Aluminum Titanate Research Articles

EPD and spark plasma sintering of bimodal alumina/titania concentrated suspensions

Alumina–aluminium titanate (A–AT) composites and laminates have been recently investigated because they can provide improved flaw tolerance and toughness associated to a microcracking mechanism. A–AT composites have been produced by slip casting and reaction sintering of submicron sized alumina and titania powders. This work deals with the preparation of thick self-sustained A–AT films from mixtures of submicron sized alumina and nanosized titania powders and further sintering by conventional and non-conventional (spark plasma sintering, SPS) methods. Suspensions were prepared in water to high solid loadings, up to 50 vol.%. Self-sustained films were obtained by aqueous electrophoretic deposition (EPD) using graphite substrates under constant current density conditions. The evolution of mass per unit area with current density and deposition time was recorded. The films were characterized in the green state and after sintering at different temperatures (1300–1400) °C. Fully dense A–AT reaction sintered materials were obtained at low temperature by SPS.

High‐Temperature Flexural Strength and Thermal Stability of Near Zero Expanding doped Aluminum Titanate Ceramics for Diesel Particulate Filters Applications

A substantial increase in sinterability, high‐temperature flexural strength, thermal stability in combination with an average thermal expansion of 0.42 × 10−6/°C (30–1000°C) is achieved through magnesium silicate (Mg3Si4O10(OH)2) doping of Aluminum Titanate (Al2TiO5) ceramics. Doped specimens exhibited the sintered density of 99% of theoretical density at 1550°C and a maximum enhancement of 169.23% (70 MPa) in flexural strength at 1200°C as compared with 26 MPa measured at 30°C. Enhancement of flexural strength at elevated temperature can be attributed to the increasing extent of thermally activated crack blunting with increasing temperature, which is further evident from the dilatometric hysteresis curve recorded for these samples. XRD investigations of undoped (Al2TiO5, AT) samples annealed at 1100°C for 5 and 10 h have shown clear evidence of decomposition to precursor oxides by 7% and 21.13%, respectively. However, the samples of magnesium silicate–doped Al2TiO5 (TAT) under identical conditions have shown no sign of decomposition, indicating significantly high thermal stability. TAT formulations were also extrusion processed to investigate the suitability of forming cellular honeycomb structures. TAT formulation with superior thermo‐mechanical properties and excellent adaptability for extrusion processing can be explored for the development of next generation diesel particulate filters (DPF).

Porous microcracked ceramics under compression: Micromechanical model of non-linear behavior

Abstract Stress–strain curves for porous microcracked ceramics (such as aluminum titanate) under compression exhibit non-linearity, hysteresis, and a sharp increase in stiffness when changing from loading to unloading. A micromechanical model is developed that expresses these features in terms of porosity and crack density. The mentioned features are linked, in a quantitative way, to closures and frictional sliding of microcracks. The model also allows one to extract information on crack densities from stress–strain curves, which provides insight into the evolution of open, closed and sliding cracks. The model is approximate due to uncertainty factors, but its predictions are generally in agreement with the data and the information conveyed by SEM images.

Preparation of the Ceramic Hollow Balls of Aluminium Titanate-Based by Rolling-Ball Method

Aluminium titanate - based hollow balls were prepared by using aluminum titanate, mullite and magnesia aluminate spinel as starting materials followed by the rolling-ball method. The effect of different pore-making agents (namely the amylum, flour, millet and urea) on the forming properties and the apparent qualities of the precursors of the hollow balls were investigated. The results show that the precursors of the hollow balls own both good forming properties and apparent qualities when using the amylum as pore-making agent; an appropriate heat treatment was carried out on the above precursors, and the obtained hollow balls have particle size of 5 mm, aperture diameter of 3 mm and wall thickness of 1 mm; the average compressive strength of the hollow balls reaches 15.0 N. Since this method is very simple and effective for preparation of the hollow balls, it may provide a new approach for preparation of high performance heat insulation-porous materials.

