Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: pcm81 on June 15, 2018, 07:29:17 PM
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I am trying to measure free acid and total acid in my home made manganese phosphate bath.
In all technical manuals about phosphating baths the titrations are done using indicators. while that works, i'd like to understand the chemistry as well as the pH curves for free acid vs total acid calculations. I tried googling, but the results come up 99% with titrations for wine making, rather than technical data for free acid vs total acid calculations.
For total acid in literature phenolphthalein is used, this is why i am GUESSING this is an equivalence point titration
But how to I titrate for free acid? In industry the bromphenol blue is used as the ph indicator. Is this just a pH=4 titration by definition or is there some science behind it, like equivalence point is the highest slope point, hence need to find derivative of pH curve etc etc etc?
Thanks ahead
PS. This is why i was asking about standardizing NaOH solution earlier.
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How are "free acid" and "total acid" defined?
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How are "free acid" and "total acid" defined?
I was actually hoping that those were standard chemistry terms and you could tell me a more in-depth answer than google.
The most "scientifically sounding" answer I found so far is here: https://www.pfonline.com/articles/free-and-total-acid-values
Total and free acid values are often measured and used to control phosphate systems, which are acidic by design (to initiate the phosphate reaction). The first titration would be for free acid. This would involve taking a bath sample and titrating it with a known standard such as sodium hydroxide (probably 0.1N or 1.0 N). An indicator is added to the solution that changes color when the titration reaches a certain pH. A common indicator for this would be bromphenol blue which changes from yellow to blue when passing through the pH range around 3.5-4.0.
To determine total acid content, you would repeat most of the same steps above, instead this time using a different indicator, possibly phenolphthalein. This will change from clear to pink in the pH range of 8.5-9.
The free acid value is used to tell you how much acid is available to initiate the phosphate reaction and exists in its original “active” state. Too low a value may indicate that the bath would have difficulty initiating the phosphate reaction. The corrective action would be to add phosphoric acid to bring it in line with the supplier’s recommendations. Too high a value could indicate too much phosphoric acid in the system which will not “build” a coating since it would tend to strip it as quickly as it forms. The supplier may have a chemical to adjust for this (possibly mono- or disodium phosphate), or may just tell you to run some scrap parts or steel wool through the system to use some of the available acid. This value will tend to rise and fall around some centerpoint that you will control around (i.e., five plus/minus 1 point).
The total acid value is meant to indicate the total amount of acid that has been put into the system and is a combination of both free acid and that which has been “neutralized” through reaction and combination with iron. In general, this number will tend to climb over time as the bath ages and, when combined with a known production quantity, may be able to give you an indication as to when to dump the bath.
These measurements are most often performed with a zinc phosphate line. An iron phosphate line will typically have a titration for total acid and a pH measurement (which basically is another way to determine free acid)
The problem i am facing is 2-fold.
#1. All industry papers / recommendations are based on total acid and free acid measured in "points" which are ml of 0.1M NaOH when titrated with bromphenol blue and phenolphthalein. As usually the case, I am sure that these testing procedures are "short cuts" to real science behind the bath chemistry. Just as folks use phenolphthalein to find equivalence point, while really the EQP is the steepest slope, not just a ph value and it's ph differs from weak acid - strong base titration to strong acid strong base titration...
#2. so, i am basically trying to reverse engineer what these titrations are actually trying to measure and then gain deeper understanding of it, to be able to know what they are measuring and how the "recommended" values would apply to my own bath concentrations; given that i might change things up with bath chemistry to experiment a bit.
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I think its jargon, and has meant something and still means something, to people who aren't chemists, and are plating bath engineers. That happens, in industry, without apology.
We're lucky on this forum, its rare that we have to fight people over "alkaline diet" or "alkaline water", which are bogus terms that even clogged Wikipedia for a while.
Good for you for trying to reverse engineer the procedure to a meaningful topic.
