Mikio Sugai

Preparation of CaSiO3 whiskers from alkali halide fluxes

Abstract CaSiO3 whiskers were prepared from fine CaSiO3 powder by use of alkali halide fluxes, NaCl, KCl, and their mixture. The CaSiO3 powder and the flux were mixed and heated at temperatures from 850 to 1000°C for 1 to 48 h. The average lengths, diameters and aspect ratios ranged from 3.24 to 10.5 μm, 0.33 to 1.12 μm and 7.1 to 21.7, respectively. The diameter of the whiskers increased with increasing heating temperature more rapidly than the length, so that the aspect ratio decreased with increasing temperature. The whiskers were considered to grow by an Ostwald ripening mechanism.

Synthesis and crystal structure of (Sr1-xCax)2FeMnOy (x=0-1.0)

Abstract (Sr 1− x Ca x ) 2 FeMnO y ( x = 0–1.0) were synthesized in air at 1150–1200 °C and their crystal structures and electric properties investigated. The perovskite-type and the brownmillerite-type compounds were formed in the compositional range x = 0–0.7 and x = 0.8–1.0, respectively. Ca 2 FeMnO y ( x = 1.0) was the brownmillerite-type compound with lattice parameters a = 0.5338 nm, b = 1.4834 nm and c = −0.5515 nm. The angle of Fe-O-Mn was 151 ° calculated from the refined structure data of Ca 2 FeMnO y . It is indicated that the FeO 4 tetrahedra and the MnO 6 octahedra are alternately arranged zigzag along the b -axis. All samples exhibited p-type semiconducting behavior.

Synthesis and oxide ion conductivity of new layered perovskite La1−xSr1+xInO4−d

Abstract New La 1− x Sr 1+ x InO 4− d compounds were synthesized and identified by the powder X-ray diffraction (XRD) method. In the composition range of 0≤ x ≤0.2, La 1− x Sr 1+ x InO 4− d compounds were prepared by heating at 1573 K in air for 36 h as single phase. Rietveld analysis of their XRD data revealed that La 1− x Sr 1+ x InO 4− d compounds possess the orthorhombic K 2 NiF 4 -type structure. Measurement of electrical conductivity as a function of oxygen partial pressure ( P O 2 ) showed oxide ion conduction for the samples below P O 2 =10 −12 atm for x =0 and below 10 −5 atm for x =0.1 and 0.2. At high oxygen partial pressure, it also showed contribution of hole conduction for the samples.

Synthesis and crystal structure of Sr2−xLaxCuTaOy

Perovskite related solid solutions Sr2−xLaxCuTaOy (0 ⩽ x ⩽ 1.0) were synthesized by solid state reaction at 1050°C in air. Two types of crystal structure were observed in the Sr2−xLaxCuTaOy system: simple cubic perovskite-type (0 ⩽ x ⩽ 0.7) and tetragonally distorted (NH4)3FeF6-type (0.8 ⩽ x ⩽ 1.0). The average valency state of copper in these solid solutions was nearly equal to +2, which was determined by iodometric titration. A significant change of the cubic lattice parameter a was not observed, and the tetragonality (ca) increased with increasing La3+ content. An ordering of Cu2+ and Ta5+ on the B site and the tetragonal distortion are found to be related to the appearance of the Jahn-Teller effect of Cu2+.

Cation ordering in the perovskite-type Sr2−xLaxCo1−yTa1+yO6

Abstract Perovskite-related solid solutions, Sr 2− x La x Cu 1− y Ta 1+ y O z , were synthesized by solid-state reaction at 1200°C in air. The crystalline phases were identified by powder X-ray diffraction. The perovskite-type solid solutions with different ordering types were observed including simple cubic perovskite-type (random), the Ba(Sr 1/3 Ta 2/3 )O 3 -type (1:2 ordering) and the (NH 4 ) 3 FeF 6 -type (1:1 ordering). The 1:2 ordering phase formed near the Sr 2 (Co 0.67 Ta 1.33 )O 6 composition. In the composition range, 0≤ y ≤0.2, the random and the 1:1 ordered phases formed. In the higher La 3+ content region, the 1:1 ordering phase was observed. The valency state of Co decreased with increasing La 3+ content and the perovskite cell expanded resulting from the increase of the average ionic radii on (Co,Ta) site. The 1:1 ordering of the ions on the octahedral site was found to be affected by the size difference of the ions more than the charge difference in this system.

Geometrical Study on Change of Pore Volume of MCM-41 Functionalized with Aminopropyl Groups

Mesoporous silicas functionalized with aminopropyl groups were synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyl triethoxysilane (APTES) and characterized by nitrogen adsorption-desorption measurements. The pore volume drastically decreased from about 900 mm 3 /g for the unfunctionalized mesoporous silica to about 300 mm 3 /g for the aminopropyl-functionalized mesoporous silica (1.65 mmol-NH 2 /g). This result was explained in terms of the surface density of the aminopropyl groups in the pore.