Modeling the impact of microcracking on the thermoelasticity of porous and microcracked ceramics

The foundations of the Integrity Factor Model are laid down and the model is discussed. The calculation of the internal stresses in microcracked materials (as a function of temperature) is done on the basis of both the macroscopic dilation and the lattice expansion measured by diffraction. The derivation is made starting from first principles for a single crystal, and then extending the approach to polycrystals, including complex microstructures, such as those containing porosity, microcracks, and multiple phases. Focus is cast on the fundamentals of the relationship between material properties and microstructure of anisotropic crystals, and on the resulting macroscopic behavior. The model is validated against experimental data, with the examples of the microcracked β-eucryptite and porous microcracked aluminum titanate composite.

Preparation of nano-sized Mg 0.6 Al 0.8 Ti 1.6 O 5 powders using the inorganic salts route

Abstract Stable magnesium aluminum titanate ceramics (Mg0.6Al0.8Ti1.6O5) compound has been successfully synthesized with a straightforward non-hydrolytic sol–gel process using an inorganic metal compound as cation source supplier at about 600 °C. The raw materials MgCl2·2H2O, AlCl3, TiCl4, and citric acid were dissolved in ethanol. Prepared gel was dried at 120 °C and calcined at various temperatures in an electric furnace. The results of X-ray diffraction (XRD) and simultaneous thermal analysis (STA) demonstrate that the direct crystallization of mono-phase magnesium aluminum titanate from fluffy precursor at a temperature below aluminum titanate decomposition temperature range is feasible. Field emission scanning electron microscopy (FESEM) and Brunauer–Emmett–Teller (BET) analysis show the nano-metric size of particles. The particle size and specific surface area of the powders varied from 16.5 to 27.6 nm and from 98.2 to 58.7 m2 g−1 according to calcination temperatures (600 and 700 °C), respectively. The nano-particles had a strong tendency to agglomerate and were partially sintered at 1100 °C.

Synthesis of Aluminum Titanate Powder at Low Temperature via Nonhydrolytic Sol-Gel Method by Using Aluminum Powder

Aluminum titanate (Al2TiO5) powder has been synthesized at low temperature via nonhydrolytic sol-gel method by using aluminum powder as aluminum source, titanium tetrachloride as titanium source, anhydrous ethanol as oxygen donor with different catalysts. The phase transformation of aluminum titanate xerogel powder during heat treatment and the influence of the mixing orders of raw materials, catalyst kinds on the synthesis of aluminum titanate were investigated by means of differential-thermal analysis (DTA-TG), X-ray diffraction (XRD), transmission electron microscope (TEM). The results indicated that aluminum titanate powder was easily synthesized at 750 °C by using AlCl3 as catalyst with a mixing order of adding TiCl4 before AlCl3 into aluminum alcohol mixture. The catalytic order of the different catalysts in the preparation process of aluminum titanate is: FeCl3> AlCl3> MgCl2. The catalyst promoted the activation of metal aluminum powder and played a major role in the synthesis of aluminum titanate powder at low temperature via nonhydrolytic sol-gel method.

Effect of Gelation Process on Preparation of Aluminum Titanate Ultrafine Powder by Hydrolytic Sol-Gel Method

Aluminium titanate (AT) ultrafine powder was prepared via hydrolytic sol-gel (HSG) method using aluminium nitrate (Al (NO3)3·9H2O) and titanium tetrachloride (TiCl4) as precursors as well as ethanol as solvent. Water required for hydrolysis reaction was supplied by the crystal water of aluminium nitrate itself. The effect of gelation processes, i.e. reflux and solvothermal treatment, on synthesis of AT powder was investigated by means of DTA-TG, XRD, SEM, and TEM, etc. The result shows that the gelation process has significant effect on the synthesis of AT powder. By reflux process, AT powder was synthesized at 1350 °C with average particle size above 1μm and serious agglomeration. Through solvothermal treatment process, however, AT powder with average particle size less than 150 nm was prepared at 1050 °C at a relatively high synthesis rate, which is due to the refinement reactants by the solvothermal treatment.

Research on Mullite-Corundum-Aluminium Titanate Composite

Mullite-aluminium titanate-corundum composite was prepared at 1300°C with refractory clay, aluminium titanate and high alumina grog as raw material, molded at pressure of 50MPa. Effect of raw material ratio on sintering and themal shock resistance of the mullite-aluminium titanate-corundum composite was researched by measurements of apparent porosity, bending strength and residual strength after water-cool, and analyses of XRD and SEM. The results showed that as refractory clay content, apparent porosity of samples decrease, bulk density and bending strength increase. When the weight ratio of refractory clay, aluminium titanate and high alumina grog is 60/10/30, themal shock resistance of sample is excellent, The XRD and SEM analysis results indicated that the mechanical and thermal proprieties are relative to the microstructure and crystal phases of the composite materials.

