Sulfuric acid and trivalent chromium ion were added to chromic acid solution and the cathodic polarization curve was varied with the reduction reaction of hexavalent chromium ion. With increases in trivalent chromium ion, the first peak current density on the cathodic polarization curve increased but the third peak decreased. With the addition of sulfuric acid, the first and third peek current densities showed behavior opposite to that when trivalent chromium ion was added. It is therefore considered that the amount of degradation of the chromium acid solution can be evaluated qualitatively by the behavior described. It is further thought that the formation of chromium oxide film was accelerated by an increase in trivalent chromium ion, while the presence of the SO42- ion of the sulfuric acid solution inhibited the formation of chromium oxide film. Thus, it seems that chromium deposition occurs initially by reduction of chromium oxide film, after which hexavalent chromium is continuously deposited by reduction due to the catalytic action of SO42-.
Oxidation tests of TiN films 2μm thick formed on SKH 51 high-speed steel substrates by reactive ion plating were carried out at 773∼1073K in the atmosphere. The TiN films changed into rutile by oxidization to these temperature. It was found that the reaction followed the parabolic rule, and the parabolic rate constant K was dependent on heating temperature T according to K=1.1×1010exp(-2.2×104/T)μ2/h. Film hardness and critical load in scratch tests both showed a slight increase with heating but eventually decrease with increasing heating temperature and time. This was due to the formation of a layer of low-hardness TiO2.
Waste treatment was studied in the electroless nickel plating line. “COD constituents” in the waste solution such as hypophosphite, phosphite, and organic compounds were oxidized completely by hypochlorite in the presence of a small amount of Cu+/Cu2+ redox catalyst in the form of the chloro complex. Phosphates and sulfates are precipitated by adding calcium salt. The filtrate is mixed with caustic soda to precipitate metal hydroxide, mostly nickel hydroxide. The reaction is simple and fast, and the process is relatively cheap compared to conventional procedures.
A new method has been developed in which Zn/Ni double coated films were electroplated onto steel substrates, and then irradiated using a high-power YAG laser to effect surface modification for alloying the Zn/Ni films. The effects of the laser irradiation on the corrosion resistance of the films was investigated by salt spray tests. It was found that the corrosion resistance of the laser-alloyed films was eight times that of zinc electroplated films, but showed less corrosion resistance than the Zn-13wt%Ni electroplated alloy film. These results are attributed to residual zinc in the alloyed films as well as to the formation of zinc oxide by effects of laser heating.
Semiconductive TiO2 thin films were deposited by RF magnetron sputtering. These films were then characterized to evaluate their NO gas sensitivity. The results are as follows; 1. TiO2 thin films deposited at a power of 700W, substrate temperature 750°C and gas pressure 1.1∼4.1Pa are all n-type semiconductive ones. 2. The specific resistivity of films deposited at gas pressures of 5.3∼10.6Pa decreased markedly compared to those deposited at 1.1∼4.0Pa. This was found to be caused by the increase in carrier concentration as a result of the large number of oxygen defects in the films. 3. The NO gas sensitivity of films deposited at 2.7∼4.0Pa was the highest of all films, and these showed a resistivity change ratio of about 20∼24% at 200°C. This high sensitivity is attributed to the decrease in the grain size of the crystal column of films.
An investigation has been conducted into the deposition of Nb-Al alloy from ambient-temperature molten salt electrolytes of AlCl3-NbCl5-BPC and AlCl3-Nb3Cl8-BPC. The results obtained are as follows. (1) An Nb-Al alloy deposit was obtained from an AlCl3-NbCl5-BPC melt of low NbCl5 content. (2) The valence of the Nb (V) ion in the melt was reduced by the addition of Al powder. In this case, an Nb-Al alloy deposit was obtained from melts with a higher NbCl5 content than in (1) above. (3) An Nb-Al alloy of 29.3wt% Nb was deposited from a 1.0AlCl3-0.90NbCl5-1.0BPC melt with Al powder (3.0wt%) and 50vol% toluene at 40mA/cm2 and 90°C. (4) An Nb-Al alloy of 23.8wt% Nb was deposited from a 1.3AlCl3 -0.07Nb3Cl8-1.0BPC melt at 10mA/cm2 and 140°C.
