Burst Pressure, Permeance of NSN pnc-Si SEPCONS with large pores
Karl, Charles and I measured the burst pressure and permeance of some 30-50-30 and 30-100-30 NSN.
Burst Pressure:
The SEPCONs readily burst at pressures under 1 psi when the flow was directed from the backside of the chip through the membrane.
The membranes were able to withstand higher pressures when the pressure was applied from the front to the back the of the SEPCON:
30-100-30 NSN – 9.7 psi max [porosity- 10%, mean pore diameter – 122 nm]
(other samples tested 4.5, 9.6, 2.0, 9.3, 6.7, 4, 8.2, 3, 2.5 psi)
30-50-30 NSN – 6 psi max [porosity- 17%, mean pore diameter – 87 nm]
(other samples tested 1.0, 4.0 psi)
Permeance:
These samples were measured with the flow passing from the front of the SEPCON chip to the back.
permeance
Sample Stack psi cc/cm2/s/bar
A 30-100-30 1 602
A 30-100-30 4 660
B 30-100-30 1 617
C 30-50-30 1 792
D 30-50-30 1 792
These numbers seem low considering Maryna’s published value from material with 12nm pores was ~950 cc/cm2/s/bar.
If the permeance is low, this may mean that not all the pores are through pores. Perhaps not surprising since the silicon layer is relatively thick… Do you have numbers for the porosity of these films? That’s the key parameter, as the pore size in itself should not matter (I am assuming you refer to the gas permeance). Another interesting point is that these thicknesses are close to or even larger than the mean free path, so there should be a negligible ballistic component, hence be careful about a direct comparison between Maryna’s data and these data, without looking at theory’s predictions.
Philippe – I added the porosity and pore size information in the post above near the burst pressure data. Yes these are gas permeance measurements using N2. Thanks for the input. I agree that any comparisons to Maryna’s data should be taken with a grain of salt. My concern is primarily with the low burst pressure. Our goal is to implement these in the INT cartridge and low burst pressure could be a real problem. I plan to reduce the nitride etch time in HF in the hopes that this will improve strength.