Piezoelectric polymer-ceramic composites are promising materials for transducer applications, and they are widely used in underwater hydrophones, biomedical imaging with ultrasound, and nondestructive testing applications. The critical factor in the 0-3 composite is to ensure homogeneous distribution of the filler in the matrix. To ensure this objective, PVDF-PZT composite was prepared by two different routes: hot press and tape casting techniques. Loss on ignition and scanning electron microscopy studies were conducted to find out the uniformity of the composites prepared. It is found that hot press technique gives better uniformity compared to tape casting technique. PZT concentration was varied from 20 to 60 vol %. Physical and dielectric properties were studied. FT-IR, DSC, and XRD characterization studies of PVDF were also recorded. Density of the composites was 2.74 to 5.13 g/cm 3 as PZT concentration increased from 20 to 60 volume fractions. The dielectric constant of composites at 1 MHz varied from 16.74 to 98.48 as PZT concentration increased from 20 to 60 volume fractions. Hot press technique that combines solution and melt processing was found to be the better method for the preparation of 0-3 composites.

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A study has been carried out to correlate the effect of sintering temperature on the microstructural, electrical and reliability aspects of Ni 0.75 Mn (2.25−x−y) Cr x Fe y O 4 (x=0 to 0.3 and y=0 to 0.3) negative temperature coefficient thermistor compositions prepared by solid-state route. The calcined and sintered compositions were characterized by X-ray diffraction and Scanning Electron Microscopy. The existence of cubic spinel single-phase region was determined by sintering Ni 0.75 Mn (2.25−x−y) Cr x Fe y O 4 samples in air at temperatures 1150 to 1250°C. X-ray diffraction patterns of samples sintered above 1200°C shows additional Bragg reflections of a rock salt structured NiO phase besides normal cubic spinel. A maximum B-value of 4044 K was obtained for Ni 0.75 Mn 1.95 Cr 0.25 Fe 0.05 O 4 composition at a sintering temperature 1250°C/3 h. The reliability of the thermistor compositions were evaluated by performing accelerated ageing based on thermal cycling test. We found that chromium enhances the reliability of Ni 0.75 Mn (2.25−x−y) Cr x Fe y O 4 (x=0 to 0.3 and y=0 to 0.3) based NTC thermistor compositions. A maximum reliability of +0.25% resistance drift was observed at sintering temperature 1200°C for 0.25 mol% chromium content. Excellent reliability of Ni 0.75 Mn (2.25−x−y) Cr x Fe y O 4 NTC thermistor compositions makes it ideal candidates for high-performance thermal sensor applications.

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ABSTRACT:The cure characteristics and mechanical properties of short-nylon-fiber-reinforced acrylonitrilebutadiene rubber composites with and without an epoxy resin as a bonding agent were studied. The epoxy resin was a good interfacial-bonding agent for this composite system. The minimum torque showed a marginal increase with the resin concentration. The maximum-minimum torque showed only a marginal change with the resin. The scorch time decreased with the fiber concentration and resin content. The tensile strength and abrasion resistance were improved and the tear resistance and resilience were reduced with the resin concentration.

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