Molten Salt Electrodeposition Research Articles

Growth Kinetics and Microstructure of Siliconized Layer by Molten Salt Electrodeposition

The siliconized layers were formed on the surface of hot rolled grain oriented silicon steel using a molten salt pulse electrodeposition method. The process was performed in the temperature range 1023-1123 K and with varying deposition time (60-180 min). The profile distribution of Si in the siliconized layer was measured using the glow discharge spectrometry (GDS) and the depth from the surface to the substrate was taken as the layer thickness. The morphology and structure were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that a longer deposition time tended to produce a larger grain and a looser, rougher layer. The phase structure of the layer was composed of Fe3Si with (110) preferred orientation in the experimental range. The longer deposition time resulted in an increase in thickness layer and the thickness of the layers ranged from 17 to 165m. Kinetic studies showed that the siliconized layer grew with a parabolic rate law, indicating the diffusion controlled growth. The activation energy for growth of siliconized layer was about 242 kJ/mol.

溶融塩電析法による活性金属を含むNiアルミナイドのコーティング

溶融塩電析法による活性金属を含むNiアルミナイドのコーティング

Improvement of Cyclic Oxidation Resistance of Fe-23 mass% Cr Alloy by Molten Salt Electrodeposition of Lanthanum

Improvement of Cyclic Oxidation Resistance of Fe-23 mass% Cr Alloy by Molten Salt Electrodeposition of Lanthanum

Effect of the Electrodeposition Temperature on the Cyclic-Oxidation Resistance of Ni Aluminide Containing Zr Formed by Molten-Salt Electrodeposition

The effect of the Al electrodeposition temperature on the cyclic oxidation resistance of Ni aluminide containing Zr formed by molten salt electrodeposition was investigated. Zr and Al were deposited by molten salt electrolysis. For the sample treated with the Al deposition at 1073 K, a layer consisting of Ni2Al3 was uniformly formed. On the other hand, for the sample treated by Zr deposition, followed by Al deposition at 1073 K, a layer consisting of Ni2Al3 and a Ni aluminide layer containing Zr on the Ni2Al3 layer were formed. Furthermore, when the Al electrodeposition temperature was changed, the concentration of Zr in the Ni aluminide layer containing Zr changed. When the Al electrodeposition was carried out at 1153 and 1173 K, the Zr was scarcely observed in the surface region of the Ni aluminide layer. The cyclic oxidation test showed that for the sample treated with only the Al deposition and the sample treated with the Zr deposition, followed by Al deposition at 1073 K, a mass reduction due to scale exfoliation took place, whereas for the samples treated with the Zr deposition, followed by Al deposition at 1153 and 1173 K, no mass reduction was observed. For these samples, after the cyclic oxidation test, a scale consisting of � -Al2O3 adhering to the substrate was formed. Consequently, it was found that the cyclic oxidation resistance of Ni was improved by Zr deposition, followed by Al deposition at 1153 and 1173 K. [doi:10.2320/matertrans.MRA2008293]

Formation of Ni-aluminide Coating Containing Hf by Molten-Salt Electrodeposition and Cyclic-Oxidation Resistance

The formation of a coating layer consisting of Ni-aluminide containing Hf on a Ni–10at.%Cr–8at.%Al alloy substrate was attempted by the electrodeposition of Hf, Ni, and Al. The cyclic-oxidation resistance for the alloy covered with this coating was then evaluated in air at 1,423 K. Ni was deposited by aqueous solution electrolysis. Hf and Al were deposited by molten-salt electrolysis. For the sample first treated with the Hf-deposition, subsequently treated with the Ni-deposition, followed by Al-deposition, a coating consisting of Ni2Al3 of about 40-μm thickness was uniformly formed on the alloy. At the center region of this coating, a Hf-concentration layer was formed. The cyclic-oxidation test showed that, for the untreated sample and the sample with only Ni and Al depositions, a mass reduction due to spallation of a scale took place during the initial oxidation period. On the contrary, for the sample with Hf, Ni, and Al depositions, a mass reduction due to spallation of a scale scarcely took place. The cross-sectional observation using SEM showed that, for the sample with Hf, Ni, and Al depositions after the oxidation test, an adhesive scale having a spiked shape was formed. This scale mainly consisted of α-Al2O3, and contained HfO2 particles. It was postulated that, for this sample, the Hf in the Hf-concentration layer diffused into the surface region of the Ni-aluminide layer, contributing to improvement in the exfoliation resistance of the scale.

