Supercorroding galvanic cell alloys for generation of heat and gas

Supercorroding magnesium alloys that operate like galvanic cells and react apidly and predictably with seawater to produce heat and hydrogen gas. The alloys are formed by a mechanical process that bonds magnesium and noble metal powder particles together in a strong electrical and mechanical bond. The alloy powders can be compacted and sintered to form barstock, etc., suitable for making self-destructing corroding links.

BACKGROUND OF THE INVENTION 
This invention generally relates to alloys which operate as short-circuited 
galvanic cells to corrode rapidly in electrolyre such as seawater. Such an 
alloy is suitable as a heat source; as a gas generator; or as a corroding 
release link. 
Sources of heat and hydrogen gas of various types are well known in the 
art, especially by virtue of earlier already issued United States Patents 
commonly assigned herewith such as: U.S. Pat. No. 3,884,216 issued May 20, 
1975 for ELECTROCHEMICAL ENERGY SOURCE FOR DIVER SUIT HEATING; U.S. Pat. 
No. 3,942,511 issued Mar. 9, 1976 for SANDWICHED STRUCTURE FOR PRODUCTION 
OF HEAT AND HYDROGEN GAS; U.S. Pat. No. 3,993,577 issued Nov. 23, 1976 for 
METHOD FOR PRODUCTION OF HEAT AND HYDROGEN GAS; and, U.S. Pat. No. 
4,017,414 issued Apr. 12, 1977 for POWERED METAL SOURCE FOR PRODUCTION OF 
HEAT AND HYDROGEN GAS. 
At least two methods have been employed in the past to achieve high 
corrosion rates. One is to construct a short-circuited battery-like cell 
of noble and active metal plates separated by an electrode gap such as 
disclosed in aforementioned U.S. Pat. No. 3,884,216. Another method is to 
form a powder by mechanically joining the discrete particles of noble and 
active powders such as disclosed in aforementioned U.S. Pat. Nos. 
3,942,511, 3,993,577 and 4,017,414 where each powder particle is a small 
galvanic cell. 
The battery-like cell has two principal disadvantages: the power output is 
dependent upon the electrode gap (internal cell resistance) and the 
resistance in the electrical short circuits (external load) limits the 
reaction rate. In order to maximize power output, the electrode gap must 
approach zero. Yet, to sustain the reaction, reaction products must be 
flushed away from the reacting surfaces. This requires a small initial gap 
between the plates. The gap creates high internal cell resistance which 
reduces the power obtainable from the cell. A further decline in power 
occurs because of the gap increase as the active plate is consumed. 
The resistance in the electrical short circuit between the noble and active 
materials can limit power output. To maximize output, the external short 
circuit resistance must be minimized. In the battery like configuration 
the resistance is kept low by providing several relatively short-length 
paths between the plates. Low resistance spacers are used to maintain the 
electrode gap. Thus, the electrical resistance is minimized within the 
configuration and material limits. 
In the powdered form where each grain of powder is a small galvanic cell 
similar to the larger battery-like cell, noble metal particles are 
mechanically joined to the surface of an active metal particle, as 
disclosed in aforementioned U.S. Pat. No. 4,017,414. The combination 
retains the property and identity of each constituent. But each cell will 
react with itself, so no electrode gap is necessary or exists. The short 
circuit path length is minimized because the particles are in direct 
contact. However, the short circuit resistance is not minimized. 
Electrical resistance between individual particles is a function both of 
physical proximity and of the oxides that exist on the bond surface 
between the metal particles (this is also true for the battery-like 
configuration). Because high resistance surface oxides are present, 
excellent mechanical contact may not assure intimate electrical contact. 
Due to the random method of joining the particles and low energy level of 
the balls used in the milling process in the aforesaid patent, some metal 
particles may not be paired into micro-cells but may remain free and will 
not react at all. Also, in this prior art powder form, the internal cell 
resistance may be minimized but the external or load resistance may be 
high. Due to the high oxide level on the bond surface, compacting and 
sintering the powders fabricated by using the prior art teachings will not 
result in barstock, etc., which has any significant mechanical strength. 
