Showing papers on "Aluminium oxide published in 1992"

Structure of AlAl and AlSi3N4 interfaces bonded at room temperature by means of the surface activation method

Abstract: Al Al joints and Al Si3N4 joints were manufactured at room temperature by means of the surface activation method. In this procedure, the surfaces to be bonded are sputter-cleaned and activated by argon fast-atom-beam (FAB) irradiation and then brought into contact with each other under a slight pressure. The primary concept of the method is based on the idea that clean metal surfaces are inherently active and react with other elements such as oxygen, nitrogen and carbon, and thus form a strong bonding with ceramics even at room temperature. Therefore it was expected that the method will be effective only in an ultra high vacuum so that the sputtered surfaces remain clean until joining. It was found, however, that such a clean environment is not necessary for joining. Surfaces activated in a vacuum containing some residual gas can be bonded very strongly and do not lose the capacity of adhering even after exposure to the residual gases after sputt-cleaning. It is found by transmission electron microscopy that the interface structure depends remarkably upon the vacuum condition in which the surfaces to be bonded are sputter-cleaned. An intermediate layer consisting of a partially amorphous phase was found in Al Al joints bonded under a vacuum pressure of 10−5Pa, while an Al Al joint without an intermediate layer was formed by ultra high vacuum bonding. It is assumed that oxygen or water in the residual gas of the vacuum was absorbed on the Al surface and dissolved into metal by the argon irradiation. Thus, an amorphous Al O solid solution or a kind of aluminium oxide is formed. Al Si3N4 joints manufactured in a high vacuum from surface activated materials showed also an intermediate layer which was, however, entirely amorphous over the whole interface and was considered to have been formed predominantly on the Si3N4 surface.

Alumina-coating of silicon nitride powder

Abstract: α-Silicon nitride powder has been coated with aluminium oxide generated by the in-situ hydrolysis of aluminium isopropoxide in isopropanol solution. TEM examinations show clearly the coating structure and the homogeneity of dispersion of the aluminium oxide over the surfaces of the silicon nitride particles. Benefits of this method of addition of densification additives are shown in a faster sintering densification rate of coated particles compared with conventionally mixed powders, and in the homogeneity of the final microstructure.

Advanced immobilization and protein techniques on thin film biosensors

Abstract: Thin film technology providing the high purity and reproducibility required of an electrode surface for structures making use of monomolecular layers requires the adaptation of surface and protein chemistry to the necessities of molecular monolayers. Stepwise chemical modification of the metal electrode surface turned out to be most practical for these biosensors. Glass and polyimide sheets as well as aluminium oxide ceramics were used as electrode carriers. An electron gun was used to coat the substrates with a platinum layer (as electrochemical electrode) up to a thickness of 60 nm. To increase the peel strength of the sensors an adhesion layer of titanium up to a thickness of 80 nm was applied underneath. Structuring of these thin films was performed by a lift off technique. Metal layers were isolated by silicon nitride or polyimide layers which were structured by plasma etching. Different chemical oxidation techniques were applied to activate the highly purified platinum for further derivatization. The platinum oxide sites were silanized in order to obtain amino or mercapto coupling groups. To activate the electrodes for protein coupling six different coupling procedures were tested to immobiize different preparations of glucose oxidase from Aspergillus niger and l -lactate oxidase from Pediococcus species. To obtain a quantitative suppression of interfering substances differential measurement employing photochemical inactivation of enzymes was the most effective method.

Characterization of various aluminium oxide layers by means of spectroscopic ellipsometry

Abstract: This paper reports the characterization of both barrier type and porous type anodic oxide films on aluminium by means of spectroscopic ellipsometry (SE). In order to show the capabilities of the technique for quantitative determination of the layer characteristics, results based on ellipsometric data are correlated with complementary information from the analytical techniques transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). It is concluded that ellipsometry yields an accurate characterization for the thicknesses and the interfacial properties of both the barrier layer and the porous layer. The porosity of the porous layer, determined with SE, is found to be in good agreement with the results obtained from TEM.

