Showing papers in "Materials protection in 2010"

Influence of Curing on Physicochemical and Tribological Properties of Waterborne Epoxy Resin-Based Bonded Solid Lubricating Coatings

Abstract: An MFT-R 4000 reciprocating friction and wear tester was performed to investigate the effect of curing conditions on the tribological properties of waterborne epoxy resin-based bonded solid lubricating coatings. The optimal curing conditions were established by combining Fourier transformation infrared (FTIR) spectrometry with differential scanning calorimetry (DSC). It was found that waterborne epoxy resin-based bonded solid lubricating coatings obtained under different curing conditions possessed different tribological properties. The optimal mass ratio of the epoxy resin emulsion to curing agent was determined to be 2∶1, while the optimal curing temperature and time were suggested as 75 ℃ and 2 h respectively. Resultant waterborne epoxy resin-based bonded solid lubricating coating showed excellent physicochemical and tribological properties, and the antiwear life was longer than that of traditional solvent-based bonded solid lubricating coating by 30%.

Microstructure and Wear Resistance of Laser Remelted Plasma Sprayed Ni-Based Alloy Coating on Copper Alloy

Abstract: Self-melted NiCrFeWBC alloy coating was prepared onthe surface of Cu alloy by plasma spraying.The plasma sprayed Ni-based alloy coating was then remelted by laser so as to im-prove the heat conductive behavior,wear resistance and corrosionresistance.The effects of laser remelting on the microstructure and wear resistance of the plasma sprayed Ni-based alloy coating were investigated by using modern analytical techniques.It wasfound that the layered structure and porosities of plasma sprayed Ni-based alloy coating entirely disappeared after laser remelting,and the dense and homogeneous laser cladding layer was metallur-gically bonded with Cu alloy substrate.At the same time,the la-ser cladding layer appeared as equiaxed crystal,dendritic crystal and cellular crystal from outside to inside,and contained precipi-tated particles of WC,W2C and Ni3B.Moreover,the laser clad-ding layer which was dominated by abrasive wear showed much better wear resistance than Cu alloy substrate and plasma sprayedNi-based alloy coating.

Corrosion and Protection of Reinforcing Steel in Concrete Structure

Abstract: A review was provided of the causes leading to corrosion of reinforcing steel in concrete structure in relation to the significant effect of corrosion behavior of the reinforcing steel on the durability of concrete structure. The importance of choosing protection technologies against corrosion of the reinforcing steel properly was emphasized. The corrosion and mechanism as well as factors affecting corrosion behavior of the reinforcing steel in concrete structure were hig-hlighted. Besides, measures of preventing reinforcing steel from corrosion were summarized.

Development and Application of Volatile Corrosion Inhibitors

Abstract: A review was provided of the current status of research and development of volatile corrosion inhibitors. It was pointed out that volatile corro-sion inhibitors had the advantages of simple usage and high effi-ciency,showing great potential as a kind of green technology for preventing metals from volatile corrosion. Moreover,the progress in the applied technology of volatile corrosion inhibitors was sum-marized ,and the development direction of volatile corrosion inhi-bition technology was discussed.

Adsorption Behavior of Residue of Lignitic Coal after Extracting Humic Acid for Cr(VI) in Sewage

Abstract: The residue of lignitic coal in Tianzhu after humic acid extraction was prepared,and the adsorption performance of the residue for Cr(VI) in sewage was evaluated.Results show that the residue of lignitic coal after humic acid extraction can well ad-sorb Cr(VI) in sewage at a room temperature of 20～ 25 ℃ and pH value of 5.The adsorption equilibrium was reached in about 4 h,and the adsorption obeyed Freundlich adsorption isothermal equation.The correlation coefficient R2 was 0.968 6,and the characteristic constant n was 2.044 6.The adsorption process could be described by Ho pseudo second-order dynamic model.