A strong mechanical and electrical bond is necessary to provide a rapidly 
corroding galvanic cell alloy. 
SUMMARY 
The supercorroding galvanic cell alloy (of this invention) is formed from a 
noble metal and an active metal, or more than two constituents can be 
used. The metals can be the same as used in the battery-like or powder 
configurations, or other metals may be used. In any case, the constituents 
are chosen based on their ability to form an alloy which will corrode at a 
predictable rate in the available electrolyte. In particular, an alloys 
that will react in seawater like a galvanic cell can be made using 
magnesium and a noble metal such as iron or nickel. Any of the usual 
methods can be employed in producing the alloy: conventional dissolution, 
mechanical alloying, etc. The proportions, particle size, and the 
homogeneity are selected to control the reaction rate. A maximum reaction 
rate can be achieved at some particular mixture proportions. The resulting 
alloy is used in either plate, bar or powder form. The plate and powder 
forms are especially suited for use as a heat source or a gas generator. A 
corroding release link can be fabricated from sintered barstock. The 
supercorroding alloys are superior to previous similar methods for 
producing heat and gas. 
Usually alloys are formed to resist corrosion. However, the alloy of this 
invention is specifically intended to operate like a short-circuited 
galvanic cell for use as a rapidly corroding alloy. By alloying the 
desired metal constituents, the two main disadvantages of previous methods 
of producing high corrosion rates are eliminated. The alloy can have 
properties different from either of the constituents. Since the alloy is a 
uniform mixture of the metals in intimate contact with each other, there 
is no electrode gap to maintain so internal cell resistance is minimized 
and the electrical short circuit resistance will be substantially a 
function only of the path length between the centers of the reacting 
masses. 
Since no electrode gap exists, the power output of a heat source 
constructed of the alloy in plate form in the short-circuited battery 
configuration will not decline as the space between the plates increases 
due to material consumption. A fluid circulation space will still have to 
exist, however, to flush away reaction products. Electrical resistance is 
the minimum attainable due to the extremely short current lengths and 
because of the intimate contact and strong mechanical bond, i.e., the 
alloying, as disclosed herein, minimizes external resistance. 
In the powdered form of the alloy all of the metal particles are coupled 
into micro-cells because of the completely uniform mixture of the alloy 
constituents. Again, the electrical contact is the optimum attainable. 
This supercorroding galvanic cell alloy has the additional feature of being 
suitable for use as corroding barstock. In this form, corroding links can 
be made for use either as primary or backup releases for oceanographic 
instruments. By adjusting the alloy composition, the reaction rates, and 
thus the release time, can be controlled.

DESCRIPTION OF PREFERRED EMBODIMENT 
A family of short-circuited galvanic cells formed from supercorroding 
magnesium alloys that react spontaneously and vigorously with seawater to 
produce heat and hydrogen gas have been developed. The galvanic cell 
alloys have been developed as a self-contained heat source for Navy diver 
use, but they may also be used to generate hydrogen gas for buoyancy, 
thermodynamic engines, and fuel cells. Because of their uniform and 
predictable behavior, the alloys can be used as corroding links to 
retrieve oceanographic equipment. 
Various cathodic materials in different proportions have been alloyed with 
magnesium. Tests were conducted to determine how the reaction is affected 
by alloy compositions and constituent proportions, temperature, and 
pressure. 
In general, magnesium reacts with seawater according to the formula: 
EQU Mg+2H.sub.2 O.fwdarw.Mg(OH).sub.2 +H.sub.2 + heat 
The reaction has a theoretical energy density of 14.929 kJ/kg (1885 W-h/lb) 
and produces 0.921 liter of gas per gram of magnesium (14.8 ft.sup.3 /lb) 
at STP. By itself, magnesium corrodes slowly in seawater because of low, 
local potential differences within the magnesium. When a suitable cathodic 
material is brought into close proximity and electrically connected with 
the magnesium, a battery is formed, and the corrosion reaction proceeds 
rapidly. The dual plate cell shown in FIG. 1 represents this 
configuration. With the electrical load replaced by a short circuit, the 
reaction proceeds even more rapidly, and the cell efficiently produces 
heat and hydrogen gas. The rate of reaction is known to be a function of 
(1) electrolyte temperature, pH, salinity, and density, (2) anode cathode 
plate spacing, and (3) ambient pressure. The effects of temperature and 
spacing on dual-plate cell performance are shown in FIG. 2. Some minimum 
gap must be maintained in order for reaction products to be removed from 
between the electrodes by electrolyte circulation. 