Sorption of technetium on inorganic sorbents and natural minerals

Abstract: The sorption behavior of the pertechnetate anion in various solid-solution systems under aerobic conditions and pH 1.3–12.5 has been investigated. Batch techniques were employed. On most of natural minerals only surface adsorption occurs. Rs-values were no larger than 2.0 ml · g−1. Adsorption on various natural minerals and rocks such as sandstone, basalt, granite, pyrite, peat and others are comparaed with the analogous processes on artificial inorganic sorbents: titanium oxides (thermoxide-34, thermoxide-3), crystaline cadmium sulfide, zirconium phosphate, and complex inorganic sorbents: antimony oxide — silicon oxide — phosphorus pentoxide, antimony oxide — silicon oxide — aluminium oxide, lithium oxide — manganese oxide — aluminium oxide — water, lithium oxide — titanium oxide —chromium oxide — water. For comparison the sorption of Tc on some organic sorbents was included. The solubility of Tc2S7 in water was measured to be 0.257 g/l. It has been shown that preliminary irradiation of sorbents such as sandstone, peat and humic acid by γ-rays with doses not less than 107 rad results in the decrease of Tc(VII) sorption.

Some new aspects of the theory of oxidation and degassing of aluminium-based alloy powders

Abstract: A study has been performed of the oxidation and degassing processes of aluminium-based alloy powders. Oxidation and hydration of gas-atomized metal powders take place during inflight solidification and cooling to room temperature, during collection and keeping in the powder collection box and during transport and storage before consolidation. Under the atomizing conditions, oxidation cannot be prevented. In contact with humid gases (air) the oxide layer on the powder surface takes up water vapour which is physically or chemically bound. A literature study shows that the oxide layer on atomized aluminium powder is amorphous and has a thickness of 2–10 nm depending on the atomizing conditions. The amount of water in the powder is sufficient to form a completely closed hydroxide layer on the outer surface of the powder. The thickness growth of the oxide layer is governed by cation diffusion. Degassing experiments were carried out by heating canned powders in vacuum. The partial pressures of evolved water vapour and hydrogen were registered as a function of temperature at a constant heating rate. Two different alloy powders were used: the first air atomized and containing 1% magnesium (Al-20Si-3Cu-1Mg-5Fe), and the second (Al-9Fe-2Mo-1Zr) magnesium-free powder, atomized by nitrogen. Much work has been done on degassing, but most of it is directed towards industrial applications. The quantitative theoretical description of the degassing phenomenon is still lacking. A new approach aiming at narrowing this gap is presented by employing Wagner's theory of high temperature oxidation of metals. The diffusion coefficient of aluminium cations through the amorphous aluminium oxide layer has been determined in the degassing temperature range by using the experimental data of Hayden et al. The diffusion coefficient of aluminium cations through the Al2O3 layer has also been evaluated from the degassing experiments. The values obtained directly from the degassing experiments are in reasonable agreement with those derived from the oxidation results. It has been concluded that extrapolation of the results obtained from diffusion experiments at high temperatures in aluminium oxides towards the temperature range of degassing cannot explain the formation of hydrogen during this process, even if the surface diffusion coefficient (much higher than lattice diffusion coefficient) is taken into account.

Method of forming a semiconductor device having self-aligned contact holes

Abstract: At the surface of a semiconductor substrate a conductor film over a silicon comprising insulating film, and the first aluminium oxide film are formed. These films are patterned to form a plurality of lines and an aluminium oxide film mask covering the top faces of the lines. Over the whole surface, the second aluminium oxide film is formed and etched back to form aluminium oxide film spacers covering the side faces of the lines. Over the whole surface a silicon oxide comprising dielectric film is formed. Anisotropic dry etching of the dielectric film and the insulating film is performed with fluorocarbon comprising gas to form self-aligned contact holes extending down to the surface of diffused layers formed at the surface of the semiconductor substrate. The self-aligned contact holes can be formed to be self-aligned with two adjacent lines because silicon-comprising dielectric films have a high etching selectivity to anisotropic dry etching with fluorocarbon-comprising gas, compared with aluminium oxide film. Isolation between the self-aligned contact hole and the interconnect is made only by aluminium oxide film spacers, resulting in suitably minimized area of the self-aligned contact holes. Besides isolation between the lines and the interconnects filling the self-aligned contact holes, and between two interconnects each filling the neighboring self-aligned contact holes, respectively, can be well secured.

