The amorphous alloys have been widely studying due to their excellent mechanical properties and well corrosion resistance.It is very easy to obtain amorphous Pd-Ni-P alloy within a wide composition range.The Pd-Ni-P alloy has unique physical-chemical performance and is a promising material in both engineering and electrocatalytic processes. Although many studies have been carried out on the Pd-Ni-P alloy prepared by physical methods,relatively little done by electrochemical method.Therefore,it is worthwhile to study Pd-Ni-P alloy prepared by simple electrodeposition method and their chemical performance.In this thesis,Pd-Ni-P alloy deposits with various morphology and composition have been prepared by electrodeposition.X-ray diffraction （XRD）,scanning electron microscope（SEM）,and energy dispersive X-ray（EDX）were employed to characterize phase structure,morphology and composition of the deposits.The thermal stability,corrosion resistance and performance of electroreduction nitrate of amorphous Pd-Ni-P deposits were investigated.And the influence of ultrasound on electrodeposition of the Pd-Ni-P alloys was also studied.The main results are as follows: 1.In the solutions containing PdCl2 1.8～5.3 g/L,NiSO4·6H2O 10 100 g/L,H3PO3 10～40 g/L,H3BO3 20 g/L,ethylene diamine 3 16 g/L,pH 4.0,50℃,Pd-Ni-P alloy films were electrodeposited at 25～100 mA/cm2.The results show that the Pd-Ni-P alloys with different composition and morphologies can obtained by controlling the concentration of PdCl2、NiSO4·6H2O or current density.The structures of Pd-Ni-P alloys as-prepared under our experiment conditions are amorphous or microcrystalline structure.2.The amorphous Pd-Ni-P alloy films still keep amorphous state under 300℃heated for 1 h,but they transfer to crystalline state when thermal treated to 350℃for 1 h and form mainly Ni3P、Ni2Pd2P phases.Based on the Tafel curves,the corrosion behaviors of the Pd-Ni-P alloys in 3%NaCl are better than Ni-P alloys.The cyclic voltammetric（CV）results indicated that the activity of electrocatalytic reduction of nitrate on an amorphous Pd33Ni60P7 alloy deposit is much higher than that of crystal Pd41Ni59alloy in a neutral 0.1 mol/L KClO4 solution.3.In the solution containing PdCl2 3.5 g/L,NiSO4·6H2O 10 g/L, H3PO3 20 g/L,H3BO3 20g/L,ethylene diamine 4.6 g/L,pH4.0,50℃,Pd-Ni-P films were prepared by ultrasonic electrodeposition. The results indicated:Pd-Ni-P alloys electrodeposited under ultrasonic condition are also amorphous structure,and the surface morphology become more compact and homogenous and the content of Pd increase.Ultrasound frequency is found to have a significant effect on the morphologies of deposits.The cyclic voltammogram showed that the ultrasonic speed the electrodeposition of Pd-Ni-P alloys,especially that of Pd2+ electroreduction.The Tafel curves of the Pd-Ni-P ultrasonic-electrodeposited showed that the corrosion resistance of the alloys is improved in 1.0 mol/L NaOH solution.
Post about "Corrosion resistance"
Study on the Performances of AZ91D Magnesium Alloy with and without Micro-arc Oxidation Coating in Oral Environment
Magnesium is an exceptionally lightweight metal as the “21st century the most potential for development and future of the green engineering materials”.It presents a great potential as medical implant material in our body,such as low price,good biocompatibility, good biodegradability as well as participates the metabolism as the positive ion which just inferior to potassium ion,sodium ion and calcium ion in the cell.However,the chemical property of magnesium alloy is so active that it has to suffering the challenge for meeting the requirements of corrosion resistance,abrasion resistance and fatigue resistance.So some surface treatments should be applied to meet the use of long-term implantation. Micro-arc oxidation（MAO）present a great potential as a surface treatment technology, through MAO,in-situ-grown ceramic coating is directly formed on the surface of magnesium alloy,by which its corrosion resistance,abrasion resistance and fatigue resistance are greatly improved.This research will introduce the AZ91D magnesium alloy into the field of oral implants,Micro-arc oxidation technology will be used to AZ91D magnesium alloy surface modification.With the method of experiment and numerical modeling,the corrosion resistance,abrasion resistance and fatigue resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating in oral environment is studied.The main results are as follows:（1）The corrosion resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating is investigated under the experiments of immersion corrosion and electrochemical corrosion.The result indicates that in the immersion corrosion experiment, within 60 days,the weightlessness of untreated samples is 20.97 times that of micro-arc samples,the electrochemical corrosion experiment enhanced the corrosion electric potential E0 of AZ91D magnesium alloy from-1.45V which without Micro-arc Oxidation Coating in artificial saliva to -0.44V which with Micro-arc Oxidation,corrosion current density I0 from 7.5×10-5A/cm2 without Micro-arc Oxidation Coating to 5.0×10-7A/cm2 with Micro-arc Oxidation.The corrosion resistance of AZ91D magnesium alloy is greatly improved with Micro-arc Oxidation Coating.