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topic 49271 p2

Galvanizing flux: Ammonium chloride requirements and analysis

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A discussion started in 2008 but continuing through 2019

June 5, 2011

Q. 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

Q. 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

Q. Hi My Dear
Please 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

A. 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
Galvanizing Consultant - Hot Springs, South Dakota 57747



July 15, 2015

Q. I am sorry to burst in like this and my presence most likely will be unwelcome to someone...

Any advice for treating skin burns caused by zinc ammonium chlorides and sweat "pooling" in waistline. all other posts and forums simply refer me to MSDS which only has first aid for ingested, inhaled or in eyes. If any of you gentlemen have experience with this I would love to hear from you. Have had burn or rash eight to ten months a year for three years now and just want it gone.

William [last name deleted for privacy by Editor]
HotDip plant employee - United States


July 16, 2015

A. William,
I'm not sure if what you really need is treatment or just better prevention. I found an MSDS for zinc ammonium chloride that lists first aid for skin contact, of course all it says is the standard rinse the area and seek medical attention. The page http://www.johnsonmfg.com/temp/HWhtml/ZCFS3p~1.htm goes into more detail about it: "ZnC12 absorption through your skin isn't likely, but absorption onto your skin is highly likely. This is due to the desire of ZnC12 to be wet. It will cling to the water molecules in the cracks of your skin, and once there, it holds on tight."

I am not a doctor, but due to the self-renewing nature of skin I rather suspect that any trapped zinc chloride will be cast off on its own eventually as long as you are not continuing to add more zinc chloride to the area. It sounds like you need better protective clothing, and maybe in the meantime some good skin moisturizer. You may want to discuss the matter further with a dermatologist and your plant's safety manager.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner


July 18, 2015

? Sir: Do you use nickel in the kettle?

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747



September 17, 2018

Q. What role does ammonium chloride play in zinc ammonium chloride flux?

Anand Kumar
Kriso Enterprise - Howrah, West Bengal, India


September 2018

A. Hi cousin Anand. Sorry, I am just the website curator and have no actual expertise in galvanizing so I can't help you, hopefully another reader will ...
But I must keep noting to the point of ennui that our regular responders keep telling us that they will not acknowledge or respond to any more abstract questions :-(
So please introduce yourself, and the actual situation you are encountering which has prompted that abstract question. Thanks, and good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



January 3, 2019

Q. Dear sirs,

I have read the Kjeldahl method is the most accurate technique to measure the NH+4 content in existing flux --
(i) has anyone really tried it? Also
(ii) existing flux consists of Fe2+ which precipitates when NaOH is added; in view of that, does the method still work efficiently?

As purchasing a set of Kjeldahl equipment costs more than RM30k in Malaysia, so would to have a confirmation from the seniors here.

Thanks,

Kean Wei Wong
Prestar Galvanising - Selangor, Malaysia
  ^- Privately contact this inquirer -^


January 5, 2019

A. In the 1980's I did many KJ tests on flux and it works just fine, but does take skill. Fertilizer companies normally have good skills in this test and likely is less expensive than getting the glassware to do it yourself. The answer is normally g/L of ammonium chloride.

You have made a mistake thinking you need to add NaOH to take out iron. You need both hydrogen peroxide and ammonium hydroxide and you must add the ammonium hydroxide first. NaOH will destroy your flux.

What is your iron (Fe+2) content? and what is flux tank size?

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747


January 6, 2019

A. The Kjeldahl analysis is not specific for ammonia. It measures total nitrogen content which, of course, includes ammonia.
It can be highly accurate in skilled hands but is slow and tedious.
A far simpler method is to boil a known sample with a known excess of sodium hydroxide until all ammonia is driven off and then titrate the residual hydroxide.
However, you cannot just buy the kit and assume that the knowledge of how to use it comes free. Even the simple method requires some basic knowledge of technique and without it you will get unreliable and misleading results.
You probably have a local college with a chemist who will give you the basics but my best advice would be to speak to your flux supplier.

geoff smith
Geoff Smith
Hampshire, England


January 7, 2019

Q. To Dr. Cook:

(i) The NaOH that I mentioned is for the Kjeldahl's method, which will only be added into a sample volume hence it will not affect the whole pool.

(ii) We do understand NH4OH and H2O2 are used to reduce iron and a filtration system is now incorporated to our flux pool, however, not all iron can be removed which causes precipitation in the sample when NaOH was added for Kjeldahl's method. Hence do I continue to cook the mixture to evaporate NH3 off or will the ppt. cause inaccuracy?

(iii) Our Fe content is kinda high which is 1.4++% as rinsing water is not changed periodically which has caused excessive carryover. We are gonna replace it.

(iv) The capacity is around 30 tonnes of liquid. With a geometry of 7m height x 3m long x 1.5m wide.

(v) As compared to Kjeldahl's method, I have considered using an NH4+ ISE. Issue is that the maximum reading can only be 1M hence was thinking of using serial dilution to make the NH4+ conc. in range and with the measurement, use back calculation to obtain the real conc. Does that make sense?

Q. To Mr. Geoff:

Thanks for the information. I am looking into the time consumption as well. As each round of testing would at least take up to 2-3 hours following the standard Kjeldahl's method; hence I am looking into the NH4+ ISE as we will need to monitor it daily for the moment as the pool is totally off spec now. What do you say?

Kean Wei Wong [returning]
Prestar Galvanising - Selangor, Malaysia


January 7, 2019

A. Geoff, KJ works perfectly for ammonium chloride in galvanizing flux. I have used it for many years and have made standard solutions containing zinc chloride, iron chloride, and other chlorides and there are no interferences. I do not share your confidence in flux suppliers testing fluxes properly. 22 years ago I made up a flux solution with a specific composition and sent portions of it to 13 companies for testing. All results were useless. World- wide there are many contaminated galvanizing fluxes. I do not expect your alteration to the KJ to work. What about the OH-1 tied up with iron or zinc at the bottom? Also what about the colors interfering with the end-point detection?