溶融塩電析法による耐水蒸気酸化性ステンレス鋼表面の創製

溶融塩電析法による耐水蒸気酸化性ステンレス鋼表面の創製

Preparation of Highly Oxidation-Resistant Surface by Molten Salt Electrodeposition

In order to prepare a highly oxidation-resistant surface for TiAl and SUS 304 stainless steel, the molten salt electrodeposition of Al or Y on these metals was carried out. The electrodeposition was conduced using a potentiostatic polarization method at constant potentials in an equimolar NaCl-KCl melt containing AlF3 or YF3 at 1023 K. After the Al electrodeposition, homogenous deposit layers were formed on the TiAl and the stainless steel. The deposited layer formed on the TiAl consisted of TiAl3. The deposited layer formed on the stainless steel consisted of some Fe aluminides. The TiAl and the stainless steel covered by the electrodeposited layers were far more resistant than the bare TiAl and stainless steel to high temperature oxidation. The Y electrodeposition on the stainless steel induced the deposition of Y particles on the stainless steel. The cyclic-oxidation resistance of the electrodeposited stainless steel was remarkably improved as compared to the untreated stainless steel.

Formation of Ni Aluminide Layer Containing La by Molten-Salt Electrodeposition and Cyclic-Oxidation Resistance

In order to improve the cyclic-oxidation resistance of Ni and SUS304 steel, the coating of a Ni aluminide containing La on both samples were carried out by the electrodeposition of Al and La in a molten salt. The electrodepositions of Al and La were conducted using a potentiostatic polarization method at 1023 K in an equimolar NaCl-KCl melt containing 3.5 mol%AlF3, and that containing 4 mol%La2O3-24 mol%NH4Cl, or 3.5 mol%LaF3. Observation and analysis of the cross-section of the specimen after polarization showed that a deposited layer consisting of a thick inner Ni aluminide layer and a thin outer layer containing a large amount of La was formed on both samples. The cyclic-oxidation resistance of the Ni specimen covered with the deposit layer having the La layer as the outer layer was higher than those of the untreated Ni specimen and the Ni specimen coated with the deposit layer without La. The stainless steel covered with the Ni aluminide showed a high cyclic-oxidation resistance in the atmosphere containing water vapor at 1273 K in comparison with untreated stainless steel, without depending on the existence of La in the deposited layer.

Improvement in Oxidation Resistance of Stainless Steel by Molten-Salt Electrodeposition of La

Improvement in the oxidation resistance of SUS304 stainless steel was accomplished by electrodeposition of La in a molten salt. The electrolysis of La was conducted using a potentiostatic-polarization method in an equimolar NaCl–KCl melt containing 3.5 mol. LaF 3 at 1023 K. Observation of the specimen surface after polarization at −1.8 V (vs. Ag/Ag+ (0.1)) for 0.18 ks showed that La particles were uniformly dispersed on the surface. The oxidation resistance of the electrodeposited stainless steel was significantly improved as compared with the untreated stainless steel. The scale formed on the untreated stainless steel after oxidation was thick and consisted of Fe2O3 and Fe3O4, whereas the scale formed on the elecrodeposited stainless steel was extremely thin, and mainly consisted of Cr2O3.

Compact Coating of Tantalum on Tungsten Prepared by Molten Salt Electrodeposition

Attempts to prepare tantalum coating on tungsten have been performed in 55 mol%LiF–35 mol%NaF–10 mol%CaF2 melt containing K2TaF7. Electrolytic deposition of tantalum was carried out by galvanostatic polarization. A conproportionation reaction also occurred that interfered with the electrodeposition and resulted in decrease in current efficiency. However, the product of this reaction was soluble, which diffused away from the electrode without contaminating the deposit. Hence, a compact electrodeposited tantalum coating was obtained on tungsten substrate. An excellent interface was possible when coating was performed in the melt containing 2 mol% K2TaF7.

