Alumina Titania Research Articles

Studies on Evaluation of the Thermal Conductivity of Alumina Titania Hybrid Suspension Nanofluids for Enhanced Heat Transfer Applications.

Extensive investigations were made and empirical relations were proposed for the thermal conductivity of mono-nanofluids. The effect of concentration, diameter, and thermal properties of participating nanoparticles is missing in the majority of existing thermal conductivity models. An attempt is made to propose a model that considers the influence of such missing parameters on the thermal conductivity of hybrid nanofluids. Al2O3-TiO2 hybrid nanofluids have a 0.1% particle volume concentration prepared with distinct particle volume ratios (k - 1:6 - k, k = 1 to 6) in DI water. The samples were characterized, and the size and shape of the nanoparticles were verified. Also, the influence of varying particle volume ratios and the fluid temperature (varying from 283 to 308 K) were examined. 2.4 and 2.1% enhancements were observed in the thermal conductivity of alumina (5:0) and titania (0:5) nanofluids (having 0.1% volume concentration), respectively. Due to the low thermal conductivity of titania nanoparticles, the conductivity of the hybrid solution is above that of titania and below that of alumina nanofluids. An empirical relation for the thermal conductivity of hybrid nanofluids is established and validated considering the individual particle size, volume ratio, and thermal conductivity of particles.

Thermal Performance Evaluation of Plate-Type Heat Exchanger with Alumina–Titania Hybrid Suspensions

This paper aims to develop models for the thermal conductivity and viscosity of hybrid nanofluids of aluminium oxide and titanium dioxide (Al2O3-TiO2). The study investigates the impact of fluid temperature (283 K–298 K) on the performance of a plate heat exchanger using Al2O3-TiO2 hybrid nanofluids with different particle volume ratios (0:5, 1:4, 2:3, 3:2, 4:1, and 5:0) prepared with a 0.1% concentration in deionised water. Experimental evaluations were conducted to assess the heat transfer rate, Nusselt number, heat transfer coefficient, Prandtl number, pressure drop, and performance index. Due to the lower thermal conductivity of TiO2 nanoparticles compared to Al2O3, a rise in the TiO2 ratio decreased the heat transfer coefficient, Nusselt number, and heat transfer rate. Inlet temperature was found to decrease pressure drop and performance index. The Al2O3 (5:0) nanofluid demonstrated the maximum enhancement of around 16.9%, 16.9%, 3.44%, and 3.41% for the heat transfer coefficient, Nusselt number, heat transfer rate, and performance index, respectively. Additionally, the TiO2 (0:5) hybrid nanofluid exhibited enhancements of 0.61% and 2.3% for pressure drop and Prandtl number, respectively. The developed hybrid nanofluids enhanced the performance of the heat exchanger when used as a cold fluid.

Thermal performance of aqueous alumina–titania hybrid nanomaterials dispersed in rotating channel

The extension of nanoliquid obtained by adding nano-powder composite or various nanoparticles in regular liquid is term as hybrid nanofluid. Hybrid nanofluids are more potential materials that significantly uplift the thermophysical feature and capacity of heat transportation instead of single nanoparticle nanoliquid. Hence, the paramount interest of this paper is to model theoretically the flow of aqueous alumina–titania hybrid nanoliquid across a rotating channel. Temperature-based viscosity is addressed. This analysis further contributes the impact of heat source and dissipation phenomena. Additionally, two different shapes of nanoparticles, namely, bricks- and needle-shaped are included. Similarity variables dimensionless the governing problem. The obtained system is solved by employing Mathematica-based NDSolve approach. The impact of various embedded variables is elucidated graphically. The presence of hybrid nanocomposite greatly affects the temperature and Nusselt number than nanoparticles. Further outcomes declared that rotation and heat source variables significantly increase the thermal field for hybrid nanophase when compared with nanophase.

