Presence Of Alumina Particles Research Articles

Multi-scale characterization of the inner surface of as-received steam generator tubes and correlation with the Ni release in primary water

The inner surface of two as-received steam generator (SG) tubes made of nickel base alloy 690 was analyzed to explain the differences in nickel release obtained for the tubes in a loop simulating the primary environment of pressurized water reactors. The roughness, microstructure and chemical heterogeneities were characterized; differences that could explain the specific behavior of the two tubes in primary water were noted. In particular, the presence of alumina particles at the surface of SG tubes influences the nickel release: their dissolution in the primary coolant induces a change in roughness and a local breakdown of the passive film.

Optical Diagnostics for Solid Rocket Plumes Characterization: A Review

In recent decades, solid fuel combustion propulsion of spacecraft has become one of the most popular choices for rocket propulsion systems. The reasons for this success are a wide range of applications, lower production costs, simplicity, and safety. The rocket’s plumes leave the nozzle at high temperatures; hence, the knowledge of produced infrared (IR) emissions is a crucial aspect during the design and tests of the rocket motors. Furthermore, rocket plume composition is given by N2, H2, H2O, CO and CO2, while solid rocket motors (SRM) additionally inject some solid particles, given by metal fuel additives in the propellant grain, i.e., aluminum oxide (Al2O3) particles. The main issue is the detection of the particles remaining in the atmosphere due to the exhaust gas of the solid rocket propulsion system that could have effects on ozone depletion. The experimental characterization of SRM plumes in the presence of alumina particles can be conducted using different optical techniques. The present study aims to review the most promising ones with a description of the optics system and their potential applications for SRM plume measurements. The most common measurement techniques are infrared spectroscopy imaging, IR imaging. UV–VIS measurements, shadowgraph, and Schlieren optical methods. The choice of these techniques among many others is due to the ability to study the plume without influencing the physical conditions existing in and around the study object. This paper presents technical results concerning the study of rocket engines plumes with the above-mentioned methods and reveals the feasibility of the measurement techniques applied.

Improving surface hardness of aluminum 6063 alloy using hardfacing

The paper discusses a trial made for the development of surface composite on the surface of aluminium alloy. Alumina particles were used as reinforcement material in the Al6063 matrix. The gas tungsten arc welding is used for surface melting and formation of surface composite. Composite layer obtained was found to have improved hardness compared to the base metal. The effect of parameters of gas tungsten arc welding on the formation and characteristics of the composite layer was also studied. Empirical relation for resultant hardness of the surface composite in terms of input parameters and their interactions is also developed. Scanning electron microscopy analysis suggested uniform distribution of alumina into the matrix. Electron dispersive X-ray spectroscopy results confirmed the presence of alumina in the composite layer. Microstructural investigation was done to study the grain structure and refinement resulting from recrystallization as well as presence of alumina particles.

A comprehensive study on synthesis behavior of nanostructured Al-Zn-Mg-Cu alloy powder with and without 3 wt.% Al2O3 particles during mechanical alloying

The mechanical alloying (MA) process was applied to synthesize nanostructured Al-Zn-Mg-Cu alloy powder and its composite with 3 wt.% Al2O3 particles. Both the alloy and the composite powders were produced by simultaneous milling of the constituents for different milling times (0–50 hours), with fixed milling technical parameters. The produced powders were characterized by the X-ray diffraction (XRD) analysis to detect the generated phases. Also, a scanning electron microscope (SEM) and a transmission electron microscope (TEM) were used to observe the morphologies and measure the crystallite size of the powders, respectively. It was found that during the production of the composite powder, the size of Al2O3 particle changed which led to unexpected outcomes. In the alloy state, the average particle size and the crystallite size were lower and the microhardness values were higher than those in the composite powder. Also, the steady state was achieved after a shorter MA time in the alloy state compared to the composite state. The major reason for these results was the changes of alumina particle size in the composite powders at the first stages of the MA process due to consuming a noticeable amount of energy, which made them ineffective. In addition, the compressibility in the composite powders was lower than that of the alloy powders due to the presence of alumina particles. Moreover, in both powders, the compressibility decreased with increasing the MA time because of the increased work hardening and the reduced flow properties.

