R3 Low Impedance AC Data [UPDATE #1 - R5 No More]

Still dizzy from the whirlwind week at ICCF18, it can be said for many of us that a little time is necessary to regain our bearings. Fortunately I didn't get TOO caught up in the storm and am maintaining the same relative path. 

For me, this week has been all about getting a new calorimeter (soon to come) on its feet and putting some wind in the interns' sails so they can get their experiments wrapped up and written before the clock strikes midnight. Be sure and check them out! Jordan and I had some fun mixing severely caustic 6.5M hot NaOH solution in the local high school's lab hood yesterday; those pictures don't take themselves, you know . With all this peripheral work in tow, I just got around to peaking at the last AC frequency sweep data. Look here if you wanna get your hands on some numbers; I neatly laid out the first and last data points in 5 minute averages over the 30 min. frequency applications. 

This figure shows the first (A) and last (B) 5 minute average of powder temperature, zeroed from ambient, at each AC frequency applied (in chronological order). The greatest ΔT was at 60KHz, however the greatest absolute rise in temperature was from 20KHz. We would have an enormous ΔT had I stepped straight from 200 to 20KHz. The bump in 2KHz A is odd. It exactly matches the A value for 6KHz which is suspicious. I can't say the data is false, but I do believe there was some experimental error - possibly in the button-pushing and dial turning required of changing frequencies. If this anomaly can't be solely ascribed to that changeover, then more investigation is certainly in order!

This figure supports the assertion that 20KHz is the preferred operating frequency as it produces the greatest response in Powder impedance and thus the greatest Ohmic heating. Note that this figure and the one below display the last 5 minutes of the application to show the frequency's effect after 30 minutes equilibration time. 

As demonstrated here, the heating effect stems from ohmic heating in the powder. The bulk is surprisingly responsive to changes in the frequency, shifting impedance and temperature immediately. On top of that, the electrical connection through the powder is a stable one, showing little change from physical perturbation.

What currently goes unanswered is if the heat effect is only true Ohmic heating, or if we are seeing acoustic heat effects as well. It looks like we may be stuck speculating with this cell design. Additionally it may be worthwhile to do more frequency sweeps yet between 15-30KHz to find the truest peak response. 

My next steps will be to turn on passive heating again and play in the 20KHz range, maybe check out the 2KHz bump as well. If we don't get pressure drops from loading, then it may be time to take the heating up a notch. Time will tell, and I'm still hopeful. We haven't seen any good loading yet!

It feels like we only go Backwards

I promised all this magnificent loading data and, to date, R5 is making me look like a fool! I'm making careful consideration to give R5's media a 50V DC slap to drive off passivating oxide layers. This setup would use the same power supply used for R3's resistance sense to save lab space, but needs working to get the leads to the other side of the reef. I will drop an update when this change occurs, hopefully not getting the message to you through messy data during the changeover. 

As always thanks for reading!

UPDATE #1 - R5 No More

The face of defeat. . .R5's T_Powder and Pressure cycle with ambient temperature. This is not the look of 'good' H₂ loading in a nanopowder. The marginal loss in overall pressure can probably be attributed to small leaks or diffusion through the cell wall.

After setting 48 Volts loose on the beast, I came out on bottom and have made the toughest decision every experimenter must face: when to quit. Bearing in mind the labor cost to maintain this test, it's obvious that time has come and gone. We really want you to feel the excitement of a 'breathing' lattice as it's loaded to high molar ratios and sporadically offgasses and readsorbs atmospheric hydrogen, and frankly, this junk isn't cutting it. 

The power is shut off to the cell in order to be taken apart and started anew with fresh 70nm Ni powder. Stay up for the blogs to follow.

The adventure begins again!