- Email: [email protected]
ASPPS dual mode thermal spray equipment using Ar added N2 working gas
Vacuum xxx (2016) 1e6
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas Yasutaka Ando a, *, Dickson Kindole a, Yoshimasa Noda b, Richard N. Mbiu c, Bernerd K. Kosgey c, Stephen M. Maranga c, Akira Kobayashi d, e, f a
Division of Renewable Energy and Environment, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558, Japan Collaborative Research Center, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558, Japan Department of Mechanical Engineering, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62,000 e 00200, Nairobi, Kenya d Malaysia Japan International Institute of Technology, University of Technology Malaysia, Jalan Semarak 54100, Kuala Lumpur, Malaysia e Graduate School of Eng., Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan f University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 April 2016 Received in revised form 25 September 2016 Accepted 14 October 2016 Available online xxx
In order to develop a low cost oxide film deposition process with short duration time, a 1 kW class Atmospheric thermal plasma spray (APS)/Atmospheric solution precursor plasma spray (ASPPS) dual mode thermal spray equipment was manufactured and film depositions of alumina (Al2O3) and titania (TiO2) by APS and titania film deposition by ASPPS were carried out. Consequently, though intensive fluctuation with intensive abrasion of electrodes occurred during plasma jet generation in case of N2 working gas, the plasma jet was stabilized and the abrasion was dramatically diminished by slight addition of Ar to N2 working gas. Since the suction type feedstock feeder could be confirmed to be available not only for powder feedstock but also solution precursor feed stock. In the case of APS, lamellar structure alumina and titania films could be deposited. However, in the case of titania films deposited by APS, a phase transformation from anatase to rutile occurred partially during film deposition. Also in the case of ASPPS, titania films including rutile and anatase were deposited. From these results, the developed equipment was proved to be available as an APS/ASPPS dual mode thermal spray equipment and this technique was found to have high potential for a low-cost oxide film deposition process. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Aluminum oxide Titanium oxide Atmospheric thermal plasma spray (APS) Atmospheric solution precursor plasma spray (ASPPS) Photo-catalyst Surface modification Chemical vapor deposition (CVD)
1. Introduction Oxide films have been used for various applications including corrosion-resistive, abrasion-resistive and thermal barrier coatings of bridges [1], semiconductor manufacturing equipment, and engines [2e4]. In addition they start to be utilized as functional film such as a photo-voltaic device, solid electrolyte, and gas sensor. Especially, because of its excellent chemical stability, alumina (Al2O3) film has been used in practice. Recently, because of its excellent photo-catalytic properties [5], titania (TiO2) film is successfully applied as a antimicrobial coating, or, photo-voltaic device for dye-sensitized solar cells (DSSC) [6]. As the oxide film deposition process, chemical vapor deposition
* Corresponding author. Division of Renewable Energy and Environment, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558, Japan. E-mail address: [email protected] (Y. Ando).
(CVD) [7], physical vapor deposition (PVD) [8] and sol-gel method [9] have been widely and dominantly used. However, since CVD and PVD have some disadvantages such as low deposition time, high initial cost due to requirement of vacuum equipment, limitation of the sample size due to dimension of the vacuum chamber, a low cost film deposition process with short duration time is demanded. As for the sol-gel method, although film deposition can be conducted by use of simple equipment, this process also has some disadvantages such as low deposition rate, limitation of the sample size due to dimension of the water bath for hydrolysis, difficulty of thick film deposition due to factors such as the internal stress generated by volume variation of the film during crystallization. On the other hand, in atmospheric thermal plasma spray (APS), since the high rate (over several hundred microns/min.) film deposition can be conducted by simple equipment in open air without any chambers, low cost film deposition with short duration time can be carried out. Also, solution precursor plasma spray (SPPS) [10e14], which is one of the plasma spray processes, can create a dense film
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Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019
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with control of film component and crystal structure as in conventional CVD because the film is created by chemical reaction among feedstocks, working gas and ambient gas. Although use of SPPS has so far been mainly conducted under low pressure environments in order to avoid oxidation of the film during operation, atmospheric SPPS (ASPPS) has started to be conducted for oxide film deposition by various laboratories only recently. Previously, authors used to deposit titania films using the developed ASPPS equipment with titanium tetra iso-butoxide (TTIB) as feedstock [15e18]. Subsequently, it was proved that the anatase film which had enough photo-catalytic properties to decolor methylene-blue droplets with 8 h UV irradiation and could generate electric power as the photo-voltaic devise of the dye-sensitized solar cell, could be deposited. Maranga, Ando et al. have been developing electric power generating systems using renewable energy devices such as small hydro, Dye-Sensitized Solar Cell (DSSC) and so on for nonelectrified rural areas in the Project for Capacity Development for Promoting Rural Electrification as part of the Renewable Energy (BRIGHT project) [19]. For lifetime elongation of the small hydro and low cost (DSSC) Solar Cell manufacturing in this area, development of alumina film and titania film deposition processes using APS is thought to be effective. However, since solid materials such as powder and wires are used as feedstock in the case of thermal spray, the flame should have enough thermal energy to melt the feedstock during flight and high power (over 30 kW class) thermal spray generating equipment is considered necessary. Therefore, it is not suitable for the non-electrified rural area because of its high equipment cost and energy consumption. Therefore, we developed a 1 kW class APS equipment [20], which will be able to be driven by electric power from batteries charged by renewable energy devices. Consequently, it could be confirmed that stainless films could be deposited using Ar working gas and alumina films also could be deposited by addition of N2 to the Ar working gas using 20 l/min. and 2 l/min. in Ar and N2 working gas flow rates, respectively. Nevertheless, since Ar is a very expensive gas, a low running cost deposition condition such as using low price N2 dominant working gas is required. In this study, in order to develop a low cost and low power oxide film deposition process with short duration time for non-electrified rural area, a 1 kW class APS/ASPPS dual mode thermal spray equipment was manufactured. Using this dual mode alumina and titania film depositions by APS and titania film deposition by ASPPS were carried out. 2. Experimental procedure Fig. 1 shows the schematic diagram of the thermal spray equipment used in this study. This equipment consists of plasma torch, DC power source, feed-stock supplying system and working gas supply system. Except the feedstock supplying system, the constitution of this equipment was the same as for the APS and the ASPPS equipment used in our previous studies and for conventional high power thermal plasma spray equipment. In the case of the conventional thermal spray equipment, the mechanically and electrically driven type powder feeder is generally used. Because the powder feeder is very expensive, a suction type powder feeder, which can feed the powder into the plasma jet by negative pressure generated by the thermal plasma jet, was developed in this study. Tables 1e3 show film deposition conditions for alumina film deposition by APS, titania film deposition by APS and titania film deposition by ASPPS, respectively. As the feedstock, alumina powder (PRAXAIR Al-1010-HP) and titania (anatase) powder were used in case of APS and TTIB (Ti(OC4H9)4) was used for ASPPS. A 15 mm 15 mm x 1 mm SUS304 stainless steel plate with grit
Fig. 1. Schematic diagram of the APS/ASPPS dual mode thermal plasma spray equipment.
