We have been running our Mars 6 for some time now and we do not experience any HNO3 vapor escape at all. The vent on ours is not metal until it connects to the main duct up above the ceiling tiles. This gives us about ten feet of acid resistant ducting. I would be more concerned about the fact that you have venting going on in your vessels. That should only be happening if the you are going over pressure as a safety release. Are you sealing the vessel caps with the seal block? It would probably be a good idea to contact CEM and have an engineer come out and check your unit. They have great response time and service. I don’t think we have ever waited more than a few days for service (the few times we have had it on this unit) and we are located just south of nowhere.
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From: PLASMACHEM-L: Analytical Chem.(ICP's, DCP's, MIP's). [mailto:[log in to unmask]] On Behalf Of Derek
Sent: Tuesday, March 21, 2017 10:32 AM
To: [log in to unmask]
Subject: Microwave digestion system question
I have some questions regarding microwave digestion systems. We have a Mars 6 microwave system and recently we noticed that our exhaust line close to the ceiling that is made of metal, the spot weld started to corrode, which led to small drips of nitric acid dripping onto the counter top. Our fix to this will be to put in an all plastic system (the original idea of using metal was not mine but facilities). I have a few questions, does anyone have any type of cold trap to catch the acid vapors as they are released to the exhaust system. I also noticed that the fan on the back of the system pulls about 1100 ft/min, we have a 40 sample carousel and when I took a measurement from the top of the carousel where the vessels would be venting closest to the fan this number decreased to about 230 ft/min. I then took a measurement near the door furthest away from the fan and this number actually decreased down to 0 ft/min. Now with a 40 sample carousel only about 3 tubes at any point in time will have 230 ft/min exhaust, leading potential for vapors to escape out the microwave door. There is no rubber gasket around that door so I have my doubts that the door is air tight when the door is closed. I have been working in the room before where I would smell nitric acid, I do think this is a flaw on this particular system regarding the ventilation. Does anyone keep their microwave system in the hood? Keeping the microwave in the hood would minimize expose to acid vapor.
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