You can tell, this is a simple titration, the reactant 0.1 N standardized NaOH is used in the same way in both cases, just the endpoints are different for the different indicators. You get two numbers, and they tell you bath "health."
This is done to determine two separate reagents with similar properties. Example: http://www.chemicalforums.com/index.php?topic=66432.msg239084#msg239084 This uses two titrations, with different indicators, to determine an unknown mixture. The explanation there clearly states that the two products become another one in the process, and then that is titrated a second time. That's likely what's happening here.
If we really understood these reactions, we could just say, "Submit sample for Ion-Chromatography" determine ratio of anions phosphate and eka-phosphate(I made that one up) and you'll know everything about your bath to two decimal places.
In fact that may be possible, but its likely the plating bath companies trade secret.
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[MOD Edit -- snip monster quote]
There is a separate titration for iron content using KMnO. But i got that under my belt already.
I think the total acid and free acid titrations in the case of phosphate bath are independent of each other. That is a different, clean, sample of the bath is used for each one. It's just the pH end points that i am struggling with to determine. Some people titrate total acid using pH meter to pH=7, others to pH=8.2... Free acid titrations i've only seen 1 "scientifically looking video" (not a guy with $10 ph meter doing wine titration) and the person was shooting for pH=4.
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.. Free acid titrations i've only seen 1 "scientifically looking video" (not a guy with $10 ph meter doing wine titration) and the person was shooting for pH=4.
See, and that actually makes sense. Comparing the endpoints of two indicators, we get two pH targets:
Bromnophenol blue: pH 3.0 to 4.6 https://en.wikipedia.org/wiki/Bromophenol_blue#Acid%E2%80%93base_indicator
Phenolpthalein: 8.2−12.0 https://en.wikipedia.org/wiki/Phenolphthalein#Indicator
You can easily use a pH meter to find those points without using indicators. You don't really have to use a new sample your each, because that's just what's going to happen anyway after you've titrated the first one.
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.. Free acid titrations i've only seen 1 "scientifically looking video" (not a guy with $10 ph meter doing wine titration) and the person was shooting for pH=4.
See, and that actually makes sense. Comparing the endpoints of two indicators, we get two pH targets:
Bromnophenol blue: pH 3.0 to 4.6 https://en.wikipedia.org/wiki/Bromophenol_blue#Acid%E2%80%93base_indicator
Phenolpthalein: 8.2−12.0 https://en.wikipedia.org/wiki/Phenolphthalein#Indicator
You can easily use a pH meter to find those points without using indicators. You don't really have to use a new sample your each, because that's just what's going to happen anyway after you've titrated the first one.
But that is where the problem is..
I can titrate for pH=3 and pH=8.2 and get some number.
I can titrate to pH of 4.6 and pH=12 and get drastically different numbers.
How do i know which of these sets of numbers is "most in-line" with online documentation available for phosphating baths recommending a certain free acid and a certain total acid...
In all titration videos the titration is done when colour change starts, so i'd guess pH=3 and pH=8.2 would be my targets. But that disagrees with pH target of 4 i see in an actual "phosphate bath acid titration" video.
https://www.youtube.com/watch?v=pglorkLU4tM
In this video the lady titrates to 4.0 and 8.2... And since she is using gloves and a ph meter about 10x more expansive than mine, i can only hope that she knows her stuff since she appears to be in a commercial environment.
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I did a test titration and the pH curve i am getting has 2 rises in it. Kind of like a titration curve for acid with 2 pKa values. One "jump" is around ph=4 and the other is around ph=7.8.
I need to get better data set with more points in those ph regions. My GUESS would be that the free acid and total acid are the 2 "equivalence" points, basically where ph curve has the steepest slope.
Does this sound reasonable?
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Try here: http://www.titrations.info/acid-base-titration
Sounds like the first end point is for H3PO4 and the second for H2PO4-.
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Got a better dataset. The first steep rise appears to have a critical point at pH=4.2. Still need to investigate the 2nd jump range to get better resolution and determine 2nd critical point.
