Glass manufacturing – Processes – With shaping of particulate material and subsequent fusing...
Patent
1987-08-19
1989-07-18
Lindsay, Robert L.
Glass manufacturing
Processes
With shaping of particulate material and subsequent fusing...
65 184, 65 22, 65134, 501 45, C03C 1100, C03B 1906
Patent
active
048490016
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of forming sintered glass bodies and to glass bodies formed by such methods.
Water soluble glass compositions have been used to provide controlled dissolution of active materials incorporated in the compositions. When the active material is inorganic it can generally be incorporated, e.g. in oxide form, in the glass composition. Organic materials however degrade at glass melting temperatures and cannot therefore be incorporated in the glass itself. In an attempt to overcome this problem it has been proposed to provide a sintered glass body the pores of which are filled with an organic material.
Conventional sintering processes, such as are used in powder metallurgy, operate at high temperatures, e.g. 1000.degree. C., and typically require a free volume in the sintered products of less than 2%. These processes cannot be used to sinter glass compositions which flow at relatively low temperatures, typically 300.degree. to 400.degree. C. In addition, these prior art techniques are not suitable for the production of small and/or intricately shaped devices owing to the fagility of the powder perform prior to sintering. Handling problems preclude the application of mass production techniques. Furthermore, in order to provide sufficient porosity for receiving a filling material, a large free volume is required. Conventional processes provide a high degree of compaction prior to the sintering stage.
The object of the present invention is to minimise or to overcome these disadvantages.
According to the invention there is provided a method of forming a sintered water soluble glass body, the method including providing a water soluble glass in particulate form, compacting the glass particles together with a binder to form a self-supporting porous body, and heating the body to a temperature above Ts-10.degree. C. where Ts is the dilatometric softening temperature of the glass, the temperature not exceeding the denitrification temperature of the glass.
According to a further aspect of the invention there is provided a device for the controlled release of an active constituent and comprising a sintered glass body as defined in the above preceding paragraph and having pores containing the active constituent.
Embodiments of the invention will now be described with reference to the accompanying drawings in which:
FIG. 1 ilustrates the thermal expansion properties of a glass,
and FIG. 2 illustrates the relationship between sintering temperature and porosity.
The porosity of the body prior to sintering is determined by the compaction pressure and by the particle size distribution of the glass. Thus, a very wide size distribution results in a low porosity. Advantageously the glass particles are sieved to provide a fraction within a predetermined particle size range. For example, we have found that, by providing a glass powder of substantially uniform particle size a free volume as high as 45% can be obtained prior to sintering. It will be appreciated that, by providing predetermined proportions of various sieve fractions the free volume prior to sintering can be controlled to a desired value. For example, by increasing the proportion of finer sieve fractions, the free volume or porosity may be reduced and vice versa.
Typically a powder water soluble glass is sieved to provide a material of substantially uniform particle size. The powder is then treated with a binder. For this purpose we prefer to employ a material that is either volatile or decomposes to volatile material at a temperature no greater than the subsequent firing temperature of the sinter. We have successfully employed camphor, which is volatile, and nitrocellulose, which decomposes to carbon dioxide, water and nitrogen, for this purpose but other materials, for example naphthalene, can of course be used. The binder may be applied to the powder in a solvent, the solvent being allowed to evaporate prior to further processing.
The treated powder is next placed in a mould and compacted under pressure to form a porous body. High pressu
REFERENCES:
patent: 1654404 (1927-12-01), Blumenberg
patent: 2390354 (1945-12-01), Clapp
patent: 4165226 (1979-08-01), Kita
patent: 4645749 (1987-02-01), Drake
Arch Alfred J.
Drake Cyril F.
Tripp Mary
Lindsay Robert L.
STC PLC
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