ABSTRACT
In the current study, Bi2/3Cu3Ti4O12 (BCTO) ceramics were prepared by mechanical ball mill of the elemental oxides followed by conventional sintering of the powder without any pre-sintering heat treatments. The sintering temperature was in the range 950-990 °C, which is 100-150 °C lower than the previous conventional sintering studies on BCTO ceramics. All the ceramic samples showed body-centered cubic phase and grain size ≈ 2-6 µm. Sintering temperature in the range 950-975 °C resulted in comparatively lower dielectric loss and lower thermal coefficient of permittivity in the temperature range from -50 to 120 °C. All the BCTO ceramics showed reasonably high relative permittivity. The behavior of BCTO ceramics was correlated with the change in oxygen content in the samples with sintering temperature. This interpretation was supported by the measurements of the energy dispersive x-ray spectroscopy (EDS) elemental analysis and activation energy for conduction and for relaxation in the ceramics.
ABSTRACT
In the current study, we report on the dielectric behavior of colossal-dielectric-constant Na1/2La1/2Cu3Ti4O12 (NLCTO) ceramics prepared by mechanochemical synthesis and spark plasma sintering (SPS) at 850 °C, 900 °C, and 925 °C for 10 min. X-ray powder diffraction analysis showed that all the ceramics have a cubic phase. Scanning electron microscope observations revealed an increase in the average grain size from 175 to 300 nm with an increase in the sintering temperature. SPS NLCTO ceramics showed a room-temperature colossal dielectric constant (>103) and a comparatively high dielectric loss (>0.1) over most of the studied frequency range (1 Hz-40 MHz). Two relaxation peaks were observed in the spectra of the electrical modulus and attributed to the response of grain and grain boundary. According to the Nyquist plots of complex impedance, the SPS NLCTO ceramics have semiconductor grains surrounded by electrically resistive grain boundaries. The colossal dielectric constant of SPS NLCTO ceramics was attributed to the internal barrier layer capacitance (IBLC) effect. The high dielectric loss is thought to be due to the low resistivity of the grain boundary of SPS NLCTO.
ABSTRACT
Environmental threats posed by the cement manufacturing industry and agro-industrial waste discharge have shifted the direction of research towards building sustainable construction without compromising the technical merits of the developed binders. Date palm trees are one of the highest numbers of trees in the world whose generated wastes can be beneficially recycled and reused by the concrete industry. In this study, ordinary Portland cement (OPC) and date palm frond ash (DPFA)-based binders were synthesized by varying ratio of DPFA/(OPC + DPFA) between the range of 0 to 0.3 at an interval of 0.1. Both base materials were characterized by physical, chemical, and thermal techniques. The developed binders were assessed by flow, setting time, and compressive strength up to 360 days of curing. Scanning electron microscopy (SEM) was performed to complement the strength results. It is postulated that the DPFA/(OPC + DPFA) ratio of up to 0.2 outperforms the DPFA-free binder in terms of the overall performance. The properties of binders were negatively affected by the total precursor composition ratio of CaO/SiO2 and Al2O3/SiO2 below 2.06 and 0.18, respectively. The optimum synergy of OPC-DPFA resulted in superior microstructural density attributed to the uniform skeletal framework of gel products. Strengths, weaknesses, opportunities, and threats analysis of the use of DPFA in cementitious materials showed that there is a high potential for its use in terms of sustainability and economic benefits. However, various weaknesses and threats associated with the use of DPFA as a cementitious material need to be resolved.
