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

Effect of water absorption on the mechanical properties of nano-filler reinforced epoxy nanocomposites

This study aimed to investigate the effect of water absorption on the mechanical properties of nano-filler reinforced epoxy nanocomposites as well as to study the influence of different types of nano-fillers such as nano-clay platelets, halloysite nanotubes (HNTs) and nano-silicon carbide (n-SiC) particles on the water absorption behaviour of epoxy based nanocomposites. Results indicated that the addition of nano-fillers into epoxy matrix was found to decrease both water uptake and diffusivity compared to unfilled epoxy. Flexural strength and modulus of epoxy based nanocomposites were found to decrease due to the water absorption. However, the addition of nano-fillers enhanced the flexural strength and modulus of nanocomposites compared to wet unfilled epoxy. Surprising, fracture toughness and impact strength of all types of nanocomposites were found to increase after exposing to water. The presence of nano-fillers increased both fracture toughness and impact strength of nanocomposites compared to wet neat epoxy

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 mechanical and fracture behaviour in nano-silicon carbide-reinforced vinyl-ester nanocomposites

Vinyl-ester/nano-silicon carbide nanocomposites were synthesised and investigated in terms of their mechanical and fracture properties. Results show that the addition of nano-SiC particles increases modulus and strength, but reduces toughness. The enhancement in strength for nanocomposites was attributed to good interfacial adhesion and good degree of dispersion. The experimental data for elastic modulus were modelled using several theoretical models. The excellent agreement with the experimental data for elastic modulus given by the Guth and Kerner models indicate that the degree of dispersion and the quality of particle/matrix adhesion were both important considerations for the prediction of elastic modulus

An Overview of Parameters Controlling the Decomposition and Degradation of Ti-Based Mn+1AXn Phases

A critical overview of the various parameters, such as annealing atmospheres, pore microstructures, and pore sizes, that are critical in controlling the decomposition kinetics of Ti-based MAX phases is given in this paper. Ti-based MAX phases tend to decompose readily above 1400 °C during vacuum annealing to binary carbide (e.g. TiCx) or binary nitride (e.g. TiNx), primarily through the sublimation of A elements such as Al or Si, forming in a porous MXx surface layer. Arrhenius Avrami equations were used to determine the activation energy of phase decomposition and to model the kinetics of isothermal phase decomposition. Ironically, the understanding of phase decomposition via exfoliating or selective de-intercalation by chemical etching formed the catalyst for the sensational discovery of Mxenes in 2011. Other controlling parameters that also promote decomposition or degradation as reported in the literature are also briefly reviewed and these include effects of pressure and ion irradiations

In situ diffraction study of self-recovery in vacuum decomposed Al 2TiO5

The ability of decomposed Al2TiO5 to undergo self-recovery or reformation during vacuum annealing was characterised by in-situ neutron diffraction. It is shown that the process of phase decomposition in Al2TiO5 was reversible and that reformation occurred readily when decomposed Al2TiO5 was re-heated above 1300°C. The kinetics of isothermal and temperature-dependent self-recovery was modelled using the Avrami equation. The influence of grain-size on the Avrami kinetics of self-recovery was also evident

Synthesis and mechanical properties of cotton fabric reinforced geopolymer composites

Geopolymer composites reinforced with different layers of woven cotton fabric are fabricated using layuptechnique. Mechanical properties, such as flexural strength, flexural modulus, impact strength andfracture toughness of geopolymer composites reinforced with 3.6, 4.5, 6.2 and 8.3 wt% cotton fibresare studied. The fracture surfaces of the composites are also examined using scanning electron microscopy.The results show that all the mechanical properties of the composites are improved by increasingthe cotton fibre contents. It is found that the mechanical properties of cotton fabric reinforced geopolymercomposites are superior to pure geopolymer matrix

Characterization of flax fabric reinforced nano-clay geopolymer composites

Geopolymer composites reinforced with flax fabrics (FF) and nanoclay platelets are synthesised and studied in terms of physical and mechanical properties. X-Ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscope (SEM) techniques are used for phase and microstructure characterisation. The nanoclay platelets are added to reinforce the geopolymer matrices at 1.0%, 2.0%, and 3.0% by weight. It is found that 2.0 wt.% nanoclay enhances the density, decreases the porosity and subsequently improves the flexural strength and toughness. The microstructural analysis results indicate that the nanoclay behaves not only as a filler to improve the microstructure of the binder, but also as an activator to support the geopolymeric reaction producing higher content of geopolymer gel. This enhances the adhesion between geopolymer matrix and flax fibres, which improves the mechanical properties of the geopolymer nanocomposites reinforced with flax fabrics

Characterisation of micro-sized and nano-sized tungsten oxide-epoxy composites for radiation shielding of diagnostic X-rays

Characteristics of X-ray transmissions were investigated for epoxy composites filled with 2–10 vol% WO3 loadings using synchrotron X-ray absorption spectroscopy (XAS) at 10–40 keV. The results obtained were used to determine the equivalent X-ray energies for the operating X-ray tube voltages of mammography and radiology machines. The results confirmed the superior attenuation ability of nano-sized WO3-epoxy composites in the energy range of 10–25 keV when compared to their micro-sized counterparts. However, at higher synchrotron radiation energies (i.e., 30–40 keV), the X-ray transmission characteristics were similar with no apparent size effect for both nano-sized and micro-sized WO3-epoxy composites. The equivalent X-ray energies for the operating X-ray tube voltages of the mammography unit (25–49 kV) were in the range of 15–25 keV. Similarly, for a radiology unit operating at 40–60 kV, the equivalent energy range was 25–40 keV, and for operating voltages greater than 60 kV (i.e., 70–100 kV), the equivalent energy was in excess of 40 keV. The mechanical properties of epoxy composites increased initially with an increase in the filler loading but a further increase in the WO3 loading resulted in deterioration of flexural strength, modulus and hardness

Characteristics of nanoclay and calcined nanoclay-cement nanocomposites

The influence of nanoclay (NC) and calcined nanoclay (CNC) on the mechanical and thermal properties of cement nano-composites presented. Calcined nanoclay is prepared by heating nanoclay (Cloisite 30B) at 900 °C for 2 h. Characterisation of microstructure is investigated using Quantitative X-ray Diffraction Analysis (QXDA) and High Resolution Transmission Electron Microscopy (HRTEM). Estimation of Ca(OH)<inf>2</inf> content in the cement nanocomposite is studied by the combination of QXDA and thermogravimetry analysis (TGA) techniques. Results showed that the mechanical and thermal properties of the cement nanocomposites are improved as a result of NC and CNC addition. An optimum replacement of ordinary Portland cement with 1 wt% CNC is observed through reduced porosity and water absorption as well as increased density, compressive strength, flexural strength, fracture toughness, impact strength, hardness and thermal stability of cement nanocomposites. The microstructural analyses from QXRA and SEM indicate that the CNC acted not only as a filler to improve the microstructure, but also as the activator to support the pozzolanic reaction. Cost-benefit analysis indicates that nanoparticles are expensive but from economic point of view nanoclay is used in very small amount (i.e. 1 wt. %) in cementitious materials. As a result nanoclay does not add any significant cost but improves the mechanical properties significantly