Effect of Zirconium on the Densification of Reactively Hot-Pressed Zirconium Carbide

Densification mechanisms involved during reactive hot pressing (RHP) of zirconium carbide (ZrC) have been studied. RHP has been carried out using zirconium (Zr) and graphite (C) powders in the molar ratios 1:0.5, 1:0.67, 1:0.8, and 1:1 at 40MPa, 800 degrees C-1200 degrees C for different durations. The volume fractions of phases formed, including porosity, are determined from the measured density and from Rietveld analysis. Increased densification with an increasing nonstoichiometry in carbon has been observed. Microstructural and X-ray diffraction observations coupled with the predictions of a model based on the constitutive laws governing plastic flow of zirconium suggest that the better densification of nonstoichiometric compositions arise from the higher amount of starting Zr and also the longer duration of its availability for plastic flow during RHP. Volume shrinkage due to reaction between Zr and C and the gradual elimination of the soft metal phase limit the final density achievable. Based on these observations, a two-step RHP carried out at 800 degrees C and 1200 degrees C leads to a better densification than a single RHP at 1200 degrees C.

Porous wide band gap BiNbO4 ceramic nanopowder synthesised by low temperature solution-based method for gas sensing applications

In this study, we report the gas sensing behavior of BiNbO4 nanopowder prepared by a low temperature simple solution-based method. Before the sensing behaviour study, the as-synthesized nanopowder was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-diffuse reflectance spectroscopy, impedance analysis, and surface area measurement. The NH3 sensing behavior of BiNbO4 was then studied by temperature modulation (50-350 degrees C) as well as concentration modulation (20-140 ppm). At the optimum operating temperature of 325 degrees C, the sensitivity was measured to be 90%. The cross-sensitivity of as-synthesized BiNbO4 sensor was also investigated by assessing the sensing behavior toward other gases such as hydrogen sulphide (H2S), ethanol (C2H5OH), and liquid petroleum gas (LPG). Finally, selectivity of the sensing material toward NH3 was characterized by observing the sensor response with gas concentrations in the range 20-140 ppm. The response and recovery time for NH3 sensing at 120 ppm were about 16 s and about 17 s, respectively.

Perovskite ceramic nanoparticles in polymer composites for augmenting bone tissue regeneration

There is increasing interest in the use of nanoparticles as fillers in polymer matrices to develop biomaterials which mimic the mechanical, chemical and electrical properties of bone tissue for orthopaedic applications. The objective of this study was to prepare poly(epsilon-caprolactone) (PCL) nanocomposites incorporating three different perovskite ceramic nanoparticles, namely, calcium titanate (CT), strontium titanate (ST) and barium titanate (BT). The tensile strength and modulus of the composites increased with the addition of nanoparticles. Scanning electron microscopy indicated that dispersion of the nanoparticles scaled with the density of the ceramics, which in turn played an important role in determining the enhancement in mechanical properties of the composite. Dielectric spectroscopy revealed improved permittivity and reduced losses in the composites when compared to neat PCL. Nanofibrous scaffolds were fabricated via electrospinning. Induction coupled plasma-optical emission spectroscopy indicated the release of small quantities of Ca+2, Sr+2, Ba+2 ions from the scaffolds. Piezo-force microscopy revealed that BT nanoparticles imparted piezoelectric properties to the scaffolds. In vitro studies revealed that all composites support osteoblast proliferation. Expression of osteogenic genes was enhanced on the nanocomposites in the following order: PCL/CT>PCL/ST>PCL/BT>PCL. This study demonstrates that the use of perovskite nanoparticles could be a promising technique to engineer better polymeric scaffolds for bone tissue engineering.