Table 1 APS alumina film deposition conditions. Substrate Working gas (Flow rate) Spray distance Discharge Current Deposition time Feedstock material
SUS304 stainless steel Ar (0.5 l/min.)/N2 (0.5e2.5 l/min.) 70 mm 50 mm 50 A, 20 V 30 s. Al2O3 powder
*Conditions for the sample shown in Figs. 4 and 5.
Table 2 APS titania film deposition conditions. Substrate Working gas (Flow rate) Spray distance Discharge Current Deposition time Feedstock material
SUS304 stainless steel Ar (0.5 l/min.)/N2 (0.5e2.5 l/min.) 100 mm 50 mm 50 A, 20 V 30 s. Anatase powder
*Conditions for the sample shown in Figs. 6 and 7.
Table 3 ASPPS alumina film deposition conditions*. Substrate Working gas (Flow rate) Spray distance Discharge Current Deposition time Feedstock material
SUS 304 stainless steel Ar (0.5e1 l/min)/N2 (0.5e2.5 l/min.) 50 mm 50 A, 20 V 1 min. Ethanol diluted TTIB**
*Conditions for the sample shown in Figs. 9 and 10. ** Titanium tetra iso butoxide (Ti(C4H9)4)(Volume ratio of TTIB/Ethanol ¼ 1/1).
blasted surface was used as the substrate. Fig. 2 shows the X-ray diffraction patterns of the Al2O3 powder, TiO2 powder and SUS304 stainless steel substrate used in this study. The substrate was horizontally set on the substrate holder and the central area of the sample was placed perpendicular to the axial center of the plasma jet. The input power for the discharge was fixed at 20 V, 50 A. After oxide film deposition, the microstructures of the films were investigated using an optical microscope and X-ray diffraction with CuKa at 40 kV and 100 mA. For confirming the hardness and adhesion strength of the deposited films, pencil scratch testing (ISO
Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019
Y. Ando et al. / Vacuum xxx (2016) 1e6
3
Table 4 State of N2 plasma jets and Ar added N2 plasma jets. Working gas
N2 Ar added N2
N2 flow rate (1/min.) <1
1.5
2
2.5
3
D
D
D
X B
X X
B
B
B
B: Continuous discharge without abrasion of electrodes.
D: Continuous discharge with abrasion of electrodes. X: Discharge was extinguished within 10 s.
In this study, the states of the plasma jets under the conditions of N2 working gas and Ar added N2 working gas were investigated. Table 4 shows the states of the plasma jets. In case of N2 working gas, although the plasma jet could not be generated continuously on the conditions of over 2.5 l/min. in a N2 flow rate, plasma jets could be generated continuously for conditions of under 2.5 l/min. However, even under 2 l/min., intensive fluctuation with intensive abrasion of electrodes occurred. On the other hand, for Ar (flow rate: 0.5 l/min.) and added N2 working gas, although the plasma jet could not be generated continuously in the conditions of over 3 l/ min., plasma jets could be generated without electrodes abrasion and intensive fluctuation of the plasma jets using under 2.5 l/min. 3.2. Alumina film deposition by APS
Fig. 2. XRD patterns of the feedstock powders and substrates used in this study. a) Feedstock Al2O3 powder. b) Feedstock TiO2 powder. c) SUS304 stainless steel substrate.
Fig. 3 shows the appearances of the Ar added N2 plasma jets without and with powder injection, respectively. As shown in this figure, the length and width of the plasma jet was dramatically increased with increasing N2 working gas flow rate. Since thermal energy was increased with increasing N2 flow rate, there was no non-melted particle in the deposited film on the condition of 2.5 l/ min. even though feedstock powder feed rate was increased with increasing working gas flow rate. Fig. 4 shows the appearance and cross-sectional optical micrograph of the alumina film coated sample and Fig. 5 shows the XRD pattern of the alumina film deposited sample for the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/ min. and d ¼ 70 mm (d: deposition distance). Since alumina films were deposited on the conditions of fixed plasma torch and substrates, a white colored alumina spot was deposited on the substrate in each case. As shown in Fig. 5 b), the lamellar structure
15184:2012) was carried out.
