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.
Synthesis of perovskite CaTiO3 nanopowders with different morphologies by mechanical alloying without heat treatment
Mechanical alloying (MA) method is one of the methods used for large scale production of different nanopowders. In this study, calcium titanate (CaTiO3: CTO) nanoparticles have been synthesized via mechanical alloying (MA) without using heat treatment. The milled powders and CTO were characterized by XRD, SEM, and zetasizer. It is found that the CTO has a diameter of 30 - 70 nm with different morphologies. The results showed the minimum time of calcium titanate synthesis via mechanical alloying without heat treatment is 70 h that formed and the range of grain size (apparent size) using Williamson-Hall equation is 69 nm. 
 
   
 
 Key words: Mechanical alloying/activation, morphology, perovskite, CaTiO3.
Energetics of collision between grinding media in ball mills and mechanochemical effects
Abstract This paper describes the physical and chemical changes such as decomposition, double decomposition, oxidation, and phase transformation reported in the literature as a consequence of solid surfaces coming into contact under mechanical forces. These changes, generally termed mechanochemical and chemomechanical effects, occur in the near-surface regions when surfaces come into contact as in abrasion between solid surfaces and repeated collisions among grinding media in ball mills. For understanding mechanochemical effects in ball mills, the normal impact between two grinding balls is quantified in terms of collision force, contact radius, contact time, and collision energy. These measures are quantitied as a function of ball sizes (diameters varying between 1 and 4 cm), ball material (steel and alumina), and collision velocity (0.4–4 m/s), using expressions developed by previous investigators from the principles of continuum mechanics.