Alumina Inclusions Research Articles

Clogging behavior of submerged entry nozzles for Ti-bearing IF steel

The nozzle clogging behavior of Ti-bearing IF steel was studied by metallographic analysis, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). According to the experimental results, nozzle clogging primarily appears three layers. There are a lot of large-sized iron particles in the inner layer and mainly slag phase in the middle and outer layers. The principal clog constituents of the inner layer are loose alumina cluster inclusions and granular shaped alumina inclusions, containing iron particles. The clog constituents of the middle layer are mainly dendrite alumina inclusions. The primary phases existing in nozzle clogging are FeO·TiO2 and FeO·Al2O3 besides α-Al2O3 and α-Fe. The FeO·TiO2 phases among the deposits adhere the deposits together firmly enough to lead to the inferior castability of Ti-bearing ultra low carbon steel compared with that of Ti-free low carbon Al-killed steel.

Design of composite porous cermets synthesized by hydrothermal treatment of CrAl powder followed by calcination

The microstructure of the porous Cr–Al metal–oxide cermet was studied by means of XRD, SEM, EDX as well as IR and Raman spectroscopy. This cermet was synthesized by mechanical alloying of Cr–Al powders in an AGO-2 planetary ball mill followed by hydrothermal treatment in a special stainless steel die and calcination in air. As a result, a highly porous monolith comprised of metal-like particles randomly distributed in the oxide matrix (Cr2O3 and Al2O3) was formed. Two types of the composite cores were found in cermets. The first one consisted of chromium phase containing nanoparticles sized from 50 to 140 nm and Al-enriched phase at the interfaces. The second one consisted of new chromium oxide phases with hexagonal Cr2N-like and fcc CrN-like structures probably with Cr2O and CrO stoichiometry. These new phases were stabilized within aggregates of the nanocomposite particles containing inclusions of alumina. The relations between different preparation stages and the cermet microstructure are discussed.

Determination of inclusions in liquid steel after calcium treatment

Nozzle blocking was eliminated by calcium-treated liquid steel through changing the chemical and phase composition of alumina inclusions in aluminium-killed steel. Three different methods were applied to determine the composition of inclusions in liquid steel: total oxygen content samples, sampling spoon samples, and “lollipop” steel samples. The results show that calcium modification of liquid steel influences the inclusion composition varying from 2wt% to 14wt% depending on the method used. The composition of inclusions contains mainly Al2O3-CaO only, or is associated with SiO2 or MgO depending on the initial input. The methods used in this study are indicators of the inclusion composition but can be improved to quantify the inclusion size.

THE FORMATION OF GRAPHITE WHISKERS IN THE PRIMITIVE SOLAR NEBULA

It has been suggested that carbonaceous grains are efficiently destroyed in the interstellar medium and must either reform in situ at very low pressures and temperatures or in an alternative environment more conducive to grain growth. Graphite whiskers have been discovered associated with high-temperature phases in meteorites such as calcium aluminum inclusions and chondrules, and it has been suggested that the expulsion of such material from proto stellar nebulae could significantly affect the optical properties of the average interstellar grain population. We have experimentally studied the potential for Fischer-Tropsch and Haber-Bosch type reactions to produce organic materials in protostellar systems from the abundant H2, CO, and N2 reacting on the surfaces of available silicate grains. When graphite grains are repeatedly exposed to H2, CO, and N2 at 875 K abundant graphite whiskers are observed to form on or from the surfaces of the graphite grains. In a dense, turbulent nebula, such extended whiskers are very likely to be broken off, and fragments could be ejected either in polar jets or by photon pressure after transport to the outer reaches of the nebula.

