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The formation of stable back beads in the first layer weld during one side multilayer welding is important to achieve high quality welded metal joints. The authors thus employed the switch back welding method for welding V groove joints without using backing plates. Moreover, in the field work, there is misalignment of both metal plates during set-up. The suitability of the welding conditions for each root gap and the misalignment were verified by observation of the arc, molten pool and external appearance of back beads. Welding conditions, namely, welding current, wire feedrate, weaving width, forward/backward stroke of switch back motion and welding speed, were controlled continuously according to root gap variations. Stable back beads were obtained for root gaps between 4 . 9 and 2 . 3 mm and misalignments between 0 . 1 and 2 . 8 mm. STWJ/393

The reactive ceramics suitable for the rotary-type solar reactor (proposed by Tokyo Institute of Technology, Tokyo) with two-step water-splitting reaction were developed. It is confirmed that O2 gas is evolved in the two-step water-splitting reaction with the reactive ceramics vigorously by rapid heating (α-O2-releasing reaction). The α-O2-releasing reaction is due to the formation of interstitial defect and the conversion of lattice oxygen into O2 gas at a nonequilibrium state. Reactive ceramics (NiFe2O4 and yttria stabilized zirconia (YSZ)-NiFe2O4 solid solution) can absorb solar thermal energy and convert thermal energy into chemical energy under high O2 partial pressure atmosphere in the α-O2-releasing reaction. Repetitive evolutions of O2 gas were observed in the two-step water-splitting reaction with YSZ-Fe3O4 solid solution and cerium based metal oxides (CeO2–NiO, CeO2–ZrO2, and CeO2–Ta2O5) at high O2 partial pressure. The CeO2–Ta2O5(Ce:Ta=90:10) released a large amount of O2 gas (3.95 cm3/g) in the α-O2 releasing reaction in the flow of air.

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