27Al MAS NMR studies of a new polyoxyaluminium cluster and its selective transformation to five-coordinate aluminium in the solid state

Abstract: Solid state 27Al MAS NMR (MAS = magic angle spinning) studies of a new large polyoxyaluminium cluster cation provide insight into its structure, and show that thermal treatment at 850 °C yields a novel transitional aluminium oxide containing a metastable five-coordinate aluminium site.

Filler for heat conducting polymers

Abstract: A pulverulent mixture of aluminium oxide with fractions of various particle size and outer shape, characterised in that it contains: (1) from 55 to 75 % by volume of spherical alpha -aluminium oxide, of which at least 90 % by weight has a particle diameter of from 20 to 120 mu m, (2) from 35 to 20 % by volume of spherical aluminium oxide, of which at least 90 % by weight has a particle diameter of from 3 to 25 mu m, and (3) from 10 to 1 % by volume of aluminium oxide having an irregular particle shape, of which at least 90 % by weight has a particle diameter of from 1 to 7 mu m, the percentages by volume adding up to 100 %. The mixture is suitable as a filler for plastics, in particular for casting resins, from which mouldings of high thermal conductivity can be produced.

Silberhaltiger Aluminiumoxid-Trägerkatalysator und Verfahren zur katalytischen Zersetzung von reinem oder in Gasgemischen enthaltenem Distickstoffmonoxid

Abstract: The invention concerns an aluminium oxide catalyst containing silver, the catalyst containing in addition copper oxide and, optionally, other promoters and active components. This catalyst is used to decompose pure nitrous oxide (N2O) or nitrous oxide in gas mixtures at elevated temperatures, and exhibits high activity.

Aluminium oxide thin films prepared by plasma-enhanced chemical vapour deposition

Abstract: Thin films of aluminium oxide have been deposited on glass, quartz, Si(100), steel, nickel, and aluminium by plasma-enhanced chemical vapour deposition (PECVD) using aluminium acetylacetonate (Al(acac)3) as precursor. The deposits are hard (up to 2370 HK) and show good adherence to the substrates. The influence of various experimental parameters on deposition rate, film composition and hardness has been studied. The bias turned out to be the most effective parameter.

Prepolymerized catalyst systems on carrier for preparation of poly-1-alkenes

Abstract: Catalyst systems for the polymerisation of C2- to C10-alk-1-enes, containing, as active constituents, metallocene complexes of metals from sub-group IV or V of the Periodic Table, and an oligomeric aluminium oxide compound, where firstly one or more metallocene complexes of metals from sub-group IV or V of the Periodic Table are combined with a solution of the oligomeric aluminium oxide compound in an inert hydrocarbon for a period of 5 to 120 minutes, the thus-activated catalyst system is subsequently converted into a suspension by precipitation with the aid of an inert, liquid hydrocarbon additionally containing a viscosity improver, and the resultant catalyst systems are then supported by brief prepolymerization of a C2- to C10-alk-1-ene at temperatures of from -60 to 20 DEG C. The catalyst systems according to the invention can be isolated, have a long shelf life and are particularly suitable for the preparation of polyalk-1-enes having a narrow molecular weight distribution and a narrow particle size distribution.

Catalyst systems on carrier for polymerization of C2-C10 alkenes

Abstract: Catalyst systems for the polymerisation of C2- to C10-alkenes, obtainable by a) adding an oligomeric aluminium oxide compound to a finely divided support, b) subsequently adding a complex compound of metals of sub-group IV and V of the Periodic Table to the product obtained from step a), and c) subsequently adding an oligomeric aluminium oxide compound to the product obtained from step b). m

Work piece coated with a hard layer and process for coating with the layer

Abstract: To produce a hard layer which is based on aluminium oxide and is extremely hard but can be prepared at substantially lower temperatures than is possible in the case of the high-temperature CVD process, the hard layer is essentially synthesised from (Al, Cr)2O3 mixed crystals having a chromium content of more than 5 atomic %.

