Phase development in system ZrO2-CaO

Čvrste otopine sustava ZrO2−CaO sintetizirane su primjenom dviju različitih sintetskih metoda: koprecipitacijom polaznih vodenih otopina, te kugličnim mljevenjem polaznih nitratnih soli. Dobiveni prekursori analizirani su pomoću DSC analize i kalcinirani na zraku na temperaturama do 1000 °C te analizirani na sobnoj temperaturi pomoću Ramanove spektroskopije, PXRD, FE−SEM i EDS analize. Fazni razvoj u sustavu ZrO2-CaO ovisi o korištenoj metodi sinteze prekursora. Precizno su određeni parametri jedinične ćelije ZrO2 tipa čvrstih otopina pomoću Rietveldovog utočnjavanja. Maksimalna topljivost Ca2+ iona (~ 45 % množinskog udjela) pojavila se u amorfnim prekursorima ZrO2 faze. Žarenje na 1000 °C smanjuje topljivost Ca2+ iona na ~ 24 %. Porastom udjela Ca2+ u čvrstim otopinama značajno se smanjuje vrijednost parametra c tetragonskog polimorfa te je određena granica prijelaza iz metastabilne tetragonske u stabiliziranu kubičnu formu kod ~ 14 % množinskog udjela kalcija.Solid solutions of the system ZrO2−CaO were synthesised using two synthetic routes: co−precipitation from aqueous solutions and ball milling of the corresponding nitrate salts. The obtained precursors were analysed using DSC and calcined in air at temperatures up to 1000 °C. Calcined samples were analysed at RT using PXRD, Raman spectroscopy, FE−SEM and EDS. The phase development of ZrO2-CaO system depend on the synthetic route used to obtain starting precursors. Precise unit-cell parameters of the ZrO2-type solid solutions were determined by using Rietveld refinements of the powder diffraction patterns. Maximum solubility of Ca2+ ions (~ 45 mol%) occured in the amorphous precursors to the ZrO2−type phase. Thermal treatment at 1000 °C decreased the solid solubility of Ca2+ ions to ~ 24 mol%. By increasing Ca2+ content the lattice parameter c in tetragonal polymorph of zirconia decreases rapidly and tetragonal to cubic phase boundary in stabilized ZrO2 was located around 14 mol% Ca