Aluminum Titanate Research Articles

Thermal decomposition of nanostructured Aluminum Titanate in an active Al matrix: A novel approach to fabrication of in situ Al/Al2O3–Al3Ti composites

The thermal decomposition of Aluminum Titanate in exposure to pure Aluminum was examined both in powder and in bulk form. Optical microscopy, FE-SEM, XRD, DSC and TGA examinations were conducted to take the possible chemical reactions between Aluminum Titanate and Al into consideration. It was found that as Aluminum Titanate particles are exposed to Al matrix, the thermal stability of Aluminum Titanate is degraded and its decomposition temperature is reduced from 850°C to 550°C. Also, the chemical reactions between Aluminum Titanate and Al start along the interfaces, and the reaction products, i.e. Al3Ti, Al2O3, TiO2 and O2 gas are left there. A mechanism was suggested to describe the Al/Al2TiO5 interactions in the interfaces. It was shown that the reaction products of nanostructured Al2TiO5 particle decomposition can be used as a source for producing in situ Al/Al3Ti and Al2O3 reinforced metal matrix composites through the solid-state powder metallurgy route. Finally, a uniformly dense microstructure including submicron Al2O3 and nanosized Al3Ti reinforcements was obtained.

Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel

An induction levitation melting (ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel (UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.

Preparation of monolithic aluminium titanate with well-defined macropores via a sol–gel process accompanied by phase separation

Abstract Monolithic aluminium titanate with well-defined macropores has been prepared through a sol–gel process accompanied by phase separation, using poly(ethylene oxide) (PEO) to induce the phase separation and formamide (FA) to control the gelation of Al 2 O 3 –TiO 2 system. Appropriate amounts of PEO and formamide allow the formation of aluminium titanate xerogel with cocontinuous macroporous structure and a monolithic shape. The pore size of the resultant dried gels is in the range of 2–3 μm and the porosity is above 60%. The as-dried gel is amorphous and completely transforms into a single phase Al 2 TiO 5 after heat-treated at 1300 °C. The macroporous structure is well maintained while the skeleton becomes smooth after heat-treatment.

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.

Impact on vehicle fuel economy of the soot loading on diesel particulate filters made of different substrate materials

Wall flow DPFs (Diesel Particulate Filters) are nowadays universally adopted for all European passenger cars.Since the properties of the filter substrate material play a fundamental role in determining the optimal soot loading level to be reached before DPF regeneration, three different filter material substrates (Silicon Carbide, Aluminum Titanate and Cordierite) were investigated in this work, considering different driving conditions, after treatment layouts and regeneration strategies.In the first step of the research, an experimental investigation on the three different substrates over the NEDC (New European Driving Cycle) was performed. The data obtained from experiments were then used for the calibration and the validation of a one dimensional fluid-dynamic engine and after treatment simulation model. Afterward, the model was used to predict the vehicle fuel consumption increments as a function of the exhaust back pressure due to the soot loading for different driving cycles. The results showed that appreciable fuel consumption increments could be noticed only in particular driving conditions, and, as a consequence, in most of the cases the optimal filter regeneration strategy corresponds to reach the highest soot loading that still ensures the component safety even in case of uncontrolled regeneration events.

A new method for fabrication of in situ Al/Al3Ti–Al2O3 nanocomposites based on thermal decomposition of nanostructured tialite

In this research, the possibility that nanostructured aluminium titanate (tialite) powder can be used as a chemical source for producing Al2O3 and Al3Ti precipitates in aluminium matrix composites has been investigated. Optical microscopy, FE-SEM, XRD, DSC and TGA examinations were used to characterize the synthesized specimens. The results showed that a porous structure and inferior mechanical properties were obtained in as-sintered samples. The further thermomechanical treatments i.e. cyclic rolling and hot extrusion improved the mechanical properties and led to a dense microstructure with a homogeneous distribution of Al2O3 and Al3Ti reinforcements. In rolled composites, the morphology of both reinforcers were blocky, but in hot extruded samples, the Al3Ti particles had a sub-micron rod-like structure and Al2O3 particles had a nano-sized distribution with an average particle size less than 100nm within the nano-grained matrix.

