Grades Of Alumina Research Articles

Utilisation of ultrasonic treatment for upgrading of hematitic/goethitic iron ore fines

Ultrasonic waves in pulps containing iron ore fines can start, or significantly intensify, particle cleaning, de-agglomeration or disintegration. Some softer minerals, often gangue minerals with lower iron contents such as kaolinite or ochreous goethite, disintegrate several orders of magnitude faster than the valuable iron-bearing minerals such as magnetite or hematite. This facilitates selective disintegration of the gangue minerals leaving the valuable minerals mostly unchanged.A set of experiments involving ultrasonic treatment of four Australian iron ore fine samples was undertaken using three different ultrasonic experimental setups. The effect of ultrasound duration, power and pulp density on the recoveries and grades of iron, alumina and silica was studied.The results showed that for hematitic/goethitic ores, the application of ultrasound enabled soft material of relatively low iron grade to de-agglomerate from the larger size fractions and report to the ultrafine size fractions. Modelled de-sliming of the ultrasonically treated ores showed that de-sliming following ultrasonic treatment could significantly improve the product iron grade, while de-sliming with a finer cut size could also improve the iron recovery compared with de-sliming identical ore that had not been pre-treated with ultrasound. It has been shown mathematically that in some scenarios it may be possible to simultaneously increase the iron grade and iron recovery in the de-slimed product if the ore has been treated with ultrasound before de-sliming.

Ceramic fibre reinforced refractory castables for very high temperature superplastic forming

AbstractIn the frame of the development of very high temperature die material solutions, two grades of alumina based ceramic fibres with a diameter close to 12 μm have been investigated as reinforcement solutions for an andalusite refractory castable. High temperature mechanical tests were performed up to 1200°C in four‐point bending conditions: rupture tests at high temperature and anisothermal creep tests. After testing, microstructural and rupture surface were observed in order to get information on deformation mechanisms and rupture processes. Results show that significant mechanical improvement were obtained up to 1100°C when compared to non reinforced refractory castables.

Dielectric loss during irradiation of a candidate ITER NBI RF ion-source insulator

Alternative NBI RF sources will require insulation for RF coils operating at about 1MHz, 60kV and moderate temperatures, in a radiation field. This is a situation which may cause electrical degradation. This is a situation known to cause electrical degradation. To test degradation and breakdown issues, a selected high purity alumina grade (Deranox 999) has been subjected to 1.8MeV electron irradiation at the expected temperatures, with a 1MHz RF high voltage applied. Dielectric loss has been studied to check degradation at the working frequency at 120°C and 240°C chosen to cover the expected temperature range. On irradiation at 120°C dielectric loss increased due to RIC and then remained constant up to 110MGy, and when irradiation ceased recovered the initial value with no permanent degradation. However at 240°C degradation was observed during irradiation, with dielectric loss increasing from 1.6×10−3 to about 3.1×10−3. Following irradiation the initial value showed permanent degradation, indicating that insulation temperature must be kept close to 100°C during operation.

ChemInform Abstract: Chemical Examination of Citrullus colocynthis Roots

Citrullus colocynth is (Hindi: Indrayan) belongs to the family cucurbitaceae. The . roots have beneficiary effects in inflammation of breast, pain in joints, in opthalmia and in uterine pains. In rheumatism equal . parts of root and long pepper is prescribed. A paste of the root is applied to enlarged abdomen of the children. I Oral administration of root powder and muscular injection is used for testicular enlargement and in Hernia. The ethanol extract of roots, shoot and fruits have exhibited antimicrobial activitiesY Literature survey revealed the presence of steroidal sapogenins, diosgenin, kryptogenin, lanosterol and ~­ sitosterol in various parts of C. colocynthis. Many medicinal properties of various parts particularly fruit , pulp and roots have motivated us, for the chemical investigation of its roots. Herein we report the isolation and characterisation of three new and four known aliphatic acids, esters and alcohols from acetone extract of the roots. The shade dried roots were extracted with acetone and separated by column chromatography using silica gel and alumina grade III to yield seven compounds characterised as tridecyl 2-methyl-19-ene-triacontanoate, heptadecyl trieicosanoate, nonaeicosanol, dotriacontanol, I-hentriacontanol, dotriacontanoic acid and tetraeicosanoic acid. Tlidecyl 2-methyl-19-ene-triacontanoate 1. (20 mg, C44Hs60 2, M ~ 646), mp 67°C; its IR spectrum showed the presence of ester and olefinic group (1740, 1170 and 1680 cmI ) and aliphatic nature of o CH3 II I H:>C-(criVI2-0-C-CH-(C~16-CH=CH-(criV9-CH::l

