Effects of Sintering Temperature and Holding Times on the Microstructure and Chemical Bond of Strontium Titanate (SrTiO3)

Strontium Titanate (SrTiO3) is one attractive material studied. In this study, SrTiO3 has been fabricated via the co-precipitation technique. The samples were sintered at 800°C and 900°C with holding times of 2 h and 4 h for each temperature. The purposes of this study were to synthesize SrTiO3 material using co-precipitation technique and to observe the microstructure and chemical bonds of the SrTiO3 as the variations of the sintering temperatures and holding times. According to the X-Ray Diffraction (XRD) results, the sintering temperatures and holding times influenced the intensity values and peak broadening. The alteration in both parameters consequently changed the crystallite size and lattice strain of the SrTiO3 material. Furthermore, the Fourier Transform Infrared (FTIR) results validated the SrTiO3 material by existence of Sr-Ti-O chemical bonds. Also, the absorption peaks of O-H, C-H, and C=O chemical bonds in the SrTiO3 declined due to the higher temperature and longer holding time demonstrating impurities declined. Therefore, according to this study, the sintering temperature of 900°C and the holding time of 4 h was the best parameter for fabricating SrTiO3 powder.

Investigation of annealing temperature on the synthesis of zincite doped cobalt ferrite using Rietveld refinement

Co-precipitation technique is used for preparing the composites of CoFe2O4/VZnO. The effect on the variation on the size of the crystals of CoFe2O4 is studied by varying the annealing temperature over the range from 500°C to 900°C. The structure of composite powder obtained after annealing was studied by Rietveld refinement and XRD. The estimation of the crystalline phases of the sample is done by XRD though Rietveld refinement. The space group and structure of zinc oxide was observed as P63mc(186) and hexagonal while that for the cobalt ferrite was Fd3m(227) and cubic. The values of all R factors was calculated and the effect of annealing temperature on the size of the crystal was discussed.

Laboratory Study on Improvement of Expansive Soil by Chemically Induced Calcium Carbonate Precipitation

This paper proposes the use of calcium carbonate (CaCO3) precipitation induced by the addition of calcium chloride (CaCl2) and sodium carbonate (Na2CO3) solutions as a procedure to stabilize and improve expansive soil. A set of laboratory tests, including the free swell test, unloaded swelling ratio test, unconfined compression test, direct shear test, scanning electron microscopy (SEM) test, cyclic wetting–drying test and laboratory-scale precipitation model test, were performed under various curing periods to evaluate the performance of the CaCO3 stabilization. It is concluded from the free swell tests and unloaded swelling ratio tests that the addition of CaCl2 and Na2CO3 can profoundly decrease soil expansion potential. The reduction in expansion parameters is primarily attributed to the strong short-term reactions between clay and stabilizers. In addition, the formed cementation precipitation can decrease the water adsorption capacity of the clay surface and then consequently reduce the expansion potential. The results of unconfined compression tests and direct shear strength tests indicated that the addition of CaCl2 and Na2CO3 has a major effect on geotechnical behavior of expansive soils. Based on the SEM analyses, new cementing crystalline phases formatted by sequentially mixing CaCl2 and Na2CO3 solutions into expansive soil were found to appear in the pore space, which results in a much denser microstructure. A laboratory-scale model test was conducted, and results demonstrate the effectiveness of the CaCO3 precipitation technique in stabilizing the expansive soil procedure. The test results indicated that the concentration of CaCl2 higher than 22.0% and Na2CO3 higher than 21.2% are needed to satisfactorily stabilize expansive soil. It is proposed to implement the precipitation technique in the field by the sequential permeation of CaCl2 and Na2CO3 solutions into soils in situ.