soluble in one another also a pure grade 99 5 al 2 o 3 alumina is used so that there is hardly any glassy phase present in the alumina to adhere to the tungsten in metallizing it is the glassy phase either added to the metallizing paint or to the ceramic which promotes adherence the formation of filament structures according to the method of the invention has several additional advantages beyond the quality of the bonds formed rounder filaments can be formed in this way the deviation from round is typically 0 001 inch which is nearly the same as that of the mandrel the mandrel dimensions determine the inside diameter of the filament also the method of the invention removes the residual stresses in the wires which were caused by drawing and wrapping the wire on the spool on which it was shipped the difference in thermal expansion of the alumina mandrel and the yarn causes an additional force to be exerted on the crossing wires when the assembly is heated since the yarn is flexible similar to a piece of string a uniform radial force is applied to the cylindrical surface of the mandrel in this way if end affects are ignored it is similar to.