[atrum]

hello all,

 I am not sure if this has been asked before, but is there a way I can use a standards digital temperature probe to measure the temperature of a corrosive compound with out compromising the temperature probe.

 Maybe by using a thermometer well?
If that is the way to go is there a way I can make one out of a pipette ?

[Arkcon]

Your standard laboratory thermometer is typically made of fairly resistant glass.  If you have to use a digital probe, you'll have to make sure with the vendor that its compatible with your sample, they may sell you a more expensive, more resistant probe.  I haven't heard of a diy thermometer, but I suppose they are possible.  You're insisting on taking roundabout methods to solve your problem.

[atrum]

Thank you for your reply.

 I am not considering making a diy thermometer just a thermometer well for my digital temp probe.

I agree that making my own thermometer would be quite a roundabout method of getting to my goal; thus I wouldn't even attempt it.

[408]

It will not will not last forever and will need tape replacing once and a while, but get some plumber's teflon tape and wrap it around the probe very carefully leaving no spaces.  This worked well enough for a stainless (I assume) metal probe to monitor the temp of a reaction occurring in 100% nitric acid.  Do not skimp on tape.

[atrum]

Thanks,

 What about Glass Tape?

[408]

I know nothing of the chemical resistance of glass tape, nor do I know exactly what it is so I cannot comment. 

[dodge305]

Be careful using glass. Many corrosives (ie. hf acid) are very good at eating through glass.  The Teflon tape suggestion is a good suggestion as long as there are not exposures to the probe itself.

[curiouscat]

Thermowells are an option. Indeed they are widely used industrially.

Downside is, they do have thermal inertia so you'll need to wait to get a good reading.

Thermowell material selection depends on what your corrosive is, but typically well will be filled with an oil for thermal contact. If you want to splurge, hastealloy, titanium or tantalum / teflon coated Stainless Steel will resist a lot of nasty stuff.

I do suspect you'll be killing a mouse with a cannon if you go this route.

[gapeev]

What is that "corrosive compound"? Will teflon sheath work? 

[atrum]

Sulfuric Acid is the primary corrosive I will be using. I am attempting to Nitrate Phthalic anhydride to 3-nitrophthalic acid.

Sulfuric acid, and Sodium Nitrate are the main chemicals in this experiment. I would much rather use a thermocouple rather than a glass thermometer due to accuracy, and  not risk destroying my equipment if I can avoid it.

I am aware that any coatings or media between the thermocouple and my solution will delay an accurate reading.

[Arkcon]

I still don't understand your use of the term 'accuracy' here.  Typical glass laboratory thermometers a very accurate, when read by people with a few minutes of training, who care about their answers.  A thermocouple connected to a digital readout is, almost by definition, less accurate.  A bit more convenient perhaps, a bit more easy for documentation if it auto-prints results -- sure.  But don't make the mistake of assuming if it has 3 places past the decimal, tose numbers are guaranteed to mean anything.  Furthermore, glass is perfectly resist ant to most common laboratory reagents -- and you haven't mentioned that you're working with a beaker full of HF, or fused alkali.