The effect of different portland cements on the alkali expansivity of five italian natural sands of known field performance was investigated using the ASTM C1260 mortar-bar expansion method. The alkali reactivity of these sands was also evaluated according to the petrographic examination, infrared spectroscopy technique, ASTM C227 expansion method, ASTM C289 and AFNOR P18-589 chemical tests. The expansivity of the sands in the ASTM C1260 test is significantly affected by both the native alkali content and the specific surface area of the portland cement while it is virtually unaffected by its mineralogical composition. For all the sands there is good agreement between the diagnoses of the ASTM C1260 and the other test methods, except ASTM C227, only when a portland cement with a Blaine surface area of 500m²/kg and a native alkali content of 1.13-1.15% Na₂O_eq is used in the ASTM C1260 test.

View full abstract

Ultrasonic mist pyrolysis was applied to electrode preparation for solid oxide fuel cell (SOFC) type reactor. La_1.8Al_0.2O₃ anode catalyst was prepared on heated YSZ substrate by the pyrolysis of the mist of lanthanum nitrate and aluminum nitrate mixed aqueous solution generated by ultrasonic transducer. Among several preparation methods, this process was most effective for the activity of anode catalyst. Operating conditions such as aqueous solution concentration, temperature and ultrasonic power were examined. The effects of these conditions on the particle characteristic such as supported amount and size were investigated. Changes of catalyst in the crystallographic characteristics were also evaluated by XRD. The particle size of the anode catalyst on YSZ substrate was found to be important for the oxidative coupling of methane in SOFC reactor. Smaller particle size was preferred for this reaction. The particle size could be easily controlled by the operating conditions of ultrasonic mist pyrolysis and then optimum preparation condition was confirmed.

View full abstract

Si-N-O ceramic fibers were prepared, at 1200-1500°C in a stream of NH₃ gas, from polycarbosilane fibers cured by thermal oxidation at 145-180°C in a stream of O₂ gas. The ceramic fibers were colorless and semitransparent in visible light. Their mechanical properties depended on the contents of oxygen introduced during the thermal oxidation curing process. Tensile strength of the Si-N-O ceramic fiber obtained by the heat treatment at 1400°C of the polycarbosilane fiber cured at 160°C was the highest among the ceramic fibers obtained in this work. The maximum tensile strength and chemical formula of the Si-N-O ceramic fiber were about 1.8GPa and Si_1.00N_1.23O_0.43, respectively. The fiber was exposed at 1000-1400°C for 1h either in air or an Ar gas in order to examine oxidation and heat resistances, respectively. Their tensile strength and Young's modulus did not change up to 1400°C by the exposure in the Ar and 1200°C in the air.

View full abstract

The vitrification range and Raman spectra of binary KO_1/2-SeO₂ and NaO_1/2-SeO₂ systems were investigated. Addition of alkali oxide results in cleavage of Se-O-Se linkages in (SeO₂)_n chains. Glass structural fragments are discussed.

View full abstract

Deformations of pre-annealed lead-silicate glass fibers were measured by the fiber-bending method during loading and unloading below the glass transition temperature. Burger model consisting of Maxwell and Voigt elements was used for the evaluation of elasticity, delayed elasticity and viscosity. In the loading process, it was found that the deformation due to the viscosity increases with time. However, the deformation due to the delayed elasticity increases rapidly for a short time and decreases with further increase in time, In the temperature range of the measurement, the viscosity of Maxwell element, representing pure viscosity decreases with increasing temperature. The viscosity of Voigt element consisting of the delayed elasticity decreases with increasing temperature and is one magnitude order lower than that of Maxwell element. The elastic constant of Voigt element consisting of the delayed elasticity decreases slightly with increasing temperature. In the unloading process, the delayed elasticity was analyzed, assuming that the elasticity of Voigt element is the same as that in the loading process.

View full abstract

Titanium carbide (TiC) whiskers were deposited on the outer surface of a graphite tube and on a graphite boat in 10 vol% methane gas stream following a heat treatment at 1000-1400°C. This temperature range was broader and lower than the 1250-1400°C range in which TiC whiskers were obtained when 5 vol% methane gas was used in a thermal-decomposition-reduction-carbonization reaction. The lattice constant of TiC whiskers deposited on the outer surface of a graphite tube after the heat treatment at 1400°C was 0.432084±0.007nm, indicating that this TiC had a stoichiometric composition. The cylindrical whiskers formed at 1050-1200°C were considered to have been grown via a vapor-solid (VS) growth mechanism. Because the side faces of the rectangular prismatic whiskers formed at 1300-1400°C were dented, whisker growth in the radial direction maybe caused by the layer stacking growth mechanism (a VS mechanism) due to two-dimensional nucleation on the {110} plane.

