Issues regarding the constant weight of the crucible in the loss on ignition test
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I reviewed many documents, which state that in the loss on ignition test, the crucible is heated to 950°C in a muffle furnace; after removing it from the furnace, it is allowed to cool slightly for 30 seconds before being placed in a desiccator to cool down to room temperature. There are doubts about this experiment. First, with such a large temperature difference, won’t the crucible in the dryer explode due to the extreme temperature difference? Second, does this method of cooling in a dryer really have no effect on the burned sample? It’s a headache – if the cooling time in the muffle furnace is too long, just like in the case of burning out samples, then cooling it in a dryer seems a bit inappropriate! I hope experts can give some guidance!
After cooling slightly, it is placed in a dryer at 100–200°C. At this temperature, which is higher than the boiling point of water, it remains in a dry state and will not absorb moisture; moreover, this temperature is not too high, so it will not explode when placed there； Cooling in the dryer is intended to prevent moisture absorption under natural conditions; why then does it have an impact on the sample? If weighing is not done at room temperature, it should be the balance that is affected, right?
The original poster is overthinking it; there’s no problem at all. But to achieve a constant weight, it is also necessary to ensure that the cooling time is consistent.
I’ve started my experiment; thank you all! However, I think that cooling it to around 100°C before placing it in the desiccator takes an excessively long time. After checking the literature, I found that the common practice is to take out the burned crucible, leave it in the air for about 30 seconds, and then place it in the desiccator to cool down to room temperature. I conducted several sets of experiments and did not observe any cracking of the crucibles. But the desiccator must be the same one; otherwise, the test results will vary significantly, and at least a constant weight cannot be ensured. I’m a beginner; please give me some guidance!
The key to this analysis is constant weight; therefore, the desiccant in the dryer must be of high quality. Crucibles generally can withstand temperature fluctuations, and at least in the analyses I have conducted, no crucibles have broken
Based on my many years of experience in shaking flasks, I believe that unless there is a high requirement for precision, as long as the drying time and cooling time are ensured (and the conditions are consistent), and the drying conditions for the empty crucible and the crucible containing the precipitate are the same (same temperature and time, around 2 hours or more), the impact will not be significant (although it is not completely without any effect)
These are the basic knowledge of analysis; you just need to take a look at this basic knowledge to understand it
It won’t explode.] We conduct experiments frequently and need to ensure that the cooling time is consistent.] The difference between the weights before and after measurement is within plus or minus 0.0002~
I have completed my experiment, and the results are satisfactory. Thank you all for your help!
I exactly need a muffle furnace at 900 degrees – thanks to the original poster!
This post was last edited by lily Colorful Desert on 2009-10-14 08:53. I would like to ask whether cracks in the muffle furnace can affect the measurement results? If so, is the impact significant? Also, what is the price of a muffle furnace with a maximum temperature of 1100 degrees?