Affordable nano powder handling

Geschrieben von Robert Greenyer am 21. April 2014.

It is exciting times here because in the next 10 days we expect to receive 75um powder from Dr. Brian Ahern and 10nm Ni from Quantum Sphere to join the special powders Bob Higgins has produced, which are also in the micro-metric range.

Brian's 10nm Ni/Pd islands in ZrO grains will need significant further processing to get them down to around 15um and this will take some weeks of grinding and we are still discussing how best to do that as the raw material is very precious.

Bob Higgins' and Brian's powders are big enough, even after grinding to operating sizes, to not loft easily (do not become airborne) and they also do not present the same health hazard that the 10nm QSI Ni may present, from inhalation, skin and eye exposure. That is not the only challenge Ni at this size presents as Ryan found out when handling their 40nm Ni powders... with even just a little humidity, these particles start to clump together and then become difficult to handle and potentially inactive. So we need to find a way to safely handle these materials whilst keeping them dry, some of the early options we were considering looked really expensive, but Alan Goldwater has been doing some great work trying to make this part of the process affordable.

First was the getting the cost of the "glove box" down... In Alan's words "Barring some serious DIY, a dry glove box looks to be expensive, even used. The basic CLEATECH plastic ones are $1k+ on eBay, and the metal ones more." That is not really practical for wide scale testing, so he looked for other options and found that a glove bag purged with Argon or Nitrogen could work with a variety of sizes available for $20-30...

Glove bag supplier

Alan adds "The nice thing about a glove bag is that after loading it, you can collapse and squeeze it to get the air out, then inflate it with dry gas. Seems to me 2 cycles of that should get down to less than 10% relative humidity (RH). So figure 4 cubic feet of gas per use (for the smallest size bag from the above source). Another advantage is that when you're done with the job, just crumple the bag up and toss it, so nano-contamination of the enclosure is not an ongoing issue. Still have to wash the scale, implements and bottles..."

Suitability test

Alan sought to test the potential of the glove bag concept, combined with a desiccant, to get to below the 10% (RH) target.

On the advice of Mathieu, he bought a WH8040 Digital Air Humidity Controller Sensor for $30.39 from Amazon.com which has a measuring range from 1%-99% AC 110V. It's also available for 220 v.a.c. supply on Amazon.co.uk, about £20.
He then activated an 8 oz silica gel fabric bag he had, by baking it at 120 C for 150 minutes, followed by 30 minutes in a convection oven (a fruit dryer) at 50 C to remove residual water vapour.
He then used a polythene bag, about 2 mil thick and 10 litre volume. He filled it with ambient air at 48% RH and then added the activated silica gel cotton bag, the RH sensor probe and closed up the bag with a wire-tie.

Figure 1: Test setup

Results

In Alan's words "After 15 minutes the meter read 20%, and at 30 minutes it was 3.5%...

...At 45 minutes, it's "off the scale" - less than 1% with this meter. Accuracy is probably ±5% at best and no calibration was attempted. But even if its ±10%, the desiccant seems to do the job."

Conclusion

Using a $30 glove bag and some activated silica gel looks like it will really work! Additionally, if the powder did not have a problem with dry air, then there would be no need for Argon or nitrogen. A Big thank you goes to Alan for taking the initiative on this one. By testing the humidity meter with an actual glove bag and more silica gel, we could develop a protocol for Nano Powder handling that would not require the RH meter so cutting the cost of this part of the process to essentially that of the glove bag.

Discussion

We are expecting to receive 4 packages of 5g of 10nm QSI powder and this will be required to be handled in 3 locations, Minnesota (testing in advanced powder reactor), France (testing in high pressure Mizuno style cell) and California (partial sintering on Ni mesh substrate for later glow discharge testing). So this finding, especially proper use of silica gel, will be immediately helpful.

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