Formation Of Aluminium Titanate Research Articles

Crack-reduced alumina/aluminum titanate composites additive manufactured by laser powder bed fusion of black TiO2−x doped alumina granules

Laser powder bed fusion is an emerging industrial technology, especially for metal and polymer applications. However, its implementation for oxide ceramics remains challenging due to low thermal shock resistance, weak densification and low light absorptance in the visible or near-infrared range. In this work, a solution to increase the powder absorptance and to reduce cracking during laser processing of alumina parts is given. This is achieved by the use of a homogeneously dispersed and reduced titanium oxide additive (TiO2−x) within spray-dried alumina granules leading to formation of aluminum titanate with improved thermal shock behavior during powder bed fusion. The impact of different reduction temperatures on powder bed density, flowability, light absorption and grain growth of these granules is evaluated. Crack-reduced parts with a density of 96.5%, a compressive strength of 346.6 MPa and a Young's modulus of 90.2 GPa could be manufactured using powders containing 50 mol% (43.4 vol%) TiO2−x.

Microstructural characterization and mechanical properties on Al2O3–TiO2 materials obtained by uniaxial pressing and extrusion

The present investigation compares for the first time the effect of the addition of TiO2 on Al2O3 ceramic materials prepared by uniaxial pressing and extrusion technique. The properties of the disc- and tubular-shaped materials were investigated using different experimental tests, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Archimedes porosity, linear shrinkage, mechanical performance and scanning electron microscopy (SEM). The XRD analysis revealed the formation of Al2TiO5 phase at 1400 °C for discs and tubes, and became more evident when the sintering was performed at 1500 °C. The increase of TiO2 loading did not affect the open porosity at a given temperature for the tubular- and disc-shaped samples. The addition of 1 wt% TiO2 led to a remarkable increase of tensile strength for the disc-shaped materials heat treated at all temperatures due to the formation of aluminum titanate. However, a further addition on the TiO2 loading appears to decrease the tensile strength of the disc-shaped samples heat treated at 1400 °C and 1500 °C. For instance, the flexural strength of the tubes improved with increasing TiO2 loading and sintering temperature from 1300 °C to 1500 °C. This effect was attributed to the occurrence of a more effective formation of Al2TiO5 on the ceramic tubes. Furthermore, the addition of TiO2 played a key role in controlling the open porosity and the microstructure as confirmed by the SEM images in ceramics obtained by uniaxial pressing and extrusion processing.

The influence of titanium and iron oxides on the coloring and friability of the blue fired aluminum oxide as an abrasive material

Abstract The quality of abrasive grains is crucial to increase the lifespan of roughing, polishing and cutting tools. The purpose of the work herein was to evaluate the variables of the blue fired aluminum oxide heat treatment process. This heat treatment process improves the physical properties of the brown fused aluminum oxide and results in a blue coloring, which uniquely identifies it within the abrasives industry. The work herein includes information beginning with the electro-fusion process of bauxite (the manufacturing of the brown fused aluminum oxide) to the Blue Fired process. It also compares the fracture resistance index between these materials. This index is the inverse of the friability. Besides the content of titanium and iron oxides, process variables such as time, temperature and atmospheric conditions are important to monitor in order to reach standard requirements. Experimental evidence measuring these parameters is presented in the article herein. The blue coloring of this aluminum oxide is explained by the optical phenomena of electron transition, and not by the formation of aluminum titanate, as some technical literature has stated. Furthermore, it was proved that the coloring of blue fired material should not be used exclusively as an indicator of the optimal abrasive characteristics of this class of aluminum oxide.

Formation of Aluminum Titanate with Small Additions of MgO and SiO2

The formation of aluminum titanate was investigated by isothermal treatments of samples obtained from equimolar mixtures of alumina and titania, containing small amounts of silica and magnesia. Results of differential thermal analysis and Rietveld refinements of data collected by X-ray powder diffraction (XRPD) showed that additions of silica in amounts used in this work did not influence the formation of aluminum titanate. However, the presence of magnesia favored the formation of aluminum titanate in two steps, first one by incorporating Mg2+ into Al2TiO5 lattice during its initial formation, and the second one by accelerating the Al2TiO5 formation, contributing to large quantities of this phase. MgO doped samples have also developed a more suitable microstructure for stabilizing of Al2TiO5, what make them promising for applications such as thermal barriers, internal combustion engines and support material for catalyst.

