Patent ID: 7691443

Claim:
A process comprising: disposing a stack in a furnace, wherein the stack comprises a preform porous structure, wherein the stack has a center open region extending through the stack and an outer region extending outside the stack, around the outside of the preform porous structure, wherein the center open region and outer region is in fluid communication via a channel; and performing a one-cycle, non-pressure gradient process comprising: heating the porous structure to an initial temperature; directing a first portion of a reactant gas mixture into the center open region of the stack; directing a second portion of the gas mixture into the outer region of the stack; and densifying the porous structure in the one cycle to achieve a desired product density, by decreasing at least one of the temperature, the percentage of reactant gas, or the pressure during the one cycle, wherein the porous structure is densified from an average density of less than about 0.60 g/cm 3 to an average density of greater than about 1.70 g/cm 3 in the one cycle.