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Ammonium chloride requirements for galvanizing flux, and analysis of same

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July 7, 2008

hi
I'm a chemical engineer in a new galvanizing plant in Egypt, a want to make a flux tank control but I can not determine the concentration of ammonium chloride in the tank, in fact the flux tank ph = 3 and I think that value is low, so I want to know the ammonium chloride content to increase it, by the way what is the suitable amount of ammonium chloride should be added to increase the ph by 1 degree per m3?
thanks,

Mohammad Saad
chemical eng - Cairo, Egypt


July 10, 2008

Measuring the pH of flux is difficult, and often misleading. Most of the usual techniques do not work.
ICP is one way to measure the ammonium chloride concentration.

Geoff Crowley
galvanizing &
   powder coating shop
Glasgow, Scotland


July 15, 2008

Sirs:
Until about 1985 I did ammonium chloride in flux using kjeidahl distillation and published the method in the magazine, METAL FINISHING. Now I use a self-developed heat of solution method which is extremely simple. This method takes advantage of the fact that when zinc chloride is dissolved in water the solution gets hot, whereas when ammonium chloride is dissolved in water the solution gets cold. Under the conditions that I use there is about a 35 C deg. differential. I have taught this method to many galvanizers who use it once or twice a month.
In another of my publications in METAL FINISHING, I sent out 13 samples all from the same batch of flux made up here in my lab with an ACN of 1.00 (ACN = ammonium chloride/zinc chloride; e.g. equal amounts of ammonium chloride and zinc chloride, this is between the double and triple salts). All 13 labs failed to provide a usable result even though most of these labs are "certified" by the US government and charge a few hundred dollars/test.
It is true that a newly dissolved flux solution has a pH near 3. The best operating pH for flux is 4.2. "pH" is pH not "ph." This is the negative log base ten of the hydrogen ion concentration (e.g. when the pH changes by one unit the hydrogen ion concentration changes ten-fold, "pH" is actually a mathematical term applied to chemistry.) Ammonium chloride is NOT what to add to change the pH! pH is NOT measured in degrees.
Geoff, I am not familiar with using ICP (inductively coupled plasma) for measuring ammonium chloride in flux solution. I am under the impression that ICP is used like AA or AE except that it is more sensitive because the temperature is hotter. AA or AE is used for 30 or 40 metals that have electrons much further from the nucleus and more easily promoted to outer shells to emit energy upon return. Actually it doesn't really matter because the folks with ICP are very reluctant to run samples with zinc in them because of the memory effect.

Regards,

Dr. Thomas H. Cook
- Hot Springs, South Dakota


August 10, 2008

thanks sirs for your support
so there is an analytical method to measure the amm. chloride conc,
actually I use a raw liquid flux solution with ( 800 g/l),
by analysis I found that the zinc chloride conc is 545 g/l
then I dilute the sample ( 1 liter water and 1 liter raw flux) so I expect that the conc. of zinc chloride will be 272.5 g/l, but I found it 331 g / l by analysis, please tell be where is the problem ( the analysis done by EDTA AND PERMANGENATE)
Second, the flux tank conditions are: ( temp=50 , baume=30, PH=3.0), if I dilute it to reach a PH=4.2 baume will be =13 - 14, so (i think that it is low ), I can not find the optimum conditions
note, thanks I now try to use the (caps lock) button to write the (PH) by the right way

M.Saad
- Cairo, Egypt


August 14, 2008

Sir:

It is possible that your local fertilizer company may have a way to test for NH4Cl. The method would likely be Kjeidahl distillation or total nitrogen. I personally would not trust the result however. If the total (ZnC2 plus NH4Cl is 800 g/liter and the ZnCl2 alone is 545 g/liter then the NH4Cl alone is 255 grams/liter (800-545). This would be an "ACN" of only 0.47 (255/545). This ACN corresponds to the mono salt which is commonly used at high concentration for continuous sheet galvanizing. It would NOT be a good flux for general galvanizing.

EDTA is the proper titrant for zinc +2 ion. There would be no use for permanganate in this titration (except to oxidize iron +2 to iron +3). This is a very messy way to determine zinc because the orange sludge formed from iron +3 would contain liquid that would also still contain zinc.
For approximate zinc chloride the density in baume does quit well if the NH4Cl is fairly well known. I have full tables for this.

Could you explain a bit more about your operation, especially the type of galvanizing that you do.

Regards,

Dr. Thomas H. Cook
- Hot Springs, South Dakota


August 22, 2008

I would determine Zn via an EDTA titration, and the ammonium chloride via an ion selective electrode.

If I/my employer was too cheap to buy the probe, I'd distill off the NH3, with the Kjeldahl method, then titrate the distillate with 0.02 N H2SO4.

