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In the spent fuel reprocessing process, a mixed solution of uranyl nitrate and plutonium nitrate is converted into mixed oxide powder by the microwave heating. To evaluate the applicability to the industrial-scale and acquire the characteristics data of the microwave heating denitration of various metal nitrate aqueous solutions based on the knowledge studied in the development of laboratory-scale basic experiments, the microwave heating characteristics and metal oxide powder properties were investigated using cerium nitrate, cobalt nitrate and copper nitrate aqueous solutions. The progress rate of the denitration reaction was depended on the position, and the denitration reaction proceeded faster at the periphery than at the center. The morphologies of the synthesized products were porous and hard dry solid for cerium nitrate aqueous solution, foamed dry solid for cobalt nitrate aqueous solution, and powdery particles for copper nitrate aqueous solution. The denitration ratio and average particle size of the synthesized products increased in the order of the cerium nitrate aqueous solution, the cobalt nitrate aqueous solution, and the copper nitrate aqueous solution. The numerical simulations revealed that the periphery of the bottom surface of the metal nitrate aqueous solution was heated by microwaves. These simulation results were consistent with the experimental results in which the denitration reaction started from the periphery of the metal nitrate aqueous solution. [ABSTRACT FROM AUTHOR]

Herein we report a new grinding method to obtain fine particles having high specific surface area which is difficult to realize a conventional dry grinding. Several inorganic carbonates and metal oxides have been studied. Planetary ball milling under dry conditions and subsequent water addition realize the particles with a crystallite size and equivalent size of the specific surface area in the nanometer range. The equivalent size could be down to 25-136 nm using our method except TiO2. Regarding ground TiO2 sample, 47 nm in the equivalent size was successfully obtained via adding KOH solution and washing process. From the view point of solubility, we proposed the mechanism for the equivalent size down to nanometer range. [ABSTRACT FROM AUTHOR]

The surface of phenolic composite material was continuously observed through borosilicate glass (BK7) during friction to verify the tribo-reduction of copper oxide (CuO) taking place at the interface. Two types of pad samples were slid against a rotating BK7 glass disk. These pad samples were made up of selected components, one of which contained CuO as an additive, from a commercial brake pad. During rubbing, dark wear tracks appeared on both pads, where debris generation and its flow were so frequent that the temporal change of these tracks was extremely fast. Using laser microscope after the friction test, small metallic spots were clearly visible on the dark wear tracks of the pad that had contained CuO. The EPMA analysis of these spots showed that the main component was Cu itself. This means that CuO was reduced to Cu, i.e. tribo-reduction took place on the dark wear tracks. Pad friction surface was also observed during friction in relatively dimmed light conditions. The orange luminescence from some spots on the dark wear tracks appeared. The orange color suggested that the temperature of these spots reached significantly high. Heating experiments evidenced that CuO powder, when mixed with phenolic resin powder, was reduced to Cu at 300 °C or higher associated with the weight decrease of mixed powder. Therefore, the luminescence at the surface indicated that the temperature was high enough to cause the degradation of phenolic resin, which promoted the reduction of CuO. It was thus confirmed from the chemical composition and luminescence color that CuO in phenolic composite material was reduced to copper during friction.

For the purpose of clarifying the water vapor effect on brake pad wear, two experiments were performed. In the first set of experiments, wear tests were conducted using four pads under three relative humidity conditions (0.8%RH, 35%RH and 65%RH). The tested pads were simplified formulation of commercial brake pad, each of which contains either CeO2, CuO, graphite as additive or no additives. Wear test results showed that wear amount of the three pads containing CeO2, CuO and non-additive at 0.8%RH was larger than those of pads at 35%RH and 65%RH. Analyses of wear debris and of the worn surfaces of both pad and disk showed that adhesion between pad and disk was relatively high at 0.8%RH. In the second set of experiments, adsorption tests of pad specimens left under 35%RH and 65%RH conditions were conducted. Test results indicated that water vapor in the environment physically adsorbed the pad materials. From the two sets of experiments, it is concluded that water vapor in ambient air adsorbed on the worn surfaces of pad and disk contributed to reduce the adhesion between them. On the other hand, adding graphite to the pad material decreased pad wear even at 0.8%RH. In order to elucidate this mechanism, the specimen of pure graphite was rubbed against disk material at 0.8%RH, 2.5%RH, 3.5%RH, and 65%RH. Wear of graphite at 0.8%RH and 2.5%RH was by some orders of magnitude higher than that at the other humidity conditions. On the disk specimen, graphite was clearly transferred at 0.8%RH. These results mean that the adhesion of graphite is very high at 0.8%RH. Therefore, the wear reduction mechanism of the pad with the addition of graphite at 0.8%RH was concluded as follows. Degraded gases from phenolic resin adsorbed the graphite surface at frictional interface, which caused to reduce its high adhesion to the disk material under very low humidity condition.