A new process for silica nano-powder dispersion in an anode electrode paste for direct ethanol fuel cells was studied by applying an excess amount of solvent (acetone) that easily evaporates after mixing the paste. A well-dispersed anode electrode results in more efficient output power than an agglomerated anode paste. Nano-silica will act as an oxidant to acetaldehyde and can form a structure that supports increased ethanol penetration into the electrode. Using gas chromatography, the acetaldehyde concentration was measured to determine the mechanism of the reaction occurring in the fuel cells.
The processes of initial deposition and film growth of crystalline Ni-Mo-P alloy films by electroless plating were investigated by transmission electron microscopy (TEM) in comparison with those of crystalline Ni-P alloy films by electroless plating.In case of the Ni-P alloy films, very fine grains are packed and grown, so closely that the grain structure is relatively uniform. Whereas in case of the Ni-Mo-P alloy films, nucleation occurs on Pd catalyst particles and the very fine grainy layer grows to a thickness of 300A. At thicknesses greater than 300A, the growth of nuclei occurs so preferentially that grain size increases.It is suggested that this film growth in the region of its thickness greater than 300A is related to the nonuniform conditions in the crystalline state.Key Words : Electroless Plating, Ni-Mo-P Alloy Film, Film Growth Process
A B S T R A C T A n electroless Ni-Zr-P c o m p o s i t e film a n d a Ni-Nb-P c o m p o s i t e film were plated a n d their heat~treating b e h a v i o r s were investigated. The addition of 20g d m -3 of metallic p o w d e r resulted in a c o m p o s i t e film t h a t c o n t a i n e d 21.2 w e i g h t perc e n t (w/o) of Zr, [13.8 a t o m p e r c e n t (a/o)], or 4.8 w/o of Nb, (2.9 a/o), respectively. B o t h metallic p o w d e r s were d i s p e r s e d uniformly t h r o u g h o u t the films. T h e metallic Ni f o r m e d by t h e crystallization of t h e Ni-P m a t r i x diffused into t h e metallic powders, a n d t h e a m o r p h o u s Ni-Zr a n d Ni-Nb p h a s e s were f o r m e d by h e a t -t r e a t m e n t at 500 ~ or 300~ S o m e parts of t h e a m o r p h o u s Ni-Zr p h a s e s a n d t h e metallic Ni p h a s e s c o m b i n e d to form intermetallic c o m p o u n d s by h e a t -t r e a t m e n t at 600~ T h e nickel-rich parts of the a m o r p h o u s Ni-Nb p h a s e were c o n v e r t e d into a m e t a s t a b l e Ni-Nb p h a s e (4 phase) or a Ni-Nb solid solution b y h e a t -t r e a t m e n t at 700~ T h e longer h e a t i n g t i m e at 400~ i n c r e a s e d t h e a m o u n t of t h e Ni-Zr amorp h o u s phase: however, it d e c r e a s e d the reactivity of t h e a m o r p h o u s Ni-Zr phase. T h e s a m e h e a t -t r e a t m e n t of 400~ did n o t give t h e c o n s i d e r a b l e c h a n g e on t h e a m o r p h o u s Ni-Nb phase. Recently, c o m p o s i t e films c o m p o s e d of a metallic plated matl:ix a n d inert particles h a v e b e e n actively i n v e s t i g a t e d b y m a n y w o r k e r s (1, 2) to i m p r o v e t h e i r wear a n d a b r a s i o n resistance (3). N o n m e t a l l i c particles, s u c h as BN, SiC, SiO2, a n d A120~, are c o m m o n l y used as t h e d i s p e r s i o n for this purpose. S o m e w o r k e r s h a v e u s e d metallic p o w d e r s s u c h as Cr, Ni, or Cu, for t h e d i s p e r s i o n (4-6); while others h a v e a t t e m p t e d to t h e r m a l l y treat t h e c o m p o s i t e film to create a n e w alloy (7-9), especially in electroless plating (9). It is also possible to create a n e w material by t h e r m a l l y t r e a t i n g an electroless c o m p o s i t e film, w h e r e t h e d i s p e r s i o n particles of h a r d l y electroless-deposited m e t a l react w i t h t h e plating matrix. This p a p e r describes t h e t h e r m a l treating b e h a v i o r of t h e electroless-plated Ni-P c o m p o s i t e films w i t h Zr or N b m e t a l p o w d e r s w h i c h have n o t b e e n u s e d as t h e dispersion. M o r e o v e r , we discuss the solid-state reaction bet w e e n t h e Ni-P m a t r i x a n d each m e t a l powder. Experimental Electroless Ni-P m a t r i x films were d e p o s i t e d to a thickness of 2 ~m by controlling t h e plating t i m e from a general a m m o n i a c a l alkaline bath. T h e c o m p o s i t i o n a n d t h e operating c o n d i t i o n s of t h e b a t h are listed in Table I. Prio...
Electrodeposition of CdTe was carried out using ammoniacal basic electrolytes containing chloride ions in order to investigate the effect of chloride ions on the electrodeposition behavior and on the properties of the resulting CdTe deposits. Photoeffect on CdTe electrodeposition, that is, the increase in the deposition rate under irradiation of white visible light onto the growing surface of the CdTe, was depressed with increasing concentration of chloride ions in the deposition bath, while all the irradiation conditions gave flat, smooth, and polycrystalline CdTe layers with almost stoichiometric composition ͑49.1-51.7 atom % Cd͒. Both the Cd content and crystallinity of the resulting deposits increased with increasing concentration of chloride ions in the electrolytes. The asdeposited CdTe layer prepared from the chloride electrolyte had an n-type conduction, although the CdTe layer obtained from the sulfate electrolyte was p-type, suggesting that chloride ions in the electrolyte became incorporated into the CdTe layer and formed the donor level.CdTe is a promising material for solar cell applications 1-5 because its bandgap of 1.45 eV at room temperature is suitable for energy conversion from sunlight to electricity. Since CdTe has a high optical-absorption coefficient, a CdTe layer with thickness of 1-2 m is enough for thorough absorption of sunlight. In addition to some dry or nonwet processes such as screen printing and closespaced sublimation, electrodeposition 6-8 has been investigated for the preparation of thin-layered compound semiconductors for solar cell applications, and the cell made up of an n-CdS/p-CdTe heterojunction has been put into production on an industrial scale. 9 Since the pioneering work of Kröger's group in the late 1970s, 6 aqueous acidic sulfate electrolytes have historically and almost exclusively been employed as the bath for CdTe electrodeposition, 10 although organic electrolytes 11 have also been studied. In contrast, we have proposed that aqueous basic, or alkaline, electrolytes containing ammonia are also suitable for the electrodeposition of a uniform CdTe layer, since these basic solutions have a relatively high solubility of Te͑IV͒ species as TeO 3 2− ions. 12-17 From the basic electrolytes, we successfully obtained smooth and flat polycrystalline CdTe deposits with a nearly stoichiometric composition at potentials positive to that of bulk-Cd deposition. 14 Furthermore, it turned out that the deposition rate was considerably increased by photoirradiation of the cathode surface during the electrodeposition. 18 In both acidic and basic media, CdTe has been electrodeposited mainly from electrolytes containing sulfate ions ͑SO 4 2− ͒ as counter anions of Cd͑II͒ ions. Although in acidic 19-23 media, electrodeposition of CdTe from some electrolytes with an additional concentration of chloride ions or from CdCl 2 electrolytes has been reported, there are few reports in basic media. 24,25 The addition of chloride ions into the plating solution yielded a CdTe layer with a better pe...
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