Ready-to-use size for coating moulds for casting - comprises fire-proof inorganic aluminium oxide particles, additives and fibres, forming agglomerate-free coating

Abstract: Ready-to-use size for coating moulds or patterns for the casting process comprises 30-85 wt.% fireproof inorganic particles pref. aluminium oxide, silicon dioxide, aluminium silicate and/or zirconium silicate, 0.01-20 wt.% additives and 5-40 wt.% fibres, of which 10-90% are organic and the rest fireproof inorganic fibres. The inorganic fibres have an average length of 50-400 microns and a dia. of 1-25 microns and are pref. of aluminium silicate, carbon, aluminium oxide, glass or rock wool. The organic fibres have an average length of 50-5000 microns and a dia. of 2-70 microns and are pref. of cellulose, polyamide, polyester, polyether, polyethylene or polypropylene. USE/ADVANTAGE - The size dries quickly to form a coating with a relatively smooth surface, free from agglomerate

Electrode layer for a fuel cell and method for producing this electrode layer

Abstract: A fuel cell air electrode with good adhesion can be applied to solid electrolytes or ceramic support plates. To produce the electrode layer, use is made of a mixed oxide of the type La1-xAxBO3 (A = Mg, Ca, Sr, Ba; B = Fe, Co, Ni, Mn, Cr; x = 0.1 to 0.2) to which 1 to 10% by weight in each case of aluminium oxide, bismuth oxide or chromium oxide or a combination of said oxides or a combination of said oxides with further oxides are added.

Low density ethylene copolymers

Abstract: Low-density ethylene copolymers obtainable by adding an aromatic hydrocarbon solution of a catalyst system containing, as active constituents, metallocene complexes of metals from sub-group IV and V of the Periodic Table and oligomeric aluminium oxide compounds, to a mixture containing ethylene, comonomers and aliphatic hydrocarbons.

Particles suitable for use as carrier particles in electrophotography

Abstract: Described are particles (I) suitable for use as carrier particles in electrophotographic processes and made up of: a) a magnetic core and b) an envelope consisting of aluminium oxide, chromium oxide, molybdenum oxide, tungsten oxide, silicon oxide, tin oxide or zirconium oxide or a mixture of these oxides. Also described are particles (II) made up of: a) a magnetic core and b) an envelope of titanium oxide and produced by decomposing titanium tetraalcoholates in the gas phase by means of water and/or oxygen in the presence of the moving cores. The invention also concerns the manufacture of the particles and their use in two-component developers for electrophotographic processes.

Partially crystalline transition aluminium oxides, process for their preparation and use thereof for the production of shaped articles which contain substantially gamma alumina

Abstract: 1. Partially crystalline transition aluminium oxides, process for their preparation and use thereof for the production of mouldings essentially comprising gamma-Al2O3. 2.1 The decomposition products obtained by the known processes still contain crystalline fractions of undecomposed aluminium trihydroxide, especially of hydrargillite and/or fractions of hydrothermally produced boehmite, and as a result the required solid state reactivity is not always achieved. 2.2 The object is to produce partially crystalline transition aluminium oxides, which have a uniform phase composition and a high solid state reactivity, and which in the rehydration process even at atmospheric pressure make it possible to achieve a high degree of conversion of the solids particles into a finely fibrous boehmite, so as to ensure efficient further processing to give mouldings, which essentially comprise gamma-Al2O3 and which have a well developed internal surface and high mechanical stability. The partially crystalline transition aluminium oxide is characterised in that the solid, in addition to aluminium having coordination numbers of 4 and 6 also comprises aluminium with a coordination number of 5 vis-a-vis oxygen, the proportion of aluminium with a coordination number of 5 comprising at least 50% of the content of aluminium with a coordination number of 4. 2.3 The Al2O3 mouldings produced by the process according to the invention are suitable for the use as adsorbents, gas purification compositions, catalyst components or catalyst supports.

Composite body, its use and process for producing it

Abstract: In order to improve the adhesion and wearing properties of a composite body with a hard metal, steel or cermet substrate or a substrate body of a nickel or cobalt-based alloy and one or more surface layers, of which the outer one preferably consists of α aluminium oxide, it is proposed that this outer layer has a fine-crystalline α modification, the diffraction lines of which measured through the half-widths with X-ray beams have half-widths which are at least three times as great as those of a powdered α aluminium oxide compact body. In order to produce this α aluminium oxide layer, it is proposed to perform a plasma-activated CVD process at temperatures of 400 to 750 °C. The composite body is highly suitable as a cutting material, a high-temperature material or a hard-wearing material for friction components.

