Swiss Aluminium Ltd.

Swiss Aluminum Ltd.

Tiberiu Mizrah

Jean-Pierre Gabathuler

Albert Maurer

Ludwig Gauckler

Peter Kaser

Klemens Heilig

Matthias Hoffmann

Olaf Frei

Manfred Doll

Bernhard Schepers

Harald Bressler

Max Frish

Viktor Bodmer

Bernd Schr/o/ Der

In certain operating conditions of diesel engines, diesel soot filters which are made of known ceramic foam and filter efficiently per se have zero or only a very low degree of particle filtration, in particular at hight exhaust temperatures and exhaust velocities, that is, above all when the diesel engines are running under full load. Ceramic foam filters for cleaning exhaust gases of diesel engines in which the surface is roughened and wherein the peak-to-peak interval is approximately 1 to 100 .mu.m, preferably 1 to 10 .mu.m, do not have this disadvantage. A ceramic foam of this kind is manufactured by roughening the surface by deposition of inorganic materials and, if required, subsequent decomposition by temperature treatment.

Ceramic foam for filters for cleaning exhaust gases of diesel engines

In a filter consisting of holoow cylindrical open-pore ceramic foam cylinder elements and an end plate made of gas-impermeable material, as an insert in a filter cup for cleaning exhaust gases of diesel engines, in which the exhaust gases flow through the active filter section essentially perpendicularly to the cylinder axis, bending moments which lead to breakage of the ceramic foam cylinder elements occur during fitting of the elements due to lack of surface evenness and plane-parallelism of the end faces. A filter of the aforementioned kind, in which the end faces of the ceramic foam cylinder elements are provided with temperature-resistant and thermal shock-resistant layers of material which are plastic at room temperature, avoids the bending moments.

Filter for cleaning exhaust gases of diesel engines

In a filter consisting of hollow cylindrical open-pore ceramic foam and an end plate made of gas-impermeable material, as an insert in a filter cup for cleaning exhaust gases of diesel engines, in which the exhaust gases flow through the active filter section essentially perpendicularly to the cylinder axis, a larger ceramic foam portion such as is used e.g. as an exhaust filter for a diesel engine for a truck or passenger service bus can be made from one piece only with increased requirements, because the necessary dimensional accuracy necessitates increased requirements, and hence the economy of using the ceramic foam is greatly impaired. Also, the back pressure increases considerably. In a filter of this type these disadvantages are avoided by providing a filter which includes two or more axially arranged ceramic foam cylinder elements between which is located a lamella made of gas-impermeable material with at least approximately the same diameter as the ceramic foam cylinder elements and with at least one opening in the ceramic foam cylinder-free region.

In the case of filters for cleaning the exhaust gases of diesel engines, the deposited soot particles are burnt at intervals at temperatures between 550.degree. to 700.degree. C. By using filters consisting of open-pore ceramic foam manufactured by coating an open-pore body which can be burnt out, with a ceramic powder suspension, burning out the substrate material at temperatures of 100.degree.-500.degree. C. and then sintering at elevated temperatures, which filters comprise a self-supporting ceramic structure with an internal surface area of the total pore system of 1 m.sup.2 /l to 10 m.sup.2 /l and an open porosity of 55-92%, the soot combustion temperature is reduced to between 400.degree. to 550.degree. C. When coated with catalytically active substances, the soot combustion temperature is even reduced to 350.degree. C.

In a filter consisting of hollow cylindrical open-pore ceramic foam cylinder elements and an end plate made of gas-impermeable material, as an insert in a filter cup for cleaning exhaust gases of diesel engines, in which the exhaust gases flow through the active filter section essentially perpendicularly to the cylinder axis, bending moments which lead to breakage of the ceramic foam cylinder elements occur during fitting of the elements due to lack of surface evenness and plane-parallelism of the end faces. A filter of the aforementioned kind, in which the end faces of the ceramic foam cylinder elements are provided with temperature-resistant and thermal shock-resistant layers of material which are plastic at room temperature, avoids the bending moments.

In filters for cleaning the exhaust gases from diesel engines having openpored foam ceramic bodies, the deposited soot particles are burned up at temperatures of between 550.degree. and 700.degree. C. at periodic intervals. In order to lower the inflammation temperature of the soot in the regeneration phase of the filter, the ceramic bodies are catalytically coated. The region of the openpored foam ceramic body first subjected to the flow of the exhaust gases of the diesel engines has at least partly a denser pore structure than the remaining foam body so that the inflammation temperature can be lowered since temperature peaks occur in these regions on account of increased soot deposits, which temperature peaks lead to inflammation of the soot located there and consequently burn up all the soot deposited in the filter.

Filter for cleaning the exhaust gases from diesel engines

The solid cathodes built into reduction cells for aluminum production have at least one workface which can be wet by the precipitated metal. The starting materials, which contain titanium, boron and carbon in powder form, are first intimately mixed in such proportions that the sum of the powdered carbon and any carbon extracted from the substrate is in excess with respect to the amount required by the starting materials to form titanium diboride. This mixture is heated under a neutral or reducing atmosphere to 1600.degree.-2200.degree. C. and held for 5-45 min at this temperature. The reaction product containing pores and channels is then heated further, to 2250.degree.-2600.degree. C., and held there for 10-60 min to form a compact titanium diboride/carbon eutectic. Subsequently, the solid cathode is cooled to room temperature.

Process for manufacturing solid cathodes

The invention relates to a process for manufacturing crystalline alumina from aluminum hydroxide which after further conventional treatment is advantageously suitable for ceramic and refractory purposes or as a lapping and polishing agent. The process is such that aluminum hydroxide with a Na.sub.2 O content of .ltoreq.0.1 wt. % with respect to Al.sub.2 O.sub.3 is subjected either directly or after prior partial dehydration to a thermal treatment above the temperature for transformation to .alpha.--Al.sub.2 O.sub.3. The aluminum hydroxide has an addition of an ammonium containing mineralizer made to it, simultaneously in the presence of boron and/or fluorine, in particular an addition of NH.sub.4 BF.sub.4. The product is characterized by way of the essentially isometric shape of the single crystals.

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Schaffhausen, Switzerland

Tiberiu Mizrah