Effect of Grain Size and Controlled Atmospheres on the Thermal Stability of Aluminium Titanate

Aluminium titanate (Al2TiO5) is an excellent refractory and thermal shock resistant material due to 25 its relatively low thermal expansion coefficient and high melting point. However, Al2TiO5 is only 25 thermodynamically stable above 1280° C and undergoes a eutectoid-like decomposition to α-Al2O3 and TiO2 (rutile) at the temperature range of 900-1280° C. Hitherto, the effect of grain size and 2 atmosphere on the kinetics of decomposition is poorly understood but experimental evidences suggest a nucleation and growth controlled process. In this paper, we describe the role of grain size and controlled atmospheres on the thermal stability of Al2TiO5. In particular, the effects of grain size 25 and oxygen partial pressure on the rate of isothermal decomposition of Al2TiO at 1100° C have been 25 investigated. Results show that the thermal stability of Al0TiO5 increases as the grain size and 25 oxygen partial pressure increases. However, both the on-set temperature nor the temperature range of Al2TiO5 thermal decomposition are not affected by the variation of oxygen partial pressure 25 present in the furnace atmosphere

Dynamic neutron diffraction study of thermal stability and self-recovery in aluminium titanate

Aluminium titanate (Al2TiO5) is an excellent refractory and thermal shock resistant material dueto its relatively low thermal expansion coefficient and high melting point. However, Al2TiO5 unstableand undergoes a eutectoid-like decomposition to a-Al2O3 and TiO2 (rutile) at the temperature range of900-1280C. In this paper, we describe the use of high-temperature neutron diffraction to study (a) thephenomenon of self-recovery in decomposed Al2TiO5, and (b) the role of grain size on the rate ofisothermal decomposition at 1100C. It is shown that the process of decomposition in Al2TiO5 isreversible whereby self-recovery occurs readily when decomposed Al2TiO5 is re-heated above 1300C,and the rate of phase decomposition increases as the grain size decreases

Characterization of thermal stability, microstructures and properties of Al2TiO5 - and Ti3SiC2- based ceramics

The focus of this thesis was to study the thermal stability of Al2TiO5- and Ti3SiC2-based ceramics, and the oxidation characteristics of Ti3SiC2 through in-situ x-ray and neutron diffraction. The decomposition behaviour of Al2TiO5 in controlled atmospheres was studied in the temperature range of 20–1400°C. Al2TiO5 decomposed at 1100°C but reformed at 1350°C. In vacuum or argon, Ti3SiC2 decomposed to TiCx and Ti5Si3Cx above 1200°C. In air, Ti3SiC2 oxidized to anatase at 600°C, and formed an outer layer of rutile at 750°C and an inner mixed layer of rutile and cristobalite at 1350°C. Tridymite formed during cooling from 1350°C to room temperature

Effect of differential uniform temperature with thickness-wise linear temperature gradient oninterfacial stresses of a bi-material assembly

The thermal mismatch induced interfacial stresses are one of the major reliability issues in electronic packaging and composite materials. Consequently an understanding of the nature of the interfacial stresses under different temperature conditions is essential in order to eliminate or reduce the risk of structural and functional failure. Approach: In this analysis, a model was proposed for the shearing and peeling stresses occurring at the interface of two bonded dissimilar materials with the effect of different uniform temperatures in the layers. The model was then upgraded by accounting thickness wise linear temperature gradients in the layers using two temperature drop ratios. The upgraded models were then compared with the existing uniform temperature model. The proposed model can be seen as a more generalized form to predict interfacial stresses at different temperature conditions that may occur in the layers. Results: The results were presented for an electronic bi-material package consisting of die and die-attach. Conclusion: The numerical simulation is in a good matching agreement with analytical results

Indentation Responses of Functionally-Graded Al2TiO5-Based Ceramics

Aluminium titanate, Al2TiO5 (AT) with the pseudobrookite structure is the only compound in the alumina-titania system. It is an excellent refractory and thermal shock resistant material due to its relatively low thermal expansion coefficient (1 ×10-6 ºC –1) and high melting point (1860ºC). However, its low mechanical strength, hardness and fracture resistance together with susceptibility to decomposition in the temperature range 900–1200ºC has limited its wider application. In this paper, the innovative tailored design of functionally- graded Al2TiO5 – based ceramics system was presented. This involves the use of a vacuum heat-treatment or die-pressing to form hard graded layers of alumina on Al2TiO5. These hard outer layers will provide hardness and wear resistance to protect the softer but damage resistant underlayers. The results will also explore unresolved issues concerning the effect of graded interfaces on their physical and mechanical performance properties

Mapping of Phase Compositions and Air-Oxidized Titanium Silicon Carbide (Ti3SiC2)

Ternary carbides such as Ti3AlC2 and Ti3SiC2 are nano-layered ceramics with the general formula Mn+1AXn (n=1-3), where M is an early transition metal, A is a group A element, and X is either carbon and/or nitrogen. These ceramics exhibit a unique combination of mechanical, electrical, thermal and physical properties such as good high-temperature strength, and excellent corrosion and damage resistance. For instance, the electrical and thermal conductivities of Ti3SiC2 are greater than that of titanium and its machinability is similar to graphite. However, these ceramics are susceptible to thermal dissociation at ~1400°C in inert environments (e.g., vacuum or argon) to form TiC and Ti5Si3C. The chemistry and kinetics of the dissociation processes involved are not yet fully understood. Surprisingly, the study of thermal stability in ternary carbides has received relatively little attention despite its importance in applications such as heating elements or the feasibility of designing functionally-graded Ti3SiC2-TiC with unique wear resistance and damage tolerance

Mechanical and wear properties of palm oil fuel ash reinforced aluminum metal matrix composite

The metal matrix composites consist of unique properties that make the materials become more attractive in a variety of industrial applications. Palm oil fuel ash (POFA) is produced from the burning of palm oil shell and husk fiber in generation plant boiler for energy generation that serve the palm oil extraction purposes. It has been discarded as agricultural industrial wastes. However, POFA contains a high percentage of hard silica (SiO2) which therefore makes it extremely valuable for manufacturing high strength composites materials including electronic, ceramic, polymer, glass, and construction materials industries. In this paper, it evaluated the use of Palm Oil Fuel Ash (POFA) particles in the production of Al-MMC in order to strengthen the properties of the base metal. Particle-size of 75 and different volume fraction of Palm Oil Fuel Ash (POFA) particles (5%, 10% and 15%) particulate-reinforced Al-MMCs are fabricated by using the stir casting method and tested for mechanical properties. The microstructure of the fabricated composite material are also studied and analyzed in this study. It was observed that the tensile and impact strength and wear resistance of the composite increased substantially as the volume fraction of reinforcing particle increased