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951.
Because silica refractory has good volume stability and creep properties at high temperature, it has been used in several furnaces. However, silica has three polymorphs (quartz, tridymite and cristobalite) and each polymorph has an- type transformation. It is known that cristobalite is the stable phase of silica between 1470° C and the melting point of silica refractories. However, sometimes cristobalite was found in silica refractories used in the stable temperature region of tridymite. Therefore, the cause and mechanism of this tridymite-to-cristobalite transformation below 1470° C was studied. Although the transformation temperature of tridymite to cristobalite was also 1470° C in the sample used in this research, it decreased on addition of Al2O3. The apparent activation energy of the tridymite-to-cristobalite transformation was found to be 787 kJ mol–1 above 1470° C and 176 kJ mol–1 below 1470° C with Al2O3 by measuring the transformation rate. It was also observed using EPIVIA that the tridymite included CaO; however, CaO and Al2O3 were located on the outside of the cristobalite which was produced below 1470°C. Therefore, it is supposed that the liquid phase was produced by the penetration of Al2O3, and impurities in the tridymite crystal diffused outside and then silica was precipitated as cristobalite. 相似文献
952.
Tadashi Kokubo Setsuro Ito Masazumi Shigematsu Sumio Sakka Takao Yamamuro 《Journal of Materials Science》1985,20(6):2001-2004
A new type of apatite-containing glass-ceramic in the system MgO-CaO-SiO2-P2O5 can form a tight chemical bond with bones and has a high mechanical strength. The cause for its high mechanical strength was examined by comparing mechanical properties of the glass-ceramics which have an identical chemical composition and different microstructures. It was found that the mechanical strength of the apatite-containing glass-ceramics is considerably increased by the precipitation of-wollastonite crystals due to an increase in fracture surface energy resulting in an increase in fracture toughness. 相似文献
953.
Yutaka Hirayoshi Takao Mizusaki Satoru Maegawa Akira Hirai 《Journal of Low Temperature Physics》1978,30(1-2):137-151
Helium-3 nuclear spin relaxation times T
1, T
2, and T
1have been measured for 3He-4He solid mixtures at the exchange plateau region (~0.5K). The 3He concentrations X
3of the samples were 7.2, 2.9, 1.8, 1.4, 0.67, 0.65, and 0.22%, and their molar volumes varied between 19.9 and 20.9cm3/mole in hcp phase. The spectral density function J() for dipolar field fluctuations was determined in the low-frequency branch from T
1measurements and in the high-frequency branch from conventional T
1measurements. It was found that J() is given by J() = cJ()|3–4 + (1–c)J()|3–3, where J()|3–4 is the spectral density function due to the 3He-4He tunneling motions, and J()|3–3 is that due to the 3He-3He tunneling motions. Using the Torrey theory, the correlation frequency of the 3He-4He tunneling motions was evaluated from T
1data, and was found to be in good agreement with Landesman 's theory.Supported in part by the Japan Society for the Promotion of Science through a grant to Y.H. 相似文献
954.
The adsorption properties of water-dissolved ozone on high silica zeolites were investigated. Adsorbed ozone was desorbed almost reversibly. The adsorption equilibrium relations were described by a linear expression written as q=betaC, where q is the amount adsorbed, C is the equilibrium concentration and beta is the equilibrium constant. Also, the beta values were strongly dependent on the SiO(2)/Al(2)O(3) ratio (mol/mol) and on the pore structure of the high silica zeolites. The larger the SiO(2)/Al(2)O(3) ratio, the larger the value of beta. ZSM-5 (SiO(2)/Al(2)O(3) ratio: 3000), which gave the highest adsorption capacity of water-dissolved ozone, was able to highly concentrate water-dissolved ozone on the adsorbent. The decomposition behavior of adsorbed ozone was also investigated. Ozone adsorbed on high silica zeolite was observed to be a little more stable than ozone existing in bulk water. The decomposition rate was independent of SiO(2)/Al(2)O(3) ratios in the range of 30-3000 or a solution pH in the range of 4-6. 相似文献
955.
Various halogenated organic compounds are formed by chlorination of water. In this study, formation of organic compounds halogenated from a reagent humic acid and extract of a leaf mold were examined under various conditions. The following overall formation equation was obtained from empirical data under the practical wide range when free chlorine remained. Here, [TOX] is the concentration of total organic halogen after t h in units of mg chlorine per liter; [TOC] and [Cl2]o are concentrations of total organic carbon and dosed chlorine in units of mg per liter; kTOX is the rate constant and and β are parameters. From the values of kTOX, and β, the character of organic substances i.e. precursor of halogenated organic compounds, in water can be evaluated. The values kTOX, and β for humic acid are 0.053, 0.28 and 0.13, and the values for extract of the leaf mold are 0.032, 0.36 and 0.15, respectively. The activation energies are 10 kJ mol−1 and 11 kJ mol−1 for the reactions of humic acid and leaf mold extract, respectively. 相似文献
[TOX]=kTOX[TOC][Cl2]otβ.
956.
We developed a novel ozonation process for water treatment using high silica zeolites as an adsorptive concentrator of water-dissolved ozone and organic pollutants, resulting in a significant increase in reaction rate. In experiments involving trichloroethene (TCE) decomposition using a tubular flow reactor, TCE decomposition was much greater in the presence of ZSM-5 (SiO(2)/Al(2)O(3) ratio=3000) than in its absence, possibly due to the high concentrations of ozone and TCE inside the adsorbent. The TCE conversion obtained in our experiments was found to reach its theoretically maximum limit. 相似文献
957.