3. Results and discussion 3.1. Effect of Ar addition on stabilization of N2 plasma jet From the experimental results in our previous study, addition of N2 was proved to be effective for increase of thermal energy of the Ar plasma jet. However, there are the following disadvantages on using Ar working gas as well as its cost. * In the case of an Ar plasma jet, the thermal energy of the plasma jet increased with increasing Ar working gas flow rate. On the other hand, the thermal energy of the plasma jet decreased with increasing Ar working gas flow rate under the conditions of N2 working gas flow rate fixed Ar/N2 plasma jets because the thermal energy of the Ar plasma jet is much lower than that of the N2 plasma jet. * In addition, since feedstock powder feed rate was increased with increasing working gas flow rate when using the suction type feedstock feeder, non-melted particle content in the deposited film was increased with increasing Ar working gas flow rate under the conditions of the N2 flow rate fixed Ar/N2 plasma jets.
Fig. 3. Appearances of the Ar (0.5 l/min.) added N2 plasma jets. (QN2: N2 flow rate).
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Fig. 4. Appearance and cross-sectional optical micrograph of the alumina film coated sample on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 70 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). a) Appearance b) Cross-section.
Fig. 6. Appearance and cross-sectional optical micrograph of the titania film coated sample on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 100 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). a) Appearance b) Cross-section.
the deposited alumina film could stand 9H pencil scratch. 3.3. Titania film deposition by APS
Fig. 5. XRD pattern of the alumina film deposited sample on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 70 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). (B: Al2O3, :: Fe-Cr (Substrate)).
alumina film with almost the same structure as that for conventional high power APS was deposited. Although the film was deposited under N2 rich working gas, alumina films without nitrides could be deposited. From these results, it was proved that an alumina film without nitrides could be obtained, even using low power and simple thermal plasma spray equipment using Ar/N2 working gas that is N2 dominant. As for the pencil scratch testing,
Fig. 6 shows the appearance and cross-sectional optical micrograph of the titainia film coated sample and Fig. 7 shows the XRD patterns of the titania film deposited samples on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 100 mm. Although the color of the feedstock (anatase) powder was white, the color of the particles turned into gray during flight in the plasma jet and the gray colored film was deposited. Concerning the micro structure of the film, also in this case, a lamellar structure film which is almost the same as that in the conventional APS equipment was shown to be deposited. However, as shown in Fig. 7, though the feedstock powder was anatase, a rutile-dominant film was deposited. As for the pencil scratch testing, since the deposited alumina film could stand the 9H pencil scratch, it was proved that a practically useful
Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019
Y. Ando et al. / Vacuum xxx (2016) 1e6
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spray equipment, titania film deposition by ASPPS using the developed APS/ASPPS dual mode thermal spray equipment was carried out. Fig. 8 shows the appearances of the Ar/N2 plasma jets. As shown in this figure, it was proved that the suction type feedstock feeder had enough potential to deliver the feedstock solution precursor into the plasma jet and this equipment is available as an APS/ASPPS dual mode thermal spray equipment. Fig. 9 shows the appearance of the titainia film deposited sample and Fig. 10 shows the XRD pattern of the titania film on the condition of QAr ¼ 1 l/ min., QN2 ¼ 0.5 l/min. and d ¼ 100 mm. Rutile dominant titania film could be deposited. However, as for the film strength, the film was Fig. 7. XRD pattern of the titania film deposited sample on the condition of QAr ¼ 0.5 l/ min., QN2 ¼ 0.6 l/min. and d ¼ 100 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). (,: Anatase, -: Rutile).
film could be deposited by using this technique also in case of titania film deposition. 3.4. Titania film deposition by ASPPS In the case of APS, it is thought to be difficult to deposit anataserich titania films because of melting of the feed stock particles during flight in the plasma jet. In a thermal spray process except for cold spray and gas deposition methods, film deposition with molten feedstock particles is inevitable. However, in ASPPS, since the oxide film was deposited by chemical reaction, the crystal structure and micro-structure of the film can be controlled by controlling the substrate temperature (that is the deposition temperature). In our previous study using micro-tube pump as feedstock feeder, it was revealed that the crystal structure of the anatase film varied from rutile to anatase and finally became amorphous with decreasing deposition temperature. If the APS/ASPPS dual mode thermal spray equipment is developed, the new function can be easily added to the APS film by using ASPPS. So, in this study, as a basic study for development of APS/ASPPS dual mode thermal
Fig. 9. Appearance of the ASPPS titainia film deposited on the condition of QAr ¼ 1 l/ min., QN2 ¼ 0.5 l/min. and d ¼ 50 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance).
Fig. 8. Appearances of the Ar and Ar/N2 plasma jets (QAr: Ar flow rate, QN2: N2 flow rate). a) Ar plasma jet b) Ar/N2 plasma jet.
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of Technology, Jomo Kenyatta University of Agriculture and Technology (JKUAT) and The Project for Capacity Development for Promoting Rural Electrification Using Renewable Energy (BRIGHT Project) of JICA.