View full abstract

The work presented here discussed the fiber reinforcement of MDF materials prepared from ordinary portland cements. The effects of fiber type, size and amount on the properties of the ordinary portland cement (OPC)-based macro-defect-free composites were investigated and the toughening mechanism was studied. The potential for increased toughness by fiber reinforcement of MDF composite has been shown. Carbon and Saffil (alumina) fiber reinforced MDF cement composites indicate high mechanical properties (127MPa in modulus of rupture and 3.3MPa⋅m^1/2 in K_1c) and their optimum fiber loading shows 10-15% by volume when a high shear mixing and extruding process were employed.

View full abstract

The thermal expansion coefficients of various perovskite-type oxides have been estimated by re-evaluating the parameters used in the Ruffa's method. The Morse potential has been used to evaluate the thermal expansion coefficient assuming the Debye model for the frequency distribution of the Morse oscillator. The parameters of the Morse potential for oxides have been empirically re-evaluated, and then the thermal expansion coefficients of various perovskite-type oxides have been estimated. The calculated thermal expansion coefficients are in good agreement with the experimental ones when the main contribution to the thermal expansion is a vibrational term. In some cases, there is a difference between the calculated and experimental thermal coefficient. The difference is considered to be due to an anomalous contribution to the thermal expansion of ferroelectric or magnetic origin. From the practical point of view, the thermal expansion coefficient of four- or five- component systems is estimated by using the experimental thermal expansion coefficients of three- component systems including the anomalous contribution. The thermal expansion coefficient of fouror five- component systems is then calculated using a model similar to the regular solution model. The calculated one thus obtained better explains the experimental one than that using the ideal solution model.

View full abstract

The sol-gel method was applied to the preparation of the rare earth (RE)-containing zircon (RE-zircon) pigments at low heat treatment temperatures. Following results were obtained.
(1) The zircon pigments containing RE's such as Pr, Nd, Sm, Eu and Er were successfully prepared from tetraethyl-orthosilicate, Si(OC₂H₅)₄, zirconium oxychloride, ZrOCl₂⋅8H₂O and halides of RE's, at the heat treatment temperature as low as 900-1000°C, if LiCl was added as a mineralizer.
(2) Obtained products were powdery or easily pulverized into fine powders even by fingers, meaning that the sol-gel method much reduces the vigorous crushing and grindings processes required in the commercial solid-state reaction method.
(3) The color of the pigments were dull-green yellow for Pr, light purple for Nd, yellowish white for Sm and yellow to pale reddish purple for Er. The chemical resistivity of all the pigments prepared in the present work satisfied the criterion “5-level” of JIS-K-5101-1991.
(4) The oxidation state of Nd and Er incorporated in the zircon pigments was considered to be trivalent on the basis of the reflectance and XPS spectra. Pr in the pigment was considered to be mainly in tetravalent.
(5) XRD measurements suggested that the trivalent RE³⁺ ions are incorporated into the zircon structure and replaces Si⁴⁺ or Zr⁴⁺ ions to form solid solutions. Co-added Li⁺ ions were considered to be also incorporated into the zircon structure to maintain the electric charge balance, In the case of Pr, tetravalent Pr⁴⁺ ions probably substituted for Zr⁴⁺ or Si⁴⁺ ions in the zircon lattice.

View full abstract

Single crystals of lead bismuth titanate (Pb₂Bi₄Ti₅O₁₈) were grown and their electrical properties were investigated by measuring the dielectric permittivity, conductivity and spontaneous polarization. The dielectric permittivity, measured at 1MHz, was 10400 in the direction parallel to the bismuth layer (crystallographic a(b)-axis) at the Curie temperature of 340°C. This value was about 30 times higher than that in the perpendicular direction (crystallographic c-axis). The DC conductivity was about two orders of magnitude higher in the direction parallel to the bismuth layer than that in the perpendicular direction at 200 to 500°C. A large anisotropy of the ferroelectricity was observed in D-E hysteresis curves at 150°C, and the existence of spontaneous polarization in the c-axis direction was experimentally confirmed, though it was much smaller than that in the a(b)-axis direction. Among the bismuth layer-structured ferroelectrics, Pb₂Bi₄Ti₅O₁₈ in the a(b)-axis direction was found to have a low coercive field and a large remanent polarization.