Mechanical Behavior Monitored by Acoustic Emission of Nanostructured Alumina–Titania Coatings

Mechanical Behavior Monitored by Acoustic Emission of Nanostructured Alumina–Titania Coatings

Temperature-Dependent Wear Behavior of Air Plasma Sprayed Alumina and Alumina–Titania Composite Coatings

Temperature-Dependent Wear Behavior of Air Plasma Sprayed Alumina and Alumina–Titania Composite Coatings

Preparation of α-alumina/γ-alumina/γ-alumina-titania ceramic composite membrane for chloride ion removal

It is a universally acknowledged truth that ceramic membranes with high heat and chemical resistance play a crucial role in the nanofiltration (NF) process under harsh conditions. Although the ceramic membranes are challenging to use for salt filtration due to pore size and surface charge constraints. In this study, sol-gel and dip-coating techniques are used to make alumina–titania composite ceramic membranes with an γ-alumina interlayer for salt rejection. Then, particle size distribution was determined using dynamic light scattering (DLS), and membrane surface quality and morphology were examined using scanning electron microscopy (SEM). The microstructural properties of the membrane have been investigated using X-Ray Diffraction (XRD). A dead-end module is used to measure water permeability and salt rejection. After calcination at 450 °C, SEM shows the crack-free membrane surfaces. The interlayer and top layer membrane thicknesses were estimated to be 1.5 and 0.5 μm, respectively. In addition, XRD measurements show an alumina crystal structure for the interlayer and anatase, rutile, and alumina phases for the composite membranes. Finally, it was shown that the amount of chlorine rejection was pH-dependent, with the rejection rate increasing from 12.7% to 67% as the pH climbed from 4 to 12. Overall, this research provides a composite ceramic nanofiltration for high-pressure desalination, and it is shown that the membrane's surface does not alter after five cycles, which allows for a long-term chemical process and it could be a promising candidate in the wastewater treatment field.

Analyzing coarsening versus densification phenomenon present in partial sintering of Al2O3/TiO2 composites

Alumina–titania (Al2O3/TiO2) composites are well-known for their physical and microstructural properties, which allow several engineering applications. However, these properties change when different sintering temperatures are used, due to the existence of two antagonistic phenomena (grain coarsening versus densification) that occurs during sintering process. The aim of this study was to evaluate the microstructural and physical properties of the alumina–titania composites and to understand these two antagonistic phenomena when different partial sintering temperatures are used. The composites were prepared from alumina and titania powders by uniaxial pressing and sintered at different temperatures (1100–1400 °C). The structural analysis showed that in addition to expected phases (α-Al2O3 and rutile), the alumina–titania composite sintered at 1100 °C presents anatase phase, while those obtained at 1300 and 1400 °C present tialite phase. The morphology analysis revealed a random distribution of grains with irregularly shaped pores. According to the Archimedes-based immersion test, all composites have a relative bulk density ranging 60.43–73.59%, showing that none of them reached the final sintering stage. Statistical analysis revealed that the average grain size of the matrix ranges from 3.62 to 5.24 μm. Moreover, the statistical analysis also showed that the grain coarsening predominates over densification for the composites sintered from 1100 to 1150 °C. The densification predominates over grain coarsening for the composites sintered from 1150 to 1200 °C, and from 1250 to 1400 °C. The two phenomena coexist only for the composites sintered from 1200 to 1250 °C.

Effect of SODs on Mechanical and Wear Behaviours of Alumina and Alumina–Titania APS Coatings on AISI304

Effect of SODs on Mechanical and Wear Behaviours of Alumina and Alumina–Titania APS Coatings on AISI304

INFLUENCE OF CARBON NANOTUBES REINFORCEMENT ON CHARACTERISTICS OF THERMALLY SPRAYED CERAMIC COATINGS

The influence of reinforcement of carbon nanotubes (CNTs) on microstructural features and mechanical properties of thermally sprayed Al2O3–3[Formula: see text]wt.%TiO2and WC–20[Formula: see text]wt.%Co coatings was investigated. Alumina–Titania coatings were deposited by Air Plasma Spraying (APS) and Tungsten Carbide–Cobalt coatings were deposited by High-Velocity Oxy-Fuel (HVOF) spraying process. The coatings obtained with reinforcement of CNTs were characterized to interpret the microstructural changes and also to evaluate the variation in their mechanical properties. The percentage composition of CNTs in both APS and HVOF coatings systems were varied in the order of 2, 4, and 6[Formula: see text]wt.%. It has been found that homogenous dispersion of carbon nanotubes in the coating systems results in increased microhardness and reduced surface roughness. Also, the microstructural features of the coating systems clearly showed that the coatings are denser with fewer pores due to the presence of CNTs.

