| abstract |
A multi-layer substrate 2 is reacted with supercritical water in a reaction chamber 14 whose cross section is in the form of an elongated hollow ellipse, and the reaction chamber 14 has a central part having a small curvature, exhibiting substantially a straight line, and end parts having a large curvature, so that the central part of the reaction chamber 14 is suitable for introducing flat materials such as multi-layer substrates 2 thereinto. Furthermore, the large curvature of the reaction chamber 14 at the ends thereof provides a wider inner surface, thereby enabling the reaction chamber 14 to be proof against a high pressure. |