Effect of Spraying in Complex Salt Fog Tests Studied by Grey Relational Analysis

Abstract: Grey relational analysis was adopted to investigate the effect of spraying in complex salt fog tests simulating corrosion in splash zone.The corrosion weight loss and corrosion potential of flame sprayed zinc coatings under four different accelerated testing conditions,including fog plus preserving,fog plus spraying,fog plus drying,and fog plus drying and spraying,were calculated.The grey relational degrees between the results in laboratory and those in actual splash zone were analyzed by using grey relational analysis method.Results show that fog plus spraying test and fog plus drying and spraying test,both involving spraying process,have better simulation performance,which indicates that introducing spraying procedure into traditional fog test and fog plus drying test could better simulate the coupling effects among fog,alternating dry and humid atmosphere,and splashing in the splash zone.

Influence of Saccharin Sodium on Performance and Microstructure of Nanocrystallne Nickel Coating Obtained by Direct Current Electrodeposition

Abstract: Nanocrystalline nickel coating was prepared by using direct current electrodeposition.The effects of concentration of saccharin sodium on the brightness,hardness,flexibility and porosity of the nanocrystalline nickel coating were investigated.The nanocrystal-line nickel coating was characterized by means of X-ray diffrac-tion and electrochemical analysis.It was found that saccharin sodium was adsorbed on the(200) plane of nickel crystal,pref-erentially restricting the growth of Ni crystal thereon and resulting in crystal refining.

Corrosion Resistance of Pulse Electrodeposited Nanocrystalline Ni Coatings in NaCl Solution and NaOH Solution

Abstract: Nanocrystalline Ni coatings were prepared by using pulse electrodeposition The corrosion behavior of the nanocrystalline Ni coatings in 35wt% NaCl solution and 100wt% NaOH solution was evaluated by using soaking and electrochemical polarization methods respectively Results indicate that the nanocrystalline Ni coatings have a low corrosion current and a wide passivation zone in 35wt% NaCl solution,and their corrosion resistance decreases gradually with the reduction of grain sizes In 100wt% NaOH solution,the corrosion resistance of the coatings increased with the reduction of grain sizes,and wide passive zones also emerged in the Tafel curves of the coatings

Application of a Novel Zn-Based Sacrificial Anode for Cathodic Protection of Steel in Soil

Abstract: The protection effect of a novel Zn-based sacrificial anode(ZLR) for steel in soil was studied by measuring constant current and protection potential. Results show that the ZLR anode has a low polarization and steady potential in soil,recording a current efficiency of over 70%. When ZLR anode,conventional Zn anode and conventional Mg anode were separately coupled with steel in soil,the lowest potential and the best protection effect were obtained for the steel coupled with ZLR anode. Besides,the humidity of soil had little effect on the potential of steel coupled with ZLR anode. The ZLR anode was comparable to Mg anode in terms of long-term cathodic protection of steel in soil.

Corrosion Behavior of Q235B Steel and L245 Steel in Dalian Soil Saturated with Water

Abstract: The corrosion behavior of two kinds of gas pipeline steels Q235B and L245 in water saturated soil of Dalian city was evaluated and compared by means of weight loss test and electrochemical impedance spectroscopy. Results show that the corrosion potential of Q235B steel is higher than that of L245 steel by 20 mV. In the initial stage of corrosion,the electrochemical impedance spectra of both steels consisted of three components including high frequency small capacitive reactance,intermediate frequency large capacitive reactance and low frequency small inductive reactance. In the later stage of corrosion,the low frequency small inductive reactance was degraded until it disappeared. With progress of time,the corrosion rate of Q235B steel increased initially and then decreased,while that of L245 steel decreased continuously. L245 steel had better corrosion resistance than Q235B steel.

Research Status and Prospect of Zn-Ni Alloy Electroplating

Abstract: A review was pro-vided of the development history of Zn-Ni alloy electroplating. The representative technology for Zn-Ni alloy electroplating was introduced,and the features of the acidic and alkalic plating sys-tems were compared. Moreover,the current status of research on Zn-Ni alloy electroplating was briefed.

Mechanism,Factors and Control Method of Naphthenic Acid-Induced Corrosion of Oil-Refining System

Abstract: A review was pro-vided of the research progress about corrosion mechanism and control of oil-refining svstems induced by naphthenic acid.It waspointed out that corrosion by naphthenic acid in processing crude oil with high acid value needed to be dealt with urgently.Based on the analysis of corrosion mechanism of naphthenic acid,themajor factors affecting corrosion,including the type and distribu-tion of naphthenic acid.operation temperature,fluid velocity and flow pattern as well as pressure,were discussed.The existentproblems and development direction of corrosion of oil-refining systems induced by naphthenic acid were also introduced.

