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The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: I. Formation, Morphology and Composition

The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: I. Formation, Morphology and Composition

metastable crystal nucleuses cannot grow and disappear at last. The alternate presence and absence of the metastable crystal nucleuses on the sample surface caused the potential fluctuated in the period of 0-40 s, as showed in the embedded figure in Fig. 1. Fig. 2e and 2f show the surface SEM morphologies of the sample immersed in the phosphating bath for 100 s and 200 s. The stable crystal nucleuses grow gradually, and the slab-like phosphate crystals with cracks and porous can be observed on the sample surface when the immersion time is 200 s. The electrochemical homogeneity of the magnesium alloy surface was damaged during the growth process from stable crystal nucleuses to slab-like phosphate crystals, which leaded to the negative movement of potential. Fig. 2g shows the surface SEM morphology of the sample immersed in the phosphating bath for 5 min. The sample surface was fully covered by the phosphate conversion coating, but there are some cracks observed as the result of the hydrogen evolution reaction. With the increase of immersion time, from Fig. 2h and 2i the width of cracks decreases gradually with the immersion time in the range from 10 min to 20 min. Fig. 2i shows the surface SEM morphology of the sample immersed in the phosphating bath for 20 min. The width of cracks is least, and the phosphate conversion coating shows a uniform, compact and integral crystal clusters structure. However, the surface SEM morphology of the phosphate conversion coating with the immersion time of 30 min is similar to that with the immersion time of 10 min, as showed in Fig. 2j. The reason may be as follows: the phosphate conversion coating has been formed completely when the immersion time is 20 min, after that, the coating was dissolved partly in the acidic and corrosive phosphating bath. The thickness of the phosphate conversion coating increased gradually from the slab-like phosphate crystals initially until the phosphate conversion coating formed completely, which lead to the positive movement of potential.
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The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: II. Effects of Components and their Content in Phosphating Bath

The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: II. Effects of Components and their Content in Phosphating Bath

This paper involved a phosphate conversion coating on magnesium alloy AZ91D. The effects of components and their content in phosphating bath on the phosphate conversion coatings were studied. The optimum content for each component in phosphating bath was zinc oxide (ZnO) 2.0 g/L, phosphoric acid (H 3 PO 4 ) 12.0 g/L, sodium fluoride (NaF) 1.0 g/L, sodium tartrate (C 4 H 4 O 6 Na 2 ) 4.0

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The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: IV. Comparison of Electrochemical Behaviors in Borate Buffer and Sodium Chloride Solutions

The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: IV. Comparison of Electrochemical Behaviors in Borate Buffer and Sodium Chloride Solutions

layer on the surface of magnesium alloys [5]. As a kind of main surface protective layer, chemical conversion coating and its preparation technology show some unique advantages, such as low cost, easy operation and so on [6]. Further, the process of phosphate conversion coating (PCC) is the one of relatively mature and low-toxic technology in the field of chemical conversion coating [7].

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The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: III. Nano-particle Modification

The Study of a Phosphate Conversion Coating on Magnesium Alloy AZ91D: III. Nano-particle Modification

Li et al. [5] reported that phosphate conversion coatings mainly provided a mechanical barrier for magnesium alloy substrate to isolate corrosion electrolytes. As insoluble solid substances, the presence of nano-particles in surface protection layer could strengthen the shielded function [13]. Hinton et al. [24] reported that due to the presence of mechanical barrier on metal and alloy surface, the diffusion and permeation process of oxygen molecule could be inhibited, which acted as a main electrochemical species for cathodic reaction. Further, Li et al. [5] also reported that when phosphate coatings were exposed in electrolytes, the occurrence of cathodic reaction mainly focused on crystal clusters, and the anodic reaction mainly occurred on naked magnesium alloy surface, especially on coating defects. As a kind of main coating defect, many cracks are observed on both the original coating and the modified coating surface in this work, as shown in Fig. 5. It is seen obviously that the crack ratio and size for the modified coatings is decreased significantly compared with those for the original coating, indicating the occurrence of anodic reaction could be inhibited on the modified coating surface. On the other hand, it was accepted generally that the grain refinement was beneficial to the corrosion resistance of surface protection layer [25-27]. As shown in Fig. 5, the crystal cluster size of the modified coatings was refined obviously in comparison with that of the original coating. Therefore, from the results of immersion test and electrochemical measurement, it is seen that the corrosion resistance of the modified coatings is better than that of the original coating.
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Effects of Chelating Agents on Electrochemical Behavior and Microstructure of Phosphate Conversion Coatings on Magnesium Alloy AZ91D