You might have luck using Nessler's reagent for the ammonia determination, if you prepared the proper matrix matched standards. Lots of set up time, but possibly quicker than the above two methods, after the initial work of making the standard curve is done.

I also don't see how ICP could be used for NH3.

Dave Wichern
- The Bronx, New York


December 3, 2008

sir
thanks for your support
actually I have a concentrated flux solution with 800 g/l, 89%zinc chloride and 11%ammonium chloride
I put the concentrated flux sol. with water into the flux tank to adjust the baume to 30, now the pH BECOME = 2.0
I want to do
1- increase the pH to 4.2
2- determine the ammonium chloride to try to adjust the components percentages ( please list the procedures of the process of heat of solution)
3- the other procedure to make a full control on the flus solution
I want to tell you some facts
1- the process is hot dip galvanizing
2-I have two rinse tanks before flux
3- the flux temp. =50 c
4- I have a flux regeneration unit by peroxide and ammonia (I will work at Jan 2009)
5- the work started from 10 months only
6- I work to prepare an acidic degreaser before the pickling process by hydrochloric acid (I'm sorry to late the reply)
thanks sir

M Saad
- Cairo, Egypt




May 18, 2011

Kind Sirs:

Greetings! I understand that Dr. Cook is saying he has a quick and simple way to determine the ammonium chloride number in the flux solution via heat of solution (or temperature difference?) however, in all honesty I cannot seem to follow through the method. Guesstimates for actual ACN can be deduced from pH and baume but still has to be based on the initial flux formulation and will take experience. For a newbie, this will be tedious. Inasmuch as Dr. Cook mentioned that he has already taught the method to galvanizers in the past, I am asking if the kind Doctor can give us the details of the procedure in this thread.

Thank you very much and more power!

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA


May 19, 2011

Sir:

The "bake and shake" method of testing flux does NOT yield ACN. It gives ACNV which is the correct way to control the volatile (ammonium chloride) and the non-volatile components (zinc chloride, ferrous chloride, and sulfate) of hot dip galvanizing flux. As I previously mentioned on this thread this method is based on the fact that ammonium chloride is endothermic (gets cold) when it is being dissolved in water and zinc chloride and iron (+2) are both exothermic (gets hot) when dissolved in water. Also ammonium chloride contributes little to baume', whereas zinc chloride and iron chloride give high baume' solutions when dissolved. The method depends on a series of known ACNV's and equipment that is calibrated. It is not possible for me to give the methods or calibrations on a web site.

Regards,

Dr. Thomas H. Cook
- Hot Springs, South Dakota, USA

May 21, 2011

Sir:

It seems to me that your quick method suits best in determining (estimating) the ACN value of an undissolved flux salt such as for quality check of bulk order in lieu of the individual analyses of ammonia, zinc, and chloride. However, pH and baume are good gauges when it comes to controlling the ACN in a flux solution. As to the differential temperature procedure, I will find time to perform it in the lab, thank you anyways. Nevertheless, Barlow is just fine for me sir.

Best regards.

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA


May 23, 2011

Barlow:

My "bake and shake method" is not quick but it is simple once it is properly set up. It gives ACNV (ACNV = ammonium chloride/(zinc chloride + iron (+2)chloride) NOT ACN. The ACNV value is quite accurate and extremely useful in controlling flux. ACN is NOT useful in the presence of high iron(+2) chloride. pH and baume' do NOT control ACN and in fact are not even related to ACN.

Regards,

Dr. Thomas H. Cook
- Hot Springs, South Dakota


May 25, 2011

Dear Dr. Cook:

Sir, I use both pH and Baume (and recently % HCl by weight) as indicators of ammonium chloride and zinc chloride balance in the flux solution depending on the initial formulation.

I make use of the fact that zinc chloride dissociates to form the HCl needed to remove the remaining iron oxides in the fluxed steel and aqueous zinc oxide that aids in providing a protective layer. It is the zinc chloride number that pulls the pH down due to the above reaction rather than the ammonium chloride number that remains as is in the solution (however, a small portion is believe to be dissociated to ammonium hydroxide). The ammonium chloride provides most of the oily protective layer that sublimes to ammonia and again HCl in the zinc bath but recombines at lower temperature forming the white smoke. This is how the ACN or ZCN becomes related with pH.

Given that zinc chloride is almost twice as heavy as ammonium chloride, this is being used as gauge to determine the need to add more zinc ammonium chloride or just ammonium hydroxide alone to convert the HCl and/or FeCl2 carryover in the flux to more ammonium chloride. As you have advised, it's not good to make use of straight ammonium chloride as pre-flux because the galvanized steel would become so clean that it can detect entrapped dross or ash in the form of pimples. Replacing the lost zinc chloride (or zinc oxide rather) is then necessary to add texture to the zinc coating and thus avoid the concern. % HCl in the flux solution is also being correlated with the amount of zinc chloride.

