Structural, magnetic and electrical characteristics of multiferroics (1-x)BaTiO3-xMgFe2O4 composites with weight fractions of x = 0.3, 0.5 and 0.7 are reported. MgFe2O4 powders were prepared using sol-gel auto combustion technique. It was combined with commercial BaTiO3 to form composites by using wet milling solid state reaction technique. Formation of tetragonal perovskite for the ferroelectric BaTiO3 and cubic spinel for the ferrimagnetic MgFe2O4 phases, were identified from the XRD pattern. The average grain size for each composite was about 0.5 μm. The M-H loop showed soft ferrimagnetic properties due to the presence of MgFe2O4 in the composites. The increment of the MgFe2O4 weight fraction increased the saturation magnetization and slightly changed the coercive field. The complex impedance plot can be represented by a parallel R and C circuit. Composite sample with x = 0.5 has the highest resistance with lowest capacitance and dielectric constant value at room temperature. The dielectric constant showed a very strong dispersion at low frequencies, due to the Maxwell-Wagner mechanism and a slight dispersion at higher frequencies. Based on the results obtained, all of the composite samples exhibited high dielectric constant and tangent loss at the low frequency range.
Tujuan kajian ini adalah untuk mengenal pasti kesan rawatan suhu yang berbeza terhadap kebioaktifan wolastonit
yang disintesis menggunakan teknik sol gel. Abu sekam padi dan batu kapur digunakan sebagai bahan awalan untuk
menghasilkan wolastonit. Nisbah campuran kalsium oksida dan silika dioksida CaO/SiO2 ditentukan pada 55:45 dan
dimasukkan ke dalam autoklaf pada suhu 135°C dengan tekanan 0.26 MPa selama 8 jam. Campuran serbuk CaO dan
SiO2 tersebut disinter pada suhu yang berbeza (1150°C dan 1250°C) dan diuji sifat kebioaktifan secara rendaman
dalam larutan cecair badan tersimulasi (SBF) selama 1,3,5,7 dan 14 hari secara in vitro. Sifat fizikal dan kebioaktifan
wolastonit sebelum dan selepas direndam dalam larutan SBF dan beberapa pencirian telah dijalankan menggunakan
teknik analisis XRD, FESEM, EDX dan FTIR. Campuran serbuk CaO-SiO2 yang telah diautoklaf dan disinter pada suhu
1250°C menghasilkan puncak tunggal pseudowolastonit. Ujian kebioaktifan menunjukkan lapisan amorfus kalsium
fosfat (ACP) dengan julat nisbah Ca/P 1.9-1.51 terbentuk lebih pantas pada sampel wolastonit yang disinter pada suhu
1250°C berbanding pembentukan ACP pada sampel tersinter 1150°C.
A series of polycrystalline samples (La1-xSmx)0.67Sr0.33MnO3 (X=0.00, 0.05 and 0.10) were prepared using the conventional solid-state reaction method. The XRD analysis indicated that all the samples were fully crystalline and in a single phase with a rhombohedral structure after a sintering at 1200ºC for 24 hours in air. Meanwhile, the Atomic Force Microscopy measurements showed that a small amount of Sm doping in La sites affected the grain growth and this might affect the grain boundary layer, thus resulting in the reduction of the Curie temperature, TC. Extrinsic magnetoresistance (MR) was observed for all the samples with a large negative MR at low field (0-0.1 or 0.2T) region, followed by a slower varying MR at high field (0.1 or 0.2-1T). The highest low-field MR value of -4.6% (at 0.1T) and -6.1% (at 0.2T) were observed for sample X=0.10 and X=0.05, respectively. Hence, these indicated that the extrinsic MR was grain size dependent and was therefore enhanced with a small amount of Sm substitution in La sites.
Bioactive composites consist of pseudowollastonite and mullite synthesized from natural resources was developed for
bone implant applications. To realize such applications, a mechanical test of these composites and in vitro bioactivity in
SBF solution were studied. The present paper reports pseudowollastonite synthesized from the rice husk ash and limestone
reinforced with 10, 20 and 30 wt. % of mullite. Influence of sintering temperature, phase composition, morphology towards
mechanical properties of various pseudowollastonite-mullite (PSW-M) composites was examined prior to the bioactivity
test. It was found that pseudowollastonite with the addition of 20 wt. % of mullite sintered at 1150°C gave the best result
for diametral tensile strength (DTS) and hardness with the value of 8.8 ± 0.15 MPa and 3.79 ± 0.13 GPa, respectively.
The obvious increment in the mechanical strength was due to the formation of liquid phase CaAl2
O3
during sintering at
1150°C. In addition, the formation of fibrous apatite (HA) layer of amorphous calcium phosphate (ACP) with Ca/P ratio
1.8 on PSW20M sample confirmed the good bioactivity of the composite.