Nanostructured aluminium titanate (Al2TiO5) particles and nanofibers: Synthesis and mechanism of microstructural evolution

In this study, aluminium titanate (AT) particles and nanofibers were synthesized through citrate sol gel and sol gel-assisted electrospinning methods in both nanostructured powder and nanofiber forms. The results of X-ray diffraction analysis, field-emission scanning electron microscopy and differential thermal analysis showed that the synthetic products benefit a nanostructured nature with a grain size less than 70nm. The optimal values for time and temperature at which a roughly pure AT is attained were determined as 2h and 900°C, respectively. It was found that the sol gel precursor bears an amorphous structure till 700°C and begins to be crystallized to alumina, anatase and AT at higher temperatures. Moreover, AT tends to decompose into rutile and alumina at temperatures higher than 900°C and its degradation rate reaches a maximum at temperatures near to 1100°C. In this synthesis, citric acid was used as a chelating agent for Al3+ and Ti4+ ions and it was shown that a low citric acid-to-metal cation ratio leads to larger numbers of nuclei during crystallization and smaller grain size. Finally, a model was suggested to describe the microstructural evolution of AT compound based on a nucleation and growth regime.

Microstructural Characterization and Thermal Properties of Aluminium Titanate/Talc Ceramic Matrix Composites

Spinel (MgAl2O4) ceramics possesses a high melting point, high hardness, a relatively low density, excellent transmittance, a high strength, a relatively low thermal expansion coe cient, high thermal shock resistance and high chemical inertness. Aluminium titanate (Al2TiO5) exhibits extremely good thermal shock resistance and low thermal conductivity coupled with good chemical resistance in molten metals. In the present work, aluminium titanate/spinel ceramics composites with di erent percentages of Al2TiO5 were prepared using powder metallurgy techniques. The microstructural, mechanical and thermal properties were characterized using X-ray di raction, scanning electron microscopy, di erential scanning calorimetry, dilatometer and hardness. Thermal shock resistance behaviour under water quenching of the as-prepared ceramics was also evaluated. Results revealed that the addition of aluminium titanate to spinel matrix improves the properties of the aluminium titanate/spinel ceramics.

Microstructural Characterization and Thermal Properties of Aluminium Titanate/Porcelain Ceramic Matrix Composites

Spinel (MgAl2O4) ceramics possesses a high melting point, high hardness, a relatively low density, excellent transmittance, a high strength, a relatively low thermal expansion coe cient, high thermal shock resistance and high chemical inertness. Aluminium titanate (Al2TiO5) exhibits extremely good thermal shock resistance and low thermal conductivity coupled with good chemical resistance in molten metals. In the present work, aluminium titanate/spinel ceramics composites with di erent percentages of Al2TiO5 were prepared using powder metallurgy techniques. The microstructural, mechanical and thermal properties were characterized using X-ray di raction, scanning electron microscopy, di erential scanning calorimetry, dilatometer and hardness. Thermal shock resistance behaviour under water quenching of the as-prepared ceramics was also evaluated. Results revealed that the addition of aluminium titanate to spinel matrix improves the properties of the aluminium titanate/spinel ceramics.

ZnO-based thin film transistors employing aluminum titanate gate dielectrics deposited by spray pyrolysis at ambient air.

The replacement of SiO2 gate dielectrics with metal oxides of higher dielectric constant has led to the investigation of a wide range of materials with superior properties compared with SiO2. Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. To overcome this bottleneck, research has focused on the development of alternative deposition methods based on solution-processable metal oxides. Here we report the application of spray pyrolysis for the deposition and investigation of Al2x-1·TixOy dielectrics as a function of the [Ti(4+)]/[Ti(4+)+2·Al(3+)] ratio and their implementation in thin film transistors (TFTs) employing spray-coated ZnO as the active semiconducting channels. The films are studied by UV-visible absorption spectroscopy, spectroscopic ellipsometry, impedance spectroscopy, atomic force microscopy, X-ray diffraction and field-effect measurements. Analyses reveal amorphous Al2x-1·TixOy dielectrics that exhibit a wide band gap (∼4.5 eV), low roughness (∼0.9 nm), high dielectric constant (k ∼ 13), Schottky pinning factor S of ∼0.44 and very low leakage currents (<5 nA/cm(2)). TFTs employing stoichiometric Al2O3·TiO2 gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with low operating voltages (∼10 V), negligible hysteresis, high on/off current modulation ratio of ∼10(6), subthreshold swing (SS) of ∼550 mV/dec and electron mobility of ∼10 cm(2) V(-1) s(-1).

