Preparation Of Nano-sized Tetragonal Zirconia Powders And Determination Of Their Critical Size

With the continuous development of nano-technology,nano-materials have been widely used in all walks of life.Nano-zirconia has some excellent physical properties and chemical properties,which is a high temperature,wear-resistant,corrosion-resistant inorganic non-metallic material.Also as a very important structural and functional material,Nano-zirconia also occupies an important seat status in nano-materials.Zirconia has three homogeneous polycrystalline structures,namely monoclinic phase?m?,tetragonal phase?t?,cubic phase?c?.different crystalline ZrO₂ has different properties and applications.The basic principle of tetragonal zirconia?t-ZrO₂?reinforced toughened ceramic materials is to enhance the effect of toughened ceramics by the effect of phase structure transformation,absorbing the damage energy and suppressing the change and extension of the crack.There is a a critical particle size of phase transition for Tetragonal zirconia: if the grain size is larger than the critical size of phase change,the tetragonal phase will be transformed into a monoclinic phase;the decrease content of tetragonal phase will greatly reduce the effect of tetragonal zirconia on the toughening effect of ceramic materials.In order to keep the tetragonal phase at room temperature and maximize the toughening effect of the ceramic matrix,it is very important to study the critical phase transition particle size of tetragonal phase.In this paper,nano-sized zirconia powder was prepared by sol-gel method,Using Zr OCl₂·8H₂O as raw material,ammonia?NH₃·H₂O?and sodium hydroxide?Na OH?as precipitants.The samples mainly in tetragonal zirconia composition,with different particle size and tetragonal phase content were obtained by different treatment processes to the precursor.The particle size and phase composition of the powders were characterized by laser nano-particle size analyzer,X-ray diffraction?XRD?and scanning electron microscopy?SEM?.The content of tetragonal phase and grain size were calculated by crystal formula and Scherrer formula,and the critical particle size of phase change of tetragonal phase zirconia nano powders was ensured when adding no stabilizer and adding different stabilizers.The study draws the following conclusions:?1?The zirconia powder was prepared by sol-gel method.The zirconia powder was in microns when the p H value of the sol was 9,and the particle size Of zirconium hydroxide precursors was less than 10 nm when p H value increased to 13.and the particle size was less than 10 nm Of zirconium hydroxide precursors.use alkaline solution and deionized water to wash respectively during the process of washing gel.The result indicate that the use of alkaline solution to clean the gel could make the particle size finer,which is in a average grain size of 1.88 nm.?2?The zirconia nano powders prepared by alkaline washing process were calcined at 600?× 2h,and the content of tetragonal phase could reach 93.2%.While tetragonal phase prepared by water washing process is just in a content of 25.4% in the same preparation process.?3?It can be concluded from the relationship between the content and the particle size distribution of tetragonal zirconia phase: The critical size of the tetragonal phase transforms to monoclinic phase is 13.0nm¹3.5nm.The critical size of phase transition of zirconia nano powders stablized by magnesium oxide,calcium oxide and yttrium oxide is in a range of 24 nm?28 nm,26nm?33.6nm,18 nm?22.6nm.?4?The zirconia nano powders prepared by alkali washing process and used magnesium oxide,calcium oxide and yttrium oxide as the stabilizer were calcined at 800?×2h.The contents of tetragonal phase are 13.2%,37.7% and 81.9% respectively.zirconia stabilized by yttrium oxide can significantly increase the content of tetragonal phase at the same calcination temperature.