Relaxor behaviour in BaBi4Ti4O15 ceramics fabricated using the powders obtained by mechanochemically assisted synthesis route

Mechanochemically activated reactants were found to facilitate the synthesis of fine powders comprising 200-400 nm range crystallites of BaBi4Ti4O15 at a significantly lower temperature (700 A degrees C) than that of solid-state reaction route. Reactants (CaCO3, Bi2O3 and TiO2) in stoichiometric ratio were ball milled for 48 h to obtain homogeneous mixture. The evolution of the BaBi4Ti4O15 phase was systematically followed using X-ray powder diffraction (XRD) technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to probe its structural and microstructural details. The electron diffraction studies established the presence of correlated octahedral rotations and associated long-range polar ordering. High-resolution TEM imaging nevertheless revealed structural inhomogeneities leading to intergrowth defects. Dense BaBi4Ti4O15 ceramics with an average grain size of 0.9 mu m were fabricated using mechanochemically assisted synthesized powders at relatively low temperature (1000 A degrees C). The effect of grain size on the dielectric and relaxor behaviour of BaBi4Ti4O15 ceramics was investigated. Fine-grained ceramics (average grain size similar to 0.9 mu m) showed higher diffusion in phase transition, lower temperature of phase transition, lower Vogel-Fulcher freezing temperature and higher activation energy for the polarization reversal than those for coarse-grained ceramics (average grain size similar to 7 mu m) fabricated via the conventional solid-state reaction route.

Low-Wear High-Friction Behavior of Copper Matrix Composites Dispersed With an In Situ Polymer Derived Ceramic

We show that copper-matrix composites that contain 20 vol. % of an in situ processed, polymer-derived, ceramic phase constituted from Si-C-N have unusual friction-and-wear properties. They show negligible wear despite a coefficient of friction (COF) that approaches 0.7. This behavior is ascribed to the lamellar structure of the composite such that the interlamellar regions are infused with nanoscale dispersion of ceramic particles. There is significant hardening of the composite just adjacent to the wear surface by severe plastic deformation.

Optical and dielectric study of strontium modified barium zirconium titanate ceramic prepared by high energy ball milling

Strontium modified barium zirconium titanate with general formula Ba1-xSrxZr0.05Ti0.95O3 ceramics have been prepared by solid state and high energy ball milling technique. The X-ray diffraction and Rietveld refinement studies show that all the compositions have single phase symmetry. The composition BaZr0.05Ti0.95O3 shows orthorhombic symmetric with space group Amm2. The structure changes from orthorhombic to tetragonal with strontium doping up to x = 0.3 and with further addition, changes to cubic. The scanning electron micrographs show that the grain size decreases with increase in strontium content. The temperature dependent dielectric behavior shows three phase transition in the parent material which merges with an increase in Sr content The transition temperature and dielectric constant decreases with an increase in Sr concentration. The phase transition becomes more diffused with increment in doping concentration. The ferroelectric behavior of the ceramics is studied by the hysteresis loop. The optical behavior is studied by the UV-visible spectroscopy and found that the optical band gap increases with Sr concentration. (C) 2015 Elsevier B.V. All rights reserved.

Origin of room temperature weak-ferromagnetism in antiferromagnetic Pb(Fe2/3W1/3)O-3 ceramic

We report the origin of room temperature weak ferromagnetic behavior of polycrystalline Pb(Fe2/3W1/3)O-3 (PFW) powder. The structure and magnetic properties of the ceramic powder prepared by a Columbite method were characterized by X-ray and neutron diffraction, Mossbauer spectroscopy and magnetization measurements. Rietveld analysis of diffraction data confirm the formation of single phase PFW, without traces of any parasitic pyrochlore phase. PFW was found to crystallize in the cubic structure at room temperature. The Rietveld refinement of neutron diffraction data measured at room temperature confirmed the G-type antiferromagnetic structure of PFW in our sample. However, along with the antiferromagnetic (AFM) ordering of the Fe spins, we have observed the existence of weak ferromagnetism at room temperature through: (i) a clear opening of hysteresis (M-H) loop, (ii) bifurcation of the field cooled and zero-field cooled susceptibility; supported by Mossbauer spectroscopy results. The P-E loop measurements showed a non-linear slim hysteresis loop at room temperature due to the electronic conduction through the local inhomogeneities in the PFW crystallites and the inter-particle regions. By corroborating all the magnetic measurements, especially the spin glass nature of the sample, with the conduction behavior of the sample, we report here that the observed ferromagnetism originates at these local inhomogeneous regions in the sample, where the Fe-spins are not perfectly aligned antiferromagnetically due to the compositional disordering. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Tuning of dielectric, pyroelectric and ferroelectric properties of 0.715Bi(0.5)Na(0.5)TiO(3)-0.065BaTiO(3)-0.22SrTiO(3) ceramic by internal clamping