Transformation of Alumina Inclusions by Calcium Treatment

The objectives of this study were to investigate reactions of calcium with Al2O3 by different model experiments both on the laboratory and on the industrial scale. Experiments with solid Al2O3 and CaO were performed between 1350 °C and 1600 °C. Reaction rate constants were determined based on scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) observations of reaction products and weight measurements of the Al2O3 reacted via dissolution of the CaO bearing phases from the specimens after the annealing period. The results showed that the formation of calcium aluminate phases proceeded rapidly at temperatures greater than 1405 °C when a liquid calcium aluminate was formed. In the lowest temperature range (1350 °C–1405 °C), when the formation of liquid phase ceased, the reaction rate was several orders of magnitude lower. Industrial trials including Ca-alloy injection into steel, sampling and SEM/EDS analyses, as well as an inclusion rating in the samples show the concept of rapid transformation of the alumina inclusions with Ca treatment.

Nucleation and Growth of Alumina Inclusion in Early Stages of Deoxidation: Numerical Modeling

In order to gain a better understanding of deoxidation phenomena, there is a need to develop a model that could involve mass transfer, nucleating and growth kinetics of inclusion to simulate unhomogeneous state at the initial stage of Al deoxidation process. Based on the computation of the model for steel droplet with aluminum at center, it is found that the reaction zone between aluminum and oxygen in liquid steel is located in a limited zone at a certain fixed time and it is moved from center to outmost with the time going. For the zone besides the deoxidizer, i.e. aluminum, the supersaturation degree SO is very high at first, and then is decreased quickly, and the main part of oxygen in steel is absorbed by nucleation. In the other side, for the outmost zone, the main part of oxygen in steel is absorbed by growth of inclusion and the growth of inclusion lasts for longer time than that of inner zones.

Growth of Small Alumina Clusters during Ladle Deoxidation

The overall purpose of this thesis work has been to further our understanding of the growth and removal of inclusions in gas- and induction-stirred ladles. The primary focus has been on alumina inclusions.Growth mechanisms were studied using data from fundamental mathematical models of gas- and induction-stirred ladles. The results showed the turbulence mechanism to be the most dominant in alumina inclusion growth. The dynamic growth and removal of inclusions in a gas-stirred ladle was studied using mathematical modelling. The model results showed concentration gradients of inclusions. The effect was most obvious in the steel flow past the removal sites: top slag, ladle refractory, and gas plume (bubble flotation). A new removal model was developed for large spherical caps bubbles.In order to verify the predicted concentration gradients for the size population of inclusions, three experiments were carried out in production. The sampling equipment enabled sampling at five different positions and different locations at the same time. The results showed that concentration gradients of inclusions do exist both in induction-stirred and gas-stirred ladles. A theoretical analysis showed that the drag force on the inclusions to be the dominating force and that therefore inclusions follow the fluid flow.The cluster behaviour of alumina inclusions were examined on steel samples taken in an industrial-scale deoxidation experiment in a ladle. The samples were examined by microscope and the results used to study cluster growth. It was found that there was rapid cluster growth due to collision during stirring and that at the end of the deoxidation experiment a majority of the small inclusions were bound in clusters. The cluster growth data determined using the microscopic results were compared with predicted cluster-growth data. A method was developed for converting the experimental data observed per unit area into data given per unit volume and vice versa. An expression for the collision diameter of the cluster was also developed. The results showed that the predicted cluster growth agreed well with the microscopic observations for the assumptions made in the growth model.

The Use of Electromagnetic Fields for the Detection of Inclusions in Aluminium

Management of inclusions is an important part of quality control within the aluminium cast house. Inclusions have a detrimental effect on many aluminium cast products. The ability to reliably detect inclusions in a timely fashion is an essential part of this process. There are a number of tools available for inclusion measurement based on different principles. Techniques for inclusion detection such as metallurgical analysis, K-Mold, Podfa, Lais, Prefil all have a delay before detailed results are available. Ultrasound provides a possible technique for an online sensor, however has not as yet managed sufficient sensitivity. LiMCA, based on the Electrical Sensing Zone, has provided the most sensitive online detection to date, but other electromagnetic techniques such as a multiple voltage array sensor offer promise of a sensor which can be built for lower cost and can sample a larger portion of the melt.