Effects of Chelating Agents on Electrochemical Behavior and Microstructure of Phosphate Conversion Coatings on Magnesium Alloy AZ91D

This paper involved the phosphate conversion coatings formed on the magnesium alloy AZ91D from various phosphating baths, each containing one of the following chelating agents: tetrasodium pyrophosphate (TSPP), amino trimethylene phosphonic acid (ATMP), and ethylene diamine tetraacetic acid (EDTA). The effects of the chelating agents on the electrochemical behavior, microstructure, composition, and corrosion protection of the phosphate conversion coatings were investigated by using potentiodynamic polarization (PDP) curves, electrochemical impedance spectroscopy (EIS) plots, scanning electron microscopy (SEM) observations, X-ray diffraction (XRD) analyses, X-ray photoelectron spectroscopy (XPS) analyses, and salt-water immersion (SWI) tests. The results showed that adding TSPP refined the microstructure of the crystal clusters. The results also showed that the phosphate conversion coating derived from the phosphating bath containing TSPP, with the most uniform, compact, and integral crystal clusters, provided better corrosion protection for the magnesium alloy AZ91D than that derived from the phosphating bath containing ATMP or EDTA. According to XPS results, the phosphate conversion coatings were composed of P, O, Zn, Mg, and Al. XRD showed that the major phases of the coatings were Zn 3 (PO 4 ) 2 , Zn 2 Mg(PO 4 ) 2 , and Zn.
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Development and Evaluation of a Chronomodulated Delivery System of Metoclopramide Hydrochloride

Development and Evaluation of a Chronomodulated Delivery System of Metoclopramide Hydrochloride

In conclusion, chronomodulated formulation of MH was developed and optimized statistically using FCCD as a DOE approach. The formulation comprised of fast disintegrating core tablets of MH, compression coated with mixture of glyceryl dibehenate, hydrogenated castor oil and dicalcium phosphate. Glyceryl dibehenate and hydrogenated castor oil were the key factors that controlled the in vitro drug release at all the time points. Night-time administration of the optimized formulation could curb the early morning symptoms of nausea and vomiting in pregnant women and also prevent hypoglycaemia among the diabetic patients with gastroparesis.
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Study on cerium doped nano TiO2 coatings for corrosion protection of 316 L stainless steel

Study on cerium doped nano TiO2 coatings for corrosion protection of 316 L stainless steel

combination with electron trapping at Ce 4+ . We make use of this advantage in the field of photocatalysis to ver- ify its improvement in the photogenerated cathodic pro- tection for metals. On the other hand, cerium nitrate is known as a corrosion inhibitor in an aqueous aggressive medium. The corrosion inhibition properties of cerium nitrate have been widely discussed in literatures [23-25]. It is generally accepted that cerium ions lead to the pre- cipitation of cerium oxides or hydroxides that suppress the corrosion reactions in the defects. Moreover, the in- corporation of corrosion inhibitors into the sol–gel films can improve the protective ability of the coatings [26,27]. We expect that the cerium ions doped in the TiO 2 coating can also enhance the self-protection prop-
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Effect of Silicate Pretreatment on Lanthanum Conversion Coating of Hot-dip Galvanized Steel

Effect of Silicate Pretreatment on Lanthanum Conversion Coating of Hot-dip Galvanized Steel

Modified lanthanum conversion coatings were obtained by immersing hot-dip galvanized (HDG) steel sheets that underwent silicate pretreatment in a lanthanum nitrate solution. The results of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements revealed that silicate pretreatment improved the protective property of the lanthanum conversion coatings, and this conclusion was then corroborated by neutral salt spray (NSS) tests. The morphology and chemical compositions of coatings were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), scanning tunnelling microscopy (STM) and Auger electron spectroscopy (AES). The results showed that many silicate particles were dispersed evenly onto the surface of HDG after silicate pretreatment; as a result, the growth of the lanthanum conversion coatings tended to be homogeneous, so that more uniform and compact coatings can be obtained.
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Synthetic Process of Environmentally Friendly TiO2 Coating on Magnesium by Chemical Conversion Treatment

