22P043-P
Photo-catalytic Properties of Titanium Oxide film
Deposited by SPPS using Air Plasma
液相前駆体エアプラズマ溶射酸化チタン皮膜の光触媒特性
Yasutaka Ando
安藤康高
Ashikaga Institute of Technology268-1, Omae-cho, Ashikaga-shi, Tochigi 326-8558, Japan
足利工業大学 〒326-8558 足利市大前町268-1
Since oxide films can be deposited by atmospheric solution precursor plasma spray (SPPS), this process is
hoped to be a high rate and low cost photo-catalytic oxide film deposition process. However, since Ar has
been mainly used as working gas conventionally, development of a low running cost SPPS process isdesired. In this study, in order to decrease the running cost of SPPS, atmospheric SPPS equipment using airworking gas was developed and titanium oxide film deposition using this equipment was carried out.
Consequently, photo-catalytic titanium oxide films could be deposited on the conditions of 50 mm indeposition distance in the case of air working gas use.

1. Introduction
Solution precursor plasma spray (SPPS) is avapor deposition process using liquid precursor as
feedstock and utilizing chemical reactivity andthermal energy of thermal plasma. Since thechemical reaction can be conducted under a hightemperature environment including ions andradicals in this process, high rate film deposition(over 10µm/min) with controlling film’s
microstructure and components can be operated[1]. Previously, titanium oxide film deposition on
stainless steel substrate by atmospheric SPPS
using Ar working gas was carried out [2].
Consequently, it was proved that photo-catalytic
titanium oxide film which had enoughphoto-catalytic properties to decolor the
methylene-blue and generate photo-electromotive
force as DSC could be deposited even in the caseof atmospheric SPPS. However, in the study,
since Ar was used as working gas, its runningcost was high enough not to be used practically.
In this study, in order to develop a low runningcost oxide film deposition process using
atmospheric SPPS, as a basic study, titaniumoxides film deposition by atmospheric SPPS
using air working gas was carried out and thephoto-catalytic properties of the deposited
titanium oxide film were investigated.
2. Experimental procedure
Atmospheric SPPS equipment used in this study
is shown schematically in Fig.1. The SPPS
equipment consisted of plasma torch, DC power
supplying system, micro tube pump (feedstocksupplying system) and working gas supplyingsystem. As the feedstock for titanium oxide film
deposition, ethanol diluted titanium tetra iso
butoxide (TTIB, Ti(OC4H9)4) was used. 15 mm x15 mm x 1 mm 304 stainless steel plates without
grit blasting were used as substrate. The substrate
was horizontally set on the substrate holder and thecentral area of the sample was placed perpendicular
to the axial center of the plasma jet. The deposition
distance (distance between the nozzle outlet of theplasma torch and the surface of the substrate) wasvaried from 50 mm to 150 mm. The deposition timewas 7 min. The input power for discharge was fixedat 100 V, 10 A. Deposition temperature (substratetemperature during film deposition) was measured
by thermometer. After Titanium oxide filmdeposition, the microstructures of the films wereinvestigated by X-ray diffraction (CuKa, 40 kV,100 mA). In addition, in order to confirm
photo-catalytic property of the film, methylene-blue
decoloration test were carried out in the UV room.
Table I shows deposition conditions.

Fig.1.Schematic diagram of atmospheric SPPS
equipment.

Working gas flow rate
Discharge power
Deposition distance
Deposition time
Feedstock material
Feedstock feed rate
Substrate

50 l/min.
10A/ 100V
50,100, 150 mm
7 min
C2H5OH diluted TTIB
200 ml /h
304 stainless steel

3. Experimental results
Figure 2 shows the appearances of the air plasma
jet and feedstock injected air plasma jet. Althoughlight purple flame was generated in the previous
study using Ar working gas [15], 20 mm long lightbrown flame was generated in this study using air
working gas. On the other hand, by injection of thefeedstock, the flame color was changed into lightyellow and the length was elongated to over 100mm. From the result that there was no liquid
feedstock droplet in the plasma jet and the color
was changed on the condition of the feedstock wasinjected, the feedstock seemed to be fully vaporized
and partially activated and ionized.

a)b)deposited on the condition of 100 mm. However,though anatase and rutile mixture film film could beobtained also on the condition of 150 mm, thedegree of crystallinity was drastically deteriorated.
d=50 mmIntensity (a.u.)

Table I. A sample table

d=100 mmd=150 mm

2θ (CuKα)

Fig.3. XRD patterns of the titanium oxide films.
( : Anatase, : Rutile, : Fe (Substrate))

Figure 4 shows the result of the methylene-blue
decoloration test in the case of the titanium oxide
films deposited on the conditions of 50 mm indeposition distance. This film indicated hydrophilic
and decolor methlene-blue droplets at the center ofthe substrates perfectly after 24 hour UV
irradiation.

Air plasma jet

Feedstock injected

Fig.2. Appearances of the air plasma jets.

In this experiment, deposition temperatures on
the conditions of 50 mm, 100 mm, 150 mm indeposition distance were 823 K, 773 K and 673 K,
respectively. In the case of the spray pyrolysis,
deposition temperature of over 873 K was required
because film deposition was conducted by only
thermo chemical reaction. On the other hand, in thecase of SPPS, since film deposition was conductedby plasma chemical reaction as well as thermo
chemical reaction, oxide film could be deposited on
the condition of below 773 K. Figure 3 shows theXRD patterns of the titanium oxide film coatedsamples on the conditions of 50 mm, 100 mm, 150mm in deposition distance. As for the crystal
structure, rutile dominant titanium oxide filmslightly including anatase was deposited in the caseof 50 mm and anatase and rutile mixture film was

10 mm

10 mm

Before UV irradiation

24 hr UV irradiation

Fig.4. Appearance of the titanium film deposited on
the condition of 50mm in deposition distance during
methylene-blue decoloration test.

4. Conclusion
In order to develop a low running costphoto-catalysis oxide film deposition process,titanium film deposition by atmospheric SPPS
using air plasma jet was carried out. Consequently,
in the case of air working gas, titanium oxide film
which has enough photo-catalytic properties toindicate hydrophilic and decolor methylene-blue
could be deposited on the condition of 50mm indeposition distance.
References[1] H. Murakami, T. Yoshida, K. Akashi: Advanced
Ceramic Materials, 3, 4 (1988) 423.
[2] Y. Ando, S. Tobe, H. Tahara: J IEEE Trans. on
Plasma Sci., 34, 4 (2006) 1229.