Effect of Pretreatment Modes of Silicon Carbide Nanoparticulates on the Properties of Electroplated Ni-SiC Nanocomposite Coatings

Abstract: The effects of pretreatment modes of SiC nanoparticles and current density on the corrosion resistance and hardness of electroplated Ni-SiC nanocomposite coatings were investigated by using electrochemical impedance spectroscopy and microhardness tests. Results show that as compared with the Ni-SiC nanocomposite coatings prepared from the bath without surfactants, the coatings obtained from the bath containing anionic-surfactant sodium dodecyl sulfate (SDS) had better corrosion resistance and higher microhardness. However, cationic-surfactant cetyl trimethyl ammonium bromide (CTAB) had an opposite influence on the corrosion resistance and microhardness of the Ni-SiC nanocomposite coatings. Besides, ultrasonic-magnetic stirring of SiC nanoparticles had no effect on the corrosion resistance of the nanocomposite coatings, but had an influence on the microhardness. Increasing current density was helpful to improving the corrosion resistance and microhardness of the nanocomposite coatings.

Synergistic Inhibition Action of Thiourea and Cetylpyridinium Bromide for X70 Steel in Solution of 30% Lactic Acid

Abstract: The inhibition action of thiourea (TU) and cetylpyridinium bromide (CPB) for X70 steel in 30% lactic acid solution,separately or in combination,was investigated by measuring electrochemical impedance spectra and potentiodynamic polarization curves It was found that both TU and CPB had inhibition function for X70 steel in 30% lactic acid solution In particular,TU combined with CPB showed better inhibition performance than TU or CPB alone When TU and CPB were mixed at a mass ratio of 1:1 and introduced as combined inhibitor into the solution of 30% lactic acid at a dose of 20 mg/L,the best inhibition efficiency was obtained

Effect of HCO_3~- on Corrosion Behavior of J55 Steel

Abstract: The effect of the concentration of HCO-3 on corrosion behavior ofJ55 steel was studied by using a potentiodynamic polarizationcurve measurement system and a scanning electron microscope,where J55 steel was tested in aqueous solution of NaHCO3 withvaried concentrations.Results show that under the present experi-mental conditions,HCO-3 accelerates corrosion of the steel at aconcentration below 0.06 mol/L,and it inhibits corrosion of thesteel at a concentration above 0.06 mol/L.With the increase ofconcentration of HCO-3,both the secondary passivation rate andrange were increased,the passivation current was reduced,andthe rupture potential was reduced in a range of 1.00～1.15V.At the same time,the cathodic reaction rate increased with in-creasing concentration of HCO-3,and an abrupt change of polari-zation current occurred when polarization potential was about-0.9 V.The main cathodic reaction for J55 steel in aqueous so-lution of NaHGO3 could be expressed as:O2+4HCO-3+4e→4CO2-3+ 2H2O.The cathodic reaction O2+2H2O+4e→40H onlv might appear at a polarization potential above-0.9V.

crostruncture and Erosion Wear Behavior of Hot-Dipping High-Chromium um Cast-Iron Coatings before and after Heat Treatment

Abstract: High-chromium cast-iron coatings were prepared on carbon steel substrate by hot dipping so as to improve the wear resistance.The microstructure of the coatings before and after heat treatment was analyzed by means of optical microscopy,scanning electron microscopy and X-ray diffraction.The erosion wear behavior of the coatings before and after heat treatment was comparatively investigated,and the morphology of the coatings after erosion was observed.It was found that the coatings were mainly composed of γ-Fe,CrC and CrB.Hard phases CrC and CrB were transformed to Cr7C3 and Cr23C6 when the coatings were heat-treated.At the same time,the erosion wear resistance of the coatings was greatly increased after heat treatment,and the erosion wear volume of the heat-treated coatings was only about 60%of that of the untreated coatings.

