Commercial-grade Alumina Research Articles

Thermovision study on Alumina’s Ra v/s Ts for AIDHVACS to control COVID-19

The current study is the authors’ next work from the thermo vision perspective of real time single sun solar field performance infrared thermography (IRT) on commercial grade Alumina solar absorber surface coatings (SASCs) to recognize surface roughness (Ra) as one of the important production process parameters. In a previous study, it was investigated with IRT, and found that Ra<1.8 is favorable and hard anodized Alumina (HAAO) coatings exhibits better surface temperature (Ts) gain as compared to organic dyed non-HAAO coatings on Aluminum substrate, and are more stable in solar field for many years in open air environment without degrading their performance. It may be useful in better optimization of SASCs specifically for personal protective equipments (PPEs) sanitization and artificial intelligence (AI) driven heating ventilation air conditioning (HVAC) systems (AIDHVACS) design to control Covid-19 in current situations.The influence of Ra of few microns ∼ <15 µm on Alumina SASCs’ Ts gain is examined. The presented study shows that more than 1.05 mm thickness of substrate flat is necessary to develop good quality of alumina coating; Ra<1.8 µm is favorably expected to the extent of Ra value approaching as close as to nanoscale ∼ 5-500 nm; local surface temperature gained is depending upon local Ra profile as well as upon surface morphology in addition to the anodizing process parameters and other environmental factors. It suggests that the optimal surface profile should be designed as an integral to the production line processes. The substrate surface chemical composition may also change while processing due to surface contact with the processing tools, which may also result in altered solar field performance due to substrate altered material composition prior to hard anodizing process, as examined with X-ray fluorescence spectrometry (XRF) and ultraviolet–visible spectrophotometry (UV-VIS). The novelty is that other studies of surface roughness parameter is focused upon convective heat transfer inside tunnel or duct solar heat absorbers e.g. air heaters, whereas the authors have focused upon surface roughness of solar radiation receiving outer surface as an important commercial production process variable having effect upon conductive heat transfer in solar thermal power systems. The AIDHVACS needs machine learning and big data analysis as the need of the hour.

A high temperature seeding technique for particle image velocimetry

Non-intrusive measurements of gas velocities via particle image velocimetry (PIV) or laser Doppler velocimetry (LDV) requires entraining particles into the flow field. There are many techniques and materials available for seeding gas phase flows. However, when the flow temperatures exceed 200 °C, the available options for seed materials becomes limited. In high temperature applications refractory seed materials are required. The established technique for seeding flows with metal oxide powders is via fluidized beds by themselves or in combination with cyclone separators. These systems are fraught with problems which limit their ability to provide consistent, uniform flow seeding. In this work, we describe a technique for reliably introducing metal oxide particles into high temperature flows. The employment of pH stabilization techniques typically used to obtain stable dispersions in ceramic processing can provide a source of seed material for high temperature air flows. By pH stabilizing submicron alumina particles in ethanol, a stable dispersion is obtained which when atomized, produces a high quality aerosol. Commercial grade alumina is used with a moderate size distribution. The technique is not limited to alumina/ethanol and is also demonstrated with an alumina/H2O system. Other ceramic powders in other polar solvents can also be used once their point of zero charge (pHpzc) of the powder in the solvent has been determined. We present an example of the pH stabilized dispersions applied to a very challenging high temperature supersonic flow and a particle dynamics analysis across a shock.

Polymer concrete with recycled PET: The influence of the addition of industrial waste on flammability

The civil construction sector has found use for a range of industrial waste products in the form of substitutes that are as effective as standard construction materials but which have the bonus of providing an ecologically sound alternative for materials that would otherwise become an environmental concern. The use of waste materials in cement and polymer composites is a prime example of this practice. While composites with polymer matrices may display excellent mechanical properties, they must also offer superior flammability resistance. The main aim of this study is to develop innovative polymer concrete composites produced with industrial alumina waste, a by-product of the steel industry. The composites used unsaturated ortoftalic polyester as binder, river sand as aggregate and fly ash as filler. Different compositions of flame retardants were tested, one with polishing alumina (residue) and one with commercial grade alumina, and these were used in concentrations of 15%, 30%, 45% and 60% by weight of resin. The properties assessed were mechanical strength, fire propagation and SEM/EDS image analysis and the results underwent statistical analysis to check for their significance. The compositions with the addition of 60% flame retardant waste showed a reduction of 85% in flame propagation times when compared with the samples without the addition of fire retardants and this was accompanied by increased mechanical resistance. No significant difference was found for the two types of flame retardant in terms of flame propagation time.