A diver heater, based on the short-circuited dual-plate cell, was built and 
tested. The cell consisted of alternate magnesium and iron plates spaced 
apart by copper washers that provided the short circuit. One of the main 
drawbacks to this construction is that as magnesium is consumed, the 
electrode gap increases and power output declines. 
To eliminate this decline and to achieve faster reaction rates, powdered 
metal mini-cells were conceived as discussed in aforementioned U.S. Pat. 
No. 4,017,414. The mini-cells were fabricated by ball-milling a mixture of 
iron and magnesium powders (using lightweight ceramic balls). The milling 
produced composite particles by mechanically bonding the constituents 
together. 
Later tests showed that accelerated reaction rates were achieved using the 
mini-cells, but that the reaction efficiency (percentage completion) in 
these prior art mini-cells was much lower than predicted. The optimum rate 
occurred between 5 and 10 percent iron content. The accelerated reaction 
rate was attributed to the close proximity of the anode-cathodic pairs and 
the relatively large cathode surface area. The low efficiency was 
attributed to poor electrical contact due to oxides that exist on metal 
surfaces and low mechanical strength of the Mg-Fe bond, as aforementioned. 
SUPERCORRODING ALLOY FORMATION 
An alloying process called mechanical alloying has been used to overcome 
the problems that limited the prior mini-cells efficiency. Mechanical 
alloying generally involves a high energy ball mill and does not use an 
inert solvent with the powdered metal particles as disclosed in 
aforementioned U.S. Pat. No. 4,017,414. The active and passive metal 
particles are processed (i.e., mechanically alloyed) dry. 
Galvanic cell alloys have been fabricated into composite particles or 
mico-cells with as much as 20 percent iron content using mechanical 
alloying techniques. Tests have shown that these magnesium-based galvanic 
cell alloys react several orders of magnitude faster and more sufficiently 
than the previous mini-cells. Because of their extremely high corrosion 
rate, these materials were named supercorroding alloys. 
Mechanical alloys can be produced, for example, in a high-energy ball mill 
by repeated flattening, fracturing, and welding of the metal constituents 
(i.e., active and passive metal particles). The energy of the impact of 
colliding steel balls, with particles trapped between them, creates 
atomically clean particle surfaces. When these clean surfaces come in 
contact during collisions, they cold-weld together. An inert atmosphere in 
the mill prevents reoxidation of the clean surfaces. This also avoids 
oxide coatings on the particle surfaces which reduce galvanic cell 
reaction. 
The tendency of powdered particles to cold-weld together predominates 
during the early stage of the process. As milling continues, particles get 
harder and more brittle, and eventually a balance results between welding 
and particle fracturing. Continued milling refines the particles' 
characteristic layered structure. The thickness of each layer in the 
composite particle decreases from repeated impacts. 
During the early stages of the milling process the particles get larger. As 
milling continues particles get harder, more brittle and break apart 
instead of deforming; the particles structure becomes more refined and the 
iron particles get smaller. At some point in the milling process, further 
milling results in a reduction of the corrosion rate. This is probably due 
to the cathode material becoming so finely dispersed throughout the anode 
material that the ratio of cathode/anode particle surface area available 
for contact with the electrolyte decreases and hence the corrosion rate 
decreases. This point is substantially less than saturation hardness for 
the material. It is important to note that to maximize corrosion rate and 
efficiency it is necessary to: (1) provide a short electrolyte path length 
between anode and cathode; (2) provide a high exposed rate of surface area 
between cathode and anode; (3) provide a strong (welded) bond between 
anode-cathode pairs; and (4) provide a very low resistance (less than 
10.sup.-4 ohms) path for external currents to flow through the corroding 
pairs. 
