GB754369A - Improvements in or relating to methods of applying light-diffusing layers to glass surfaces - Google Patents

Abstract

754,369. Electric incandescent lamps. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 8, 1954 [July 9, 1953], No. 20010/54. Class 39(2). [Also in Group XV] In order to improve the adhesion of a lightdiffusing coating produced upon a glass surface, such as the interior surface of a lamp bulb, by burning magnesium or magnesium alloys whereby finely divided magnesium oxide is deposited, the glass surface is .treated with. gaseous oxidation products of phosphorus, either during or prior to the deposition of the magnesium oxide. The treatment with the gaseous oxidation products of phosphorus is preferably carried out simultaneously with the application of the magnesium oxide, since the temperatures are then sufficient to ensure the reaction of the oxidation products with the glass surface. When the phosphorus is burned in the bulb beforehand it may be necessary to heat the glass to a temperature exceeding 150‹C. during, or for some time after, that treatment in order to obtain the desired action upon the glass. Satisfactory adhesion may be obtained by burning 15 milligrams of red or white phosphorus within a bulb having a surface area of about 100 square centimetres. Alternatively phosphorus compounds e.g. PzOs, P 2 O 5 or PH 3 may be used in amounts sufficient to yield the necessary quantities of oxidation products. The magnesium oxide may be applied to the glass surface by burning alloys of magnesium with other metals, e.g. lithium, aluminium, silicon &c., relative compositions of which are given in the Specification. Preferably the glass surfaces upon which the coatings are to be deposited are previously rendered light diffusing by etching. The magnesium or magnesium alloy, and the substances that produce oxidation products of phosphorus by combustion may be burnt in a container of quartz, tungsten, tantalum or similar refractory materials within the bulb, and the heat for combustion initiated electrically by a filament, carbon arc, high frequency heating or, as shown in Fig. 1, by passing current through a metal container 7 in which the materials are placed. The neck of the inverted bulb 3 is fitted upon a holder 2 on a stand 1, and the container 7, which is made of tungsten and supported upon two insulated current supply conductors 5, 6, is introduced through the aperture in the holder 2. A supply of oxygen and/or air for combustion is fed through a tube 4 located between the conductors 5, 6. Alternatively a supply of gases which yield oxidation products of phosphorus may be fed through the tube 4.