Journal of Asian Ceramic Societies

Shanthala, V.S.; Shobha Devi, S.N.; Murugendrappa, M.V.

doi: 10.1016/j.jascer.2017.02.005pmid: N/A

AbstractPolypyrrole and polypyrrole/copper zinc iron oxide (copper zinc ferrite) nanocomposites were synthesized by in-situ polymerization using Ammonium Persulphate as oxidising agent. The nanocomposites were synthesized by mixing polypyrrole and copper zinc iron oxide in different weight percentages. The formation of nanocomposites and changes in the structural properties were investigated by characterizing the samples using XRD, FTIR, SEM and EDX analysis. The size of the particle was analysed by XRD using Scherrer equation and found to be in 20 nm range. DC conductivity was measured in the temperature range 300 K–473 K. The DC conductivity was found to be constant for the temperature range from 300 K–433 K. But the conductivity showed an exponential increase for the temperature 433 K–473 K, and it obeys Arrhenius relation. Activation energies were evaluated from Arrhenius plots for all compositions. Results show that incorporation of additive material significantly reduces the activation energy for the DC conductivity of the composites, and the decrease in the activation energy is also dependent on the amount of the nanoparticles in the composites. As the polymers are used in the various manufacturing products, this study indicates the possibility of using such polymers in the form of composites as superior insulating material in the fields of electrical or electronic insulation and allied areas.

Tasca, Julia E.; Lavat, Araceli E.; González, María Gloria

doi: 10.1016/j.jascer.2017.02.004pmid: N/A

AbstractThe synthesis, structural, spectroscopic and morphological characterization; as well as the evaluation of the catalytic properties, of a family of oxides La2MMnO6, with M = Co, Ni and Cu are presented in this work. The materials were obtained by solid state reaction and through citrate route. The structure was determined by X-ray diffraction and a correlation was found between the crystal cell parameters and the M(II) cation sizes, as a consequence of MO6 and MnO6 octahedral ordering. According to infrared spectroscospic characterization of the materials prepared by citrate route, a diminution of the M4+-O bond strength was observed, according with M(II) sizes, in the sequence: Cu > Ni > Co. More labile O species should be present in La2CoMnO6-CIT. The electron microscopy morphology of this oxide confirmed the presence of agglomerated tiny particles. The presence of nanometic crystallites was confirmed by transmission electron microscopy. The catalytic tests, using propane as reaction test, were carried out in a fixed bed micro reactor, coupled with an “on line” chromatograph. The materials obtained by citrate route, despite M(II) cations, are better suited for propane combustion and the catalyst La2CoMnO6 is the most active of the investigated series with T90 ∼ 500 °C.

Takahashi, Hiroaki; Nagata, Hajime; Takenaka, Tadashi

doi: 10.1016/j.jascer.2017.03.002pmid: N/A

Abstract(Bi0.5Na0.5)TiO3 [BNT] is expected as one of candidate lead-free materials because these ceramics show relatively good high-power piezoelectric properties. In this study, we tried to understand the bending strength and fracture behavior of the BNT-based ceramics. To measure the bending strength, a three-point bending test on the basis of JIS was conducted using 12.0 × 4.0 × 1.0 mm3 specimens. An average bending strength, σA, of pure BNT ceramics sintered at 1100 °C for 2, 12 and 24 h were 217, 195 and 187 MPa, respectively. It is cleared that the σA increased with decreasing the sintering time, (grain size and pore size). We also investigated the bending strength of Nb2O5 doped BNT ceramics [BNT-Nb x, x = 0.05 ∼ 1.5 wt%] and MnCO3 doped BNT ceramics [BNT-Mn x, x = 0.5 and 1.0 wt%]. Values of the σA of BNT-Nb 0.5 and BNT-Mn 0.5 were 222, and 188 MPa, respectively. It is clarified that soft dopants (Nb) can improve the bending strength of BNT-based ceramics. Additionally, hot-pressed BNT [HP-BNT] were sintered at 1050 °C for 5 h, and the σA of HP-BNT was 245 MPa.

