Thermite, what is it?
xof...@gmail.com
Aluminum and Iron Oxide. My question is what percent of each? Does
anyone have more specific info on Thermite? Or another substance that
burns hotter?
dave e
No info on thermite for you, pyro.
Nuclear reactions burn hotter. Read the "Radioactive Boyscout" for
info on how to do one of those in your back yard.
http://www.dangerouslaboratories.org/radscout.html
Personally, I'm skeptical of the source. Every year I assign my
students to read "The Radioactive Boyscout", and discuss the questions
they might ask to determine if a news story is legitimate. I always
get interesting responses. One student this year wrote "Its illegal
for journalists to lie".
Dave
donald haarmann
-----------
Burn hotter? Using a liberal interpation of "burning" my Miller plasma torch produces
a 30 000o flame. Cuts copper and aluminium like a hot knife cuts butter.
If its chemical reactions you seek -
o o o
Fahrenh Celsius Kelvin
eit
Carbon 9032 5000 5300
subnitride/O2
Cyanogen/O2 8672 4800 5100
Hydrogen/F2 7232 4000 4300
Aluminium/O2 7592 6872 3800
Acetylene/O2 5684 3140 3413
MAPP/O2 5301 2977 3250
n-Butane/O2 5252 2900 3173
MPS/O2 5200 2870 3143
Propylene/O2 5200 2870 3143
Propane/O2 5162 2850 3123
Methane/O2 4856 2680 2953
Hydrogen/O2 4820 2660 2933
CO/O2 4712 2600 2873
Acetylene/Air 4352 2400 2673
Cyclopropane/ 4190 2310 2583
Air
Decane/Air 4109 2265 2538
Hydrogen/Air 3713 2045 2318
CO/Air 3560 1960 2233
Propane/Air 3497 1925 2198
n-Butane/Air 3450 1895 2168
Methane/Air 3407 1875 2148
Tetracyanoethylene/? 4000oK+
... between 5500 and 6000oK one reaches "the limits of chemistry."
[The late] Herbert Ellern. Military and Civian Pyrotechnics.
Chem. Pub. Co. 1968
---------
Thermit(e) Redux
Thermite - the reaction between any of the three forms or iron oxide and aluminium, is
only one of many reactions possible between aluminium and metal oxides. Another
name for aluminium metal oxide reactions is: "Goldschmidt" reactions, in honor of Dr.
Hans Goldschmidt who starting 1895 obtained numerous patents on these and others
using phosphides, arsenides, silicides, and borides. He also coined the term "Thermit"
now a registered trademark owned in the US by Thermex Metallurgical.
The most common used in welding is the combination of ferric oxide and aluminium.
3Fe3O4 [Ferrosoferric (black iron) oxide] + 8Al -> 9Fe + 4Al2O3 5590o F 719 Kcal
3FeO [Ferrous oxide] + 2Al -> 3Fe + Al2O3 4532o F 187 Kcal
Fe2O3 [Ferric (red iron) oxide] + 2Al -> 2Fe + Al2O3 5360o F 181 Kcal
Magnesium can be used in place of aluminium. However, there are two disadvantages
too using magnesium in place of aluminium. The higher melting point of magnesium
oxide 2852o C vs 2015o C for aluminium results in little if any molten iron. Also,
magnesium is much more costly!
There are a number of other "Goldschmidt" reactions!
Because the ignition temperature is appx. 2000o C an igniter is required. There are two
standard ones -
a-
b-
BEFORE LIGHTING ASK YOURSELF -. What am I going to do with the
resulting mad hot molten iron???? Catching it in water is a really bad idea. It can
explode. Not only can it. IT HAS. Dry sand is best.
--
donald j haarmann
---------------------------------
The explosion removed the windows,
the door and most of the chimney.
It was the sort of thing you expected in
the Street of Alchemists. The neighbours
preferred explosions, which were at least
identifiable and soon over. They were better
than the smells, which crept up on you.
