SiO2 ceramic is one of the most important candidate materials for high-frequency microwave ceramics with very low dielectric constant (εr) at around 3.8 and low dielectric loss. However, a high sintering temperature must be provided during the preparation, which restricted their further application in low temperature co-fired ceramic (LTCC) field. In the present work, Li2MoO4-(1+δ)SiO2 (δ = -0.5, -0.2, 0, 0.2, 0.5 mole) ceramics were prepared by solid-state reaction method and sintered at 800 °C. XRD, SEM, EDS and Raman spectroscopy techniques were used to study the phase composition and crystal structure. The ceramic samples were composed of both Li2MoO4 and SiO2 phases. The εr values decrease with increased δ, which agree with the Lichtenecker logarithmic rule. The quality factor (Q×f) value initially increased and then decreased with increased δ. When evaluated as a microwave dielectric material, the Li2MoO4-(1+δ)SiO2 ceramics show excellent dielectric performance with a low dielectric constant (εr = 4.807) and high Q×f values of ～21000 GHz at δ = 0 as sintered at 800 °C, which is a possible candidate for LTCC.
Raman spectra of 15 mol% Ba-substituted Sr2Ta2O7 have been successfully obtained at temperatures up to 1773 K by a continuous-wave ultraviolet Raman spectroscopic system. The Raman spectra do not change significantly with an increase in temperature, despite the P21 → Cmcm transition. The present result is described in terms of the parameter related to temperature variation at constant pressure, defined in a similar way to the Gruneisen parameter. Raman bands located above 220 cm-1 show smaller values of the parameter than lower frequency modes, suggesting that these higher frequency modes are assigned to TaO6 internal modes. Due to the strong Ta—O chemical bonds, the dipole moments in the TaO6 octahedra and the ferroelectric polarization in the whole crystal lattice can be induced by the Ba substitution without large deviation of the Ta—O—Ta bond angles from 180°, which enhances the photocatalytic performance.
Polycrystalline olivine-type sulfides, Mn2SiS4, Mn2GeS4, Fe2SiS4, and Fe2GeS4, are prepared by solid-state reactions and spark plasma sintering. Among these sulfides, only the electrical conductivities and Seebeck coefficients of Fe2SiS4 and Fe2GeS4 are measurable, owing to their narrower energy gaps compared with those of Mn2SiS4 and Mn2GeS4. Although Fe2SiS4 and Fe2GeS4 exhibit low electrical conductivities, their Seebeck coefficients and thermal conductivities are relatively high and low, respectively, demonstrating their potential as good thermoelectric materials. The highest zT value, 0.008, is obtained for Fe2GeS4 at 700 K, which can be enhanced by hole carrier doping and heavy elemental partial substitution.
A pulley-type SMA heat-engine using Ti-Ni shape memory alloy (SMA) driven by low-temperature waste heat energy was investigated. We have proposed and fabricated a pulley-type heat-engine using tape-shaped SMA element for the purpose of improving of the life span of pulley-type SMA heat-engine. However, shape memory and mechanical characteristics of SMA deteriorate with increasing number of thermal cycles. Therefore, effects of thermal cycling on the shape memory and mechanical characteristics of the tape-shaped SMA element are investigated in this study. The chemical composition of the specimen is Ti-45.0Ni-5.0Cu (at%), heat treatment condition is 673K for 3.6ks and the specimen is memorized horizontal shape. The number of thermal cycling (N) is varied from 0 to 105. Transformation temperatures are almost constant as the N increases to 1×103. However, each difference of transformation temperature (Ms-Mf and As-Af) decrease when the N is within a range of 5×103 to 1×104, above which it increases. Mechanical properties improve with increase of N when the N is up to 1×104, above which it deteriorates. Furthermore, 2-stage martensitic transformation appears when N is above 5×104. These tendencies are caused by the variation of dislocation density and residual martensitic phase with the increasing of N.
A heat-engine using Ti-Ni shape memory alloy (SMA) has been investigated as a system for waste heat recovery potential. We had proposed a new SMA heat-engine with a forced cooling system in the pulley because of the cooling efficiency improvement of the SMA element. In this study, for the purpose of the further improvement of the pulley-type SMA heat-engine with a forced cooling system, we fabricated the new cooling mechanism with the idler wheel, and effects of cooling position on the output power characteristics of this engine are investigated. As a result of experiment, irrespective of cooling position, the output power increases with increase of the tensioning displacement provided by idler wheel. This tendency is because the applied strain of SMA element increases as the increase of tensioning displacement. Moreover, the installation of idler wheel leads to the unsymmetrical heating of SMA element, and then the bias torque is generated. When the idler wheel is installed at the position before the SMA element contacts with a bottom pulley, the bias torque with same rotative direction of heat-engine is generated. Therefore, the most desirable installation position of the idler wheel is the position before the SMA element contacts with a bottom pulley.
Metal doped SiO2 thin films, which show strong luminescence by UV excitation, were prepared by a sputtering deposition method using metal oxide and SiO2 powder mixed targets. Electron density and temperature of the plasma using powder target was almost same independent for the mixture of powder target. However, peak intensity ratio of the plasma depends on the intensity of the powder target mixture. XPS measurements suggest that metal doped SiO2 thin films can be prepared using metal oxide and SiO2 mixture powder target, and their concentration ratio also depend on the powder target mixture.
Direct carboxymethylations for aliphatic hydroxyl groups in weeds such as Tall fescue (Festucaarundinacea, TF), Sweeping lovegrass (Eragrostis curvula, SL) and Canada goldenrod (SolidagoCanadensis, CG) were carried out in 2-propanol / 30 % NaOH at 55 °C for 3.5 hrs. Under the typical conditions, carboxyletylated TF (TF-CM), SL-CM and CG-CM were obtained at yields of 145%, 135% and 148% based on each dry weight of lignocellulosics, respectively. Although degrees of substitutions of these CM materials were only small values such as 0.08-0.11, almost all materials were easily dissolved into water. Structural features were investigated using FT-IR and UV-Vis. Visocosities of 1% (w/w) aqueous solutions or suspensions of CM derivatives were measured by vibrating viscometer under different temperatures and pH. Since there are differences on viscosities between TF and CG in spite of same degrees of substitution, properties were different due to different structures of plant tissues.