G Processing and characterization of CaTiO 3 perovskite ceramics
Calcium titanate (CaTiO3) ceramics with perovskite structure were produced by solid state reaction. Calcium carbonate (CaCO3) and titanium dioxide (TiO2) were mixed (in molar ratios 1/1 and 3/2), and the obtained mixtures were calcined at 1150 °C in successive thermal cycles. The obtained samples were characterized by differential thermal analysis, thermogravimetry, X-ray diffraction, measurement of particle size distribution and linear thermal shrinkage. XRD results indicated that the samples have perovskite CaTiO3 structure with small amount of secondary CaO and TiO2 phases, and their phase composition depends on the heat treatment conditions. The measured values of electrical resistivity were within the characteristic range of insulating materials and approach values corresponding to semiconducting ceramics.
Green Synthesis of Nano-sized Calcium Titanate CaTiO3 Using Solid State Mechano-Chemical Solventless Method and its Characterization
Calcium titanate (CaTiO3) is used as a thermally sensitive resistance element in one of the important materials of ferroelectric ceramics due to its negative temperature coefficient. It has other wide range of applications as components of capacitors, RAM, SYNROC (used for immobilization of nuclear waste). In the present work, we report the preparation of nano-sized calcium titanate (CaTiO3) by using solid state mechano-chemical solventless method, which fulfills the requirements of green chemistry. The starting materials used for this synthesis were CaCO3 and TiO2. They were mixed in equimolar ratio (1:1). The mechanical grinding of the reactant mixture was carried in high energy micronizer ball mill by varying the milling time for 0.5h, 1h, 2h, 4h and 5h resulting the peak intensity decrease for the mixture of CaCO3 and TiO2 accompanied by decrease in particle size. The as-synthesized products were characterized by X-ray diffraction (XRD) at different stages of milling. After milling, the mixture was calcined at 800 o C for 2 hrs. The XRD patterns confirmed the synthesis of nano-sized material of CaTiO3 at low temperature with high purity.
Changes in Quartz During Heating and the Possible Effects on Si Production
In Si and FeSi production, the main Si source is SiO2, in the form of quartz. Reactions with SiO2 generate SiO gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO2 modifications with cristobalite as the stable high-temperature phase. Transformation to cristobalite is a slow process. Its rate has been investigated for several industrial quartz sources and has been shown to vary considerably among the different quartz types. Other differences in behavior during heating between these quartz sources, such as softening temperature and volume expansion, have also been studied. The quartz-cristobalite ratio will affect the rate of reactions involving SiO2. The industrial consequences and other implications of the observed difference between quartz types are discussed. Initial studies of industrial quartz were published by Ringdalen et al. In the current work, a new experimental method has been developed, and an investigation of several new quartz sources has confirmed the earlier observed large variation between different sources. The repeatability of the data has been studied and the effect of gas atmosphere investigated. The results from the earlier work are included as a basis for the discussion.