Nevertheless, there is no substitute to an accurate volumetric or spectrophotometric ammonia, zinc, and chloride analysis to really have full control of the ACN.

Regards.

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA


May 26, 2011

Barlow:

I have read, with great concern, your last posting several times. In fact I have given your last posting much thought today. You and I are obviously NOT communicating on this website. I have numbered your sentences and I can start to respond as follows:
(1)pH, Baume,' HCl, or original formulation are in no way related to ACNV of a process flux solution.
(2)ZnCl2 does not dissociate into HCl. Zinc oxide is insoluble in water. Zinc chloride provides a layer that inhibits rust.
(3)Kindly define your "zinc chloride number." What does "zinc chloride number pulls down the pH," Mean? What is your proof that--"a small portion is believed to be dissociated to ammonium hydroxide?"

I cannot further respond to postings that are contrary to my education and experiences of nearly 40 years working in hot dip galvanizing.

I think I will buy a fishing license and some worms tomorrow and go fishing for walleye and bass :-)

Regards,

Dr. Thomas H. Cook
- Hot Springs, South Dakota


First of two simultaneous responses -- June 2, 2011

Barlow:

The fishing was very good. To continue:
(4)The oily "protective layer" IS LIKELY OIL. The white smoke is mostly ammonium chloride and aluminum chloride. (5) ACN is NOT related to pH in any way. What is "ZCN?" (6) What do you mean that "zinc chloride is almost twice as HEAVY as ammonium chloride?" How can it be that "to convert HCl and/or FeCl2 carryover into the flux to more ammonium chloride?" (7) I have NOT advised: "it's not good to use straight ammonium chloride as flux because it would make the steel too clean and cause dross pimples." (8)Where did you get the idea to "add texture" to the flux solution? Rather texture to the zinc coating? I do not understand your statement. "...and thus avoid concern." About what?? (9)The %HCl in the flux is NOT related to the amount of zinc chloride. (10)Interestingly it is MUCH easier to get ACNV directly with the simple bake and shake method.

I need to go fishing again.

Regards, Dr. Thomas H. Cook, Hot Springs, South Dakota, USA

Dr. Thomas H. Cook
- Hot Springs, South Dakota


Second of two simultaneous responses -- June 2, 2011

Dear Dr. Cook,

Sir, it's my pleasure to have taken your attention hook, line, and sinker (I hope the idiom is apt lol), and I am very thankful for that. Nonetheless, hereunder is my side of the story if I may say so:

1) I was relating pH, Baume, %HCl as I call it since others use the term "free acidity", with your ACN term or the Ammonium Chloride Number and not the ACNV of which I do not know and I failed to ask but was expecting the same thing except for the "V" part.
2) I did my "BAKE and shake" testing for the % HCl in pure ammonium chloride and a double salt to fortify my gained knowledge on flux salts which eventually led me also to conclude that only a small amount of ammonium chloride dissociated to form the HCl product or at least after being buffered with the other ammonium hydroxide formed owing to the tremendous amount of "endothermic" energy involved which I did not bother to calculate. An aqueous solution of ammonium chloride did not pull the solution pH below 5 at the prepared concentration similar to its share in the double salt the double salt did.
3) What I actually meant when I said Zinc Chloride Number was, technically the salt "ratio" or the weight of zinc chloride over the weight of ammonium chloride which is the exact opposite of the ACN. Sir, I have read somewhere that zinc oxide is an amphoteric oxide and that, yes, it does not dissolve in water (and alcohol) but is soluble in most acids such as HCl.

I hope I have cleared myself.

Best regards,

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA


June 2, 2011

Barlow:

It occurred to me that you may have tried to get my attention. It is unlikely to happen again. The fishing today was a bit slow but we saw a mother goose and four babies.

The "V" part means using both zinc chloride and iron (II) chloride in the denominator as I previously reported.

I am not able to follow your reasoning in your next few sentences.

In the USA there are some flux companies that use "ratio" which is the inverse of ACN (1/ACN = ratio). This ratio is NOT the OPPOSITE of ACN. Amphoteric means that a material can act as an acid or a base and thus soluble in both.

The "bottom line" on the bake and shake method is that any solid flux when dissolved in water gets colder when the ACNV is higher. Or with sufficiently low ACNV gets hotter (as it is dissolved in water) as the ACNV gets lower.

The method(s) are easy and quite accurate once it is fully calibrated and tables are developed, as I have done.

Now I have other "fish to fry."