（2）The X-ray diffraction（XRD）analysis shows the ceramic coating is mainly composed of some oxides which are similar to spine,such as Mg2Al4Si5O18, Mg0.87Al1.83O3.61,MgSiO3 and Mg2Al.Besides this,the ceramic coating also contains some multiple oxides which have magnesium and aluminum in them,the ceramic coating combine tightly with magnesium alloy,it can separate corrosive agent with bulk material, improve the performance of corrosion resistance and abrasion resistance of AZ91D magnesium.（3）The abrasion resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating in the artificial saliva is studied by the wear experiment using the facility of MM-200 which is produced by Nanjing University of Science & Technology. The result shows that the volume loss of AZ91D magnesium alloy without Micro-arc Oxidation Coating is greater than Ti6A14V alloy,the micro-oxidation magnesium alloy is the least.The abrasion resistance of AZ91D magnesium alloy is greatly improved with Micro-arc Oxidation Coating.（4）The abrasion resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating in the artificial saliva is also researched by numerical simulation using the method of finite element.The result shows the similar tendency that the abrasion resistance of AZ91D magnesium alloy is greatly improved with Micro-arc Oxidation Coating.（5）After the AZ91D magnesium alloy is Micro-arc Oxidation treated,the affection to fatigue resistance of the ceramic coating’s thickness and Young’s modulus is studied by finite element.The conclusion is that under the specifically condition of oral environment, the thickness and Young’s modulus of ceramic coating have no essential influence to the fatigue of tooth material.The model will not be destroyed under the cyclic load of infinite times in oral cavity.It is suitable to be denture material to repel fatigue.
Zirconium alloys are widely used as fuel claddings and internals in water-cooled nuclear reactors, due to its low thermal neutron capture cross-section, reasonable mechanical properties and adequate corrosion resistance in high temperature water. As the first safety barrier in reactors, fuel claddings are attacked by radioactive fission products and high temperature water. Waterside corrosion resistance becomes a key issue to be improved by composition adjustment, structure modification and surface treatment.In this paper, the matrixes and the oxide films of surface nano-structure (SNS)Zircaloy-4 alloy, as well as the coarse-grain structure(CGS) Zircaloy-4 alloy have been analyzed by means of TEM, SEM and XRD. Corrosion experience were operated in autoclave under the condition of 673k/10.3MPa. We draw conclusions as following:1、After high speed shot-peening(HSSP) processing, nano-structure (ns) layer was successfully obtained on the surface of Zircaloy-4.The final structure was characterized by nano-structure grains layer, ultrafine grains structure layer and basal coarse-grains structure. The mean grain sizes of them were several nano-meters, hundreds nano-meters and gradually to several micrometers respectively.2、The grain refinement mechanism during HSSP treatments proposed as follow: the peening loads will generate dislocations and eventually result in plastic deformation by twining in the surface layer of the material. Under repeated peening loads, grain refinement occurs in the random orientation twining grains through necking and closing off of small lengths of twins, as well as the movement of high-density faults . With the increase of peening time, ns layer will be developed and its thickness increases too.3、The TEM show that, after 42 days’ corrosion period, the corrosion only occurred on the grain boundary inω-Zr layer of SNS Zicaloy-4,while the CGS Zicaloy-4 corrosion seriously.4、The corrosion power function n of SNS Zicaloy-4 is much smaller than that of CGS Zicaloy-4, which indicates that the SNS Zicaloy-4 is much more protected.5、The transition time of corrosion rate of SNS Zicaloy-4 is about 100 days, however, the CGS Zicaloy-4 occurs at about 42 days, which mean that corrosion process of the former is lag behind than the latter.6、The XRD analysis shows that the value of stress in the oxide film of SNS Zicaloy-4 is higher than that of CGS Zicaloy-4, which is helpful to maintain the tetragonal zirconia, so to low down the corrosion rate. Experimental evidences indicated that the ns Zircaloy-4 has better corrosion resistant property. Not only the grain refinement can influence the corrosion resistance of Zircaloy-4, but also the alloy composition, heat treatment technique, the surface condition, chemistry of reactor coolant, temperature of reactor coolant , irradiation effects and so on. Ether of them changes, the corrosion property is change. Therefore, in order to have a comprehensive knowledge about the corrosion properties of Zircaloy-4, synthetically consideration of these factors are necessary.
