Cliff:
Huh? That was a response to your original assertion that "Tungsten
carbide is not an alloy."
Here's the contextual bit from the Encarta excerpt you seem to keep
missing:
"Compounds that contain both a metal or metals and certain nonmetals,
particularly those containing carbon, are also called alloys. The most
important of these is steel."
Besides, is a substance composed of two or more metal an alloy, or not?
Bottom line is that you took something out of context to make it appear
that something was said that wasn't. Now you're trying to defend that
action by continuing to ignore the context? LOL
Quit wasting my time with your silly trolling word games.
<Newsgroups: alt.machines.cnc,rec.crafts.metalworking...>
I was wondering where this mess came from. :)
Just got done with a metallurgy class and WC is not an alloy it's
a compound. When looking at binary Phase Diagrams the straight
verticle lines are compounds.
Right. :)
The tool-material, "Tungsten Carbide" is like a composite material.
The manufacturing of WC tools resembles a ceramic material.
Ooops. :)
The E.E. wasn't written by metallurgists huh? :)
Alvin in AZ
Alvin:
Ahh but we're not talking about just WC, but WC with a cobalt binder to
make "Carbide" tooling.
Again, it seems to depend on who you ask.
Here's an interesting excerpt from your own metallurgy newsgroup.
===========================================================1. Dr Alun J. Carr
Newsgroups: sci.engr.metallurgy
From: snipped-for-privacy@ucd.ie (Dr Alun J. Carr)
Subject: Re: Can someone tell me what WC is?
Richard Larker wrote:
Again, 'hardmetal' comes from the German. The hard phase was known by
the
Germans as 'hartstoffe' and the sintered material, with metallic binder,
as
'hartmetalle'. According to Scwarzkopf & Kieffer (Schwarzkopf, P. &
Kieffer, R. (1953) Refractory Hard Metals, New York: Macmillan):
In English -- at least in a number of American and English
publications,
including this book -- the term "hard metals" is used for the
binder-free substances as well as for the cemented materials. In
view of
the physical properties, particularly the electrical
conductivity which
clearly indicates metallic bonding, the use of the term for
binder-free
substances also appears justified.
In English, we would also refer to the hard phase as an 'Interstitial
Alloy' (Goldschmidt, H. J. (1967) Interstitial Alloys, London:
Butterworth), because it is _not_ a ceramic. WC, TiC, ZrC, TiN, etc. are
all brittle solids, with hardnesses similar to ceramics, but unlike
ceramics, the interatomic bonding is predominantly _metallic_ (evidenced
by, amongst other things, the high electrical conductivity (see above),
and
the metallic lustre). To quote Schwarzkopf & Kieffer again (ibid):
The term "hard metals" is used to specify a group of
high-melting hard
substances which have metallic character although, on the basis
of
chemical composition, they would be considered inorganic
compounds.
Typical representatives of these materials are the refractory
carbides
of the transition metals of the fourth to sixth groups of the
periodic
system, such as, particularly, the carbides of tungsten,
titanium, and
tantalum.
It is therefore incorrect to refer to cemented carbides as 'cermets', as
they contain no ceramic. To do so is a sign of intellectual laziness
(unfortunately common in the hard materials community today -- I do not
intend to attack Dr Larker personally: I feel he has been misinformed),
merely classifying all hard substances as 'ceramics', merely because
they
are 'hard', when one should instead consider the nature of the
interatomic
bond as the basis for a system of classification.
Alun
--
Dr Alun J. CARR Phone: +353-1-7061989
Mechanical Engineering Dept. +353-1-2693244 x1989
Cliff:
=========================================================...Max-Planck Society, Berlin, and their colleagues investigated the
electronic structure of a quasicrystalline alloy of
aluminum-nickel-cobalt (AlNiCo) by means of angle-resolved
photoemission.
======================================================== Interesting, but exactly what do these aluminum-nickel-cobalt
quasicrystals have to do with the properties of tungsten carbide
tooling? Are you trying to make a parallel that both quasicrystals and
tungsten-carbon-cobalt are alloys?
Cliff:
Actually I believe it was "Carbide Tooling" made up of Tungsten carbide
& a Cobalt binder that I was referring to, which is as yet, unresolved
to my satisfaction since they retain the free electrons of metals, and
therefore share the properties of metals.