View full abstract

Faraday effect and absorption spectrum measurements have been performed at room temperature for fluoroaluminate, borate and Ga₂S₃-based glass samples containing 5 cat%Eu²⁺. The Verdet constant (V_c) of fluoroaluminate and borate glasses containing 5 cat%Eu²⁺ was negative, and the absolute value of V_c decreased with increasing wavelength. In contrast, the V_c of Ga₂S₃-based glass containing 5 cat%Eu²⁺ was negative in the short wavelength region, while it became positive in wavelength regions longer than 635nm. The effective transition wavelength, λ_t, of glasses containing Eu²⁺ has been calculated based on the Van Vleck and Hebb theory. The influence of a glass matrix on the Faraday effect in Eu²⁺-containing glasses was discussed.

View full abstract

Bending creep rates for fired specimens (3×1×0.2cm) of Amakusa Touseki (pottery stone, chiefly containing quartz, sericite, kaolinite and 0.97% Fe₂O₃) and alumina-added (-30%) products were measured. A bending creep curve up to 3h consisted of primary and secondary steps. The creep rate (10^-7-10^-4s^-1) in the primary step slowly decreased with increasing bending strains and then decreased rapidly in the secondary step. The mean creep rates in the primary step were obtained in the temperature range from 900 to 1050°C under stresses of 5, 10 and 20MPa. These primary creep rates decreased with alumina addition. The creep rate vs. creep stress showed linear relations on the log-log diagram, and their mean slope values were 1.26±0.27, suggesting a presence of a rate-determining step of diffusion or solution-precipitation reaction in the viscous liquid of the grain boundary. The amount of the viscous liquid phase was estimated as 38 to 21% for the alumina additions of 0 to 30% at 985°C (temperature of the liquid phase formation) in the system K₂O-Al₂O₃-SiO₂ and its composition of the liquid was estimated 10% K₂O, 11% Al₂O₃ and 79% SiO₂. However, the added alumina almost remained without reaction. The decreasing activation energies from 450kJ⋅mol^-1 to 150kJ⋅mol^-1 with alumina additions up to 30% were obtained.

View full abstract

GdCo₂B₂C_x (x=0-1) has been synthesized to study the role of C in the formation of a new quaternary compounds RT₂B₂C (R=rare earth, T=transition metal); RT₂B₂C belongs to a tetragonal system with ThCr₂Si₂ derivative type. Samples of GdCo₂B₂C_x (x=0, 0.25, 0.50, 0.75 and 1.00) were prepared by the arc-melting synthetic method. According to backscattered SEM study, the obtained compound of tetragonal phase was observed as rectangular, narrow-ribbon and wide-ribbon for x=0, 0.25-0.75 and 1.00 in GdCo₂B₂C_x, respectively. The lattice parameter a sligtly decreased, while the lattice parameter c and the unit cell volume increased appreciably with increasing x in GdCo₂B₂C_x. This result shows that C element serves to expand the entire unit cell in the shape of a square column composed of R atoms (eight at the corners) especially along the c-direction, and permit T atoms, which are too large for the normal lattice, to join in combination. The role of C to form the quaternary borocarbides RT₂B₂C has been demonstrated.

View full abstract

The resistance of Ag-doped antibacterial ceramics for the scales sticking to urinals was investigated. The scales sampled from actual urinal mainly consisted of hydroxyapatite. Similar hydroxyapatite was formed experimentally by using the urease medium containing Ca. The hydroxyapatite was precipitated from the medium with an increasing in pH. The urease medium containing Ca having microorganisms, which were sampled from an actual urinal, was dropped on an Ag-doped antibacterial ceramic, an ordinary ceramic, and a polystyrene petri dish, and then cultured at room temperature. Although viable count in the medium on the ordinary ceramic and polystyrene petri dish increased after cultivating for 23d, viable count in the medium on the antibacterial ceramic decreased. The pH of the medium on the ordinary ceramic and the polystyrene petri dish increased and precipitation of hydroxyapatite was observed. In the case of the antibacterial ceramic, the pH did not change and precipitation was not observed. In addition the antibacterial ceramic suppressed the generation of NH₃ gas as compared with the others. The result give a possibility that antibacterial ceramics can reduced the scales of actual urinals.

