Electrodeposition Of Tungsten Research Articles

Toward Tungsten Electrodeposition at Moderate Temperatures Below 100 °C Using Chloroaluminate Ionic Liquids

The electrodeposition of tungsten at moderate temperatures (<100 °C) has been of significant interest for the fabrication of thin films and microelectromechanical system components to decrease energy consumption and increase process safety. In this study, we investigated the electrochemical reduction of WCl4 and WCl5 in 1-ethyl-3-methylimidazolium chloride (EMIC) and EMIC–AlCl3 ionic liquids at 80 °C–120 °C. W-rich films with a thickness of approximately 1 μm were obtained from the Lewis acidic EMIC–AlCl3–WCl5 bath, whereas the other baths did not yield any deposits. The films obtained from the EMIC–AlCl3–WCl5 bath at 80 °C had higher W contents of 54 at.% than those obtained at 120 °C. X-ray absorption near-edge structure spectra of the W-rich films indicated that W existed in an oxidized state. The findings of this study can be used as a guide to explore optimal electrolytes and electrolytic conditions for the electrodeposition of metallic W at moderate temperatures.

(Invited) Effect of Temperature on the Crystal Structure and Surface Morphology of W Films Electrodeposited from Csf–Cscl Eutectic Melt

1. IntroductionTungsten is a metal with excellent properties such as high heat resistance, high strength, and low thermal expansion, and is used for carbide tools, heat sinks, and fusion reactor diverters. However, due to its hardness and brittleness, tungsten is difficult to process into complex shapes and thin films. If tungsten plating on materials with good processability becomes possible, the range of applications will be greatly expanded. Therefore, as one of the plating methods, electrodeposition of tungsten in high-temperature molten salts has been investigated [1–3].Our group has previously reported the electrodeposition of α-W films in molten KF–KCl–WO3 at 923 K and mixed phase films of α-W and β-W in molten CsF–CsCl–WO3 at 873 K [4]. We also reported that β-W films with mirror-like surface were electrodeposited in molten CsF–CsCl–WO3 at 773 K [5]. In the present study, we investigated the effect of bath temperature on the smoothness and crystal structure of W films electrodeposited from molten CsF–CsCl–WO3. We varied the temperature from 773 to 923 K and the cathodic current densities from 6 to 25 mA cm−2, and analyzed the electrodeposited W films on Cu plate substrates by XRD and SEM/EDX.2. ExperimentalThe experiments were carried out in eutectic CsF–CsCl melt (50:50 mol%, melting point 713 K) with WO3 (1.0 mol%) additive at various temperatures in the range of 773–923 K. The melt was placed in a graphite crucible and the experiments were conducted in an argon atmosphere in an airtight SS container. Cu plates were used as working electrodes and a glass-like carbon rod was used as a counter electrode. A Pt wire was used as a quasi-reference electrode and the potential was calibrated by Cs+/Cs potential measured at a Ag electrode. Samples prepared at cathodic current density of 6–25 mA cm−2 were washed with distilled water to remove adhered salts, and then analyzed by XRD and SEM/EDX.3. Results and DiscussionFig. 1 shows the appearance of the samples obtained at 6–25 mA cm−2 and 773–923 K. No electrodeposits were obtained at 25 mA cm−2 and 773 K, which is due to the co-deposition of Cs metal fog because the potential during the electrolysis was close to 0 V with respect to Cs+/Cs potential. In other conditions, gray or silvery colored deposits were obtained. In particular, a mirror-like surface was obtained at 6 mA cm−2 and 773 K, indicating that the electrodeposited W film had a highly smooth surface. Fig. 2 presents the XRD patterns of the electrodeposits; all the XRD patterns were attributed to metallic W. However, only β-W was detected below 823 K, both α-W and β-W were detected at 873 K, and only α-W was detected at 923 K. This result indicates that the crystal structure of W obtained in molten CsF–CsCl–WO3 varies with bath temperature.To investigate the smoothness of each obtained W film, we performed cross-sectional SEM observation and surface roughness (Sa) measurement. Fig. 3 shows the cross-sectional SEM images. At all bath temperatures, the lower the current density, the smoother the surface becomes, and the higher the current density, the more uneven the surface becomes. This is because the concentration gradient of W(VI) ions in the diffusion layer becomes larger, and the electrodeposition of W proceeds preferentially on the convex surface. It was found at the same low current density that the lower the bath temperature, the higher the smoothness. In particular, the mirror-like W film obtained at 6 mA cm−2 and 773 K showed almost no irregularity in the cross-sectional SEM image. The surface roughness Sa was as small as 0.32 μm, indicating that the W film was extremely dense and smooth. The reason for the smoother surface at lower bath temperatures is speculated to be due to the crystal structure of β-W and the suppression of crystal growth.AcknowledgementThe present address of Kouji Yasuda is Graduate School of Engineering, Kyoto Univ.

