Boron oxide-silicon dioxide mixed oxide

Details Boron oxide-silicon dioxide mixed oxide Boron oxide-silicon dioxide mixed oxide

2000-04-03

2001-06-05

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S027000, C501S066000, C501S133000, C423S278000, C423S326000, C423S337000, C423S513000

Reexamination Certificate

active

06242373

ABSTRACT:

This application is based on application Ser. No. 19624392.0 filed in Germany on Jun. 19, 1996 and provisional application Ser. No. 60/029,845 filed in the United States on Oct. 29, 1996, the content of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a boron oxide-silicon dioxide mixed oxide, a process for its preparation, and its use.
2. Prior Art
Document DE-A 21 22 066 describes the use or pyrogenically produced mixed oxides of boron with silicon, aluminum, titanium and/or iron having a boron content of 2 to 20 wt. %, calculated as elementary boron, as a filler in organopolysiloxane compositions (for example bouncing putty). In particular these mixed oxides contain 5 to 10 wt. % of boron, calculated as elementary boron. These mixed oxides can be prepared by using metals and/or metal compounds according to Ullmanns Enzyclopadie der technischen Chemie, (Ullmanns Encyclopedia of Industrial Chemistry), Vol. 15 (1964), p.726. They are preferably prepared from volatile compounds of boron and silicon, aluminum, titanium and/or iron, especially the chlorides of the aforementioned elements, in the presence of water formed in situ at temperatures above 800° C., i.e. by flame hydrolysis. The mixed oxides obtained have a BET surface of 100 to 400 m
2
/g.
According to the example given in document DE-A 21 22 066, 4.8 kg/h of SiCl
4
and 1.2 kg/h of boron trichloride are vaporised and burnt together with 1.5 m
3
/h of hydrogen in a combustion chamber, under the addition of 4.2 m
3
/h of air. The temperature in the combustion chamber is more than 800° C. The resultant mixed oxide contains 82.5 wt. % of SiO2 and 17.5 wt. % of B
2
O3 (=5 wt. % of boron) calculated as boron and has a BET surface of 180 m
2
/g.
The known boron oxide-silicon dioxide mixed oxide has the disadvantage that it occurs in very finely divided form having a BET surface greater than 100 m
2
/g. It is unsuitable for use as a raw material in glass-making.
The known process has the disadvantage that boron trichloride is used as starting material for the boron oxide. Boron trichloride is a poisonous compound with a boiling point of 12.5° C. When used at room temperature special safety measures are therefore necessary. The commercially available boron trichloride may contain noticeable amounts of poisonous phosgene as impurity.
The object of the invention is therefore to prepare a boron oxide-silicon dioxide mixed oxide that does not have these disadvantages.
SUMMARY OF THE INVENTION
The invention provides a boron oxide-silicon dioxide mixed oxide, which is characterised in that it has a BET surface of less than 100 m
2
/g, preferably 10 to 80 m
2
/g, in particular 25 to 50 m
2
/g.
The proportion of boron oxide-may be from 0.01 to 40 wt. %.
In a further development of the invention the boron oxide-silicon dioxide mixed oxide may contain a further oxide or further oxides of metals and/or metalloids as a constituent of the mixed oxide.
Such metals or metalloids may be aluminum, titanium or zirconium.
In a preferred embodiment the boron oxide-silicon dioxide mixed oxides according to the invention may be prepared pyrogenically.
The known process of flame hydrolysis may preferably be employed for this purpose. This process is described in Ullmanns Enzyclopadie der technischen Chemie, 4th Ed., Vol. 21 (1982), pp. 464 and 465.
The boron oxide-silicon dioxide mixed oxide according to the invention having a BET surface of less than 100 m
2
/g, preferably 10 to 80 mg
2
/g, in particular 25 to 50 m
2
/g, can be prepared by vaporising silicon halides and/or organosilicon halides, for example methyl trichlorosilane, preferably the chloride SiCl
4
with a vaporisable boron compound, for example trimethyl borate, separately or together, optionally with the addition of vaporisable compounds of the metalloids and/or metals aluminum, titanium, zirconium, for example AlCl
3
, ZrCl
4
, TiCl
4
or the like, mixing the vapours together with a carrier gas, for example air and/or nitrogen, in a mixer unit, preferably in a burner of known construction, with hydrogen as well as air and optionally further gases such as oxygen and nitrogen, reacting the gases in a flame, then cooling the hot gases and the solid, separating the gases from the solid, and optionally removing halide or raw material residues adhering to the product by a heat treatment with moist air.
The process according to the invention has the advantage that the trimethyl borate that is used is miscible in all proportions with SiCl
4
, and it is therefore possible to adjust the ratio exactly. Since the boiling point of trimethyl borate of 68° C. is sufficiently close to the boiling point of silicon tetrachloride, it can be vaporised jointly with silicon tetrachloride from a vaporisation unit.
The boron oxide-silicon dioxide mixed oxide according to the invention, which may optionally also contain TiO
2
, Al
2
O
3
and/or ZrO
2
, can be used to make high-purity glasses. The high purity and the adjusted particle fineness of the mixed oxide according to the invention are of particular advantage.


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CPI Basic Abstracts Journal; Sep. 9, 1987: No. 87-194590/28.*
Ullmans Encyclopedia Industrial Chemistry; 1993; vol. A23, pp. 635-640.*
Chem. Abstracts; 1; vol. 94, No. 8; Abstract 49/11N, Apr. 1980.*
Ullmans Encyclopedia der technischen Chemie; 1982; vol. 21 pp. 464-465.*
Ullmans Encyclopedia der technischen Chemie; 1964, vol. 15, p. 726.

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