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AMchemistry
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Zinc Thermite?
Hey guys is it possible to make a zinc thermite using ZnO with Al or will the zinc metal evaporate of the heat of the reaction? Here's the formula
3ZnO + 2Al -->3Zn + Al2O3
-AMchemistry
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blogfast25
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Quote: Originally posted by AMchemistry  | Hey guys is it possible to make a zinc thermite using ZnO with Al or will the zinc metal evaporate of the heat of the reaction? Here's the formula
3ZnO + 2Al -->3Zn + Al2O3 |
The zinc will evaporate, its boiling point is only 907 C! In all likelihood this is or will be close to a flash powder.
To make matters worse, the Standard Heat of Formation of ZnO is really small (NIST: - 350.5 kJ/mol0, so the Standard Heat of Reaction is really high:
about - 625 kJ/mol Al2O3
[Edited on 22-1-2014 by blogfast25]
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Zyklon-A
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First, zinc is most likely too reactive to be reduced by Al, although Al is more reactive, they're pretty close on the activity series, so the
reaction would be very slow if at all.
Second why would you want to do that at all? Can you not get Fe2O3?
Also, 3ZnO + 2Al -->3Zn + Al2O3 would be called an equation, not a formula.
I don't think it would matter if it boiled at all.
[Edited on 22-1-2014 by Zyklonb]
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blogfast25
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| Quote: Originally posted by Zyklonb | First, zinc is most likely too reactive to be reduced by Al, although Al is more reactive, they're pretty close on the activity series, so the
reaction would be very slow if at all.
[Edited on 22-1-2014 by Zyklonb] |
The 'activity series' (you mean the electrochemical reduction potentials) has NOTHING, NADA, ZILCH to do with this. The aluminothermic reaction isn't
conducted in water and the driving enthalpies are ENTIRELY different.
The activity series doesn't say ANYTHING about speed either: thermodynamics makes no pronouncements about KINETICS.
Also, zinc cannot be reduced by ANYTHING, its oxidation state is already zero (and it doesn't exhibit negative ones).
'Can you not get Fe2O3'. Sheesh. Because Fe2O3/Al is the only interesting aluminothermic reaction? Please don't make me p*ss myself!
Stop posting NONSENSE! 
[Edited on 22-1-2014 by blogfast25]
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bfesser
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blogfast25; calm down. If you're going to nitpick,
do it well: 3 ZnO + 2 Al → 3 Zn + Al<sub>2</sub>O<sub>3</sub>
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bismuthate
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"Zinc oxide can react violently with aluminium and magnesium powders"
A quote from the wiki page on zinc oxide ( http://en.wikipedia.org/wiki/Zinc_oxide )
It would help us help you if you told s what the purpose of the reaction is.
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TheChemiKid
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I have tried zinc oxide thermite. It works, but is less violent than almost all other thermites. I would describe it as a bit more reactive than
titanium thermite.
When the police come
\( * O * )/ ̿̿ ̿̿ ̿'̿'̵͇̿̿з=༼ ▀̿̿Ĺ̯̿̿▀̿ ̿ ༽
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blogfast25
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| Quote: Originally posted by TheChemiKid | | I have tried zinc oxide thermite. It works, but is less violent than almost all other thermites. I would describe it as a bit more reactive than
titanium thermite. |
Then you are almost certainly doing something wrong. Comparing one thermite to another is dubious in any case. Did you use the same type of aluminium?
Comparable powder granulometry? The same type of ignition method? I can make Classic Thermite run really slowly if I want to.
With a Standard Reaction Heat of - 625 kJ/mol, only about 200 kJ/mol short of ferric thermite and more than twice the value of TiO2 thermite, this
should burn very well and probably deflagrate quickly due to the evaporation of the formed zinc.
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Metacelsus
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The hot zinc vapor will most likely further react with air: 2 Zn + O2 -> 2 ZnO
Be careful of breathing zinc-containing fumes: https://en.wikipedia.org/wiki/Metal_fume_fever
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Oscilllator
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Today I tried the zinc thermite myself:
23.7g powdered ZnO was mixed with 5.3g of Aluminium powder (a 0.1g excess of aluminium). The zinc oxide was prepared as outlined in this thread. I then attempted to ignite this mixture with a comercial sparkler, the method I have successfully used for all my previous thermites
(Si, Mo, Fe).
The thermite mixture completely failed to ignite! I tried again with a spoonful of Fe2O3 thermite on top, but this still didn't work. I added some
more (~1g) of Al powder and tried to ignite with another Fe2O3 booster and this did not work either! It appears that zinc thermite is very far away
from a "flash powder".