Terry Pratchett
Salmon Egg
1146693933.0...@j33g2000cwa.googlegroups.com, "xof...@gmail.com"
<xof...@gmail.com> wrote:
Thermit does not burn! There is a simple replacement reaction in which
aluminum replaces the iron in hematite. This leaves molten iron behind that
can be used for welding or other repair. I don't know what the correct
proportions are, but start out with a stoichiometric mixture.
Bill
-- Ferme le Bush
Richard Herring
donald haarmann <donald-...@worldnet.att.net> writes
><xof...@gmail.com
>
>| Thermite, hottest burning substance I know of, it is composed of
>| Aluminum and Iron Oxide. My question is what percent of each? Does
>| anyone have more specific info on Thermite? Or another substance that
>| burns hotter?
>
>
>
>-----------
>Burn hotter? Using a liberal interpation of "burning" my Miller plasma
>torch produces
>a 30 000o flame. Cuts copper and aluminium like a hot knife cuts butter.
>
>If its chemical reactions you seek -
>
>
> o o o
> Fahrenh Celsius Kelvin
> eit
>
>Carbon 9032 5000 5300
Wow. Exactly nine thousand and thirty-two degrees F!
Er, by that reckoning shouldn't the "kelvin" column read 5273?
--
Richard Herring
number6
Richard Herring wrote:
> Wow. Exactly nine thousand and thirty-two degrees F!
> Er, by that reckoning shouldn't the "kelvin" column read 5273?
or 5273.16 :-)
I ran a lab once that ran losses on a product at 538 degrees C ... I
thought there was some magical significance until I realized it was
just 1000 degrees F ...
I don't recall the number (29.167g ??) but in precious metals fire
assay labs we weighed that exact amount out ... now that was a magical
number ... as the resulting mg of silver (and gold after parting)
recovered would represent the Troy Ounces per Avoirdupois Ton present
...
mrda...@gmail.com
donald haarmann wrote:
> <xof...@gmail.com
>
> | Thermite, hottest burning substance I know of, it is composed of
> | Aluminum and Iron Oxide. My question is what percent of each? Does
> | anyone have more specific info on Thermite? Or another substance that
> | burns hotter?
>
>
>
> -----------
> Burn hotter? Using a liberal interpation of "burning" my Miller plasma torch produces
> a 30 000o flame. Cuts copper and aluminium like a hot knife cuts butter.
30,000 F or C?
Is that temperature typical for Miller plasma torches?
donald haarmann
<mrda...@gmail.com> wrote in message news:1146871076.1...@v46g2000cwv.googlegroups.com...
--------
Sorry it is degrees F . I took the number of a civilian web site.
http://www.millerwelds.com/education/articles/articles55.html
I'll give you a WAG. The temperature is typical for all plasma torches. The only difference is their current
rating which determines the thickness of material that can be cut. See the Millerwelds site for sundry details.
beav
wrote:
works great with Cr2O3 and MnO2, also.
ggogle it up. i made it a couple times in HS when i was in my bomb
phase of chemistry education.
very showy in the dark.
>
Salmon Egg
"beav" <BEAV...@NETSCAPE.NET> wrote:
>> Thermit does not burn! There is a simple replacement reaction in which
>> aluminum replaces the iron in hematite. This leaves molten iron behind that
>> can be used for welding or other repair. I don't know what the correct
>> proportions are, but start out with a stoichiometric mixture.
>>
>> Bill
>> -- Ferme le Bush
>
>
>
> works great with Cr2O3 and MnO2, also.
>
> ggogle it up. i made it a couple times in HS when i was in my bomb
> phase of chemistry education.
>
> very showy in the dark.
In high school, I prepared manganese thermit using a stoichiometric mixture.
I labeled it as such. One of the chemistry teachers wanted to do damage to
me because it did not produce liquid metal for her demonstration.
