Grades Of Alumina Research Articles

In-beam dielectric properties of alumina

The dielectric properties (permittivity and loss tangent) of a 99.7% purity alumina grade have been measured over a wide frequency range (1 kHz-15 GHz) before and after 2 MeV electron irradiation at different temperatures. The dielectric properties at 15 GHz were measured during irradiation. Both prompt and fluence effects are observed together with permanent changes which continue to evolve following irradiation. The behaviour is complex, consistent with both radiation induced electronic effects and aggregation processes.

Raw Materials for Alumina Ceramics

A brief presentation is made of the raw materials for alumina ceramics. The important source is the alumina trihydrate resulting from the Bayer process. Purification of the Bayer aluminate liquor to minimise organics, iron oxide and silica, reduction of sodium oxide content, special conditions of precipitation and calcination and fine grinding of the calcined material lead to the production of various grades of alumina. Other processes involve acidification of the aluminate liquor followed by drying and calcination or treatment of aluminium amalgam with water to precipitate aluminium hydroxide. Typical properties and applications of alumina ceramics are discussed. A survey of the world scene is made and the situation in India is briefly reviewed. The importance of introducing collaborative efforts to accelerate activities in this field in India is stressed.

Insulator dielectric properties during irradiation

The use of insulators for fusion applications is subject to considerable uncertainty due to the lack of a reliable database about the dielectric properties of insulator materials during irradiation at different frequencies. A set-up for the room-temperature measurement of these properties during electron irradiation at 15 GHz is described. Sapphire, spinel, beryllia and several alumina grades have been measured. Some very complex flux and fluence effects are observed. Several sapphire samples degraded by the RIED effect at 250 and 450°C are examined.

Alumina ceramics for heating systems

Data on the dielectric properties of several high purity (> 99.7%) commercial alumina grades and sapphire are presented in wide frequency (1 kHz-145 GHz) and temperature (100 K–500 K) ranges. Loss tangent values show differences over more than three orders of magnitude. For fusion applications and in the frequency range of ICRH and LH, the loss tangent effect is consistent with relaxation processes and it is found that values as low as 10 −5 are available. On the other side, in the frequency range of ECRH the loss tangent can be dominated either by relaxation processes or by the interaction with intrinsic lattice vibrations.

Three-body abrasive wear of ceramic materials

The three-body abrasive wear characteristics of eight different ceramic materials, including alumina, silicon carbide and sialon, have been studied using angular quartz and silicon carbide particles as abrasive media. Cemented carbide and high speed steel were included as reference materials in the tests. The influence of type of abrasive particles on wear rate and dominating wear mechanisms is reported. Relationships between material properties, wear rate and identified wear mechanisms are discussed. Of the materials investigated, an alumina grade, reinforced with 25 vol.% silicon carbide whiskers, shows the highest abrasion resistance. Wear rates as well as wear mechanisms of the materials investigated are found to be strongly dependent on type of abrasive particles. For all materials, the harder silicon carbide abrasive medium results in a higher wear rate than for the quartz abrasive medium. Brittle fracture is the dominating wear mechanism of the materials when tested with quartz particles, while brittle fracture in combination with severe plastic deformation is the dominating wear mechanism of the materials when abraded with silicon carbide particles. Based on the present work, it is proposed that high hardness in combination with high fracture toughness is required for high abrasion resistance of ceramic materials. However, other material parameters such as grain size, porosity, secondary phases, impurities, etc. will also influence the wear characteristics. Further, it is believed that the deterioration characteristics of the abrasive particles are important factors influencing both wear rate and wear mechanisms of the ceramic materials.

New potentials for high mechanical strength grades of polycrystalline alumina for EC waves windows

New potentials for high mechanical strength grades of polycrystalline alumina for EC waves windows

New potentials for high mechanical strength grades of polycrystalline alumina for EC waves windows

A fine grained high purity alumina grade and a composite of alumina and 5% zircona have been characterized as possible candidates to be used in rf windows. Both dielectric and mechanical properties are measured. The room temperature permittivity is around 9.84 and 10.28, respectively without significant frequency dependence. Its temperature dependence shows a T 2 law for both types of materials. The room temperature loss tangent goes from 2 to 15×10 −5 and from 6 to 39×10 −5 respectively in the frequency range between 17 to 145 GHz. The temperature dependence shows a strong decrease at low temperatures for the fine grained alumina and almost no temperature dependence for the alumina/zircona composite. The obtained bending strength data are 370 ± 50 and 584 ± 66 MPa, respectively. These results indicate that the material grades are attractive for use in cryogenically cooled and in backup rf window designs.

