Ajay Kaushal

Injectability of calcium phosphate pastes: Effects of particle size and state of aggregation of β-tricalcium phosphate powders.

The present study discloses a systematic study about the influence of some relevant experimental variables on injectability of calcium phosphate cements. Non-reactive and reactive pastes were prepared, based on tricalcium phosphate doped with 5 mol% (Sr-TCP) that was synthesised by co-precipitation. The varied experimental parameters included: (i) the heat treatment temperature within the range of 800-1100°C; (ii) different milling extents of calcined powders; (iii) the liquid-to-powder ratio (LPR); (iv) the use of powder blends with different particle sizes (PS) and particle size distributions (PSD); (v) the partial replacement of fine powders by large spherical dense granules prepared via freeze granulation method to simulate coarse individual particles. The aim was contributing to better understanding of the effects of PS, PSD, morphology and state of aggregation of the starting powders on injectability of pastes produced thereof. Powders heat treated at 800 and 1000°C with different morphologies but with similar apparent PSD curves obtained by milling/blending originated completely injectable reactive cement pastes at low LPR. This contrasted with non-reactive systems prepared thereof under the same conditions. Hypotheses were put forward to explain why the injectability results collected upon extruding non-reactive pastes cannot be directly transposed to reactive systems. The results obtained underline the interdependent roles of the different powder features and ionic strength in the liquid media on determining the flow and injectability behaviours.

Dielectrical Properties of CeO2 Nanoparticles at Different Temperatures.

A template-free precipitation method was used as a simple and low cost method for preparation of CeO2 nanoparticles. The structure and morphology of the prepared nanoparticle samples were studied in detail using X-ray diffraction, Raman spectroscopy and Scanning Electron Microscopy (SEM) measurements. The whole powder pattern modelling (WPPM) method was applied on XRD data to accurately measure the crystalline domain size and their size distribution. The average crystalline domain diameter was found to be 5.2 nm, with a very narrow size distribution. UV-visible absorbance spectrum was used to calculate the optical energy band gap of the prepared CeO2 nanoparticles. The FT-IR spectrum of prepared CeO2 nanoparticles showed absorption bands at 400 cm-1 to 450 cm-1 regime, which correspond to CeO2 stretching vibration. The dielectric constant (εr) and dielectric loss (tan δ) values of sintered CeO2 compact consolidated from prepared nanoparticles were measured at different temperatures in the range from 298 K (room temperature) to 623 K, and at different frequencies from 1 kHz to 1 MHz.

Successful aqueous processing of a lead free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 piezoelectric material composition

We report on the successful aqueous processing of a lead free piezoelectric 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) composition with the final functional properties of the materials unaffected by the various processing steps involved. X-ray diffraction results show a single tetragonal perovskite crystalline phase for the as-received sintered BZT–BCT powder. The purity of the perovskite phase for BZT–BCT powder was found to be controlled even after ageing the material in water for 24 h as a successful surface treatment against hydrolysis. An aqueous suspension of surface treated BZT–BCT powder with 50 vol% solid loading was successfully transformed into micro-sized granules via a freeze granulation (FG) method. Various structural, electrical and mechanical properties of sintered BZT–BCT-FG and BZT–BCT-NG ceramics consolidated from freeze granulated and non-granulated (NG) powders, respectively, were measured. The dielectric constant (er) values of the BZT–BCT-FG sample were found to be higher, with lower dielectric loss (tan δ) values in comparison with those of a sample prepared from the BZT–BCT-NG powder at all temperatures and with all frequency ranges tested. Nanoindentation results revealed that the ability to oppose deformation was nearly 10-fold higher for BZT–BCT-FG (6.93 GPa) than for BZT–BCT-NG ceramics (543 MPa). The functional properties of BZT–BCT-FG samples confirmed the benefits of the aqueous processing approach in comparison with traditional dry pressing.

Lead-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 powder surface treated against hydrolysis – a key for a successful aqueous processing

The properties of functional ceramics and their performance in industrial applications are strongly affected by the processing treatments. We report on long term stability of aqueous 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) suspensions. The effects of aging time on pH and on the leaching extents of Ba, Zr and Ca elements were systematically investigated for the naked, and the surface treated particles against hydrolysis. Suspensions with solid loadings (Φ) up to 60 vol%, pseudoplastic flow behaviours and long term colloidal stability could be achieved from the surface treated powder. A fractal dimension (D) of ∼1.97 to 1.98 was estimated for the BZT–BCT suspensions from the yield stress (τy) versus (Φ) dependence, suggesting a reaction limited cluster aggregation (RLCA) type of particle aggregation with a substantial rearrangement occurring in the aggregates under shearing. The maximum solid loading (Φm) ≈ 61 vol% was determined. The concentrated and stable suspensions represent a stride for successful processing of functional BZT–BCT ceramic components via various aqueous colloidal shaping methods (slip casting, gel-casting, etc.) for large scale industrial applications.

Flux growth and effect of cobalt doping on dielectric, conductivity and relaxation behaviour of 0.91Pb[Zn1/3Nb2/3]O3–0.09PbTiO3 crystals

Crystals of 1 mol% cobalt-doped Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (PZNCT) have been grown using a high-temperature self-flux method. A pure perovskite phase with mixed symmetry at room temperature was observed using X-ray diffraction analysis. Their electrical properties were further investigated by measuring temperature- and frequency-dependent dielectric constant (e) and loss (tan δ) behaviour of as-grown crystals. To study the degree of dielectric relaxation, modified power law fitting and Lorentz-type quadratic fitting were performed. The as-grown PZNCT crystals showed a low Curie temperature (Tc ~131 °C) with a rhombohedral–tetragonal phase transition temperature (Trt) of 104 °C. The piezoelectric coefficient (d33) value at the optimized poling field was found to be ~1000 pC N−1. Complete electrical characterization revealed the growth of high-performance PZNCT crystals with enhanced remnant polarization (34.23 μC cm−2) and low coercive field (6.97 kV cm−1) with cobalt doping. The conduction and relaxation mechanisms of grown PZNCT crystals have been discussed in detail.

Correction: Dielectrical Properties of CeO2 Nanoparticles at Different Temperatures.

There is an error in affiliation 3 for author Hossein Abbastabar Ahangar. The correct affiliation should be: Department of Chemistry, Faculty of Science, Najafabad Branch, Islamic Azad University, Najafabad, Isfahan, Iran.

Enhanced local piezoelectric response in the erbium-doped ZnO nanostructures prepared by wet chemical synthesis

Abstract Pure and erbium (Er) doped ZnO nanostructures were prepared by simple and cost effective wet chemical precipitation method. The successful doping with phase purity of prepared ZnO nanostructure was confirmed by X-ray diffraction (XRD) and their Rietveld analysis. The change in structural morphology of nanoscale features of prepared ZnO nanopowders on Er doping was observed from their scanning electron microscopy (SEM) images. The presence of Er in prepared ZnO nanopowder was further confirmed from corresponding energy dispersive X-ray spectroscopy (EDX) spectra of scanned SEM images. Piezoelectric properties of before (green samples) and after sintering of consolidated compact of synthesized nanopowders were successfully measured. The out-of-plane (effective longitudinal) and in-plane (effective shear) coefficients of the samples were estimated from the local piezoresponse.