Madalch
> I labeled it as such. One of the chemistry teachers wanted to do damage to
> me because it did not produce liquid metal for her demonstration.
I've tried thermite variations with copper(II) oxide, manganese
dioxide, and tin(II) oxide- all worked nicely. The tin reaction gave
off liquid metal that stayed liquid for a substantial period of time
(hardly surprising considering the melting point of tin).
beav
Cu and Sn, too? hmmm. i'd always thought it was to the three
contigous metals.
and my Mn thermite left chips of Mn metal, after you screened the
debris.
Madalch
> was to the three contigous metals.
No- I think the oxide of any metal less reactive than aluminum (which
is most of them) will probably work fine. It depends somewhat on the
physical form of the oxide- I know I couldn't get it to work with the
chromium(III) oxide left over from the volcano reaction.
donald haarmann
|
| No- I think the oxide of any metal less reactive than aluminum (which
| is most of them) will probably work fine. It depends somewhat on the
| physical form of the oxide- I know I couldn't get it to work with the
| chromium(III) oxide left over from the volcano reaction.
-----------
Should work.....
Preparation of the metal.-Chromium metal can be prepared by reducing chromium
sesquioxide with carbon in the electric furnace ; or better, by the aluminothermic
process, which is also called, after its inventor, the H. Goldschmidt's process (1905). An
intimate mixture of chromium sesquioxide and aluminium powder, A, Fig. 187, is placed
in a refractory clay crucible so that about two-thirds of the crucible is filled. A mixture of
sodium or barium peroxide and aluminium powder is placed over this, as at B, Fig. 187.
A piece of magnesium ribbon, C, is stuck into the latter mixture, and a layer of
powdered fluorspar, D, is placed over all. The crucible is then set in a tray of sand and
the magnesium ribbon, C, ignited. When the flame reaches the peroxide mixture, B,
THE ALUMINIUM IS OXIDIZED WITH EXPLOSIVE VIOLENCE, AND CARE MUST BE
TAKEN TO PROTECT THE FACE AND HANDS ACCORDINGLY. [emphasis added]
The heat of the combustion of the aluminium in the ignition mixture, B, starts the
reaction between the chromic oxide and the aluminium, and it spreads throughout the
entire mass in a few seconds. The chromic oxide is reduced to metal, and the
aluminium is oxidized to alumina: Cr203 + 2AI = 2Cr + Al203. When the crucible is
cold, a button of metallic chromium will be found on the bottom. The slag is nothing but
fused alumina which has crystallized so as to form a kind of artificial corundum. This
has been called corubin to distinguish it from natural corundum. The corundum slag is
used as a refractory and abrasive agent. When chromic oxide is reduced, the slag
contains small artificial rubies. In Goldschmidt's works at Essen, about 100 kilograms of
chromium [forsooth!] are produced at a single charge. The process occupies less than
half an hour. Manganese, iron, and man other metals can be produced in a similar
manner. Titanium, alloyed with iron—ferro—titanium—is produced by the same
process. So much heat is evolved during the reaction that even the most refractory
metals and minerals are melted. Indeed, a temperature equivalent to that of the electric
are-furnace, 3000o, can be generated in a few minutes. The method is in some ways
superior to the electric furnace process-it is quicker, cheaper, and the products are free
from carbon contamination.
JW Mellor
Modern Inorganic Chemistry
1933
See also The Home Chemist - Popular Science Monthly - September, 1941.
----------
I would note in passing that some termit(e) reactions go a lot faster then you would expect.
My experience w/ MnO2, albeit some 50+ years ago, is that with fine mesh size materials it
does not burn... it goes POOF! One of the Cu oxides ... ditto.
A copper oxides (I can look up which one) is used in "Cadweld" to weld copper ground wires to
copper clad ground rods and with a modified formula to cast iron pipe.