The resulting mechanically alloyed powders are small particles consisting 
of matrices of active metal having smaller particles of passive metals 
dispersed throughout. The micrograph of FIG. 3 shows a cross-section of a 
portion of an active metal particle (e.g., magnesium) having many smaller 
passive metal particles (e.g., iron) dispersed within the active metal 
matrix. The active metal particle is shown as white and the smaller 
passive metal particles shown as black. Many of the passive metal 
particles are shown as elongated having been flattened in the milling 
process; the longest dimension of the active iron particles is about 30 
microns. As is discussed below, the preferred powdered alloy particle size 
is between 80 and 100 mesh. The intimate (atomic level) contact between 
the alloy constituents, low electrical resistance and high ratio of 
exposed cathode to anode surface areas are the keys to rapid corrosion 
rate. 
Powder alloy performance was evaluated by recording gas evolution as a 
function of time; this was used to determine reaction completion (energy 
output) and reaction rate (power). 
Percentage reaction completion at a particular time is calculated from the 
ratio of the volume of gas produced at that time to the maximum 
theoretical gas production. Power is calculated essentially from the slope 
of the percent-completion-versus-time curve. Maximum gas production is 
calculated from the basic reaction equation using the actual amount of 
magnesium in a given weight of alloy. 
A series of experiments was conducted to select an optimum milling time and 
particle size for further tests. Maximum reaction rate and reaction 
efficiency were used as a basis of evaluation. Visual observation of the 
reaction revealed that particles that passed through a 100-mesh sieve 
would not stay submerged in the seawater, but instead would float on the 
surface and form a foam. This resulted in reduced reaction rates. It was 
later observed that particles larger than 100 mesh would cycle from the 
bottom of the flask to the seawater surface and then sink. The cycling was 
caused by the formation of a hydrogen bubble which buoyed the mini-cell 
particle. The hydrogen bubble was shed at the surface, and the particle 
sank. As a result, particles that would not pass through a 100-mesh sieve 
were used in subsequent tests. The estimated particle size is between 80 
and 100 mesh. 
Various tests and experiments were conducted and many of the results are 
shown in the curves of FIGS. 4-11 and 13-19. 
As previously discussed, continued milling refines the layered structure 
and results in a reduction of exposed cathode surface area. To determine 
the effect of this refinement on the reaction rate, magnesium-based alloys 
of 5 atomic percent iron were milled for 5, 15 and 20 minutes each and 
tested. The effect of the milling time on the reaction rate shows that the 
longer the powders are milled, the more homogeneous they become, and the 
more homogeneous powders react most rapidly. Percent completion is shown 
in FIG. 4. The alloy milled for 20 minutes reached the highest percent 
completion in the least time. (The test of the alloy milled for 5 minutes 
were terminated prior to reaching completion, but, clearly, it reacts much 
more slowly.) 
Additional alloys were fabricated and tested to determine the effect of 
further milling on reaction rate. The time to maximum temperature rise of 
the water in an open beaker was recorded. FIG. 5 shows, in a general way, 
the effect of milling time on the reaction rate .DELTA.T. An optimum 
milling time occurs when the time to reach a maximum .DELTA.T is the 
least. In this particular case alloys milled for 20 minutes showed the 
highest temperature rise in the least amount of time. Prolonged milling 
resulted in a reduction of the reaction rate. The reduced reaction rate is 
particularly attributed to a reduction in the cathode to anode surface 
area exposed to the electrolyte. It is expected that continued milling 
would result in further reduction in the reaction rate and that the 
reaction rate would be substantially reduced by the time that the alloy 
was milled to saturation hardness. Based on these results, the remaining 
alloys were prepared under conditions similar to the 20-minute alloy. 