Here is the dataset in case if anyone wants for their own research. I did several titrations all with 10ml starting sample of the bath with addition of H2O to cover the ph meter.
The NaOH was standardized with KHP and was terermined to be 0.0937M
0.1M equiv ml of NaOH in H2O pH
0 2.96
0.465 3.03
0.93 3.1
1.86 3.27
2.325 3.41
2.79 3.58
3.255 3.88
3.72 4.31
4.65 5.04
7.44 5.64
8.37 5.73
9.3 5.8
10.23 5.9
11.16 5.98
12.09 6.06
13.02 6.15
13.95 6.25
14.88 6.33
15.81 6.44
16.74 6.52
17.67 6.61
18.6 6.7
20.46 6.87
21.855 7
22.32 7.03
22.785 7.08
23.25 7.14
24.18 7.24
25.11 7.35
28.83 8.11
29.295 8.3
29.76 8.5
0 2.79
0.465 2.83
0.93 2.94
1.395 3.04
1.86 3.13
2.325 3.27
2.511 3.33
2.79 3.43
2.976 3.52
3.162 3.65
3.441 3.84
3.72 4.14
3.813 4.29
3.9525 4.37
4.185 4.56
4.4175 4.62
4.65 4.75
4.929 4.86
5.1615 4.91
5.487 4.97
5.673 5.02
6.045 5.07
6.603 5.17
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I'm also in process of trying to make successful and repeatable manganese phosphate path for coating various steel parts. I ordered Bromothymol Blue and Phenolphthalein Solution as indicators for titration (should arrive within a week).
Formula i'm going to try is:
9.26 g/L H3PO4
12.61 g/L HNO3
3.3 g/L Mn
Source: http://www.scielo.org.mx/pdf/jmcs/v57n4/v57n4a10.pdf
I assume that those concentrations are for 100% acids? So when my H3PO4 is 85% and HNO3 is 52% and my manganese is in form of Mn02 i would have to use following amounts for 1 liter of water?:
10,9 g/l H3PO4 (85%)
25,2 g/l HNO3 (52%)
5,2 g/l MnO2 (Mn 63% O2 37% mass %)
Next question i have is also how to determine total and free acid in solution. Everywhere i've read TA & FA is in "points", what does it mean exactly?
Best explanation i've found is in here: http://imghost1.indiamart.com/data2/FJ/TM/MY-1736813/zinc-phosphates.pdf (explains how to maintain some commertial zinc phosphate bath).
Total Acid Points (TA)
reagents: 0.1 N sodium hydroxide solution
indicator: phenolphthalein
procedure: 1. Pipette 10 ml bath sample into a 250 ml Erlenmeyer flask.
2. Dilute approx. 50 ml deionized water.
3. Add 5 drops of indicator.
4. Titrate with 0.1 N sodium hydroxide solution from colorless to
light pink.
calculation: consumption in ml = TA Points
correction: for each missing Total Acid Point = addition of 5 ml/l ZP5
Free Acid Points (FA)
reagents: 0.1 N sodium hydroxide solution
indicator: bromphenol blue
procedure: 1. Pipette 10 ml bath sample into a 250 ml Erlenmeyer flask.
2. Dilute with approx. 50 ml deionized water.
3. Add 5 drops of indicator.
4. Titrate with 0.1 N sodium hydroxide solution from yellow to blue.
calculation: consumption in ml = FAPoints
correction: To neutralize 1 Free Acid Point add 0.4 g/l Na OH (prediluted in
water, 10 %).
So even if i have maybe very different composition (HNO3+H3PO4 vs ?) i could still take 10ml sample of my path and add X ml of 0.1N NAOH to get TA & FA points?
Therefore: X ml 0.1N NAOH it takes / 10ml path sample = total acid points or free acid points
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9.26 g/L H3PO4
12.61 g/L HNO3
3.3 g/L Mn
(...)