Studies on water-injection cyclone for processing iron ore fines

Attempts are made to evaluate the feasibility of using a water-injection cyclone for the concentration of iron ore fines. The separation characteristics of clay fines, containing large amounts of alumina and silica, from the iron values are discussed. The effects of critical variables, such as injection water rate, truncated cone diameter, spigot opening and vortex finder diameter, on the performance of a water-injection cyclone in terms of iron, alumina and silica grades; iron recoveries; and alumina and silica rejections are discussed. A set of 16 full-factorial experiments (24) was carried out to gain an understanding of the individual and interaction effects of the variables. The results indicate that classifying iron ore fines containing 63.0% iron, 2.5% alumina and 3.5% silica through a water-injection cyclone can produce concentrates with iron grades greater than 66.0% and alumina and silica contents less than 1.5% and 2.0%, respectively, at different study conditions. The achievable iron recovery values are greater than 88%, and alumina and silica rejections are more than 80% and 50%, respectively, within the specific study conditions. While the truncated cone diameter, injection water rate and spigot diameter influences the alumina rejection to a considerable extent, it is mostly influenced by the vortex finder diameter. The iron recovery and silica rejection values are mostly influenced by spigot diameter and truncated cone diameter. The effect of injection water on the concentration characteristics depend on the prevalent truncated cone diameter and spigot diameter conditions.

In situ formation of zirconia–alumina–spinel–mullite ceramic composites

A study was made to prepare and characterize multicomposite containing zirconia–mullite–spinel [ZrO 2–Al 6Si 2O 13– xMgAl 2O 4 (0.25 ≤ x ≤ 4)]. This multicomposite was prepared by reaction sintering of relatively pure commercial grades of zircon, alumina and magnesium carbonate. Spinel and mullite could be in situ formed, while ZrO 2 evolved mainly in monoclinic polymorph. The sintering properties in terms of bulk density (BD) and apparent porosity (AP) were measured. The formed phases were identified by X-ray diffraction pattern (XRD). Cold crushing strength (CCS) of the fired and thermally shocked bodies was evaluated. The fractured surfaces of the fired compacts were scanned by SEM. The results showed great dependence on the firing temperature as well as zircon content, type and amount of glassy phase. XRD exhibited that all samples contain m-ZrO 2 and Al 2O 3 and with decreasing the amount of MgO and increasing zircon, the spinel phase decreases while mullite begins to form at high zircon contents. Batches containing mullite, ZrO 2 and Al 2O 3 gave higher mechanical properties. Also, all samples retained more than 90% of their original strength after being subjected to 20 cycles of thermal shock (Δ t = 1000 °C).

Particulate multi-phase polymeric nanocomposites

The present research focuses on a model system of a blend of two immiscible polymers containing an inorganic nanofiller, exploring the effect of various melt processing procedures on structuring and on the resulting properties. Binary polypropylene/alumina and ternary polypropylene/nylon/alumina composites were produced by batch compounding under various processing conditions and compositions. Several types of polypropylene and alumina grades were examined. The alumina nanoparticles vary primarily in their mean particle size (13, 50, 500 nm). The morphology of the nanocomposites produced and their thermal, and rheological properties were studied. It was found that under certain processing conditions the nanoparticles significantly affect the morphology of the polypropylene/nylon polymer blend causing compatibilization. Also, the alumina nanoparticles affect the melt viscosity of the polypropylene/nylon blends, whereas their effect on either polypropylene or nylon melts was found insignificant. POLYM. COMPOS., 27:425–430, 2006. © 2006 Society of Plastics Engineers

Water‐Lubricated and Dry‐Running Properties of Ceramic Journal Bearings

AbstractJournal bearings and other well‐defined sliding surfaces are important for numerous moving mechanical assemblies. Quite often sliding surfaces are produced on particular components during fabrication, for which reason the manufacturer needs to know the properties of the materials in order to optimise production processes and the running‐in characteristics of the sliding surfaces. This paper describes application‐orientated tests to support the selection of ceramic materials for water‐lubricated and unlubricated journal bearings and similar sliding surfaces. The ceramics studied were different grades of alumina, sialon, silicon carbide, and zirconia. The most promising results were obtained with a dense, sintered silicon carbide.

