Bactericidal silicon dioxide doped with silver

Details Bactericidal silicon dioxide doped with silver Bactericidal silicon dioxide doped with silver

2000-09-08

2002-07-23

Pak, John (Department: 1616)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Biocides; animal or insect repellents or attractants

C424S417000, C424S618000, C424S619000, C424S724000, C423S335000, C423S336000, C423S337000, C514S951000

Reexamination Certificate

active

06423331

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application is based on German Application DE 199 43 057.8, filed Sep. 9, 1999, which disclosure is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a pyrogenically prepared silicon dioxide doped with silver or silver oxide by means of an aerosol and having bactericidal properties, and to a process for its preparation and its use. The invention relates also to use of this doped silicon dioxide in dispersions or as a filler in rubber and silicone rubber.
BACKGROUND OF THE INVENTION
It is known to dope pyrogenically prepared silica in one step in a flame using a special process. (DE 96 50 500 A1). That process is a combination of high-temperature flame hydrolysis with pyrolysis. That doping process is to be distinguished from the older, so-called “co-fumed process”, in which the gaseous starting materials (for example SiCl
4
gas and AlCl
3
gas) are pre-mixed and burnt together in a flame reactor.
SUMMARY OF THE INVENTION
In the doping process, an aerosol is fed into a flame in which a pyrogenic oxide is produced by flame hydrolysis, the aerosol containing a salt of the compound to be doped.
It has now been found that if silver salts dissolved in water are used as the starting material for the aerosol, a doped pyrogenic silica having bactericidal properties is obtained as the product.
The invention provides a pyrogenically prepared silica doped with silver or silver oxide by means of an aerosol. The silica is characterized in that the base component is a silica prepared pyrogenically by flame oxidation or, preferably, by flame hydrolysis. The silica is doped with a doping component of from 0.0001 wt. % up to 20 wt. %, the doping amount preferably being in the range from 1 to 10,000 ppm, and the doping component is a salt or a salt mixture of a silver compound or metallic silver or mixtures thereof. The BET surface area of the doped oxide is from 1 to 600 m
2
/g, preferably in the range from 40 to 400 m
2
/g.
The invention further provides a process for the preparation of the pyrogenically prepared silica doped with silver or silver oxide by means of an aerosol, which process is characterized in that an aerosol is fed into a flame such as is used for the pyrogenic preparation of silica by flame oxidation or, preferably, by flame hydrolysis, the aerosol is mixed homogeneously with the gas mixture used for the flame oxidation or the flame hydrolysis before the reaction, then the aerosol/gas mixture is allowed to react in the flame and the resulting pyrogenically prepared silicas doped with silver or silver oxide are separated from the gas stream in a known manner. An aqueous solution containing salts or salt mixtures of silver or the metal itself in dissolved or suspended form or mixtures thereof is used for the preparation of the aerosol, The aerosol is produced by atomization by means of a two-component nozzle or by a different method of aerosol production.
The following may be used as salts: Ag(NO
3
), Ag
2
(SO
4
), Ag
2
O, or the salts may be complexed with complexing agents or ammonia.
The process of flame hydrolysis for the preparation of pyrogenic oxides is known from Ullmanns Enzyklopädie der techn. Chemie 4th edition, Vol. 21, p. 464.


REFERENCES:
patent: 4292290 (1981-09-01), Tunison, III
patent: 6328944 (2001-12-01), Mangold et al.
patent: 0 850 876 (1998-07-01), None
patent: 0 995 718 (2000-04-01), None
Akifumi et al., “Optical Waveguides and Manufacture Thereof”, STN Database Accession No. 129:60395 CA XP002150667 and JP 10 133043 A (Hitachi Cable, Ltd., Japan) May 22, 1998.
Formenti et al., “Preparation in a Hydrogen-Oxygen Flame of Ultrafine Metal Oxide Particles”, J. of Colloid and Interface Science, vol. 39, No. 1 (Apr. 1972), pp. 79-89.
Database WPI, Sec. Ch, Week 199923 Derwent Publications Ltd., London, GB; Class D22, AN 1999-272888 XP002151264 and JP 11 086757 A (Nippon Electric Glass Co.), Mar. 30, 1999.

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