Petroceramics has been working on the liquid silicon infiltration process for over 15 years, playing a key role in the development of the carbon-ceramic materials for automotive applications. Petroceramics owns the patent "Method for the infiltration of a porous material with a second material and related plant (WO2012123907, EP2686285, CN103547549, US2014072710) which claims an innovative LSI process.
The driving force of the silicon infiltrations is the capillarity force. The temperature and the vacuum level regulate the silicon wettability with respect to the preform. By changing these parameters the process can be enhanced or inhibited.
In the standard process the infiltration is performed in vacuum at temperatures between 1414°C (silicon melting point) and 1650°C. The infiltration occurs above the silicon melting point, at a temperature is affected by the vacuum level. During the heating up, the preform is gradually and slowly filled with silicon as a result of incremental capillarity forces which grow as the temperature increases.
In our approach a partial inert gas pressure is applied in the furnace during the heating up. As a result the infiltration is at first inhibited and the preform can be heated at temperatures above the silicon melting point without undergoing infiltration. At a well defined temperature the infiltration can be suddenly activated by a fast pressure drop.
At high temperatures the process is so fast that the system can be considered as adiabatic and the thermal energy of the exothermic Si-C reaction contributes more efficiently to accelerate the infiltration. In these conditions the capillarity forces are so strong that pores are filled simultaneously, regardless their size. This turns in a rapid infiltration which can be achieved in few minutes and not in hours as it would be in the conventional process.
The final porosity of the infiltrated material is dramatically reduced. The reaction rims between carbon fibers and molten silicon are minimized and the carbon fibers are better preserved.

                                           Pressure – temperature diagram showing regions where the infiltration is activated or inhibited. Following our 
                                                 innovative approach the infiltration is activated at high temperature by a fast partial pressure drop.

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