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Abstract: Electrospun ZrO2 fibers have been prepared by heat treating the composite fibers of polyvinyl alcohol and zirconium n-propoxide precursors. Composite fibers prepared from acetic acid stabilized electrospun solution show non-beaded behaviour and possess diameter in the range of 130–440nm. Fibers have been characterized by XRD, SEM and AFM measurements. Tetragonal to monoclinic phase transformation takes place during the heat treatment of composite fibers up to 1050°C without the morphology degradation. [Copyright &y& Elsevier]

Ultra-fine PMN-PT (65/35) powder was synthesized following a polymer precursor based chemical synthesis technique. The auto-ignited powder containing negligible amounts of carbonaceous residue (∼0.6 wt%) could be sintered directly without any further calcination. A mixture of perovskite and pyrochlore phase was detected in the auto-ignited powder by XRD analysis. The amount of pyrochlore phase decreased with increasing the annealing temperature and pure perovskite phase was obtained in the sample at 950°C. Scanning electron microscopy of the uniaxially pressed and sintered samples revealed the rectangular shaped grains. The dielectric properties of the sintered pellets were measured at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline samples of the nominal composition Pb0.76−x Sm x Ca0.24Ti0.98Mn0.02O3 were prepared using a solid state reaction technique. Single-phase formation was checked through X-ray diffraction. Dielectric properties were studied as a function of frequency and temperature. The transition temperature determined from dielectric constant vs. temperature plots was found to decrease with increasing Samarium substitution. Poling field was optimized to achieve maximum piezoelectric properties. Piezoelectric coefficients e.g. d 33, d 31, g 33, g 31, g h, d h, k t and k p were measured. The experimental results successfully showed that samarium substitution is helpful to obtain a much higher value of thickness electromechanical coupling coefficient, k t (∼57%) while maintaining a smaller planar electromechanical coupling coefficient, k p in PCT ceramics. [Copyright &y& Elsevier]

Pb0.76-3x/2LaxCa0.24Mn0.02Ti0.98O3 (PLCT), x=0–0.08 (in steps of 0.02), ceramics were prepared by conventional mixed oxide technique. The samples were sintered at an optimized temperature of 1150°C. Phase and microstructural analysis were carried out using X-ray Diffraction (XRD) and scanning electron microscope (SEM) to study the effect of lanthanum on PCT ceramics. Both experimental and theoretical densities for all the samples were also determined. Phase analysis shows the single-phase material with tetragonal structure and the decrease in tetragonality is observed with the increase in the amount of lanthanum in the base composition. Detailed dilatometric investigations were performed in order to study the shrinkage behaviour and dominating shrinkage mechanism in the present system. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline samples of lanthanum-modified PCT ceramics with composition Pb0.76−3 x /2La x Ca0.24Mn0.02Ti0.98O3 (PLCT); (in steps of 0.02) were prepared by using conventional dry ceramic technique. Samples were sintered at 1150°C. X-ray analysis confirmed the formation of single-phase compound with tetragonal crystal structure. Dielectric properties were studied in detail as a function of frequency and temperature. From temperature variation of dielectric constant, Curie temperature (T c) was determined. Discussion on hysteresis behaviour for all the samples at room temperature is presented. Dielectric constant at room temperature shows an increasing trend and Curie temperature shows decreasing trend with the increase in lanthanum in PCT ceramics. Curie temperature determined from thermal expansion behaviour of sintered samples was found to be in good agreement with that determined from dielectric studies. Piezoelectric properties show a significant improvement with lanthanum substitution. [Copyright &y& Elsevier]

Abstract: High-density samarium modified lead calcium titanate ceramics were successfully prepared by using a novel mechano-chemical activation technique, which skips the calcinations steps at an intermediate temperature that is always required in the normal conventional technique. Better densification could be achieved by activation process. XRD study showed single-phase formation with tetragonal structure and microstructural study revealed almost uniform grain size of 1.4μm. Dielectric study demonstrated sharp peak in dielectric versus temperature plots and slightly low value of the T c as compared to that observed for samples prepared by conventional technique. The mechanical alloying technique rendered drastic improvement in piezoelectric properties. The ratio of electromechanical anisotropy (k t/k p) was obtained to be ∼62 as compared to 52 in the case of samples by conventional process. Comparison in the structural and electrical properties is discussed in detail for conventional versus mechano-chemical alloying process. [Copyright &y& Elsevier]

Single perovskite phase of PMN-PT (68:32) composition was prepared using highly reactive fumed titania as starting material. The calcination temperature of 700°C was found to be the optimum temperature for the formation of single perovskite phase in the present system. Experimental density of the material was found to be 94% of the theoretical density. Room temperature dielectric constant (ε ′) and dielectric loss (tanδ) of the material at 1 kHz were found to be 2277 and 0.065 respectively. From polarization versus electric field (P-E) hysteresis loop, remanant polarization (P r ) and coercive field (E c ) were found to be ∼⃒ 22 μ C/cm 2 and ∼⃒ 3.90 kV/cm respectively. Strain versus bipolar electric field (S-E) behaviour showed the development of a giant strain of ∼⃒ 1%, whereas less hysteresis behaviour in S-E plot of poled samples indicates the suitability of the material for actuator applications. [ABSTRACT FROM AUTHOR]