Effect of Adding Cr2O3/Fe2O3 on Aluminum Titanate Properties

The effect of adding Cr2O3/Fe2O3 and sintering temperature on the crystal structure, decomposition, and sintering capacity of aluminum titanate prepared from ferroalloy plant alumina-titania slag and rutile is considered. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used in order to determine the crystal phase and microstructure of each series of specimens, X’pert Plus software is used for calculating aluminum titanate crystal lattice parameters, and the Archimedes method is used to determine apparent density and open porosity. Research results show that aluminum titanate may be synthesized from alumina-titania slag and rutile by solid phase reaction. Structural defects, formed as a result of the action of adding Cr2O3/Fe2O3, accelerate ion diffusion in aluminum titanate. Thermal defects, caused by action of high temperature, also facilitate aluminum titanate formation. The rate of aluminum titanate decomposition is reduced due to a solid solution within which Cr3+ and Fe3+ in the Cr2O3/Fe2O3 additive substitute for Ti4+ and Al3+.

Microstructure and strength of fused high alumina materials with 2.5 wt% zirconia and 2.5 wt% titania additions for refractory applications

High alumina alumina–zirconia–titania (AZT) materials have a high potential to resist thermal shock due to complex microcracking. In this study, therefore, the microstructure, phase composition, porosity and strength were investigated dependent on the cooling rate of fused raw materials, the sintering temperature and a thermal shock treatment. X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, dilatometry, true density, porosity and strength analysis were conducted. By slow cooling of fused AZT, stabilized aluminum titanate formed in the raw material whereas by fast cooling the formation or stabilization was prevented. The formation of new aluminum titanate during sintering occurred above 1300°C. Stabilization by solid solutions with e.g. titania—forming at sintering temperatures above 1450°C—was superior to the stabilizing effect of crack growth retarding additives like zirconia. After sintering at 1450°C the fast cooled material contained unstabilized aluminum titanate whereas the titanate in the slowly cooled AZT was stabilized. But the strength losses with thermal shock were comparable and both effects beneficial: the presence of stabilized aluminum titanate and the decomposition of the titanate. The additives deposited in the fast cooled material between and inside of the alumina grains. In the slowly cooled material they deposited mainly inter-granular. Consequently, in the fast cooled material the alumina grains cracked, leading to lower strengths. AZT may reach its full potential to resist thermal shock for reactant particle sizes below 63μm, inter-granular deposition areas without exception and an open porosity below 20%. Sintering temperatures above 1300°C were beneficial if the raw material contained unconverted reactants of the aluminum titanate formation.

Non isothermal kinetic study of the aluminium titanate formation in alumina-titania mixtures

Aluminum titanate (Al2TiO5) is a high refractoriness material with excellent thermal shock resistance. Hence it is suitable for several applications at elevated temperatures where insulation and thermal shock resistance are required. Such as components of internal combustion engines, exhaust port liners, metallurgy, and thermal barriers. The thermal instability of Al2TiO5 at high temperature is another characteristic of this material that has been studied and controlled by the incorporation of several additives. The Al2TiO5 formation from pure oxides presents an endothermic peak in the differential thermal analysis (DTA). The thermodynamic temperature is 1280 ºC. But experimentally, as in every other DTA experiment, these peaks strongly depend on the heating rate: this fact has been extensively employed for the kinetic study of transformation processes and the mechanism determination of chemical reactions. Both activation energies (Ea) and nucleation rates can be obtained from these experiments. The present work reports the formation Ea of Al2TiO5 prepared from pure oxides at air atmosphere by the Kissinger DTA based methods. Previously the particle size distribution of the starting powders together with X-ray diffraction analysis of the starting powders and the resulting materials was carried out. The properties of the Al2TiO5 formation were grouped into two groups corresponding to the low and high heating rates, below and over 5 K/min. Ea values were obtained after the Avrami (n) constant evidenced that the crystallization mechanism is strongly related to the heating rate, even in the wide range studied which includes the technological ones(0.5-40 K/min).