One possible reason for this is that the Zinc oxide powder I used was relatively coarse compared to some of the other thermites I have tried, however
I estimate it still had a grain size of <0.1mm, so that was probably only part of the problem. Perhaps I should try preparing some ZnO by a
different method, but I doubt this will change the results much.
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blogfast25
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@Oscillator:
I'll try this very shortly with some commercial, high purity, very fine ZnO.
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Fantasma4500
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ahhh.. we still got quite the lack of vitamin D from the still missing sunlight in the dark months i see ^^
''Zinc chloride[edit]
Zinc chloride smoke is grey-white and consists of tiny particles of zinc chloride. The most common mixture for generating these is the zinc chloride
smoke mixture (HC), consisting of hexachloroethane, grained aluminium and zinc oxide. The smoke consists of zinc chloride, zinc oxychlorides, and
hydrochloric acid, which absorb the moisture in the air. The smoke also contains traces of organic chlorinated compounds, phosgene, carbon monoxide,
and chlorine.''
>zinc oxide
>aluminium powder
related, yes? also this HC smoke composition is said to be one of the best, hexachloroethane can be made yourself but its if im not absolutely
entirely wrong something around CCl4, something where you need chloroform or similar solvent from starting point, in which most would regard a
valuable chemical to posess.. i remember before the norwegian guy went about buying off polish sites the site he bought from sold hexachloroethane..
its not even that long time ago, i got no reason to feel old yet.. damn
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blogfast25
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What is the source of your citation, Antiswat?
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AJKOER
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I understand Blogfast's energy argument, but I have a technical issue with it that may (or may not) be of any significance here with respect to visual
comparisons of thermites. It relates to how energy is manifested in any given reaction. For me, some reactions like H2 and Cl2, have obvious kinetic
and temperature demonstrations, others heat and light. Now, Wikipedia on the forms of energy (see http://en.wikipedia.org/wiki/Forms_of_energy ), as one reference, to quote:
"In the context of physical sciences, several forms of energy have been identified. These include[need quotation to verify]:
>Kinetic (≥0), that of the motion of a body
>Potential, a category comprising many forms in this list
>Mechanical, the sum of (usually macroscopic) kinetic and potential energies
>Mechanical wave (≥0), a form of mechanical energy propagated by a material's oscillations, e.g. that of ocean surface waves or that of sound
>Chemical
>Electric
>Heat is just that amount of thermal energy being transferred (in a given process) in the direction of decreasing temperature.
>Mechanical work is just that amount of (mechanical) energy being transferred (in a given process) due to displacement in the direction of an
applied force.
>Magnetic
>Radiant (≥0), that of electromagnetic radiation including light
>Nuclear, that of binding nucleons to form the atomic nucleus
>Ionization, that of binding an electron to its atom or molecule
>Elastic
>Gravitational
>Intrinsic, the rest energy (≥0) equivalent to an object's rest mass
>Thermal, a microscopic equivalent of mechanical energy"
Wikipedia also notes "Some entries in the above list constitute or comprise others in the list. The list is not necessarily complete."
So, bottom line, I suspect that an energy value for a reaction, while generally a good rule of thumb, may not actually speak to a particular thermal
energy only (or kinetic energy) comparison between thermites (thermal is but one of many forms of energy).
As an illustration, we are given two baskets of fruit, one of which is of reputedly higher value than the other. Without knowing the actual
composition of fruits, the relative value to the buyer could be problematic unless one is willing to assume uniform compositions on average.
[Edited on 24-1-2014 by AJKOER]
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blogfast25
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| Quote: Originally posted by AJKOER |
So, bottom line, I suspect that an energy value for a reaction, while generally a good rule of thumb, may not actually speak to a particular thermal
energy only (or kinetic energy) comparison between thermites (thermal is but one of many forms of energy).
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Actually it does and most smooth running thermites would be difficult to identify by how they look, so similar they tend to be.
There is no ‘particular thermal energy’: there is only enthalpy.
Imagine an adiabatic enclosure, inside of which a chemical reaction is carried out: no energy (in whatever form) or mass can escape from it or enter
it. By definition W = 0 (no mechanical work is performed) and ∑H = 0 (the sum of all enthalpies is zero).
Assuming correct values for the Standard Enthalpies of Formation are used, the calculated Standard Enthalpy of Reaction will be correct and is real.