High-purity aluminum specimens were subjected to heat treatment at 823K for 3h in air, and anodized galvanostatically at Ta=293-353K with a constant current density in a neutral borate solution, and the effects of anodizing temperature (Ta) on the formation and dielectric properties of the anodic oxide films were examined. During anodizing, the rate of increase in anode potential, dEa/dta, was found to be much larger for specimens that were subjected to heat treatment than for those that were not, reaching a maximum at Ta=313-333K. The Al3+ dissolution current for the heated specimens was smaller than that for unheated specimens at all values of Ta, and increased considerably with increasing Ta. At all values of Ta except 353K, the anodic oxide films formed after thermal oxidation were composed of three layers: an outer amorphous oxide layer (thickness δo), a middle crystalline oxide layer (δc), and an inner amorphous oxide layer (δi). With increasing Ta, the δo and δi decreased but δc increased. At 353K, the film formed after thermal oxidation showed a single layer of crystalline oxide. The dielectric properties of thermal/anodic oxide films changed considerably with Ta and Ea, and this was understood to be due to penetration of the electrolyte solution into voids in the oxide films. The mechanism of film formation during anodizing after thermal oxidation is discussed in terms of the crystallization and electrochemical dissolution of the amorphous oxide layers.
A study was conducted on the durability of steel sheet coated with PVC using polyester adhesives that can be activated at a temperature of 180°C. Assuming a case in which the PVC becomes degraded and a corrosive electrolyte reaches the adhesive layer, the corrosion behavior of Zn-Co-Mo electroplated steel sheet coated with polyester adhesive only in 5%NaCl was studyed mainly by the AC impedance method. The film resistance (Rf) of polyester adhesives cured at 180°C was higher than that of conventional acrylic/epoxy adhesives, and the decrease in Rf and the increase in the capacitance (Cf) were smaller than those of conventional acrylic/epoxy adhesives in 5%NaCl immersion tests. It was found that there was good correlation between AC impedance measurement and corrosion resistance and adhesion. It is considered that the excellent corrosion resistance of steel sheet coated with polyester adhesives is due mainly to the addition of silane coupling agent to the polyester adhesives.
A study was conducted on the effect of base metals on the corrosion resistance of steel sheet coated with PVC using polyester adhesives. To examine the corrosion behavior at the adhesive/base metal interface, AC impedance measurements were made on steel sheets coated with adhesive only, when immersed in 5%NaCl. Base metals investigated were Zn and Zn-Co-Mo electroplated steel sheets and hot-dipped Zn, Zn-5%Al and Zn-55%Al plated steel sheets. The film resistance and corrosion resistance of the adhesives were affected by the plating of base metal, with Zn-Co-Mo plating showing superior corrosion resistance to Zn plating. In the cace of hot-dip plating, steel sheets plated with alloys containing Al showed excellent corrosion resistance. It was considered that the corrosion products, such as Co, Mo and Al compounds, under the adhesives affected the film resistance of adhesives measured by the AC impedance method and corrosion resistance.
The behavior of under-film corrosion on beverage can stocks has been investigated. It was found that; (1) Lacquer delamination with under-film corrosion is due to a cathodic disbonding reaction beneath the lacquer, which proceeds gradually from the scratched bare site to the neighbouring lacquered site. (2) Thee degree of delamination has a relatively good correlation with the amount of anodically dissolved iron, but even if an equivalent cathodic reaction occurs beneath the film, the delaminated area is changed by the lacquer delamination characteristics of the interfaces between the lacquer and the substrates. (3) Materials treated cathodically in chromic acid have high oxygen overpotential and exhibit success in preventing under-film corrosion when not deformed. When deformed, materials with and unbroken coated layer are needed so as to expose less of the bare steel.
Monitoring of electroless palladium plating baths using hypophosphite as a reducing agent and ethylenediamine (en) as a complexing agent was investigated by FTIR ATR spectrometry. Linear relationships were obtained between the absorbance of the characteristic absorption bands and the concentrations of Pden22+ complex, en, hypophosphite and phosphite. In continuously used baths with large accumulations of phosphite, the ATR spectra of phosphite, Pden22+ complex and hypophosphite overlapped, but even in these cases compositions could be determined by curve fitting.