Gadolinium's temperature
CM, Sat Jan 20 2007, 04:59PM"Gadolinium's temperature is observed to increase when it enters certain magnetic fields". What I'd like to know is does the temperature of Gadolinium remain increased as long as the magnetic field remains constant... or is the temperature increase of Gadolinium just momentary... due to a 'magnetic moment' and eventually returns to it's starting temperature. Another way to phrase my question is.. when Gadolinium is placed in a strong magnetic field for 60 mins, will the temperature increase of the Gadolinium be for 60 mins? or will the temperature increase be only a short moment. CM
Re: Gadolinium's temperature
..., Sat Jan 20 2007, 05:57PM
I am not sure about this (haven't done any real chem work for a in months) but I believe that the process works by: 1. the metal when not in a magnetic field has a thermal capacity of some value X joules/moles*K 2. putting it in a magnetic field disrupts the magnetic dipoles, which increases the crystals entropy, and the heat capacity (some value Y). So now it has a heat capacity of X-Y joules/moles*K, but the energy in the sample remains constant (assuming it is well insulated), so the temperature must go up. 4. removing the field realigns the dipoles, increasing the heat capacity, so the temp drops.
So, placing it in a field for 60 minutes would cause the temp to stay high for all 60 minutes, assuming it is well insulated.
But don't get too excited, we are talking temp changes on the order if 1C/tesla...
..., Sat Jan 20 2007, 05:57PM
I am not sure about this (haven't done any real chem work for a in months) but I believe that the process works by: 1. the metal when not in a magnetic field has a thermal capacity of some value X joules/moles*K 2. putting it in a magnetic field disrupts the magnetic dipoles, which increases the crystals entropy, and the heat capacity (some value Y). So now it has a heat capacity of X-Y joules/moles*K, but the energy in the sample remains constant (assuming it is well insulated), so the temperature must go up. 4. removing the field realigns the dipoles, increasing the heat capacity, so the temp drops.
So, placing it in a field for 60 minutes would cause the temp to stay high for all 60 minutes, assuming it is well insulated.
But don't get too excited, we are talking temp changes on the order if 1C/tesla...
Re: Gadolinium's temperature
CM, Sat Jan 20 2007, 06:25PM
1C/tesla ... equivilent to 1.8F/tesla?
CM, Sat Jan 20 2007, 06:25PM
1C/tesla ... equivilent to 1.8F/tesla?
Re: Gadolinium's temperature
Bored Chemist, Sat Jan 20 2007, 06:26PM
For a give degree of insulation the cooling will be that same no matter how the Gd was heated. If you warmed it up with a lit match or jut by holding it in your hand it would cool down afterwards,
In fact that whole point of using Gd as a cooling agent depends on a 3 stage process.
You put the stuff in a magnetic field and it warms up a bit. You leave it and it cools ack down to the temperature of the surroundings then you switch off the magnetic field and the Gd cools down to colder than it started.
Bored Chemist, Sat Jan 20 2007, 06:26PM
For a give degree of insulation the cooling will be that same no matter how the Gd was heated. If you warmed it up with a lit match or jut by holding it in your hand it would cool down afterwards,
In fact that whole point of using Gd as a cooling agent depends on a 3 stage process.
You put the stuff in a magnetic field and it warms up a bit. You leave it and it cools ack down to the temperature of the surroundings then you switch off the magnetic field and the Gd cools down to colder than it started.
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