溶融塩電析によるＭｏシリサイドの生成

溶融塩電析によるＭｏシリサイドの生成

Tantalum protective thin coating techniques for the Chemical Process Industry: Molten salts electrocoating as a new alternative

A comparison of corrosion resistance and basic properties of solid tantalum with other high-performance materials used in the Chemical Process Industry (CPI) is given. The corrosive chemicals taken into consideration are strong acidic media. Secondly, it is pointed out that tantalum, which exhibits excellent corrosion resistance, owing to a rapid build-up of passivating protective film in oxidizing conditions, also has good mechanical, thermal and electrical properties which suggest its use when little or no metallic corrosion is tolerated. Thirdly, tantalum thin-layer, coated onto a usual base metal, which offers the same protection as solid metal and avoids its expensive use, is treated. Fourthly, numerous tantalum-coating techniques for clad-vessel and CPI devices are reviewed and compared. Amongst these coating techniques, this paper focuses mainly on two techniques which give a very thin, protective coating against corrosion. Thus, Chemical Vapor Deposition (CVD) and Molten Salt Electro-deposition (MSE) are especially enhanced. Finally, MSE which is still not widely used for manufacturing clad-vessels is examined in greater detail.

ChemInform Abstract: Nonaqueous Electrodeposition of Niobium from Propylene Carbonate and Acetonitrile

Despite its many outstanding properties, including superconductivity, corrosion resistance, and a high melting point, niobium remains one of the most elusive metallic elements for successful electrodeposition under mild conditions. Some factors which may contribute to the difficulty of electrodeposition include a rather negative reduction potential, which leads to interference by hydrogen evolution in aqueous solutions; the tendency of niobium species to react with oxygen or moisture to form electrochemically inactive species, and to even abstract oxygen from certain non-aqueous solvents like dimethylsulfoxide; and the tendency of niobium to form stable cluster compounds at low valent states. current successful methods for electrodeposition involve either high temperature (i.e. > 700/sup 0/C) molten salt electrodeposition in alkali halide mixtures (2-5), or cryogenic electrodeposition from pure liquid halogens, interhalogens, or hydrogen halides, such as HF. The authors report here preliminary results on the electrodeposition of niobium from organic solvents at room temperature. This approach affords two unique advantages. First, it allows a simpler electrochemical cell to be used compared to those used for the corrosive and toxic alkali fluoride melt or the volatile HF. Second, thermally induced lattice disorder may potentially be minimized so that the niobium film may be better suited for technologicalmore » applications.« less

Nonaqueous Electrodeposition of Niobium from Propylene Carbonate and Acetonitrile

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Conditions for stable growth of epitaxial GaP layers by molten salt electrodeposition

The conditions necessary for stable growth of epitaxial GaP layers by molten salt electrodeposition on silicon and GaP substrates were studied. The usefulness of silicon as a substrate material was limited by a thermal expansion mismatch with GaP and by its reactivity with the melt. Smooth, coherent GaP layers were grown on GaP substrates at growth rates up to 23 μm/h (20 mA/cm2) at 800°C.

The synthesis of GaAs by molten salt electrolysis

Molten salt electrodeposition of gallium arsenide is reported the first time. Deposition occurred at 720–760°C, from a molten solution containing NaAsO 2 and Ga 2O 3 in a B 2O 3-NaF solvent.

The use of proton-excited X-rays for thin-film profiling

Measurement of characteristic X-rays excited at the surface of a solid by proton bombardment provides quantitative compositional analyses that, when combined with low-energy argon ion sputtering, can be used to provide depth profiles of thin films. Several examples of the use of this technique will be presented to demonstrate its broad applicability. Proton-excited X-ray (PEX) analyses are obtained with 100–200 keV proton bombardment and energy-dispersive X-ray analyses using both lithium drifted silicon solid-state detectors and gas-flow proportional counters. Using the appropriate X-ray production cross sections and geometrical and X-ray absorption factors, the absolute number of atoms/cm 2 of a particular element is obtained for the thin film. As successive sections of the film are removed using 1 keV argon ion sputtering, the number of atoms/cm 2 of a particular element that remains is accurately monitored thereby generating an integral profile that can, subsequently, be differentiated to produce the depth profile. From measured values of the sputtering yield, the depth scale can be reported in angstroms. The PEX profiling technique has been routinely used in the characterization of corrosion products, electrodeposited coatings, surface alloys, and metal/oxide interfaces as well as in the determination of absolute sputtering yields. Specific examples to be described come from extensive studies of corrosion films formed in geothermal brines, molten-salt electrodeposition of platinum group alloys, surface alloys fabricated by ion implantation, and studies of the metal/oxide interfaces resulting from low-temperature oxidation of iron.