This study systematically investigates the phenomenon of internal clamping in ferroelectric materials through the formation of glass-ceramic composites. Lead-free 0.715Bi(0.5)Na(0.5)TiO(3)-0.065BaTiO(3)-0.22SrTiO(3) (BNT-BT-ST) bulk ferroelectric ceramic was selected for the course of investigation. 3BaO - 3TiO(2) - B2O3 (BTBO) glass was then incorporated systematically to create sintered samples containing 0%, 2%, 4% and 6% glass (by weight). Upon glass induction features like remnant polarization, saturation polarization, hysteresis losses and coercive field could be varied as a function of glass content. Such effects were observed to benefit derived applications like enhanced energy storage density similar to 174 k J/m(3) to similar to 203 k J/m(3) and pyroelectric coefficient 5.7x10(-4) Cm-2K-1 to 6.8x10(-4) Cm-2K-1 by incorporation of 4% glass. Additionally, BNT-BT-ST depolarization temperature decreased from 457K to 431K by addition of 4% glass content. Glass incorporation could systematically increases diffuse phase transition and relaxor behavior temperature range from 70 K to 81K and 20K to 34 K, respectively when 6% and 4% glass content is added which indicates addition of glass provides better temperature stability. The most promising feature was observed to be that of dielectric response tuning. It can be also used to control (to an extent) the dielectric behavior of the host ceramic. Dielectric permittivity and losses decreased from 1278 to 705 and 0.109 to 0.107 for 6% glass, at room temperature. However this reduction in dielectric constant and loss increases pyroelectric figures of merit (FOMs) for high voltage responsivity (F-v) high detectivity (F-d) and energy harvesting (F-e) from 0.018 to 0.037 m(2)C(-1), 5.89 to 8.85 mu Pa-1/2 and 28.71 to 61.55 Jm(-3)K(-2), respectively for 4% added ceramic-glass at room temperature. Such findings can have huge implications in the field of tailoring ferroelectric response for application specific requirements. (C) 2015 Author(s).

Performance analysis of 1200 kV ceramic disc insulator string under normal and faulted conditions

In the recent years there has been a considerable increase in demand for the electrical power requirement in our country. Presently the transmission system voltages has increased to 765 kV ac and 800kV dc, keeping in view of the future demand experimentation and simulation studies for 1200 kV ac and 1100kV dc transmission are under progress. In the present study an attempt is made to compute the surface potential, electric field across the string of ceramic disc insulators used for 1200kV ac systems. The studies are carried out under normal, polluted conditions and for the case of insulator string containing faulty discs. A computer code using surface charge simulation method (SCSM) is developed for the present analysis. Also a new technique which enhances the surface potential and electric field strength for the existing ceramic disc insulators is presented.

A novel in-situ polymer derived nano ceramic MMC by friction stir processing

Fiction stir processing (FSP) is a solid state technique used for material processing. Tool wear and the agglomeration of ceramic particles have been serious issues in FSP of metal matrix composites. In the present study, FSP has been employed to disperse the nanoscale particles of a polymer-derived silicon carbonitride (SiCN) ceramic phase into copper by an in-situ process. SiCN cross linked polymer particles were incorporated using multi-pass ESP into pure copper to form bulk particulate metal matrix composites. The polymer was then converted into ceramic through an in-situ pyrolysis process and dispersed by ESP. Multi-pass processing was carried out to remove porosity from the samples and also for the uniform dispersion of polymer derived ceramic particles. Microstructural observations were carried out using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) of the composite. The results indicate a uniform distribution of similar to 100 nm size particles of the ceramic phase in the copper matrix after ESP. The nanocomposite exhibits a five fold increase in microhardness (260HV(100)) which is attributed to the nano scale dispersion of ceramic particles. A mechanism has been proposed for the fracturing of PDC particles during multi pass FSP. (C) 2015 Elsevier Ltd. All rights reserved