--------------
Chemical demo goes out of control
An explosion occurred during a chemical demonstration at the University of Illinois,
Urbana-Champaign, earlier this month. The widely used demonstration of the thermite
reaction-which involves the reaction of iron oxide and powdered aluminum to form iron
and aluminum oxide-was part of the university's annual Engineering Open House for
local high school and grade school students. There were 200 to 300 people in the
chemistry lecture hall at the time of the explosion. Four teachers and 23 students were
taken to the hospital, where they were treated and released. The injured suffered first-
and second-degree burns and minor cuts. Chemistry professor Steven S. Zumdahl,
who was conducting the demonstration, says it had just been run successfully using
sand as a receptacle for the molten iron. But when the sand was replaced with water,
something went wrong. Jiri Jonas, head of the department of chemical sciences, says a
committee, including university and local safety experts, has been appointed not only to
determine what went wrong with the thermite demonstration, but also to review all
safety issues surrounding the open house.
C&EN 23
March 12, 1990
--------------------------
57.4 / Thermit Welding
Welding Handbook
Sixth Edition
Section Three
Part B
Welding, Cutting And Related Processes
AWS 1971
PRINCIPLES OF OPERATION
Basically, thermit is the generic name given to reactions between
metal oxides and metal reducing agents. The usual oxides are
those that have low heats of formation, and the usual reducing
agents reducing agents are those which, when oxidized, have high
heats of formation. The excess heats of formation of the
products, as compared with the starting materials of the
reaction, represent the heat produced by the reaction. The
reaction. Typical thermit reactions is an exothermic one
are as follows:
3FeAl + 8Al ----> 9Fe + 4Al203 (5590'F/3088-C) 719.3 Kcal
3FeO + 2Al 3Fe + AL203 (4532'F/2500-C) 187.1 Kcal
Fe203 + 2Al 2Fe + Al203 (5360'F/2960'C) 181.5 Kcal
3CuO + 2AI 3Cu + Al203 (8790'F/4865'C) 275.3 Kcal
3CU20 + 2AI 6Cu + Al203 (5680'F/3138'C) 260.3 Kcal
3NiO + 2AL 3Ni + Al203 (5740'F/3171'C) 206.6 Kcal
Cr203 + 2AI 2Cr + Al203 (5390'F/2977'C) 546.5 Kcal
3MnO + 2AI 3Mn + Al203 (4400'F/2427'C) 403 Kcal
3MnO2 + 4AI 3Mn + 2Al203 (9020'F/2771'C) 1041 Kcal
[one of these values is wrong!]
Note that in All of the exothermic reactions listed, Aluminum
has been used as the reducing agent. Magnesium can Also be used,
but it has limited usefulness because of the very high melting
point of the oxide. Slags from magnesiothermic reactions are not
formed at a sufficiently high temperature to be fluid. The use of
magnesium is, therefore, confined to those applications where
fluid reaction products are not desired.
The first reaction in the aforementioned series is the one most
commonly used in thermit welding, and the major portion of this
discussion will refer to it. The proportions are roughly three
parts of iron scale to one part of Aluminum. The theoretical
temperature resulting from this reaction is 5590'F (3088'C).
Radiant heat loss and losses to the reaction vessel, or crucible,
however, reduce this temperature to about 4600'F (2538'C).
Other additions to adjust the metal for chemistry and the slag
for fluidity serve to further reduce the temperature. In
practice, filler weld metal temperatures are about 3800'F
(2093'C). >>The reaction is non-explosive, and regardless of
size, requires less than one minute to complete itself.<< [This
statement applies ONLY TO IRON OXIDE THERMIT. Several thermit's
shown burn that fast! /DJH/] ! No fire hazard is incurred under
normal conditions of handling and storing thermit mixtures, since
an initial temperature of more than 2200'F (1205'C) is needed for
ignition.
