Fused quartz article having controlled devitrification

A method of forming a doped coating on an exposed surface of a fused quartz article, the fused quartz article comprising a body comprising fused quartz and a coating disposed on an exposed surface of the body, the doped coating comprising a plurality of metal cations, each having a valence of less than 4, wherein the plurality of metal cations comprises cations of at least one of an alkali metal, an alkaline earth metal, a rare earth metal, and combinations thereof, wherein the plurality of metal cations is present within the doped coating in a concentration of at least about 0.1 atomic percent, the method comprising the steps of:

• a) providing a silica slurry, the silica slurry being doped with a plurality of metal cations comprising cations of at least one of an alkali metal, an alkaline earth metal, a rare earth metal, and combinations thereof;
• b) providing a fused quartz article;
• c) applying the silica slurry to an exposed surface of the fused quartz article;
• d) drying the silica slurry on the exposed surface;
• and
• e) fire polishing the exposed surface to form the doped coating on the exposed surface.

A method of improving the creep-resistance of a fused quartz article, the fused quartz article comprising a body comprising fused quartz and a coating disposed on an exposed surface of the body, the coating comprising a plurality of metal cations, each having a valence of less than 4, wherein the plurality of metal cations comprises cations of at least one of an alkali metal, an alkaline earth metal, a rare earth metal, and combinations thereof, wherein the plurality of at least one metal cation is present within the coating in a concentration of at least about 0.1 atomic percent, and wherein the body undergoes a transition to a cristobalite crystal structure at a temperature in a range from about 1000° C. to about 1600° C., the method comprising the steps of:

• a) providing a silica slurry, the silica slurry being doped with a plurality of metal cations comprising cations of at least one of an alkali metal, an alkaline earth metal, a rare earth metal, and combinations thereof;
• b) providing a fused quartz article;
• c) applying the silica slurry to an exposed surface of the fused quartz article;
• d) drying the silica slurry on the exposed surface;
• e) fire polishing the exposed surface, wherein the silica slurry, after drying forms a doped coating on the exposed surface;
• and
• f) heating the fused quartz article and the doped coating to a temperature in a range from about 1000° C. to about 1600° C., thereby nucleating cristobalite crystals on the exposed surface, wherein the cristobalite crystals enhance the creep resistance of the fused quartz article.