Designing Novel Sulphate-based Ceramic Materials as Insertion Host Compounds for Secondary Batteries

Rechargeable batteries have propelled the wireless revolution and automobiles market over the past 25 years. Developing better batteries with improved energy density demands unveiling of new cathode ceramic materials with suitable diffusion channels and open framework structure. In this pursuit of achieving higher energy density, one approach is to realize enhanced redox voltage of insertion of ceramic compounds. This can be accomplished by incorporating highly electronegative anions in the cathode ceramics. Building on this idea, recently various sulphate- based compounds have been reported as high voltage cathode materials. The current article highlights the use of sulphate (SO4) based cathodes to realize the highest ever Fe3+/Fe2+ redox potentials in Li-ion batteries (LiFeSO4F fluorosulphate: 3.9V vs Li/Li+) and Na-ion batteries (Na2Fe2(SO4)(3) polysulphate: 3.8V vs Na/Na+). These sulphate-based cathode ceramic compounds pave way for newer avenues to design better batteries for future applications.

Effect of applied pressure on densification of monolithic ZrCx ceramic by reactive hot pressing

The effect of applied pressure on reactive hot pressing (RHP) of zirconium (Zr):graphite (C) in molar ratios of 1:0.5, 1:0.67, 1:0.8, and 1:1 was studied at 1200 degrees C for 60 min. The relative density achievable increased with increasing pressure and ranged from 99% at 4 MPa for ZrC0.5 to 93% for stoichiometric ZrC at 100 MPa. The diminishing influence of pressure on the final density with increasing stoichiometry is attributed to two causes: the decreasing initial volume fraction of the plastically deforming Zr metal which leads to the earlier formation of a contiguous, stress shielding carbide skeleton and the larger molar volume shrinkage during reaction which leads to pore formation in the final stages. A numerical model of the creep densification of a dynamically evolving microstructure predicts densities that are consistent with observations and confirm that the availability of a soft metal is primarily responsible for the achievement of such elevated densification during RHP. The ability to densify nonstoichiometric compositions like ZrC0.5 at pressures as low as 4 MPa offers an alternate route to fabricating dense nonstoichiometric carbides.

Structural, Optical, and Piezoelectric Response of Lead-Free Ba0.95Mg0.05Zr0.1Ti0.9O3 Nanocrystalline Powder

Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x = 0.025-0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x = 0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response aside from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 and 723 cm(-1) characteristic of tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm, respectively. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. A piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature.

Primary and rechargeable zinc-air batteries using ceramic and highly stable TiCN as an oxygen reduction reaction electrocatalyst

Primary and secondary zinc-air batteries based on ceramic, stable, one dimensional titanium carbonitride (TiCN) nanostructures are reported. The optimized titanium carbonitride composition by density functional theory reveals their good activity towards the oxygen reduction reaction (ORR). Electrochemical measurements show their superior performance for the ORR in alkaline media coupled with favourable kinetics. The nanostructured TiCN lends itself amenable to be used as an air cathode material in primary and rechargeable zinc-air batteries. The battery performance and cyclability are found to be good. Further, we have demonstrated a gel-based electrolyte for rechargeable zinc-air batteries based on a TiCN cathode under ambient, atmospheric conditions without any oxygen supply from a cylinder. The present cell can work at current densities of 10-20 mA cm(2) (app. 10 000 mA g(-1) of TiCN) for several hours (63 h in the case of 10 mA cm(-2)) with a charge retention of 98%. The low cost, noble metal-free, mechanically stable and corrosion resistant TiCN is a very good alternative to Pt for metal-air battery chemistry.