From: tarl@sw.stratus.com (Tarl Neustaedter)
Newsgroups: alt.sci.physics.new-theories
Subject: Daedalus
Date: 24 Nov 92 04:40:30 GMT
Organization: Stratus Computer, Inc.
NNTP-Posting-Host: coyoacan.sw.stratus.com

Let's try this for an experiment in adding some purpose to this group.
In Nature, there is a column titled "Daedalus", which appears to be a
long-running joke. It will have some off-the-wall theory, frequently on
building some actual piece of equipment, which can be quite entertaining.

This weeks' column is titled "Metal Blowing":

Metals and their alloys are usually crystalline. Ultra-fast cooling can
produce amorphous, glassy metal in tiny amounts, much prized for its
distinctive properties. Daedalus now proposes to make it in bulk. His
scheme depends on the fact that the electrical resistance of almost every
metal rises on melting.

Imagine, he says, a molten metal carrying a current; imagine a small
crystal forming within it. Its lower resistance will divert the current
preferentially through itself, forming a local short-circuit. The resulting
concentration of heat could melt the crystal again. So a suitable current
could prevent a metal or alloy from crystallizing as it cooled. The tiny
crystals nuclei, essential to start the process, would be obliterated as
fast as they formed. Ultimately, the metal would get too cold to crystalize
at a detectable rate. The current could then be turned off and the product
quenched to room temperature. A supercooled liquid, a true metallic glass,
would result.

DREADCO's metallurgists are now melting all sorts of alloys in a modified
induction furnace, and slowly reducing (but not shutting off) the current.
With proper control, the current-carrying metal should solidify in glassy
form. The resulting alloys should have all sorts of interesting new 
mechanical, chemical, and magnetic properties.

For a start, they might have a very wide range of useful compositions.
The craziest random assortment of scrap metals, quite incompatible if melted
into a crystalline alloy, should solidify in the induction current-field as
a perfectly homogeneous and useful metallic glass. Furthermore, a really
complicated mixture of metals should have a very low effective melting
point. As a glassy alloy, it should soften to a viscous liquid which
could be shaped, moulded or even blown at not much above room temperature.

Once metal can be blown like glass, hollow metal objects from teapots and
kettles to car bodies and airframes could be blow-moulded in one operation,
simply by scaling up standard glass-working techniques. At the highest
moulding temperatures, the metal might begin to crystallize again; but
that could have an advantage too. If the hot product were 'seeded' at one
point by a single crystal at the desired orientation, the crystallization
front would spread uniformly through the whole mass. The resulting structure,
however complex, would consist of one single grainless metallic crystal.
DREADCO metallurgists are divided as to whether it would be immensely strong
or absurdly flexible. Either way, exciting new engineering techniques should
open up.
						David Jones
----------------
What's wrong with the above? I'm no materials scientist, but I see what
look like a number of flaws, which I'll list below (working from bottom
to top). I'd enjoy seeing corrections or further additions to the list.

  1) If you end up with a single-crystal metal, it should be brittle,
     not flexible.
  2) If you could cause crystallization by warming up the amorphous glass,
     adding a single seed crystal would not cause the entire structure
     to orient around it. You'd have spontaneous crystals forming elsewhere,
     giving the normal chaotic crystal interfaces.
  3) If the metal actually did have such a low melting point, it would not
     likely have a plastic-type viscosity allowing "blowing". As long as it
     is a single alloy, it is likely to have an abrupt transition between
     solid and liquid. And I'm not convinced amorphous metal would have a
     dramatically lower melting point than crystalline metal.
  4) I'm not convinced that you could lower the temperature of a metal while
     preventing formation of crystals with an induction furnace. If a crystal
     has a lower resistance than the liquid, it will pass more current and
     generate more heat - but enough to re-melt the crystal, while not heating
     up the entire mass? I don't think so, but don't have the tools to
     calculate heat dissipation and transmission with electric induction in
     a metal right at it's melting point.

Comments, anyone?
-- 
         Tarl Neustaedter	tarl@sw.stratus.com
         Marlboro, Mass.	Stratus Computer
Disclaimer: My employer is not responsible for my opinions.