Corrosion behavior of polymeric materials was studied. The form of degradation of organic materials were classified and arranged, then the behavior and mechanism of it were explained from unified approach method from relativity of the diffusion and reaction rate and the structure of corrosion product point of view. Furthermore, form an analogy of metallic corrosion theory, the degradation of polymeric materials mainly on thermosetting resins was explained.
Nitrous acid affects the corrosion of metals such as stainless steels in nitric acid. However nitrous acid is not particularly stable in nitric acid and the analytical methods available are quite involved. Accordingly, the calculation of nitrous acid concentration from redox potential was tested in the HNO3-H2O system as a convenient in situ analysis method. The calculation process is based on Nernst's equation and the required thermodynamic data were obtained from published values. The available thermodynamic data allow calculation of nitrous acid concentration from 273K to 373K for 0%-100% HNO3. The redox potential was measured in 8kmol·m-3 HNO3 under NO bubbling and the nitrous acid concentration was determined by a Colourimetric method. The calculated data were compared with the measured data and a good agreement was found. It was found that the corrosion potential of stainless steel is influenced by nitrous acid concentration in nitric acid solution. The calculation process is useful for in-situ analysis of nitrous acid species in HNO3-H2O system and understanding the behavior of the cathodic reaction associated with nitric acid corrosion.
The FRP as the esthetic orthodontic wire was fabricated with biocompatible CaO-P2O5-SiO2-Al2O3 (CPSA) glass fibers and PMMA. In this study both the mechanical properties and biocompatibility of the FRP wire were investigated. All wires were approximately 0.5mm in diameter Young's modulus could be regulated in proportion to the volume fraction of glass fibers from 20GPa to 40GPa under dry condition corresponding to the conventional metal wires. However, deload/load ratio at 1.0mm in deflection was deteriorated from 80.9% to 23.3% after 30 days exposure to water. The coating layer could well function as the moisture protector so that the deterioration of the ratio was improved to 56.7%. In the histological study of long term implantation of CPSA FRP wires (4 weeks), the organization had almost completed either by separation or by covering with the granulation tissue. Macrophages and foreign body giant cells were scarcely observed. Therefore it could be thought that they had good biocompatibility.
Since 5-Chloro-2-methyl-4-isothiazolin-3-one (CMI) has relatively wide antibacterial spectrum, and low toxicity to human, it is widely used as a bactericide and fungicide, or a slime control agent for a cooling tower. The minimum inhibitory concentration of CMI to E. coli K-12 was 1.6mg·l-1. Short time (-45min) exposure of E. coli K-12 to CMI solution of 20mg·l-1 prolonged lag phase of the cell growth. On the other hand, normal logarithmic growth phase was observed after the lag phase. When E. coli K-12 was exposed to CMI of 1.0mg·l-1 for 25 hours, the sterilization fraction reached to 99%. CMI concentration of more than 10mg·l-1 and more than 5 hours exposure time were needed for attaining 99.9% sterilizing fraction. The antibacterial activity of CMI to E. coli K-12 cells embedded in 0.6% agar was high in the upper layer of the biofilm and low in the bottom layer of the biofilm. When activated sludge was supplied with artificial sewage with CMI of 20mg·l-1, bacteria resistant to CMI became dominant in the bacterial consortia.
The growth mechanisms of oxide films thermally formed on copper have been studied using “double sweep cyclic voltammetry” in strongly alkaline electrolytes. It was found that an electrolyte of 6M KOH+1M LiOH allowed perfect resolution of catholic waves due to the reduction of Cu2O and CuO. The effect of the types of anion on copper oxidation mechanism was investigated in many factors of corrosion. Copper sheets were prepared by pre-immersion in various electrolytes of sodium salt, followed by heating in air at 80°C and 90% RH. The formation kinetics of each oxide films followed the parabolic rate law with a few exceptions. These were confirmed that the formation of the oxide films was accelerated with the increase of ions on copper and that the oxidation rate of Cu2O or CuO was controlled by the types of anion.
Being a martensitic stainless steel with high strength, excellent workability and good damping capacity, 12% Cr steel is widely used for turbine blades. In recent years, there has been an increased demand for larger blades in order to increase the efficiency. Because turbine blades require a high strength material, it has become an important issue how far the hardness threshold can be extended. Accordingly, a study of the effect of precipitates on hydrogen embrittlement was conducted using SUS 410J1 steel as a test material, for the purpose of determining guideline for the selection of high strength 12% Cr steel. SUS1 410J1 steel used in this study did not suffer from cracking due to hydrogen embrittlement when stable M2N was precipitated. Thus, it is concluded that the cracking could be prevented when precipitates become stable.