View full abstract

Microstructure and electrical properties of La-doped seiconductive SrTiO₃ bicrystals were investigated. SrTiO₃ bicrystals having several kinds of twisted angle were prepared by hot pressing at 1662°C, 0.1MPa for 5h in air. Angular shaped boundary layers were observed between the crystals. Many closed pores were observed at the center of boundary layers, and open pores were observed at the edge of boundary layers. Non-linear I-V characteristics across the junction of the bicrystals were measured on as prepared samples. The non-linear coefficient of the sample was relatively larger than that of a simple junction without boundary layers. The I-V characteristics of bicrystals could be changed from non-linear to linear by heating the sample in an H₂-N₂ mixed gas atmosphere. Furthermore, by heating in an O₂ atmosphere the linear I-V characteristics of the samples reversed to non-linear.

View full abstract

High-density YSZ multilayer stacking thin films were synthesized by the ultrasonic spray ICP flash evaporation method. A mixed aqueous solution of zirconium nitrate and yttrium nitrate was atomized with an ultrasonic nebulizer and fed to thermal RF plasma to deposit YSZ thin films on silica glass substrates or (001) MgO single-crystal substrates. YSZ thin films on both substrates had (111) and (001) orientations normal to the substrates. YSZ thin films on the silica glass substrates were not oriented parallel to the surface of the substrates, whereas YSZ thin films on (001) MgO substrates were oriented parallel to the surface of the substrates. Their epitaxial relationships were (100) (001) YSZ//(001) MgO, [001] [100] YSZ//[100] MgO and (111) YSZ//-(001) MgO, [112] YSZ//-[110] MgO. Thick multilayer stacking films were synthesized by 6 repetitions of cyclic deposition (repeated heating-deposition-cooling-cleaning procedures). In the multilayer stacking films the above orientational relationships were maintained. By applying the cyclic depoisition procedure, heterolayer stacking films could also be grown, in which the composition of the first layer was, 3.1 mol% YSZ and that of the second layer was 11.1 mol% YSZ. The microstructure of the heterolayer-stacked dense film is almost the same as that of homolayer-stacked films. A distinct layer boundary, which is thought to result from the cyclic deposition method, or heterolayer stacking could not be observed by SEM, though peaks from each layer could be detected in the XRD analysis.

View full abstract

Al₂O₃-coated TiC whiskers, which were synthesized by the homogeneous precipitation technique using urea, were used as raw materials in the precipitation of TiC whisker-dispersed Al₂O₃ ceramics, and the effects of the coating and sintering conditions on the structure and mechanical strength of composite were investigated. Use of the Al₂O₃-coated TiC whiskers changed little the dispersion state of TiC whisker in the composite. On the other hand, the formation of titanium oxycarbide at the interface between the matrix and whisker was promoted. The increase in the bonding force at the Al₂O₃-TiC interface resulted in an increase in the mechanical strength of the composite. To improve the mechanical strength of the composite, however, precise control of reaction at the Al₂O₃-TiC interfaces by controlling the amount of the Al₂O₃ coating as well as the hot-pressing conditions was found to be important. As a result, the composite ceramics sintered at 1600°C for 30min using Al₂O₃ (25 vol%)-coated TiC whisker showed the bending strength of 560MPa (about 1.8 times higher than Al₂O₃ ceramics sintered under the same hot-pressing conditions) at room temperature.

View full abstract

Computer simulation of an additive reaction process in dual-phase microstructures was performed by a stochastic technique based on the decrease in system internal energy. The dual-phase microstructures were constructed using a two-dimensional trianglar lattice. The reaction occurred initially at the reactant interfaces, and then subsequently proceeded by transport of the reactants through the product. The driving force of the reaction is a function of the energy change due to the phase change, grain boundary energy and interface energy changes. The product formation strongly depended on the magnitude of the driving force and initial configuration of the reactant grains. The reactivity was enhanced by increasing the number of triple junctions formed by a grain boundary and interface between the reactants. Control of the initial configuration of the reactant grains localizes the formation sites of the product. Analysis of the fraction reacted as a function of time by applying the Johnson-Mehl-Avrami equation shows that the kinetics follow two-dimensional Jander-type diffusion, when the reaction proceeds only through the products.