Formation and densification behavior of reaction sintered alumina–20 wt.% aluminium titanate nano-composites

Densification and reaction sintering behavior of the alumina–20wt.% aluminium titanate nano-composites were studied. Nano TiO2 powders were used in achieving the aluminium titanate phase during reaction sintering of alumina and titania. High resolution X-ray diffraction (HR-XRD) and scanning electron microscopy (SEM) results revealed that the aluminium titanate formation was affected by heating rate and soaking time at the elevated temperatures. The content of aluminium titanate phase decreased during increment of heating rate and increased during increment of soaking time at sintering temperature. Final densities of the sintered composites at 1550°C were lower than those sintered at 1450°C which can be explained by the grain cracking phenomenon induced by thermal expansion mismatch. The residual strain of the aluminium titanate grains released after grain cracking. The Al2TiO5 grains cracked along the (010) crystallographic planes because of the most positive expansion of the b-axis, and the lattice parameter b reverted to its original value after grain cracking.

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.

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.

Role of particle size of alumina on the formation of aluminium titanate as well as on sintering and microstructure development in sol–gel alumina–aluminium titanate composites

With a view to develop low temperature fine grained alumina–aluminium titanate composite, influence of alumina particle size on the temperature of formation of the aluminium titanate, sintering behaviour and microstructure development of alumina–aluminium titanate composite prepared through a sol–gel core shell approach is reported. The alumina matrix composite containing 20 wt% aluminium titanate has been prepared from alumina powders having different average particle size in the range 300–600 nm. The alumina particle size appears to have no significant influence on the formation temperature of in situ formed aluminium titanate. However, the microstructural analysis of the dense ceramic showed that the average grain size of the alumina–aluminium titanate composite increases with increase in the alumina particle size. XRD analysis indicated the absence of rutile titania in the sintered composite ensuring complete formation of aluminium titanate. Smaller starting alumina particle size led to finer grain size composites. The present study therefore shows that although the starting particle size of alumina has no significant role on the lowering of formation temperature of aluminium titanate, it does influence the microstructure of the composite.

Solid-phase processes in a ceramic matrix in the system SiO2 – Al2O3 – TiO2 With addition of fibrous nanostructural aluminum oxide

The formation of a composite ceramic based on the system SiO2 – Al2O3 – TiO2 with the addition of γ- and α-Al2O3 nanostructural powders during heat treatment in the temperature range 1300 – 1400°C is investigated. It is established that the introduction of γ-Al2O3 reactive nanostructural powder stimulated a solid-phase reaction between the silica and alumina with mullite being formed, while the addition of α-Al2O3 powder led to the formation of aluminum titanate. These processes altered the phase composition and the porous and crystalline structure of the composites and increased their physical – chemical and thermophysical properties.

Al 2O 3 @ TiO 2—A simple sol–gel strategy to the synthesis of low temperature sintered alumina–aluminium titanate composites through a core–shell approach

A simple sol–gel based core–shell approach for the synthesis of alumina–aluminium titanate composite is reported. Alumina is the core and titania is the shell. The coating of titania has been performed in aqueous medium on alumina particle by means of heterocoagulation of titanyl chloride. Further heat treatment results in low temperature formation of aluminium titanate as well as low temperature sintering of alumina–aluminium titanate composites. The lowering of the reaction temperature can be attributed to the maximisation of the contact surface between the reactants due to the core–shell approach involving nanoparticles. The mechanism of formation of aluminium titanate and the observations on densification features in the present process are compared with that of mixture of oxides under identical conditions. The sintered alumina–aluminium titanate composite has an average grain size of 2 μm.