The Tribological Properties of NiCr–Al2O3–TiO2 Composites at Elevated Temperatures

Ni-based composite that contains TiO2 and Al2O3 was prepared by powder metallurgical hot pressing method. TiO2 and Al2O3 being added to Ni-based composite at the same mass fraction and the effects on some mechanical and tribological properties of the composites when rubbing against alumina ball were investigated from room temperature to 700 °C. The results show that the tribological properties of the composites were improved by adding TiO2 and Al2O3 simultaneously. The best comprehensive properties of mechanics and tribology were obtained when TiO2 and Al2O3 in the alloy have the same content of 10 wt%. The friction coefficient and wear rate of the composites decrease with the increasing of temperature and TiO2 and Al2O3 contents, and the composites with addition of 10 wt% TiO2 and 10 wt% Al2O3 exhibit the lowest friction coefficient (0.32) and wear rate (1.71 × 10−5 mm3/N m) at 700 °C. XRD and SEM equipped with EDS analysis shows that the lubrication films consist of aluminum titanate and several kinds of titanium oxide formed on rubbing surface with the temperatures elevated. The synergistic action of titanium oxide and aluminum titanate and NiTiO3 in the wear surface at high temperature is responsible for the improving of tribological properties of the composites.

Green synthesis and characterization of Ag1/2Al1/2TiO3 nanoceramics

Abstract Single phase silver aluminum titanate (Ag1/2Al1/2)TiO3, later called AAT, nanoceramic powder (particle size 2 to 7.5 nm) was synthesized by a low-cost, green and reproducible tartaric acid gel process. X-ray, FT-IR, energy dispersive X-ray and high resolution transmission electron microscopy analyses were performed to ascertain the formation of AAT nanoceramics. X-ray diffraction data analysis indicated the formation of monoclinic structure having the space group P2/m(10). UV-Vis study revealed the surface plasmon resonance at 296 nm. Dielectric study revealed that AAT nanoceramics could be a suitable candidate for capacitor applications and meets the specifications for “Z7R” of Class I dielectrics of Electronic Industries Association. Complex impedance analyses suggested the dielectric relaxation to be of non-Debye type. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were performed using the impedance data. Electric modulus studies supported the hopping type of conduction in AAT. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in AAT. The ac conductivity data were used to evaluate the density of states at Fermi level and minimum hopping length of the compound.

Microstructure Changes of Aluminum Titanate Refractory Doped SiO2 and ZrO2 in Molten Steel

Microstructure Changes of Aluminum Titanate Refractory Doped SiO2 and ZrO2 in Molten Steel

Al2TiO5–mullite porous ceramics from particle stabilized wet foam

Aluminium titanate (Al2TiO5)–mullite porous ceramics were synthesized by a direct foaming method, using α-Al2O3, TiO2, and SiO2 as starting materials. The initial suspension for Al2TiO5 was prepared by adding TiO2 suspension to an equimolar amount of partially hydrophobized colloidal Al2O3 suspension. A secondary suspension was prepared using molar composition 3:2 Al2O3/SiO2, and blended to the initial suspension in (0, 10, 20, 30 and 50)vol%, to obtain the mullite phase in the sintered sample. The wet foam exhibits an air content of 80–92% and Laplace pressure from 1.30 to 2.23mPa, which results in 68–83% foam stability. It also exhibits a much higher adsorption free energy of about 2.2×10−13J to 2.7×10−13J at the interface, which results in irreversible adsorption of particles at the air–water interface, leading to outstanding foam stability. The final suspension was foamed, and the wet foam was sintered at 1500°C for 1h. Phase identification was accomplished using X-ray diffraction, and microstructural analysis was performed by field emission scanning electron microscopy.

Effect of zirconia and aluminium titanate on the mechanical properties of transformation-induced plasticity-matrix composite materials

Metal-matrix composite materials composed of an austenitic stainless steel with different ceramic particle reinforcements were investigated in this study. The test specimens were prepared via a powder metallurgical processing route with extrusion at room temperature. As reinforcement phase, either magnesia partially stabilized zirconia or aluminium titanate with a volume content of 5% or 10% was used. The mechanical properties were determined by quasi-static compressive and tensile loading tests at ambient temperature. The microstructure characteristics and failure mechanisms during deformation contributing to significant changes in strength and ductility were characterized by scanning electron microscopy including energy dispersive X-ray spectroscopy and electron back-scatter diffraction, and by X-ray diffraction. The composite materials showed higher stress over a wide range of strain. Essentially, the deformation-induced formation of α′-martensite in the steel matrices is responsible for the pronounced strain hardening. At higher degrees of deformation, the material behavior of the composites was controlled by arising damage evolution initiated by particle/matrix interface debonding and particle fracture. The particle reinforcement effects of zirconia and aluminium titanate were mainly controlled by their influences on martensitic phase transformations and the metal/ceramic interfacial reactions, respectively. Thereby, the intergranular bonding strength and the toughness of the steel/ceramic interfaces were apparently higher in composite variants with aluminium titanate than in composites with magnesia partially stabilized zirconia particles.

