Tooth enamel is the hardest material in the human body, and it is mainly composed of hydroxyapatite (HAp)-like mineral particles. As HAp has a hexagonal crystal structure, X-ray diffraction methods can be used to analyze the crystal structure of HAp in teeth. Here, the X-ray diffraction method was applied to the surface of tooth enamel to measure the orientation and strain of the HAp crystals. The c-axis of the hexagonal crystal structure of HAp was oriented to the surface perpendicular to the tooth enamel covering the tooth surface. Thus, the strain of HAp at the surface of teeth was measured by X-ray diffraction from the (004) lattice planes aligned along the c-axis. The X-ray strain measurements were conducted on tooth specimens with intact surfaces under loading. Highly accurate strain measurements of the surface of tooth specimens were performed by precise positioning of the X-ray irradiation area during loading.The strains of the (004) lattice plane were measured at several positions on the surface of the specimens under compression along the tooth axis. The strains were obtained as tensile strains at the labial side of incisor tooth specimens. In posterior teeth, the strains were different at different measurement positions, varying from tensile to compressive types.

A liquid metal electrochemically deposited in CaCl2 or its chloride melts serves as an effective reductant for active metal oxides. Although a very low oxygen concentration can be achieved at a considerably high electrolysis efficiency, the existence of small amount of water impurity in molten chlorides, which is very difficult to detect, causes low electrolysis efficiency. In this study, to clarify the morphological and thermal characteristics of a cathodic electrode in a slightly hygroscopic LiCl-KCl-CaCl2 melt, we simultaneously performed electrochemical measurements and thermal measurements using an ultrafine thermocouple inserted inside a Mo electrode (i.d. 1.57 mm). 2 Concomitantly, changes in the electrode interface were recorded at 500-μs intervals using a synchronized high-speed digital camera. Despite the small amount of water included in the system, the measured heat absorption was much smaller than thermodynamically predicted, which suggested that the generated hydrogen decreased the purity of the liquid alloy electrodeposited on the cathode surface possibly through hydride formation. By using the synchronized thermal measurement, it was possible to trace the change in the electrodeposition pattern of impurity water quickly and sensitively, which was difficult to determine in only the electrochemical potential-current response.

Titanium dioxides were reduced to metallic titanium via molten salt electrolysis using CaCl 2. It was reported that the ef ciency was low because some side reactions produced carbon precipitates. To produce titanium more ef ciently, these electrochemical side reactions were examined by cyclic voltammetry CV. O 2 reacted with the carbon anode to form CO and CO 2 gas bubbles, which easily dissolved into the molten salt and formed CO 3 2 , subsequently generating carbon powder. CV was performed after interrupting electrolysis temporarily. The electrochemical reduction of CO 3 2 in the cathodic scan was not observed, suggesting that CO 3 2 was spontaneously reduced by Ca during electrolysis. Anodic reactions preceding Cl 2 gas generation occurred in three steps: CO and CO 2 gas generation related to O 2 , and successive CO 2 generation related to CO 3 2 .

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