Expanding tip plugs and method of using and making the same

A tip plug configured for sealing a center hole of a soot preform during at least one processing step for processing the soot preform, wherein the soot preform remains porous during the at least one processing step, the tip plug comprising:

• a glass composition comprising:
• SiO2 in an amount that is greater than or equal to 90 mol % and less than or equal to 99.9 mol %;
• and
• a foaming agent;
• wherein the foaming agent is configured to cause the tip plug to expand during the at least one processing step, thereby sealing the center hole of the soot preform without causing a gas to be released from the tip plug into the center hole of the soot preform;
• and
• wherein the viscosity of the glass composition is less than or equal to 109 poise at 1100° C. and/or greater than or equal to 105 poise at 1400° C.

A tip plug configured for sealing a center hole of a soot preform during at least one processing step for processing the soot preform, the tip plug comprising:

• a shaft including a first end, a second end, and a through hole extending through the first end and the second;
• a cap coupled to the first end of the shaft and defining a compartment, wherein the through hole of the shaft is configured for establishing fluid communication between the compartment defined by the cap and an environment in which the soot preform is processed during the at least one processing step;
• and
• an expanding pellet disposed inside the compartment.