Dr. Thomas H. Cook
- Hot Springs, South Dakota


June 4, 2011

Dear Dr. Cook:

On ACN and Ratio, isn't it sir that mathematically the expression: ratio = 1/ACN means that ratio is inversely proportional to ACN where the term inverse is synonymous with opposite? Moreso, by substitution:

Ratio = 1/(wt. NH4Cl/wt. ZnCl2)

multiplying both the numerator and the substituted denominator with the inverse of the substituted denominator will yield the following:

Ratio = 1 x (wt. ZnCl2/wt. NH4Cl) / (wt. NH4Cl/wt. ZnCl2) x (wt. ZnCl2/wt. NH4Cl) where the denominator cancels out and becomes 1 therefore what remains out of the equation will be:

Ratio = (wt. Zncl2/wt. NH4Cl) / 1, OR simplifying
Ratio = wt. ZnCl2/wt. NH4Cl, which now becomes the exact opposite of ACN.

Whew! I never expected this discussion would end up with algebra and a hot seat.

All the best.

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA


June 5, 2011

Dear Dr. Cook:

Sir, I just read the second half of your numbered concerns and I can't help but answer your queries to wit:

a) From the respective MSDS's of the flux salts

NH4Cl ZnCl2
Solubility: 29.7 g/100 g water 423 g/100 g water
Density: 1.53 g/ml 2.91 g/ml
pH: 5 (10% aq. sol'n.) about 4 (aq. sol'n.)
Boiling Pt.: 520 732
Melting Pt.: 338 (sublimes) 290

b)Adding ammonium hydroxide to the flux solution

b.1 2NH4OH + FeCl2 (in the flux sol'n. from carryover) = 2NH4Cl + Fe(OH)2
b.2 NH4OH + HCl (in the flux from carryover) = NH4Cl + H2O

I was actually making an analogy from your previous commentary on straight ammonium chloride as pre-flux where you said "Ammonium chloride alone as a hot dip galvanizing flux solution is extremely bad. It is even worse if the molten zinc is high grade. After fluxing in ammonium chloride the steel corrodes badly before it reaches the kettle and the zinc spatter is extreme. With high grade zinc the dross pimples are entrained in the zinc giving many sandpaper pimples on the steel, especially on highway guardrail.". I theorized that because ammonium chloride breaks down into HCl and NH3 in the zinc bath, the reaction simultaneously clean and galvanize the dipped item making the previous (unremoved) iron oxidation from the flux solution very evident on the article when it leaves the molten zinc bath.

Nevertheless, I must agree that nothing much happens to the pickled material when it reaches a flux solution of pure ammonium chloride except however to the formation of a protective layer. I'm also having this idea that the oily characteristic of the protection may be proprietary.

That's how far I got Sir.

Thank you and best regards.

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA


June 5, 2011

Dear Dr. Cook:

Sir, to augment on what seems to me like an oily protective layer on the fluxed material of which I think is proprietary combination, I am now with the belief that it might not be oil after all but trapped moisture by zinc chloride since ZnCl2 itself is hygroscopic and even deliquescent. Ammonium chloride alone dries up to a white powdery material.

Regards,

barlow campano Barlow Campano
galvanizing chemist - Jeddah, KSA




December 30, 2011

Hi My Dear
Pl. Guide me about "how to remove ferric chloride in flux solution"
My Tank has 80 Ton Capacity and sedimentation has been for a very long time .

happy new year
best regards
shsamiei

Shahriyar Samiei
- Tehran, Iran


January 6, 2012

Sir:

There are three forms of iron that can be in a galvanizing flux tank:

(1) Metallic iron with oxidation number 0. This would come from workpieces falling into the flux tank or steel shot from "sandblasting". This metallic iron dissolves slowly or moderately fast depending on the pH of the flux. Metallic iron can be removed using a strong magnet.

(2) Ferrous iron with an oxidation number +2 is formed when metallic iron dissolves in a flux solution with a pH lower than 5. This type of iron is titratable using hexavalent chromium. In excess in the flux solution it causes excess ash and in the case of a "wet" kettle causes dross. It also causes thicker zinc on the product. If the ferrous iron is more than about 3% there is no reason to try to purify (remove iron) because the entire tank will turn to solid ferric hydroxide.

(3) Ferric iron with oxidation number +3 is caused by oxidation of ferrous iron by a pH higher than 5 by air or peroxide. Ferric iron precipitates with three hydroxides to form orange, insoluble ferric hydroxide that goes to the bottom of the flux tank.

Nearly forty years ago I went around the USA purifying flux solution (removing iron and sulfate, if sulfuric acid was used as the pickle). When the sulfate was about 1.5% and the iron (+2) was about 0.6%, upon purification the %GZU decreased from about 9% to about 6%. The money yearly savings were usually between $0.5 to $1 million/year from zinc savings and much, much less zinc clean-up. Ahh--The Old Days.

To remove the iron (+3) sludge you get scoop shovels and put the orange sludge into barrels. It's a sweaty job.

Regards,

Dr. Thomas H. Cook
- Hot Springs, South Dakota

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