Effects of Multiple Metal Oxides on Properties of ZTA-5TiO 2 -5MgO Composites

Abstract

The aim of this thesis is to investigate the effects of different oxides on the properties of zirconia toughened alumina (ZTA) composites, for structural (cutting tool) and biomedical (dental and orthopedic implants) applications, through a powder mixing route, which allows tailoring the properties as well as compositions and sintering temperatures.

Alumina (Al 2 O 3 ) is the most widely used ceramic oxide. It has several inherent properties like high hardness, elastic modulus, thermal and chemical stability and excellent wear and corrosion resistivity. It also shows outstanding biocompatibility. But the major drawback of alumina is its brittleness due to its lower fracture toughness value and its sintering temperature also high. To overcome the limitations of alumina, zirconia reinforced for increasing the toughness of alumina through stress induced transformation toughening mechanism.

Zirconia toughened alumina (ZTA) is the most promising advanced structural ceramics due to its superior mechanical properties such as high hardness, strength, fracture toughness, thermal and chemical stability as well as wear and corrosion resistivity. It has been considered as a very high-performance ceramic tool due to its diverse applications in structural, mechanical, electrical, biomedical and some other advanced engineering fields. The resistance to failure of ZTA is a great technical challenge for the researchers.

Previous researches focus on the addition of different oxides to zirconia toughened alumina (ZTA) for the improvement of different physical, microstructural and mechanical properties. Addition of titania (TiO 2 ) increases density and reduces sintering temperature. Addition of magnesia (MgO) increases stability and hardness through pinning effect. Addition of ceria (CeO 2 ) also increases stability and fracture toughness by forming cerium aluminate (CeAl 11 O 18 ). Addition of calcia (CaO) increases fracture through forming elongated platelet shape hibonite (CaAl 12 O 19 ) phase.

Addition of an individual oxide increases the specific mechanical, microstructural and physical properties of zirconia toughened alumina (ZTA). But overall mechanical properties of zirconia toughened alumina (ZTA) may be improved by adding more than one or multiple oxides. So, we have in vision to add more than two oxides in ZTA (zirconia toughened alumina) for getting the best mechanical as well as thermal properties.

In this research, ZTA with 15 wt.% zirconia (ZrO 2 ) and combined with equal (5 wt.%) amount of titania (TiO 2 ) and magnesia (MgO) were prepared by conventional pressure less sintering technique through simultaneously addition of calcia (CaO) and ceria (CeO 2 ) from 0-5 wt.% consecutively at 1400-1650°C for 3 hours. The raw materials were nano grade alpha alumina (α-Al 2 O 3 ), 3 mol% yttria stabilized zirconia (3YSZ), titania (TiO 2 ), magnesia (MgO), ceria (CeO 2 ) and calcia (CaO) powders of high purity. Density, Vickers microhardness, Diametral tensile strength, Fracture toughness, Crystallite size, Cytotoxicity and Antimicrobial susceptibility test of the samples were performed.

Almost 95% of the theoretical density was obtained by this process. The Vickers microhardness value of around 11.72 GPa was also found for ZTA-5TiO 2 -5MgO with 5 wt.% CeO 2 very close to higher density. The diametral tensile strength and fracture toughness value of around 125 MPa and 13.34 MPa.m 1/2 were achieved for ZTA-5TiO 2 -5MgO and ZTA-5TiO 2 -5MgO containing 5 wt.% CeO 2 and 3 wt.% CaO combinedly. Phase contents and identification were done by using X-ray diffractometer with rietveld refinement analysis. Surface morphology with roughness properties were observed by following FESEM and AFM techniques. To ensure biocompatibility, cell viability and antimicrobial susceptibility tests were carried out. The variations in mechanical properties as well as biocompatibilities of the samples with sintering temperature and composition were studied during this research.