This run employed W cathode materials supplied by Dr. Mizuno. Two different types of W sheet were supplied to us. One is very shiny material and 0.20 mm thick. The other has a mottled appearance and is 0.48 mm thick. For this run we used the mottled stuff.

Unfortunately, during shipping to us and handling here at EarthTech, all of the spot welds made by Dr. Mizuno broke. We had to weld the cathode sheet to the W lead wire using the TIG fusion method developed for our own cathodes. By the way, we were not surprised at the broken welds. Our own experience with fusion-welded W indicates that the welds are extremely brittle. After performing this weld, we subjected the repaired cathode to the acid-etching procedure prescribed by Dr. Mizuno (i.e. 2 hrs in dilute HF/HNO₃ followed by 2 hours in aqua regia).

Run 7 was the first in this series to employ a quartz vessel. We acquired the 200 ml tall form spoutless beakers from Technical Glass Products.

We were going to use high-purity HPLC water for this run but things just didn't work out. After losing the first shipment, UPS nonchalantly delivered the second shipment yesterday at noon in a cardboard box that was actually dripping liquid. The glass bottle inside had broken! Fortunately it was only water.

Run 7 used 0.1M K2CO3 electrolyte made with distilled water, the same as all previous runs in this series.

 

Results:

The color legend and vertical scales for this plot are as follows:

Pin (0-200 watts)

Pout (0-200 watts)

Tcell (0-100° C)

Vcell (0-200V)

Icell (0-5A)

Tin (39-41° C)

The horizontal scale covers 3 hours.

 In Run 7 we deliberately varied the independent drive parameter, Vcell, in the hopes that excess heat might appear at a particular excitation level. Three voltage levels were explored. The first, 145.9 volts, was sufficient to make the cathode emit a reddish-orange blackbody glow. At the second and third voltage levels (118.3 and 95.6 respectively), the cathode was not glowing perceptibly. However, at all of these voltages, the cathode was covered with the dancing white sparks that are typically observed in this experiment. Data was averaged over the three near-equilibrium periods indicated by white lines in the plot above. Results for the three periods are presented in the table below.

A plot of Pout/Pin with +/- 2% error bars (estimated) shows no significant trend.

During this run, a Fluke 87 True RMS meter was connected in series with the cell to provide an independent measure of the cell current. Here is a typical observation:

The last entry, I avg, was calculated by dividing the Clarke-Hess power by the Clarke-Hess voltage. Note that it is significantly lower than the I (Clarke Hess) value. That is because the Clarke-Hess displays RMS current, which will be substantially higher than average current for a "spikey" waveform like this. Note also that the calculated value for I avg agrees very well with the current reported by the Fluke 87. This is somewhat surprising because the Fluke is advertised as a true RMS meter, yet it is clearly reporting the average current in this case. Maybe the RMS computation only functions on the AC ranges. This current measurement was made with the meter set for DC current.

During the 145.9 volt plateau, we observed 2.6 times as much gas coming from the cell as predicted by the average current, which was 0.84 amps at the time. If all of this gas was due to dissociated H2O, the caloric value escaping the cell was 3.3 watts. This power adds to the observed Pout raising it to 123.8 watts, about 1.8% more than the observed Pin of 121.6 watts.

During the 118.3 volt plateau, we observed 1.9 times as much gas coming from the cell as predicted by the average current, which was 0.88 amps at the time. If all of this gas was due to dissociated H2O, the caloric value escaping the cell was 2.5 watts. This power adds to the observed Pout raising it to 106.2 watts, about 1.7% more than the observed Pin of 104.38 watts.

We didn't measure the gas flow during the last voltage plateau.

This calorimeter system does not have an on-line flowmeter. A constant-displacement pump provides a nearly constant flow rate that has proven to be very stable in the past. Actual flow rate is measured periodically during a run with a stopwatch and 0.01g balance and recorded in a notebook. In view of the excellent flow stability usually observed we typically check the flow rate only at the beginning and end of a run.

At the beginning of this run, the flow rate was measured at 4.77 gm/sec. That value was entered into the data acquisition program and then used for all subsequent data points. At the end of this run...to our great surprise...the flow rate was measured at 4.65 gm/sec! That is 2.5% relative below the starting flow rate, an unprecedented change. Having the actual flow rate lower than the flow expected by the program produces an equivalent positive error in the reported Pout. Unfortunately, we don't know when the flow rate shifted to the lower rate. If it was early in the run, it would explain the ~2% apparent excess observed when the caloric value of the escaping gases was considered.

As a result of this experience, we are once again considering the implementation of an on-line flow measurement system. It should be an interesting engineering challenge!

........

These photos were taken after the run with the cell operating out of the calorimeter enclosure. The stirrer was operated just as it was during the run for all three photos. In the left photo, the cell has no electrolysis current flowing. The cathode is visible in the center of the cell. Note the dark coloration over portions of the cathode area. This coloration appeared during the run. The tip of the temperature probe is just above the cathode to the right. The white blur in the bottom of the cell is the teflon-coated stir bar. The blur below the cell is the spinning permanent magnet that drives it. In the center photo, electrolysis is underway. The cloudy appearance is due to the swirling bubbles in the electrolyte. The right photo was taken without the flash to reveal the cathode incandescence.