Abstract: The present invention relates to ZrO.sub.2 - and SiO.sub.2 -based ceramic fibers in which the weight ratio between SiO.sub.2 and ZrO.sub.2 is comprised between 99 and 0.7. The tetragonal ZrO.sub.2 phase is stable at temperatures comprised between 0.degree. and 1500.degree. C. The process comprises the preparation of: a solution of Zr(OR.sup.1).sub.4, where R.sup.1 is an alkyl or aryl, Si(OR.sup.2).sub.4, where R.sup.2 is alkyl or aryl, an organic solvent and an acid. Vapor-phase water is bubbled in said solution, then the obtained solution is drawn and the fibers thus obtained are heated to obtain the crystallization of ZrO.sub.2 and SiO.sub.2.

Abstract: The invention is concerned with a method of producing in-line dyed fibers, in a gel state, characterized in that it essentially consists of extruding the spinning dope in a coagulum bath, stretching the resulting filaments, scrubbing said filaments to remove residual solvent, passing the resulting filament tow through a dyeing bath at an overall rate in excess of 4 cm.sup.3 bath per second per square centimeter of tow surface area. The overall rate, being preferably in the 4 to 10 cm.sup.3 /sec per cm.sup.2 range, is achieved by means of crossflows to the forward advance direction of said tow, and alternately directed to and from said tow, the tow residence time in the dyeing bath being no longer than 5 seconds. The tow is then subjected to a dye fixing heat treatment, and is then scrubbed, finished, and dried. The method is particularly suitable for use with substantially acrylic and modacrylic fibers.