Mullite fabrication from natural kaolin and aluminium slag

The structural transformations of kaolin–aluminium slag mixtures during heating were studied using differential thermal analysis (DTA), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The amount of formed mullite increases with the firing temperature. At 1500°C, the mullitization of the mixture is almost complete. The morphology of the formed mullite is bimodal (primary and secondary phases). The primary mullite, formed from processing of kaolin by the gradual collapse of metakaolin from 990°C, has a shape of elongated crystals. The other hand, the secondary mullite formed by solution-precipitation from the glass phase in the presence of alumina particles has a shape of acicular grains.

Effect of the Sandblasting Process on the Surface Properties of Dental Zirconia

This paper presents the effect of the sandblasting and sintering processes on the surface properties of some commercial yttria stabilized zirconia (Y-TZP) for monolithic dental restorations in dentistry. The surface properties of dental zirconia can be improved further through various surface treatment methods, like surface abrasion, roughening, chemical treatment, tribochemical coating, or selective infiltration etching. But all these treatments are made on the sintered samples, not on the pre-sintered discs as are delivered by the dental suppliers. The hypothesis of this paper was that the mechanical effect on the surface of pre-sintered disc of Y-TZP assured by airborne-particle abrasion with alumina will be maintained after the sintering process. Additionally, we will follow the presence of alumina particles on the Y-TZP surface after airborne-particle abrasion process. Surface modifications of the experimental samples was performed by sandblasting for 15 s with Al2O3 particles (average particle size 83 mm) at pressure of 2 bars, using a SAB-Caloris equipment. Morphological and surface changes in the sandblasted, respectively sandblasted and sintered samples of Y-TZP are examined by using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. It is found that the surface modifications made on the pre-sintered Y-TZP disc remain after sintering process, which not affects these mechanical modifications of the surface. Also, it was detected the presence of alumina particles on the Y-TZP samples after airborne-particle abrasion process and for this reason we recommend the use of zirconia particle for airborne-abrasion process.

Effect of Annealing Temperature and Alumina Particles on Mechanical and Tribological Properties of Ni-P-Al2O3 Composite Coatings

In this study, the effect of annealing temperature and alumina particles on micro-hardness, corrosion, wear, and friction of Ni-P-Al2O3 composites coating is studied. The electroless nickel composite coating with various alumina particle content is deposited on a mild steel substrate. The corrosion behaviour and tribological behaviour (wear and friction) of the composite coated samples are investigated and compared with Ni-P coated samples. The micro-hardness, wear resistance, and corrosion resistance of the composite coating improved significantly after heat treatment (400 °C) and in the presence of alumina particles. The composite coating deposited with alumina particle concentration of 10 g/L in an electroless bath and heat treated at 400 °C shows excellent results compared to Ni-P, as-deposited Ni-P-Al2O3 coating and coatings heat treated at different annealing temperature (200 °C, 300 °C, and 500 °C). Microstructure changes and composition of the composite coatings due to incorporation of alumina particles and heat treatment are studied with the help of SEM (scanning electron microscopy), EDX (energy dispersive X-ray analysis and XRD (X-ray diffraction analysis).