Synthetic Process of Environmentally Friendly TiO2 Coating on Magnesium by Chemical Conversion Treatment

Magnesium (plate or mesh, AZ91, AZ80, AZ61, etc.) was used as a basic material. Prior to use, the magnesium was treated with a surface active agent for 5 minutes at 323 K and then washed with distilled water. In addition, the magnesium was etched using alkaline and acid solution to remove a thin layer of magnesium hydroxide and to increase its surface area. As a coating process using a chemical conversion treatment, TiO 2 coatings were prepared by dipping magne-

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Synthesis and Electrochemical Characterization a Coating of β -Tricalcium Phosphate Deposited on Steel 316LVM

Synthesis and Electrochemical Characterization a Coating of β -Tricalcium Phosphate Deposited on Steel 316LVM

Beta tricalcium phosphate thin films they were deposited on austenitic steel by means of a magnetron sputtering with r.f. (13.56 MHz) from tricalcium phosphate (TCP) which it was used as a sputtering target. In order to study the effect of the content of the coating; in the corrosion rate and electrochemical response function of time (0, 24, 196 and 720 hours) of the coated steels, corrosion rate is studied by polarization curves Tafel and the electrochemical response by electrochemical impedance spectroscopy, microstructural characterization was performed using scanning electron microscopy (SEM). Finding himself a decrease of 32% in the corrosion rate for the system evaluated to 720 hours. The ion exchange capacity indicates an increase in corrosion resistance.
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Effect of nano hydroxyapatite coating on the osteoinductivity of porous biphasic calcium phosphate ceramics

Effect of nano hydroxyapatite coating on the osteoinductivity of porous biphasic calcium phosphate ceramics

A hydrothermal deposition method was applied to prepare nHA for coating, using analytical grade reagents purchased from Alfa Aesar. First, 0.3 mol/L ammonium dihydrogen phosphate and 0.5 mol/L nitrate tetrahydrate calcium solution were prepared in deionized water. Then 20 g PVP (polyvinylpyrrolidone) was added to the am- monium dihydrogen phosphate solution, which was heated with stirring until the PVP was completely dis- solved, and after the pH value of the solution had been adjusted to 11 with concentrated aqueous ammonia, BCP was added to the solution. Calcium nitrate tetrahy- drate solution was added under ultrasonic irradiation at a rate of 2 mL/min into the above reaction mixture, with continued ultrasound for 30 minutes, and the resulting mixture was transferred to the hydrothermal synthesis reactor (Qiang-Qiang Instruments, Shanghai, China) and maintained under hydrothermal conditions at 120°C for 12 hours. After completion of the reaction, the reaction vessel was naturally cooled to room temperature, and then the nHA-coated, porous BCP ceramic samples were re- moved, filtered, washed with anhydrous ethanol and dis- tilled water alternately, and dried at room temperature before being ready for use.
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Development of Hot Melt Coating Technique for Taste Masking of Chloroquine Phosphate Tablets

Development of Hot Melt Coating Technique for Taste Masking of Chloroquine Phosphate Tablets

The average weight of tablets was 0.537 gm. and all the tablets were within ±5% of it.Thus, the batches complieduniformity of weight test. Also the hardness of tablets was in acceptable range 259.6-280.1 Newton, the friability was 0.119 % and a disintegration time was noted at 5 min 30 sec. hence core tablets was prepared for coating . Coating formula optimization for hot melt coating: For taste masking by HMC technique, precirol ATO 5 was selected, it is partial glyceride used as coating agent for taste masking, modified release of the dosage form. It has M.P.50- 60℃, insoluble in water, and one of the effective solvent free alternative for Hot Melt Coating technique .The viscosity of molten precirol ATO 5 estimated at 65 ℃ at 34.3mPas obtained at shear rate 94.8 S -1 , which make it good partial
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Evaluation of the Wear-Corrosion Process in Beta-Tricalcium (β-TCP) Films Obtained by Physical Vapor Deposition (PVD)

