Lithium ion batteries (LIB) have been widely applied as power sources for electric devices owing to their light weight and high energy densities. A large amount of cobalt (Co) was used as cathode materials in the LIB, so establishment of Co recycling from spent LIB is demanded. Optimization of heating and grinding process on classification for Co recycling before physical separation from spent LIB was investigated in this study. Lithium cobalt oxide (LiCoO2) in spent LIB was transformed to CoO, which was more easily decomposed than LiCoO2 by heating process. Coexisting materials of carbon as an anode in the LIB promoted LiCoO2 decomposition at a lower temperature than the theoretical value for LiCoO2. Furthermore, slow heating rate was effective for grain growth of Co oxide and Co metal. In the grinding process, iron ball as high density media was more effective grinding media than wooden ball as low density media. It was suggested that heating process at low temperature with slow heating rate and grinding process by using high density media could promote the separation of Co and Al by screening process.
In application of amorphous silica originated from rice husks to industrial raw materials, fine particles less than a few microns are strongly required in the market. A long-time mechanical milling process is necessary to refine raw silica materials due to their high hardness, and results in a remarkable advance of the products cost. In this study, high efficiency refining technique of silica materials using the conventional milling process was proposed. When burning rice husks at 450 ～ 600 ℃ without air supply, the organic elements such as cellulose, hemi-cellulose and lignin are completely changed to very brittle carbides, and resulted in formation of layer-structures consisting of silica and carbides in the ashes. These brittle carbides easily lead to the fragmentation of hard silica materials, and very fine particles are successfully prepared by milling process. Raman spectroscopy and SEM-EDS analysis was effective to optimize the burning temperature of rice husks to obtain the carbide layers in the ashes. For example, when more than 34 wt% carbonized elements are contained in the ashes, one hour conventional milling process is enough to prepare fine amorphous silica particles with a mean particle size less than 1 μm. In comparison with silica materials with no carbide, the above refining technique remarkably reduced the milling process time to about 1/10. Finally after the secondary combustion of the refined ashes to thermally resolve the carbides and remove the carbon elements, the application of the optimized combustion temperature from 750~850 ℃ resulted in high-purity fine silica particles with a low carbon content less than 0.06 wt%.
The effect of addition of Sn and rare earth element (REE) have been investigated by hardness, tensile and impact absorbed tests, microstructural analysis using optical, scanning electron and transmission electron microscopes (SEM, TEM). Values of hardness and ultimate tensile strength increased increasing with Sn contents upto 0.1 mass% with and without REE, while elongation and impact energy were decreased. Spheroidal graphite in alloys including REE and Sn became finer with increasing Sn contents, and the 0.6Sn alloy had a spheroidal graphite which has clear sphere with smooth surface as the same as alloys including Sb in our previous report. Spheroidal graphite in this study was also indexed as a graphite structure by SAED analysis.
In electronic wire weld between the Al tub and CP wire plated pure Sn, single-crystal Sn whiskers easily form and can cause problems such as short circuits. We found that the growth of Sn whiskers in the weld zone of Al electrolytic condenser leads was suppressed by controlling the cooling rates of the weld. We observed that the whisker formed only when Al and Sn are mixed. Following the examination of the effect of the microstructure in order to understand the whisker formation mechanism and how to prevent whisker growth we concluded that the microstructure is strongly affected by the cooling time Tc from 933K (Al melting point) to 503K (Sn melting point) of the weld. The whisker did not form in weld when the cooling time Tc is 230s, for example, air cooling by using the simulated Al-Sn alloy. The Sn phase grain was large, i.e. more than several hundred μm. On the other hand, the large number of Sn whisker were observed in the case of Tc=20s. The size of Sn phase is about 5μm. Finally, there was no whisker when the cooling time Tc was 7s, e.g. by the cupper chill plate. The Sn phase grain size is smaller than 1μm that is comparable to the minimum diameter of a whisker. . Considering the microstructure of weld, the whisker growth can be prevented with respect to the size of the Sn phase, i.e. larger than several hundred micron or smaller than one micron.