Modified Lead Calcium Titanate (PCT) compositions with representative formula, Pb 0.76 - x Sm x Ca 0.24 Ti 0.98 Mn 0.02 O 3 (x = 0–0.1 in steps of 0.02) were prepared by conventional dry ceramic method. Effects of samarium substitution on physical, structural properties and thermal behaviour of PCT ceramics are reported here. All the samples were subjected to XRD analysis and were found to have single phase with tetragonal structure up to 8 mol% Sm substitution. The variations of density and tetragonality have been studied with samarium content. Microstructural analysis shows the uniform grain growth with increasing Sm concentration. Dilatometric study has been done to predict sintering schedule of the green samples. [ABSTRACT FROM AUTHOR]

Structural and thermal properties of PCT ceramics are studied by the substitution of Ta in the titanium site. Samples with compositional formula Pb0.76Ca0.24Mn0.02Ti0.98-5x/4TaxO3 with the variation in x from 0 to 0.04 in steps of 0.01, were prepared by the conventional dry ceramic method. Single-phase formation was confirmed from the X-ray analysis and all the samples show tetragonal structure. Lattice parameters "c" and "a" were found to decrease and increase with substitutional parameter x. respectively. Tetragonality (c/a) decreases with increasing Ta content. Dilatometric study was done lo analyze the shrinkage behaviour of green and sintered samples. [ABSTRACT FROM AUTHOR]

Alumina-mullite ceramic shell moulds were developed to cast single-crystal hollow high-pressure turbine blades (SX-HPTB). Mullite and fine alumina powders were used as fillers. Two colloidal silica binders were used to bind the filler particles. One colloidal silica binder (binder A) had no polymer and the second colloidal silica binder (binder B) had 8 wt % polymer. Eight slurry compositions with fine alumina substitution (0, 10, 30 and 50 wt %) were prepared. Silica cores were used to achieve hollow castings. The effect of alumina substitution and binders on the slurry characteristics, flexural strength of green and fired samples, air permeability and self-load sag resistance was studied. It was observed that with an increase in alumina percentage, the test specimens showed increased viscosity, pick-up weight, density, green strength and fired residual strength. In addition, the slurries prepared from binder B possessed larger values of viscosity and pick-up weight compared to the slurries prepared from binder A. The residual strength of fired test specimens containing binder A was higher than those containing binder B. The test specimens with 30 wt % fine alumina substitution showed the highest self-load sag resistance w.r.t. each test temperature. Also, the air permeability of the fired samples was higher than the green (de-waxed) samples. The casting of hollow HPTB components was performed at two temperatures (1525 °C and 1550 °C) using nickel-based superalloy CMSX4. The HPTB components, cast at 1550 oC from ceramic shell mould having binder B and 30 wt % fine alumina substitution, resulted in an acceptable aerofoil profile and surface roughness. [ABSTRACT FROM AUTHOR]

Ceramic shell moulds for investment casting of shrouded low-pressure turbine (LPT) blades were prepared by using colloidal silica binder and partial substitution of the zircon filler with fine alumina. Among the two ceramic slurry systems designed, the first slurry system comprised of polymer-free colloidal silica binder, and the second slurry system comprised of polymer-containing colloidal silica binder. The samples prepared from the first slurry system showed higher fired residual strength and self-load sag values (lesser sag resistance). The casting of shrouded LPT blades was carried out at 1525 °C and 1550 °C using CM247LC superalloy. Ceramic shell moulds prepared from the second slurry system, containing 30 wt% of fine alumina filler, yielded aeronautical grade casting (at 1550 °C) of blades with required dimensional accuracy and average surface roughness. Microstructural analysis of the cut surfaces of self-load sag tested samples was carried out to understand the effect of fine alumina substitution on shell characteristics. [ABSTRACT FROM AUTHOR]

The investment casting process was adopted to cast a low-pressure turbine rotor (LPTR) blisk. The casting was carried out in vacuum at 1525 °C by using BZL12Y superalloy. Ceramic shell moulds for the casting were prepared by two different fillers (mullite and zircon), two types of colloidal silica binders (polymer-free binder-A and polymer-containing binder-B) and cobalt aluminate solution. The shell specimens having binder B showed improved green strength and self-load sag resistance in comparison to their counterparts having binder-A. Samples prepared from the slurry compositions having binder-A showed higher residual fired strength than the samples prepared from slurry compositions having binder-B. Defect-free castings of LPTR blisks with fine equiaxed grains were obtained by using ceramic shell moulds containing binder-B and cobalt aluminate solution. The LPTR blisks cast from the ceramic shell moulds having binder-A showed hot tear defect along-with coarse grains. Irrespective of the filler, the LPTR blisk cast by using ceramic shell moulds and cobalt aluminate showed fine grains. The average surface roughness values of LPTR blisks cast from ceramic shell moulds, having binder-B and binder-A, were observed to be in the acceptable range even though castings with binder-A showed marginally lower surface roughness. [ABSTRACT FROM AUTHOR]