Screening protocol for identifying inorganic oxides with anti-oxidant and pro-oxidant activity for biomedical, environmental and food preservation applications

Free radicals are known to play a key role in the human body. When considering potential biomaterials, their interaction with free radicals needs to be considered at an early exploratory stage. In this contribution, we identify inorganic oxides that exhibit a free radical scavenging capacity. A convenient screening protocol was developed for identifying the anti-oxidant properties of highly dispersed inorganic materials. The method compares the degradation of an organic dye with radicals in the absence and presence of the material under investigation. The radicals are generated via Fenton chemistry over a heterogeneous goethite catalyst in a phosphate buffer. The procedure conveniently evaluates the anti- or pro-oxidant capacity of a large set of materials with routine laboratory equipment. Semi-quantitative EPR measurements of the radical concentration using a spin-trapping agent were used to validate the screening procedure. Besides the documented cerium oxide, four other materials were identified to exhibit comparable or even better anti-oxidant activity: aluminium titanate, antimony oxide, titanium silicalite-1 zeolite and titanium xonotlite; pro-oxidant activity was demonstrated for several zeolites.

Pressure slip casting and cold isostatic pressing of aluminum titanate green ceramics: A comparative evaluation

Aluminum titanate (Al2TiO5) green bodies were prepared from mixture of titania and alumina powders with different particle sizes by conventional slip casting (CSC), pressure slip casting (PSC) and cold isostatic pressing (CIP). Precursor-powder mixtures were evaluated with respect to the powder properties, flow behaviours and shaping parameters. Green densities were measured and correlated with the fractographs. A substantial increase in green densities up to 60 %TD (theoretical density of 4.02 g/cm3, calculated based on rule of mixtures) is observed with the application of 2-3 MPa pressure with PSC. While particle size distribution and solid loading are the most influential parameters in the case of CSC, with PSC pressure also plays a key role in achieving the higher green densities. Being a dry process, high pressure of > 100 MPa for CIP is essential to achieve densities in the range of 60-65 %TD. Slip pressurization under PSC conditions facilitate the rearrangement of particles through rolling, twisting and interlocking unlike CIP processing where pressure is needed to overcome the inter-particle friction.

Friction and wear performance of nickel and molybdenum-reduction cast iron composite brake blocks including ceramic foams

High speed trains in the northern area of Japan use alloyed cast iron brake blocks including nickel (Ni) and molybdenum (Mo). Reducing the Ni and Mo contents of the alloyed cast iron brake blocks would be beneficial because they are rare metals with variable prices. Ni and Mo play important roles in increasing the friction coefficient and decreasing the wear of brake blocks at high speeds. Brake blocks with reduced contents of these metals must maintain a sufficient friction coefficient and wear characteristics at high speeds. Cast iron composite brake blocks with reduced Ni and Mo contents were prepared using two types of alumina: aluminum titanate and silicon carbide foams to maintain the friction coefficient and decrease the wear characteristics at high speeds. These blocks were tested on a full-scale dynamometer, and the friction and wear performance of one of the best performing blocks were tested under real operating conditions. The friction coefficients of all reduced Ni, Mo cast iron composite brake blocks were higher than those of conventional blocks at high speeds. The wear of the reduced Ni, Mo cast iron composite brake blocks containing alumina blended with aluminum phosphate (AlPO4) foam was significantly decreased as compared with that of conventional blocks. Under real operation, the friction coefficients of conventional and reduced Ni, Mo brake blocks were similar under normal braking conditions, but those of conventional brake blocks were lower than those of the reduced Ni, Mo blocks under emergency braking conditions. The lower friction coefficient of conventional brake blocks under emergency braking conditions is likely caused by the adhesion of wear particles to the wheel tread. While the wheel tread was not worn by conventional brake blocks, it was worn by the reduced Ni, Mo blocks under emergency braking conditions.

