Abstract: A polycrystalline fused product based on brownmillerite, includes, for more than 95% of its weight, of the elements Ca, Sr, Fe, O, M and M?, the contents of the elements being defined by the formula XyMzFetM?uO2.5, wherein the atomic indices are such that 0.76?y?1.10, z?0.21, 0.48?t?1.15 and u?0.52, 0.95?y+z?1.10, and 0.95?t+u?1.10, X being Ca or Sr or a mixture of Ca and Sr, M being an element chosen from the group formed by La, Ba and mixtures thereof, M? being an element chosen from the group formed by Ti, Cu, Gd, Mn, Al, Sc, Ga, Mg, Ni, Zn, Pr, In, Co, and mixtures thereof, the sum of the atomic indices of Ti and Cu being less than or equal to 0.1.

Abstract: The invention relates to solutions of cellulose destined to be extruded or spun, containing a tertiary amine oxide as solvent for the cellulose and in particular the N-oxide of N-methylmorpholine. It consists of using ammonium chloride or calcium chloride as additive in the preparation of these solutions.