Synthesis, characterization and thermochemistry of Cs-, Rb- and Sr-substituted barium aluminium titanate hollandites

Titanate hollandites are of considerable interest for immobilization of radioactive Cs, its daughter product Ba and related radionuclides Rb and Sr. In this study, we synthesized three hollandites, Ba1.18Cs0.21Al2.44Ti5.53O16, Ba1.17Rb0.19Al2.46Ti5.53O16 and Ba1.14Sr0.10Al2.38Ti5.59O16, using sol–gel methods. Rietveld analysis of synchrotron XRD data shows that they adopt the tetragonal structure (space group I4/m), and their cell parameters increase with increasing cation size (Sr2+→Rb+→Cs+). Standard enthalpies of formation of these hollandites were determined from drop solution calorimetric measurements with lead borate as the solvent at 973K. Their formation enthalpies are similar, consistent with the occurrence of extensive cation substitutions in hollandites. Further energetic analysis with respect to BaTiO3 and SrTiO3 perovskites and other oxides reveals decreased thermodynamic stability from Cs- to Rb- to Sr-hollandite. This trend is consistent with the phase assemblage observed in Synroc, where Cs+, Rb+ and Ba2+ enter into hollandite, whereas Sr2+ occurs in perovskite.

チタン酸アルミニウム焼結体の微細構造および機械的特性に及ぼす造孔剤添加の影響

Aluminium titanate (Al2TiO5, AT) has a large uniaxial anisotropy of thermal expansion on the crystallographic orientation, which generates microcracks in the ceramics. Owing to microcraks, which buffer thermal expansion, AT shows especially low thermal expansion. On the other hand, microcracks remarkably decrease a mechanical strength and sometimes induce the destruction of specimens due to crack growth. In this study, AT ceramics containing various amounts of pore forming additives of different particle diameter were prepared by firing at various temperatures. The effects of contents and particle sizes of pore forming additives on microstructures and mechanical properties of AT ceramics were examined. In the case of lower contents of pore forming additives, visible large cracks causing the destruction were observed on the surfaces of the specimens and bending strengths decreased with increasing firing temperature. On the other hand, the bending strength of the specimens containing higher amounts of pore forming additives scarcely depended on firing temperatures. The pore spacings decreased with increasing additives content and decreasing particle size of additives. Therefore, large cracks causing decline of bending strength were difficult to occur in the specimens containing higher amounts of additives because crack growth was effectively prevented around pores, resulting in less decline of bending strength with firing temperature. The inhibition of crack growth was effective in the case of the additive with small particle size. As a result, the bending strength of the specimen containing the additive with small particle size was higher than that of the specimen with the large size additive.

Flow Analysis during Soot Trapping on Aluminum Titanate Ceramics Filter with Hexagonal Cell Geometry

Flow Analysis during Soot Trapping on Aluminum Titanate Ceramics Filter with Hexagonal Cell Geometry

Residual strain scanning of alumina-based ceramic composites by neutron diffraction

Residual strain profiles were measured by neutron diffraction in alumina-aluminum titanate ceramic composites sintered at two different temperatures, namely 1450 and 1550°C. The results show that irrespective of the direction and the sintering temperature, the obtained profiles are almost flat, with very similar results for both temperatures. In addition, the results demonstrate that the alumina is in compression whereas the aluminium titanate is subjected to tensile residual stresses.

Upgraded production of (1R,5S)-1-hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one from cellulose catalytic pyrolysis and its detection in bio-oils by spectroscopic methods

Catalytic pyrolysis of cellulose was carried out focusing on the selective production of the anhydrosugar (1R,5S)-1-hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one (LAC), a promising chiral chemical for application in organic synthesis. The catalyst Sn-MCM-41, montmorillonite K10 or aluminum titanate nanopowder was used by a suitable pyrolysis reactor performing the processes at 500°C and 350°C. After a workup adapted to optimize the production of LAC and to facilitate the following purification, its amount in the produced bio-oil samples was established by 1H NMR spectroscopy using the standard-addition method. A further quantitative analysis was based on FT-IR technique performed using a CaF2 liquid cell and employing the calibration-curve method. Both the methods, which do not require any pre-treatment steps, provided comparable values (±1%) in terms of LAC abundance in bio-oil samples and validation of the FT-IR based method made it a rapid and efficient tool for quantitative LAC detection also without need of carbonyl band deconvolution. The data showed that (i) Sn-MCM-41 promoted the highest LAC production by pyrolysis at 500°C (7.6±0.1wt.% from cellulose), with a lower than 1% decrease in the presence of this catalyst after a regeneration cycle, and (ii) the cheap and eco-friendly montmorillonite K10 emerged as the best alternative, with a yield from cellulose of 4.8±0.1wt.% at 500°C and 4.6±0.1wt.% at 350°C.