Evaluation of the Wear-Corrosion Process in Beta-Tricalcium (β-TCP) Films Obtained by Physical Vapor Deposition (PVD)

the total impedance evaluation. This behaviour may indicate that the coating confers an excellent corrosion resistance when in contact with the electrolytic solution. However, when evaluating the coating system as a function of time, acceleration 5 times greater than the corrosion rate is evident for a period of 2160 hours (Table 2). This behaviour is explained by the load and accelerated dissolution conditions that result in increased velocities as a function of the evaluation time [34]. Additionally, due to the columnar structure present in the films, wear in this type of materials is compromised. The shape of the cathodic polarization curves is such that the spontaneous formation of a thin layer of oxide on the surface of the coatings can be deduced. At a time of evaluation of 2160 hours the film alters its topography by dissolution phenomena. However, this dissolution is minimal and is related to the values in the corrosion rate. The removal of the oxide layer is due to the cyclic load during the test. The amount of ions released depends on mechanical wear for which reason the material is dissolved 5 times more up until 2160 hours of study.
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Effect of surface nanocrystallization on corrosion behaviour of coated steel in chloride solution

Effect of surface nanocrystallization on corrosion behaviour of coated steel in chloride solution

Figure 3 shows that the Cr and Mo alloys were distributed in the original coarse-grained (CG) and shot-peened nanocrystalline (NC) 15CrMo steel. The high-energy shot peening increased the content of Cr and Mo in the top surface layer of 15CrMo steel (Fig. 3 (same magnification)). The distribution of Cr and Mo elements in the NC layer was more uniform than those in the CG sample. If the Cr and Mo passive alloy elements joined to form a conversion coating, then it could affect the corrosion resistance of the conversion coating. Thus, the surface NC layer can largely improve the surface activity and change the atomic distribution characteristic of the steel. This may have unknown and important effects on the formation process and properties of the surface conversion coating. The effect degree of the NC structure on the conversion coating is related to the type of the conversion coating.
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Application of Laser Removal Processing on Magnesium Alloy Anodized from Phosphate Solution

Application of Laser Removal Processing on Magnesium Alloy Anodized from Phosphate Solution

corroded in the full face (Fig. 7(a)). This result indicates that AZ31B magnesium alloy is extremely prone to corrosion. Corrosion resistance of the specimen treated by conversion treatment (Fig. 7(b)) was more excellent than that of the untreated AZ31B substrate, however, this specimen was also corroded in the full face. Dow17 anodized specimen (Fig. 7(c)) had an excellent corrosion resistance in compar- ison with the conversion treatment, however, this specimen in the area where a coating was removed by the laser irradiation, was intensely corroded. This corrosion is attrib- uted to the removal of the passive coating by the laser irradiation.
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A Novel Waterborne Epoxy Coating with Anticorrosion Properties on Rusty Steel

A Novel Waterborne Epoxy Coating with Anticorrosion Properties on Rusty Steel

As reported in the literature, for better anticorrosive performance, coatings should be well adhered on the metallic substrate, so the rust on the surface of steel piece and hull must be removed thoroughly before painting by sand blasting or degreasing [21]. However, the cost of sand blasting and degreasing are more than half of the total construction and the level of sand blasting surface treatment must be above Sa2.5. In addition, sanded blasting cannot be performed at the corner points and concave points of steel pieces but remove rust by handwork. Therefore, it is important to develop a high efficiency anticorrosive coating which can be applied in moist, oil or rusty conditions.
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Friction and Wear Properties on AZ91D Magnesium Alloy Treated by Anodizing from Phosphate Electrolytic Solution