Phase composition and microstructure of alumina grades G-00, G-0, and GSK produced in Russia

Phase composition and microstructure of alumina grades G-00, G-0, and GSK produced in Russia

Mullite-corundum chamotte and products based on Arkalyksk and Berlinsk clays

A comprehensive investigation was made of the sintering of Arkalyksk and Berlinsk clays. A technology was developed for obtaining mullite-corundum chamotte on the basis of Arkalysksk clay and alumina grade G-O and also mullite corundum articles based on this chamotte and plastic Berlinsk clay.

Investigations on ceramic materials for fusion technology

Abstract Thermophysical and mechanical properties were measured on SiC as an irradiation-resistant First Wall (FW) protection material and on various low loss microwave window materials. An evaluation shows that SiC may not to be excluded from use for FW protection, but only moderate plasma disruption impacts could be tolerated. For the HF window development several grades of alumina, A1N, and spinel were extensively tested for their thermal and mechanical properties and with respect to HF absorption at ≈ 145 GHz. Alumina and particularly sapphire are superior in dielectric properties, but if thermal stresses are taken into account, the best grades of A1N are preferable. This could be demonstrated by parametric lifetime calculations for windows of a given design. The tolerable HF power densities are, however, still unsatisfactory. Irradiations deteriorate both thermal conductivity and dielectric loss.

Chemical class separation of shale oils by low pressure liquid chromatography on thermally-modified adsorbants

Shale oils from Green River (USA) and Condor (Australia) were fractionated into compound classes by low pressure liquid chromatography on five columns in series containing successively less thermally-deactivated grades of alumina. No preliminary acidic and basic extractions were required, resulting in fewer polymeric artefacts than in other procedures. Irreversible adsorptive losses were minimized by the use of deactivated adsorbants and evaporative losses were minimized by the use of highly volatile solvents and small solvent volumes. Compounds identified include linear alkanes, isomeric linear alkenes, isoprenoid alkanes and alkenes, linear alkanonitriles, 2-, 3- and 4-alkenones, cyclopentanones, cyclohexanones, benzenes, styrenes, indans, indenes, 1-phenylalk-1-enes, naphthalenes, biphenyls, 3–5 ring aromatics, phenols, pyridines, quinolines, benzoquinolines, indoles, dihydroindoles and carbazoles. Particular compound classes may be isolated without performing a full chromatographic separation of all classes.

Influence of the type of alumina and additives on the properties of corundum heat-insulating refractory

We studied the properties of corundum heat-insulating refractories in relation to the alumina-containing components the type and amount of additive, and the firing temperature with the same amounts of polystyrene. We showed the advantage of using as the bonding part of the batch finely milled unfired alumina grade G-00, and as the filler — unmilled alumina GK. By varying the concentrations and composition of the additives, it is possible to obtain corundum lightweight refractories with densities of 0.75–1.1 g/cm3, and compressive strengths of 2–10 N/mm2. With an increase in the firing temperature the apparent density and strengths increase, and at 1780°C their values come within the range 1.0–1.35 g/cm3 and 5–25 N/mm2. In order to reduce the after-contraction of the goods fired at 1750°C it is desirable to use Cr2O3 as additive, and to increase the strength after firing at 1780°C — MgO.

高濃度充てんアルミナ‐熱可塑性樹脂系の混練と流動特性に及ぼす粉末特性の影響

Kneading torque and apparent viscosity were investigated on several series of alumina-thermoplastic resin systems selected from six kinds of alumina and three kinds of resin. The curves of kneading torque vs time at 453K were classified into four patterns which were dependent on resin type and alumina grade. The change of the pattern was also brought about by the change of solid concentration in the same alumina-resin system. The torque after 1h showed a good correlation with the apparent viscosity measured at the same temperature by a capillary type viscosimeter. The apparent viscosity of alumina-polypropylene and -polystyrene systems at high solid concentrations of 50% and 60% was influenced by the tap or compaction density of powders much more than by their surface area or size. The relative compaction density was an excellent parameter to estimate the flow and kneading properties at high solid concentrations. The alumina-polyethylene system, however, behaved somewhat curiously, because the type of degradation of polyethylene caused by the mechanical and thermal mixing was different from that of polypropylene or polystyrene.

Dielectric properties of neutron irradiated insulators

Abstract The dielectric properties (eand tan δ) of aluminium oxynitride (AlON), and two grades of commercial alumina (99.9% and 97.5% A1203) have been measured after neutron irradiation doses to faiences ranging from 1017 to 1020 n/cm2. The measurements span the frequency range 0.1 to 65 MHz and thus include the ion cyclotron resonance frequencies currently being considered for plasma heating in fusion reactors. The permittivity (Ψ) has been measure by a two fluid technique with an accuracy of better than + / - 1%. A 2% increase in permittivity has been observed after irradiation to 1019 n/cm2. The dielectric loss in AlON increased by approximately × 10 while that for the alumina increased by approximately × 3. After neutron irradiation to 1019 n/cm2, there was little difference in the loss factor of the irradiated alumina and AlON. The less pure ceramic (97.5%) was found to have lower loss than the high purity material. This may indicate the contribution of grain boundaries to the loss as the 99.9% mater...