Assuming 1 mol of the reaction proceeds to completion (when ΔG is quite negative and thus K is large), the Reaction Enthalpy ΔH is generated
and has nowhere to go but into heating the reaction products. The contents of the adiabatic enclosure thus heats up acc. ΔH = n
C<sub>p</sub> (T – 298) with T the adiabatic end temperature (and C<sub>p</sub> the molar heat capacity of the reaction
product mix and n the number of moles of reaction products). Enthalpies of any change of state (melting or vaporising) also need to be accounted for,
if they occur. But in any case ∑H = 0.
This is true for any reaction, including H2 + Cl2, in the case of an adiabatic system.
In the case of ‘open’ thermites (open crucible) the situation changes but only to a degree. Assuming no significant volatility, the thermite
doesn’t do any mechanical work either. But it will lose some electromagnetic radiation, in the form of IR and VIS radiation, emitted by the hot
reaction products. Low power can generate an awful lot of light though (imagine a 150 W bulb), which is why the calculated adiabatic end temperatures
remain good and widely used predictors for well-designed (and open) metallothermic reactions, especially those that run fast (shorter reaction times
leave less time for heat transfer, all other things being equal).
Most of the other energy forms you listed don’t come into it: even if you run the reaction on a fast moving train (kinetic energy) high up in the
mountains (potential energy), these are not affected by the reaction and the reaction enthalpy is not affected by them.
[Edited on 24-1-2014 by blogfast25]
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Fantasma4500
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http://en.wikipedia.org/wiki/Smoke_screen -- blogfast
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blogfast25
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Thanks, AS. If a mixture of ZnO and Al powder, 'doped' with inert heat sinks like ZnCl2 and C2Cl6 burns, then surely also a 'naked' mixture of ZnO and
Al powder must burn too.
I'm testing this one tomorrow.
[Edited on 24-1-2014 by blogfast25]
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blogfast25
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Well, I couldn’t get that ZnO/Al thermite to light up significantly for love nor money!
7.6 g commercial ‘Red Label’ ZnO (30 – 40 BET sq. meter/g, a very fine, fluffy powder) was mixed with 1.7 g Al powder (63 micron), loaded into a
40 ml crucible and attempted to light with a mixture of KClO3/Al and a piece of Mg ribbon. To my surprise nothing happened: the ignition mix lit up
and then… nothing!
To that mixture was the added another 1.9 g Al powder and although that did light, it burned very slowly for a couple of minutes and then fizzled out.
Barely 10 % (at a glance) had reacted.
I suspected part of the problem was the very low apparent density of the mixture: about 0.2 g/ml. This is due to the ZnO being such a fluffy, light
powder. That doesn't of course promote much contact between the reactants.
So about 30 g of it [ZnO] was mixed with deionised water to a paste and this paste was then dried in a pyrex dish on a high setting electrical plate,
until all steam evolution stopped. During heating the ZnO turned slightly yellow but on cooling it returned to its original white colour. I see to
recall this thermochromism is normal for ZnO.
The dried ZnO was ground to a fine flower in a granite mortar and pestle. 20.6 g of it and 4.6 g Al powder were mixed and treated as above. Note that
the volume of this mixture was only about 30 ml, so an apparent density of close to 1, much higher than the initial mix.
But it too did not light. Adding another 5 g of Al powder did cause some reaction but as before it fizzled quickly.
I’m quite befuddled by this. I might make an attempt with a pre-heated mixture, assuming 'activation energy' is the problem here.
[Edited on 25-1-2014 by blogfast25]
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Lambda-Eyde
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Although zinc sounds like a relatively pleasant element, please do not underestimate it. Let this serve as a reminder for you guys who like to
experiment with thermites: www.anvilfire.com/iForge/tutor.php?lesson=safety3/demo...
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
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siegfried
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Mixed 5 grams of ZnO with 2 grams of Al; when ignited, using a fuse, with a 65/35 mixture of KClO4 + powdered Ti it reacted with a blinding flash
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blogfast25
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| Quote: Originally posted by siegfried | | Mixed 5 grams of ZnO with 2 grams of Al; when ignited, using a fuse, with a 65/35 mixture of KClO4 + powdered Ti it reacted with a blinding flash
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Nice one. Was there anything left in the crucible?
That's a very exotic ignition mix you're using, Siegfried.
I prepared some 20 g of homemade ZnO yesterday, it's drying now.
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blogfast25
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| Quote: Originally posted by siegfried | | Mixed 5 grams of ZnO with 2 grams of Al; when ignited, using a fuse, with a 65/35 mixture of KClO4 + powdered Ti it reacted with a blinding flash
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Nice one. Was there anything left in the crucible?