Electrodeposition of Tungsten from Molten KF–KCl–WO3 and CsF–CsCl–WO3

Introduction Tungsten metal is known for its robustness, especially high melting and boiling points and hardness. However, its hardness and brittleness make it difficult to work. Thus, electrodeposition of flat and dense tungsten films is worth investigating. There are a number of reports on the electrodepositon of tungsten from high temperature molten salts such as fluorides [1], chlorides [2], oxides [3], etc. It is known that dense and coherent tungsten deposits are more easily obtained from molten fluorides compared to molten chlorides. One drawback of typical fluoride melts like LiF–NaF–KF is difficulty in removing the adhered molten salts by water washing because LiF and NaF have limited solubility to water [4]. Although good tungsten deposits can be electrodeposited from molten oxides [3], the operation temperature tends to be very high, typically over 1123 K.From this background, we proposed new electrolyte baths, molten KF–KCl [5,6] and CsF–CsCl. Since all the components salts of KF, KCl, CsF and CsCl have large solubility to water [4], solidified salts on deposited films can be easily removed by water washing. Results & Discussion First, electrodeposition of tungsten was investigated in eutectic KF–KCl melt to which WO3 was added at 923 K. Cyclic voltammograms at copper and gold electrodes indicated the deposition of tungsten metal at more negative potential than 1.55 V vs. K+/K. The effects of electrolysis conditions on the morphology of deposits were studied by changing the cathodic current density from 12.5 to100 mA cm−2. As shown in Fig.1(a), a dense tungsten film with a thickness of approximately 20 µm was obtained on a copper substrate electrode at 12.5 mA cm−2 for 120 min. From the Raman spectra of molten KF–KCl and molten KF–KCl–WO3 at 923 K, the coordination structure of W(VI) complex ion was indicated to be fac-[WO3F3]3−.Secondly, eutectic CsF–CsCl melt was used to lower the operation temperature. After adding 2.0 mol% of WO3, the electrodeposition was investigated using copper and gold electrodes at 823–923K. As shown in Fig.1(b), a flat and dense tungsten film was obtained by galvanostatic electrolysis at 12.5 mA cm−2 for 120 min at 873 K. Acknowledgement This study is supported by Sumitomo Electric Industries, Ltd. The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University.

Electrodeposition of Dense Tungsten Films from Molten KF-KCl-WO3 and Csf-Cscl-WO3

Tungsten metal is known for its robustness, especially high melting and boiling points and hardness. However, its hardness and brittleness make it difficult to work. Thus, electrodeposition of dense tungsten films is worth investigating. There are a number of reports on the electrodepositon of tungsten from high temperature molten salts such as fluorides, chlorides, oxides, etc. It is known that dense and coherent tungsten deposits are more easily obtained from molten fluorides compared to molten chlorides. Although good tungsten deposits can be electrodeposited from molten oxides, the operation temperature tends to be high, typically over 1123 K. One drawback of typical fluoride melts like LiF-NaF-KF is difficulty in removing the adhered molten salts by water washing because LiF and NaF have limited solubility to water.From this background, we proposed new electrolyte baths, molten KF-KCl and CsF-CsCl. Since all the components salts of KF, KCl, CsF and CsCl have large solubility to water, adhered salts to deposited films can be easily removed by water washing.First, electrodeposition of tungsten was investigated in eutectic KF–KCl melt to which WO3 was added at 923 K. Cyclic voltammograms at copper and gold electrodes indicated the deposition of tungsten metal at more negative potential than 1.55 V vs. K+/K. The effects of electrolysis conditions on the morphology of deposits were studied by changing the cathodic current density from 12.5 to100 mA cm-2. As shown in Fig.1 (a), a dense tungsten film with a thickness of approximately 20 µm was obtained on a copper substrate electrode at 12.5 mA cm−2 for 120 min. From the Raman spectra of molten KF–KCl and molten KF–KCl–WO3 at 923 K, the coordination structure of W(VI) complex ion was indicated to be fac-[WO3F3]3−.Secondly, eutectic CsF-CsCl melt was used to lower the operation temperature. After adding 2.0 mol% of WO3, the electrodeposition was investigated using copper and gold electrodes at 823-923K. As shown in Fig.1 (b), a dense and smoother tungsten film was obtained by galvanostatic electrolysis at 12.5 mA cm−2 for 120 min at 873 K. Figure 1

Electro-deposition tangsten coating on low activation steel substrates from Na2WO4-ZnO-WO3 melt salt

Tungsten coating is considered as a promising alternative material for plasma facing materials (PFC) in future fusion devices. The electro-deposition of tungsten in Na2WO4-ZnO-WO3 melt at 1173 K on low activation steel substrates was studied in this work. Adherent and smooth tungsten films were deposited under various pulsed current conditions. The crystal structure and microstructure of tungsten deposits were characterized by XRD, SEM and EDX techniques. The results show that pulsed current density and duty cycle have a significant influence on tungsten nucleation and electro-crystallization phenomena. Uniform and smooth tungsten coating with high purity and high adherence is obtained on low active steel substrates as cathodic current density ranges from 35 to 25 mA·cm−2.