Experimental and Numerical Investigation of Residual Stress in Coatings on Steel

Abstract In the present work, an alumina–titania (13 %) coating has been deposited by the air plasma spray process on a mild steel substrate by preheating the substrate to different temperatures. Coating thickness was measured by a scanning electron microscope, the hardness of coatings was measured, and morphology was also checked. The crack compliance technique has been used to determine the residual stress, as it is a very simple method, and also, it is compatible with conventional machining equipment and wire electric discharge machining equipment. Specimens were cut by the diamond cutter up to certain depth in microns, and the strain relieved was recorded. For finding out the residual stress, these recorded values of strain have been used by doing a finite element analysis (FEA) using the ANSYS 15.0 (Ansys, Inc., Canonsburg, PA) software. For validation of the model, uniaxial tension was applied on a sample by using the INSTRON universal testing machine (Instron Inc., Norwood, MA), and strain values at both the coating side and the substrate side were recorded and matched with the model under the same value of the load. After verifying the model, an equation has been developed using the Minitab software (Minitab Inc, Bengaluru, India), and the strains previously recorded were used as an input to the equation obtained, and the value of residual stress was calculated. The maximum value of residual stress was found at the coating–substrate interface, and the values of residual stress for sample preheated at 250°C, 200°C, and 150°C were found to be compressive, with the magnitude of −176.28 MPa, −243.54 MPa, and −255.42 MPa, respectively.

ROLE OF FRICTION ENERGY AND TRIBO-REDUCTION IN ABRASIVE WEAR OF ALUMINA–TITANIA COATINGS

This paper addresses friction energy-induced reduction of TiO2 during abrasive wear and friction of alumina–titania coatings with different TiO2 content. Alumina–13% titania and alumina–40% titania coatings were deposited by atmospheric plasma spray technique. An improvement in fracture toughness and better densification of coatings was observed with an increase in titania content. Alumina–40% titania coating showed lower friction coefficient and higher abrasive wear resistance than alumina–13% titania coating. An increase in friction energy was associated with enhanced reduction of TiO2 to Ti2O3 and an increase in the extent of gamma alumina to alpha alumina phase conversion. These observations along with structural and mechanical properties of coatings could explain differences in tribological response of these coatings. Friction energy parameter (FEP) was used to identify different regimes of wear and degradation mode of coatings.

Microstructure and tribological behavior of laser cladding TiAlSi composite coatings reinforced by alumina–titania ceramics on Ti–6Al–4V alloys

Titanium composite coatings have been fabricated by laser cladding with a mixed powder of TiAlSi and Al2O3–13%TiO2 on Ti–6Al–4V alloy substrates. The effects of different content of Al2O3–13%TiO2 on the microstructure and properties of the laser cladding titanium composite coatings have been studied. The microstructure, chemical composition, phase constituent, hardness distribution and tribological properties of the titanium composite coatings were investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), Vickers micro-hardness tester and a pin-on-disc friction and wear testing apparatus, respectively. The results show that the titanium composite coatings reinforced by Al2O3–13%TiO2 mainly consist of Ti3Al, Ti3AlC2, TiAl, α-Al2O3 and TiO2. The cladding coatings possess compact and uniform structure. With the increase of Al2O3–13%TiO2 content from 0 to 20%, the microhardness of the coatings increases, which reaches a maximum of around 770 HV0.3 when the addition content is 20%. The average coefficient of friction of the titanium composite coatings with the Al2O3–13%TiO2 content of 0, 10, 20 and 30% is 0.592, 0.430, 0.435 and 0.438, respectively. The composite coating with 20% content of Al2O3–13%TiO2 particles possesses the lowest wear loss.