Masayuki Hirabayashi Katsuhiro Narasaki Shoji Tsunematsu Yoshiyuki Kimura Seiji Yoshida Hiroshi Murakami Takao Nakagawa Akira Ohnishi Toshio Matsumoto Hidehiro Kaneda Keigo Enya Masahide Murakami 《低温学》2008,48(5-6):189-197
The AKARI satellite (formerly known as ASTRO-F) is Japan’s first infrared astronomical satellite. AKARI is equipped with the infrared camera (IRC) and the far-infrared surveyor (FIS), which are cooled below 7 K. The AKARI’s 68.5 cm telescope, which is made of SiC, is also cooled below 7 K. A unique feature of the AKARI cryostat is that it uses both cryogen and mechanical coolers. Using mechanical coolers, the helium lifetime can be greater than one year with 170 L of liquid helium. AKARI was launched on February 21, 2006 (UT), from the Uchinoura Space Center (USC). It has been performing successfully in orbit. 相似文献
958.
Satoshi Sasaki Atsuyoshi Nakayama Yutaka Sasaki Takao Mizusaki 《Journal of Low Temperature Physics》2008,151(5-6):1113-1148
We have measured the temperature and magnetic-field dependences of the sound velocity for one longitudinal and two transverse
waves in the low field phase (LFP) and the high field phase (HFP) of nuclear spin ordered bcc solid 3He crystals with a single magnetic domain along the melting curve. From sound velocity measurements for various crystal orientations
as a function of the sound propagation direction, we determined the elastic stiffness constants, c
ij
(T,B). In the LFP with tetragonal symmetry for the nuclear spin structure, we extracted six nuclear spin elastic stiffness constants
Δc
ij
ℓ
(T,0.06 T) from the temperature dependence of the sound velocity at 0.06 T and Δc
ij
ℓ
(0.5 mK,B) from the magnetic-field dependence of sound velocity at 0.5 mK. In the HFP with cubic symmetry for the nuclear spin structure,
we extracted three Δc
ij
h
(T,0.50 T) at 0.50 T and Δc
ij
h
(0.5 mK,B) at 0.5 mK. At the first-order magnetic phase transition from the LFP to the HFP at the lower critical field B
c1, large jumps in sound velocities were observed for various crystal directions and we extracted three
. Using the thermodynamic relation between Δc
ij
and the change in the internal energy for the exchange interaction in this system, ΔU
ex(T,B), Δc
ij
are related to the generalized second-order Grüneisen constants Γ
ij
X
≡∂
2ln X/∂
ε
i
∂
ε
j
as Δc
ij
(T,B)=Γ
ij
X
ΔU
ex(T,B), where X represents some physical quantity which depends on the molar volume and ε
j
is the j-th component of a strain tensor. In the LFP, the Δc
ij
ℓ
(T,0.06 T) were proportional to T
4, and Δc
ij
ℓ
(0.5 mK,B) were proportional to B
2. We extracted
for the spin wave velocity in the LFP, s
ℓ
, from Δc
ij
ℓ
(T,0.06 T) and
for the inverse susceptibility, 1/χ
ℓ
from Δc
ij
ℓ
(0.5 mK,B). In the HFP, Δc
ij
h
(T,0.50 T) were proportional to T
4 and Δc
ij
h
(0.5 mK,ΔB) were proportional to ΔB(≡B−B
c1). We obtained
for the spin wave velocity in the HFP, s
h
, from Δc
ij
h
(T,0.50 T) and
for B
c1 from Δc
ij
h
(0.5 mK,ΔB). The values obtained for
and
were compared with the Multiple Spin Exchange model (MSE) with three parameters by using analytic expressions for s
ℓ
and χ
ℓ
. The three-parameter MSE does not agree with the observed Δc
ij
in the LFP.
相似文献
959.
Takayuki Kunimatsu Akira Matsubara Ken Izumina Toshihiro Sato Minoru Kubota Takeo Takagi Yuriy M. Bunkov Takao Mizusaki 《Journal of Low Temperature Physics》2008,150(3-4):435-444
Superfluid 3He A-like and B-like phases in 98% aerogel have been studied under rotation up to 2π rad/s by using cw-NMR and Homogeneous Pressing Domain (HPD) NMR at 29 mT and 3.0 MPa. Triplet superfluid 3He has continuous symmetries whose degeneracies are lifted by small perturbations of magnetic field, boundary condition of
the sample cell, counterflow and global anisotropies of aerogel. We report NMR results of the two typical samples in aerogel
under rotation, which are almost identical in the phase diagram, T
c
and the critical velocity of the multiplication of vortex but are very different in textures and responses to the flow with
each other. One samples (S-D) is slightly compressed by squeezing and thermal stress and thus has global anisotropic deformation
along the sample axis. The other cell (S-H) has randomly(not uniaxially)-oriented global anisotropy. In the S-D, we observed
a large negative shift in cw-NMR and spin wave and HPD in the B-like phase. Comparing textures determined by NMR and its response
to the counterflows between two samples, we discuss how the long-range order of the continuous symmetry and textures are controlled
by orientation effects due to global anisotropy in aerogel.
相似文献
960.
A series of CuZr binary alloys with wide composition range were fabricated through ARB and HPT techniques using pure Cu and Zr metals as the starting materials. Bulk alloy sheets with thickness of about 0.8 mm after ARB process and alloy disks with 0.30 mm in thickness and 10 mm in diameter after HPT process can be obtained, respectively. The structures of all the alloys were found to be gradually refined with the increase of ARB cycles or HPT rotations. As a result, nanoscale multiple-layered structure was formed for the 10 cycled ARBed specimens, which could partially transform into amorphous phase during subsequent low temperature annealing. While for the as-HPTed sample, the alloy was completely amorphized after 20 rotations without any heat treatment. The thermal stabilities of the amorphous alloys were studied. The deformation behavior and the amorphization mechanism during the ARB and HPT process were put forward and discussed. 相似文献