Abstract: This provides a proton conductive material capable of operating from a low temperature range to a middle temperature range and being produced easily at low cost and a process for producing the same. This also provides a hydrogen concentration cell, a hydrogen sensor and a fuel cell equipped with the proton conductive material. The proton conductive material contains the element of calcium, the element of sulfur and the element of hydrogen, respectively, and having a proton conductivity of not less than 10?6 S/cm at room temperature. The proton conductive material can contain Ca in an amount of not less than 10% by weight and not more than 45% by weight calculated as CaO, S in an amount of not less than 15% by weight and not more than 60% by weight calculated as SO3, and H in an amount of not less than 5% by weight and not more than 55% by weight calculated as H2O. The proton conductive material can also contain P in an amount of not less than 0.1% by weight and not more than 50% by weight calculated as P2O5.

Abstract: A tubular metal pipe and a solidified melt of a precursor of oxide superconducting material which is placed in contact with the metal pipe are subjected to heat treatment in an oxidizing atmosphere and at a temperature above the partial fusion temperature of the solidified melt to oxidize the metal pipe from its inside and outside and, as the oxidation proceeds, a melt of the solidified melt is effused through the tubular metal oxide layer to form a superconducting layer on its surface. This makes it possible to easily obtain a hollow oxide superconductor wherein a superconducting material layer is formed outside the metal oxide layer.

Abstract: A method of fabricating a superconducting ceramic pipe including the steps of: melting a ceramic powder having a predetermined composition to form a melt; filling a supporting tube with the melt by a suction caused by a vacuum pressure; partially solidifying an outer part of the melt near the tube to form a shell (i.e., a ceramic pipe); discharging an inner unsolidified part at the center of the tube from the tube by gravity, to form a solidified ceramic pipe on the inside surface of the tube; and heat treating the ceramic pipe to convert it into a superconducting pipe. When a supporting tube with a bottom plate is used, the melt is poured into the tube, and the tube is turned over to remove an unsolidified melt, whereby a superconducting ceramic pipe with a bottom is fabricated.

Abstract: A phosphate glass such as calcium metaphosphate (Ca(PO.sub.4).sub.2) is heat-treated in a temperature gradient to obtain a crystallized glass (glass-ceramics) made of oriented fiber like crystals which has high bending strength in an abraded state.