We studied the formation of anodic oxidation coating on aluminum in a mixture bath of aliphatic monoamine and organic acid salts without ammonium fluoride. Aluminum was anodized in aliphatic monoamine baths (methylamine, ethylamine, propylamine, and buthylamine) containing organic acid salts (formic, acetic, oxalic, tartaric, and citric acid salts), at a bath temperature of 20°C, and a current density of 1A·dm-2. Anodized films formed in monoamine baths containing ammonium tartrate and triammonium citrate. Film was found to be thinner about 4-5μm when formed in monoamine baths containing ammonium tartrate and triammonium citrate than film when formed in baths containing ammonium fluoride about 7-8μm. SEM observation of film showed that film formed in mathylamine baths containing ammonium tartrate or triammonium citrate had a smoother surface than that formed in other amine baths containing ammonium tartrate or triammonium citrate. The smooth surface was apparently formed by dissolution of the film surface in an amine alkaline bath. (tartrate bath pH=11.4 or citrate bath pH=11.7). Pore diameters of film formed in amine baths containing tartrate and citrate were about 25-45nm.
The hydrogen content of JIS-50C steel was measured in H2SO4 and HCl aqueous solutions of various concentrations using an electrochemical measurement technique. The hydrogen content increased with an increase in the HCl concentration and rapidly increased as the HCl concentration increased beyond that of a 3 N solution. The hydrogen content increased slowly with an increase in the H2SO4 concentration, but did not increase rapidly even when the H2SO4 concentration increased beyond 3N. The hydrogen content did not change significantly even when the temperature of the aqueous acid solution increased from 30 to 60°C. The hydrogen content was greater in the HCl solution than in the H2SO4 solution when the acid concentration was greater than 2.5N.
The pit growth behavior of high purity aluminum foil in electrolytic capacitors used for DC etching in a hot HCl solution has been studied using grained foil. Hemispherical patterns with diameters of about 1∼3μm and cubic patterns with widths and lengths of 7∼15μm were formed by electrolytic grainings in HNO3 and HNO3/HCl solutions, respectively. By using cubic or hemispherical patterns, uniform distributions of pits were obtained for a surface that was untreated and one that was pre-treated during the early stage of DC etching. Tunnel pits were distributed most uniformly on hemispherical patterns grained at 1C/cm2. Surface dissolution occurred as clusters of tunnel pits at the intersection of hemispherical patterns above a graining charge of 10C/cm2. For cubic patterns grained at up to 30C/cm2, the distribution of tunnel pits became uniform with an increase in the charge for graining. As a result, grainings affected the expansion of the surface area as measured by capacitance after DC etching. Cubic patterns are more effective for an increase in capacitance than hemispherical patterns.
A double zincate pretreatment of Al for plating was investigated in a LiOH-based zincate solution. The zinc deposition rate from the LiOH-based zincate solution was lower than that from NaOH or KOH-based solutions, resulting in decreased deposition of Zn and dissolution of the Al substrate. This phenomenon was interpreted as a large coordination number for water molecules to bond with Li+ ions compared to Na+ and K+ in the zincate solutions. For a LiOH-based zincate solution at a concentration near the solubility limit of water, the concentration of free water molecules decreases due to a strong restriction around Li+ ions. This situation results in a decrease of the activity coefficient of OH- which leads to dissolution of the Al substrate, and decreases the coordination number for water molecules to in relation to Zn(OH)42- ions to accelerate the electron transfer from and Zn deposition on the Al substrate. Addition of Fe(III) ions to the LiOH-based zincate solution increased the rate of Zn deposition, suggesting that the co-deposition of Fe obstruct the growth of Zn deposition and results in imperfect insulation of the Al substrate by Zn deposition.
The simultaneous codeposition of PTFE and α-alumina with nickel from Watts type bath was investigated. Nonionic surfactant (Triton-X 100) was added to the bath as a dispersing agent of PTFE. In the absence of α-alumina, PTFE particles did not codeposit, while they could codeposit in the presence of α-alumina pariticles. In order to clarify the PTFE codeposition promoting effect of α-alumina, interactions between the partcles and chemical species in the bath were also investigated.