View full abstract

Porous ceramics with a skeleton structure of aluminum borate (9Al₂O₃⋅2B₂O₃) whiskers were in-situ synthesized by firing a compact of mixed powder comprising aluminum hydroxide, boric acid and an additive of nickel oxide at 1150-1350°C. By adjusting the compacting pressure, a porous ceramic having a porosity of about 20 to 80%, which corresponds to a whisker volume fraction of about 80 to 20%, can easily be prepared. Fine open pores remain in the porous ceramic, and the pore radius can be controlled by the compacting pressure and the sintering temperature. As a result, the porous ceramic has an average pore radius of about 0.04 to 0.81μm. Because whiskers were strongly bonded to other whiskers, the porous ceramics exhibited very high strength, and would never cause any inhalation hazard. Flexural strength of porous ceramics increased with increasing the whisker volume fraction and the amount of NiO additive, and ranged from 21.1MPa to 193.8MPa for whisker volume fraction of 25 to 80%. Porous ceramic have a potential use as a reinforcement of metal matrix composites, a structural material, a heat insulating material, and a filter medium.

View full abstract

Preparation and some properties of 20 and/or 30 mass% Shirasuballoons (diameter 6.6, 10.4 and 31.5μm) added lightweight pottery were studied to develop their high strength with high porosity. Mixed slip of Shirasuballoons and pottery clay was prepared y adding 0.3 mass% water glass. The green compacts consolidated by a slip casting were dried at 110°C and sintered at 1150-1250°C for 1h in air. Bulk density of the lightweight pottery was decreased by addition of Shirasuballoons. Closed porosities of the lightweight pottery were almost independent on diameters of Shirasuballoons. Open porosities of the lightweight pottery, however, were affected by the diameter of Shirasuballoon. The open porosity of the lightweight decreased with the addition of 20 and 30 mass% Shirasuballoons in diameter of 6.6μm, compared with that of without Shirasuballoons, but they increased with the addition of 20 mass% Shirasuballoons in diameter of 10.4 and 31.5μm. Flexural strength of the lightweight pottery do not decreased with the addition of Shirasuballoons in diameter of 6.6μm; compared with that of original pottery clay, but decreased with the addition of Shirasuballoons in diameter of 10.4 and 31.5μm.

View full abstract

Dielectric property and sinterability of 0.95MgTiO₃⋅0.05CaTiO₃ modified with B₂O₃ or V₂O₅ were inverstigated. Addition of B₂O₃ decreased the firing temperature and did not affect dielectric property. On the other hand, addition of V₂O₅ also decreased the sintering temperature more extensively than B₂O₃, but influenced the dielectric property. The scanning electron microscopy (SEM) observation suggested that addition of B₂O₃ or V₂O₅ make a large amount of liquid phase. X-ray diffraction (XRD) analysis revealed that B₂O₃ decreases the MgTi₂O₅ phase, but that V₂O₅ increases both MgTi₂O₅ and Ca₅Mg₄V₆O₂₄ phases. It is supposed that the liquid phase which was created by addition of B₂O₃ or V₂O₅, increased mainly sinterability at low firing temperature, but that addition of V₂O₅ also created the MgTi₂O₅ and Ca₅Mg₄V₆O₂₄ phases during the sintering process, which decrease dielectric property seriously.

View full abstract

We studied the properties of the anatase sols obtained by heating the PTA solution at 100°C for 2 to 20h and the photocatalytic activities of the films prepared from the sols for the vegetable oil degradation, obtaining the following results:
(1) Well-dispersed anatase sols were obtained by heating the PTA solution at 100°C for 2-6h.
(2) The sols consisted of fine particles smaller than 20nm and arrowhead-like particles larger than 20nm, and had high specific surface areas (180-245m²⋅g^-1).
(3) The photocatalytic weight losses of the vegetable oil on the films prepared from the sols obeyed the zero-order kinetics.
(4) The film prepared from 6A showed the highest photocatalytic reaction rate, which was slightly lowered by increasing final heat treatment temperature up to 400°C.

View full abstract

Three-dimensional (3D) carbon fiber reinforced Si₃N₄ composites have been fabricated using slurry infiltration and repeated infiltration of organosilicon (polysilazane) resin. Volume fractions of the fiber and Si₃N₄ powder of the slurry-infiltrated body were about 42 and 32%, respectively. Open porosity was decreased from 26% after the slurry infiltration to approximately 9% after the repetition of the polysilazane infiltration and pyrolysis. The relative density of the body which underwent the pyrolysis of polysilazane at 1873K reached 89.4% after 6 cycles. However, the highest flexural strength and fracture toughness were obtained at a pyrolysis temperature of 1673K. Further reduction of open porosity to less than 2% was accomplished by hot-pressing at 1873K. The maximum values of flexural strength and fracture toughness were 360MPa and 9.8MPa⋅m^1/2, respectively.

View full abstract