metalresearcher - 28-3-2018 at 09:38
Yesterday I mixed some CaSO4 (burnt dead and crushed plasterboard) with Al powder in a 136:72 ratio and I ignited it electrically with an iron wire.
First in open air and then in vacuum.
It reacted vigorously without sound.
After the reaction the pressure within the 1 liter jar surged to from almost zero to 0.3 bar (02:04 in video) and when I let air into the jar (02:27,
slow motion at 03:06) a small dull explosion occurred with some light.
I am curious which flammable gas was in the jar. The only possibility would be H2 due to moisture in the mixture or the container (an YTONG cell
concrete bricklet).
Assume 1 liter of 0.25 bar = 1/100 mol H2 from 1/100 mol H2O which is 0.18 gr moisture. Would that be possible ?
https://www.metallab.net/jwplayer/video.php?v=L2NsaXBzL0NhU0...
RawWork - 28-3-2018 at 10:06
Calcium Sulfate reduced to Calcium Sulfite, or Calcium Oxide and Sulfur Dioxide. Sulfur dioxide may have been reduced to sulfur and sulfide.
Depends...
Sulfur reacting with air to form sulfur dioxide.
Or sulfur dioxide reacting with air to form sulfur trioxide.
Or more reactions at once.
[Edited on 28-3-2018 by RawWork]
Sulaiman - 28-3-2018 at 10:51
I think that there may be many chemicals in plasterboard added for differing reasons.
I'd try again with 'pure' reagents, if available.
AJKOER - 28-3-2018 at 18:20
I recall some homes had to remove existing plasterboard for health reasons. Recollection was the use of cheap plasterboard containing formaldehyde
(see "An Investigation on Formaldehyde Emission Characteristics of Wood Building Materials in Chinese Standard Tests: Product Emission Levels,
Measurement Uncertainties, and Data Correlations between Various Tests", at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4675528/ ).
[Edited on 29-3-2018 by AJKOER]
unionised - 29-3-2018 at 05:19
Most things that might explain an explosion (and formaldehyde in particular) will not survive the process of powdering and dead burning.
Calcium sulphide is a fairly strong reducing agent. It's possible that it oxidised back to the sulphate.
wg48 - 29-3-2018 at 06:07
I suggest you determine if the explosion is reproducible. If it is try different amounts of aluminium powder, different sources of the calcium
sulphate, a different sulphate, wait longer before allowing the air in so the initial react products have cooled down.
If you can adjust the camera so its set to a fixed lower sensitivity (so the image is almost black until the explosion occurs) you may be able to see
what ignites. Take safety precautions such as screen between you and the chamber just in case the next explosion is more violent.