Incandescent W Experiment
Runs 8, 9, & 10 27AUG98
Starting with Run 8, we added a H2+O2 recombiner to the system. This recombiner consisted of a chamber full of Pd-coated alumina catalyst pellets plumbed into the exit gas line from the cell. The recombiner was located outside the calorimeter enclosure and its main purpose was to remove H2 and O2 from the exit gas stream so any additional gases present could be collected and analyzed. Our goal was to determine the composition of the "excess gas" observed in Run 7.
For Run 8 we simply connected the recombiner chamber directly to the hose leading out of the cell. Shortly after the electrolysis power was applied to the cell, the recombiner began working and the heat of formation of H2O caused portions of the catalyst pellets to become red hot. This heat source ignited the 2H2+O2 stream coming out of the cell and the flame raced back into the cell and exploded the gas in the cell's head space!
Fortunately the cell is well contained inside the calorimeter and there was no external damage from the explosion. However, most of the internal parts of the cell and the glassware were shattered. Below is a photo of the temperature sensor after the explosion:
For Run 9 we added a flame arrestor between the recombiner and the cell. This device consisted of a tight roll of fine Cu screen stuffed tightly into a glass tube. The roll was about 8 cm long and was expected to cool the advancing flame front below the ignition temperature thus extinguishing the flame.
It didn't work. Run 9 exploded just like Run 8, again shattering the glasswork, breaking the W rod, and generally irritating the investigators.
For Run 10 we removed the flame arrestor and installed an all-metal water bubbler trap in its place. The exiting gas has to bubble through the water in this trap before reaching the recombiner. Due to the construction of the trap, a flashback cannot force its way backwards through the trap unless it expels all the water from the trap...very unlikely.
Run 10 proceeded without exploding the cell but, during the warm-up phase, the gas between the recombiner and the bubbler trap exploded disconcertingly on a regular basis. Fortunately the apparatus withstood these shocks without any damage and we were able to proceed with the run.
Once the air had been purged from the cell during electrolysis warm-up, the recombiner succeeded in reacting all of the exiting gases from the cell. This was dramatically demonstrated by a complete stoppage of bubbling in the gas volume apparatus downstream of the recombiner and cold trap.
However, when we switched the cell into incandescent mode by raising the voltage to ~150 volts, gas began to come through the recombiner, through the cold trap, to the gas volume apparatus and the bubbling resumed. Presumably this was the "excess gas" observed but not isolated on previous runs. Interestingly, the presence of the excess gas made the periodic explosions stop.
Using a 500 cc graduated cylinder we collected all of the excess gas generated by Run 10's incandescent period, which lasted only about 10 minutes. The total was 215 ml at 34° C (yes, it's hot in our lab).
We extracted some of the collected gas into a syringe and injected it into a flame. It burned with the characteristic nearly-colorless flame of hydrogen. Assuming it is hydrogen, the collected quantity represents 8.5E-3 moles. If this H2 is coming from the reaction W + 3H2O --> WO3 + 3H2 then 1/3 that many moles of W had to be consumed in the process. That's 2.8E-3 moles of W or .52 grams. In our haste to rebuild the apparatus after Run 9 we forgot to weigh the particular W rod used in Run 10. However, it now weighs 0.46 grams less than our only remaining unused W rod...pretty close to the predicted weight loss from the reaction hypothesized above.
This photo shows the rod used in Run 10 alongside a new W rod. The right ends of both rods were aligned so you could see how much of the used rod has been eroded. The rod diameter is 0.062" or 1.58 mm.
The calorimetric results of Run 10 are displayed in this plot. As you can see from the Ein and Eout traces and the displayed total values for Ein (222474 joules) and Eout (214102 joules), the final energy balance again shows a shorfall...this time about 4%.
Is this energy shortfall explained by the 215 cc of H2 gas we collected? The formation of WO3 from W and O2 is exothermic and yields 841,000 joules/mole. To get the necessary O2 for one mole of WO3, however, 3 moles of H2O have to be dissociated and that costs 858,000 joules. Thus the hypothesized reaction is only slightly endothermic and, for the quantity of WO3 formed in this run, would absorb only ~50 joules. The observed shortfall is ~8,000 joules.
A more likely cause of the shortfall is simply calorimetry error. This is a highly erratic experiment that places severe demands upon the input power measuring instrument and the overall data acquisition system. In addition, the temperature regulation system that keeps Tin nominally constant is unable to handle the rapidly changing heat loads perfectly. The resulting excursions in Tin cause corresponding errors in the Pout signal. In other words, agreement to within 4% on this experiment is probably as good as we can ever expect.
We would like to acknowledge significant support of our efforts on this experiment from the members of the Vortex-L Internet discussion group. Many of the suggestions offered on that forum have been adopted in this work. Thanks!