Application of chance-constrained programming based on multi-objective simulated annealing to solve a mineral blending problem

This paper addresses the optimal blending of different available ores in such a way that the total expected cost of buying ore is minimized while satisfying the quality specifications. The risk limitation criterion used consists of the simultaneous minimization of the variance of the total cost. The problem is solved by Chance-Constrained Programming (CCP) based on multi-objective simulated annealing. The technique is able to deal with the stochastic nature of the variables in the blending problem. In generic form the objectives are to minimize expected value and standard deviation of cost in such a way as to meet the blend requirements within the specified reliability level. The variability of each variable in each flow is quantified by semi-variograms. Each flow is simulated to reproduce the characteristics, or behaviour, of the phenomenon as observed in the available data. The expected value of each variable in each flow is calculated by averaging of the simulated values. The problem expressed in terms of CCP is transformed into an appropriate deterministic equivalent, which is a non-linear optimization problem. The new form of the problem is solved by multi-objective simulated annealing. A case study is carried out to demonstrate the technique. The problem is formulated in terms of iron, silica and alumina grades with four ore sources. Pros and cons of the technique are discussed.

The onset of damage in shocked alumina

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Bourne N. K. 2001The onset of damage in shocked aluminaProc. R. Soc. Lond. A.4572189–2205http://doi.org/10.1098/rspa.2001.0804SectionRestricted accessThe onset of damage in shocked alumina N. K. Bourne N. K. Bourne Royal Military College of Science, Cranfield University, Shrivenham, Swindon SN6 8LA, UK () Google Scholar Find this author on PubMed Search for more papers by this author N. K. Bourne N. K. Bourne Royal Military College of Science, Cranfield University, Shrivenham, Swindon SN6 8LA, UK () Google Scholar Find this author on PubMed Search for more papers by this author Published:08 September 2001https://doi.org/10.1098/rspa.2001.0804AbstractShock wave profiles have been measured simultaneously using the velocity interferometry system for any reflector (VISAR) and embedded foil stress gauges. The gauge is backed using a transparent rear window made of polymethylmethacrylate, through which the laser beam entering the VISAR cavity is also shone. The technique is applied to grades of alumina of differing purity shocked just above the threshold normally taken to be the Hugoniot elastic limit (HEL). In the case of one of the aluminas, the result is analogous to metals with a small spall (dynamic tensile strength) signal recorded. In the case of the other materials, the signals show marked differences, indicating both the need for simultaneous measurement using a variety of sensors and the limitations of the present definitions for the mechanical thresholds in dynamic compression (HEL) and tension (spall strength). Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Zheng Z, Wang E, Liu X, Duan Z, Zhang L, Ou Z and Zhong J The Dynamic Response of Brittle Materials under Impact Loading, International Journal of Nonlinear Sciences and Numerical Simulation, 10.1515/ijnsns-2016-0019, 18:2, (115-127) Zinszner J, Erzar B, Forquin P and Buzaud E (2015) Dynamic fragmentation of an alumina ceramic subjected to shockless spalling: An experimental and numerical study, Journal of the Mechanics and Physics of Solids, 10.1016/j.jmps.2015.08.014, 85, (112-127), Online publication date: 1-Dec-2015. Sun Zhan-Feng , He Hong-Liang , Li Ping and Li Qing-Zhong (2012) The spall strength and shock compressive damage of AD95 ceramics, Acta Physica Sinica, 10.7498/aps.61.096201, 61:9, (096201), . Bourne N (2008) The relation of failure under 1D shock to the ballistic performance of brittle materials, International Journal of Impact Engineering, 10.1016/j.ijimpeng.2007.08.001, 35:8, (674-683), Online publication date: 1-Aug-2008. Zhang C, Kalia R, Nakano A, Vashishta P and Branicio P (2008) Deformation mechanisms and damage in α-alumina under hypervelocity impact loading, Journal of Applied Physics, 10.1063/1.2891797, 103:8, (083508), Online publication date: 15-Apr-2008. Bourne N, Millett J, Chen M, McCauley J and Dandekar D (2007) On the Hugoniot elastic limit in polycrystalline alumina, Journal of Applied Physics, 10.1063/1.2787154, 102:7, (073514), Online publication date: 1-Oct-2007. Bourne N (2006) Impact on alumina. I. Response at the mesoscale, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 462:2074, (3061-3080), Online publication date: 8-Oct-2006. Bourne N (2006) Shock propagation through alumina observed at the mesoscale, Journal of Applied Physics, 10.1063/1.2161423, 99:2, (023502), Online publication date: 15-Jan-2006. Bourne N (2005) The shock response of float-glass laminates, Journal of Applied Physics, 10.1063/1.2058196, 98:6, (063515), Online publication date: 15-Sep-2005. Millett J, Bourne N and Dandekar D (2005) Delayed failure in a shock-loaded silicon carbide, Journal of Applied Physics, 10.1063/1.1923161, 97:11, (113513), Online publication date: 1-Jun-2005. Bourne N (2002) Shock–induced brittle failure of boron carbide, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 458:2024, (1999-2006), Online publication date: 8-Aug-2002. This Issue08 September 2001Volume 457Issue 2013 Article InformationDOI:https://doi.org/10.1098/rspa.2001.0804Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Published online08/09/2001Published in print08/09/2001 License: Citations and impact Keywordsfailureshock wavespolycrystalline aluminasstrengthimpact loadinghigh strain-rate