That's a very exotic ignition mix you're using, Siegfried.
I'm fairly convinced there's something wrong with my ZnO (it's density remains uncharacteristically low, compared for instance to my CuO). So I
prepared some 20 g of homemade ZnO yesterday, it's drying now.
[Edited on 27-1-2014 by blogfast25]
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AJKOER
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OK, I think we can agree that the usual rule of thumb does not apply to a ZnO/Al thermite.
First, we have a very unique compound (ZnO) that displays thermochromic properties as witnessed by Blogfast. Also, per Wkipedia ( http://en.wikipedia.org/wiki/ZnO), thermal heating produces a non-stoichiometric decomposition reaction resulting in the loss of some O2 forming a
slightly Zinc enriched compound.
In addition, together ZnO/Al may even display a temperature-dependent photoluminescence (see http://www.researchgate.net/publication/245537069_Room-tempe... ). Also, ZnO/Al2O3 displays a blue shift (see http://wr.lib.tsinghua.edu.cn/sites/default/files/1120915317... ).
Also, Wikipedia ( http://en.wikipedia.org/wiki/ZnO ) notes the use of ZnO as a fire retardant.
My speculation is that this thermite reaction occurs when ZnO is in a vapor state. Now normally, by direct heating, this vaporization occurs at a
temperature approaching 2,000 C, but can be lowered, to quote from Wikipedia on ZnO:
"ZnO decomposes into zinc vapor and oxygen at around 1975 °C with a standard oxygen pressure. Heating with carbon converts the oxide into zinc vapor
at a much lower temperature (around 950°C).[12]
ZnO + C → Zn(vap) + CO
Zinc oxide can react violently with aluminium and magnesium powders, with chlorinated rubber and linseed oil on heating causing fire and explosion
hazard.[13][14]"
Interestingly, this last comment from Wiki appears to actually exceed Blogfast's expectation.
Perhaps speculating, even replacing Zinc oxide with Zinc Acetate and an oxygen source (in an attempt to form nano-sized ZnO particles, as for example
in this source, "In situ thermo-TOF-SIMS study of thermal decomposition of zinc acetate dihydrate" at http://onlinelibrary.wiley.com/doi/10.1002/jms.721/abstract , or even this, "Synthesis of ZnO nanowires by thermal decomposition of zinc acetate
dihydrate" at http://www.sciencedirect.com/science/article/pii/S0254058408... ) may perform better (or even potentially explode with Aluminum powder).
Similarly, one may able to employ Zinc oxalate (see, for example, "Mechanism and kinetics of thermal decomposition of zinc oxalate" at http://www.sciencedirect.com/science/article/pii/S0040603104... ,or see, "Thermal decomposition of zinc oxalate dihydrate: Kinetics of dehydration
and pyrolysis in various atmospheres" at http://onlinelibrary.wiley.com/doi/10.1002/jctb.2720241005/a... ).
[Edited on 27-1-2014 by AJKOER]
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blogfast25
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AJ:
I believe the explanation for non-ignition of my ZnO/Al mix is quite mundane: the powder I used has a very low bulk density due to high
‘structure’, see also the fairly high BET surface area value. As a result I was attempting to ignite an ‘air thermite’, not a ZnO thermite.
The treatment with water only very partly destroyed that structure.
The decomposition of ZnO at high temperature is as expected: ZnO doesn’t have a high Formation Enthalpy and like several other monoxides in that
neighbourhood is much less stable than most D-block oxides. With a modest value for ΔG, the equilibrium constant K for MO === > M + ½ O2
becomes large at high temperatures.
My homemade ZnO is almost ready, bar a short calcination at medium-high Bunsen heat to drive off the last bits of water.
[Edited on 27-1-2014 by blogfast25]
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Oscilllator
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blogfast25 is it your intent that your homemade zinc oxide be more dense, and so promote a better reaction? If so, I have doubts that it will work
based on my experience.
My zinc oxide was prepared by the decompostion of zinc carbonate at around 1000 degrees. The zinc oxide was gooey and bright yellow at this
temperature, and the resulting material is quite hard, so I think its safe to say its calcined. I measured the density of the product just then
(uncompacted) and it came out at 2.0g/cm3. Wikipedia's published density is 5.6g/cm3 but although my measured density is far
below that I think my powder had a high enough density that some doubt is cast on the role of density in how easy the thermite is to ignite.
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