The process of cathodic electrolytic formation of molybdenum oxide films from molybdate-citrate bath was investigated using Hull-Cell test, cathodic polarization measurement and UV absorption spectra measurement of the solution. pH, temperature and the concentration ratio of citrate ions to that of molybdate ions were changed. Chemical states of the deposited films were evaluated by XPS (X-ray photoelectron spectroscopy). The results of Hull-Cell test and cathodic polarization curves showed that molybdenum oxide film was deposited in the presence of citrate ions in the bath and the deposition rate was related to the bath pH and temperature of the solution. UV spectra indicated the formation of citrate-molybdate complexes which induce the deposition of molybdate oxide films. From the XPS analysis, the film was found to be a layered structure of Mo/MoO2/MoO3, in which metallic Mo was detected only on the substrate of Iron family elements, Ni, Fe, and only the second layer of MoO2 grew thicker by electrolysis.
By the heat treatment of a ultra low carbon hot-rolled steel containing 0.31mass%Si-1.02mass%Mn, not only readily oxidizable elements such as Si and Mn but also Fe were internally oxidized at the steel surface region. The scale of the steel acted as the source of oxygen for internal oxidation. The composition of the grain-boundary oxides differed from those in the grain, presumably due to the difference in oxygen potential ; oxides at the grain-boundary consisted mainly of Fe-Si-Mn-O, while oxides in the grain consisted mainly of Si-Mn-O. The internal oxidation layer remained after scale pickling and cold rolling. Fe containing grain-boundary oxides, arranged in layers by the cold rolling process, were considered to act as the oxidant of Si and Mn, which diffuse toward the steel surface in recrystallization annealing. By not only the low Si and Mn activity due to the depletion layer formed during the heat treatment, but also the redox reaction between the grain-boundary oxides and solute Si and Mn, the amounts of Si and Mn selective surface oxidation were remarkably decreased. The resultant suppression of the selective surface oxidation brought about improvement in the wettability by molten Zn of the annealed sheet steel surface.
An internal strain in deposits and amount of hydrogen evolved at the beginning of iron electroplating were evaluated, and the influence of hydrogen evolution on the internal strain was also discussed. The internal strain was measured using resistance wire type strain gauge put on the reverse side of copper electrode. On the other hand, the amount of hydrogen gas evolved during iron electroplating was in-situ evaluated from its buoyancy produced by hydrogen gas using electromagnetic balance. The hydrogen evolved during iron electroplating influenced greatly on the formation of internal strain in iron deposits. Especially, a part of hydrogen codeposited with iron spontaneously leaked from the iron crystal to the outside, which caused an internal tensile strain in iron deposits. The measurement of buoyancy produced by the hydrogen gas using electromagnetic balance also enabled us to evaluate the amount of atomic hydrogen that incorporated in iron deposits during electroplating and then released after anodic dissolution of the iron deposits. A large portion of hydrogen evolved at the beginning of the electroplating was included in iron deposits and the hydrogen content was ca 16mol.% at current density of 30mA/cm2. However, after consecutive iron electroplating of only 1.3C/cm2 the hydrogen content in deposits decreased greatly to ca 5mol.%.
Tin oxide thin films have been deposited by means of liquid phase deposition using tin fluoride as a precursor. A uniform film was obtained at room temperature with stirring the precursor solution. There were a large amount of hydroxyl groups in the deposited films. However, due to annealing in air, a Sn-O-Sn network was formed in the films through dehydration condensation between the hydroxyl groups resulting in the formation of the films consisting mainly of SnO2. The annealing improved the crystallity of the films as well. The resistivity decreased down to 1.2×10 -2Ωcm by the annealing at 673K. However, the annealing at higher temperatures resulted in the increase in resistivity due to the decrease in carrier mobility and concentration.
A defect associated with the use of a Sargent bath, a widely used chromium plating device, is the substantially lower current efficiency of chromium compared to that of other metals. It has been reported that the use of a formic acid bath leads to the production of amorphous-structured chromium deposits with a higher current efficiency. However, it is difficult to use this process commercially, because of difficulties involved in maintaining the bath. The purpose of this study was to examine in detail the conditions for chromium deposition in a formic acid bath with the objective of developing an optimum plating method with a higher current efficiency and a higher deposition rate. In order to realize a higher deposition rate, the effect of agitating the solution, via the use of a rotating disk electrode (RDE) apparatus, was examined. The findings show that the rate of deposition and current efficiency increased with increasing current density. By rotating the specimen, however, plating with bright surfaces was obtained more easily and under a wide variaty of plating conditions. The appearance of the surface of the deposited chromium was affected by the current density, the aging time of the solution used, and the rotating speed. We conclude that the morphology of the deposited chromium is closely related to the Cr3+ concentration in the proximity of the surface of the specimen.
Display devices of rare-earth metals ion-implanted into an anodic alumina film on aluminum substrate were studied. The red, green and blue color of the electroluminescence can be emitted from the devices of implanted metal ions Eu+, Tb2+ and Tm2+, respectively. A weak blue luminescence is available from Tm2+ as a color center. The divalent state of europium ions, which acts as the blue color center, is discussed for the possibility of bright blue luminescence. However, even if Eu+ is implanted into the anodic alumina film, only the red luminescence of Eu3+ can be observed. The cause of this examined using the results of the DV-Xα computer simulation, XPS and measurement of luminescent spectra. It is suggested that Eu2+ can be stable in a columdum structure of alumina. Furthermore, the implanted position was not a vacancy of alumina, but was thought to replace the aluminum atom.
Hydroxyapatite(HAp) coating using HAp particles including alkoxysilyl group(s) was developed as a novel method for the introduction of HAp on metal substrates. The derivatives of HAp having alkoxysilyl group(s) were synthesized by the reaction of HAp particles with various isocyanates in DMF, followed by addition of monoalkoxysilane or bis (alkoxysilane). In these derivatives of HAp, the alkoxysilyl group(s) was/were hydrolyzed in ethanol with water and acetic acid to prepare the precursor suspension solutions. The titanium plate or the stainless steel (SUS316L) plate, which was dip-coated using these suspension solutions, was heat-treated at 200°C. The coated metal surfaces were observed by microscope and SEM. As a result, it was found that the metal surfaces were coated by HAp most effectively when the HAp-urethane-urea derivative having the urea linkage in the molecule, which was synthesized from 1,3-bis (isocyanatomethyl) cyclohexane, was used in the coating. The peeling test of this HAp coating indicated that the most of the coated HAp particles remained on the metal surfaces.