We investigated two aspects of zirconium tungstate (ZrW2O8). First, we investigated the formation of ZrW2O8 in a sol-gel process that used tungsten (VI) chloride and zirconium chloride oxide 8-hydrate as raw materials, and ethanol and 2-butyl alcohol as solvents. Crystalline ZrW2O8 powder was obtained by heat treated between 600 and 777°C in air for one hour. ZrW2O8 ceramics could not be made using a conventional sintering process because the ZrW2O8 decomposition to WO3 and ZrO2 when it was heated to over 777°C. However, we made dense ZrW2O8 ceramics by heating ZrW2O8 amorphous powder at 600°C for 10 minutes by using spark plasma sintering. Second, we used X-ray diffraction analysis and DSC to clarify how humidity affects the thermal expansion properties of ZrW208. Low density ZrW2O8 ceramics showed positive thermal expansion between room temperature and 120°C. On the other hand, high density ceramics showed negative thermal expansion between room temperature and 400°C. Both ZrW2O8 powder and lower density ceramic have H2O either on or in their particles. The H2O prevented any other influence besides that of the thermal expansion property of ZrW2O8.
This study verified an effect of their steam curing method on their delayed expansion when using the ettringite generating type high strength additive, to propose their safe using method. When increasing the steam curing temperature, anhydrite contained in the additive will remain to be unreacted. Thereafter, it was found that the anhydrite reacted at a wet environment, to increase formation of the ettringite to bring the delayed expansion. And, it can be thought that by thermal decomposition of the ettringite there increases SO3 in CSH, to further rise risk of the delayed expansion. When the steam curing temperature exceeds 80°C, there would form a risk to further increase the delayed expansion. To control the delayed expansion, it was found to be important to endeavor not to excessively rise the curing temperature, to fix sulfate ion as the ettringite, and not to form transfer of the sulfate ions into solidified concrete.
Calcium ferrite compounds were synthesized by solid state reaction of fine particle mixtures of Ca (OH) 2 and Fe203 (Ca/Fe=0.33-3.00) in order to investigate their catalytic performances for VOCS decomposition. The influence of Ca/Fe ratio was studied in order to find which crystal phase of calcium ferrite produced the best catalytic performance. The brownmillerite type calcium ferrites (Ca2 Fe2 O5, Ca/Fe=1.00) showed higher reduction ability of Fe cations than those of other calcium ferrite phases, resulting the highest catalytic activity at low temperatures above 200°C. The brownmillerite type calcium ferrite also showed a high performance for the decomposition of nonchlorine VOC such as propylene, benzene and toluene, but a significant decrease of the catalytic activity was found in the decomposition of chlorobenzene due to the reaction between chlorine and calcium ferrite. Moreover the fixation behavior of chlorine contents onto the calcium ferrite was also investigated in order to clarify the chlorination reactivity of the catalyst. The calcium ferrite catalyst was found to be a good sorbent for fixing chlorine content during the catalytic decomposition of chlorobenzene at 700°C.
The effect of Al substitution for Zr on the sinterability of SrZrO3 powders was studied by means of XRD, BET, and SEM. The density of SrZrO3 increased with increasing amount of Al, and the sinterability of SrZrO3 was greatly improved by the substitution. The highest density of 94% was achieved for SrAl0.02Zr0.98O2.99ceramics prepared after calcining at 1300°C and firing at 1600°C for 3 h. The analysis of isothermal shrinkage curves exhibited that the diffusion mechanism changed from grain-boundary to volume diffusion by the formation of oxygen vacancy. The dielectric constant of the present SrZr1-xAlxO3-δ ceramics increased to around 45 from 20 of pure SrZrO3 ceramics in the frequency range 1 kHz to 100 kHz.
Raman spectra of BaTa2O6 have been successfully obtained at temperatures up to 1573 K for the first time, using a continuous-wave ultraviolet Raman spectroscopic system designed to measure the Raman scattering from materials at high temperature. The typical Raman spectra of the orthorhombic phase (Type I) were recorded in the region of room temperature to 1573 K. 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 250 cm -1 and the mode at 169 cm -1 show smaller values of the parameter than lower frequency modes below 250 cm -1 except the mode at 169 cm-1, suggesting that these higher frequency modes and the mode at 169 cm-1 are assigned to TaO6 internal modes.
Ten Si-Fe-Mg mixed hydrous oxide samples were synthesized with changing Si, Fe (III) and Mg molar ratio. The characterization and the adsorption ability of their samples for cations and anions were examined. The specific surface areas were 155-351 m2·g-1 and the Dore volumes were 0.193-0.527cm3·g-1. Samples with high molar ratio of Mg had a similar structure to the Layered Double Hydroxide (LDH), other samples were amorphous. The metallic element molar ratio affected to the adsorption ability, i.e. high Si molar ratio samples had the cation exchange abilities and high Mg molar ratio samples had the anion exchange abilities and the samples containing Si and Mg with equal molar ratio had cation and anion adsorption abilities. However, the high Fe molar ratio sample had high adsorption capacities for arsenate, arsenic and phosphate ions. These results showed that possibility of synthesizing Si-Fe-Mg mixed hydrous oxide samples as adsorbents, which have the adsorption ability for specific ion and/or simultaneous adsorption ability for cation and anion.
Alumina-based electric wave absorbers for 60 GHz were conducted, and their absorbing properties were designed by means of no-reflection analysis based on complex permittivity. Furthermore, the effect of carbon content on the absorbing characteristics was studied. The result showed that 1.2 mm thickness alumina ceramics including 1.2% carbon provided preferable absorption value of more than 20 dB, which were almost equal to the calculated and designed ones. This paper describes design and manufacture process, and assessment method of the no-reflection materials.