Atmospheric corrosion products of copper were identified by scanning electron microscopy, X-ray microanalyzer, X-ray diffraction, and electron diffraction. The samples were exposed to the air for periods of 1/2, 1, 3, and 6 months. The results obtained were as follows: (1) The corrosion products were composed of chlorides, sulfur compounds, and oxides. Among them, the constituents identified were Cu₂O, CuCl, 3Cu(OH)₂⋅CuCl₂, and Cu₂S. (2) In conclusion, it is very defective to make analysis of the corrosion products only by X-ray diffraction and electron diffraction with simple results of measurements. Therefore, the analysis must be made with comprehensive knowledge by using other various techniques as possible.

抄録全体を表示

Tin-zinc alloys of low zinc content are believed to have high corrosion resistance when they are used for protective films on steel surface. This paper describes the following studies: an optimum composition for protective films was selected by electrochemical measurements of the cast alloys; and, zincate-stannate baths and gluconate baths were investigated to obtain such alloy deposits from baths free from cyanides and fluorides. The following results were obtained: (1) The static potential of tinzinc alloys was base enough to act as a sacrificial film for steel, and the potential of an alloy containin more than about 10% of zinc showed almost the same value as that of single zinc. (2) The anodic dissolution in NaCl solution and the formation of white precipitate on the alloy surface in a salt spray test more readily occurred with the increase in zinc content of the alloy. (3) It was difficult to obtain alloy deposits of lower zinc content from zincate-stannate baths under normal plating conditions. (4) A semi-bright zinc alloy deposit of lower zinc content was obtained from the bath containing 0.25mol/l of metal and 0.50mol/l of Na-gluconate with an additive such as 0.25mol/l of triethanolamine, 2.5-5g/l of polyethyleneglycolnonylphenylether (PEGNPE), 0.2-1g/l of peptone, and 0.04-0.06g/l of o-vanillin at pH=5. It was observed that a deposit of fine luster was apt to be obtained at a composition of nearly equi-molecular ratio between tin and zinc. (5) It was further observed that a deposit of highest zinc content was obtained from gluconate baths containing 20 and 35% of zinc at pH=5, and the zinc content of deposit was almost equal to that of the bath when the plating was conducted at a current density of 1-2Amp/dm².

抄録全体を表示

The oxidation of 18Cr/10Ni/Ti stainless steel diffusion-coated with aluminum was studied with respect to the change of aluminum concentration with time near the surface of metal. Samples prepared for the oxidation tests were diffusion-coated at 750, 850, 950, and 1, 050°C for 1, 3, and 5hrs. The oxidation was conducted in the stationary atmosphere at temperatures of 850, 950, and 1, 050°C. The oxidation behavior was discussed by measurements of weight increase, electron probe microanalysis, X-ray diffraction analysis, and scanning electron microscopy. The results of experiments were as follows: (1) It was proved that diffusion coating of 18 Cr/10 Ni/Ti stainless steel with aluminum was effective for the improvement in oxidation resistance. (2) At 1, 050°C, the critical aluminum concentration for the formation of oxide scale (in which α-Al₂O₃ was the main component) on the interface between the matrix and oxide scale was about 2%. (3) When the aluminum concentration on the interface was higher than about 2%, the weight increase by oxidation was greater with the increase of aluminum concentration on the interface. (4) It was observed that most of oxidation complied with the Parabolic Law except for the early stage of oxidation. (5) The time to breakaway was proportional to the square of cubic root of the amount of penetrated aluminum.

抄録全体を表示

The effects of anions on the electrochemical machining of mild steel were investigated. The cell used for the electrochemical machining tests was of a fixed electrode type, consisting of a copper tube cathode (4mm in outside and 3mm in inside diameter) and a plane steel anode. The electrolytes used were 2mol solutions of NaCl, NaNO₃, NaClO₃ and NaH₂PO₄. The current efficiency for dissolution of the steel in NaCl solution was approximately 100%. The efficiencies in NaNO₃ and NaClO₃ solutions were less than 100%, but increased with the increase of the current densities. The efficiency in NaH₂PO₄ solution was about 3%. The cell voltages in NaCl, NaNO₃ and NaClO₃ solutions gradually increased with the machining time under the effect of electric resistance between the electrodes. The cell voltage in NaH₂PO₄ solution showed the maximum value immediately after the start of electrolysis, when sparks were emitted between the electrodes; but, afterwards, it kept a higher constant value. The profiles of the machined surfaces were measured with a specially designed device, and a method for estimating the degree of stray cutting was proposed. The un-machined surface was not corroded during the machining process in NaClO₃ solution. It was also shown that good dimensional control resulted from a small current in NaClO₃ solution.

抄録全体を表示

The anodic polarization behavior of mild steel and pure iron under high current densities was investigated by using a flow-channel cell in 2mol solutions of NaCl, NaNO₃, NaClO₃ and NaH₂PO₄ at 25°C. The overpotential transients during galvanostatic electrolysis and the potential decay transients after switch-off activation were measured. It was proved that iron was dissolved in active state in NaCl solution; but the dissolution was inhibited by the formation of a passive film in NaH₂PO₄ solution. In NaNO₃ and NaClO₃ solutions, the formation of the anodic film in the early stages of electrolysis, followed by the breakdown of the film, was derived from the potential decay transients. The anodic dissolution mechanism of a transpassive iron electrode in NaNO₃ and NaClO₃ solutions was proposed from the fact that the quantity of electricity necessary for the breakdown of the film depended upon the polarization current density. This mechanism proposed could successfully explain the dependence of the current efficiency for dissolution of iron on the current density, and it was applied to the interpretation of anodic dissolution behavior obtained in the electrochemical machining experiments reported in the preceding paper.

抄録全体を表示

The effects of additives and super-heated water vapor treatment on the composition and structure of boehmite films were studied by measurement of weight changes, X-ray diffractiometry, thermal analysis, infrared spectra, and measurement of impedance. Al specimens of 99.85 and 99.99% in purity were Pretreated and dipped in boiling baths of 0.03-0.15mol triethanol amine, diethyl amine, and monoethyl amine for 0-60min. After the boiling treatment, some specimens were treated in super-heated water vapor at 4kg/cm² for 30min. The following results were obtained: (1) The effects of amines as additives were remarkable: the weight of coated film was 10-15 times as large as that in case of no amine additives. The super-heated water vapor treatment resulted in the increase in the coated weight of boehmite films. (2) Bayerite was not generally contained in boehmite films having been formed in boiling water and various amine solutions; but some of boehmite badly crystallized was often contained. Such boehmite films produced would be assumed to be pseudo-boehmite, because of containing hydrate with 1.7-1.9 H₂O per Al₂O₃. (3) The crystallization of boehmite films was not developed by the super-heated water vapor treatment. However, the hydration degree decreased to 1.5-1.6 H₂O per Al₂O₃ and the impedance of the films increased. (4) It was considered that boehmite films consisted of thin, but dense inner layer adjacent to the metal and a thicker and more permeable outer layer; the former was mainly composed of monohydrate and the latter of hydroxide. (5) It was also considered that the corrosion resistance of boehmite films depended upon the film thickness and the amount of monohydrate.

抄録全体を表示