Plasmonics properties of trimetallic Al@Al2O3@Ag@Au and Al@Al2O3@AuAg nanostructures

Bimetallic and trimetallic nanoparticles have attracted significant attention in recent times due to their enhanced electrochemical and catalytic properties compared to monometallic nanoparticles. The numerical calculations using Mie theory has been carried out for three-layered metal nanoshell dielectric–metal–metal (DMM) system consisting of a particle with a dielectric core (Al@Al2O3), a middle metal Ag (Au) layer and an outer metal Au (Ag) shell. The results have been interpreted using plasmon hybridization theory. We have also prepared Al@Al2O3@Ag@Au and Al@Al2O3@AgAu triple-layered core–shell or alloy nanostructure by two-step laser ablation method and compared with calculated results. The synthesis involves temporal separations of Al, Ag, and Au deposition for step-by-step formation of triple-layered core–shell structure. To form Al@Ag nanoparticles, we ablated silver for 40 min in aluminium nanoparticle colloidal solution. As aluminium oxidizes easily in water to form alumina, the resulting structure is core–shell Al@Al2O3. The Al@Al2O3 particle acts as a seed for the incoming energetic silver particles for multilayered Al@Al2O3@Ag nanoparticles is formed. The silver target was then replaced by gold target and ablation was carried out for different ablation time using different laser energy for generation of Al@Al2O3@Ag@Au core–shell or Al@Al2O3@AgAu alloy. The formation of core–shell and alloy nanostructure was confirmed by UV–visible spectroscopy. The absorption spectra show shift in plasmon resonance peak of silver to gold in the range 400–520 nm with increasing ablation time suggesting formation of Ag–Au alloy in the presence of alumina particles in the solution.

SYNTHESIS OF Cu–Al2O3 METAL MATRIX NANOCOMPOSITE POWDER FROM CuO AND Al POWDERS BY USING HIGH ENERGY PLANETARY FAST MILLING

Cu–Al2O3 metal matrix nanocomposite powder has been synthesized from CuO and Al powders using high energy planetary fast milling. Mechanical alloying was used to produce 20% Vol. Alumina as a reinforcement phase in copper matrix. Reactive milling between Cu ( Al ) solid solution and CuO powders lead to formation of Cu–Al2O3 metal matrix composite. To obtain Cu ( Al ) solid solution, Cu and Al powders with Cu:Al atomic ratio of six were mechanically alloyed for 50 h. XRD analysis showed that during the reaction of Cu ( Al ) solid solution and CuO , Al solute is extracted from Cu ( Al ) solid solution and reacted with oxygen of CuO to form alumina particles while copper turning back to pure Cu . Presence of alumina particles with sizes smaller than 50 nm was observed in TEM micrographs.

Ultrasound-induced cytolysis of cancer cells is enhanced in the presence of micron-sized alumina particles

Micron-sized alumina particles have been shown to enhance sonochemical free radical formation in aqueous solutions and simultaneously increase the solution temperature and acoustic (white) noise, effects attributable to enhanced inertial cavitation [T. Tuziuti, J. Phys. Chem. A 109 (2005) 4869–4872]. In the current study, the same ultrasound exposure system was applied to in vitro cancer cells as a model system to determine the effect of alumina particles on the long-term survival of cells and on the major pathways of cell death, i.e., either apoptosis or necrosis. Following 6h of incubation after ultrasound treatment, it was found that the cells died mainly through necrosis, irrespective of whether the exposure was conducted in the presence of alumina particles or not. Alumina particles were non-toxic to cells alone, but were found to decrease the long-term survivability of cells that survived the initial exposure. This effect depended on the size and concentration of particles. These results correlated well with the effect of alumina particles on the sonochemical oxidation of KI under the same exposure conditions. Spin-trapping with 5,5-dimethyl-pyroline N-oxide (DMPO) and electron spin resonance spectroscopy indicated that the sonochemical formation of OH radicals increased in the presence of alumina particles. The current study is consistent with the well known observation that micron-sized particles enhance the acoustic cavitation process.