Processing and characterization of sol–gel titania membranes

In this work we present a structural characterization of sol–gel titania membranes obtained in both supported and unsupported forms. We used two commercial grade alumina supports obtained from Whatman and Rojan Advanced Ceramics. The unsupported membranes were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), nitrogen sorption, and X-ray powder diffraction (XRD). Morphological studies were performed in both supported and unsupported membranes using a field emission scanning electron microscope (FE-SEM). In order to evaluate the performance of the supported membranes, single-gas permeation experiments were carried out at room temperature with nitrogen, helium, and carbon dioxide. We concluded from nitrogen sorption experiments that increasing the membrane heat treatment temperature leads to samples with lower specific surface areas and greater pore sizes. Close packed titania particles of uniform size were observed in SEM micrographs of unsupported membranes. The SEM analyses also revealed the presence of titania coatings on supported membranes. Some of the obtained membranes showed a separation capacity for He/CO2 and He/N2 larger than that expected for the Knudsen mechanism in the investigated pressure range. However, a good part of the analyzed samples showed an improvement of their separation capacity with increasing the feed pressure.

Microstructure, mechanical and tribological properties of microwave sintered calcia-doped zirconia for biomedical applications

Among the available ceramics materials for load bearing bio-implant applications, Y-TZP is superior (fracture toughness: ∼10 MPa m 0.5) for its better mechanical properties. However, due to concerns related to property degradation of Y-TZP during long exposure in body fluid, the current work is taken up to study the feasibility of developing stabilised zirconia ceramics in CaO–ZrO 2 system, using microwave sintering (MW) technique. The present paper reports the processing, microstructure and tribological properties of microwave sintered Ca-doped ZrO 2 based ceramics. An important experimental result is that MW sintering to greater than 90% theoretical density can be achieved in Ca-PSZ (8 mol% CaO) and Ca-FSZ (16 mol% CaO) ceramics by sintering at 1585 °C for 1 h. The sintered materials exhibit Vickers hardness ∼8–10 GPa, which would allow them to be used as load bearing implants. Also, a modest fracture toughness (∼6 MPa m 0.5) was measured for Ca-PSZ, which is better than commercial grade alumina. So, it is possible to synthesize a material which has better combination of hardness and toughness than other commercially available bioceramics like alumina, hydroxyapatite, TCP, etc. Considering its specific application for THR (total hip replacement), tribological experiments using fretting wear tester serve to provide data about the wear behaviour of the proposed materials. The fretting experiments were conducted against a bearing-steel counterbody in air as well as in a SBF (simulated body fluid) environment. The wear behaviour of the investigated tribocouple is dominated by the formation of Fe oxide/chloride layer at the worn surface.

Wear of zirconia-dispersed alumina at ambient temperature, 140 °C and 250 °C

Commercial grade alumina along with 5, 10, 15 and 20 wt.% zirconia-dispersed aluminas were tested for their wear resistance at ambient temperature, 140 °C and 250 °C using a pin on disk tribotester fitted with a hot stage. The sample suite was investigated for physical characteristics including hardness, fracture toughness, bulk density, alumina grain size and zirconia grain size. The wear track and wear debris were investigated using profilometry, SEM as well as TEM. The 5 wt.% zirconia-dispersed aluminas had the lowest wear volume loss over the temperature range. The alumina sample exhibited a wear dependence with relative humidity which is attributed to the formation of a tribochemical layer. Investigation of the tribochemical layer using SEM/EDS and TEM electron diffraction showed the tribochemical layer to be aluminium hydroxide. The major wear mechanism for all samples was brittle fracture.

