relatively low pH and is very fluid. However, as" the reaction products 

 accumulate, both the pH and density increase so that, by the end of the 

 first hour, stabilized values have been established based on the slurry 

 removal and electrolyte addition rate. Although the full effect of these 

 parameters is not understood, it is known that a high pH and a thick 

 slurry can block the anodic reaction thereby reducing the reaction rate. 



These factors appear to account for a large portion of the initially 

 high reaction rate, but they are augmented by the anode edge reaction. 

 New plates have a substantial edge area that is not normally used in 

 power calculations. However, this area apparently contributes to the 

 initial reaction rate (dotted line). As the reaction proceeds, the edge 

 area diminishes; in fact, the plate dimensions ar<=t reduced as shown in 

 Figure 9. 



As would be expected, the high initial reaction rate from the above 

 factors results in rapid magnesium comsumption during the first hour. 

 The rate of consumption decays rapidly until an electrolyte equilibrium 

 condition is attained. At this point (1-1/2 to 2 hours into the test) 

 the consumption rate is governed primarily by electrode gap, which is 

 evidenced by the similar slopes of the dashed and solid lines during the 

 remaining test hours (Figure 8). Because of the high initial reaction 

 and early electrode gap increases, the reaction rate is lower than pre- 

 dicted from the parametric tests during the later hours of the test. 



In accordance with the decaying power curve, a cell that delivers 

 the desired power at the end of its operating period, delivers excess 

 power initially. A number of tests were conducted to determine if the 

 high initial and resultant low final rates could be better balanced to 

 provide a flatter power 'curve; these tests are summarized in Table 3. 

 The most effective modification was to alter the anode dimensions to 

 reduce or eliminate the edge effect. This was accomplished by fabrica- 

 ting anodes of slightly larger dimensions than the cathode. Thus, the 

 edge was located far enough away from the cathode to significantly 

 reduce the edge effect. The modification was used on all subsequent 

 dual-plate cell construction. 



Other Parameters Affecting Reaction Rate. Variations in the cathode 

 thickness and surface condition and in the electrolyte "alinity affect 

 the reaction rate. Thick cathodes have the lowest electrical resistance 

 and produce the highest reaction rates (Figure 10). However, cathodes 

 thicker than 0.060 inch (0.15 cm) do not noticeably improve cell perfor- 

 mance. On the other hand, thin cathodes [0.001 in. (0.003 cm)] are 

 desirable because they minimize weight, but they also warp, and, con- 

 sequently, the electrode gap cannot be reliably maintained. A cathode 

 thickness of 0.010 inch (0.03 cm) was selected as a compromise between 

 minimum weight, reasonable structural strength, and power output. 



It was discovered that the output of a cell with 0.010-inch thick 

 cathodes could be increased by as much as 30% by sandblasting the cathode 

 surface (Figure 11). The rough surface greatly increases the number of 