Effect of electrochemical and mechanical parameters on the lubrication behaviour of Al 2O 3 nanoparticles in aqueous suspensions

The effect of alumina nanoparticles suspended in an aqueous acetate buffer solution on the tribocorrosion behaviour of a 316L steel/alumina sliding contact was investigated using a reciprocating wear test rig equipped with an electrochemical cell. Through the addition of 10% volume of alumina nanoparticles to an acetate buffer solution it was possible to reduce the coefficient of friction by a factor of 2 and the stainless steel wear by a factor of 10 and this over a range of electrochemical and mechanical conditions. The presence of alumina particles caused a significant wear on the alumina counter part. The lubricating behaviour of the suspension was comparable to a commercial oil in water emulsion used for metal cutting. The lubricating effect was attributed to a third body formed by nanoparticles trapped within the contact. The agglomeration state of the alumina particles and their size were found to play a critical role.

Effect of Presence of Nano-Size Alumina Particles on the Properties of Elemental Magnesium

In present study, elemental magnesium was reinforced with nano-size alumina particles (50-nm). The composite samples were synthesized using the technique of powder metallurgy and the effect of extrusion temperature and sintering on the end properties was particularly investigated. The results of microstructural characterization studies confirmed the presence and reasonably uniform distribution of alumina particles. Results obtained from extruded unsintered samples revealed that the hardness and dimensional stability of magnesium increases with an increasing presence of alumina particles while the 0.2%YS, UTS and ductility deteriorated. Results further revealed that including sintering step and extruding at higher temperature lead to an increase in dimensional stability, hardness, 0.2%YS, UTS and ductility for an alumina content as low as one percent by weight.

On the growth of 4H–SiC by low-temperature liquid phase epitaxy in Al rich Al–Si melts

Abstract The growth of 4H–SiC by low-temperature liquid phase epitaxy was studied in Al–Si melts. The temperature ranged from 1000°C to 1200°C. Some problems, which were sources of non-homogeneity of the growth or low reproducibility of the process, were identified and reviewed: (1) local delayed wetting of the seed by the melt, (2) morphological (3) presence of alumina particles on the liquid, (4) high reactivity of the melt with graphite at temperature above 1200°C, (5) formation of crystallites on the surface upon cooling. The solutions proposed to avoid or limit these problems are: (1) deposition of a Si layer before the growth, (2) careful backside gluing, (3) a two-step procedure involving the pre-dipping in the melt of a graphite rod on which alumina particles agglomerate, (4) growth at temperature lower than 1200°C. No solution was found to avoid the crystallites formation upon cooling.

Electrolytic Codeposition of Ni ‐ γAl2 O 3 Thin Films

The effects of current density, particle concentration, and agitation on composite electrodeposition have been investigated and a comparison made to the deposition of pure nickel using a rotating disk electrode. The nickel deposition efficiency and nickel polarization behavior are both substantially altered by the presence of alumina particles in the bath. Troughs in the nickel efficiency and kinks in the nickel polarization curves were observed which were not present during the deposition of pure nickel. The appearance of anomalous behavior in these measurements coincides with the appearance of a peak in particle incorporation into the film. This behavior has been ascribed to competition between the charge‐transfer controlled nickel deposition reaction, and the mass‐transfer limitation of the alumina deposition process at high currents.

Acidic Biopolymers as Dispersants for Ceramic Processing

AbstractSome acidic biopolymers serve as dispersants for colloidal processing of ceramics. One biopolymer we tested was alginate, a heteropolysaccharide containing two carboxylic sugar acids, D-mannuronic and D-guluronic. Kelp alginate was a suitable dispersant, provided that its viscosity was reduced by partial acid hydrolysis. Low molecular weight polymers rich in guluronic acid proved to be better dispersants than those rich in mannuronic acid, perhaps due to their greater charge density caused by their buckled molecular configuration. In situ processing of ceramic materials was tested by growing the alginate-producing bacterium, Azotobacter vinelandii, in the presence of alumina particles. Growth occurred at 15 vol% alumina in medium. Alumina particles which were exposed to such treatment showed a high packing density comparable to that with purified polymer. We also tested polypeptide polymers of the dicarboxylic amino acids, glutamate and aspartate, which also served as excellent dispersants for small alumina particles.