Control of Ca addition for improved cleanness of low C, Al killed steel

In this work, heat trials (14 heats made on two sequences) were conducted to identify the minimum Ca addition possible for preventing submerged entry nozzle clogging and for improving the steel Cleanness. These trials were conducted on two sequences, the first one aimed at reaching the minimum Ca addition practically possible and the second aimed at stabilising this addition level. Evaluation of the results was carried out using metallographic microscope observation and SEM/EDX analysis. It was found that submerged entry nozzle clogging was successfully prevented by decreasing the amount of Ca addition from 0·095 to 0·06 kg Ca/ton steel. Moreover, it was possible to identify the effect of such addition level on converting alumina inclusions to globular Ca–aluminate and reducing the CaS inclusion formation range from 4–41 to 0·05–7·61%.

26Al decay: Heat production and a revised age for Iapetus

We revisit the appropriate energies to be used for computing heat production from 26Al decay. Due to the complexity of the decay scheme of this radioisotope, previous geophysical studies have used values ranging from 1.2 to 4 MeV per decay. The upper bound corresponds to the difference in mass energy between the 26Al and 26Mg ground states. This includes energy carried away by neutrinos, which does not contribute to heating planetary material. The lower bound does not account for the heating caused by the absorption of the γ rays from the excited 26Mg, or for the annihilation energy deposited in the material if the decay occurs inside even small planetesimals. Based on the calculations described by Schramm et al. [Schramm, D., Tera, F., Wasserburg, G.J., 1970. The isotopic abundance of 26Mg and limits on 26Al in the early Solar System. Earth Planet. Sci. Lett. 10, 44–59] updated with the most recent nuclear constants, we recommend using a heat production value of 3.12 MeV per decay, which is the total energy of disintegration minus the energy carried off by the neutrinos. This heat production value is higher than the value used in the modeling of Iapetus by Castillo-Rogez et al. [Castillo-Rogez, J., Matson, D.L., Sotin, C., Johnson, T.V., Lunine, J.I., Thomas, P.C., 2007. Iapetus’ geophysics: Rotation rate, shape, and equatorial ridge. Icarus 190, 179–202] by about a factor 2.5. The resulting estimate of the time of formation of Iapetus is shifted by about 1 Myr, to between ∼3.4 and 5.4 Myr after the production of the calcium–aluminum inclusions (CAIs).

Experimental and numerical study of the Young’s modulus vs temperature for heterogeneous model materials with polygonal inclusions

Abstract This work is related to the thermomechanical behaviour of industrial refractory materials. The microstructural complexity of such materials and the strong influence of the elastic properties on the resistance to thermomechanical sollicitations, lead us to study first of all the Young’s modulus of heterogeneous model materials with a simplified microstructure. The studied materials are composed of a glass matrix surrounding polygonal alumina inclusions. These two materials exhibit a dilatometric dissension sufficiently large to induce, during a thermal cycle, thermal stresses able to damage the matrix/inclusions interfaces. The present study deals with the Young’s modulus variations of the studied model materials according to the temperature. The numerical simulation of the matrix/inclusions interfaces behaviour was carried out using the Abaqus FEM code whose contact tool “Debond” allows to account for the interface matrix damage during a thermal cycle. The results show the ability of this tool to well describe the evolution of damage in function of the temperature. The Young’s modulus of the model materials was also measured using ultrasonic technique. A good agreement of the numerical and experimental results is obtained.

Motion behavior of non-metallic particles under high frequency magnetic field

Non-metallic particles, especially alumina, are the main inclusions in aluminum and its alloys. Numerical simulation and the corresponding experiments were carried out to study the motion behavior of alumina particles in commercial pure aluminum under high frequency magnetic field. At the meantime, multi-pipe experiment was also done to discuss the prospect of continuous elimination of non-metallic particles under high frequency magnetic field. It is shown that: 1) results of numerical simulation are in good agreement with the experimental results, which certificates the rationality of the simulation model; 2) when the intensity of high frequency magnetic field is 0.06 T, the 30 μm alumina particles in melt inner could migrate to the edge and be removed within 2 s; 3) multi-pipe elimination of alumina particles under high frequency magnetic field is also effective and has a good prospect in industrial application.

