosion resistance behavior

Phosphating is a widely adopted treatment in industry for many purposes. In this paper, carbon steel was pretreated with sodium silicate before phosphating. X‐ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurements were used to evaluate the pretreatment effect by sodium silicate on the phosphating layer. The results demonstrate that the phosphate layer pretreated by sodium silicate has a better corrosion resistance as compared with the un‐pretreated ones. More compact and uniform coatings composed of finer crystals were obtained with the pretreatment of sodium silicate.     

Two-Stage Passivation of Zinc by Solutions of Sodium Dodecylphosphonate and Trialkoxysilanes

Protection of Metals and Physical Chemistry of Surfaces - Abstract—The ability of improving the protective properties of layers formed on zinc in the presence of sodium dodecylphosphonate...     

微波硬化水玻璃砂型内温度场分布特性及影响因素初步研究

采用热电偶温度测量传感器,通过单点测量方式,研究了微波硬化水玻璃砂型内部温度场的分布规律,分析了微波加热时间、微波加热功率、水玻璃加入量以及炉内加热位置等工艺参数对砂型内部温度场分布规律的影响.结果表明:微波硬化水玻璃砂型内温度分布呈"内高外低"的正温度梯度分布;微波加热时间、微波加热功率及水玻璃加入量对砂型整体温度高低有影响,但不改变温度场分布规律;水玻璃模数及炉内加热位置对砂型整体温度及温度场分布规律都没有明显影响.     

水玻璃改性对水玻璃砂再生循环使用性能的影响

水玻璃改性技术在提高水玻璃砂强度,改善其溃散性的同时,也对水玻璃旧砂经干法再生后循环使用的砂性能产生了影响。试验测试了水玻璃旧砂受热温度对其溃散性的影响,比较了普通水玻璃和改性水玻璃在水玻璃旧砂溃散性上的区别,测试研究了多次循环使用后水玻璃再生砂残留强度的变化,分析了所用改性水玻璃粘结剂对水玻璃旧砂再生回用后的性能产生影响的原因和机制。结果表明,水玻璃改性有利于水玻璃砂的再生循环使用。     

Stannate and permanganate conversion coatings on AZ31 magnesium alloy

The formation of stannate and permanganate–phosphate conversion coatings on AZ31 magnesium alloy was investigated in situ by EIS measurements and their protective performances were studied by different electrochemical techniques in diluted (0.05 M) sodium sulphate solution.The influence that short or long treatment times exert on the performances of such conversion coatings is discussed. While permanganate–phosphate baths always built layers characterized by penetrating cracks, long stannate baths produced layers without interconnected porosity, but were defective. This accounted for the initial greater protectiveness achieved with the stannate treatment; nevertheless, the easy penetration of the electrolytic solution through such a layer quickly decreased its corrosion resistance.     

影响酯硬化水玻璃砂性能因素的探讨

分析了应用酯硬化水玻璃砂生产铸钢件的优越性;探讨了影响酯硬化水玻璃砂的各项因素;指出根据材料特性,选择最佳配方完全可以满足铸钢行业的需要     

Inhibition of mild steel by polyphosphates

The influence of sodium polyphosphate on the corrosion of mild steel in solution of sodium chloride having the same concentration as sea water has been studied by polarization and potential measurements. It has been shown that the corrosion of mild steel can be effectively reduced by the addition of small amounts of polyphosphates in the presence of divalent cations such as Ca, Mg, Zn and dissolved oxygen. A thin transparent film of amorphous structure was found to be deposited on the surface of metal treated with the solution containing polyphosphate and calcium ions. The mechanism of inhibition by polyphosphates in the presence of calcium and magnesium can be explained by formation of a glass-like film deposited on cathodic areas which increases cathodic polarization. In the presence of oxygen, polyphosphates favour the process of passivation.     

Influence of sodium silicate concentration on properties of micro arc oxidation coatings formed on AZ91HP magnesium alloys

In a base solution containing 10 g/L sodium hydroxide and 12 g/L phytic acid, the influence of sodium silicate concentration on the formation and properties of anodic coatings obtained by micro arc oxidation (MAO) on magnesium alloys was systematically studied. The results demonstrate that sodium silicate can increase the solution conductivity, decrease the final voltage and change the coating color. Amorphous magnesium silicate is detected and the silicon content in the coatings continually increases with the increasing of sodium silicate concentration. Silicate ions can simultaneously combine with magnesium and aluminum ions to develop anodic coatings, while phytic acid radicals preferentially react with magnesium ions. Sodium silicate can further improve the corrosion resistance of MAO treated magnesium and the coating shows the best corrosion resistance in the base solution with 10 g/L sodium silicate.     

Effect of SiO2:Na2O molar ratio of sodium silicate on the corrosion resistance of silicate conversion coatings

Passivation treatment by sodium silicate solution is considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of hot-dip galvanized (HDG) steels. In this paper, a transparent silicate coating was formed on the surface of HDG steel by immersing in sodium silicate solution with SiO₂:Na₂O molar ratio in the range from 1.00 to 4.00. The parameter about the SiO₂:Na₂O molar ratio of silicate solution has been discussed using corrosion resistance and surface morphology. Tafel polarization, electrochemical impedance spectroscopy (EIS) measurements and neutral salt spray (NSS) test show that silicate coatings increase the corrosion resistance of HDG steels. From the results obtained, it is deduced that the optimum SiO₂:Na₂O molar ratio is 3.50. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), and reflectance absorption infrared spectroscopy (RA-IR) show that there are no obvious differences of the chemical composition and structure in various silicate coatings. The silicate coatings mainly consist of zinc oxides/hydroxides, zinc silicate and SiO₂. However, atomic force microscopy (AFM) images reveal that the surface of silicate coatings with a molar ratio of 3.50 is more compact and uniform than other silicate coatings.     