References
Fig. 10. XRD pattern of the ASPPS titania film deposited on the condition of QAr ¼ 1 l/ min. and QN2 ¼ 0.5 l/min. and d ¼ 50 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). (-: Rutile, :: Fe-Cr (Substrate), +: Cu and Cu2O (derived from the anode of the plasma torch)).
broken by scratching using a B pencil butt could stand the softer 2B pencil scratch. In addition, in case of ASPPS, erosion of the anode of the plasma torch occurred since thermal energy of the plasma jet was increased due to TTIB injection even under the condition of an Ar-rich working gas. 4. Conclusions In order to develop a low cost oxide film deposition process using thermal spray equipment, a 1 kW class APS/ASPPS dual mode thermal spray equipment was manufactured and oxide film deposition was carried out. Consequently, the following conclusions were obtained. 1) Although abrasion of electrodes occurred in case of a N2 plasma jet, alumina films could be deposited without abrasion of electrodes when using Ar added to the N2 plasma jet. In addition, it was proved that lamellar structured alumina films with practical strength could be deposited even using a 1 kW class APS equipment. 2) Although phase transformation from anatase to rutile occurred during film deposition, lamellar structure titania films with practical strength could be obtained. 3) Also in case of ASPPS, the suction type feedstock feeder is available for continuous feedstock feed without droplet creation. Also a rutile-rich titania film could be deposited. Acknowledgements The authors acknowledge the supports from Ashikaga Institute
[1] S. Kuroda, J. Kawakita, Marine exposure tests of thermal sprayed coatings in Japan, Proc. Therm. Spray 2003 (2003) 343e352. [2] K. Sridhar, R. Reji Kumar, M. Narasimha, Int. J. Mod. Eng. Res. 3 (3) (2013) 1435e1441. [3] N. Curry, K. VanEvery, T. Snyder, N. Markocsan, Thermal conductivity analysis and lifetime testing of suspension plasma-sprayed thermal barrier coatings, Coatings 4 (2014) 630e650. [4] D.R. Clarke, M. Oechsner, N.P. Padture, Thermal-barrier coatings for more efficient gas-turbine engines, MRS Bull. 37 (10) (2012) 891e897. [5] K. Hashimoto, H. Irie, A. Fujishima, TiO2 photocatalytics: a historical overview and future prospects, Jpn. J. Appl. Phys. 44 (12) (2005) 8269e8285 [Part1]. [6] B. O'Reagan, M. Gratzel, A low-cost, high-efficiency solar cell base on dye sensitized colloidal TiO2 films, Nature 353 (1991) 737e739. [7] M.V. Baryshnikova, L.A. Filatov, A.S. Petrov, Sergey E. Alexandrov, CVD deposited titania thin films for gas sensors with improved operating characteristics, Chem. Vap. Depos. 21 (2015) 327e333, 10-11-12. [8] S.E. Cordes, PVD-alumina coatings on cemented carbide cutting tools: a study about the effect on friction and adhesion mechanism”, Tribol. Industry 34 (1) (2012) 24e28. [9] X. Wang, G. Wu, B. Zhou, J.Shen “optical constants of crystallized TiO2 coatings prepared by sol-gel process, Materials 6 (2013) 2819e2830. [10] N. Sanpo, C.C. Berndt, A.S.M. Ang, J. Wang, Effect of the chelating agent contents on the topography, composition and phase of SPPS-deposited cobalt ferrite splats, Surf. Coatings Technol. 232 (15) (2013) 247e253. [11] L. Pawlowski, Suspension and solution thermal spray coatings, Surf. Coatings Technol. 203 (19) (2009) 2807e2829. [12] P. Michaux, G. Montavon, A. Grimaud, A. Denoirjean, P. Fauchais, Elaboration of porous NiO/8YSZ layers by several SPS and SPPS routes, J. Therm. Spray Technol. 19 (1) (2010) 317e327. [13] S.V. Joshi, G. Sivakumar, T. Raghuveer, R.O. Dusane, Hybrid plasma-sprayed thermal barrier coatings using powder and solution precursor feedstock, J. Therm. Spray Technol. 23 (4) (2014) 616e624. [14] H. Murakami, H. Nagai, T. Irokawa, T. Yoshida, K. Akashi, Super high rate thermal plasma CVD of ceramics, J. Ceram. Soc. Jpn. 97 (1121) (1989) 49e55. [15] Y. Ando, S. Tobe, H. Tahara, Photo-catalytic TiO2 film deposition by atmospheric TPCVD, Vacuum 80 (2006) 1278e1283. [16] Y. Ando, S. Tobe, H. Tahara, Rapid deposition of photo-catalytic oxide film by liquid feedstock injection TPCVD in open air, IEEE Trans. Plasma Sci. 34 (2006) 1229e1234. [17] Y. Ando, S.-Y. Chen, Y. Noda, Photocatalytic titanium oxide film deposition by atmospheric TPCVD using air as the working gas, IEEE Trans. Plasma Sci. 41 (2013) 1850e1855. [18] Y. Ando, Rapid deposition of titanium oxide and zinc oxide films by solution precursor plasma spray, IEEJ Trans. FM 130-A (2010) 935e940. [19] JICA's website, URL, http://www.jica.go.jp/kenya/english/office/topics/topics 131115.html. [20] Y. Ando, N. Noda, A. Kobayashi, “Al2O3 Film Deposition by Atmospheric Thermal Plasma Spray Using 1kW Class Electric Power Source”, Front. Appl. Plasma Technol. 7 (2) (2014) 55e60.
Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019
Contents lists available at ScienceDirect
Vacuum journal homepage: www.elsevier.com/locate/vacuum
Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas Yasutaka Ando a, *, Dickson Kindole a, Yoshimasa Noda b, Richard N. Mbiu c, Bernerd K. Kosgey c, Stephen M. Maranga c, Akira Kobayashi d, e, f a
Division of Renewable Energy and Environment, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558, Japan Collaborative Research Center, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558, Japan Department of Mechanical Engineering, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62,000 e 00200, Nairobi, Kenya d Malaysia Japan International Institute of Technology, University of Technology Malaysia, Jalan Semarak 54100, Kuala Lumpur, Malaysia e Graduate School of Eng., Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan f University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 April 2016 Received in revised form 25 September 2016 Accepted 14 October 2016 Available online xxx
In order to develop a low cost oxide film deposition process with short duration time, a 1 kW class Atmospheric thermal plasma spray (APS)/Atmospheric solution precursor plasma spray (ASPPS) dual mode thermal spray equipment was manufactured and film depositions of alumina (Al2O3) and titania (TiO2) by APS and titania film deposition by ASPPS were carried out. Consequently, though intensive fluctuation with intensive abrasion of electrodes occurred during plasma jet generation in case of N2 working gas, the plasma jet was stabilized and the abrasion was dramatically diminished by slight addition of Ar to N2 working gas. Since the suction type feedstock feeder could be confirmed to be available not only for powder feedstock but also solution precursor feed stock. In the case of APS, lamellar structure alumina and titania films could be deposited. However, in the case of titania films deposited by APS, a phase transformation from anatase to rutile occurred partially during film deposition. Also in the case of ASPPS, titania films including rutile and anatase were deposited. From these results, the developed equipment was proved to be available as an APS/ASPPS dual mode thermal spray equipment and this technique was found to have high potential for a low-cost oxide film deposition process. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Aluminum oxide Titanium oxide Atmospheric thermal plasma spray (APS) Atmospheric solution precursor plasma spray (ASPPS) Photo-catalyst Surface modification Chemical vapor deposition (CVD)
1. Introduction Oxide films have been used for various applications including corrosion-resistive, abrasion-resistive and thermal barrier coatings of bridges [1], semiconductor manufacturing equipment, and engines [2e4]. In addition they start to be utilized as functional film such as a photo-voltaic device, solid electrolyte, and gas sensor. Especially, because of its excellent chemical stability, alumina (Al2O3) film has been used in practice. Recently, because of its excellent photo-catalytic properties [5], titania (TiO2) film is successfully applied as a antimicrobial coating, or, photo-voltaic device for dye-sensitized solar cells (DSSC) [6]. As the oxide film deposition process, chemical vapor deposition
* Corresponding author. Division of Renewable Energy and Environment, Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558, Japan. E-mail address: [email protected] (Y. Ando).
(CVD) [7], physical vapor deposition (PVD) [8] and sol-gel method [9] have been widely and dominantly used. However, since CVD and PVD have some disadvantages such as low deposition time, high initial cost due to requirement of vacuum equipment, limitation of the sample size due to dimension of the vacuum chamber, a low cost film deposition process with short duration time is demanded. As for the sol-gel method, although film deposition can be conducted by use of simple equipment, this process also has some disadvantages such as low deposition rate, limitation of the sample size due to dimension of the water bath for hydrolysis, difficulty of thick film deposition due to factors such as the internal stress generated by volume variation of the film during crystallization. On the other hand, in atmospheric thermal plasma spray (APS), since the high rate (over several hundred microns/min.) film deposition can be conducted by simple equipment in open air without any chambers, low cost film deposition with short duration time can be carried out. Also, solution precursor plasma spray (SPPS) [10e14], which is one of the plasma spray processes, can create a dense film
http://dx.doi.org/10.1016/j.vacuum.2016.10.019 0042-207X/© 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019
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with control of film component and crystal structure as in conventional CVD because the film is created by chemical reaction among feedstocks, working gas and ambient gas. Although use of SPPS has so far been mainly conducted under low pressure environments in order to avoid oxidation of the film during operation, atmospheric SPPS (ASPPS) has started to be conducted for oxide film deposition by various laboratories only recently. Previously, authors used to deposit titania films using the developed ASPPS equipment with titanium tetra iso-butoxide (TTIB) as feedstock [15e18]. Subsequently, it was proved that the anatase film which had enough photo-catalytic properties to decolor methylene-blue droplets with 8 h UV irradiation and could generate electric power as the photo-voltaic devise of the dye-sensitized solar cell, could be deposited. Maranga, Ando et al. have been developing electric power generating systems using renewable energy devices such as small hydro, Dye-Sensitized Solar Cell (DSSC) and so on for nonelectrified rural areas in the Project for Capacity Development for Promoting Rural Electrification as part of the Renewable Energy (BRIGHT project) [19]. For lifetime elongation of the small hydro and low cost (DSSC) Solar Cell manufacturing in this area, development of alumina film and titania film deposition processes using APS is thought to be effective. However, since solid materials such as powder and wires are used as feedstock in the case of thermal spray, the flame should have enough thermal energy to melt the feedstock during flight and high power (over 30 kW class) thermal spray generating equipment is considered necessary. Therefore, it is not suitable for the non-electrified rural area because of its high equipment cost and energy consumption. Therefore, we developed a 1 kW class APS equipment [20], which will be able to be driven by electric power from batteries charged by renewable energy devices. Consequently, it could be confirmed that stainless films could be deposited using Ar working gas and alumina films also could be deposited by addition of N2 to the Ar working gas using 20 l/min. and 2 l/min. in Ar and N2 working gas flow rates, respectively. Nevertheless, since Ar is a very expensive gas, a low running cost deposition condition such as using low price N2 dominant working gas is required. In this study, in order to develop a low cost and low power oxide film deposition process with short duration time for non-electrified rural area, a 1 kW class APS/ASPPS dual mode thermal spray equipment was manufactured. Using this dual mode alumina and titania film depositions by APS and titania film deposition by ASPPS were carried out. 2. Experimental procedure Fig. 1 shows the schematic diagram of the thermal spray equipment used in this study. This equipment consists of plasma torch, DC power source, feed-stock supplying system and working gas supply system. Except the feedstock supplying system, the constitution of this equipment was the same as for the APS and the ASPPS equipment used in our previous studies and for conventional high power thermal plasma spray equipment. In the case of the conventional thermal spray equipment, the mechanically and electrically driven type powder feeder is generally used. Because the powder feeder is very expensive, a suction type powder feeder, which can feed the powder into the plasma jet by negative pressure generated by the thermal plasma jet, was developed in this study. Tables 1e3 show film deposition conditions for alumina film deposition by APS, titania film deposition by APS and titania film deposition by ASPPS, respectively. As the feedstock, alumina powder (PRAXAIR Al-1010-HP) and titania (anatase) powder were used in case of APS and TTIB (Ti(OC4H9)4) was used for ASPPS. A 15 mm 15 mm x 1 mm SUS304 stainless steel plate with grit
Fig. 1. Schematic diagram of the APS/ASPPS dual mode thermal plasma spray equipment.
