15DEC99
After Run 1 we explored possibilities for preventing the rapid burning away of the insulating teflon sheath around the W cathode wire. We discovered that steatite “fish spine” (small ceramic tube sections intended for high-temperature wire insulation) slipped over the usual teflon covering appeared to provide a great deal of improvement.
This photo shows a new cathode with the fish spine pieces in place. Note: this particular piece of W was visibly fractured by the shearing process. Normally we would not use such a piece but the main purpose of this run was to test out the new insulation technique.
We started the run with the usual warm-up period allowing the electrolyte (0.2 M K2CO3) to get up to about 80°C before applying the higher voltages. After making the transition to glow-discharge electrolysis at about 150 volts, we increased the voltage slowly in 10-20 volt steps over the next 15 minutes to 250 volts.
As you can see from the yellow trace in this plot, the cell temperature rose quickly into the high 90’s and approached 100°C as the voltage rose to 250 volts. Note also that the input power (green trace plotted on a -50 to 450 watt scale) rose more-or-less steadily with increasing voltage. It seems that this type of electrolysis tends to draw a constant current. Therefore, as the voltage is increased the input power increases. At just after 1 hour elapsed time, the voltage was held constant at 250 volts (blue trace). Note that, at first in this period, the input power (green trace) was more-or-less constant at about 275 watts. This is a LOT of power to be dissipating in a 200 ml beaker with only 100 cc of electrolyte! The conditions in the cell were so violent that we could not actually see the cathode. It was obscured by a storm of swirling bubbles.
This is the usual shot through the calorimeter peephole and normally you can see the rectangular outline of the cathode quite well. At this point, however, the cell was just a bright orange glow.
This photo shows the vigorous jet of steam blowing out of the vent hose during this period. This volume of steam was too much for our tiny condenser so we just let it blow and looked at total electrolyte loss after the run.
Unfortunately, something odd happened after we had been at 250 volts for about 5 or 6 minutes. As you can see from the green input power trace, the input power began to climb precipitously, apparently without reason. When it exceeded 350 watts, we shut down the experiment by removing the electrolysis voltage (note that the cell temperature actually reached 100°C momentarily before shutdown). Upon disassembly of the cell, we found the strangest conglomeration on the cathode.
These three views of the used cathode reveal that the lower piece of fish spine cracked into two pieces which did not fall to the bottom of the vessel as one would expect but instead became bonded to the remains of the eroded W cathode sheet with a mysterious glassy grayish substance! Considering the violent conditions inside the cell, this occurrence is nearly unbelievable. We have no idea how this happened.
Power Balance: Note in the plot above that the observed output power (purple trace) is nearly half of the measured input power! This huge shortfall in power balance is apparently due mainly to heat losses via steam exiting the cell. After the run it was observed that the cell had lost about 45 cc of electrolyte. That takes about 100,000 joules to evaporate. The run was terminated prematurely (so we could open the calorimeter and see what had happened) but you can see from the energy totals that the shortfall is about 115,000 joules…reasonably close to the calculated steam losses considering the fact that we didn’t wait for all the heat energy to be collected after the run.
It is apparent that we need to make some changes in our calorimetric procedures in order to obtain good power balance measurements on this high-voltage experiment. It is tempting to place a water-cooled condenser in the head space of the cell to return the evaporated water to the electrolyte before it leaves the cell…but that is quite a departure from the procedures of Mizuno and Ohmori.