To start the reaction, a special ignition powder, or "first
fire" mixture, incorporating peroxides, chlorates or chromates as
the oxidizing agent, and Aluminum dust, or magnesium, silicon, or
titanium powders as the reducing agent are required. This
ignition powder can be lighted by a burning magnesium ribbon, by
the flare of a match, or by a spark. This will, in turn, burn
with enough heat to reach the 2200'F (1205'C) ignition
temperature of the main thermit powder.
Thermit mixtures employed for welding often contain other
materials in addition to the iron oxide and the Aluminum. By the
addition of these materials, variables such as the time and
temperature of the reaction, and the chemical analysis of the
produced weld metal, can be controlled. As an example, additions
of metallic elements either in the form of pieces of metal, which
are melted during the reaction, or in the form of secondary
exothermic reactions chosen from the list of equations, make
possible wide variations in weld metal analysis. By like token,
mechanical properties of the weld metal can be varied over a
broad range. As-cast tensile strengths between 50,000 psi and
130,000 psi, with inversely corresponding elongations of over 49%
in 2-in. to Almost zero, are possible. The metal responds in the
usual manner to heat treatment.
-----------
H. Ellern
Military and Civilian Pyrotechnics
chapter 30
Solid Products
The thermite process described earlier for destructive
purposes and as a mere heat source was originally
destined for the production of metals, alloys, and certain
compounds, and the uses of the physical effects of the
reactions were an afterthought. Tissier in 1856 (67) and
Beketov in the 1860's (3) first observed the strong reducing
power of aluminum powder in dry reaction, but aluminum,
as a new material (Wohler 1828), was then much too
expensive for commercial uses. Dr. Hans Goldschmidt, in
mumerous patents from 1895 on, (51) claimed production
of the majority of metals end their alloys? and of phos-
phides, arsenides, silicides, and borides by reduction of the
oxides or respective salts with aluminum, both in
more-or-less finely dispersed state. He also coined the
original tradename Thermit*, which eventually became the
common term "thermite" (sometimes, and of dubious
legality, "thermit"). The technique itself is important enough
to employ the special term Aluminothermics, and many
details on the subject are found under this heading in the
Encyclopedia Americana. (25) A similarly extensive
description of the thermite process is found in Volume 3 of
Ullmann's encyclopedia (22) under Aluminothermie.
Information on the present uses of thermite in the United
States was given to the author privately. (475)
Pyrotechnic production delivers the metal at extremely
high temperature so that it can be used in situ for welding
of rails, repairing heavy machine parts, or producing small
castings. Some metals that are difficult to liberate by
conventional methods are easily obtained, pure or as
definite alloys, for convenient admixture in the manufacture
of specialty steels. Metal produced by the thermite process
is entirely free from carbon, which is always a contaminant
in metallurgical processes with coke or charcoal. Such
carbon is a detriment to certain usages. Finally, nothing
could be simpler and more convenient than preparing a
limited amount of any one of a large variety of rare or rarely
produced metals and their alloys by what may be called a
"push-button method." For these reasons, pyrotechnic
production of solids by the Goldschmidt process or one of
its variants is an important technological method.
In a general way, the thermite reaction is the reduction of
a metal oxide by a reactive metal leading to the oxide of
the reductant and to the metal from the reduced oxide. The
prototype reaction, also the commercially and technically
most important, is the following:
8AI + 3Fe3O -> 4AI2O3 + 9Fe + 795 kcal (exothermic)
The heat output of this reaction per gram of reactants is
0.87 kcal/g or 3.7 kcal/cm3 (theoretical) and must be called
moderate, both on a weight or actual volume basis (the
density of the unconsolidated mixture, the form in which the
material is used, is about 2 g/cm3). The heat output is a
little higher for the reaction
2AI + Fe203 -> Al2O3 + 2Fe + 203 kcalI (exothermic)
which yields 0.95 kcal/g. The preference for the use of
"black" iron oxide, sometimes called ferrosoferric oxide,
may derive from the fact that a coarse but reactive, scaly
product of relatively large surface area is available as
hammerschlag (German for hammer-beaten, meaning
blacksmith's scales)—the result of surface oxidation of bulk
iron during heating in air. Together with a coarse ""rained"
aluminum, this yields just the proper reaction speed and
heat concentration for optimal temperature and promotion
of coalescence of the metal below and the slag above it.
