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The Preparation and Surface Modification of Nano-zirconia Powder

Author: GuoJiangTao
Tutor: MaTieCheng
School: Dalian University of Technology
Course: Materials Science
Keywords: microemulsion combustion nano-zirconia preparation surface modification mechanism
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Type: Master's thesis
Year: 2009
Downloads: 24
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Abstract

Zirconia is a very important engineering and functional oxide ceramics due to its highmelting point (~2700℃), low thermal conductivity, high ionic conductivity, excellentmechanical properties and good chemical performances. Moreover, the appliances which aremade by ultrafine ZrO2powders such as solid-state electrolyte, oxygen sensors, catalystsupport, thermal barrier coating, optical fiber connectors and toughened ceramics, are usedwidely in various fields. Especially in recent20years, zirconia ceramics have attracted lots ofresearchers’ attentions. Usually, components made by nano-zirconia powders tend to attainbetter performance in the application fields, which has acted as a driving force for thedevelopment of novel preparative routes for ultrafine ZrO2powders.Although the appliances’ performance relate with zirconia powders heavily, how tosynthesising of spherical ZrO2powder powder with uniform size distribution and gooddispersibility is still a very big challenge. Based on combustion synthesis and microemulsionmethod, a improved design was done on the process of preparing nano-zirconia powder, and asaving time and energy consumption, convenient and rapid technology was developed. Fornano-powders have small particle size, large surface area and high activity. They are oftenheavily agglomerated during transportation, storing and sintering，resulting in unfavorableinfluence on their properties. In order to solve this problem，Powder surface modification wasadopted in this paper. All the affecting factors were investigated and the property of thepowder was characterized by XRD, TEM, SEM, IR, Laser particle size analysis and thecombustion mechanism of this novel preparation route was also explored. Furthermore, aphysical model of powder preparing by microemulsion-combustion method was established.The main research work and results are as follows:(1) The precipitations were formed in the water droplets by dropping concentrated aque-ous ammonia as precipitator to the microemulsion system of cyclohexane/water(precursorsolution)/TritonX-100/isobutyl alcohol. The influence of zirconium salt solution concen-tration、pH of the mixture and appropriate ratio among the oil/water/surfactant phase are analyzed. The result shows that the concentration of zirconium salt solution has no remarkabeinfluence, the ratio among the oil/surfactant/assistant surfactant phase should be10:3:2andthe pH of the mixture must reach9.0in the end of the precipitation process.(2) A certain amount of concentrated aqueous nitric acid was added to the mixture afterthe precipitation process, which could accelerate the phase separation and act as oxidant agentin the following heat treatment process. In the heat treatment step, the precipitationcontinuously bulged according to the volatility gas such as HCl, NH3and H2O(g) beingreleased, while the heat energy which come from the combustion process accelerated thedecomposition of Zr(OH)4. The pH of the mixture after added concentrated aqueous nitricacid should be in2~3.(3) Compared with the powders which were prepared of microemulsion method under650℃heat treatment for2hours. In the microemulsion-combustion method,the employmentof nitric acid in the synthesis system was confirmed to have accelerated combustion,depressed agglomerate, shortened synthesis time and favored to obtain sphericalnanostructured ZrO2powders with crystallites having a mean diameter smaller than30nmunder calcined temperature of550℃for2hours.(4) A reaction occured at the surface of ZrO2powders and phthalate when they wereunder ultrasonic dispersion in toluene solvent. Since so many-OH bonds exist onnanostructured ZrO2powders, which can work with-COOH bonds existed in phthalatemolecules and H2O borned. After the mixture was heated, water was removed from thetoluene solvent and a thin film made of phthalate molecules coated on the the surface of ZrO2powders.The phthalate coated nano-zirconia powder is very stable in atmosphere, which isheplful to the application of nano-zirconia powder.

The Preparation and Surface Modification of Nano-zirconia Powder

Abstract

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