Alumina tipped spring tine points—Field assessments

Engineering ceramics are a group of materials which can have excellent wear resistance by virtue of their high hardness. Alumina is one such material, and its wearing characteristics in the soil have been investigated. As part of this research programme, an alumina tipped spring tine point has been developed and tested over a period of five years, which included the launch of a commercial product during Summer 1982. Field trials were carried out to assess the reliability of ceramic tips manufactured in two grades of alumina using three different methods. A cold pressed and sintered tip in the more impact resistant grade of alumina was chosen for commercial prototype points produced in 1981. Subsequent field trials have proved the reliability of the prototype point in a variety of soil types although variations in performance have been noted. Mean wear ratios for steel/ceramic points have been determined from their average change in length for equal distances travelled. These ratios ranged from 3·2:1 to 8·2:1 over the period from Autumn 1981 to Spring 1984, with an overall mean wear ratio, derived from all the test sites, of just under 6:1.

Optimizing the Aluminas Used in Reduction Pots

The rational operation of reduction pots involves a great many constraints. Some of the major ones, namely automation of feed systems, pollution abatement, and improved working conditions, are directly linked to the grade of alumina used. Their respective importance depends, however, on the type of pot in question. Aluminium Pechiney has carried out theoretical studies, applied studies, bench-scale, and industrial tests aimed at optimizing the grade of alumina used in each type of pot. Specifications are specially adapted to take into account the specific surface, moisture content, grain size distribution, resistance to powdering, and extent to which the alumina crystals are ordered.

Investigating various types of alumina for the production of corundum refractories

The grades of alumina investigated and designed for the refractories industry contain from 99.4 to 99.74% Al2O3 which is substantially higher than specified by GOST 6912-74 in terms of impurity contents.

Materials

BA Chemicals Ltd., Chalfont Park, Gerrards Cross, Bucks. SL9 0QB, are now able to offer fine grades of alumina and alumina hydroxide powders which will be of interest to coatings manufacturers.

Determination of the active-ingredient content of technical and formulated DNOC and dinoseb and technical dinobuton by spectrophotometry. A Collaborative International Pesticides Analytical Council study

A spectrophotometric method is described for the determination of the activeingredient content of technical and formulated DNOC (2-methyl-4, 6-dinitrophenol) and dinoseb (2-sec-butyl-4, 6-dinitrophenol), and technical dinobuton (2-sec-butyl-4, 6-dinitrophenyl isopropyl carbonate). The method involves a preliminary clean-up on Woelm neutral alumina (grade I). Impurities are eluted from the column while the active ingredient is retained at the top of the column. The active ingredient is then eluted as its butylammonium salt and determined spectrophotometrically. Dinobuton samples require a preliminary separation from free dinoseb, de-esterification on the column and determination using the dinoseb procedure. Results obtained from international collaborative studies are presented and discussed.

アルミナとヘマタイトの浮選分離に関する研究

Flotation behavior of artificial alumina and artificial hematite, alone and in 1: 1 mixture, was investigated by laboratory flotator in a wide range of pH using C6-C12 fatty acid soaps with the intention of separating alumina from hematite.Experimental results are summarized as follows.1) Separation of artificial alumina and artificial hematite was possible with caprylate (C8) flotation by making use of potassium fluoride as a depressant for alumina. It was essential to regulate the pH of solution at 5.5-6.5 in order to obtain successful results. Both grade and recovery of alumina as a sink were more than 85% in the case where 2×10-3M (2.3kg/ton of ore) Potassium fluoride and 7×10-5-1×10-4M (0.2-0.3kg/ton of ore) sodium caprylate were used. Natural hematite was also used for comparison.2) In the case of the mixture of artificial alumina and natural hematite, no satisfactory results were obtained by the above method, which may be interpreted in terms of the poor floatability of natural hematite as compared to artificial one. In this system, separation was achieved by using tartaric acid as a depressant for natural hematite at pH 6.4 with caprate (C10) soap flotation; the grade and recovery of alumina as a froth were 82% and 96%, respectively, under the conditions of 5×10-4M (2kg/ton of ore) sodium caprate, 1×10-3M (3kg/ton of ore) tartaric acid, and pH 6.4.3) Preferential depression of hematite by tartaric acid was also applicable to the mixture of artificial alumina and artificial hematite, although less marked results was indicated as compared to the system containing natural hematite; the grade and recovery of alumina as a froth were 60-70% and 80%, respectively, at 1.5×10-4M (0.6kg/ton of ore) sodium caprate, 1×10-3M (3kg/ton of ore) tartaric acid, and pH 5.5-6.5.