mat@mtx5b.UUCP (Mark Terribile) (05/05/85)
I hope that a question about real things in the real world isn't out of
place here.
Consider the specific heat of various materials. The specific
heat of metals is very low ... approximately one fifth to one tenth that of
water. Ceramics and glassy materials have specific heats that are
approximately the specific heat of water, give or take a factor of one part
in three.
Now it is possible to take certain metals in the molten phase and
cool them very rapidly, as by spraying them against a rotating wheel cooled
by liquid nitrogen. The result is an amorphous, non-crystaline solid made
from the metal in question: a metallic glass.
Is the specific heat of such a material more reminiscent of the
specific heat of the metallic phase of the material, or is it reminiscent
of the specific heat of glass?
--
from Mole End Mark Terribile
(scrape .. dig ) hou4b!mat
on 5/1/85 ..,,. mtx5b!mat
,.. .,, ,,, ..,***_*.chas@gtss.UUCP (Charles Cleveland) (05/09/85)
Followup-To:net.physics Keywords:specific heats, metallic glasses, ceramics In article <1397@mtx5b.UUCP> mat@mtx5b.UUCP (Mark Terribile) writes: >I hope that a question about real things in the real world isn't out of >place here. > > Consider the specific heat of various materials. The specific >heat of metals is very low ... approximately one fifth to one tenth that of >water. Ceramics and glassy materials have specific heats that are >approximately the specific heat of water, give or take a factor of one part >in three. > > Now it is possible to take certain metals in the molten phase and >cool them very rapidly, as by spraying them against a rotating wheel cooled >by liquid nitrogen. The result is an amorphous, non-crystaline solid made >from the metal in question: a metallic glass. > > Is the specific heat of such a material more reminiscent of the >specific heat of the metallic phase of the material, or is it reminiscent >of the specific heat of glass? If you examine specific heats in some reasonable units (such as calories per degree kelvin per atom) you will find that there is no systematic variation is specific heats as one moves between materials belonging to the classes you consider. Thus it is unsurprising that the specific heat of a metallic glass is about the same as that of a metallic liquid or a metallic crystal or water or a stained-glass window. The variations do not particularly have to do with crystalline vs. amorphous or insulator vs. conductor. These are about room temperature considerations (specific heat dominated by 'lattice vibrations'. If someone undertakes such a comparison and disagrees, I would be interested to hear about it. I only spent about 15 minutes looking at the numbers, although the result seems reasonable to me. -- Charles Cleveland Georgia Tech Surface Studies Georgia Tech School of Physics Atlanta, GA 30332 ...!{akgua,allegra,amd,hplabs,ihnp4,masscomp,ut-ngp}!gatech!gtss!chas ...!{rlgvax,sb1,uf-cgrl,unmvax,ut-sally}!gatech!gtss!chas
gv@hou2e.UUCP (A.VANNUCCI) (05/14/85)
In article <1397@mtx5b.UUCP> mat@mtx5b.UUCP (Mark Terribile) writes: >I hope that a question about real things in the real world isn't out of >place here. > > Consider the specific heat of various materials. The specific >heat of metals is very low ... approximately one fifth to one tenth that of >water. Ceramics and glassy materials have specific heats that are >approximately the specific heat of water, give or take a factor of one part >in three. > > Now it is possible to take certain metals in the molten phase and >cool them very rapidly, as by spraying them against a rotating wheel cooled >by liquid nitrogen. The result is an amorphous, non-crystaline solid made >from the metal in question: a metallic glass. > > Is the specific heat of such a material more reminiscent of the >specific heat of the metallic phase of the material, or is it reminiscent >of the specific heat of glass? From the book "University Chemistry" by Bruce H. Mahan, (c) 1969 by Addison Wesley. " Section 3.7 According to the law of Dulong and Petit, the heat capacity of one gram atom of a solid element is approximately 6.3 cal/deg. We have seen that the application of this rule is not limited to elements, for experiments show that the heat capacity of many solids, elemental or compound, is 6 cal/deg *per mole of atoms*. Of course, there are exceptions to this law. There are many substances whose heat capacities, measured at room temperature, are much smaller than predicted. These exceptional substances are high-melting crystals that are made up of light atoms, such as boron, carbon and berillyum. Moreover, the Dulong and Petit law fails for all substances if the heat capacity is measured at low temperatures. That is, the heat capacity of a solid is not constant, but increases with increasing temperature. At the absolute zero of temperature the heat capacity of all substances is zero. As the temperature is raised, the heat capacity increases, but at different rates for different substances. Finally, in the limit of very high temperatures, the heat capacity of all solids is 6.3 cal/deg *per mole of atoms*. The key to understanding the temperature dependence of the heat capacities of solids was supplied by Einstein in 1905....." Indeed, that is the work for which Einstein received the Nobel prize. It turns out that the departure from the Dulong and Petit law at low temperatures is a quantum-mechanical effect and played a key role in the development of Quantum Mechanics. Giovanni Vannucci AT&T Bell Laboratories HOH R-207 Holmdel, NJ 07733 hou2e!gv
gv@hou2e.UUCP (A.VANNUCCI) (05/20/85)
In a previous posting I wrote: > From the book "University Chemistry" by Bruce H. Mahan, (c) 1969 by > Addison Wesley. > > " Section 3.7 > > According to the law of Dulong and Petit, the heat capacity of one > gram atom of a solid element is approximately 6.3 cal/deg. We have seen > that the application of this rule is not limited to elements, for > experiments show that the heat capacity of many solids, elemental or > compound, is 6 cal/deg *per mole of atoms*. Of course, there are > exceptions to this law. There are many substances whose heat capacities, > measured at room temperature, are much smaller than predicted. These > exceptional substances are high-melting crystals that are made up of light > atoms, such as boron, carbon and berillyum. Moreover, the Dulong and Petit > law fails for all substances if the heat capacity is measured at low > temperatures. That is, the heat capacity of a solid is not constant, but > increases with increasing temperature. At the absolute zero of temperature > the heat capacity of all substances is zero. As the temperature is raised, > the heat capacity increases, but at different rates for different > substances. Finally, in the limit of very high temperatures, the heat > capacity of all solids is 6.3 cal/deg *per mole of atoms*. > > The key to understanding the temperature dependence of the heat > capacities of solids was supplied by Einstein in 1905....." > > > Indeed, that is the work for which Einstein received the Nobel > prize. It turns out that the departure from the Dulong and Petit law > at low temperatures is a quantum-mechanical effect and played a key > role in the development of Quantum Mechanics. I doublechecked my statement about Einstein's Nobel prize and I found that I made a mistake. The Encyclopaedia Britannica says that Einstein's 1921 Nobel Prize was for "services to theoretical physics, especially the discovery of the law of the photoelectric effect". I would like to thank those who sent me mail pointing out this mistake. Giovanni Vannucci AT&T Bell Laboratories HOH R-207 Holmdel, NJ 07733 hou2e!gv