Preparation of Nanocrystalline Calcia-Stabilized Tetragonal Zirconia by High-Energy Milling of Baddeleyite Andrey O. Zhigachev,* Alexey V. Umrikhin, and Yuriy I. Golovin Nanocenter “Nanotechnology and Nanomaterials”, G.R. Derzhavin Tambov State University, Tambov, The Tambov Region, 392 000, Russia Boris Y. Farber Zircoa Inc, Solon, OH 44139 For the first time, zirconia nanocrystalline powders were derived using baddeleyite as raw material by ultrafine milling. Pow- ders containing 19 vol% of monoclinic phase were produced by milling of baddeleyite with addition of 11 mol% of CaO. Crys- tallite size of tetragonal and cubic phases in resulting powders is 3–5 nm and about 15 nm in the case of monoclinic phase. Typical agglomerate’s size found by scanning electron microscopy ranges from ~0.1 to 10 μm. Sintered ceramics with tetragonal zirconia content of 95 vol% and crystallite size of ~50 nm are produced from the powders. Introduction Zirconia is known to exist at ambient pressure in three different crystallographic forms: monoclinic, tetrag- onal, and cubic. 1 Phase composition of zirconia ceramics is generally determined by temperature, concentration of stabilizing metal oxide (CaO, MgO, Y 2 O 3 , CeO 2 ), and crystallite size. 2 Zirconia possesses a unique combination of properties: high-temperature stability (up to 2500°C), chemical inertness, thermal shock resistance, high hardness and fracture toughness, 3 and high ionic conductivity. 4 Modification of phase composition allows material properties tailoring for a wide range of applications. 1,5 The well-known Y-TZP and Ce-TZP — high-qual- ity fine-grained ceramics with superior mechanical char- acteristics — are usually produced from high-purity chemically precipitated zirconia. Zircon (zirconium silicate) is used as a source raw material for production of chemically precipitated zirconia. There are some results showing that zirconia ceramics with controlled properties can also be synthesized from naturally occurring mono- clinic zirconia — baddeleyite 6,7 ; however, it is not yet demonstrated that fine-grained zirconia ceramics can be produced from this material. Use of baddeleyite provides a possibility of synthesis of zirconia ceramics without expensive and complicated chemical treatment of zircon. An obvious challenge for this task is finding an eco- nomic processing route to obtain a fine-grained zirconia powder from baddeleyite. Due to chemical inertness of zirconia, traditional chemical precipitation approach for baddeleyite processing will be too complicated and expensive. It is known that nanocrystalline ceramic pow- ders can be derived by ultrafine milling, 8 although mill- ing effect on structure and phase composition of zirconia powders was considered mostly for chemically precipitated zirconia. 9–11 In this work, we studied possibility of synthesis of fine-grained zirconia ceramics from baddeleyite by ultra- fine milling, using CaO as phases stabilizer. 12 Experimental Procedure Baddeleyite concentrate (Kovdor, Russia) was used as a raw material. Its chemical composition is given in Table I. 13 Ultrafine milling of the baddeleyite concen- trate was carried out in a planetary mill (Pulverisette 7 Premium Line, Fritsch, Germany). Baddeleyite powders with no addition of stabilizer were dry milled for 2.5, 5, 10, 15, 25 h, with respec- tive analysis of powders derived after each period of milling. Milling for 5 h was found to be optimal in terms of milling efficiency of raw baddeleyite (see Results and Discussion). For that reason we used 5 h milling time for stabilized composition with reagent grade calcia (Reachem, Moscow, Russia) content — 11 mol%. Concentration of CaO was chosen to obtain coex- istence of tetragonal and cubic phases in a solid solution of calcia in zirconia 12 to avoid spontaneous tetragonal to monoclinic transformation in “understabilized” grains. *andreyzhig2009@gmail.com © 2015 The American Ceramic Society Int. J. Appl. Ceram. Technol., 1–8 (2014) DOI:10.1111/ijac.12377