Oxide glasses have unique thermal properties. In the present work, it was investigated that how the thermal properties vary with composition. In this work, the ternary glasses of the form 40TeO2-(60-x)V2O5- xNiO with different molar percentage 0≤x≤20 have been prepared by standard rapid melt-quenching method. DSC curves of these ternary glasses have been investigated in the range (150- 500oC) at heating rates φ=3, 6, 9, 10 and 12K/min. Then, using their crystallization temperature (Tcr) and Avrami index (n), their crystallization activation energy (Ec) were calculated. Generally, results of this work show that the decreasing trend of crystallization activation energy, which can be attributed to the increasing of non-bridging oxygen's and increasing of fragility. The obtained values of (n) show that it fluctuates around n≈ 1, which can be attributed to surface or one-dimensional crystal growth of probably needle-like tellurium crystals.
In this research, the densification of magnesia nanopowder with a mean particle size of about 100 nm was investigated by spark plasma sintering undera pressures of 80 MPa and at temperature range from 1000 °C to 1400 °C and a heating rate of 50 °C/min for 20 minutes. The density of the samples slowly increased with increasing sintering temperatures to 1200 °C. Afterwards, with more increasing of temperature, decreasing density and increasing of grain growth were observed. Grain growth was analyzed during the sintering process with the classic grain growth theory. The results of the survey on the density showed that the highest densification rate occurred at 1100 ℃. The activation energy of grain growth was Obtained 452.24 kJ / mol. The MgO ceramic spark plasma sintered at 1200 °C for 20 min demonstrated the highest infrared transmittance of 67 % at the 5.6 μm wavelength.
In the present research work, (60-x)V2O5-xNiO-40TeO2 amorphous bulk compositions with different molar percentages of 0≤x≤20 mol%, were prepared by well-known rapid melt-quenching method. Differential scanning calorimetry (DSC) at different heating rates (φ) was used to thermal analyze and to obtain more insight in to the thermal stability, glass forming tendency and so calorimetric characteristics of the present glasses. The characteristic temperatures such as glass transition temperature (Tg), the temperature corresponding to the onset of crystallization (Tx) and also the crystallization temperature (TCr) were obtained at different heating rates, to evaluate the key kinetic parameter of activation energy of crystallization (Ec) by using Ozawa and Kissinger methods. Generally, results of this work show that the glass with x=10 has the highest thermal stability and glass forming tendency and so has very good resistance against thermal shocks; for the understudied samples, one can observe the decreasing trend of crystallization activation energy with increase of NiO content, which can be resulted by increasing of non-bridging oxygen's (NBOs).
