Densification of porous bodies

Abstract

A porous perform body is infiltrated with carbon by a thermal gradient process using a multi-portion heating element to heat the body. Selected portions of the heating element are supplied with power to create the thermal gradient between different areas of the preform body.

1 . A method of heating a porous preform body to a temperature at which a carbon-containing gas can be cracked to deposit carbon in the pores, the method comprising placing the body adjacent a multi-portion heating element so that the portions thereof align with corresponding portions of the body, and supplying power to a selected portion of the heating element whereby to apply heat to the corresponding selected portion of the body and create a thermal gradient between the selected body portion and an adjacent portion or portions of the body and exposing the body to a carbon containing gas.  
     
     
         2 . A method according to  claim 1 , wherein adjacent portions of the multi-portion heating element are used to heat corresponding portions of the body to different temperatures whereby to create a thermal gradient between the respective portions of the body.  
     
     
         3 . A method according to  claim 1  or  2 , wherein the heating element is constructed to heat by induction.  
     
     
         4 . A method according to any preceding claim, wherein the heating element comprises a base comprising an induction heating element shaped into substantially concentric coils and means are present to power each coil individually.  
     
     
         5 . A method according to  claim 1  or  2 , wherein the heating element is an induction heating element made up of vertically spaced coils, disposed about the body and arranged to heat layers within the body.  
     
     
         6 . A method according to any preceding claim, wherein each portion has a respective power supply.  
     
     
         7 . A method according to any of  claims 1  to  5 , wherein a common power source is present together with switch means for each coil.  
     
     
         8 . A method of infiltrating a porous body with an infiltrating gas, the method comprising locating the body adjacent a multi-portion heating element so that the portions thereof align with corresponding portions of the body, and supplying power to a selected portion of the element whereby to heat a corresponding portion of the body to a selected temperature and to create a thermal gradient between that selected portion of the body and an adjacent portion or portions of the body and then contacting the selected portion with the infiltrating gas whereby to infiltrate the porous body in a relatively short time period.  
     
     
         9 . A method according to  claim 7 , wherein the infiltration of the selected portion is continued until a predetermined level has been achieved following which the process is repeated to adjacent selected portions in succession whereby to infiltrate substantially all of the body to substantially uniform level in a relatively short time period.