ChemInform Abstract: Electrodeposition of Tungsten in ZnBr2-NaBr and ZnCl2-NaCl Melts.

The electrodeposition of tungsten has been investigated in the molten salt systems and at 450°C. Voltammetric results showed that the reduction of tungsten species is an irreversible process. Electrodeposits were mixtures of α‐ and β‐tungstens, the former being the thermodynamically stable phase. α‐Tungsten exhibited the shape of cubic crystallites which tended to grow larger, whereas β‐tungsten always had a crystal size smaller than 1 μm. The β‐tungsten was formed during the initial stage of electrodeposition, irrespective of the substrate material, and remained predominant at high current densities or in pulsed electrolysis. It is likely that the phase transition of β‐tungsten to α‐tungsten occurs when the size of the β‐tungsten crystallites becomes larger than a critical value.

Electrodeposition of tungsten from ZnCl 2–NaCl–KCl–KF–WO 3 melt and investigation on tungsten species in the melt

The electrodeposition of tungsten in ZnCl 2–NaCl–KCl–KF–WO 3 melt at 250 °C was further studied to obtain a thicker deposit. In the ordinary electrolysis at 0.08 V vs. Zn(II)/Zn, the current density decreased from 1.2 mA cm −2 to 0.3 mA cm −2 in 6 h. A thickness of the obtained tungsten layer was 2.1 μm and the estimated current efficiency was 93%. A supernatant salt and a bottom salt were sampled after 6 h from the melting and were analyzed by ICP-AES and XRD. It was found that the soluble tungsten species slowly changes to insoluble ones in the melt. The soluble species was suggested to be WO 3F − anion. One of the insoluble species was confirmed to be ZnWO 4 and the other one was suggested to be K 2WO 2F 4. Electrodeposition was carried out under the same condition as above except for the intermittent addition of WO 3 every 2 h. The current density was kept at the initial value and the thickness was 4.2 μm. The intermittent addition of WO 3 was confirmed to be effective to obtain a thicker tungsten film.

Electrodeposition of Tungsten, Molybdenum and Double Carbides of Tungsten (Molybdenum) and Nickel (Cobalt) from Low-Temperature Halide-Oxide Melts

We investigated the processes of electrochemical deposition of metallic tungsten and molybdenum, carbides of molybdenum and tungsten by methods of cyclic voltammetry, electrolyses from halide-oxide melts at temperature 550 {degree sign}C. Conditions of joint electroreduction of fluoride complexes of tungsten and molybdenum, carbon dioxide and ions of nickel and cobalt in halide-oxide melts are found at temperature 550 {degree sign}C. Optimum conditions of obtaining of metallic tungsten and molybdenum, carbides of tungsten (molybdenum), double carbides tungsten with nickel (cobalt) from halide-oxide melts are determined.

Electrodeposition of tungsten and molybdenum metals and their carbides from low-temperature halide-oxide melts

The electrodeposition of tungsten and molybdenum metals and their carbides from the halide-oxide melts at a temperature of 550°C is studied using cyclic voltammetry and potentiostatic and galvanostatic electrolyses. The conditions of concurrent electroreduction of fluoroxide complexes of tungsten and molybdenum with carbon dioxide and also with nickel and cobalt ions in the halide-oxide melts at 550°C are found. The optimal conditions for the production of tungsten and molybdenum metals, tungsten (molybdenum) carbides, and binary carbides of tungsten with nickel (cobalt) from the oxide-halide melts are determined.

Electrodeposition of Tungsten, Molybdenum and Double Carbides of Tungsten (Molybdenum) and Nickel (Cobalt) from Low-Temperature Halide-Oxide Melts

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Electroplating with Tungsten and Tungsten–Molybdenum Alloys from Metaphosphate-containing Halide–Oxide and Oxide Melts

The electrochemical behavior of dimeric tungsten complexes in metaphosphate-containing melts is studied potentiometrically and voltammetrically. The electrodeposition of tungsten and tungsten–molybdenum coatings from halide–oxide and oxide melts and the correlation between the properties of deposits and the conditions of electrolysis are investigated.