Other mill parameters such as speed of mill and ball size (milling energy) 
and ball to powder ratio contribute to the reaction characteristics. For a 
particular combination of anode and cathode materials and for a particular 
batch size these parameters can be optimized as shown in FIG. 15. Samples 
A. B and C of magnesium with 9.8 iron (Mg-9.8 Fe) alloy were prepared 
using different milling parameters. In FIG. 15 the parameters used for 
milling sample A were optimum for a magnesium anode material with 9.8 
atomic percent iron. 
Magnesium alloys with different percentages of iron were prepared and 
tested; the results are plotted in FIG. 6. (Up to 10 percent iron, 
reaction rate increases with increasing iron content. Up to about 10 
percent iron, the reaction is evidently limited by the amount of cathode 
present. Beyond 10 percent, the iron begins to mask active areas of the 
magnesium, reducing the reaction rate.) They show that the reaction rate 
depends strongly upon cathode material content up to approximately 10 
atomic percent. Several tests of the alloy with 20 percent iron showed a 
significant decrease in the reaction rate. This phenomenon is believed to 
be caused by the reduction of exposed anode surface area due to the 
increased cathode content. 
Cathodic percent does not appear to strongly affect the level of reaction 
completion. Thus, a particular alloy can be selected on the basis of 
reaction rate or on the basis of energy density. A summary of energy 
density and other characteristics of alloys tested is shown in Table I. 
The table shows that energy density (kJ/kg of alloy) decreases with 
increasing cathode content, while peak power increases. 
TABLE I. 
______________________________________ 
Characteristics of Various Alloys 
Cathode 
content Energy Peak Average 
(% by Density Power Power** 
Alloy* weight) (kJ/kg) (W/gm) (W/gm) 
______________________________________ 
5 minutes 
10.8 (Fe) 13.3 4 3.7 
15 minutes 
10.8 (Fe) 13.3 28 26.1 
20 minutes 
10.8 (Fe) 13.3 83 60.9 
0.5 (Fe) 1.1 14.8 6 5.6 
1 (Fe) 2.3 14.6 8 8 
3 (Fe) 6.6 14.0 31 20 
5 (Fe) 10.8 13.3 220 69 
10 (Fe) 20.3 11.9 279 114 
20 (Fe) 36.5 9.5 76 51 
1 (Cu) 2.6 14.6 6 2.9 
3 (Cu) 7.5 13.8 14 6.4 
5 (Cu) 12.1 13.2 22 10.7 
10 (Cu) 22.5 11.6 35 18.7 
5 (Ti) 9.4 13.6 2 1.5 
5 (Cr) 10.1 13.4 4 3.8 
5 (C) 2.5 14.6 9 4.4 
5 (Ni) 11.3 13.3 163 100 
______________________________________ 
*Identified by cathodic atomic percent or milling time 
**Average power energy liberated at t (time to peak power) .times. 2 
divided by t. 
Stored strain energy from the milling process was thought to have an effect 
on the reaction. To test this idea, pure magnesium was milled and reacted. 
There was no significant difference between the reaction of milled and 
unmilled magnesium powders. Thus, the conclusion was reached that strain 
energy does not appreciably affect the reaction rate. 
A small number of other alloys have been produced and evaluated. Some were 
magnesium based with a variety of cathodic materials; others were aluminum 
and zinc based. A family of percent completion curves for magnesium based 
alloys with 5 atomic percent, Cu, C, Cr, and Ti is shown in FIG. 7. (For a 
fixed cathode proportion, reaction rate is dependent on cathode material.) 
An alloy of 5 atomic percent nickel was tested and found to react 
similarly to the 5 percent iron. Carbon is also used the same as a passive 
cathodic metal in the alloy, as shown in Table I and FIG. 7, since carbon 
acts like a passive metal in galvanic cells. The mechanical alloy 
composition can be varied to adjust the corrosion rate. 
The results of tests clearly show that iron and nickel are the most 
reactive of the cathode materials tested. Table I shows that 5 percent 
carbon has a slightly higher energy density than iron, but its power 
output is much lower. 