Enhanced properties of alumina–aluminium titanate composites obtained by spark plasma reaction-sintering of slip cast green bodies

Full dense alumina+40vol.% aluminium titanate composites were obtained by colloidal filtration and fast reaction-sintering of alumina/titania green bodies by spark plasma sintering at low temperatures (1250–1400°C). The composites obtained had near-to-theoretical density (>99%) with a bimodal grain size distribution. Phase development analysis demonstrated that aluminium titanate has already formed at 1300°C. The mechanical properties such as Vickers hardness, flexural strength and fracture toughness of bulk composites are significantly higher than those reported elsewhere, e.g. the composite sintered at 1350°C show values of about 24GPa, 424MPa and 5.4MPam1/2, respectively. The improved mechanical properties of these composites are attributed to the enhanced densification and the finer and more uniform nanostructure achieved by non-conventional fast sintering of slip-cast dense green compacts.

Effect of Titania Additive on Structural and Mechanical Properties of Alumina–Fluorapatite Composites

Mechanical properties of alumina–fluorapatite composites with different titania additive amounts (0, 0.5, 1, 1.4, 2, 3, 4 and 5 wt%) have been investigated between 1200 and 1600 °C. The optimum values of densification and mechanical properties of composites have been reached with 1.4 wt% of titania after the sintering process at 1500 °C for 1 h. Thus, the rupture strength of alumina–26.52 wt% Fap–1.4 wt% TiO 2 reaches 75 MPa. At higher temperature and beyond 1.4 wt% TiO 2 , the densification and mechanical properties were hindered by the formation of both intergranular porosity and secondary phase. X-ray diffraction (XRD) analysis of alumina–Fap–TiO 2 composites shows the formation of aluminium titanate (Al 2 O 3 –TiO 2 : Al 2 TiO 5 ). The 27 Al magic angle scanning nuclear magnetic resonance analysis of Al 2 O 3 –Fap–TiO 2 composites reveals the presence of octahedral and pentahedral aluminium and novel environment relative to tetrahedral aluminium sites.

Impact of the non-linear character of the compressive stress–strain curves on thermal and mechanical properties of porous microcracked ceramics

Abstract Complementary to recent theoretical work, this paper describes implications of the non-linear stress–strain behavior observed in porous microcracked ceramics. Practical aspects of this behavior under uniaxial compression are discussed. In particular, it is shown that the axial moduli of porous microcracked aluminum titanate and cordierite change upon application of a constant or ladder-like time protocol load. The extent of change depends on material microstructural features, such as texture, porosity and microcrack density, as well as on the applied load. In fact, the underlying mechanism is microcrack closure (or even healing), which causes stiffening of the material; at the same time, a uniaxial compressive load can also open new microcracks, or propagate existing ones via microcrack sliding, thus softening the material. The change in the elastic response of the material is accompanied by changes in other properties, such as thermal expansion.

Mineral-Oxide-Doped Aluminum Titanate Ceramics with Improved Thermomechanical Properties

Investigations were carried out, on the effect of addition of kaolinite (2Al2O3·3SiO2·2H2O) and talc (Mg3Si4O10(OH)2) in terms of bulk density, XRD phases, microstructure, as well as thermal and mechanical properties of the aluminium titanate (AT) ceramics. AT ceramics with additives have shown enhanced sinterability at 1550°C, achieving close to 99% of TD (theoretical density) in comparison to 87% TD, exhibited with pure AT samples sintered at 1600°C, and found to be in agreement with the microstructural observations. XRD phase analysis of samples with maximum densities resulted in pure AT phase with a shift in unit cell parameters suggesting the formation of solid solutions. TG-DSC study indicated a clear shift in AT formation temperature with talc addition. Sintered specimens exhibited significant reduction in linear thermal expansion values by 63% (0.4210−6/C, (30–1000°C)) with talc addition. Thermal hysteresis of talc-doped AT specimens showed a substantial increase in hysteresis area corresponding to enhanced microcrack densities which in turn was responsible to maintain the low expansion values. Microstructural evaluation revealed a sizable decrease in crack lengths and 200% increase in flexural strength with talc addition. Results are encouraging providing a stable formulation with substantially enhanced thermomechanical properties.