Technology for Micro-Arc Oxidation of Mg Alloy Wheel Hub

Abstract: The practical application of micro-arc oxi-dation of Mg alloys was explored by using Mg alloy wheel hubswith a large area as examples.The micro-arc oxidation parame-ters for the Mg alloy wheel hubs were optimized,and the quality of the resulting micro-arc oxidation coating was tested and meas-ured.Results indicate that micro-arc oxidation technology can be satisfactorily used for the surface treatment of Mg alloy wheel hubs,and relevant research might be meaningful and useful to the massive production of surface treatment of magnesium alloys with a large area.

Wear Resistance of Electroless Functionally Gradient Ni-P Coating

Abstract: Three kinds of homogeneous Ni-P coatings with different phosphorus contents and functionally gradient Ni-P coating were prepared by using electroless plating. The hardness, binding strength and wear resistance of the coatings were compar-atively investigated. The effect of gradient composition and micro-structure on the wear resistance of the gradient coating was stud-ied. Result shows that the Ni-P gradient coating has higher hard-ness than homogeneous Ni-P coatings with high and middle P contents, but has lower hardness than homogeneous Ni-P coatings with low P contents. After being heat treated at 400 ℃ for 1 h, the gradient Ni-P coating had the maximum hardness. The gradi-ent Ni-P coating had good binding strength to substrate, and showed better wear resistance than the three kinds of homogene-ous Ni-P coatings under the same test conditions. The wear re-sistance of the gradient Ni-P coating was increased by nearly one to two times after heat treatment. Moreover, the gradient Ni-P coating had a more stable friction coefficient with less fluctuation as compared with the three kinds of homogeneous Ni-P coatings. In general, gradient composition and microstructure contributed to the increasing binding strength and wear resistance of the gradient Ni-P coating.

Electrodeposition of Co-Zn Alloy in Choline Chloride-Urea Ionic Liquid

Abstract: Co-Zn alloy coating was prepared via electrodeposition in choline chloride-urea ionic liquid. The effects of cathode potential, concentration ratio of Co(Ⅱ) to Zn(Ⅱ) , temperature and deposition time on the elec-trodeposition behavior were investigated, and the properties of the alloy coating were also analyzed. Results indicate that uniform amorphous Co-Zn alloy coating with metallic luster and good ad-hesion to substrate can be readily obtained by properly adjusting the composition of the choline chloride-urea ionic liquid and elec-trodeposition parameters as well, and the Co content can reach 90% ( mass fraction) .

Microstructure and Corrosion Resistance of Laser Surface Melting Modified Layer on High Chrome Steel

Abstract: A 5 kW continuous CO2 laser sys-tem was performed for laser surface melting of high chrome steelThe microstructure and corrosion resistance of the laser surfacemelting modified layer were analyzed by using a scanning electronmicroscope and an electrochemical test rig Results show that thehigh chrome steel experienced initial corrosion attack at theboundary of the carbides and matrix, leading to severe corrosionof the matrix and exposure of a large amount of carbides on thecorroded surface Laser surface melting obviously modified thestructure of the as-received steel, leading to the refined grains,complete dissolution of reticular carbides, as well as solid solu-tion of C and alloying elements in austenite dendrites The corro-sion resistance of steel increased

Corrosion Resistance of Electroless Ni-Co-P Coating Prepared on AZ31 Magnesium Alloy in Acidic Plating Bath

Abstract: Ni-Co-P alloy coating was deposited on AZ31 magnesium alloy by electroless plating so as to improve the corrosion resistance.The microstructure,surface morphology and composition of the Ni-Co-P alloy coating were analyzed by means of X-ray diffrac-tion,scanning electron microscopy and energy dispersive spec-trometry.The corrosion resistance of the coating was measured by conducting dropping tests and electrochemical tests.Results show that the Ni-Co-P coating prepared from acidic plating bath has amorphous cell-like structure with P content as much as 9.41 % ,which was much higher than that of the same coating prepared from an alkaline bath.After being coated with Ni-Co-P alloy coating,the corrosion current of the Mg alloy substrate was de-creased by three orders of magnitude,showing significantly in-creased corrosion resistance.