Ceres’ evolution and present state constrained by shape data

We model Ceres’ thermo-physical-chemical evolution by considering a large range of initial conditions as well as various evolutionary scenarios. Models are constrained by available shape measurements, which point to a differentiated interior for Ceres. We address the role played by hydrothermal activity in the long-term evolution of Ceres and especially the evolution of its hydrosphere. We suggest that models with times of formation shorter than about 5 My after the production of calcium–aluminum inclusions are more likely to undergo hydrothermal activity in their early history, which affects Ceres’ long-term thermal evolution. We evaluate the conditions for preserving liquid water inside Ceres, a possibility enhanced by its warm surface temperature and the enrichment of its hydrosphere in a variety of chemical species. However, thermal modeling of the hydrosphere needs to be further investigated. We show that shape data can help constrain the amount of hydrated silicate in the core, and thus the extent of hydrothermal activity in Ceres. We discuss the importance of these results for the Dawn mission’s arrival at Ceres in 2015.

Application of Al-Mg Alloy in Bearing Steel

There is less study about the effect of magnesium on characteristics of bearing. In the paper, the bearing steel was modified by three types of Al-Mg alloys. Firstly, the total oxygen content value was measured, and then the inclusion size, shape and chemical composition were analyzed by optical microscopy, SEM and EDX. The results show that, after treated by Al-Mg alloy, the total oxygen content descends remarkably and the alumina inclusion with big size and different shapes transform into spinel with small size and spherical shape. The optimal effect of inclusion modification is acquired after treated by NO. 3 Al-Mg alloy containing 16.55 wt% Mg, most of the inclusions in steel are spinel and magnesia, and the size of 96.23 wt% inclusions is less than 3μm.

Morphology and growth of alumina inclusions in Fe–Al alloys at low oxygen partial pressure

The degree of supersaturation is a factor that influences the Al2O3 inclusion characteristics in steel. The influence of the addition of a large amount of Al in the molten steel on the formation, growth and morphology of Al2O3 inclusions was investigated by laboratory scale experiments. Consecutive steel samples were taken during the deoxidation process and subjected to chemical analysis (ICP-AES), automated image analysis (AIA) and scanning electron microscopy (SEM) assessment with respect to the extracted inclusions. The characterisation and quantification of Al2O3 particles show different growth processes, leading to variations in particle size distribution as well as in the morphology.

Influence of non-metal inclusions on mechanical properties of CLAM steel

The effect of the size and distribution of non-metal inclusions on mechanical properties of the China low activation martensitic steel (CLAM) was investigated. The tensile and Charpy V-notch impact tests showed that electroslag remelting improved the tensile properties and reduced the ductile brittle transition temperature (DBTT). Inclusion detection of CLAM by optical microscopy and scanning electron microscope showed that both the dimensions and quantities of the alumina inclusions decreased and their distributions became more uniform after remelting. The better refinement and distribution uniformity of alumina inclusions were considered as the main possible reasons for the improvement of the mechanical properties of CLAM steel after remelting.

