Method For Producing Ultra-High Purity, Optical Quality, Glass Articles
A method for producing ultra-high purity, optical quality, glass articles is disclosed which involves: 1. compacting metaloxide or metal loidoxide to granules having a mean particle size of less than about 1 millimeter; 2. optionally fully sintering the granules to produce high purity, artificial sand; 3. casting the granulesar artificial sand by conventional techniques, such as, slip casting, to form a high density, porous, green body; 4. optionally drying and partially sintering the green body; 5. optionally fully sintering the green body under vacuum, and 6. optionally hot isostatic pressing the fully sintered green body whereby the metal oxide or metalloid oxides is a pyrogenic silicon dioxide powder with a BET surface area of 30 to 90 m2/g, a DBP index of 80 or less, a mean aggregate area of less than 25000 nm2 and a mean aggregate circumference of less than 1000 nm, wherein at least 70% of the aggregates have a circumference of less than 1300 nm or a high-purity pyrogenically prepared silicon dioxide having metal contents of less than 0.2 μg/g.
1 . A method for producing a fused glass article comprising the steps of:
a) compacting metal oxide or metalloid oxide to granules having a mean particle size less than about one millimeter;
b) optionally sintering the granules at a temperature less than about 1.100° C., the density of the granules after sintering being approximately equal to their maximum theoretical density;
c) forming a green body from the granules or mixture of the granules according to step a) and/or step b), wherein theses granules can be sintered granules using uniaxial, cold isostatic and hot isostatic powder pressing, slip casting, extrusion, moulding and injection moulding;
d) optionally drying and partial sintering the green body in a chamber by (i) raising the temperature of the chamber optionally to above about 1000° C., and (ii) optionally introducing chlorine gas into the chamber and/or subjecting the chamber to a vacuum and/or purging the chamber with an inert gas; and
e) optionally fully sintering the green body in a chamber by raising the temperature of the chamber within a temperature range from about 1.200° C. to a temperature above about 1.720° C. while optionally purging the chamber with helium or applying a vacuum to the chamber.
2 . The method of claim 1 including the additional step after step (e) of hot isostatic pressing the fully sintered green body in a chamber by raising the temperature of the chamber to above about 1.150° C. and introducing an inert gas into the chamber at a pressure above about 100 psig (6,895 bar).
3 . Method according to claim 1 , characterised in that the metal oxide or metalloid oxide is a pyrogenic silicon dioxide powder with
a BET surface area of 30 to 90 m 2 /g,
a DBP index of 80 or less
a mean aggregate area of less than 25000 nm 2 ,
a mean aggregate circumference of less than 1000 nm, wherein at least 70% of the aggregates have a circumference of less than 1300 nm.
4 . Method according to claim 1 , characterised in that the metal oxides or metalloid oxides is a high-purity pyrogenically prepared silicon dioxide, characterised by a metal content of less than 9 ppm.
5 . Method according to claim 4 , characterised in that the metal oxide or metalloid oxide is a high-purity pyrogenically prepared silicon dioxide, characterised by the following metal contents:
Li
ppb
<=10
Na
ppb
<=80
K
ppb
<=80
Mg
ppb
<=20
Ca
ppb
<=300
Fe
ppb
<=800
Cu
ppb
<=10
Ni
ppb
<=800
Cr
ppb
<=250
Mn
ppb
<=20
Ti
ppb
<=200
Al
ppb
<=600
Zr
ppb
<=80
V
ppb
<=5