Abstract: An aluminum electrode foil for an electrolytic capacitor has a sponge-like etching layer formed on at least one of the surfaces thereof, and the sponge-like etching layer is reduced in a direction of thickness. The aluminum density of the reduced sponge-like etching layer `d2` is set from 0.8 to 2.2 g/cm.sup.3.

Abstract: A raw aluminum foil for use to prepare electrolytic condenser electrodes has an aluminum purity of 99.9% or higher and contains 50-500 ppm of Mg. A method of etching the raw foil to prepare the electrodes consists of a primary etching step and a secondary etching step, and the primary etching is conducted in an aqueous bath containing 3-10% by weight of HCl and 10-40% by weight of H.sub.2 SO.sub.4, at 70.degree.-90.degree. C. and with a current density of 10-40 A/dm.sup.2. The secondary etching is conducted electrolytically or chemically in a further bath containing 3-10% by weight of HCl, with or without 1% or less of H.sub.2 C.sub.2 O.sub.4 added to the further bath, at a bath temperature of 70.degree.-95.degree. C. and with a current density of 0-10 A/dm.sup.2.

Abstract: An aluminum foil to be etched for use as the electrolytic condenser electrodes is composed of a foil body of an aluminum purity of 99.9% or higher, and an oxide layer 20-70 .ANG. thick and formed due to contact of the foil body with an oxidizing atmosphere. At least one etching nuclei-forming element is concentrated in a boundary region and/or in an outermost surface region of the oxide layer, the boundary region being disposed between the foil body and the oxide layer, and both the regions having a thickness of 20 .ANG. or less. The ratio in ion intensity of a maximum concentration of the elements in these regions to a concentration of the elements in the inner layer of the foil body is 1.2-30. There are three patterns in distribution of the elements, so that the maximum concentration is in a predetermined ratio to the concentration in the surface region, the inner layer or a minimum concentration appearing between the regions.

Abstract: The fins of an aluminum heat exchanger are treated with a coating composition comprising an alkali silicate, an inorganic hardening agent and a water-soluble organic high-molecular-weight compound, whereby a hydrophilic coating is formed over the surfaces of the fins.

Abstract: A process for preparing a hollow aluminum extrudate for use in a vacuum characterized in that dry air or pure oxygen is supplied to the hollow portion of the shaped material being extruded. During the extrusion, the inner surface of the extrudate defining the hollow portion is held out of contact with the atmospheric air containing water to form a compact oxide coating on the inner surface without permitting formation of any hydrated oxide coating.

Abstract: A hollow extrudate for use in a vacuum is produced by a process comprising the steps of hermetically closing the forward open end of a hollow shaped material immediately after extrusion from a billet, cutting the shaped material after a predetermined length thereof has been subsequently extruded and hermetically closing the cut end at the same time, and cutting off the closed ends. The billet is a composite material composed of a core of aluminum having a high purity of at least 99.9% and an aluminum alloy cladding. The extrudate obtained has an inner layer and an outer layer corresponding to the core and the cladding, respectively.

Abstract: An aluminum material for use in a vacuum is produced by a process comprising the steps of removing a hydrated oxide coating from the surface of a worked aluminum material to obtain a clean surface in a dry state, and heating the aluminum material in an oxygen gas-containing atmosphere out of contact with the water-containing atmosphere to form an oxide coating on the dry clean surface.

Abstract: The fins of an aluminum heat exchanger are treated with a coating composition comprising an alkali silicate and a low-molecular-weight compound having carbonyl and are thereafter heated for drying, whereby a hydrophilic coating is formed over the surfaces of the fins.

Abstract: A process for treating the surface of aluminum foil for use as an electrode of electrolytic capacitors to increase the surface area of the foil to the greatest possible extent includes the three steps of pre-etching treatment, intermediate nitric acid treatment and post-etching treatment. The pre-etching treatment is conducted electrolytically in an aqueous solution of chromic acid and at least one of chromic acid and chromates. The intermediate nitric acid treatment is carried out by immersing the pre-etched foil in an aqueous solution of nitric acid to remove a chromate film formed by the pre-etching from the foil surface, especially from the interior of the resulting pits. The post-etching treatment is conducted electrolytically in an aqueous solution of hydrochloric acid, or hydrochloric acid and an oxidizing acid.

Abstract: An aluminum evaporator including a refrigerant tube and fins with a hydrophilic surface is prepared by forming a chemical coating over the surface of its components as assembled into a product or before fabrication, and thereafter forming a hydrophilic layer over the coating by treating the resulting components with a solution of silicic acid, silicate or colloidal silica.