Distortion and cation ordering in LaSr(Ni1−xCux)TaO6

Abstract The perovskite-type solid solution LaSr(Ni 1− x Cu x )TaO 6 was synthesized and characterized by powder X-ray diffraction and iodometric titration. The stoichiometric solid solutions were synthesized at 1050–1100°C in air. The compounds for 0≤ x ≤0.6 have the (NH 4 ) 3 FeF 6 -type structure with ordering between (Ni 2+ , Cu 2+ ) and Ta 5+ . Tetragonal distorted (NH 4 ) 3 FeF 6 -type phases due to the Jahn-Teller effect formed in the compositional range, x ≥0.7 and the monoclinic distortion was observed for x =0.9 and 1.0. This result suggests that the tetragonal distortion occurs when the amount of Cu 2+ becomes more than 35% of the octahedral site in this system.

Synthesis and crystal structure of the oxygen defect perovskites containing copper and tantalum

Perovskite-related solid solutions, Sr 2-x La x Cu 1-y Ta 1+y O 2 , were synthesized by solid state reaction at 1050-1080°C in air. The crystalline phases were identified by powder X-ray diffraction. Three types of crystal structure were observed including simple cubic perovskite-type. tetragonal perovskite-type and tetragonally distorted (NH 4 ) 3 FeF 6 -type structure in which Cu 2+ and Ta 5+ were ordered alternatively. The average valency state of copper in these solid solutions was nearly equal to + 2. The tetragonal phases were observed in a compositional range, z ≥ 5.85, regardless of cation composition. The tetragonality (c/a) for both the perovskite-type and (NH 4 ) 3 FeF 6 -type phases increased with increasing oxygen content. Ordering between Cu 2+ and Ta 5+ was not observed in the Sr-rich composition. These facts suggest that oxygen content affects the appearance of the Jahn-Teller effect of Cu 2+ leading to the tetragonal distortion and that the cation on the A-site affects the ordering of the cation on the B-site.

Synthesis and electrical properties of (La1-xMx)3Ni2TaO9 (M=Ca, Sr)

Abstract Perovskite related compounds, (La 1− x M x ) 3 Ni 2 TaO 9 ( M = Ca , Sr ), were synthesized by the metal nitrate decomposition method. Single-phase solid solutions were obtained in the composition range 0⩽ x ⩽0.20 in both ( M = Ca , Sr ) systems. The crystal structure of the solid solutions is slightly distorted (NH 4 ) 3 FeF 6 -type structure. All the solid solutions exhibit p-type behavior with activation energies in the range from 0.13 to 0.22 eV. The value of the Seebeck coefficient of the solid solutions indicates the existence of hole carriers. The behavior of the compositional dependence of the unit cell volume indicates the presence of Ni 3+ ions.

On the Process of Formation of CaO by Reducing Gypsum

The authors investigated in detail the reducing reaction processes of gypsum in the nitrogenous atmosphere without oxygen. Then we clarified the effect of oxygen by introducing air on the samples in order to study the reaction in the industrial process, and tried some experiments to get some suggestions on the conditions favourable to the industrial process.(1) The reactions are as follows;CaSO4+2C→CaS+2CO2…(1)3CaSO4+CaS→4CaO+4SO2…(2)2CaSO4+C→2CaO+CO2+2SO2…(A)There are two steps in the reducing processes of gypsum. The first reduction step (1) begins near 750°C, proceeds quickly between 800° and 900°C and completes almost at 1000°C. The second step begins near 900°C, proceeds quickly between 1000° and 1200°C and completes almost at 1250°C.Sulphur is formed by the reaction (3) which occurs simultaneously with the reaction (2), but the reaction (3) is not so active as the reaction (2).CaSO4+3CaS→4CaO+2S2…(3)The following reactions did not occur in this experiments.CaSO4+4C→CaS+4CO…(4)CaSO4+CO→CaO+CO2+SO2…(5)(2) The amount of CaS formed in the first reduction step is proportional to the amount of the reducing agent. We discussed the appropriate amount of the agent in order to promote the reaction rate effectively and to make the reaction (2) complete.(3) Pressing of raw mixtures decreases the loss of the reducing agent due to the combustion and promotes the reactions.(4) It is observed that burning of sulphur with the introduction of air reduces sulphur trouble in the process and promotes the reaction (2) with the production of sulphur dioxide.(5) Anthracite and coke were used as the reducing agent in this experiments. Anthracite showed a better results rather than coke.(6) In the first reduction step, when CaSO4 was used CaS is formed much more than CaSO4⋅2H2O was used. But in the second decomposition step there is no obvious difference in the two cases.