Maldhure, Atul V.; Wankhade, Atul V.

doi: 10.1016/j.jascer.2017.04.010pmid: N/A

AbstractIn-situ formation of cross-linked carbon nanotubes network reinforced the refractory matrix and helps to improve the mechanical properties at elevated temperature. In this paper, the effect of modified phenol-formaldehyde (PF) resin binder on the various mechanical properties of alumina–magnesia–carbon (AMC) refractories was investigated. Initially, PF resin was modified by adding a different proportion of nickel catalyst. The AMC specimens (with the 7% carbon) were prepared by using 5% of modified PF resin. The pressed samples were cured at 180 °C for 24 h and characterized by XRD, Raman spectroscopy, and FE-SEM. The characterisation shows that, in-situ formation of graphitic carbon and carbon nanotubes network in the specimens due to modification of PF resin. In-situ formation of phases leads to enhancement of density and mechanical properties of refractory at elevated temperature due to the reinforcing effect.

Ohashi, Tomomi; Miyoshi, Yuki; Katagiri, Kiyofumi; Inumaru, Kei

doi: 10.1016/j.jascer.2017.04.008pmid: N/A

AbstractStrontium titanate nanocube-dispersed mesoporous silica (STO(NC)-MPS) nanocomposite was examined as a photocatalyst for the photoreduction of CO2. Copper (Cu) was examined as a co-catalyst, and the results showed that it was effective for the production of CO under a flow of CO2 and UV irradiation in water. As confirmed by gas chromatography–mass spectrometry, 13CO was produced in the presence of 13CO2, thus demonstrating that CO was generated upon photoreduction of CO2. Simultaneous formation of O2 suggested that water acted as a reductant in the photocatalysis process. Moreover, Cu supported on STO(NC)-MPS showed higher selectivity toward CO2 reduction when compared with Cu-supported composite prepared from mesoporous silica and SrTiO3 that was synthesized by conventional solid state reaction. Thus, the current findings highlight the characteristics and advantages of SrTiO3 nanocubes and their nanocomposites with mesoporous silica as photocatalysts for CO2 photoreduction.

Zhang, Jian; Sun, Yi; Shimai, Shunzo; Peng, Xiang; Zhao, Jin; Zhou, Guohong; Wang, Shiwei

doi: 10.1016/j.jascer.2017.05.002pmid: N/A

AbstractTetramethyl ammonium hydroxide (TMAH) has been demonstrated to increase solids loading effectively and to accelerate gelling rate of alumina slurries gelled by Isobam (a copolymer of isobutylene and maleic anhydride) system. With 0.5 vol% addition of TMAH, solids loading of alumina slurry was increased from 56 vol% to 58 vol%. Meanwhile, storage modulus (G’) of the slurry with 56 vol% solids loading was increased from 964 Pa to 2850 Pa at a testing time of 30 min. The enhanced dispersing and gelling behavior was ascribed to the hydrolysis and hydrophobic modification of Isobam by TMAH. Flexural strength of the final alumina ceramics from 58 vol% solids loading was 543 ± 10 MPa, higher than that of the ceramics from 56 vol% solids loading (531 ± 13 MPa).

Serrano Pérez, E.; Martinez Gutierrez, H.; Martinez Gonzalez, K.J.; Marín Moares, E.; Juárez López, F.

doi: 10.1016/j.jascer.2017.05.004pmid: N/A

AbstractSpark plasma sintering (SPS) technique was used to densify 7 mol% yttria-stabilized zirconia (7YSZ) powder with Gd2O3-particles, at temperatures ranging between 1000 and 1200 °C. Fine dispersion of Gd2O3-particles into a full-densified matrix was achieved. Shrinkage and microstructure, as well as porosity were investigated. The fine Gd2O3-particles distributed into 7YSZ matrix have influence over the sintering consolidation and final microstructure. An increment in the spark plasma sintering temperature around 70 °C is detected when Gd2O3 particles are present. The thermal characterization was performed using the photothermal infrared radiometry technique. Both thermal diffusivity and thermal conductivity display a similar sigmoidal (Boltzmann type) behavior with the Gd2O3 concentration in the samples.

