Freezing Temp of Glycerin?

[Roach]

Can someone help me? I need to know the temperature at which glycerin and ammonia freezes, and I can't seem to find this info in my books.


Thanks,
Roach

 

[dmprice1]

MP of NH3 is -77.7 C, and glycerol is 18 C.

 

[CarlB]

According to CRC Handbook, at 1.0 Atm pressure:

F.P. of glycerine = 17.0 degrees F

ammonia (aqua) - some other properties listed, but not freezing point

Partial answer anyway..
Carl

 

[Roach]

I have a liquid-filled pressure guage that is specified as a "glycerin" filled guage to dampen vibration. It is outside, and I know that it gets colder than 64ºF (18ºC) outside. It must be a solution of some sort, or maybe I am missing something. The liquid does not turn to solid when it is cold outside. Do you know why?

Thanks,
Roach

 

[trihydrate]

According to my C.R.C. handbook the melting point of Glycerol is 17.9° C. A note is added that it "solidifies at a much lower temperature".

 

[Roach]

I understand that this has to be the case, or our pressure gauges wouldn't move in the winter. How can something "melt" at a temperature, when it isn't a solid below that temp?????????????????????

What does the substance do at 17.9ºC that it doesn't do at any other temp????

Thanks for the info Trihydrate. I thought this was correct, but it made no sense to me. Guess it is best that I stick with mechanics.

Thanks,
Joey

 

[scheffler]

I have been looking into the different properties of glycerine myself. I have seen that the melting point of glycerol is around 18 C and two separate sources that list the viscosity of pure glycerol at a temp. of 10 C.

Maybe the containers, the guage and the viscometers from the reports, were super clean and the glycerol was supercooled.

I was looking into using a glycerol-water mixture as a substitute for mineral oil in a hydraulic system.
The temperature of the fluid will be controlled, so the viscosity of the fluid will not be a problem.
I have searched through all of the literature available to me and have found little mention of it being used as a hydraulic fluid.
Is there any reason why it isn't commonly used as a hydraulic fluid?

 

[PeterPiper]

I worked on a glycerine distillation plant for a time. To memory the freezing point of pure glycerine is about -10°C and the melting point somewhere around +18°C.

It was of some concern that unlagged lines would freeze in winter and it would be a problem to melt the lines again. In test the lab was unable to get the glycerine to freeze although it does become very viscose. We believe small impurities were changing the melting and freezing point significantly.

scheffler - One reason for not using water/glycerine solutions could be, microbial action becomes fairly rapid below a 70% glycerine concentration. Above this it is too conc for bacteria to thrive.

 

[sciguyjim]

Maybe this will help. Maybe the higher freezing point given for glycerine is more of a glass transition point at which it becomes too thick to pump, yet actual solidification occures at the lower temps given.

I remember hearing in college that glycerine could be supercooled in clean containers and so stay liquid at far lower temps than expected. Once it freezes though it cannot be supercooled again because of microscopic collections of molecules here and there retaining the crystalline pattern and acting as nucleation points in the future. This caused some headaches in early attempts to pump it through pipelines in cold climates.

 

[25362]

Glycerol when added to water drops the MP (was used as antifreeze). The minimum FP of a water mix would be at 70% glycerin: -37.8C.

Glycerol, as water, has a strong intermolecular (and intramolecular H-bond effect that makes its BP as high as 290C. I wonder whether this could be the explanation for the disparity between its MP and a lower FP.

I can bring an example of paraffin waxes which are mixtures of hydrocarbons. The so-called mycrocrystalline waxes show "congealing" points that are invariably lower than the drop "melting" points.

Undercooling of pure liquids below their freezing points is possible: carefully undercooled water has been studied at -30C !

Amorphous solids such as glass and polymers -they don't form well defined crystals- can be cooled (supercooled) way below their freezing points until they solidify because of the lack of sufficient order in their molecular structure and arrangements to allow for short-distance intermolecular attraction effects to take place.

Somebody rightly said: the more I learn the more confused I am.