What are the factors for misfire for Bomb Calorimeter to happen? Recently I've noticed that this equipment can't give a result because of misfire during the operation. And I've noticed that the electrode (both electrodes for holding the fuse) are a little bit oxidized. After I clean it with sand paper and sonicate for 30 minutes then the operation going very smooth.
So my question is, does electricity flow on the surface of the electrodes or in the interior? Will the Purified Oxygen can cause the electrode to be oxidized very fast?
Model: Parr 6400
A long time ago, at the lab, we did combustion calorimetry using a Prolabo bomb. And we met the problem you mention. Of course, when the final state is ill defined, no meaningfull data can be obtained. Since the mass of sample used in our experiments was large (.1 g), in order to get a good combustion (O2 pressure about 15 bar), we used a small bed of nitocellulose (made at lab) and the sample (powder form) was laid on it.
A platinium wire warmed at high temperature (discharge of a electrical condenseur) started the combustion of the cotton, and of the powder.
Nitrocellulose was prepared on immersing commercial surgical cotton into concentrated nitric acid during ¼ h, and washing it with water, and dried it.
Of course, (as you know), a large number of corrective terms must be precisely known such as heat of combustion of nitrocellulose, and electrical heat for starting the combustion.
It seemed us better to use fluorine combustion, and built a fluorine combustion calorimeter. However, this is a very difficult and dangerous experiment to handle. I hope that it could be usefull, and good lucke.
Electricity will flow in the interior of the electrodes and fuse wire (especially if the exterior is a non-conductive oxide as you say). Therefore, it's unlikely that this is the source of your problem.
It is more likely that you have a poor connection with your wire and the circuit is open. It's possible that the insulator or o-ring on the electrode is damaged and is causing a short.
It's also possible that your fuse wire is actually too long, which increases its resistance and can cause it to heat and melt before it's able to ignite your sample (or cotton auxiliary fuse if you're using one).
If your sample is not highly combustible and just difficult to ignite, your oxygen content might not be high enough. You should fill it to 30atm of oxygen, essentially as pure as possible (purge to vacuum and fill with oxygen, repeat 2-3 times). I wouldn't worry about it causing your bomb to oxidize since it's alloy 20, a nickel alloy with excellent corrosion resistance that is built for these conditions and worse. Simply using a larger sample might help. If that fails, you could also try putting in a more combustible material to help ignite the sample, like the cotton thread Parr suggests or NC as suggested in a previous answer if you need some serious help (though your data quality may suffer as a result).
To help diagnose the issue, are you finding that your wire has melted but your sample is not combusted? Have you checked your electrodes with a multi-meter to see if you have good connection or a short somewhere? Is your bomb able to maintain 30 atm or is there a leak?
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