US3837825A — Process for making transparent silica glass

Claim 1

Independent Claim 179 words

A process for manufacturing precision amorphous silica glass articles from amorphous silica comprising at least 99.95 percent silica and having an average particle size no greater than 70 microns comprising forming, drying and firing a slip-cast article from said silica having a shape that is capable of being insidesupported during sintering, placing the dry rigid slip-cast article on a heated refractory support shaped to fit against the inner surface of said article, rapidly heating the article on said support from a temperature below 2200* F. to a sintering temperature of at least 3000* F., maintaining the temperature of the article from about 3000* F. to about 3150* F. in a vacuum or a helium atmosphere of a furnace for a period of at least several minutes to coalesce the particles while maintaining the original shape of the article, said period being such as to maintain the entire glass article in the amorphous state, said receptacle being sintered in said furnace until the glass is transparent, cooling the resulting transparent amorphous silica glass article, and removing it from said support.

Claim 2

Dependent Claim 179 words

A process for manufacturing precision amorphous silica glass articles from amorphous silica comprising at least 99.95 percent silica and having an average particle size no greater than 70 microns comprising forming, drying and firing a slip-cast article from said silica having a shape that is capable of being insidesupported during sintering, placing the dry rigid slip-cast article on a heated refractory support shaped to fit against the inner surface of said article, rapidly heating the article on said support from a temperature below 2200* F. to a sintering temperature of at least 3000* F., maintaining the temperature of the article from about 3000* F. to about 3150* F. in a vacuum or a helium atmosphere of a furnace for a period of at least several minutes to coalesce the particles while maintaining the original shape of the article, said period being such as to maintain the entire glass article in the amorphous state, said receptacle being sintered in said furnace until the glass is transparent, cooling the resulting transparent amorphous silica glass article, and removing it from said support.

Claim 3

Dependent Claim 42 words

A process as defined in claim 1 wherein the furnace temperature is maintained higher than the temperature of the internal surface of said article during heating of the quartz article so that gas trapped in the article tends to move radially outwardly.

Claim 4

Dependent Claim 33 words

A process as defined in claim 2 wherein the quartz article is heated from a temperature below 2200*F. to a temperature of at least 3000*F. in less than one minute to minimize devitrification.

Claim 5

Dependent Claim 29 words

A process as defined in claim 3 wherein the article is maintained under a high vacuum at a sintering temperature in said range until the article reaches full density.

Claim 6

Dependent Claim 42 words

A process as defined in claim 1 wherein an atmosphere of helium gas is provided in the furnace during heating of the quartz article and the article is maintained at a sintering temperature in said range until the article is substantially transparent.

Claim 7

Dependent Claim 23 words

A process as defined in claim 1 wherein the furnace temperature during heating of said quartz article is not in excess of 3200*F.

Claim 8

Dependent Claim 48 words

A process according to claim 1 in which the maximum temperature of the transparent article during sintering in said furnace is no more than 3200* F. and in which the article is heated from below 2200* F. to said maximum temperature in no more than about 8 minutes.

Claim 9

Dependent Claim 75 words

A process according to claim 1 in which, prior to sintering, the slip-cast article Is heated to a high temperature not in excess of 2200* F. under a high vacuum, such vacuum drying removing the surface water of hydration on the silica particles so that the finished transparent amorphous silica glass article has an infrared absorption beta OH factor as measured on an infrared spectrophotometer below 0.04 at a wave length of approximately 3.5 micron.

Claim 10

Dependent Claim 181 words

A process for mass producing precision transparent amorphous silica glass receptacles comprising placing on a heated refractory support a dry rigid slip-cast receptacle formed of amorphous silica particles comprising at least 99.95 percent silica, said refractory support being shaped to fit and support the inner surface of said receptacle, rapidly heating said receptacle on said support from a temperature below 2200* F. to a sintering temperature in the range of about 2950* F. to about 3150* F., maintaining the receptacle on said support at a temperature in said range in a furnace in a helium atmosphere or in a vacuum for a period up to about 6 minutes to coalesce the particles while maintaining the glass in the amorphous state, the heating being controlled to maintain the original shape of the receptacle as it approaches full density and to effect sintering until the glass is transparent, cooling the resulting transparent amorphous silica glass receptacle, removing the glass receptacle from the refractory support, placing another slip-cast amorphous silica receptacle on said support, and repeating the process to form other transparent glass receptacles.

