Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2

Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO₂-B₂O₃-SiO₂ were prepared keeping (BaO + PbO)/TiO₂ ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO₃ crystallizes in lead-rich glasses while BaTiO₃ precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO₃ does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.     

Dielectric properties of the system Ca1−xYxTi1−xCoxO3(0.00 ⩽ x ⩽ 0.15)

The dielectric behaviour of the compositions withx0.15 in the system Ca_1–x Y _x Ti_1–x Co _x O₃ sintered and cooled in air has been studied. Space-charge polarization which arises due to the presence of chemical inhomogeneities at the micro-level contributes significantly to their dielectric constant. The composition with x=0.05 exhibits temperature and frequency-independent dielectric constant and very small dielectric loss.     

Studies on chemical resistance of polyesters

Chlorendic anhydride based polyester ( I ,) tetrachlorophthalic anhydride based polyester ( II ), dibromoneopentyl glycol based polyester ( III ,) general purpose polyester ( IV ,) blend of dibromoneopentyl glycol based polyester with general purpose polyester ( V ,) chlorendic anhydride and dibromoneopentyl glycol based polyester ( VI ), and a blend of chlorendic anhydride based polyester and dibromoneopentyl glycol based polyester ( VII ) were prepared and their chemical resistance and moisture absorption studied in various reagents, acid, alkali, and water, at 25 and 65°C. It is found that the polyester ( III ) is the least affected in the presence of the acids. In 20% NaOH, there was a decrease in weight for all polyesters at both the temperatures compared to the control except the polyester ( VII ). Increase in weight of all the polyesters was observed during the absorption of moisture both at 25 and 65°C. The increase was higher at higher temperature. Polyester ( III ) thus shows the least absorption of moisture.     

CTAB-caped Cu nanoparticles doped on zeolitic imidazolate framework-ZIF-67 as bifunctional catalysts for oxygen-reduction and evolution reactions in alkaline media

Journal of Porous Materials - In order to facilitate the large-scale applications of rechargeable Zn–air batteries, non-noble-metal based materials with high activity for oxygen reduction...     

Low Cost Porous Alumina with Tailored Microstructure and Thermal Conductivity Prepared using Rice Husk and Sucrose

This study demonstrates a cost‐effective way to fabricate porous ceramics with tailored porosity and pore microstructure using 5–40 wt% rice husk (RH) in <75 μm, 75–180 μm, 180–355 μm, 355–420 μm, and 420–600 μm size, as pore former. Sucrose, used as binder, also acted as a pore former. Porous alumina compacts with 20%–66% volume fraction porosity and 50–516 μm pore size (length) were successfully fabricated. Microstructure of samples reveal randomly oriented elongated coarse pores and fine pores (avg. size 4 μm), created during burnout of RH and sucrose, respectively. Samples with isolated and/or interconnected pores were fabricated using this process. Thermal conductivity of the samples prepared was measured using Transient Plane Source (TPS) technique. Thermal conductivity ranges from 1.2 to 24 W/mK. Experimental results agree closely with predictions made based on Effective Medium Theory (EMT) for a two‐phase system.     

The behavior of hydrogen and carbon monoxide with graphite ferric chloride—II Effect of activation

The H₂ isotherms on graphite, C₈FeCl₃ and C₁₀FeCl₂ are identical but when activated, C₈FeCl₃ shows higher absorption. This suggests that the metallic Fe produced on activation of C₈FeCl₃ in H₂ at 375°C is on the surface and is not intercalated. The activated intercalation compound, C₈FeCl₃, catalyzes the production of hydrocarbons from CO + H₂ but at a slower rate than on activated mixture of graphite and hydrated ferric oxide-chloride. It also has a smaller area of exposed Fe. Finally, it has been shown that the thermal decomposition of FeCl₃ to FeCl₂ + Cl₂ in the range 150–300°C is displaced toward FeCl₂ in the presence of CO because Cl₂ is removed to form COCl₂. However, no Fe is produced by this interaction.     

Crystallization, microstructure development and dielectric behaviour of glass ceramics in the system [SrO · TiO2]-[2SiO2 · B2O3]-La2O3

Various glasses in the system (65 – x)[SrO · TiO₂]-(35)[2SiO₂ · B₂2O₃]-(x)La₂O₃, where x = 1,5,10 (wt%) were prepared by melting in alumina crucible (1375–1575 K). Heat treatment schedules were selected from DTA plots of respective glasses. X-ray diffraction studies of glass ceramic samples containing different concentrations of La₂O₃ revealed the formation of Sr₂B₂O₅, Sr₃Ti₂O₇ and TiO₂ (rutile) phases. The addition of La₂O₃ results in the development of well formed, elongated crystallites of different phases. Results of the dielectric behaviour demonstrate higher values of dielectric constant for some of the glass ceramic samples. This can be ascribed to the relaxation polarization at the crystal-glass interface due to conductivity differences between crystalline and glassy phases.     

Effect of manganese and cobalt doping on conductivity of ZnO based varistors: a study by complex plane modulus

Effect of manganese and cobalt doping (0.50 mole%) on electrical properties of ZnO based varistors has been studied using complex plane modulus analysis. It is found that total resistivity of Mn doped sample is more as compared to that of Co doped sample. This has been ascribed to existence of Mn in variable valence states viz. Mn²⁺, Mn³⁺ and Mn⁴⁺ which promotes hopping conduction leading to increase in the conductivity as compared to Co doped sample, in which Co exists predominantly in +3 state with traces of Co²⁺ or Co⁺⁴ states. This accounts for its less conductivity. Mechanism of conduction is the same for grains and grainboundaries.