Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 20Citation - Scopus: 24Preparation of Monodisperse Silica Spheres and Determination of Their Densification Behaviour(Elsevier Ltd., 2014) Topuz, Berna; Şimşek, Deniz; Çiftçioğlu, MuhsinMonodisperse silica spheres in the 50-520 nm size range were prepared by using the Stober process. Diffusive growth has been determined from Nielsen chronomal analysis for the 520 and 310 nm monodisperse silica spheres. The densification behaviour and evolution of the microstructure of the sphere compacts indicated an inverse dependence of shrinkage rate on the sphere size due to viscous sintering. The increase in sphere size from 50 to 500 nm shifted the densification temperature from ∼ 1120 °C to 1240 °C. The amorphous nature of the spheres was conserved up to 1200 °C where cristobalite crystal nucleation started and complete transformation to cristobalite phase has been observed upon heat treatment at 1300 °C. The activation energies for viscous sintering according to the Frenkel and Mackenzie/Shuttleworth models were calculated as 125 and 335 kJ/mol, respectively. These substantially low activation energies can be attributed to the presence of a significant level of silanol groups.Article Citation - WoS: 22Citation - Scopus: 28The Effect of Zinc Stearate on Thermal Degradation of Paraffin Wax(Springer Verlag, 2008) Gönen, Mehmet; Balköse, Devrim; İnal, Fikret; Ülkü, SemraIn this research, the effects of zinc stearate addition on paraffin wax degradation were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energies of wax decomposition in nitrogen and air atmospheres were determined as 76 and 37 kJ mol-1, respectively applying Kissinger method to TG data. The degradation rate constants of paraffin containing zinc stearate (0.1-0.5%) were found to be almost two times greater than that of paraffin only in air atmosphere. However, zinc stearate did not affect the rate constants in nitrogen significantly.