Friction and Wear Properties on AZ91D Magnesium Alloy Treated by Anodizing from Phosphate Electrolytic Solution

anodized coating and SUJ2 ball, except for the hardness. Figure 6 shows the secondary electron images and X-ray maps obtained by the FE-EPMA analysis for the wear tracks of the various coatings and against the SUJ2 ball after the friction and wear testing. On the untreated specimen, magnesium, aluminum, and oxygen were distributed on the worn part of the substrate. The magnesium and aluminum were then derived from the AZ91D magnesium substrate. The distribution of oxygen seems to occur by the oxidation according to the exothermic reaction based on the friction. Also, iron, which was a main component against the ball, was not detected. Next, magnesium and aluminum derived from the AZ91D magnesium substrate and oxygen as well as iron, which is a main component, were distributed on the worn part against the ball. It was proven that the AZ91D magnesium substrate had intensely transferred to the SUJ2 ball due to adhesion. From the results of no iron in the wear debris shown in Table 5 and the evidence of no transfer from the SUJ2 ball to the AZ91D magnesium substrate, the SUJ2 ball seems to only abrade the AZ91D substrate. Besides, the behavior of the specimen with the conversion treatment was also similar to that described above, except for the phosphorus derived from the conversion coating.
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Effect of Processing Factors and Ambient Conditions on Phytic Acid Conversion Coating on Zinc by Atmospheric Corrosion Monitor Sensor

Effect of Processing Factors and Ambient Conditions on Phytic Acid Conversion Coating on Zinc by Atmospheric Corrosion Monitor Sensor

In order to investigated the difference of these conversion coatings with phytic acid for different immersion time, surface morphological analysis of treated zinc plate was conducted. Fig. 3 presents the SEM images of the conversion coatings. Table 1 lists the chemical composition of these coatings determined by EDS. The SEM morphology of the conversion coating with 60 minutes immersion time shown in Fig. 3(a) reveals that there are network-like wide cracks and discontinued bulk coating. The bulk coating contains 30.19 wt% phosphor verified by EDS in table 1, while the bottom of cracks contains 4.18 wt% phosphor. The conversion coating being immersed in phytic acid for 15 minutes has fewer and narrower cracks, and the phosphor weight percent of both coating and cracks is less too. There are no cracks on the conversion coating immersing for 1.5 minutes and the conversion coating contains 2.45 wt% phosphor. It can be seen that the conversion coating of 1.5 minutes is thin and may be self-assembled monolayer (SAM) [34,35,40]. The geometrical feature of the specimen surface could affect the current density distribution during the chemical reactions [41- 45], thus influencing the corrosion rate. According to the detected data with ACM sensors shown in Fig. 2, the SAM of 1.5 minutes has the best protection capability.
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Investigation of the corrosion behavior of phosphate coated magnesium in a Kokubo Solution.

Investigation of the corrosion behavior of phosphate coated magnesium in a Kokubo Solution.

without coating. The decrease and increase of impedance as a function of immersion time, observed in Figure 3 and Figure 7, could be explained considering the species diagram of Figure 6, and the alkalization reactions as a result of Mg oxidation as it follows: the impedance obtained after one day of immersion in phosphate solution (pH = 10) is higher than the impedance of 99.97 wt. % Mg. After 5 days of immersion, the impedance decreases as a consequence of an increase in the Mg oxidation reaction. According to Equations (3) and (4), Mg oxidation promotes the alkalization of the interphase, which favors the formation of Mg(HPO 4 ) 2 by Equation (3).
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Experimental and Investigation on Piston by Using Yttrium Oxide

Experimental and Investigation on Piston by Using Yttrium Oxide

ABSTRACT: Diesel engines are widely used in transport sector and other areas. Improvement of performance and reduction of smoke density (Emissions) is the important aspect in the combustion ignition engine. The performance of the engine can be increased by the following factors: (a) Reducing the heat energy going out as waste through exhaust gas, (b) Increasing compression ratio (c) Using proper injection timing, (d) Using catalyst coating on the piston top in the combustion chamber. In this project coating on the piston top is selected. This method improves the performance of engines, also reduces the smoke density (Emissions). Many researchers are studying the performance analysis aspects and are coming with useful results. Hence in this experiment an attempt has been made to study the performance of Diesel engine by using the metal catalyst coatings on piston top of Internal Combustion Engine. To overcome the problems of low efficiency and high smoke density of diesel engine, it was decided to coat the catalyst on the top surface of the piston and to speed up the combustion process, supplying more quantity of oxygen at the time combustion. This process of coating the piston will give the better result.
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