Madheshiya, Abhishek; Gautam, Chandkiram; Kumar, Subodh

doi: 10.1016/j.jascer.2017.05.003pmid: N/A

AbstractTwo series of glasses were synthesized by conventional rapid melt-quench method for different glass systems 55[(PbxBi1-x).TiO3]-44[2SiO2B2O3] and 65[(PbxBi1-x).TiO3]-34[2SiO2B2O3] doped with 1 mole percent of La2O3. X-ray diffraction study of synthesized glass sample shows amorphous nature while the glass ceramic sample revealed a cubic crystal structure due to devitrification of the glass as major crystalline phase of bismuth titanium oxide. X-ray absorption spectroscopy measurements in transmission mode were carried out and confirm the maximum value of absorption coefficient, 3.05 at energy 13450 eV for lead free glass ceramic sample. Scanning electron microscopy and contact angle measurements were also performed to explain the surface morphology. Energy dispersive X-ray analysis confirmed the presence of grains of bismuth titanium oxide and its elemental analysis with O, Ti, Si, Bi nanoparticles. The inclusions of La2O3 results in development of well interconnected crystallites were formed as major phase of bismuth titanium oxide.

Kumada, Nobuhiro; Koike, Narumi; Nakanome, Kousuke; Yanagida, Sayaka; Takei, Takahiro; Miura, Akira; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro

doi: 10.1016/j.jascer.2017.05.005pmid: N/A

AbstractRutile-type solid solutions; Ni1−xCoxTi(Nb1−yTay)2O8 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) were prepared by high temperature solid state reaction. The solid solutions of noibates (y = 0) had a rutile-type structure and those of tantalates (y = 1.0) had a trirutile-type one. The trirutile-type structure appeared in the composition of y ≥ 0.4. The crystal structures of these solid solutions for niobates and tantalates were refined by using synchrotron X-ray powder diffraction data and the R-factors were Rwp = 1.76–1.92% and Rp = 1.13–1.19% for niobates and Rwp = 10.3–12.2% and Rp = 6.78–9.14% for tantalates. Their lattice parameters for noibates ranges from a = 4.69413(2) to 4.70411(2) Å and c = 3.02187(1) to 3.03242(1) Å and those for tantalates ranges from a = 4.6946(2) to 4.7065(2) Å and c = 9.0829(3) to 9.1164(4) Å. The optical band gap for these solid solutions ranged from 1.63 to 2.50 eV and only NiTiTa2O8 exhibited photocatalytic activity for phenol decomposition under UV light irradiation. The dielectric constants for four end members, NiTiNb2O8, CoTiNb2O8, NiTiTa2O8 and CoTiTa2O8 were 25–75 in the temperature range from room temperature to 300 °C.

Sokolář, Radomír; Keršnerová, Lucie; Šveda, Mikuláš

doi: 10.1016/j.jascer.2017.06.001pmid: N/A

AbstractThe aim of the article is to find the optimal fluxing agent for porcelain body regarding to the possibility of the lowest firing temperature. Sintering behaviour of dry pressed test samples made from the mixture of kaolin and three different types of industrially milled feldspar rocks, bone ash and quartz sand with similar granulometry as dependence of water absorption on the firing temperature was investigated. The most intensive fluxing agent for the sintering is bone ash—the mixture containing bone ash (20wt.%) showed sintering temperature 1200 °C. That is about 50 °C lower compared with the most intensive feldspar based fluxing agent—potassium feldspar rock containing 75% of pure microcline.