Preparation of Zn-Al2O3 and Zn-TiO2 Composite Films Plated from Non-Suspended Solution by Using Electrochmical Techniques
Authors: Koiwa Ichiro , Kamiyama Shota 
Published: February 2020

A composite plating film that contains particles in the plated films have been investigated. The coexistence of nonmetal particles in metallic matrix improve the mechanical and chemical properties such as wear resistance, self-lubrication, corrosion resistance and metal-polymer adhesion. The plating baths for composite plating usually contain codeposited powders. However the powders in the bath generally detriorate bath stability and make filtalization difficult. A composite plated film which is plated bath without powder, non-suspended solution, is strongly requested. Dr. S.Oue and his co-workers have reported that Zn-Al2O3 composite films were plated from non-suspended solution by using quaternary ammonium salt1). The zinc matrix with aluminum oxide particles composite films from non-suspended solution containing quaternary ammonium salts were also investigated. The plating bath contains 520 mol/m3 ZnSO4·7H2O and 79 mol/m3 Al2(SO4)3·14-18H2O as metal source. A quaternary ammonium salts of benzyldimethyltetradecylammonium chloride dehydrate (BDTAC, Wako Co.,Ltd.) was used in this study. An observation by transmission electron microscopy (TEM). Two different deposits were observed, one is needle-shaped deposit and the other is closely packed fine particle area. Magnified photograph shows closely packed fine particle area and fine particles are clearly observed. From results of composition analyses, the A area, needle-shaped deposit, is composed of 82.6 at% zinc, 17.0 at% aluminum and 15.7at％ oxygen. As the same matter, the B area, closely packed fine particle area, is composed of 45.6 at% zinc, 29.2 at% aluminum, 20.6 at％ oxygen and 4.5 at% sulfur. The zinc content of area A, needle-shaped deposit, is much higher than that of area B, closely paced fine particle area. On the other hand, the aluminum content of area B is much higher than that of area A. It is concluded based on above results that the needle-shaped deposit is mainly composed of Zn or ZnO, and the fine particle is mainly composed of θ-Al2O3 from transmission high energy electron diffraction (THEED) observation. The origin of sulfur is not clear. Next, a composite Zn-TiO2 plated film from non-suspended solution has been investigated. The plating bath 390 mol/m3 ZnSO4·7H2O and 20 mol/m3 TiOSO4・1-2H2O as metal source. A quaternary ammonium salts of 1.0 mol/m3 benzyldimethylphenylammonium chloride was used in this study. Since a titanium easily changes to hydroxide, 9.0 mol/m3 sodium gluconate is added as a complexing agent. In the case of Zn-Al2O3 composite plating, galvanostatic method is effective to increase Al content. The aluminum content increased with increasing current density. On the other hand, in the case of Zn-TiO2 composite plating, a pulse plating method is effective for to increase Ti content in the films. A titanium content decreased abruptly with increasing duty cycle and reached minimum content at 0.5 duty cycle, and then increased with increasing duty cycle. The titanium content increased with increasing current density less than 500 A/m2 and reached at maximum titanium content, 35.9 at%, then the titanium content decreased with increasing current density. From X-ray photoelectron spectroscopy (XPS) measurement, Ti was confirmed as oxidic state, TiO2. Since titanium dioxide has two kinds of crystal structure, rutyl and anatase. Next, a crystal structure was investigated. Figure 1 shows TEM observation results of Zn-TiO2 plated films from non-suspended solution as the same method as Zn-Al2O3 plating using quaternary ammonium salts. Figure 1a shows bright image of TEM micrograph. A grain is clearly observed and its diameter is about 10nm. Figure 1b shows results of transmission high energy electron diffraction (THEED) and Fig.1c summarizes results of Fig.1b. Three different of crystals have been observed by THEED, anatase type TiO2, Zn and ZnO. Since the anatase type TiO2 shows photocatalytic properties. It is expected that the composite Zn-TiO2 plated films show photocatalytic properties. These results shows the composite film have been prepared from non-suspended solution by electrochemical techniques.
Reference
1) S. Oue, H. Nakano, S. Kobayashi, T. Akiyama, H. Fukushima, and K. Okumura, J. Surf. Finish. Soc. Jpn. 53, pp.920-925(2002) [In Japanese]

Figure 1