Low temperature synthesis of aluminium titanate by an aqueous sol–gel route

Formation of aluminium titanate (AT) has been achieved at low temperature through sol–gel process using boehmite and titanium hydroxide as precursors by controlling the particle size at nanoscale followed by in-situ peptisation. The formations of AT phase, particle size distributions, sintering and thermal expansion characteristics, and microstructural features have been reported. DTA and XRD analysis have been performed to confirm the formation of AT. A 94% relative density was obtained for aluminium titanate sintered at 1550 °C with controlled grain size in the range of 2–3 μm.

Structural Evolution During Reaction to Form Aluminum Titanate from Sol-Gel Precursors

Aluminum titanate ceramic materials have been obtained by field-activated sintering of amorphous sol-gel powder precursors. Aluminum titanate formation started at 1000°C. The structural evolution with temperature from the amorphous sol-gel state to the final fully densified ceramic product has been monitored by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and electron microscopy. The full crystallization of aluminum titanate occurred at 1200°C. The grain size of the specimen densified at 1300°C was between 150 and 500 nm.

Synthesis of Aluminium Titanate Powder by Sol-Gel Technology

The ceramic raw materials, aluminum titanate (β- AlTiO 5 ), were prepared by the sol-gel method. To produce aluminum titanate powder, aluminum and titanium alcoxides were used as precursors with the addition of hydrochloric acid aiming to produce a translucent gel to minimize the precipitate formation. The most translucent gel obtained showed, by thermal treatment, a typical structural evolution: the direct crystallization of the aluminum titanate phase at 900°C. In this temperature the aluminum titanate phase was detected after 3 hours treatment. With 900 °C for 5 hours treatment, the phase becames well crystallized without any change in its characteristics within 10 hours treatment. At 1400°C occurred the formation of aluminum titanate in all prepared samples. The sol-gel method minimized a residual α-alumina and rutile phases when compared with one obtained by conventional method of oxide admixtures.

Aluminum titanate formation by sold-state reaction of alumina and titania

Aluminum titanate formation by sold-state reaction of alumina and titania

Grain Orientation of Aluminum Titanate Ceramics during Formation Reaction

ABSTRACTA microstructural change during the formation reaction of aluminum titanate from a mixture of rutile and corundum powders has been studied. The characterization was carried out using a polarization microscope, a scanning electron microscope and a micro-focus X-ray diffractometer. The formation of aluminum titanate was controlled by a nucleation step. The formation reaction proceeded to form spherically oriented regions of aluminum titanate grains among the matrix of rutile and corundum. At the end of the reaction, the specimen was entirely filled with the oriented region of consisting several hundred micrometers. The oriented region was composed of primary aluminum titanate grains of several micrometers and pores. Large cracks due to a thermal expansion anisotropy were formed at the boundaries of the orientated regions. The formation of the oriented region was caused by a small change in free energy, increasing elastic energy, and the endothermic nature of the reaction.

FTIR Study of High Temperature Phase Formation In Sol-Gel Aluminium Titanate

Fourier Transform Infrared Spectroscopic (FTIR) investigation has been carried out to study the structural changes and coordination of Al and Ti in the sol-gel derived aluminium titanate system as a function of temperature (65°–1400°C). An analysis of the FTIR spectral patterns shows that both octahedral as well as tetrahedral coordinations are present up to 800°C. At 1100°C, octahedral coordination is more predominant due to the formation of α-alumina. At 1300°C and above, the coordination is purely octahedral due to the formation of aluminium titanate.

Influence of Aluminum Titanate Formation on Sintering of Bimodal Size‐Distributed Alumina Powder Mixtures

The sintering behavior of green compacts, in which coarse alumina particles formed a skeletal structure and fine alumina and/or fine titania particles filled the voids of the skeletal structure, was investigated. Sinterability of the green compacts changed according to the titania content in the fine powder. The titania content of 33 mol% was the most effective for the densification. The volume expansion due to the aluminum titanate formation occurred in the voids of the skeletal structure, and the densification of the skeletal structure progressed more because the grain growth between the fine and coarse alumina particles did not proceed. As the titania content decreased, the densification did not progress more than that of the compact with 33 mol% titania content because the grain growth proceeded more. As the titania content increased, the expansion of the compacts was larger, and large grains were formed by the reaction between the titania and coarse alumina particles. Therefore, densification became difficult.