Sciencemadness Discussion Board - Zinc Thermite?

Zinc Thermite?

AMchemistry - 22-1-2014 at 07:56

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

blogfast25 - 22-1-2014 at 10:29

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]

Zyklon-A - 22-1-2014 at 10:30

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]

blogfast25 - 22-1-2014 at 10:35

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! :mad:

[Edited on 22-1-2014 by blogfast25]

bfesser - 22-1-2014 at 10:48

blogfast25; calm down.

Quote: Originally posted by Zyklonb

Also, 3ZnO + 2Al -->3Zn + Al2O3 would be called an equation, not a formula.

If you're going to nitpick, do it well: 3 ZnO + 2 Al → 3 Zn + Al2O3

bismuthate - 22-1-2014 at 13:08

"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.

TheChemiKid - 22-1-2014 at 13:50

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.

blogfast25 - 22-1-2014 at 14:14

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.

Metacelsus - 22-1-2014 at 18:49

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

Oscilllator - 23-1-2014 at 03:25

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.

blogfast25 - 23-1-2014 at 05:45

@Oscillator:

I'll try this very shortly with some commercial, high purity, very fine ZnO.

Fantasma4500 - 23-1-2014 at 13:01

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

blogfast25 - 23-1-2014 at 13:05

What is the source of your citation, Antiswat?

AJKOER - 23-1-2014 at 16:05

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]

blogfast25 - 24-1-2014 at 10:02

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).

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 Cp (T – 298) with T the adiabatic end temperature (and Cp 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]

Fantasma4500 - 24-1-2014 at 13:41

http://en.wikipedia.org/wiki/Smoke_screen -- blogfast

blogfast25 - 24-1-2014 at 13:58

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]

blogfast25 - 25-1-2014 at 08:10

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]

Lambda-Eyde - 25-1-2014 at 08:39

Quote: Originally posted by Cheddite Cheese

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

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...

siegfried - 26-1-2014 at 19:04

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

blogfast25 - 27-1-2014 at 06:12

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

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.

blogfast25 - 27-1-2014 at 06:12

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

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]

AJKOER - 27-1-2014 at 08:06

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]

blogfast25 - 27-1-2014 at 11:55

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]

Oscilllator - 28-1-2014 at 01:18

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.

blogfast25 - 28-1-2014 at 11:01

@Oscillator:

It's not the density per se that I believe may have an influence but rather better contact between the reagents. The original Red Label ZnO I used has an apparent density of only 0.2 g/ml, as opposed to an actual density of 5.6 g/ml: that's an awful lot of air! I believe this low apparent density is due to structure of the ZnO grains (highly branched), which may not be conducive to good contact between the reagents. This contact may loosely correlate with apparent density of the termite mixture, even though density itself means nothing (low density oxides like SiO2 can also be 'thermited')

My prepared ZnO is now fully ready and I may test it later on tonight, if not tomorrow.

[Edited on 28-1-2014 by blogfast25]

blogfast25 - 28-1-2014 at 13:08

The apparent density of the homemade ZnO weighed in at 0.98 g/ml, still quite low.

The first test with 20.6 g of this ZnO and 4.6 g Al 32 micron, ignited again with KClO3 + Al and Mg ribbon as fuse, lasted longer than any other attempt so far, produced a lot of smoke but fizzled out after about a minute. On inspection it was clear that only a small portion of the mixture had reacted. Here’s the set up BEFORE ignition:

The non-combusted part of the mix was recovered, sieved and another 4.6 g of Al powder added and mixed in very thoroughly.

And this mixture flashed, big style: for about 1 second the assembly looked like an inverted rocket motor, with a 1 m high flame, which died out as instantly as it had come about. Lots of smoke wafted away (I was up wind).

On inspection the crucible showed to be basically empty:

Close up of the crucible:

At 4 o'clock are what I believe to be the remains of the ignition mix.

Note that Siedfried's account (sadly lacking in detail) mentions a ZnO/Al ratio close to the mixture that flashed. Whether a ZnO/Al self-sustaining mixture of stoichiometric ratio is possible remains an open question.

[Edited on 28-1-2014 by blogfast25]

symboom - 9-12-2020 at 10:05

Although this is referring to zinc oxide as the oxidizer has anyone tried copper oxide and zinc
Or other transition metals oxides with zinc
I imagine oxides of
Copper
Nickel
Bismuth
Lead
Indium
Gallium
Tin
Cobalt
Possibly manganese
I'd have to double check references on this.

Zinc and copper oxide
https://youtu.be/43KTuDdMviA

[Edited on 9-12-2020 by symboom]

Opylation - 13-12-2020 at 21:05

If your aim is to obtain cheap zinc metal there’s about 5g per penny post 1982

Edit: I’ve seen copper oxide used in videos and it is less than tame. The reaction goes off in a faction of a second spewing material everywhere

[Edited on 14-12-2020 by Opylation]