In-beam dielectric properties of alumina at low frequencies

Loss tangent data for three commercial alumina grades measured in the range 0.1–300 kHz together with the effect of radiation are presented. Very different dielectric behaviour has been found for the three grades irradiated at 150°C and 250°C with 1.8 MeV electrons at dose rates of up to 3.5 kGy/s. In the case of Ceraten C9999, an extremely pure alumina, the increase in the loss tangent with dose rate and its dependence on frequency is due to the dc radiation induced conductivity (RIC). For Wesgo AL995 and Morgan Matroc Vitox 999 the behaviour is more complex. The influence of an applied electric field has also been examined. The importance of material selection is noted, as is the dose-dependent degradation for Wesgo AL995.

Determination of alpha and beta alumina in ceramic alumina by X-ray diffraction

Determination of alpha alumina (α-Al 2O 3) content has been one of the oldest X-ray diffraction (XRD) methods of analysis. However, rhombohedral aluminas may have a variety of morphological forms for which there are marked differences in relative intensities of their major XRD reflections (the preferred orientation effect). In addition, a specimen X-ray diffracting power may vary making it difficult or impossible to employ a reference material. Consequently, comparing intensities of selected reflections from a sample with those of a reference material may cause a serious analytical error. A conventional XRD and a Rietveld approach were used to analyze nine commercial ceramic aluminas, three NIST standards and two special grades of alumina for alpha and beta alumina (β-Al 2O 3=Na 2O·11Al 2O 3) content. The samples were also analyzed by scanning electron microscopy (SEM) to assess morphology. Increasing the number of XRD reflections analyzed from two to eight did not improve the reliability of the quantification process. The morphological differences among samples could not have been minimized that way. Conventional XRD (two to eight reflections) indicated alpha alumina values varying from 88 to 106% while the Rietveld analysis (full pattern) attributed 100% for all but two. These two samples were found to contain beta alumina. Initial Rietveld refinements indicate that the beta phase contains only a fraction of the total Na 2O content. The preferred orientation was computed for 14 specimens and assessed using a relative scale. The Rietveld least-square refinements would not only provide relatively quick, but also reliable information on alpha and beta content, as well as unit cell parameters of alpha and beta phases.

Effect of humidity on microwave dielectric losses of porous alumina

The microwave dielectric loss in highly porous alumina is measured in dry and moist atmospheres. Data are compared with those for sapphire and a fully densified alumina grade. Results indicate that the combination of humidity and porosity gives rise to a very high dielectric loss which is drastically reduced by replacing the moist atmosphere by dry gas. Measurements over a wide frequency range from 1 mHz to 100 MHz indicate that the origin of the microwave loss is due to the high frequency tail of a low frequency process. This low frequency loss peak shifts to lower frequencies with decreasing humidity, explaining the observed dependence of the microwave loss on humidity.

Role of environment on the surface degradation of Wesgo AL995

Wesgo AL995 alumina samples have been irradiated with 1.8 MeV electrons in high vacuum, dry air, and helium. The irradiations have been carried out at 450°C and approximately 10 −10 dpa/s, 700 Gy/s with applied electric fields of between 100 kV and 1 MV/m. Severe electrical surface degradation has been observed for this specific alumina grade during irradiation in vacuum, but not in air or helium. The irradiation of the surface is an important factor in the degradation. One possibility is that radiation enhanced vacuum reduction takes place, which may be related to the large grain size and low density of this alumina grade.

The effects of γ-irradiation on subcritical crack growth in alumina

A constant load test rig is described which allowed the time to fracture to be measured for ceramic bars loaded in 4-point bending while exposed to 1.5 Gy/s of 60Co γ-rays. Two grades of alumina, 97.5% and 99.5%, were used to compare subcritical crack growth (SCCG) under constant load with and without exposure to γ-radiation. Dynamic fracture tests on 30 samples of each material were used to determine the Weibull modulus from which the critical failure stress values for the γ-irradiated and non-irradiated samples fractured under constant load could be determined and used to compare failure times. The time to failure for a given ratio of applied stress to critical stress was found to increase by a factor ≈9 for γ-irradiated 97.5% alumina, but the same dose rate reduced the time to failure of the 99.5% alumina by ≈2. Measurement of the length of cracks extending from the tensile surface of test samples showed a much higher proportion of short cracks in a γ-irradiated, 97.5% alumina sample compared to a non-irradiated sample which had predominantly longer cracks. The crack size distribution in γ-irradiated 99.5% alumina showed a significant increase in the number of large cracks leading to a shorter time to failure. It was concluded that ionising radiation inhibits crack growth in aluminas with silica-rich grain boundary phases.

