Figures 17 and 18. Nickel produced the only reaction that was competi- 

 tive with iron. For other applications the data presented may aid in 

 selecting an initial trial alloy composition. 



Mechanically alloyed magnesium powders are well suited for a heater 

 designed to deliver variable or constant power. At a reaction tempera- 

 ture of 140 F (60 C), approximately 0.01 pound (5 grams) of alloy (10% 

 iron by weight) will produce 1,000 watts for 1 minute and wiJl be 90% 

 reacted. A possible configuration for a powder alloy heater is shown in 

 Figure 19; its control circuitry is shown in Figure 20. The rapid and 

 efficient reaction characteristics allow the powder to be fed continu- 

 ously into the reaction tube with the assurance that only a small 

 fraction of the available energy will be ejected from the tube as unre- 

 acted powder. 



An estimate of energy density is 800 to 900 W-hr/lb of slurry (6.3 

 to 7.1 MJ/kg) compared with 500 W-hr/lb of slurry (3.95 MJ/kg) for the 

 previous powdered metal tests. Thus, a highly efficient, variable 

 power heater is conceivable using powdered magnesium alloy as an 

 energy source. 



Summary of Experimental Investigation 



The experimental work demonstrated that the dual-plate cell could 

 provide adequate power for the worst case (2,000-watt) diver application. 

 The cell reaction rate was found to be a function of both electrode gap 

 and electrolyte temperature. Other factors, such as electrolyte condi- 

 tion and circulation, affect cell operation to a much lesser degree. 

 The most important factor that controls the overall cell effectiveness/ 

 performance is the power decay resulting from anode depletion (increas- 

 ing electrode gap). Attempts to provide direct control to minimize this 

 effect showed that inert cone spacers would be the best approach. A 

 simple means for implementing the cone spacers while providing adequate 

 anode/cathode flexible current paths is yet to be devised. 



The bi-polar electrode cell offers simpler and more efficient 

 construction than the dual-plate cell, but present anticipated cost of 

 cell fabrication is excessive. 



The powdered metal cell offers the advantage of controllable power 

 output and, consequently, more efficient use of the magnesium. In the 

 past, the disadvantage has been that the specific output was lower than 

 the dual-plate cell. The magnesium-iron alloy (Maglron) powder appears 

 to have a specific output competitive with the dual-plate cell because 

 of a much lower electrical resistance. Further improvements in slur- 

 rying may increase the proportion of active to inert ingredients, thus 

 increasing specific output. In such a case, the powdered alloy may 

 prove to be superior to the dual-plate cell. 



The characteristics of the three cell types are summarized in 

 Table 6. 



11 