Incorporation of lead and titanium into a porous alumina membrane during Pb(Zr0.52Ti0.48)O3 nanotube synthesis

We report the identification and characteristics of lead aluminate (Pb2Al2O5 or PbAl12O19)/aluminum titanate (Al2TiO5) formed as a result of the interaction between a Pb(Zr0.52Ti0.48)O3 (PZT) precursor and a porous alumina membrane (PAM) during PZT nanotube synthesis. The surface morphology and composition of PZT nanotubes were examined as a function of the etching time and annealing temperature, and the diffusion of elements over nanometer length scales during PZT nanotube formation was investigated based on analysis using field emission transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray microscopy. As the annealing temperature increased, the volume of lead aluminate/aluminum titanate increased, suggesting that considerable diffusion of Pb and Ti occurred and, in turn, dramatically affected the nanotube characteristics. The diffusion of Pb and Ti was clearly evident, resulting in the formation of a distinct lead aluminate/aluminum titanate at the PZT nanotube/PAM interface.

Microstructure and mechanical properties of Al2O3–20 wt%Al2TiO5 composite prepared from alumina and titania nanopowders

In the present work, Al2O3–20wt%Al2TiO5 composite was prepared from reaction sintering of alumina and titania nanopowders. The nano-sized raw powders were reconstituted into nanostructured particles by ball milling. Then, the nanostructured reconstituted powders were pressed and pressureless-sintered into bulk ceramics at 1300, 1400, 1500°C for 2h. The phase composition and microstructures of reconstituted powders and as-prepared ceramic composites were characterized by using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope and energy-dispersive spectrometer (EDS). The microstructural analysis of the ceramic showed that the average grain size of the alumina–aluminium titanate composite increases with increasing the temperature. Also, SEM proved the existence of a proper interface between Al2TiO5 and Al2O3 grains and preferential distribution of aluminium titanate particles in the grain boundaries. XRD analysis indicated the absence of rutile titania in the sintered composite ensuring complete formation of aluminium titanate. The hardness of the samples sintered at 1300, 1400, 1500°C were 4.8, 6.2 and 8.5GPa, respectively.

Application of optical methods to investigate the non-linear asymmetric behavior of ceramics exhibiting large strain to rupture by four-points bending test

Abstract Large strain to rupture behavior is essential, for refractory materials, to improve their thermal shock resistance. The non-linear comportment under loading of specific developed ceramics associated to their type of microstructure (micro-cracked) leads to the possibility to increase their strain-to-rupture level. Aluminum titanate (AT: Al 2 TiO 5 ) ceramics are one of these materials and are characterized by a mechanical behavior strongly dependent on their microstructure. Indeed, this behavior can vary from a fragile one to a large non-linear one according to the degree of microcracking present within the material. The paper here presented is devoted to the study of this nonlinear behavior thanks to four-points bending test associated with digital image correlation technique to determine kinematics fields. Results highlight the asymmetric character of the mechanical behavior of a microcracked aluminum titanate. A comparison between the Young moduli and fracture strength obtained using conventional and ones identified by digital image correlation will be done.

Nanoindentation of Al2O3/Al2TiO5 composites: Small-scale mechanical properties of Al2TiO5 as reinforcement phase

Abstract The mechanical properties of alumina/aluminum titanate composites (Al 2 O 3 /Al 2 TiO 5 ) were evaluated and analyzed by nanoindentation. Indentations with different penetration depths were performed, and residual imprints on specimens were located and observed by combining complementary characterization techniques. The mechanical response of composites was found to be determined by grain size of alumina and aluminum titanate, as evaluated from indentations performed at 1500 nm of penetration depth. On the other hand, small indents in individual grains permitted to assess the hardness as well as the elastic modulus of non-cracked particles of Al 2 TiO 5 through implementation of different analytical indentation models. The attained values for the local mechanical properties were validated through critical comparison of them with those predicted by the rule of mixtures. Results showed no evidence of microcracking on grains of the reinforcing phase for all the tested composites, before and after low penetration depth indentations. Elastic modulus of Al 2 TiO 5 was found to be higher than the values reported on bulk aluminum titanate, presumably because of the absence of microcracking for small grain sizes. The bulk composite mechanical response is finally discussed on the basis of contributions from those of the individual phases.