Matsufumi Takaya

Chrome-free surface treatments for magnesium alloy

Conversion coatings for magnesium have traditionally been based on immersion treatment in a solution containing hexavalent chromium compounds. However, the need for a replacement surface treatment has been strongly emphasized by the present environmental drive to eliminate hexavalent chromium. The development of permanganate bath chemical conversion coatings for magnesium alloys was studied, using mass gain measurements, measurements of corrosion potential, X-ray diffraction, X-ray photoelectron spectroscopy and microscopic examination. The chemical conversion coating obtained from a permanganate bath consists of a film, composed mainly of manganese oxides and magnesium oxide or hydroxide. Such films were found to be amorphous composite coatings. The corrosion resistance of permanganate chemical conversion coatings was comparable with that of chromating.

Antibacterial iodine-supported titanium implants

Deep infection remains a serious complication in orthopedic implant surgery. In order to reduce the incidence of implant-associated infections, several biomaterial surface treatments have been proposed. This study focused on evaluating the antibacterial activity of iodine-supported titanium (Ti-I(2)) and its impact on post-implant infection, as well as determining the potential suitability of Ti-I(2) as a biomaterial. External fixation pins were used in this experiment as trial implants because of the ease of making the septic models. The antibacterial activity of the metal was measured using a modification of the Japanese Industrial Standards method. Activity was evaluated by exposing the implants to Staphylococcus aureus or Escherichia coli and comparing reaction of pathogens to Ti-I(2) vs. stainless steel and titanium controls. Ti-I(2) clearly inhibited bacterial colonization more than the control metals. In addition, cytocompatibility was assessed by counting the number of colonies that formed on the metals. The three metals showed the same amount of fibroblast colony formation. Japanese white rabbits were used as an in vivo model. Three pins were inserted into both femora of six rabbits for histological analysis. Pin sites were inspected and graded for infection and inflammation. Fewer signs of infection and inflammatory changes were observed in conjunction with the Ti-I(2) pins. Furthermore, osteoconductivity of the implant was evaluated with osteoid formation surface of the pin. Consecutive bone formation was observed around the Ti-I(2) and titanium pins, while little osteoid formation was found around the stainless steel pins. These findings suggest that Ti-I(2) has antimicrobial activity and exhibits cytocompatibility. Therefore, Ti-I(2) substantially reduces the incidence of implant infection and shows particular promise as a biomaterial.

Evaluation of corrosion and wear resistance of hard cermet coatings sprayed by using an improved HVOF process

Research for alternatives of hard chrome plating has been widely carried out in the world. High-velocity oxygen-fuel (HVOF)-sprayed cermet coating is one of such alternative candidates. Depending on the cermet powder for spraying, however, sometimes the density of the sprayed coatings is not sufficient for desired corrosion resistance. A gas-shroud (GS) attachment for use with commercial HVOF, which is effective in suppressing oxidation of sprayed particles while raising the velocity of sprayed particles, has been developed. The GS-HVOF spray has been successfully applied to corrosion resistant alloys such as HastelloyC. In this study, a WC cermet system with corrosion and wear resistance was sprayed using a gas-shroud attachment. Porosity in the coatings was observed by the microscopic observation of cross sections. Corrosion and wear resistance was evaluated by alternating current corrosion monitoring in artificial seawater and abrasive wear-tester, respectively. Coatings deposited by the gas-shroud HVOF were superior in terms of both corrosion and wear resistance to coatings formed by the conventional HVOF. The density of the sprayed coatings was improved using the gas-shroud attachment, resulting in superior corrosion and wear resistance.

Friction behaviour of anodic oxide film on aluminum impregnated with molybdenum sulfide compounds

In order to improve the lubricity and wear resistance of aluminum anodic oxide films, it is necessary to ensure the film layers are dense to prevent cracking, and to harden the films as well as reduce the shear stress of the film surfaces. From this view point, lubricious, hard anodic oxide films have been studied in the past, but fully satisfactory results have yet to be realized. In this paper, we report on our study of the re-anodizing of anodic oxide film in an aqueous solution of (NH)MoS. Molybdenum sulfide and compounds filled the 20-nm diameter pores of the film, creating internal stress which compressed the film, suppressing the occurrence of cracks and reducing the friction coefficient.

