As electronic devices and mainboards become smaller, the need for thermal conductive materials having excellent internal heat dissipation is increasing. In this study, nano thermal grease was prepared by mixing in copper nanopowder, which is used as a heat transfer medium in thermal grease, which is a kind of thermal conductive material, with silicon oil. In addition, copper powder was mixed with graphene and alumina, respectively, and the thermal conductivity performance was compared. As a result, the thermal conductivity improved by 4.5 W/m·k over the silicon base, and the upward trend of thermal conductivity increased steadily up to 15 vol. %, and the increasing trend decreased after 20 vol. %. In addition, the increased rate of thermal conductivity from 0 to 5 vol. % and 10 to 15 vol. % was the largest.
Glass transition and stickiness characteristics of fresh and Lactobacillus brevis‐fermented sea tangle powders, at different storage temperature and water activities (aw), were investigated. For both powders, glass transition temperature (Tg) decreased from 75°C to −72°C with increasing aw from 0 to above 0.9. Sticky point temperature (Ts) was higher than Tg by about 13−22°C, and also decreased with increasing aw. Higher Tg and Ts values were measured for fermented powder, and for powders stored at higher temperatures. Microstructure analysis revealed water‐induced particle aggregation and caking at aw >0.43. A storage stability study found that fermented powder was more stable than a fresh one, and a low storage temperature was preferred due to reduced molecular mobility. When stored at 4°C, the fermented powder remained non‐sticky as long as the aw remained below 0.8 (or the moisture content was below 0.76 g/g dry matter).
Practical applications
Sea tangle (Saccharina japonica) contains γ‐aminobutyric acid (GABA), a major inhibitory neurotransmitter having beneficial physiological effects, such as diuretic, hypotensive, and tranquilizing activities. Fermentation of sea tangle with Lactobacillus brevis can increase the amount of GABA by about 100 times. However, the use of fermented sea tangle powder is greatly limited because its moisture‐induced stickiness and glass‐to‐rubbery state transition by strong hygroscopic nature significantly reduce the stability, safety, and quality of the powder during handling, processing, storage, and distribution. The present study provides a useful guideline for the safe and effective use of fermented sea tangle powder by providing information essential for understanding the relationships among the moisture sorption, glass transition, and stickiness of the powder.
Starting from the quaternary Cu 47 Ti 34 Zr 11 Ni 8 alloy, the compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni alloys was systematically investigated. Quaternary Cu-Ti-Zr-Ni alloys can be cast directly from the melt into copper molds to form fully amorphous strips or rods with the thickness of 3-6 mm. The evidence of the amorphous nature of the cast rods was provided by X-ray spectra. The measured glass transition temperature (T g ) and crystallization temperature (T x ) were obtained for the alloys using differential scanning calorimetry (DSC) at the heating rate of 20 K/s. In the results, the differences between the glass temperature and the crystallization temperature (ΔT x =T x -T g ) are measured with values ranging up to 33-55 K. The reduced glass transition temperature (T rg ), which is the ratio of the glass temperature to the liquidus temperature (T l ), is often used as an indication of the glass-forming ability of metallic alloys. For the present Cu-Ti-Zr-Ni alloys, this ratio is typically in the range of 0.5838-0.5959, characteristic of metallic alloys with good glass-forming ability. The elastic constants for several selected alloys were measured using ultrasonic methods. The values of the elastic shear modulus, bulk modulus, and Poisson's ratio were also given.
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