To verify the dependence of the reaction process on cathode content (shown 
by the magnesium-iron alloys) a series of tests on magnesium-copper alloys 
was conducted. The results of the copper family tests are shown in FIGS. 8 
and 9. (The time to reach a given percent completion varies approximately 
inversely with the amount of copper in the alloy. The effect of copper 
content is dramatically illustrated as doubled copper content results in 
approximately doubled peak power outputs, i.e, reaction rates.) FIG. 8 
shows that the time to reach 50 percent completion is reduced by about 
half as the amount of copper is doubled. This geometric relationship is 
dramatically illustrated by the power curves of FIG. 9; peak power is 
approximately doubled as copper content is doubled. 
Other alloys based on zinc and aluminum in place of magnesium have been 
fabricated and tested. The cathode materials were iron and copper. In 
seawater, none of these alloys showed a reactivity as great as the 
unalloyed base magnesium powder, so they have not been pursued further. 
Tests were conducted to determine the effect of electrolyte temperature and 
ambient pressure on the reaction. For the temperature tests the seawater 
was preheated (or cooled) to the desired temperature before adding it to 
the alloy. The test results, plotted in FIGS. 10 and 11, show the reaction 
to be a strong function of the electrolyte temperature. Increasing the 
temperature increases the reaction rate. Peak power is strongly related to 
reaction temperature. Attempts were made to use starting temperatures 
above 60.degree. C.; however, the reaction is so rapid that the bath could 
not maintain a constant temperature, and the seawater invariably boiled. 
Samples of a magnesium based alloy with 9.8 atomic percent iron were 
compacted in the form of barstock (1.07 cm square by 6.5 cm long) and 
discs (1.27 cm dia by .32 cm thick). The completion was performed at 70, 
140, 280, 420 and 550 M pascals. Some of the 550 M pascal samples were 
sintered at different temperatures and time of sinter; further samples 
were prepared using 500 M pascal compaction pressure and 700.degree. F. 1 
hour CO.sub.2 atmosphere sinter conditions. 
Testing of the sintered samples showed that tensile strength increases 
slightly with sinter temperature while shear strength peaks at 700.degree. 
F. Time of sinter does not appear to effect the mechanical properties. As 
might be expected, mechanical strength increases with increasing 
compaction pressure as is shown in FIG. 16. 
Corrosion rate decreases with increasing compaction pressure as is shown in 
FIG. 17. This is to be expected since the compacted powdered alloy is more 
dense and less active surface area is available for corrosion. 
Mechanical properties of several different magnesium based materials is 
shown in Table II below. Barstock samples of each material were tested to 
determine the time to tensile failure when a fixed tensile load was 
applied to the long axes of the bar. A 0.6 cm wide circumferential strip 
about the center of the bar was exposed to seawater. Also disc samples 
were tested to determine the corrosion rate of a flat surface as well as 
the reaction rate for each sample. 
TABLE II. 
______________________________________ 
Properties of Compacted* and Sintered* Alloys 
Trans- 
Sin- verse 
tered Rupture Shear 
Den- Strength Strength 
PM sity M M 
Alloy No. (g/cc) Pascals 
(kpsi) 
pascals 
(kpsi) 
______________________________________ 
Mg- .7 Fe 
1311 1.79 68.9 (10) 61.3 (8.9) 
Mg-1.6 Fe 
1308 1.81 64.8 (9.4) 59.3 (8.6) 
Mg-4.3 Fe 
1309 1.93 61.3 (8.9) 63.4 (9.2) 
Mg-9.8 Fe 
1306 2.10 71.7 (10.4) 
66.8 (9.7) 
Mg-19 Fe 
1310 2.42 67.5 (9.8) 68.2 (9.9) 
Mg-4.3 Cu 
1312 1.87 44.1 (6.4) 50.3 (7.3) 
Mg-4.4 Ni 
1313 1.94 74.1 (10.4) 
66.8 (9.7) 
Mg-4.3 C 
1314 1.78 88.9 (12.9) 
65.5 (9.5) 
Mg-4.6 Ti 
1315 1.89 93.7 (13.6) 
80.6 (11.7) 
______________________________________ 
*Compacting pressure 550 M pascals (40 TSI) 
Sintered 700.degree. F./1 hr./CO.sub.2? 