I assume that those concentrations are for 100% acids? So when my H3PO4 is 85% and HNO3 is 52% and my manganese is in form of Mn02 i would have to use following amounts for 1 liter of water?:
10,9 g/l H3PO4 (85%)
25,2 g/l HNO3 (52%)
5,2 g/l MnO2 (Mn 63% O2 37% mass %)
Sounds OK, with the exception of the Mn. Even after browsing the paper I have no idea in what form Mn(II) was put in the solution. I strongly doubt it was metallic Mn as it will consume some of the acid, and using MnO2 doesn't sound OK, as it will not only consume acid but it will also introduce Mn(IV), not Mn(II).
Best thing you can do it to try to contact authors and ask.
i've read TA & FA is in "points", what does it mean exactly?
That you are reporting the result using an artificial unit:
calculation: consumption in ml = FAPoints
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Tnx for info. I was going to try MnO2 since it's cheaply available and i've found it used in DIY phosphating recipes. What Mn compound would be preferred (that can be actually purchased from chemical supplier). MnCO3 is also smth i know i could purchase.
Regarding titrating i found patent from 1961 where it's written:
. The term points acidity as employed in the phosphating art represents the number of milliliters of 0.1 normal sodium hydroxide solution required to neutralize a milliliter sample of a phosphating solution in the presence of phenolphthalein as an indicator.
So no matter what mixture of acids i use i can take 10ml of path solution and titrate it with 0.1N NAOH. If it takes 100ml of NAOH solution to neutralize solution if would indicate that my solution has 10 points of total acid (100ml/10ml=10)?
PS since English is not my first language i have hard time understating scientific text.
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. The term points acidity as employed in the phosphating art represents the number of milliliters of 0.1 normal sodium hydroxide solution required to neutralize a milliliter sample of a phosphating solution in the presence of phenolphthalein as an indicator.
So no matter what mixture of acids i use i can take 10ml of path solution and titrate it with 0.1N NAOH. If it takes 100ml of NAOH solution to neutralize solution if would indicate that my solution has 10 points of total acid (100ml/10ml=10)?
Yes, looks like that's how it is intended to work.
Beware: dissolution of MnCO3 will consume the acid as well.
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Since putting readily available Mn compounds to solution will consume acid it's probably best to dissolve for example Mno2 (that i have at hand) in H3PO4, reaction should be following?:
4H3PO4 + 3MnO2 = 6H2O + Mn3(PO4)4
H3PO4 98g/mol (82% = 120g acid).
MnO2 87g/mol
4x 98g (=392g (480gr @ 82%) + 3x 87g (=261g) = water + Mn3(PO4)4 (i assume that it's insoluble in water?)
After reaction has taken place i can add Mn3(PO4)4 as source of Mn to phosphating solution?
If i mix water, h3po4, Mno2 ... solution will be very dilute and MnO2 will have hard time dissolving IMO + it will gradually reduce acidity as it reacts.
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If anything, I would look for some well soluble Mn(II) salt, phosphate doesn't look like one.
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I have very limited experience actually running a phosphating bath, just started messing with it very resonantly, but here is what I have learned so far:
1. You will have allot of white/grey sludge in the bath. It needs to be filtered. Here is a video showing just how much of this waste accumulates: https://www.youtube.com/watch?v=tvaCYUvxQGw
Sludge is phosphate combined with dissolved solids in water and some free iron.
2. Total iron content needs to be monitored and should be around 0.2%. At 0.6% iron content the bath is toast. You monitor it with potassium permanganate titration. Here is a video for iron titration: https://www.youtube.com/watch?v=kxMEeDoeH4E
According to literature i read the bath PH can vary from 1.5 and higher with 2.5-2.9 range producing the most uniform coating.
I tried adding Mn-oxide but i do not see any reaction with phosphoric acid. I also tried to ball mill the Mn-oxide and still see no visible reaction. I will next try to use metallic Mn powder...
