Abstract: An optical fiber (F) is pulled by a capstan (6) from a silica preform (1) whose bottom end (20) is softened in an oven (2). After cooling, said fiber is coated with an organic protective coating by means of a coating device (4). According to the invention, the surface of the fiber is reheated under tension by means of a torch (14) upstream from the covering device. Tension stresses in the softened surface layer are therefore relaxed. Cooling, followed by the fiber-drawing tension being removed after the capstan (6) cause said surface layer to be put under permanent compression, thereby reducing the risk of the fiber breaking. The invention is applicable to manufacturing fibers having improved characteristics.

Abstract: An outer casing (1) and an inner mandrel (2), both of which are cylindrical and are substantially coaxial, with powder (3) for manufacturing the tubular parts (11) filling the space which lies between them, contain a stationary distance piece (5) disposed against a shoulder (4) formed in the upper portion of the mandrel (2) and around the upper portion. A cover (6) also is provided around the upper portion and bears firstly against the upper end of the stationary distance piece (5) and secondly against the end of the casing (1), the cover (6) being hollowed out so as to provide an annular space (7) around the stationary distance piece (5), a moving distance piece (8) being disposed in the space (7) and bearing against the surface of the powder (3) so that during isostatic compression, the upper end of the moulded part (11) can extend into the space (7) while driving the moving distance piece (8).

Abstract: A method of manufacturing beta alkaline alumina parts and in particular beta sodium alumina parts in which the following successive steps are carried out:A. Alumina powder and an alkaline carbonate powder are intimately mixed together in quantities such that a predetermined ratio Al.sub.2 O.sub.3 /Na.sub.2 O is obtained;B. Said intimate mixture is heated in an open crucible;C. Said mixture is allowed to cool freely;D. The powder thus obtained is crushed;E. Said parts are shaped; andF. Said parts are sintered;said parts being disposed for this purpose in a sintering chamber, which is at least partially made of a refractory material which includes a mixture of three ingredients, namely beta alumina fire clay obtained by melting and crushing into grains with a grain size of about 0.5 mm, beta alumina cement or binding agent obtained from an alpha alumina and sodium carbonate mixture by reaction in the solid state and at a temperature of about 1200.degree. C.

Abstract: The invention relates to a method of preparing beta alkaline alumina parts particularly for use as solid electrolytes in electric cells of the sodium-sulphur type. It consists in mixing alumina and an alkaline carbonate in predetermined quantities, heating the mixture, crushing after cooling, forming the parts, sintering them and, after said forming, but prior to sintering depositing a layer of a compound of said alkaline metal on the surface of the parts in contact with the atmosphere to create an atmosphere rich in sodium in the immediate vicinity of the parts during sintering for compensating any loss of the element which may occur from the parts and minimizing the loss of alkaline metal by diffusion towards the outside of the parts.

Abstract: Method for manufacturing alkaline beta alumina parts, consisting in heating a mixture of alumina and of sodium carbonate, in crushing the powder obtained, in shaping the parts, in sintering them at 1650.degree. C, those parts being arranged in a sintering enclosure suitable for creating, in the vicinity of the parts, an atmosphere which is rich in sodium. The invention is implemented in the embodiment of an electrolyte for sodium-sulphur cells.

Abstract: The alpha alumina part is heated to between 1400.degree. C and 1600.degree. C for 10 to 20 hours in a mass of alkaline carbonate or aluminate. It is then disposed in contact with a blank of the alkaline beta alumina part in a sintering enclosure suitable for establishing an atmosphere which is rich in alkaline metal and in heating this enclosure to between 1600.degree. C and 1700.degree. C for between 30 minutes and 4 hours, so as to sinter the alkaline beta alumina part while effecting the connection thereof to the alpha alumina part. The invention is used in manufacturing sodium-sulphur type electric cells.