Table 1 APS alumina film deposition conditions. Substrate Working gas (Flow rate) Spray distance Discharge Current Deposition time Feedstock material
SUS304 stainless steel Ar (0.5 l/min.)/N2 (0.5e2.5 l/min.) 70 mm 50 mm 50 A, 20 V 30 s. Al2O3 powder
*Conditions for the sample shown in Figs. 4 and 5.
Table 2 APS titania film deposition conditions. Substrate Working gas (Flow rate) Spray distance Discharge Current Deposition time Feedstock material
SUS304 stainless steel Ar (0.5 l/min.)/N2 (0.5e2.5 l/min.) 100 mm 50 mm 50 A, 20 V 30 s. Anatase powder
*Conditions for the sample shown in Figs. 6 and 7.
Table 3 ASPPS alumina film deposition conditions*. Substrate Working gas (Flow rate) Spray distance Discharge Current Deposition time Feedstock material
SUS 304 stainless steel Ar (0.5e1 l/min)/N2 (0.5e2.5 l/min.) 50 mm 50 A, 20 V 1 min. Ethanol diluted TTIB**
*Conditions for the sample shown in Figs. 9 and 10. ** Titanium tetra iso butoxide (Ti(C4H9)4)(Volume ratio of TTIB/Ethanol ¼ 1/1).
blasted surface was used as the substrate. Fig. 2 shows the X-ray diffraction patterns of the Al2O3 powder, TiO2 powder and SUS304 stainless steel substrate used in this study. The substrate was horizontally set on the substrate holder and the central area of the sample was placed perpendicular to the axial center of the plasma jet. The input power for the discharge was fixed at 20 V, 50 A. After oxide film deposition, the microstructures of the films were investigated using an optical microscope and X-ray diffraction with CuKa at 40 kV and 100 mA. For confirming the hardness and adhesion strength of the deposited films, pencil scratch testing (ISO
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3
Table 4 State of N2 plasma jets and Ar added N2 plasma jets. Working gas
N2 Ar added N2
N2 flow rate (1/min.) <1
1.5
2
2.5
3
D
D
D
X B
X X
B
B
B
B: Continuous discharge without abrasion of electrodes.
D: Continuous discharge with abrasion of electrodes. X: Discharge was extinguished within 10 s.
In this study, the states of the plasma jets under the conditions of N2 working gas and Ar added N2 working gas were investigated. Table 4 shows the states of the plasma jets. In case of N2 working gas, although the plasma jet could not be generated continuously on the conditions of over 2.5 l/min. in a N2 flow rate, plasma jets could be generated continuously for conditions of under 2.5 l/min. However, even under 2 l/min., intensive fluctuation with intensive abrasion of electrodes occurred. On the other hand, for Ar (flow rate: 0.5 l/min.) and added N2 working gas, although the plasma jet could not be generated continuously in the conditions of over 3 l/ min., plasma jets could be generated without electrodes abrasion and intensive fluctuation of the plasma jets using under 2.5 l/min. 3.2. Alumina film deposition by APS
Fig. 2. XRD patterns of the feedstock powders and substrates used in this study. a) Feedstock Al2O3 powder. b) Feedstock TiO2 powder. c) SUS304 stainless steel substrate.
Fig. 3 shows the appearances of the Ar added N2 plasma jets without and with powder injection, respectively. As shown in this figure, the length and width of the plasma jet was dramatically increased with increasing N2 working gas flow rate. Since thermal energy was increased with increasing N2 flow rate, there was no non-melted particle in the deposited film on the condition of 2.5 l/ min. even though feedstock powder feed rate was increased with increasing working gas flow rate. Fig. 4 shows the appearance and cross-sectional optical micrograph of the alumina film coated sample and Fig. 5 shows the XRD pattern of the alumina film deposited sample for the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/ min. and d ¼ 70 mm (d: deposition distance). Since alumina films were deposited on the conditions of fixed plasma torch and substrates, a white colored alumina spot was deposited on the substrate in each case. As shown in Fig. 5 b), the lamellar structure
15184:2012) was carried out.