The temperature reached by the reacting mass has been
given as 2000-3000°C (one may encounter similar figures
given in °F that are erroneous)? but is probably limited by
the boiling point of aluminum, which is below 2500°C. If the
reaction is too fast because of small particle size of the
components, or especially because oxides are used that
have low heats of formation, such as the oxides of copper,
lead, or bismuth, the process may exhibit explosive
violence.
On the other hand, when the heat of formation of the
aluminum oxide is only moderately higher than that of an
equivalent amount of the oxide that is to be reduced, the
reaction may not take place, or only sluggishly, or lead to
alloys of unused aluminum and the liberated metal. A
typical case is that of titanium, where the reaction between
aluminum and titanium (IV) oxide (TiO2) comes to an
equilibrium leading to alloys of the two metals and also to
formation of titanium (II) oxide (TiO), which collects in the
slag.22 For zirconium, the alloy ZrAIB has been named as
the aluminothermic product.5l2 In such cases, some
modifications of the basic process can achieve the goal of
making a pure metal. There are at least four such
modifications, all of which are either used or have been
proposed or patented in the period since 1894.
One of these variants is the addition of a more active,
more heatforming but chemically related oxide. Thus in the
case of chromium a few percent of a Cr(VI) compound
(K2Cr2O7 or CrO3) will increase the yield of a consolidated
"regulus" of chromium on the bottom of the crucible from
the main reaction: (67)
2AI + Cr2O3 -> Al2O3 + 2Cr + 129 kcal (exothermic)
which on an equivalent basis amounts only to 21 kcal
compared with 33 kcal for the Al/Fe3O4 reaction.
(Equivalence means the amounts of metal and oxides able
to react with or containing a gram equivalent of oxygen, i.e.
8 g.) Similarly for manganese where the dioxide reacts too
violently and the monoxide is unsuitable, a mixture of the
two is effective, as quoted from a German patent by
Ullmann,22 or the compound Mn3O4 can be used.
The second method involves the addition of high heat
producing extraneous oxidizers. Frequently mentioned are
barium peroxide and other strong oxidizers such as lead
dioxide, sodium persulfate (Na2SO6) and even chlorate.
Kuhnes13 claims such additions for the aluminothermic
production of numerous metals, and Cueilleron and
Pascand for aluminum/titanium alloys. (514)
A third modification and one that already had been
claimed in the original Goldschmidt patent5ll and by many
successors is the replacement, all or in part, of the
aluminum by other reductants. Among the replacements or
additives are calcium, silicon, magnesium, calcium carbide
(CaC2), misch metal, and boron. Misch metal has been
used by Weiss and Aichelsls for producing vanadium and
niobium (columbium), the latter, however, forming
aluminum alloys rather than pure metal. Vanadium is now
made from the vanadium oxides (V203 or V2Os) with
calcium in the presence of calcium chloride, "thermally
initiated" in an argon atmosphere. (513)
The last modification to be mentioned here consists of
starting the reaction at a previously elevated temperature,
thus gaining the advantage of promoting it without
introduction of foreign materials or expensive reductants. It
must however be noted that in such a scheme we move
away from a simple pyrotechnic production and are back at
a more-or-less conventional metallurgical operation; in fact,
this is precisely the case in metallurgical processes where
the thermite reaction is performed in furnaces. Thus
Ullmann22 cites the production of 250 kg of ferrotitanium
alloy from 600 kg of the mineral Ilmenit, aluminum "griess,"
and lime, the reaction time being only 7 min. Other
examples of the high-temperature thermite process are the
formation of titanium and zirconium from their dioxides with
magnesium powder and fluxes after heating the mixture
under argon above 1000°C. (517) Under hydrogen,
zirconium hydride is obtained in a quite similar
operation.5l3 Iron/titanium alloys are obtained, according to
a Japanese reference,Sl9 with varying titanium content
from 10—50%, the amount increasing with increased
starting temperature.
