Another possible technique for avoiding this problem is to electro- 

 plate the cathodic material to one side of the anode. Thus, cell con- 

 struction would be simplified by eliminating the need for a separate 

 iron cathode. Also, cathodic and anodic currents would be shared. With 

 this technique, as the anode thickness decreases, a constant thickness 

 cathode remains to conduct a portion of the anodic current. An addi- 

 tional benefit is that the anode provides some structural strength to 

 the cathode so that thinner cathodes could be used. 



A 1,000-watt version of this cell was constructed and tested. The 

 electroplating consisted of iron deposited onto a copper substrate that 

 was plated onto one side of the magnesium. During the plating process, 

 higher than normal plating currents were used to achieve the greatest 

 possible cathode surface area (similar to sandblasted iron). 



The cell produced approximately 20% more power than a comparable- 

 area dual-plate cell (see Figure 11). This increase was probably due to 

 (1) the measures taken to increase the surface area and (2) the low 

 resistance electrical current path provided by the copper substrate. 



To better understand the bi-polar electrode reaction, a single 

 bi-polar electrode was placed in seawater. There was very little self- 

 reaction, and il ocurred only near the edges of the electrode. This 

 self-reaction rate was low because the current paths through the electro- 

 lyte were too long except at the edge; there the anode-cathode separation 

 was only about 1/16 inch (0.16 cm) (approximately the electrode 

 thickness) . 



Powdered Metal Cell 



A preliminary investigation of magnesium and iron powder mixtures 

 as possible heat sources is described in Reference 12. The tests 

 included loose mixtures of size-graded magnesium and iron particles as 

 well as mixtures of particles that had been mechanically bonded together 

 by ball-milling* to produce microgalvanic cells. The results show that 

 ball-milled mixtures produce the highest reaction rates and that the 

 reaction is strongly influenced by particle size (area exposed to the 

 electrolyte) . 



Further tests were conducted to develop a heat source with a greater 

 specific output (W-hr/lb of cell) than the dual-plate cell [approximately 

 800 W-hr/lb of cell (6.3 MJ/kg)]. A means of controlling the heat 

 output was also sought. 



Small-scale tests were run to determine the best cathodic material 

 for sustaining the reaction and the minimum percentage necessary to 

 produce heat at a usable rate. The test results were compared by the 

 rate of hydrogen evolution (directly related to power output) from five 



Ball-milling produces intimate contact between the particles. 



■ a a mi B rt ii ^ . i^*^^ ^■.^„- iJ ,.... || 



l > * MI '"' >h1 " 1 " "fmfofoim > fv i .r.. ■tt-.T^, tn- M l ..-^^^..^^« ^ a gaifc^v T || ; , 