3. Results and discussion 3.1. Effect of Ar addition on stabilization of N2 plasma jet From the experimental results in our previous study, addition of N2 was proved to be effective for increase of thermal energy of the Ar plasma jet. However, there are the following disadvantages on using Ar working gas as well as its cost. * In the case of an Ar plasma jet, the thermal energy of the plasma jet increased with increasing Ar working gas flow rate. On the other hand, the thermal energy of the plasma jet decreased with increasing Ar working gas flow rate under the conditions of N2 working gas flow rate fixed Ar/N2 plasma jets because the thermal energy of the Ar plasma jet is much lower than that of the N2 plasma jet. * In addition, since feedstock powder feed rate was increased with increasing working gas flow rate when using the suction type feedstock feeder, non-melted particle content in the deposited film was increased with increasing Ar working gas flow rate under the conditions of the N2 flow rate fixed Ar/N2 plasma jets.
Fig. 3. Appearances of the Ar (0.5 l/min.) added N2 plasma jets. (QN2: N2 flow rate).
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Fig. 4. Appearance and cross-sectional optical micrograph of the alumina film coated sample on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 70 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). a) Appearance b) Cross-section.
Fig. 6. Appearance and cross-sectional optical micrograph of the titania film coated sample on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 100 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). a) Appearance b) Cross-section.
the deposited alumina film could stand 9H pencil scratch. 3.3. Titania film deposition by APS
Fig. 5. XRD pattern of the alumina film deposited sample on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 70 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). (B: Al2O3, :: Fe-Cr (Substrate)).
alumina film with almost the same structure as that for conventional high power APS was deposited. Although the film was deposited under N2 rich working gas, alumina films without nitrides could be deposited. From these results, it was proved that an alumina film without nitrides could be obtained, even using low power and simple thermal plasma spray equipment using Ar/N2 working gas that is N2 dominant. As for the pencil scratch testing,
Fig. 6 shows the appearance and cross-sectional optical micrograph of the titainia film coated sample and Fig. 7 shows the XRD patterns of the titania film deposited samples on the condition of QAr ¼ 0.5 l/min., QN2 ¼ 0.6 l/min. and d ¼ 100 mm. Although the color of the feedstock (anatase) powder was white, the color of the particles turned into gray during flight in the plasma jet and the gray colored film was deposited. Concerning the micro structure of the film, also in this case, a lamellar structure film which is almost the same as that in the conventional APS equipment was shown to be deposited. However, as shown in Fig. 7, though the feedstock powder was anatase, a rutile-dominant film was deposited. As for the pencil scratch testing, since the deposited alumina film could stand the 9H pencil scratch, it was proved that a practically useful
Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019
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5
spray equipment, titania film deposition by ASPPS using the developed APS/ASPPS dual mode thermal spray equipment was carried out. Fig. 8 shows the appearances of the Ar/N2 plasma jets. As shown in this figure, it was proved that the suction type feedstock feeder had enough potential to deliver the feedstock solution precursor into the plasma jet and this equipment is available as an APS/ASPPS dual mode thermal spray equipment. Fig. 9 shows the appearance of the titainia film deposited sample and Fig. 10 shows the XRD pattern of the titania film on the condition of QAr ¼ 1 l/ min., QN2 ¼ 0.5 l/min. and d ¼ 100 mm. Rutile dominant titania film could be deposited. However, as for the film strength, the film was Fig. 7. XRD pattern of the titania film deposited sample on the condition of QAr ¼ 0.5 l/ min., QN2 ¼ 0.6 l/min. and d ¼ 100 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). (,: Anatase, -: Rutile).
film could be deposited by using this technique also in case of titania film deposition. 3.4. Titania film deposition by ASPPS In the case of APS, it is thought to be difficult to deposit anataserich titania films because of melting of the feed stock particles during flight in the plasma jet. In a thermal spray process except for cold spray and gas deposition methods, film deposition with molten feedstock particles is inevitable. However, in ASPPS, since the oxide film was deposited by chemical reaction, the crystal structure and micro-structure of the film can be controlled by controlling the substrate temperature (that is the deposition temperature). In our previous study using micro-tube pump as feedstock feeder, it was revealed that the crystal structure of the anatase film varied from rutile to anatase and finally became amorphous with decreasing deposition temperature. If the APS/ASPPS dual mode thermal spray equipment is developed, the new function can be easily added to the APS film by using ASPPS. So, in this study, as a basic study for development of APS/ASPPS dual mode thermal
Fig. 9. Appearance of the ASPPS titainia film deposited on the condition of QAr ¼ 1 l/ min., QN2 ¼ 0.5 l/min. and d ¼ 50 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance).
Fig. 8. Appearances of the Ar and Ar/N2 plasma jets (QAr: Ar flow rate, QN2: N2 flow rate). a) Ar plasma jet b) Ar/N2 plasma jet.
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of Technology, Jomo Kenyatta University of Agriculture and Technology (JKUAT) and The Project for Capacity Development for Promoting Rural Electrification Using Renewable Energy (BRIGHT Project) of JICA.