Pb–Pb dating of chondrules from CV chondrites by progressive dissolution

To refine absolute Pb–Pb ages of chondrules, we have experimented with progressive dissolution procedures of chondrules in the CV chondrite Allende in an attempt to effectively remove terrestrial contamination and generate Pb fractions of sufficient size and spread in 207Pb– 206Pb space to adequately define meaningful isochrons. Samples are extricated from the matrix, ultrasonicated, abraded and repeatedly pre-cleaned by ultrasonicating in distilled ethanol, water and acetone. Subsequent steps of weak HCl and HBr acids combined with ultrasonic agitation and modest heating effectively removes terrestrial contamination in most samples we analyzed. Subsequent exposure to warm 4 M HNO 3 typically isolates the least-radiogenic component of the stepwise dissolution series. Continuing the dissolution steps with HCl of increasing molarity with longer and higher temperature heating steps returns more radiogenic Pb fractions. The most radiogenic Pb fraction typically corresponds to the first warm 1 M HF step with subsequent steps in stronger HF yielding progressively less radiogenic signatures. Importantly, the Pb components extracted in the dissolution of the final residues with 28 M HF + 14 M HNO 3 typically lie slightly below the isochron defined by previous steps, corresponding to a slightly younger 207Pb /206Pb model age than the inferred real age. The wide range of total Pb contents (20–> 2000 pg) in different fractions returned by this method requires analyses by TIMS using a high-efficiency Pb emitter, 202Pb/ 205Pb double spike and diligent monitoring of laboratory Pb blank. As expected, U and Pb are highly and variably fractionated during the procedure such that no U/Pb age information is recovered. A multi-chondrule fraction from the CV chondrite Allende yields an age of 4565.32 ± 0.81 Ma, which is statistically younger than calcium–aluminum inclusions from the CV chondrite Efremovka.

Application of Al-free deoxidizer in rail steel manufacture

Because there are a lot of influences of alumina inclusions on the performance of rail steel, it is reasonable to adopt the deoxidization method with Al-free deoxidizer. According to the characteristics of Al-free deoxidization process, the control of aluminum content, the deoxidization with ladle furnace(LF) slag, the deoxidization process under vacuum by carbon, and the inclusions modification technology by calcium treatment were studied. All of them were applied to practical production. The results indicate that the adoption of Al-free deoxidization process leads to the total oxygen content in the steel below 20 ppm, which meets the requirement of clean rail steel.

Electron microscopy analysis of crystalline silicon islands formed on screen-printed aluminum-doped p-type silicon surfaces

The origin of a not yet understood concentration peak, which is generally measured at the surface of aluminum-doped p+ regions produced in a conventional screen-printing process is investigated. Our findings provide clear experimental evidence that the concentration peak is due to the microscopic structures formed at the silicon surface during the firing process. To characterize the microscopic nature of the islands (lateral dimensions of 1–3 μm) and line networks of self-assembled nanostructures (lateral dimension of ≤50 nm), transmission electron microscopy, scanning electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis are combined. Aluminum inclusions are detected 50 nm below the surface of the islands and crystalline aluminum precipitates of ≤7 nm in diameter are found within the bulk of the islands. In addition, aluminum inclusions (lateral dimension of ∼30 nm) are found within the bulk of the self-assembled line networks.

Experimental and numerical study of the elastic modulus vs temperature of debonded model materials

This work takes place in the frame of a general study dealing with the thermomechanical behaviour of industrial refractory materials. Because both the microstructural complexity of such materials and the strong influence of the elastic properties on the resistance to thermomechanical solicitations, the Young’s modulus of heterogeneous model material with simplified microstructure is studied in a first time. The studied materials are composed of a glass matrix surrounding alumina inclusions. These two materials exhibit a dilatometric dissension sufficiently large to induce, during a thermal cycle, thermal stresses able to damage the matrix/inclusions interfaces. The present study deals with the Young’s modulus variations according to the temperature in the case of model materials exhibiting debonding matrix/inclusions interfaces. It follows two other studies, at room temperature, devoted to the case of heterogeneous model materials exhibiting bonded and debonded interfaces respectively. The numerical simulation of the interfaces behaviour was carried out using the Abaqus FEM code whose the contact tool “debond” allows to account for the interface matrix damage during a thermal cycle. The rigidity of the modelled samples is obtained by simulating a pure tensile test under imposed stress then by using the Hooke’s law. The results show the strong influence of the meshing density at the crack tip so as that of the location of the initial damage regarding the loading direction during the tensile test. Moreover, samples fully similar to the numerical model were manufactured and their Young’s modulus was measured by using an ultrasonic technique. The comparison of the numerical and experimental results may be considered as satisfactory.