Composition for metallization

Abstract: PURPOSE:To provide a composition for metallization suitable for a ceramic substrate, in particular, the one consisting of aluminium nitride as a main component utilized for a ceramic package or a hybrid integrated circuit (hybrid IC). CONSTITUTION:In a composition consisting of copper powder and glass powder for metallization, mixed powder consisting of bismuth oxide, silicon oxide, boron oxide, lead oxide, and aluminium oxide, is primarily melted and is glazed, and this is used as the glass powder. At least any one of oxides of chrome, calcium, zinc, and of titanium is added to the glass powder and they are mixed together, to stabilize bismuth. Metallization of excellent adhesion and of good solder wettability can thus be carried out without carrying out a special preliminary process for a substrate of aluminium nitride.

Aluminium atom formation in electrothermal graphite atomizer atomic absorption spectrometry studied by in situ spectroscopic measurements of aluminium and aluminium hydride

Abstract: The aim was firstly to measure quantitatively the partial pressures of Al, AlO and AlH in a graphite atomizer under analytical conditions for the determination of the Al The absorbance spectrum of AlH was registered photographically With 500 ng of Al in an aqueous solution the partial pressures of Al and AlH were estimated to be of the same order of magnitude, ie, 10 Pa, both species appearing at 2200 K The large amount of AlH formed might explain the incomplete atomization and should, together with H2, be considered in mechanistic descriptions of Al atom formation Aluminium oxide could be observed in neither a spatially isothermal (integrated contact tube) nor a non-isothermal (commercially available Massmann-type) atomizer Secondly, the aim was to investigate the effects of several analytical variables on the Al and AlH signals This was performed in a series of experiments using fractional factorial designs The main result was that for decreasing masses of Al, the ratio of AlH to Al decreased and the Al signal became sensitive to a new set of variables Therefore, an atomization model based on measurements performed using microgram amounts of Al is probably not valid at the nanogram or picogram level

Silver-containing carrier catalyst, and a method for the catalytic decomposition of nitrous oxide

Abstract: Disclosed is a silver-containing carrier catalyst for the decomposition of nitrous oxide present as the pure gas or in gas mixtures. The carrier catalyst includes an aluminium oxide carrier with a BET surface area of 26 to 350 m2/g. Also disclosed is a method in which the carrier catalyst proposed is used for the selective catalytic decomposition of nitrous oxide present as the pure gas or in gas mixtures at elevated temperatures.

Scanner window coated with hard material and then with lubricous coating

Abstract: A scanner window through which a laser beam is projected to define a scanning pattern comprises a substrate formed of light transmissive material which allows the laser beam to project through a light transmissive hard material layer deposited onto the substrate, and a light transmissive lubricous coating deposited onto the hard material resulting in the scanner window having improved resistance to abrasive wear The substrate may be a glass; the hard material may be aluminium oxide, aluminium nitride, zirconium oxide, yttrium oxide, diamond, diamond-like carbon, silicon nitride, boron nitride or mixtures thereof; and the lubricous coating may be diamond-like carbon, diamond, polytetrafluoroethylene, polyethylene, tin oxide, indium oxide, zirconium oxide, yttrium oxide, silicone polymers, boron nitride, aluminium oxide and mixtures thereof An adhesive material of tin oxide, aluminium oxide, boron nitride, yttrium oxide, or Schott evaporation glass may be disposed between the substrate and the hard material A light transmissive lubricous polymer, eg a silicone, polytetrafluorethylene or polyethlene, may be disposed over the lubricous coating material The light transmissive hard material may be produced by a variety of processes, eg plasma sputtering, electron-beam evaporation, ion-plating or a reactive ion-beam sputtering technique In any one of these processes the other layer may be made by the same technique

Particles suitable as carriers for electrophotography.

Abstract: Described are particles (I) suitable for use as carrier particles in electrophotographic processes and made up of: a) a magnetic core and b) an envelope consisting of aluminium oxide, chromium oxide, molybdenum oxide, tungsten oxide, silicon oxide, tin oxide or zirconium oxide or a mixture of these oxides. Also described are particles (II) made up of: a) a magnetic core and b) an envelope of titanium oxide and produced by decomposing titanium tetraalcoholates in the gas phase by means of water and/or oxygen in the presence of the moving cores. The invention also concerns the manufacture of the particles and their use in two-component developers for electrophotographic processes.