References
Fig. 10. XRD pattern of the ASPPS titania film deposited on the condition of QAr ¼ 1 l/ min. and QN2 ¼ 0.5 l/min. and d ¼ 50 mm (QAr: Ar flow rate, QN2: N2 flow rate, d: deposition distance). (-: Rutile, :: Fe-Cr (Substrate), +: Cu and Cu2O (derived from the anode of the plasma torch)).
broken by scratching using a B pencil butt could stand the softer 2B pencil scratch. In addition, in case of ASPPS, erosion of the anode of the plasma torch occurred since thermal energy of the plasma jet was increased due to TTIB injection even under the condition of an Ar-rich working gas. 4. Conclusions In order to develop a low cost oxide film deposition process using thermal spray equipment, a 1 kW class APS/ASPPS dual mode thermal spray equipment was manufactured and oxide film deposition was carried out. Consequently, the following conclusions were obtained. 1) Although abrasion of electrodes occurred in case of a N2 plasma jet, alumina films could be deposited without abrasion of electrodes when using Ar added to the N2 plasma jet. In addition, it was proved that lamellar structured alumina films with practical strength could be deposited even using a 1 kW class APS equipment. 2) Although phase transformation from anatase to rutile occurred during film deposition, lamellar structure titania films with practical strength could be obtained. 3) Also in case of ASPPS, the suction type feedstock feeder is available for continuous feedstock feed without droplet creation. Also a rutile-rich titania film could be deposited. Acknowledgements The authors acknowledge the supports from Ashikaga Institute
[1] S. Kuroda, J. Kawakita, Marine exposure tests of thermal sprayed coatings in Japan, Proc. Therm. Spray 2003 (2003) 343e352. [2] K. Sridhar, R. Reji Kumar, M. Narasimha, Int. J. Mod. Eng. Res. 3 (3) (2013) 1435e1441. [3] N. Curry, K. VanEvery, T. Snyder, N. Markocsan, Thermal conductivity analysis and lifetime testing of suspension plasma-sprayed thermal barrier coatings, Coatings 4 (2014) 630e650. [4] D.R. Clarke, M. Oechsner, N.P. Padture, Thermal-barrier coatings for more efficient gas-turbine engines, MRS Bull. 37 (10) (2012) 891e897. [5] K. Hashimoto, H. Irie, A. Fujishima, TiO2 photocatalytics: a historical overview and future prospects, Jpn. J. Appl. Phys. 44 (12) (2005) 8269e8285 [Part1]. [6] B. O'Reagan, M. Gratzel, A low-cost, high-efficiency solar cell base on dye sensitized colloidal TiO2 films, Nature 353 (1991) 737e739. [7] M.V. Baryshnikova, L.A. Filatov, A.S. Petrov, Sergey E. Alexandrov, CVD deposited titania thin films for gas sensors with improved operating characteristics, Chem. Vap. Depos. 21 (2015) 327e333, 10-11-12. [8] S.E. Cordes, PVD-alumina coatings on cemented carbide cutting tools: a study about the effect on friction and adhesion mechanism”, Tribol. Industry 34 (1) (2012) 24e28. [9] X. Wang, G. Wu, B. Zhou, J.Shen “optical constants of crystallized TiO2 coatings prepared by sol-gel process, Materials 6 (2013) 2819e2830. [10] N. Sanpo, C.C. Berndt, A.S.M. Ang, J. Wang, Effect of the chelating agent contents on the topography, composition and phase of SPPS-deposited cobalt ferrite splats, Surf. Coatings Technol. 232 (15) (2013) 247e253. [11] L. Pawlowski, Suspension and solution thermal spray coatings, Surf. Coatings Technol. 203 (19) (2009) 2807e2829. [12] P. Michaux, G. Montavon, A. Grimaud, A. Denoirjean, P. Fauchais, Elaboration of porous NiO/8YSZ layers by several SPS and SPPS routes, J. Therm. Spray Technol. 19 (1) (2010) 317e327. [13] S.V. Joshi, G. Sivakumar, T. Raghuveer, R.O. Dusane, Hybrid plasma-sprayed thermal barrier coatings using powder and solution precursor feedstock, J. Therm. Spray Technol. 23 (4) (2014) 616e624. [14] H. Murakami, H. Nagai, T. Irokawa, T. Yoshida, K. Akashi, Super high rate thermal plasma CVD of ceramics, J. Ceram. Soc. Jpn. 97 (1121) (1989) 49e55. [15] Y. Ando, S. Tobe, H. Tahara, Photo-catalytic TiO2 film deposition by atmospheric TPCVD, Vacuum 80 (2006) 1278e1283. [16] Y. Ando, S. Tobe, H. Tahara, Rapid deposition of photo-catalytic oxide film by liquid feedstock injection TPCVD in open air, IEEE Trans. Plasma Sci. 34 (2006) 1229e1234. [17] Y. Ando, S.-Y. Chen, Y. Noda, Photocatalytic titanium oxide film deposition by atmospheric TPCVD using air as the working gas, IEEE Trans. Plasma Sci. 41 (2013) 1850e1855. [18] Y. Ando, Rapid deposition of titanium oxide and zinc oxide films by solution precursor plasma spray, IEEJ Trans. FM 130-A (2010) 935e940. [19] JICA's website, URL, http://www.jica.go.jp/kenya/english/office/topics/topics 131115.html. [20] Y. Ando, N. Noda, A. Kobayashi, “Al2O3 Film Deposition by Atmospheric Thermal Plasma Spray Using 1kW Class Electric Power Source”, Front. Appl. Plasma Technol. 7 (2) (2014) 55e60.
Please cite this article in press as: Y. Ando, et al., Alumina and titania films deposition by APS/ASPPS dual mode thermal spray equipment using Ar added N2 working gas, Vacuum (2016), http://dx.doi.org/10.1016/j.vacuum.2016.10.019