Electrodeposition of Tungsten and Related Voltammetric Study in a Basic ZnCl2­NaCl (40-60 mol %) Melt

The electrodeposition of tungsten and voltammetric experiments were performed in basic (40-60 mol %) melts containing various tungsten compounds at 450°C. In constant potential electrolysis, metallic tungsten was obtained from and but not from and Similar to the case of acidic melt (60-40 mol %), the oxide ion or an oxochlorotungsten species may participate in the electrodeposition process. The presence of molecular oxygen does not interfere with the process. © 2000 The Electrochemical Society. All rights reserved.

Electrodeposition of Tungsten in ZnBr2 ‐ NaBr and ZnCl2 ‐ NaCl Melts

The electrodeposition of tungsten has been investigated in the molten salt systems and at 450°C. Voltammetric results showed that the reduction of tungsten species is an irreversible process. Electrodeposits were mixtures of α‐ and β‐tungstens, the former being the thermodynamically stable phase. α‐Tungsten exhibited the shape of cubic crystallites which tended to grow larger, whereas β‐tungsten always had a crystal size smaller than 1 μm. The β‐tungsten was formed during the initial stage of electrodeposition, irrespective of the substrate material, and remained predominant at high current densities or in pulsed electrolysis. It is likely that the phase transition of β‐tungsten to α‐tungsten occurs when the size of the β‐tungsten crystallites becomes larger than a critical value.

Studies on the electrodeposition from organic solutions of metals that are difficult to deposit from aqueous solutions

This paper deals with studies on electrodeposition from organic solutions of metals that are impossible (aluminium, beryllium, lithium) or difficult (tungsten, molybdenum) to electrodeposit from aqueous solutions. First, Al(CF 3COO) 3 and Be(CF 3COO) 2 were synthesized; their solubilities in various organic solvents and the specific electrical conductivities of the solutions were measured, and then electrodeposition of aluminium and beryllium was attempted with these solutions. Electrodeposition of aluminium and beryllium was found to be possible and, especially with aluminium, a smooth and lustrous deposit was obtained from a methanol solution with a cathodic current efficiency of about 30%. Electrodeposition of lithium was tried with organic solutions containing LiNO 3, LiClO 4 or LiCl as an electrolyte; lithium was found to be electrodeposited from a solution LiNO 3 and N,N-dimethylacetamide at an efficiency of over 70%. Electrodeposition of tungsten and molybdenum was attempted with organic solutions containing the phosphoric acid compounds of each metal as electrolyte. It was found that tungsten and molybdenum, each together with its respective oxide, could be electrodeposited from a solution of phosphotungstic acid, H 3BO 3, NH 4Cl, H 2O 2 and HCONH 2 and from a solution of phosphomolybdic acid, citric acid, NC 4Cl, H 2O 2 and HCONH 2 respectively.

タングステン-鉄電着合金の組成と構造を決定する機構について

Electrodeposition of iron-tungsten alloys from aqueous ammoniacal alkaline tartrate electrolytes is studied by means of electron diffraction of cathode deposits and chemical analysis of the solution sorbed on them. In resemblance to the adsorption of irregular binany system, the metal component of lower concentration in bulk electrolyte is preferentially adsorbed at non-polarized electrode. This paper describes that this adsorption is important in studying induced codeposition. The electrodeposition of crystalline Fe3W having a non-equilibrium superlattices of DO19 type was found. A geometric requirement for the formation of these crystals was presented. The effect of codeposition of hydrogen on inhibition of this requirement was shown, which accounts for the observed structural transition of alloys prepared under different conditions. The stoichiometry present in the cathode deposits supports the correlation previously proposed between metal composition of electrolyte in the bulk and that at the cathode surface. Qualitative description can be given of the alloy composition using the values of metal composition of ions at the cathode surface and certain reluctance of tungsten in codeposition. This description will be in better agreement with the experimental results on the assumtion that the electrodeposition of tungsten is catalyzed by multiplets of iron atoms deposited in particular geometric structure.

Investigation of cathodic polarization occurring during simultaneous discharge of iron and tungsten ions

1. An investigation of the simultaneous deposition of iron and tungsten has shown that the separation potential for the alloy is 100 mv less than the separation potential for iron and 300 my less than the standard potential of tungsten. 2. It has been shown that the possibility of discharging tungsten ions depends on the depolarizing action of the simultaneous discharge of iron and tungsten ions. 3. It has been shown also that there is no periodic variation in the potential during the electrodeposition of tungsten and iron; which is in conflict with Holt's ideas on the layered deposition of iron and tungsten.