A new slurry evaluation technique by using ultrasonic attenuation

AbstractThe present paper deals with an application of the ultrasonic attenuation technique to evaluate slurry characteristics. Ultrasonic attenuation coefficients were observed for commercial-grade alumina powders with different dispersion/agglomeration conditions controlled by the amount of dispersant added or the pH adjustment. For slurry with relatively low solids content, attenuation increases linearly with an increase in the attenuation distance, suggesting that interaction forces between particles does not play an important role in the attenuation behavior. Experimental results for slurries with high solids content, however, reasonably demonstrated that changes in ultrasonic attenuation should be caused by the interaction forces. A methodological measurement of the amount of attenuation confirms that the ultrasonic attenuation behavior would be mainly affected by the boundary conditions between the particle surface and the surrounding dispersion medium, not by the dynamic conditions at contacts of particles.

Immobilization of CdS Nanoparticles Formed in Reverse Micelles onto Alumina Particles and Their Photocatalytic Properties

CdS nanoparticles, prepared in a reverse micellar system, were immobilized onto thiol-modified commercial-grade alumina (Al2O3−SH) by a simple operation. The resulting composite, Al2O3−CdS, could be utilized as a photocatalyst for the generation of H2 from 2-propanol aqueous solution. The better stability of CdS nanoparticles against photoirradiation was obtained with Al2O3−CdS than with silica-immobilized CdS nanoparticles (SiO2−CdS). The photocatalytic activity of Al2O3−CdS was affected by the quantity of CdS on Al2O3−CdS, and the quantity of the thiol groups on alumina particles.

Grain boundary structure and intergranular segregation in Al 2O 3

The relationship between intergranular segregation and grain boundary (GB) crystallography was investigated by TEM/EDX on a Mg and Ti doped commercial-grade alumina. A large enrichment of titanium and impurities such as calcium and silicon occurs at nearly all grain boundaries. The well ordered twin boundaries do not contain segregation nor some grain boundaries whose plane is parallel to a dense plane of alumina for both grains. In grain boundaries with a high segregation level the nature and content of the major element strongly vary with GB crystallographic parameters, depending on the orientation of the grain boundary plane. HREM studies of grain boundary structure do not reveal any intergranular glassy phase in the material.

Effect of the conditions of obtaining aluminum hydroxide and oxide on the properties of powders and their sintering

A study of the effect of the conditions of obtaining aluminum hydroxide and alumina on the properties of the powders showed that fine milling and washing with water increase their dispersion and decreases the content of the alkali compounds. After fine milling and washing with water, the phase composition of the commercial-grade alumina undergoes a change: its a-Al2O3 content decreases due to the transformation into the hydrated forms of Al2O3. Fine milling and washing of the alumina obtained from anode slimes lead to a significant reduction of the content of the alkali compounds in it and significantly improve the degree of sintering at 1650°C at a specific surface less than that of the milled commercial-grade alumina, i.e., the sintering temperature is 100°C lower than that required for the milled alumina of KirAF.

Evaluation of the activity of aluminum oxide powders

Increasing the heat-treatment temperature of the commercial-grade alumina does not have the same effect on the adsorption characteristics and the specific surface of the material. The maximum of the Δμ=f(t) plot corresponds to the phase transformation temperature of γ-Al2O3 into corundum. The dependence of the adsorption activity of the fired as well as the unfired aluminum oxide on the duration of milling has an extremal nature; at the same time, the magnitude of the specific surface monotonically increases up to a certain limit indicating the existence of a limiting (maximum) value of energy that can be accumulated in a solid during mechanical treatment. When investigating the technological operations in which the interaction processes of the dispersed phase with the dispersing medium (for example, slip casting) play an important role, it is advisable to study the adsorption potential of the material along with its specific surface.

The technology and properties of corundum heat storage materials

A technology was developed for the production of corundum lenses from unfired commercial grade alumina containing over 99% Al2O3. The porosity of the lens is 20% or less, the cold-crushing load varies 650–2900 kgf, and the abrasion resistance approaches that of cast corundum balls.

Corundum refractories from commercial grade alumina

The Snigirev Division of the Vnukovo Refractories Plant has started producing corundum chamotte with a water absorption not above 3% from commercial alumina for the manufacture of corundum refractories for applications in metallurgy and other branches of industry. The principle of briquetting formed the basis for a production technology of corundum refractories in which firing at 1700°C gives a product of a porosity of 17–20% and a cold crushing strength of 800–1300 kg/cm2 for an Al2O3 content of over 98%. The porosity can be reduced by 3–4% by firing at 1750°C.