This is a two-part study of a novel Sr-Ca-Ni-Y-B silicate sealing glass for solid oxide fuel cells (SOFC). In this paper (Part I), the effect of NiO on glass forming, thermal, and mechanical properties was studied with two different approaches: glass making and composite glass. In the following paper (Part II), sealing and interfacial microstructure of candidate composite glass with 10 vol.% NiO will be addressed. In Part I, higher NiO content in the glass resulted in precipitation during the glass making process, and the sintered powder compacts of these glasses showed extensive macro- and micro-cracks. Coefficient of thermal expansion (CTE) showed large decrease for glass with higher NiO contents. On the other hand, glass-based composites showed no fracture even with NiO content as high as 15 vol.%. The CTE of the composite glass, which increased with increasing NiO content (consistent with the rule of mixtures prediction), could be adjusted to match the CTE of SOFC components. Phase characterization by XRD identified phases of YBO3 and NiO in the glass, which were likely responsible for the poor mechanical and thermal properties for the glass making approach. (C) 2007 Published by Elsevier B.V.