Characteristics of a 4 K Gifford–McMahon cryocooler using the Gd2O2S regenerator material

In order to improve the cooling power at 4.2 K, performance of a Gifford–McMahon cryocooler was investigated. We focus on regenerator materials and structure of 2nd stage regenerator. A ceramics regenerator of Gd₂O₂S (GOS) was used in the cold part of the 2nd stage regenerator. To utilize the GOS effectively, we applied a layered structure to the 2nd stage regenerator. It was divided into three parts along the length for the temperature distribution, to which lead (Pb), HoCu₂ and GOS spheres were filled. The cooling power improved to 0.22 W at 4.2 K. The electric power consumption is 1.3 kW. When only Pb and HoCu₂ (without the GOS) are filled, the cooling power is 0.15 W at 4.2 K. The experimental results show that GOS is very effective to increase the cooling power at 4.2 K.     

Numerical analysis of active magnetic regenerators for hydrogen magnetic refrigeration between 20 and 77 K

A model active magnetic regenerator refrigerator (AMR) with the Brayton-like operation cycle was analyzed by numerical cycle simulation in the temperature range between 20 and 77 K. In order to study the performance using magnetic material with various transition temperatures T_c, entropy of magnetic material with second order phase transition was calculated using mean field theory and Debye approximation. The cooling performance is shown to be high when the heat exhaust temperature is close to the transition temperature. It is shown that the optimized operation condition depends on both T_c and operation temperatures. Multi-layered AMR beds were shown to improve the performance of AMR. Multi-stage AMR was also discussed.     

Magnetocaloric effect of (ErxR1−x)Co2 (R = Ho, Dy) for magnetic refrigeration between 20 and 80 K

Two series of RCo₂ compounds, (Er_xHo_1−x)Co₂ and (Er_yDy_1−y)Co₂, were investigated as magnetic refrigerants for hydrogen liquefaction. A large magnetocaloric effect (MCE) was observed just above the Curie temperature (T_c) of these compounds which both undergo a first-order magnetic transition. The isothermal entropy change ΔS and the adiabatic temperature change ΔT_ad of these compounds were larger than those of other Laves-phase materials such as RAl₂ and RNi₂. However, the temperature range of the large MCE for these compounds was limited. It has been shown that T_c increases almost linearly against the de Gennes factor, and can be controlled by changing the concentration of the rare earth elements while maintaining a first-order transition. By measuring the magnetization and heat capacity, we obtained temperature entropy (T–S) diagrams, which are essential for analyzing the magnetic refrigeration cycle. Both series of compounds showed high potential for use in a regenerative thermal cycle, especially as a combination of several compositions to cover a wide temperature range.     

Highly flame retardant coating consisting of starch and amorphous sodium polyborate

Mixture of starch and amorphous sodium polyborate (SPB) is found to show high flame retardancy, when its aqueous solution is deposited and dried on organic polymer materials such as polyethylene terephthalate (PET) nonwoven, rigid polyurethane (RPU) foam, and polypropylene (PP) nonwoven. The PET nonwoven (10 mm thickness) and the RPU foam (10 mm thickness) coated with the mixture endure the premixed flame of butane gas burner with length of 100 mm for more than 12 min. The PP nonwoven (0.7 mm thickness) endures the nonpremixed flame with length of 65 mm in the 45 degrees Meckel burner test for more than 2 min. The backside temperatures in the both tests remain below 130 °C. The thermal analyses and the SEM observation indicate the mechanism that the SPB foam promotes the carbonization of starch and that the carbonized layer together with the SPB foam insulate inside from oxygen and heat.     

Metal-free isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide derivatives: The effect of methyl substituents of pyridine N-oxide on the isotactic specificity and the proposed mechanism for the isotactic-specific radical polymerization

The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures in the presence of pyridine N-oxide (PNO) derivatives were investigated. It was found that the methylation at meta-positions of PNO improved the isotactic specificity induced by PNO, whereas the methylation at ortho-positions prevented the induction of the isotactic specificity. NMR analysis revealed that NIPAAm and PNO derivatives formed predominantly 2:1 complex through a hydrogen-bonding interaction. Furthermore, the induction of the isotactic specificity was attributed to the conformationally limited propagating radicals. Based on these findings, the mechanism of the isotactic-specific radical polymerization was discussed.     

Technology in emulsified particle size control by new mixing method

The best pulverization of emulsions that can be achieved using conventional mixing blades is in the micrometer realm. Now, with our new 'thin-film spin system' high-speed mixer, it is possible to attain pulverization in the nanometer realm. The particle size distribution can now be controlled to achieve an almost single distribution state. Particles can be pulverized without being severed, preventing secondary agglomeration after processing. This new mixing system also solves many of the problems common to conventional pulverization processes.