Development of dense Al2O3–TiO2 ceramic composites by the glass-infiltration of porous substrates prepared from mechanical alloyed powders

In this work bio-composites were obtained by infiltrating porous alumina–titania (Al2O3–TiO2) substrates with a lanthania-rich (La2O3) glass. Al2O3–TiO2 substrates were fabricated using high-energy milled powder mixtures of two different compositions with molar ratios of 3:1 and 1:1, uniaxial compaction under 100 MPa and sintering at 1300 °C - 2 h or 1400 °C - 2 h. The high energy milling process of the powders resulted in homogeneous, extremely fine mixtures. For comparison, as-received Al2O3 and TiO2 powders were also mixed at a proportion of 3:1 and sintered at 1600 °C - 2 h. The sintered substrates presented α-Al2O3 and β-Al2TiO5 (aluminium titanate) as crystal phases and relative densities ranging between 65.5 ± 2% and 69.4 ± 1.2% of the theoretical density. These porous substrates were infiltrated with a lanthania containing glass at a temperature of 1140°C-2h. The resulting ceramic composites exhibited high density, varying between 94 to 99% of the theoretical density, Vickers hardness ranging between 895 ± 14 HV and 1036 ± 33 HV, fracture strength ranging between 218 ± 28 MPa and 254 ± 18 MPa and a fracture toughness (KC) higher than 2.6 MPam1/2. Phase analysis of the infiltrated substrates by X-ray diffraction indicated the decomposition of aluminium titanate into alumina and titania besides the formation of lanthanum borosilicate, LaBSiO5. In addition, all compositions studied presented non-cytotoxic behaviour and low chemical solubility, inferior to 75 μg/cm2.

Mechanical strengths and thermal properties of titania-doped alumina aerogels and the application as high-temperature thermal insulator

Alumina (Al2O3)-based diphasic aerogels have better physical properties than those of pure Al2O3 aerogel according to previous studies. In the present research, we focused on an alumina–titania (Al2O3-TiO2) diphasic aerogel. A series of Al2O3 aerogels were synthesized and studied with and without minor TiO2 dopants (up to 10 mol%). We found that the pure Al2O3 aerogel, which had the fiber-like particles, was stronger than those with TiO2 dopants that possessed the sphere-like particles. However, the sphere-like particles make the TiO2-doped Al2O3 aerogel (with 3 mol% TiO2) possessing the largest specific surface area (SSA) of 650 m2/g, much larger than that of the pure Al2O3 aerogel (326 m2/g). This work proved that fiber-like particles enhance strength but reduce SSA of Al2O3 aerogel. At last, ceramic fibers reinforced Al2O3 aerogel composites with the sizes of 20 cm width × 20 cm length × 1 cm thickness were fabricated. The aerogel composites possessed a thermal conductivity of 0.136 W/m K at 1000 °C, better than those of the ceramic fiber blankets itself (0.30 W/m K), indicating potential application as high-temperature thermal insulator.

High temperature oxidation behavior of thermally sprayed alumina—titania coatings on nickel based superalloys

In this paper, high temperature oxidation behavior has been studied on thermally sprayed nickel based superalloys. Alumina—titania powder was deposited on Hastelloy and Inconel 718 using atmospheric plasma spray process. Investigations were carried out at 1000 °C for fifty hours under cyclic process. From the experimental results, the corrosion kinetics has been calculated from mass change per unit area. The tested samples were subjected to metallurgical characterization studies using SEM, EDS and XRD analysis. It has been confirmed that the presence of iron has highly influenced in the formation of metal oxide (FeO) scale on exposed surface with nickel and chromium. The repeated thermal cycle has influenced iron oxide to spall thermal coatings on prolonged exposure. It was due to the intermediate oxide scale that has grown between the coatings and substrate on Inconel 718. The metallurgical reactions were studied and reported in detail.

Properties of Alumina-Titania Coating Formed by a New Multi-Chamber Gas-Dynamic Accelerator

Thermal-sprayed alumina–titania coatings (Al2O3:Ti wt ratio = 60:40) were prepared by a new multi-chamber gas-dynamic accelerator. The coatings were examined by using scanning electron microscopy, X-ray phase analysis and Vickers hardness tester at a test load 0.2 kg. The coating was well-adhered with corrosion-resistant steel substrate. The results show that the microstructure of the alumina–titania coatings consists of areas with different degrees of melting: the lamella built up from the fully melted particles of the powder, and partially melted areas. The developed coating is highly dense (porosity is less than 0.7%). Research results show that hardness of alumina–titania coatings (Al2O3:Ti wt ratio = 60:40) can achieve up to 655 HV0.2 and the specific wear rate of alumina-titania coatings is 52.40∙10-5 mm3 (m∙N)-1.