Claim 11

Dependent Claim 181 words

A process for mass producing precision transparent amorphous silica glass receptacles comprising placing on a heated refractory support a dry rigid slip-cast receptacle formed of amorphous silica particles comprising at least 99.95 percent silica, said refractory support being shaped to fit and support the inner surface of said receptacle, rapidly heating said receptacle on said support from a temperature below 2200* F. to a sintering temperature in the range of about 2950* F. to about 3150* F., maintaining the receptacle on said support at a temperature in said range in a furnace in a helium atmosphere or in a vacuum for a period up to about 6 minutes to coalesce the particles while maintaining the glass in the amorphous state, the heating being controlled to maintain the original shape of the receptacle as it approaches full density and to effect sintering until the glass is transparent, cooling the resulting transparent amorphous silica glass receptacle, removing the glass receptacle from the refractory support, placing another slip-cast amorphous silica receptacle on said support, and repeating the process to form other transparent glass receptacles.

Claim 12

Dependent Claim 40 words

A process according to claim 9 in which the molded receptacle is placed on said refractory support while said support is at a temperature of about 2500* to 3000*F. to effect rapid heating of the article and to minimize devitrification.

Claim 13

Dependent Claim 28 words

A process according to claim 9 in which the molded quartz receptacle is formed by slip casting and is thoroughly dried before being mounted on said refractory support.

Claim 14

Dependent Claim 26 words

A process according to claim 11 in which the receptacle is slip cast in a porous concave mold having an internal surface coated with graphite particles.

Claim 15

Dependent Claim 48 words

A process according to claim 11 in which said receptacle is a cup-shaped crucible with a wall thickness from about 0.1 to about 0.3 inch and said crucible is heated in said furnace to a sintering temperature within said range which is not in excess of about 3100*F.

Claim 16

Dependent Claim 45 words

A process according to claim 9 in which the furnace temperature is maintained higher than the temperature of the internal surface of said receptacle during heating of the quartz article so that gas trapped in the walls of said receptacle tends to move radially outward.

Claim 17

Dependent Claim 61 words

A process according to claim 9 in which said refractory support is a graphite susceptor having a convex upper surface shaped to fit the inner surface of said receptacle and said molded receptacle is placed on said susceptor while the latter is at a temperature of about 2500* to 3000*F. to effect rapid heating of the receptacle and to minimize devitrification.

Claim 18

Dependent Claim 80 words

A mass production process according to claim 9 in which said graphite susceptor is moved between a heating position within an induction furnace and a cooling position outside said furnace wherein the susceptor is enclosed in a container having a non-oxidizing atmosphere, the helium atmosphere of the furnace being maintained at a temperature above 3000*F. and above that of the graphite susceptor, whereby trapped gas in the quartz article will move radially outwardly away from the surface of said susceptor.

Claim 19

Dependent Claim 83 words

A mass production process according to claim 16 in which said container has refractory enclosing walls at the bottom and sides and an opening at the top which may be aligned with the furnace opening at the bottom of the furnace to permit vertical movement of the graphite susceptor between said furnace and saiD container, and in which said container is moved horizontally to a loading position where said susceptor is lifted and exposed to permit removal of the transparent quartz glass receptacle.

Claim 20

Dependent Claim 119 words

A mass production process according to claim 17 in which the molded fused quartz receptacle is placed on the graphite susceptor at said loading position, said receptacle and said susceptor are lowered into said refractory container, said container is advanced to a position under the furnace in alignment with the furnace opening, said susceptor and said molded receptacle are raised into said furnace and held in the furnace for a predetermined period of time not in excess of six minutes, said susceptor and said receptacle are then lowered into said container and maintained in said cooling position for a predetermined period of time not in excess of one minute, and said container is then returned to said loading position.

Claim 21

Dependent Claim 32 words

A mass production process according to claim 18 in which the graphite susceptor is bathed in an inert gas during mounting and removal of the receptacle to minimize oxidation of the susceptor.

Claim 22

Dependent Claim 106 words

A mass production process according to claim 9 in which each molded receptacle is formed by slip casting pulverized fused amorphous quartz cullet having an average particle size no greater than 70 microns, said refractory support is a graphite mandrel, said mandrel is heated by induction in an induction furnace, and each receptacle is rapidly heated on said mandrel and in said furnace to form a transparent quartz glass receptacle with a peripheral wall thickness from about 0.08 to about 0.15 inch and having a shock resistance such that the article will not crack when submerged in water at 70*F. when the glass temperature is 2000*F.

Claim 23

Dependent Claim 24 words

A process according to claim 9 in which said particles comprise amorphous silica having an average particle size not in excess of 70 microns.

Claim 24

Dependent Claim 39 words

A process according to claim 9 in which said amorphous quartz glass receptacle is cooled to a temperature below 2700*F. in a period of time not in excess of about one minute before being removed from said refractory support.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1977-09-23	1978-03-25	1978-09-24	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1981-09-23	1982-03-25	1982-09-24	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1985-09-23	1986-03-25	1986-09-24	$7700.00	Window Closed / Lapsed

Process for making transparent silica glass

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