Dielectric spectroscopy of alumina ceramics over a wide frequency range

Aluminum oxide (either in single or polycrystalline form) is one of the insulator materials with broad application in high radiation environments. Despite this demanding use, very different values for the dielectric properties have been found in the literature before and after irradiation. In order to obtain a reliable database, the dielectric properties of several unirradiated commercial alumina grades have been measured over a wide frequency (1 kHz to 15 GHz) and temperature range (100 to 300 K). Loss tangent differences over three orders of magnitude have been observed. The possible explanations and the role of some impurities (mainly Mg and Fe) are analyzed.

Role of Different Grades of Indigenous Alumina on Development of Mullite Brick

In the present investigation, five different types of calcined alumina were incorporated in the formulation of mullite shapes to have a compartative study of the materials. The mullite compositions were pneumatically rammed at a pressure of 100 kg.cm−2 and fired at 1420°C for 4 hours. The results indicate mullite shapes possessing high spalling resistances (+ 30 cycles water quenching from 1000°C to room temperature) and improved cold crushing strengths after 25 cycles of spalling test.

Carbon Contamination at Silver Surfaces: Surface Preparation Procedures Evaluated by Raman Spectroscopy and X-ray Photoelectron Spectroscopy

The quantity and chemical nature of carbonaceous impurities remaining on polycrystalline Ag surfaces after preparation depend on the protocol used for cleaning. The effectiveness of several preparation protocols was investigated in this study: mechanical polishing with successively finer grades of alumina, Ar+ sputtering, chemical polishing, and chemical polishing followed by Tl underpotential deposition. The impurities detected on polycrystalline Ag surfaces subjected to these preparation procedures are carbon, oxygen, and aluminum, and these are qualitatively and quantitatively identified with X-ray photoelectron spectroscopy. With Raman spectroscopy, these carbonaceous impurities are qualitatively identified as graphite, hydrocarbon, and cyanide species, the last of these being present only on the chemically polished surfaces.

The effects of angle of impact and material properties on the erosion rates of ceramics

One of the major areas of wear in the generation of power from coal occurs in the pneumatic transport of the pulverised fuel from the coal mills to the burners. This erosion of the pipes is vastly accelerated at the pipe bends, therefore the choice of lining material is extremely important. This paper addresses the problem through the systematic erosion testing, at different angles of impact, of fifteen erosion resistant materials, to determine their feasibility as lining materials. Other factors examined in this paper are the effects of target, erodent and system variables on erosion rates. Of the materials tested two were tungsten carbide cobalt cermets while the others were all ceramics most of them various grades of alumina. It is shown that the relative hardness of the target and erodent does not provide a clear prediction of erosion resistance. Microtoughness measured, using the indentation method, and modulus of rupture were found to give a good indication of erosion resistance with the materials tested. Threshold velocity and angle effects have also been observed and have been related to a change in the erosion mechanism. It has been found that at high angles of impact, 90° and 60°, material removal occurs through the formation of lateral fracture and the formation and removal of chips from the surface. While at the lower angles of impact, 45° and 30°, damage appears to be predominantly plastic in nature with damage accumulation necessary for the formation of lateral cracking.

Thermal Stability of Ceramic Materials in Microwave Heating

Thermal stability was examined theoretically for various commercial grades of alumina heated by microwave energy. The critical temperature for thermal runaway was evaluated as a function of Biot number and ambient temperature, employing various functional forms of the dependence of dielectric loss with temperature. Field‐temperature relationships were derived for the limit of small temperature gradients in the specimen. Finite difference methods were used under conditions where significant temperature gradients were sustained in the specimen. The critical temperature approached limiting asymptotes for the extremes in Biot number, with smooth variation in the intermediate regime. Stability diagrams were constructed which denote regions of stability and their dependence on important system parameters. The effects of ambient temperature on critical temperature were determined analytically and compared with experimental observations on heating alumina fiber bundles by a hybrid configuration utilizing an external suseptor. The results have implications for temperature control near the critical temperature and the design of hybrid heating systems.