Method for the chemical vapor infiltration of refractive substances

摘要

Method for chemical vapor infiltration of refractory substances, wherein a porous structure is subjected in a reaction zone to the flow of a gas containing at least one gaseous precursor, wherein the partial pressure of the precursor and the dwell time of the gas are set at a given temperature in such a manner that a deposition reaction of the precursor occurs in the porous structure in the partial pressure range of the saturation adsorption and the reaction of the precursor is limited in each stage of the infiltration in such a manner that during the flow through the reaction zone no more than 50% of the precursor are deposited as a solid phase in the porous structure, and the exposure of the porous structure to the flow occurs in a stack of superimposed layers through ring-shaped vertical circumferential gaps (A, B) as well as through transverse gaps (C) which are open towards the circumferential gaps (A, B). The outer circumferential gap (A) is open both towards the inlet side and towards the outlet side of the reaction zone, while the inner circumferential gap (B) is closed towards the inlet side and towards the outlet side and has a gap width that is greater than the outer gap (A).

主权项

1. Method for chemical vapor infiltration of at least one refractory substance, in which method a porous structure is subjected in a reaction zone, which is heated to a predetermined reaction temperature, to the flow of a gas containing at least one gaseous precursor forming a solid phase by deposition reaction, wherein the partial pressure of the gaseous precursor and the dwell time of the gas while passing through the reaction zone are set at the predetermined reaction temperature in the reaction zone in such a manner, that
a deposition reaction of the precursor occurs in the partial pressure range of saturation adsorption, and that the deposition reaction of the gaseous precursor is limited in each stage of the infiltration in such a manner that no more than 50% of the gaseous precursor supplied in the gas are reacted for deposition of the solid phase in the porous structure while the gas is passing through the reaction zone, wherein the porous structure is exposed to the flow in ring-shaped layers of at least one vertical stack of the superimposed ring-shaped layers, the stack being arranged in a vertical direction between an inlet side and an outlet side of the reaction zone, through vertical circumferential gaps (A, B) of a ring-shaped radially outer circumferential gap (A), defined at an inner circumference thereof by the radially outer sides of the layers and at an outer circumference thereof by a radially inner side of a reactor wall, and a ring-shaped radially inner circumferential gap (B), defined at an inner circumference thereof by a radially outer side of a central core of the stack and at an outer circumference thereof by the radially inner sides of the layers, as well as through transverse gaps (C) extending between the layers transverse to the vertical direction and through transverse inlet side and outlet side end gaps (D, E) each extending between the inlet side and the outlet side of the reaction zone and the respective neighboring layer of the stack, wherein each of the transverse gaps and each of the end gaps are open towards both of the circumferential gaps (A, B), and each of the circumferential gaps has a gap width between said inner and outer circumferences thereof that is constant between the transverse gaps at least in a circumferential direction of the stack, wherein said gaps are arranged in such a manner that inlet side and outlet side ends of the outer circumferential gap are vertically open towards the inlet side and towards the outlet side of the reaction zone, and inlet side and outlet side ends of the inner circumferential gap are vertically closed towards the inlet side and towards the outlet side of the reaction zone, and the ratio of the gap width of the radially inner circumferential gap (B) to the gap width of the radially outer circumferential gap (A) is greater than 1 and at most 20, and the ratio of a gap width of each of the transverse gaps (C) to the gap width of the radially outer circumferential gap is 0.25 to 12, so that the layers of the stack are subjected to branch flows of the gas from the outer circumferential gap (A) through the transverse gaps (C) and into the inner circumferential gap (B), and gas from the inner circumferential gap (B) flows out through the outlet side end gap (E).