Polymer-assisted co-precipitation route for the synthesis of Al $$_{2}$$ 2 O $$_{3}$$ 3 –13% TiO $$_{2}$$ 2 nanocomposite

The present investigation reveals the effect of processing parameters on the properties of alumina–titania (Al\(_{2}\)O\(_{3}\)–TiO\(_{2}\)) nanocomposites. A polymer-assisted (Pluronic P123 triblock co-polymer) co-precipitation route has been employed to synthesize \(\hbox {Al}_{2}\hbox {O}_{3}\)–\(\hbox {TiO}_{2}\) nanoparticles. As a surfactant, pluronic P123 polymer exhibits hydrophobic as well as the hydrophilic nature simultaneously which detains the agglomeration and hence the nano size particle have been obtained. Effect of surfactant concentration on morphology and particle size of product has also been investigated. Thermal behaviour of the prepared powder samples have been studied using differential scanning calorimeter/thermal gravimetric analysis and dilatometer. Formation of aluminium-titanate \((\hbox {Al}_{2}\) \(\hbox {TiO}_{5})\) phase has been confirmed using X-ray diffraction analysis. It has been observed by field emission scanning electron microscopy analysis that the particle size reduced effectively (below 100 nm) when polymer-assisted co-precipitation route is used instead of the simple co-precipitation technique. A highly dense microstructure of sintered samples has been obtained, driven by reduced particle size.

Erosive wear resistance of dimpled ceramic coatings on mild steels

PurposeThe purpose of this study is to determine the effect of dimpled texture on ceramic coating towards erosion wear.Design/methodology/approachThe methodology of this experiment is based on ASTM G73, which is for erosion test for rotating apparatus. Mild steels samples were coated with alumina titania via the plasma spray method, and surface modification was done by producing different dimple densities using laser surface texturing. Two mediums were used: seawater environment and slurry environment.FindingsDimples of 150 μm diameter and 50 μm depth have proved to be successful in entrapping wear debris and other foreign materials during the erosion test. It was clearly noted that coatings with the highest number of dimples with 43 per cent had significantly improved the microhardness of the coated mild steels by twofold.Originality/valueAll this while, texturing was done only on substrate material. None was done on ceramic coating.

Effect of TiO2 Incorporated with Al2O3 on the Hydrodeoxygenation and Hydrodenitrogenation CoMo Sulfide Catalysts

The influence of TiO2 incorporation in Al2O3 support was investigated in the catalytic activity of hydrodeoxygenation (HDO) and hydrodenitrogenation (HDN) reactions. Alumina–titania supported CoMo sulfide catalysts (mole ratio 1:0, 1:0.25, 1:50, 1:0.75, and 0:1) were prepared by sol-gel method. The CoMo sulfide catalysts were characterized by BET, NH3-TPD, H2-TPR, XRD and TEM techniques. Guaiacol and quinoline were used as model compounds in HDO and HDN reactions, respectively. The liquid products were examined by GC-FID and GC-MS. The results suggest that TiO2 incorporated Al2O3 support obviously involves the catalytic activity on the HDO and HDN reactions. The role of the partial incorporation of TiO2 into Al2O3 was discussed.

Phase transformation in the alumina–titania system during flash sintering experiments

We show that phase transformation in the alumina–titania system, which produces aluminum-titanate, follows an unusual trajectory during flash sintering. The experiments begin with mixed powders of alumina–titania and end in dense microstructures that are transformed into aluminum-titanate. The sintering and the phase transformation are separated in time, with the sintering occurs during Stage II, and phase transformation during Stage III of the flash sintering experiment. Stage III is the steady-state condition of flash activated state that is established under current control, while Stage II is the period of transition from voltage to current control. The extent of phase transformation increases with the current density and the hold time in Stage III.