Novel tribological properties of anodic oxide coating of aluminum impregnated with iodine compound

Abstract Several iodine compounds are well known as solid-state lubricants in the halogen family, however, satisfactory results of their use in the manufacturing industry have not been reported. Subsequently the anodic oxide coating of aluminum impregnated with iodine compound in the concrete inclusion complex with iodine was prepared successfully by an electrochemical method and tribological properties of obtained anodic oxide coating were investigated [Proceedings of INTERFINISH 2000 15th World Congress and Exhibition Congresshaus Garmish-Parten—Kirchen, (2000)]. Iodine compound was found in micro-pores as iodine (I) of 0.1 mass% and formed iodophor of an amorphous structure. The tribological properties of obtained anodic oxide coating were estimated by friction and wear testing. The yielded coefficient of dynamic friction of a sample with iodine compound was less than 0.1. Obtained anodic oxide coating impregnated with PTFE, namely TUFRAM. The coefficients of dynamic friction of obtained anodic coating ADC12 aluminum die casting or A6061 aluminum alloy have proved to be lower in comparison with thin-film Sn on anodic oxide coating by electroplating. From these results, the impregnation of iodine compounds in the micro-pores of anodic oxide coating has proved to lower the coefficient of dynamic friction. We think this phenomenon originates from the orthorhombic system and lamellar structures of the iodine compound used this time, which are well known as solid lubricants.

Structure and Corrosion Behavior of Conversion Coatings on Magnesium Alloys

We studied various types of surface treatments for magnesium alloys that involved the application of chromium or manganese by measuring their corrosion potential using X-ray diffraction, X-ray photoelectron spectroscopy, auger electron spectroscopy, and microscopic examination. The chromium-conversion coating is composed primarily of amorphous trivalent chromium oxide (or hydroxide) and a fluoride of magnesium and aluminum. The permanganate-conversion coatings, we obtained by adding HF to the immersion bath, consisted of a film that was composed primarily of manganese oxides and magnesium fluoride, We found that these films formed an amorphous composite coating In addition, we examined the corrosion resistance of AZ91D magnesium alloy die-cast panels with various surface treatments. The exposure tests, we performed in Miyakojima, indicated that the anodic c oxidation coating and the MX1-type surface treatment containing chromate, which result in relatively thick coatings, are superior in corrosion resistance. The corrosion resistance of permanganate chemical conversion coatings is comparable with that of chromium conversion coatings.

Fabrication of a micro-patterned diamond film by site-selective plasma chemical vapor deposition

Abstract By means of microwave plasma chemical vapor deposition (CVD), diamond was synthesized onto platinum (Pt), silicon (Si) and silicon dioxide (SiO2) surfaces. The nucleation density of diamond on the Pt surface was much higher than on the other surfaces. In particular, the difference between that on the Pt and on the SiO2 surfaces was in the order of 106. Based on this great difference in nucleation densities, a novel method for fabricating diamond micropatterns was developed and successfully demonstrated. In this method, a micropatterned Pt film was prepared on a SiO2 substrate as a template to be treated by plasma CVD. Diamond grains grew selectively onto the Pt micropattern while the surrounding SiO2 remained undeposited. Thus, a positive micropatterned diamond film identical to the Pt micropattern was fabricated. Sub-micrometer resolution was achieved with this site-selective plasma CVD.

Site-selective diamond growth using a platinum film and a silicon oxide mask

In order to fabricate diamond microstructures, we have developed a site-selective microwave plasma chemical vapor deposition (MW-PCVD) method, which is based on the great difference, in the 106order, between the nucleation densities of diamond on Pt and SiO2 surfaces. First, we prepared a substrate consisting of a Pt film covered with a SiO2 layer on which holes of a 2 μm×2 μm square were fabricated by photolithography. Next, diamond was synthesized onto this substrate by MW-PCVD using a mixture of CH4 and H2 as a reaction gas. Under appropriate conditions, diamond crystals selectively nucleated in the holes where the Pt film surface was exposed, while the surrounding SiO2 surface remained undeposited. A microdiamond array was successfully fabricated by this method. Diamond crystals of ∼2 μm are precisely arranged at vertical and lateral intervals of 20 μm.

Chemical bonding in carbon nitride films studied by X-ray spectroscopies

Carbon nitride films are deposited using dc magnetron sputtering in a N2 discharge. The nature of chemical bonding of the films is investigated using X-ray photoelectron spectroscopy, near-edge X-r ...

Growth of (100) orientation diamond film deposited by MWPCVD methods using the gaseous mixtures of CH4, CO and H2

Abstract Diamond films with a polycrystalline structure have been synthesized on a silicon substrate using the gaseous mixtures of methane, carbon monoxide and hydrogen using the method of microwave plasma chemical vapor deposition (MWPCVD). The growth characteristics of the diamond film were studied by SEM technology and X-ray diffraction. The experimental results show that gaseous mixtures of methane, carbon monoxide and hydrogen at appropriate proportions and concentrations [H2:CH4:CO = 100:1:(1–10), H2 flow is 100 sccm] are advantageous to the deposition of (100) textured diamond film and rotating substrate is beneficial to obtain diamond films with uniform growth. The nature of the substrates used in the experiments has no appreciable influence on the orientation of the diamond films. High quality diamond films of 1 inch in diameter, with uniform growth and (100) orientation were synthesized using suitable conditions.