FIG. 18 shows that time to corrosion failure decreases (or reaction rate 
increases) as the percent cathode content increases. For other cathode 
materials nickel reacted fastest, with iron, titanium, copper and carbon 
in decreasing order. 
Surface corrosion rates for all samples tested are shown in FIG. 19. As was 
expected from the results of previously discussed tests surface corrosion 
rate increases with increasing cathode content and varies with cathode 
type. Corrosion rates from 70 to over 300 micrometers per hour were 
obtained. 
Supercorroding alloys were conceived as heat sources for use by divers. In 
this application it is essential to provide rapid generation of heat and 
high reaction efficiencies. The magnesium-iron alloys appear to be well 
suited for this task. 
One configuration for a fuel-type heater using supercorroding alloys of 
this invention is shown in FIG. 12. In this system the powdered mechanical 
alloy 12 (i.e., galvanic cell composite particles) is slurried with inert 
ingredients which do not react with the components but which facilitate 
pumping the reactants to the electrolyte. An externally pressurized 
bladder 13, for example, (or other suitable slurry feed device) can be 
used to pump the slurried powdered alloy 12 into open-ended reaction tube 
14 at 15 via a slurry flow rate controller 16. Approximately equal volumes 
of seawater and slurry are injected into reaction tube 14. Seawater is 
injected into tube 14 at 17 by means of seawater pump 19. The heat 
produced by the reaction of the powdered alloy with seawater is removed by 
the counterflow fluid in main heat exchanger tube 20 (i.e., heat 
production section) that surrounds tube 14. Fresh incoming seawater at 
inlet 21 is preheated in the seawater preheat exchanger 22 (i.e, energy 
recovery section) which is separated from main heat exchanger 20 by a 
partition. Reaction tube 14 passes through both heat exchanger sections 20 
and 22. Cooled slurry is expelled at the opposite end as shown in the 
drawing. Fresh water is preheated by the expelled reactants and products 
in order to conserve energy. Preheated seawater is then pumped out from 
heat exchanger 22 at 24 and injected at inlet 17 into reaction tube 14. 
The rates at which the slurry and seawater are injected into reaction tube 
14 can be varied to control the amount of heat generation. Water in main 
heat exchanger 20 which surrounds reaction tube 14 is heated by transfer 
of heat generated from the reaction of seawater with the slurried alloy. 
The heated fluid (e.g., water) is then circulated via outlet 26 through a 
water circulation garment, such as disclosed in aforementioned U.S. Pat. 
No. 3,884,216, worn by the diver (e.g., diver load) by means of warm water 
pump 27. Water from the diver's suit is then returned to the main heat 
exchanger 20 via inlet 28 for reheating. Control of heat in the diver's 
suit (i.e., rate of warm water circulation flow, etc.) is by means of a 
diver-operated temperature set point control 29, for example. 
A typical inert slurry mixture fo facilitate the addition of the mechanical 
alloyed reactants to the electrolyte in a reaction chamber by pumping the 
inert slurry containing the powdered alloy through feed lines, for 
example, is given below: 
______________________________________ 
Proportion 
Constituent (by weight) 
______________________________________ 
Supercorroding alloy powder 
up to 447.0 
Methoxy polyethylene glycol 
394.0 
N-oco beta amino butyric acid 
3.0 
Colloidal silica at least 19.7 
Diethylenetriamine 1.0 
______________________________________ 
A preferred embodiment of the foregoing slurry was a completely inert gel 
like slurry containing in proportion by weight: magnesium-iron powder 
447.0, methoxy polyethylene glycol, 394.0, N-oco beta amino butyric acid 
3.0, colloidal silica 19.7, diethylenetriamine 1.0. 
In slurry form, the powdered supercorroding reactants can be supplied to an 
electrolyte on a demand basis. By varying the slurry addition rate to a 
reaction chamber, power can be controlled. 
A second application for the supercorroding alloys is to produce hydrogen. 