As the above-mentioned formation of zirconium hydride
shows, not only metals but also various compounds can be
the end product of a thermitic process. Silicides, such as
the compound BaSi2 from the peroxide and oxide with
silicon, have been quoted by Ullmann22 from German
patents. The lower oxide of titanium (TiO) has been
described as obtainable from the dioxide and
magnesium.5' A very hard form of artificial corundum
(crystalline aluminum oxide) of superior quality for grinding
and polishing operations is the byproduct of the
above-described production of chromium metal. (22)
Because the sulfides of metals have a lower heat of
formation than the oxides, some difficult-to-obtain metals
can be made from their sulfides with aluminum. This
process has been described by Gardner 520 for niobium
(columbium) and tantalum from their disulfides (NbS2 and
TaS2), whereby the relatively volatile by-product Al2S3
distills off above 1550°C. It is an interesting coincidence
that the production of the same two metals by reduction of
the pentoxides Nb2Os and Ta2Os with silicon can be
performed under formation of silicon (II) oxide (SiO), which
volatilizes in vacuum.
Solid SiO, reacted with the oxides of zinc, magnesium or
manganese in a vacuum, forms the metals, which in turn
distill off. (61)
The welding or the repairing of heavy machinery with
thermite is somewhat different from the formerly described
welding and brazing operations by pyrotechnic heat
(Chapter 26), because here the metal produced becomes
part of the joint or crack, or replaces a worn or broken-off
piece. For these purposes, a forging type (with man-
ganese), a cast-iron type (with added ferrosilicon), or a
so-called wabbler thermite of great mechanical strength for
building up worn machine parts have been formulated.
While other methods of repairing machine parts, such as
electroslag and submerged-arc welding, have become
popular, the thermite process has remained competitive
because it requires no capital investment and is easily
performed as a one-at-a-time operation. Normally, a certain
amount of preheating is desirable, but recently a "Self-
Preheat" process has dispensed with this. (621)
In the field of rail welding, the thermite process
supplements and sometimes replaces flash or
gas-pressure welding. The latter methods require very
costly factory installations. They furnish rails about
one-quarter of a mile long, which are hauled to the point of
field installation. Here one can resort to the old-fashioned
mechanical joining (a source of most maintenance on a
railroad) or use field welds. The best of these is the
thermite weld. It may be used exclusively with specialty
items such as crossings, for haulage tracks in coal mines,
and for crane rails. (475)
The thermite process is also suitable for the butt-welding
of reinforcing bars of large diameter. Here the thermite
process has remained competitive with other methods such
as arc welding because it produces a true fusion weld of
high tensile strength. Economically, it requires a lower labor
cost, thus offsetting the higher expense for material. (475)
A relatively new development is the combination of
metals and ceramic in compacts called cermets. The
purpose is to combine the high refractoriness, resistance to
oxidation, electrical insulation, and retention of
compression strength on heating—all properties of ceramic
bodies—with the ductibility and thermal shock resistance of
metals. (522)
Obviously the thermitic processes can serve this purpose
when, for instance, the oxide of the finished cermet is
produced from aluminum powder, which liberates the
metals in reaction with an oxide of a suitable metal such as
chromium or cobalt. An excess of aluminum oxide and
addition of other refectory oxides or clay to the thermitic
formulation is needed for the desired cermet.
The reaction can be extended to the formation of
complex mixtures with heavy-metal silicides, borides, or
carbides in lieu of metal.
