Glass manufacturing – Processes – With shaping of particulate material and subsequent fusing...
Patent
1997-09-17
2000-01-04
Silverman, Stanley S.
Glass manufacturing
Processes
With shaping of particulate material and subsequent fusing...
65391, 65 211, 651361, 65144, C03B 900, C03B 1910, C03B 2300, C03B 3700
Patent
active
060097248
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a process for preparing glass, more specifically glass powder or glass films.
The term "glass" is used for an inorganic material that is amorphous except for the crystalline phased forms in the amorphic matrix during cooling or during a thermal post-treatment, such as ceramic glass. The glass concerned is glass whose basic components are the oxides of silicon, sodium and calcium.
The term "biologically active glasses" or "bioactive glasses" (abbreviated to BAG) is used in this text to refer to a generic class of materials which also belong to the "glasses" but which furthermore: of the biological tissue in which they are implanted; as the base, together with additives to control the solubility, such as calcium fluoride. Sodium and calcium can at least partly be substituted by other alkali or alkaline earth metals.
As regards the technique for applying coatings of bioglass, reference is made to the work by A. Ravaglioli and A. Krajewski: BIOCERAMICS, published by Chapman & Hall, 1992 (ISBN 0 412 34960 4) pp 228-229, which describes a technique by means of which the glass is applied as a coating on a substrate by slip casting, in the form of a dispersion in a liquid with a binder, i.e. after manufacture of the glass in the usual manner, by melting at temperatures in the region of 1,450.degree. C. After this, the substrate with the coating must be heated to high temperatures, specifically above 1,100.degree. C., a technique which is not always favourable for the properties of the substrate. The work further describes how coatings can also be applied by plasma spraying with glass powder obtained from glass prepared in the conventional way, or by dipping (rapid immersion) in molten glass.
The patent literature also contains detailed descriptions of techniques for manufacturing powders with particular moulding characteristics, if required with a narrow distribution of the grain size. In summary it can be said that these texts all describe techniques based on material that is reduced in its dimensions by physical pre-treatment, such as grinding, from which a suitable fraction is separated out. In a last operation, the particles are then if required converted to a suitable geometry, e.g. spherical particles. Examples are: U.S. Pat. No. 4,783,214; 4,715,878 and 4,756,746 and DE 41 00 604.
The use of plasmas is also extensively described in the literature. An example is the growth of glass rods for fibre optic purposes in a plasma torch. The substances introduced into the plasma torch in this case have the same structure as those obtained after treatment in a plasma torch (Siemens Forschung- und Entwicklungsbericht Bd. (1975) No. 5 pp 310-317). In DE-A-1906209 a technique is also described for the continuous preparation of ceramic products by melting in an arc or flame of ceramic particles.
BAGs have a long history of biomaterials since their introduction by Hench in 1969. The mechanical and biological properties of BAGs and BAG ceramics have been extensively described around the world in many contributions to scientific journals. The different techniques for the synthesis and application of coatings on metal substrates are also well documented. In this connection, reference is made to the book "An introduction to bioceramics" edited by L. L. Hench and J. Wilson (Adv. Ser. in Ceramics, Vol. 1, World Scientific, 1993. ISBN 981-02-1400-6 or 981-02-1626-2 (pbk)), in which the authors of the different chapters refer to the most relevant literature references. Concerning the technique for applying bioglass coatings, reference can be made to the above-mentioned work by A. Ravaglioli and A. Krajewski.
The disadvantages of the process by which the glass powder has so far been prepared can be summarised as follows: melting the glass must be carried out in expensive crucibles (e.g. platinum), at least if the glass is not be contaminated by unwanted substances. During the melting of relatively small amounts, the composition cannot be kept under control. Since this process has normally to be carried out a
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J. Grabmaier, et al., "Growth of Quartz Glass Rods for Fiber Optics in a Plasma Torch Using Powdered SiO.sub.2 Starting Material", Research and Development Reports, vol. 4, No. 5, pp. 310-317, 1975.
Brauns Etienne
Helsen Jozef A.
Proost Joris
Ruller Jacqueline A.
Silverman Stanley S.
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