Hydrogen can be used in either ocean buoyancy applications or for powering 
hydrogen-type fuel cells which produce electrical energy. Hydrogen is 
especially suited for buoyancy applications because of its low molecular 
weight. A comparison of the molecular weights and buoyancy factor (pounds 
of water displaced/pound of gas) is shown in FIG. 13. One kilogram (2.2 
lbs) of 5 atomic percent magnesium-iron alloy is capable of producing 800 
liters (28 ft.sup.3) of hydrogen at STP in less than 5 minutes. The 
buoyancy factor (weight of seawater displaced to the weight of fuel) of 
this alloy is shown in FIG. 14. 
There are many ways that supercorroding galvanic cell alloys can be used to 
produce hydrogen. If a totally controlled production rate is desired, a 
slurry metering system similar to the diver heater application could be 
used. For small buoyancy generators (less than 4500 N (1000 lbs)), gas 
could be generated by rupturing a plastic pouch containing the alloys. The 
pouch would be located below the container that collects the gas; this 
container would be attached to the object to be lifted. 
Another application for the supercorroding galvanic cell alloys is in the 
construction of sintered self-destructing corroding links, dics, etc., as 
discussed above. For example, the alloy powders can be sintered to form 
barstock, such as shown in FIG. 20, suitable for making self-contained 
corroding links, or can be sintered to form corroding discs such as shown 
in FIG. 21. In many ocean engineering applications a timed release device 
is needed to shed temporary hydro-dynamic drag reduction shrouds or to aid 
in recovering instrumentation. The link can be in the form of a round pin 
which holds the object to be released to an anchor or instrument package. 
A variety of devices are presently used. Most of the devices are either 
not totally reliable or are extremely expensive. Prior art type corroding 
links require two separate parts (anode and cathode) that must be 
electrically connected to promote the link destruction. The electrical 
connections to the parts are often unreliable and break down. Since the 
supercorroding galvanic cell alloys are inherently self-destructing, the 
need for electrical connections is removed. Release times can be 
controlled either by sizing the dimensions of the supercorroding alloy or 
by selecting the alloy composition. Either way, a variety of corroding 
links, such as shown in FIG. 22 for example, that last for periods of 
minutes to hours can readily be manufactured using the present 
supercorroding galvanic cell alloys. In the disc form, as in FIG. 21, for 
example, one surface is exposed to the ambient seawater. When mounted on a 
device, upon immersion the surface will corrode and the disc will 
eventually fail. The failure can be used to facilitate flooding and 
scuttling or to activate other mechanical and electrical functions. If 
desired, barstock, such as in FIG. 20, for example, or pre-formed links 
such as in FIG. 22 can be coated with an epoxy except for a 
circumferential area about the center to preclude seawater contact from 
all but the exposed center area. 
Desirable failure time for corrodable linkage devices varies depending on 
the application. For example, it may be desired to retrieve a sampling 
device within one to eight hours of deployment. In another application, it 
may be desirable to scuttle a surface float such as a sonobuoy after eight 
to ten days of operation. 
As a heat source, the alloys can be used to warm divers or melt ice in 
arctic regions. The hydrogen produced can be used to power fuel cells and 
internal combustion engines, or to provide buoyancy for lifting heavy 
objects from the ocean floor. 
Supercorroding alloys have advantages over the prior art type fixed-plate 
cells and mini-cells in diver heating applications. They are at least an 
order of magnitude more reactive than either the fixed-plate cell or the 
mini-cells. They are independent of external electrical resistance and 
internal electrical resistance is minimal. They are significantly more 
efficient than the previous type powdered mini-cells and have a much 
greater energy density than the fixed-plate cells. Reaction rates can be 
selected by choosing the composition of the alloy. The output of hydrogen 
produced can be varied by controlling either the reaction temperature or 
the metering rate of the alloy to a reaction chamber. 
By forming a wide variety of alloys, a range of reaction rates can be 
obtained. Alloys can be chosen for use by matching their reaction rates to 
the application: high rates are suitable for heat and gas generation; low, 
steady, predictable rates are suited to corroding links. 
Obviously many modifications and variations of the present invention are 
possible in the light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims the invention may 
be practiced otherwise than as specifically described.