Here's a tid-bit on Carbides, note the last section on WC:
=============================================================http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/carbon.php#carbides
Carbides: Covalent, Ionic, and Interstitial
Although carbon is essentially inert at room temperature, it reacts with
less electronegative negative elements at high temperatures to form
compounds known as carbides. When carbon reacts with an element of
similar size and electronegativity, a covalent carbide is produced.
Silicon carbide, for example, is made by treating silicon dioxide from
quartz with an excess of carbon in an electric furnace at 2300 K.
SiO2(s) + 3 C(s) SiC(s) + 2 CO(g)
Covalent carbides have properties similar to those of diamond. Both SiC
and diamond are inert to chemical reactions, except at very high
temperatures; both have very high melting points; and both are among the
hardest substances known. SiC was first synthesized by Edward Acheson in
1891. Shortly thereafter, Acheson founded the Carborundum Company to
market this material. Then, as now, materials in this class are most
commonly used as abrasives.
Compounds that contain carbon and one of the more active metals are
called ionic carbides.
CaO(s) + 3 C(s) CaC2(s) + CO(g)
It is useful to think about these compounds as if they contained
negatively charged carbon ions: [Ca2+][C22-] or [Al3+]4[C4-]3. This
model is useful because it explains why these carbides burst into flame
when added to water. The ionic carbides that formally contain the C4-
ion react with water to form methane, which is ignited by the heat given
off in this reaction.
C4- + 4 H2O CH4 + 4 OH-
The ionic carbides that formally contain the C22- ion react with water
to form acetylene, which is ignited by the heat of reaction.
C22- + 2 H2O C2H2 + 2 OH-
At one time, miners' lamps were fueled by the combustion of acetylene
prepared from the reaction of calcium carbide with water.
Interstitial carbides, such as tungsten carbide (WC), form when carbon
combines with a metal that has an intermediate electronegativity and a
relatively large atomic radius. In these compounds, the carbon atoms
pack in the holes (interstices) between planes of metal atoms. The
interstitial carbides, which include TiC, ZrC, and MoC retain the
properties of metals. They act as alloys, rather than as either salts or
covalent compounds.
============================================================> Later you seemed to be claiming that metal Carbides were metals...
See the above section on Interstitial carbides which retain the
properties of metals as opposed to ionic and covalently bonded carbides
that are generally non conductive.
The term "alloy" is not always defined in a consistent manner. Some
definitions would include the intimate mixing of powders in powder
metallurgy, some don't.
Ceramic is another term that seems to be limited in consistently
addressing all the structural varieties & combinations of materials
considered "ceramic", IMO.
============================================================http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Structure/ceramic.htm
Ceramic Structures
The two most common chemical bonds for ceramic materials are covalent
and ionic. The bonding of atoms together is much stronger in covalent
and ionic bonding than in metallic. This is why ceramics generally have
the following properties: high hardness, high compressive strength, and
chemical inertness. This strong bonding also accounts for the less
attractive properties of ceramics, such as low ductility and low tensile
strength. The absence of free electrons is responsible for making most
ceramics poor conductors of electricity and heat.
However, it should be noted that the crystal structures of ceramics are
many and varied and this results in a very wide range of properties. For
example, while ceramics are perceived as electrical and thermal
insulators, ceramic oxide (initially based on Y-Ba-Cu-O) is the basis
for high temperature superconductivity. Diamond and silicon carbide have
a higher thermal conductivity than aluminum or copper.
============================================================
Cliff:
Sorry, I left out a part of my sentence. It should have read:
You seem to be functioning under the impression that ceramic, or more
correctly cermet, AND ALLOY are mutually exclusive terms.
Cliff:
I posted an Encarta definition of alloy that included the process of
powder metallurgy. You responded with a reference to the "CRC Materials
Science and Engineering Handbook", but didn't list what they said OR an
address to check exactly what they said, just that they think WC is a
ceramic. I responded with the observation that you seem to think that
the term ceramic and alloy are mutually exclusive. Do you?
Silly nonsense remarks neither adds support to your position nor makes
you appear particularly objective. Either you have something
intelligent to contribute related to the subject matter at hand, or you
don't.
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