It is certainly that nano-materials will have an attractive application prospects because of their outstanding properties, but the corrosion resistance maybe is the negative factor. At present investigations, the impact of surface nanocrystallined zircaloy on corrosion resistance is contradictory; no coincident opinion can be drawn. Therefore, revealed the corrosion mechanism, by studying the corrosion properties of surface nanocrystallined zircaloy, can provide experimental basis for optimizing of existing alloys and developing of novel alloys.One side of the simple was subjected to high-speed shot preening treatment in order to achieve a surface nanocrystallization structure in a certain depth. The oxide films of nanocrystallization Zircaloy-4 alloy in autoclave at 673K/10.3MPa steam have been observed by XRD、SEM、EDS、TEM, respectively in this paper. We draw conclusions as following:（1） Results of 160 days corrosion test under the 673K/10.3MPa condition show that the weight gain of nanostructure Zircaloy-4 is less than that of traditional structure, which indicate that nanostructure Zircaloy-4 has a better corrosion resistance.（2） The M/O interface of nanostructure Zircaloy-4 is more regular and smoother, which imply that, no or less clusters of pores develop in nanostructure.（3） The absence of Oxygen-rich area at the M/O interface of nanostructure Zircaloy-4, indicates that the corrosion process is lag of the traditional structure Zircaloy-4（4） The result of TEM observation indicates that t-ZrO2 formed as a protected coating at the M/O interface in nanostructure zircaloy-4Experimental evidences indicated that the nanocrystalline zircaloy-4 could delay the transition of the corrosion. Simultaneously, the metal/oxide interface of nanostructure Zircaloy-4 was more regular and glossy than that of coarse-grain structure Zircaloy-4. Furthermore, many equiaxed grains were discovered in the oxide films formed on the nanostructure basis, which indicated that nanostructure Zircaloy-4 had a better corrosion resistance. This paper showed the corrosion resistance improvement of nanocrystallization Zircaloy-4 alloy had relation with the percentage of tetragonal-Zirconia, the stress of tetragonal-Zirconia and the high compressed stress of oxide film. However about the corrosion resistance mechanism of nanocrystallizaion Zircaloy-4 alloy should be researched and discussed in the further.
With high-conductivity,high-scalability,high-durability and high- machinability,copper is widely used in the automotive, electrical, electr- onics, electrical appliances and meters, chemicals, metallurgy, machinery, and other industry sectors.In this paper, Al- Fe multi-element penetration has been carried on copper with the method of solid-proliferation. Thermodynamic analysis and study is conducted in the process of co-penetration. The layer micro- structure ,organizations and diffusion mechanism were investigated in details. Thermodynamics and kinetics of oxidation are studied on copper and penetrated copper.The results show that the temperature jumps twice at 400 and 500 degree Celsius in the process of penetration.The expected ratio of the materials,the furnace temperature holding time,the heating rate can to a certain extent impact the heating curve of the penetration tank and the layer thickness.After the process of multi-penetration,a layer is generated on the copper surface.This layer is composed of attachment layer,diffusi- on layer and fusion layer,the layer organization containsα,β,γand I phase.The penetrated copper has better anti-oxidation ability than the non-penetrated copper at the temperature 300 degree Celsius,but has worse anti-oxidation ability at the temperature 400 and 500 degree Celsius.The corrosion ability of the penetrated copper is worse than the non-penetrated copper in 22%HCl and 45% H2SO4 and is better in 3.5% NaCl at room temperature.The average prescription relative error of the temperature data of penetration process is about 20% between the calculative results and the the experimental results,and the correlation coefficient are all above 0.95.
