Development of porous plug phase separator and superfluid film flow suppression system for the Soft X-ray Spectrometer onboard ASTRO-H

ASTRO-H is the sixth Japanese astronomy satellite scheduled for launch in 2014. The Soft X-ray Spectrometer instrument is onboard ASTRO-H. This is a 6 × 6 array of X-ray microcalorimeters with an energy resolution of <7 eV at 0.5–10 keV. Superfluid liquid helium is utilized as a part of the cooling system. To retain the liquid helium in the tank under zero-gravity, a porous plug phase separator made of sintered stainless is used. Since the vapor mass flow rate is only 29 μg/s, any additional superfluid film loss influences the lifetime of the liquid helium. Therefore, a film flow suppression system consisting of an orifice, a heat exchanger, and knife edge devices is adopted based on the design used for the X-ray Spectrometer onboard Suzaku. The film flow will be suppressed to <2 μg/s, sufficiently smaller than the vapor flow rate. In the present investigation, the design and ground experiments of a helium vent system composed of the porous plug and film flow suppression system are presented. The results show that the phase separation and the film flow suppression are satisfactorily achieved.     

Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: I, Tobermorite Formation and Reaction Behavior of Slag

The chemical reactions in the formation of autoclaved aerated concrete (AAC) block were investigated. The samples were prepared using blast furnace slag at 180°C under saturated steam pressures for various times from 1 to 128 h. Autoclaving for 1 h yielded 1.1-nm tobermorite with higher Al substitution and lower Ca/(Al + Si) ratio than that made without slag, due to the high solubility of the slag during the initial stage of reaction. This suggests that the utilization of slag has an advantage of reducing processing time. On further reaction, the crystallinity of the tobermorite increases and its Ca/(Al + Si) ratio decreases, becoming constant after 64 h. After a long period of autoclaving. thick reaction rims are formed around unreacted slag particles, interrupting the diffusion of Ca from slag to matrix.     

Natural 1.1 and 1.4 nm tobermorites from Fuka, Okayama, Japan: Chemical analysis, cell dimensions, Si NMR and thermal behavior

A natural specimen of tobermorite, which contained both 1.1 and 1.4 nm phases, was studied by optical microscopy, X-ray powder diffractometry (XRD), EPMA, analytical TEM, ²⁹Si NMR and TG-DTA, and the results were compared with those for a specimen from Crestmore, California. The sample, occurring as a vein in contact with metamorphic rocks, could be divided into three zones. In two of the zones containing only the 1.1 nm phase, about 10% of the Si were substituted by Al. The third zone was an intergrowth of 1.1 and 1.4 nm tobermorites and contained almost no Al. The basal spacings of the 1.1 and 1.4 nm tobermorites were changed mainly to 0.9 nm by heating at 300 °C for 24 h but in some parts remained at 1.1 nm. ²⁹Si NMR results showed that silicate anions in the 1.1 nm tobermorite were double chains, which changed mainly into single chains, on heating at 300 °C. XRD results indicated that natural tobermorites are more highly crystalline than the synthetic ones of calcium silicate products.     

29Si NMR Spectroscopy of Silicate Anions in Hydrothermally Formed C-S-H

Hydrothermal treatment of lime–silica mixtures under saturated steam pressures below 200°C usually gives C-S-H as an initial product, which reacts further to give crystalline calcium silicate hydrates. In this paper, C-S-H was hydro–thermally prepared using CaO and silicic acid at Ca/Si ratios of 0.3 to 2.0 and 120° to 180°C for 2 h. The C-S-H was examined mainly using ²⁹Si NMR by the magic angle spinning gate proton decoupling and cross polarization magic angle spinning methods. XRD for all of the C-S-H showed bands at 0.304, 0.280, 0.183, and 0.166 nm. NMR results showed that all of the C-S-H contained single chains of silicate anion, which became progressively longer as the Ca/Si ratio decreased, i.e., as the system became richer in silica. This was independent of the preparation temperature. The 0.8 ratio preparations at 180°C contained small amounts of double-chain structure of 1.1-nm tobermorite. The reaction processing in the lime- silicic acid mixtures is also discussed.     

Aluminum-Substituted Gyrolite as Cation Exchanger

A successful Al-substituted gyrolite has been hydrothermally synthesized at 220°C under saturated steam pressure, and its cation exchange characteristics for K⁺ and Cs⁺ ions have been investigated. Al-substituted gyrolite took up K⁺ and Cs⁺ ions of 14 and 20 mequiv/100 g, respectively, and these removal amounts are smaller than those by Al-substituted tobermorites (ca. 80 mequiv/100 g). It was found that Al-substituted gyrolite exhibited selectivity for univalent cations in the following order: Na⁺ < K⁺ < Cs⁺ in the low-concentration regions of K⁺ and Cs⁺ ions. Al-substituted gyrolite did not lose its crystallinity and morphology, and its basal spacing did not change in the cation exchange. These results, therefore, suggest that Al-substituted gyrolite may be useful for separation and waste disposal.     

Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: II, Fracture Toughness and Microstructure

The mechanical properties were investigated for autociaved aerated concrete (AAC) block samples, prepared using blast furnace slag at 180°C under saturated steam pressures for various times from 1 to 128 h. The mechanical properties of AAC made using slag are comparable to those made without slag. With increased autoclaving time, the compressive strength increases due to the binder effect of the 1.1-nm tobermorite. In contrast, the fracture energy G _F. and resistance to crack growth decrease with increase of autoclaving time. This dependency is caused by the formation of voids around unreacted slag particles.     

Air and fuel starvation of phosphoric acid fuel cells: A study using a single cell with multi-reference electrodes

The changes in the anode and cathode potentials in the horizontal plane of a phosphoric acid fuel cell (PAFC) under starving conditions for either air or fuel were studied using a single cell furnished with twenty-four reference electrodes which were located around the anode or the cathode. When air starvation occurred, both the anode and cathode potentials became nearly 0 V against RHE, and hydrogen generation began to occur on the cathode side. Fuel starvation occurred when fuel utilization became more than 95%, and the cathode potential in the fuel outlet area shifted significantly toward the positive and, simultaneously, CO and CO₂ were detected in the air exhaust gas, indicating the occurrence of carbon corrosion of the cathode components. By further increasing the fuel utilization, the cell voltage changed to negative and the anode potential in the fuel outlet area became the highest. At that time, significant amounts of CO and CO₂ were detected in the fuel exhaust gas, indicating the occurrence of carbon corrosion of the anode components. Immediately after the termination of fuel starvation, the cathode potential in the fuel outlet area shifted quickly and remarkably toward the positive, and exceeded 1 V against RHE in a few seconds.     

Hydrothermal reaction between CSH and kaolinite for the formation of tobermorite at 180°C

11 Å tobermorites were made from C---S---H (Ca/Si = 1.14) and kaolinite with Ca/(Si+Al) = 0.8 and Al/(Si+Al)= 0.15 at 180°C. The C---S---H was prepared from colloidal silica and lime at 130°C and 180°C for 2 h. Reaction gives in succession C---S---H, poorly crystalline Al-substituted tobermorite, and highly crystalline Al-substituted tobermorite. The addition of kaolinite markedly accelerates the formation of tobermorite within 4 h, more effectively with C---S---H prepared at 130°C than with that prepared at 180°C. X-ray fluorescence diffractometry shows that the Al coordination number is a mixture of 4 and 6 in the initial products and shifts to 4 with an increase in processing time. This agrees with the results for the degree of reaction of the kaolinite.