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eutectic deja vu

updated sat 17 mar 01


Howard Scoggins on fri 16 mar 01

This conversation we are having on glazing has me in
its grip. Bear with me for a short exposition on one
aspect of the process: Eutectic Reactions.

I spent fifteen years working as a GeoEngineering
Technician. I did field surveys for minerals, sample
prospecting and lab analysis. All directed towards
engineering applications. Damn near zero tolerance
analysis for all kinds of building. I worked under
the supervision of a Tarheel GeoEngineer who is one
of the best in the business, a former Kanopolis boy
name of Steve Deal.( Have to give Steve a plug, he
was my teacher.)

I learned that eutectic reactions ( the synonym is
THAW) can be 1) reversible in some materials at low
tempertures--less than 100F, and
2) irreversible in other materials at temperatures
starting at 400F. (Vitrification is only ONE kind of
an irreversible reaction.)

In both cases the time necessary for the eutectic
reaction depends upon a host of factors: Nature of
the material's composition, distribution in the
sample, available water and range of temperature
fluctuation, etc.

Reversible eutectic reactions. A few years back my
group was hired to do the soils analysis for a new
runway at McCarran, the Las Vegas Airport.
In common with many areas where there are
substantial alkali deposits, the airport site was
highly reactive. That is, at around 84/87F there was
a 1 inch EXPANSION per 100 feet at 85F. Below that
temperature there is a corresponding CONTRACTION.
But this was not a CONSTANT linear relation. Where
the alkali was more concentrated, the expansion,
contraction was greater; where the alkali was less
concentrated the E/C
rate was lower.

What is the bottom line? Any runway built on that
stuff would "work" constantly, unless the substrata
was altered. Excavaion,acidization and fill remedied
that, along with an water impervious polymer lining
to isolate the runway from its surrounding soils.

How does this relate to glazing? Simple, the
composition of pure materials alone will not
accurately predict the expansion/contraction factor.
Eutectic reaction (fluxing, for instance) is
impacted by other factors, some of which we can not
yet quantify. Thus the massaging of numbers to make
elements easy to quantify is not a very useful
answer, either. The expression of Kaolin as
Al203.2Sio2.2h20 is an example of this. In
engineering that I am familiar with, we have not
expressed Kaolin this way since Strom Thurman was a

I have nothing against "formula/formulae" (Have to
include the Brits) but I am skeptical of formulas
whose elements are simplified beyond any
correspondence with reality. Maybe we need a
CLAYCRAY computer to grapple with the problem.

Whew! Howard Scoggins