The aluminum electrolytic cell has been developped rapidly these years and the need of qualified refractories used as cathode linings has increased greatly. Because of refractories’contact with the molten cryolitic bath, their corrosion resistance to molten cryolitic bath becomes a very important influence factor for the sevice life of the aluminum electrolytic cell. At present, there is no standard test method in china.It’s very urgent to work out an industry standard of testing method for refactories’corrosion resistance to molten cryolitic bath.The stduy established the static crucible test method to evaluate and compare the corrosion resistance. Based on the chinese practical application of refractories in this field,silica-alumina bricks and dry barrier power were used to carry out the experiments in this work.This method regulated the testing conditions such as temperature,keeping time,sample preparation,cryolitic bath ratio, testing atmosphere and result expression. This method is not only simple and practical, but also easy to prepare samples and fit for all kinds of refracroy material. Moreover, a computer software was designed to calculate the corrosion results which was easy to use and calculated results were accurate and reliable.In this study, the influence factors of the corrosion resistance of refractories to molten cryolitic bath at the different bath ratios and testing atmospheres were discussed. The result shows that: 1.With the increase of the bath ratio, the content of the NaF in cryolitic bath increased, which made the refractories be corroded worse and worse. 2.the corrosion resistance of refractories to molten cryolitic bath in reducing atmosphere was better than in the oxiding atmosphere and the samples hardly showed penetration in the reducing atmosphere.The reason for that should be that there produced much more nepheline in the reducing atmosphere which stopped further penetration. 3.At the same cryolitic bath ratio,when the Al2O3 content increased, the corrosion degree to silica-alumina refractroies increased and with the silimar Al2O3 content, the corrosion degree decreased when the pore dimension increased.
Study on the Corrosion Behavior of Connection System of Stainless Steel to SMA and the Elimination Systerm of Water or Sand in Crude Oil
Fe-based shape memory alloy pipe was widely used to the construction structures in resent years with its unique advantage. Shape memory alloy connection is a new kind of connection method for pipeline. When use those method,the choice of stainless steel tube is a very important. The pitting potential and the galvanic corrosion should be considered. The fill stuff of Tachoing complex connection was study in this paper. It is founded that the best ratio of phosphoric acid solution and CuO is 1:3, the value of connection stress is about 6.3e~6N/m~2. The gap of stainless pipe and Shape memory pipe is a important factor affect the strength of connections, to a certain extent , the greater bonding strength is increased as the gap decreased. The pitting potential of different stainless steel with polarization curves with method was studied. It was found that pitting potential of different stainless steel varies widely. The pitting potential of stainless steel for surface with veins(FW) is better than for the surface is like mirror(JM). Cr element has a great influence on the pitting potential. Pitting potential of 445FW stainless steel which has more Cr is greater than 441FW stainless steel. In addition, the grain size of the crystals is very important to the corrosion performance. Because the size of 304FW grain is bigger than 304JM, the pitting potential of 304FW stainless steel is far greater than 304JM. The different surface treatment method of the stainless steel is also important for the corrosion performance. In this paper, the galvanic current between the heated SMA and three stainless steel were measured through the electrochemical system. It is manifest that 304 stainless steel is more suitable to connections to SMA pipe.In the offshore oil industry, acetate and methanol mixed solution was used for the removing of sand and sea water which ensuring not freezing in low-temperature environment. It is found that the proportion of acetic acid and water for 75%: 25% of the mixture in an environment of -30oC in 10 days has not frozen. The corrosion performance of carbon steel and stainless steel in the above system were studied. Corrosion rate of those two kind of material in acetic acid(75%) and methanol (25%) are wose than in acetic acid (75%)and water(25%) system.. So it is feasible that water can replace methanol in the removing of sand and sea water system. At the same time, a inorganic inhibitor (Copper sulfate) and an organic corrosion inhibitors (Urotropine) were selected, it is found that for carbon steel the former is better than inhibitor CRW85582 and CRW82328,and the latter is also better than inhibitor CRW82328(used in project)for carbon steel and stainless steel.
