Hideaki Takashima

Development of catalyst materials being effective for microwave sterilization

Abstract Recently, airborne virus infections have emerged as some of the most challenging medical problems. To prevent the threat of infection, the processes of sterilization have been studied widely. Microwave sterilization has many advantages in comparison with conventional methods. It is able to raise the temperature of a material in a short time and selectively heat the material. This results in the reduction of usage and the rapid completion of sterilization. We developed a novel microwave sterilization system that can raise the temperature in quite a short time using a lower microwave power (100 W). Filters made with Kao wool (Al2O3) were coated with TiO2 (anatase) by sol–gel method and used to trap microorganisms. In addition, these filters were coated with Pt or Ag by impregnated method. We also prepared a Tyranno-fiber textile filter and a honeycomb SiC filter. Two microorganisms, Bacillus subtilis ATCC 9372 and Bacillus stearothermophilus ATCC 7953, were used in this experiment, where either microorganism was loaded onto a filter. After irradiation, filters loaded with B. subtilis and B. stearothermophilus were incubated for 48 h in a TSB medium (Bactoe Tryptic Soy Broth, Becton, Dickinson and company sparks, MD) at 37 and 56 °C, respectively. B. subtilis and B. stearothermophilus loaded on to Ag-impregnated filters were sterilized in 30 and 15 s, respectively. The Tyranno-fiber textile filter and the honeycomb SiC also filter showed effective microwave sterilization. These results showed that this system could sterilize B. subtilis and B. stearothermophilus in quite a short time and that microwave absorbable materials are effective as microwave sterilization filters.

Growth of Ce3+-doped Li6Gd(BO3)3 Single Crystals under Ultralow Oxygen Partial Pressure

Ce3+-doped Li6(Gd0.99Ce0.01)(BO3)3 single crystals have been grown by the floating zone method in argon atmosphere with an ultralow oxygen partial pressure, pO2≈10-23 Pa (Condition A) or under a conventional reduction gas of diluted H2 (Condition B). The intensities of the excitation and emission spectra of such crystals in the UV–visible spectrum (VIS) region obtained by optical measurements under Condition A were 20% higher than those under Condition B. X-ray photoelectron spectroscopy (XPS) revealed that the ratio of Ce3+ to Ce4+ in crystals grown under Condition A was larger than that in crystals grown under Condition B.

Microwave Sterilization by TiO2 Filter Coated with Ag Thin Film

Microwave sterilization for E.coli and/or B. subtilis was investigated. We prepared the filters made of A₂O₃ wool coated with Ag and/or TiO₂ and the urethane foams filter. Ag and TiO₂ played an important role in the sterilization system, because OH radical (*OH) may be generated on the surface of the filter. We discussed about the MW sterilization mechanism by detecting the *OH from XPS analysis of V₂O₈ thin films. We proposed the mechanisms of microwave sterilization, which was mentioned about *OH effects.

Evaluation by extended Hückel method on the hardness of the B–C–N materials

Abstract Hard materials, e.g. diamond and cubic boron nitride (c-BN), are widely applied to improve the lifetime and the performance of many kinds of cutting and forming tools. These materials are usually used at high temperature, so the study of stability on these materials at high temperature is very important. However, diamond is a low resistance to the oxidation, it should be replaced with the boron-based hard materials. Recently, boron–carbon–nitrogen (B–C–N) ternary materials are expected to possess a high hardness, a high thermal stability at high temperature. We estimated the hardness and the stability of B–C–N materials at high temperature by the extended Hückel method. The extended Hückel method is one of the molecular orbital calculations and needs the cluster model of materials for the calculation. The cluster model of B–C–N materials was regarded as a zinc blende structure. In the present work, we used two physical quantities, i.e. a cohesive energy and anenergy fluctuation, as a measure of hardness and stability of materials. The cohesive energy indicates the coherenceof bonds between atoms. The energy fluctuation shows the reactivity of materials. Hardness, structure, solid-state properties and reactivity of materials can be estimated from these physical quantities. When the composition of B–C–N materials was boron: 25 at.%, nitrogen: 25 at.% and carbon: 50 at.%, the cohesive energy was the lowest. This result implies B–C–N ternarymaterials are not harder than c-BN and/or diamond. Cubic-BN was the lowest energy fluctuation of B– C–N materials, and the energy fluctuation increased as increasing of carbon atom. The reactivity of B–C–N materials was high at a high temperature with an increase of carbon atoms. These results imply that B–C–N materials are not suitable for the hard cutting materials.

Microwave Sterilization Using Catalyst Material Filter

We developed a new microwave sterilization system that can rapidly raise filter temperature by microwave irradiation with a low microwave power. We prepared filters made of A2O3 wool to trap microorganisms. The filters were coated with TiO2 (anatase) by the sol–gel method before use. The filters were impregnated with each of two kinds of metals, Pt and Ag. We also prepared Tyranno-fiber (SiC continuous fiber containing small amounts of Ti, O) cloth and honeycomb SiC as filters. Two microorganisms, Escherichia coli and Bacillus subtilis were the targets in the present study. Cells of E. coli and B. subtilis loaded on the Ag-impregnated filter can be sterilized within 5 s by microwave irradiation. Tyranno-fiber cloth and honeycomb SiC were also effective for microwave sterilization. These results indicated that this technique enables rapid sterilization of E. coli and B. subtilis, and that microwave absorption materials, such as SiC and graphite, are effective for microwave sterilization filters.

Synthesis of Amorphous Germane by Tunneling Reactions of Hydrogen Atoms with van der Waals GeH4 Films at Cryogenic Temperatures

The reactions of hydrogen atoms with a thin GeH4 film condensed on a substrate at 10 K led to the formation of amorphous-like solid film. The solid products were analyzed by in-situ Fourier transform-infrared spectroscopy, ex-situ spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. It was found that the solid products were mainly composed of hydrogenated amorphous germane and polygermanes. It was proposed that the singlet GeH2 which is the intermediate product in the consecutive reactions of H with GeH4 inserts into the neighboring Ge–H bonds resulting in the Ge–Ge bond network. It was found that up to the equivalent ~23 GeH4 monolayers from the top surface of the reactant GeH4 film were converted to the solid product but not deeper.

Thermal Analysis of Joule Heat Generated on Metal Thin Film by Microwave Irradiation

The microwave heating of the catalyst coated with nickel thin film was modeled and calculated. The theory was established by using Maxwell equation and so on. The result corresponded with experimental one. The theory also shows the relationship between the film thickness and the microwave power absorbed.

Reduction of Sr in Sr3MoO6 Compounds Melted under Ultralow Oxygen Partial Pressure

Sr3MoO6 was melted in Ar atmosphere under an ultralow oxygen partial pressure (ULOPP) of p(O2)=10-20 Pa by a lamp-image furnace at 1830–1900 K. Sr3MoO6 melted in Ar atmosphere was yellow, whereas Sr3MoO6 melted under ULOPP changed from yellow to metallic ash-gray luster. X-ray Photoelectron Spectroscopy analysis showed that the Sr in Sr3MoO6 was strongly reduced chemically to a metallic state and that the binding energy of Mo was shifted to the high-energy side.