When zirconium silicate (ZrSiO4) or a mixture of ZrO2 and
SiO2 is reacted with aluminum in the presence of aluminum
oxide and then reheated, zirconium silicide (ZrSi2)
becomes the major product. Titanium dioxide (TiO2) and
boron (III) oxide (B2O3) with aluminum similarly form
titanium boride (TiB2). If the reduction of the oxides such
as TiO2 or SiO2 with aluminum is performed in the
presence of carbon black, the carbides TiC and SiC are
formed embedded in aluminum oxide. (523) This subject is
also treated in a British patent titled "Autothermic Fired
Ceramics. (524)
In all these cases it appears that the exothermic process
must be initiated by heating the preformed pellets, etc. in a
furnace. This is again the above-described
high-temperature process in which the need for promoting
reactivity by an initial high temperature derives either from
the dilution of the reactants with oxides, the low treat output
of the main reaction, or both.
In Chapter 19, it was indicated that the dispersion of
alkali metals at high altitudes is a new tool in space
exploration. Instead of merely evaporating the metals by
pyrochemical heat sources, one might think of producing
them by chemical reaction and dispersing the resulting
metal vapors in the rarefied atmosphere.
Lithium, sodium, potassium, rubidium, and cesium have
been produced by reacting their chromates, dichromates,
sulfates, molybdates, or tungstates with an excess of
zirconium powder. The reactions, in general, are violent or
even explosive and yield impure metals, but if the
zirconium is in larger excess, the process is said to take
place smoothly and gently and the metals are obtained in
high yield and nearly free from oxide. The processes are
cited in Supplements II and III to Volume II of Mellor's
Treatise3' as performed in a vacuum and by heating the
mixtures to temperatures of 250—1000°C —mostly below
500°C. Since these reactions are strongly exothermic,
there is not the slightest doubt that pyrotechnic initiation will
lead to satisfactory performance. The dissemination of the
evaporating metals should take place under the
high-altitude conditions just as well as the distilling off "in
vacuo" in the laboratory.
The indicated chemical reactions are not the only ones
that because of strongly exothermic performance might be
used for chemical dispersion—the decomposition of alkali
and alkaline-earth azides being one other example.
However, since this subject is at the moment merely
speculative in the possible application to space exploration,
the examples given should suffice to indicate approaches
that will likely have been realized by the time this book
reaches the public.
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* Thermit is still a registered trademark owned in the U.S.
by Thermex Metallurgical, inc., Lakehurst, N. J.
---------
I have a lot more. If your in a hurry you could retrive my old posts at deja.com.
--
donald j haarmann
-------------------------------
In heaven the police are British, the cooks French,
the lovers Italian -- and it's all organized by the
Germans. In hell, the police are French, the
cooks British, the lovers German -- and its all
orgainized by the Italians.
Anon.
dave e
It should be possible to react aluminum with chromium III oxide. This
was one of the compounds Goldschmidt used when he invented the thermite
reaction. I inquired about this very reaction on this newsgroup about
two years ago, but haven't tried it.
Flinn Scientific offers a safe alternative to the full scale thermite
demo; a pair of large iron ball berrings, one of them rusted, and the
other covered in aluminum foil. When knocked together, the energy at
the point of contact is high enough to oxidize some of the aluminum,
and creates a loud "bang".
Dave
Madalch
> This was one of the compounds Goldschmidt used when he
> invented the thermite reaction.
I'm sure it is- I'm just saying that it didn't work for me, presumably
because the chromium(III) oxide I was using was too disperse (or
fluffy).
Unknown
>,;> Cu and Sn, too? hmmm. i'd always thought it
>,;> was to the three contigous metals.
>,;
>,;No- I think the oxide of any metal less reactive than aluminum (which
>,;is most of them) will probably work fine. It depends somewhat on the
>,;physical form of the oxide- I know I couldn't get it to work with the
>,;chromium(III) oxide left over from the volcano reaction.
I had this one assigned in an inorganic synthesis course. I tried many
procedures that didn't work. Then I ran across one that used a mixture
of Cr2O3 and CrO3. This one worked. I got a nice ingot of chromium
metal.