Magnesium alloys have attracted great attention for applications in automotive, electrical and aerospace industries because of their low density, high specific strength and high specific stiffness, etc. However, magnesium has a very low normal electrode potential, which makes it become one of the most active structural metals. This paper use three surface treatment methods（micro-arc oxidation、direct chemical plating, chemical conversion） to produce protective coatings magnesium alloys. The coatings can increase the corrosion resistance of magnesium alloy and extend the service life.Micro-oxidation coating was prepared on the surface of ZK61 magnesium alloy in silicate and aluminate systems. With the increasing of time and current density, the amount of micropores in the micro-arc oxidation coating decreases, but the size of micropore and the roughness of coating become greater, and thickness shows a linear growth, adhesion force decrease significantly. The corrosion increases first and then declines with the processing time and current density. Current density shows a greater impact on composition of micro-oxidation film. The coating is mainly composed of MgO （periclase, syn） and MgAl2O4 （spinel） in aluminate system. The coating contains MgO （periclase, syn）, Mg2SiO4 （forsterite, syn） and SiO2 in silicate system. The optimum processing parameters for magnesium alloy are in a processing time of 40 min and a current density of 0.20 A/cm2.Direct chemical nickel plating was processed on ZK61 magnesium alloy based on the main salt of basic nickel carbonate and reductant of sodium hypophosphite. Coating has no obvious defects, and surface morphology shows cell bar shape, pH has greater impact on surface morphology. With the increase of pH value, cell bar shape reduces in size first and then increases. With increasing of thiourea concentration, depositing rate decreases straightly. The corrosion resistance of coating increases with the increasing of temperature and time, and increases first and then declines with increasing of pH value. The optimum processing parameters for direct electroless nickel plating are in a processing thiourea density of 1mg/L, temperature of 85℃, time of 60min and pH value of 6.4.Surface morphology of conversion film shows broken tile flake, and has cracks and obvious flaws. With increasing of temperature、time and pH value, the cracks increases in size. Thickness rises with increasing of time and temperature, increases first and then decreases with increase of pH value. The corrosion increases first and then reduces with increasing of time、temperature and pH value. The film is mainly composed of Mg3（PO4）2. The optimum processing parameters for phosphate chemical conversion are in a processing time of 15min, temperature of 40℃, and pH value of 3.5.
Aluminum silicon alloy has many excellent performances, such as smaller density, higher intensity. The corrosion sensitivity of alloy will be beincreased by adding silicon and magnesium. The alloy will be eroded at atmosphere environment. In this paper, the sulfuric acid anodic oxidation has been selected. The process of surface pretreatment is optimized according to studying the effects of degreasing, alkaline cleaning, desmutting on the film mass. Based on the anode oxidation mechanism, the effects of craft parameters, electrolyte concentration, electrolyte temperature, oxidation current density, oxidized time, additive and post-sealing treatment on the oxide film’s quality was discussed. The corrosion resistance of oxide film was qualitative analysed by mensurating AC impedance chart and polarization curve. Considering the ornament performance and corrosion resistance of oxide film, the optimal craft parameter could be obtained ultimately.The morphology, component, microstructure of anodic oxide films are characterized by SEM, XRD and EDS. The results showed that the anodic film is composed of amorphous alumina and has compact and homogeneous surface. Potassium dichromate dropping test, sodium hydroxide dropping test and 240 hour’s neutral salt spray fogtest (NSS) were applied to anodic oxide film, the results indicate that the films which are prepared under the optimum oxidization process conditions were of the resistance to acid, alkali and salt. Electrochemical behavior of anodic oxide films in NaCl solution was studied by means of electrochemical impedance spectroscopy (EIS) and polarization curves. The results revealed that the film after sealing has the better corrosion resistance and the film’s corrosion resistance is relative to the chloride concentration of the NaCl solution.
With the rapid development of science and technology, the relationships between humans and ocean were strengthened by the human activities including exploitations and researches of ocean resources. Metals especially the engineering material that was used in seawater suffered a severe corrosion in marine condition. Since the metal corrosion phenomenon is a big problem in marine environmental,urgent research works on developing corrosion resistant material is a task for academic institutions. Based on the excellent physical and chemical properties of TiO2 film, we want to make full use of the hydrophobic performance of TiO2 film in dark condition. The hydrophobic surface may isolate the direct contact between the surface and solution, reduce the ocean microbe attachment phenomenon and improve the material’s corrosion resistance.First,titanium oxide films were formed on metallic titanium substrates by employing a thermal treatment under air atmosphere. Component of the oxide films were characterized by XRD technique.Contact angle tester and scanning electronic microscopy(SEM) methods were employed to investigate relationship between wetting propeties and microstructure of the oxide film,base on the wetting principles we have successfully improved the hydrophobic property of the oxide film .Second,sunlight effects on the wetting property of tatanium oxides film was also involved in our experiments. Natural seawater immersion experiments was employed in dark and sunlight irradiation condition. Through the electrochemical tests after immersion experiments we foud that: the hydrophilic TiO2 film suffered a photo-corrosion effect in seawater solution due to its semiconductor properties under sunlight; The hydrophobic TiO2 film exhibited a good corrosion resistance. Third,we have studied the microbe attachment state on TiO2 film surface. Results indicated that: the photo-reaction on TiO2 film under sunlight condition possesses the fuction to kill microbes at TiO2 film/seawater interface and the TiO2 film exhibited a favorable microbe attachment prevention property.