Sir, Iron (III) hydroxide at the bottom of the boil flask does not interfere. If you can find a fertilizer company nearby, that does KJ every day, they may do it for a small fee. Here the cost is $25/sample and I have one client that does testing this way. The specific ion electrode for ammonia is high priced and the flux needs to be well diluted with distilled water. From which country do you buy flux? Is your kettle very deep as you indicate?

I now use my bake and shake method and it is easy with excellent results. I have a number of clients that also use the method to advantage. It is based on "heat of solution." ZnCl2 gets hot when dissolved and ammonium chloride gets cold when dissolved. Also there is a second method using density to get ACN directly.

We are working on a Dynamic test (four steps) for testing flux. The first takes a 2 inch x 2 inch x 1/4 inch angle 5 inches long and pickling it and fluxing it and seeing if it will galvanize in 20 seconds. All of my clients have passed this test. There are three more steps in the dynamic testing. I am considering posting it on this web site.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747


simultaneous January 9, 2019

Q. Dear Dr Cook,

Thank you very much for your experienced opinions. I am wondering does the bake and shake method only cater for new flux preparation or can it be used as a method to measure ACN of existing flux. I am wondering this as the temperature of the existing flux is already fixed so how does the heat of solution is used to find out the ACN?

Thanks,

Kean Wei Wong [returning]
Prestar Galvanising - Selangor, Malaysia


January 9, 2019

Dr Cook: I agree completely that KJ is a perfectly good and accurate method in capable hands.
My point was to question if it is suitable for someone with limited analytical experience; otherwise the question would not have been asked.
The indirect method I suggested is simple, quick and in inexperienced hands probably as accurate as KJ would be.
However, your advice to farm out the work is by far the best option.

geoff smith
Geoff Smith
Hampshire,
      England




January 30, 2019

Q. Hi
I am a mechanical engineer but work in hot dip galvanized pipe industry in Vietnam. My factory has been in operation for only 1 year and there are some problems related to product quality. Zinc layer after plating does not adhere to the iron layer, but it is inflated when carrying out bending test (%Si and %P in iron not more than 0.02%, zinc oven temperature is 450 °C, time of soaking tube in zinc furnace about 2 minutes). I think it may be because the ratio of ammonium chloride and zinc chloride is not suitable (ammonium chloride = 271 g/L, zinc chloride = 175 g/L). Hope someone will give me the best rate for this flux and explain to me the reason above.

This is my method; I hope it helps someone:
- ZnCl2: take 1 ml of sample solution + 50 ml of water + 25 ml of pH10 buffer (buffer pH10 = 54 g NH4Cl into 500 ml of distilled water, add 350 ml of NH4OH 25% in, determine with 1L of distilled water) + a small amount of substance EBT directive (Mordant Black T). Titrate with EDTA solution 0.2M until it turns green (EDTA 0.2M = 74.45 g C10H14O8Na2.2H2O dissolves in hot water and set 1L of distilled water).
Zn2+ (g/L) = EDTA volume 0.2M x 11.65
ZnCl2 (g/L) = EDTA volume 0.2M x 24.27

- NH4Cl: take 1 ml of sample solution + 75 ml of water + 1 ml K2CrO4 2%. Titrate with 0.1N AgNO3 solution until red.
NH4Cl (g/L) = 5.77 x AgNO3 0.1N volume - 1,924 x Zn2+

(I am not good at english so I use googletranslate, so readers are hard to understand).

PHAM NGUYEN XUAN TRUONG
Vina One Steel Manufacturing Corporation - Ho Chi Minh, Vietnam


January 31, 2019

A. Pham, By pipes galvanizing 1 year you are certain to have much Fe+2 carry-over from your HCl pickle into the flux and there may be as much FeCl2 in the flux as there is ZnCl2. The Fe+2 in your flux can be easily titrated with dichromate.

What does "inflated" mean? Does it mean "peeled off"

I prefer P at 0.01% or lower.

Your methods for testing ZnCl2 and NH4Cl, I understand perfectly, but they do not work. Iron interferes with the zinc test and if you are using "hard" well water so does calcium. For NH4Cl you are getting total Cl-1 and doing a subtraction. You cannot get correct NH4Cl from wrong ZnCl2 and total Cl-1.

I recommend that you do the first and fourth tests in my new dynamic flux tests as shown in the on-line library on this website. Then post the results on this website. photo (of 20 second test) and minutes (for cook-off time).

FLUX: What country do you buy your flux? What is your flux density (g/ml)? What is temperature of flux? What is color with 50 ml flux + bromophenol blue? Do you have an effective wetting agent in your flux solution? Are your problems (post photos) mostly on the outside or inside of the pipes? What diameters of pipes do you galvanize?f What is TDS (total dissolved solids) of your tap water? Do you have water softener?

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota 57747



February 19, 2019

Q. Hi everyone!

I want to produce ZnCl2.NH4Cl solution with baumé of 30° and ZnCl2 ratio: 34%.

How do I do it? Should I add the chemicals separately or is there any process for this production technique? Is the thing to be done to mix the chemicals in determined amounts?

I researched many books and forums but I didn't find anything for this situation.

Thank you in advance

fatih kulak
- Istanbul, Turkey

----
Ed. note: Readers, please always introduce yourself as you ask your questions. From the placement of your question, Fatih, we assume that you are a well trained chemist or chemical engineer in a properly equipped and regulated chemical manufacturing plant, not a student who will blow themself up if someone mentions hydrazine :-)



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