Mechanism of the corrosion inhibition of Zn Anode in NaOH by gelatine and some inorganic anions

The quantity of electricity required for passivation of Zn anode in NaOH solutions has been determined in absence and presence of different concentrations of gelatine, phthalic acid, sodium sulphide, sodium silicate or potassium chromate. The results obtained for gelatine in dilute alkali conform with a simple Langmuir model, whereas deviations are observed for the rest of the additives. The concentrations needed to establish a certain inhibiting efficiency increase wth increase in alkali concentration. The results are interpreted in the light of dissolution-precipitation mechanism.     

中国铁路机车车辆铸钢件生产现状和发展趋势

介绍了我国铁路机车车辆铸钢件生产的发展过程.特别是近十多年来的技术进步,使铸件的产量和质量迅速提高,一些工厂的铸钢件完全达到了发达国家的水平,并大量出口.长期以来一直使用的ZG230-450已被符合美国AAR-M201标准的低合金钢所取代,水爆清砂工艺已被禁止使用,多种造型新工艺如有机酯硬化水玻璃砂工艺、真空造型工艺已成功地用于制造各种铁路铸钢件,使用了三十多年的普通CO2-水玻璃砂造型将迅速被淘汰.还指出了当前我国铁路铸钢件生产上存在的一些问题,提出了应采取的措施和将来的发展方向.     

Protective ability of cerium-containing conversion films on aluminium

The options for electroless deposition of conversion films of lanthanum group metal oxides, in particular cerium, as an alternative to chromate conversion films (containing Cr⁶⁺) have been studied on aluminium. The main task of the study was to establish the influence of copper ions as a component of electrolytes for conversion treatment on the processes of formation and on the corrosion protective ability of cerium oxide films.

It has been ascertained that the electrochemical activation of the aluminium surface in the presence of Cu²⁺ in the electrolyte, leads to formation of oxide layers richer in cerium and possessing a better protective ability.

The presence of active cathodic sections of electroless, contact-deposited Cu has been shown to promote the corrosion activity of the system, due to the possibility of the appearance of micro-galvanic couples Al/Cu. A model experiment has been carried out to establish the inclination of the system to pitting corrosion. It has been shown that at the studied concentration of Cu²⁺ in the electrolyte the character of the corrosion does not change observably but there is a catalysing effect of the copper ions in the working electrolyte. The copper islands on the Al surface also have a catalysing effect, which is dominating in the processes of cerium oxide film formation. The chemical state and the composition of the conversion films have been defined by XPS measurements.     

Formation and Surface Structural Features of Crystalline Ceramic Nanocomposite Coatings on Aluminium Using Lithium Sulphate with Silicate Additive

We have synthesized a series of the ceramic coatings by anodization of aluminium using lithium sulphate and sodium silicate additive.Our experiments show that the present coatings are nanocomposites in nature,consisting of a mixture of nanocrystalline alumina,silica,aluminium silicate and mullite; the formation of alumina was similar to conventional anodizing technology,while the formation of mullite was attributed to an addition of sodium silicate.The microhardness of the coatings progressively increased with the increasing current density up to 0.2 A/cm2,which could mainly be attributed to the decrease of porosity in the interfacial region of the oxides up to the range.From the performance of the coatings against corrosion(Tafel/Nyquist plots),it was inferred that the coatings fabricated by lithium sulphate–sodium silicate bath have enhanced corrosion resistance(Rp=3.12 kΩ),as well as better microhardness value than that of the lithium sulphate bath alone(Rp=660.96 Ω) which confirm the perception that the silica particles included in the anodized alumina matrices randomly.Presence of Al,Si and O indicated that the electrolyte components had been intensively incorporated into the coatings.     

Das Korrosionsverhalten von feuerverzinktem Stahl in kalten und warmen Modellwässern in Abhängigkeit einer CO2- und/oder O2-Spülung und von der Kalkhärte

Corrosion behaviour of hot dip galvanized steel in cold and warm model waters with gassing by CO₂ and/or O₂ and as a function of lime hardness In oxygen-or carbon dioxide free waters the corrosion is due to the evolution of hydrogen from water; this corrosion is accelerated by higher chloride contents. It is therefore advisable to keep chloride contents below 150 mg/l Cl^?. In the presence of oxygen the zinc coating is attacked by oxygen; here, too, the influence of chlorides is quite evident. The presence of a certain water hardness gives rise to the formation of protective layers. When the water contains carbon dioxide the corrosion is of the acid type; it is inhibited, however, by protective layer formation. It should be borne in mind, that the hardness of water has a favourable effect only in cold waters, while it is very deleterious in warm waters. Water flow gives rise to accelerated corrosion. Pitting can be prevented by oxygen elimination or by the formation of protective layers. This layer formation is optimum under lime-carbonic acid equilibrium conditions.     

Stress corrosion cracking of armco iron in phosphate solutions

The stress corrosion cracking of Armco iron was examined in 0.033 and 1.0 M sodium orthophosphate solutions of pH 4.0, 7.0, and 9.0 at 25–100°C in constant strain-rate tests. In 1 M solution of pH 4.0 there formed in Armco iron deep intergranular cracks at potentials ? 150 to ? 50 mV (SCE) and anodic currents of 0.4–8 A/m², and also shallow transgranular cracks at ca. ? 250 to ? 50 mV and 1–30 A/m². Intergranular cracking has been associated with the presence of the oxide passivating film of moderate protectiveness and it was ascribed to deterioration of this film on grain boundaries of the metal by segregated admixtures. Transgranular cracking has been associated with the presence of less protective layers and their rupture along deformation bands.