Total acid to free acid ratio of around 6 or 8 seems to be suggested in most text i've read with free acid being between 3 and 6 points. A point is a milliliter of 0.1M NaOH solution.
I tried mixing NaOH by weight, but it does not store well and since NaOH will have unknown fraction of moisture as a hydrate you really should standardize the solution you use for free/total acid titration vs a primary standard like KHP or Oxalic acid. I went with KHP.
You will have to titrate with KMnO for iron. KMnO solution needs to be standardized as well. Literature i've seen used Oxalic Acid to standardize KMnO. I'd like to know if i can use KHP in place of oxalic acid, since have higher purity KHP available on hand.
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I'd like to know if i can use KHP in place of oxalic acid, since have higher purity KHP available on hand.
No. KHP doesn't work for redox titration.
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I'd like to know if i can use KHP in place of oxalic acid, since have higher purity KHP available on hand.
No. KHP doesn't work for redox titration.
I suspected that. Was hoping... since some folks used oxalic in place of KHP for acid/base standardizations. Oh well, i guess i have to wait a bit for oxalic acid to ship in.
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If anything, I would look for some well soluble Mn(II) salt, phosphate doesn't look like one.
In all literature that i have seen so far the Mn donor was MnO2. Interesting to note that Mn3(PO4)4 is not soluble in water. Sooo, as much as i'd like to make Manganese phosphate and just add it to the phosphate bath, i am not sure that it would even prove useful since it won't dissolve in water.
I am guessing that mangenese dioxide reaction with phosphoric acid has to happen at the surface that is being phosphate treated, to then be immediately incorporated into phosphate deposit as it drops out of solution?
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I did some testing yesterday - all day and in end i had some results.
At first i was trying to add ingredients to water by formula i mentioned earlier but it gave no results. Coating did'nt adhere. There was FA/TF ratio was 1:2 and there most likely was very little dissolved manganese ions in solution.
Test piece looked like this: https://imgur.com/aKWbcsx
Then i messed around with solution, added MnCO3 + H3PO4 (several times) total amounts approx 35g + 30g (to 500mil of water). Ended up with FA/TA 1:8,5 and test piece was like that https://imgur.com/pBfLdp8
Altho it's nice small crystals it looks most part to be iron phosphate (grey color). There was either not enough Mn ions or test piece didn't like to e inside that heavy sludge.
What produced results was: I added ~70g of MnO2 + 80g H3PO4 (85%) + 100ml of water + 1,5g steel wool and boiled that concentrate for some time. Later i added some more water so there was approx 500ml total.
I let it cool and settle and took 150ml of clear liquid (consentrate) and added ~400ml of water. PH of that solution was approx 3. FA/TA 1:5.
I got nice even coating with that. Only thing is that crystals were little on the big side that formed. But i think that because it was sandblasted part (surface roughness) it contributed to that as well little bit. https://imgur.com/R24StqJ
Those are my findings from yesterday.
What i'm planning to do is find optimum ratio between H3PO4, MnO2 and water to make concentrated solution that i can later dilute and use as i need - i'm open for suggestions :).
Also some testing with accelerators. NaNo3 & HNO3
Does anyone know some conditioner that would make Mn crystals small and even?
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I did one additional test with MnCO3.
i took 70g MnCO3, 110g 85% H3PO4, 150ml h2o, 1,5g steel wool. Mixed togather, boiled until reaction stopped (took quite a while).
I let it sit and i extracted clear liquid. Settement (<-spelling?) remaining was light grey.
I added 100ml of this concentrate to 850ml water + ~0.2g NaNO3. For some reason white flaky settement appeared. https://imgur.com/tecwCGm
Added test piece and i left it there for 40 min. When i returned there was no bubbling remaining. Coating was very fine grain.
https://imgur.com/CPN2flw
PH was ~2,7 FA was ~4, TA 30 ratio 7,5. <- those are approx values i have 10y old uncalibrated Chinese ph meter.
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I coated 2 things with solution i made last and even tho in test piece it was fine (fine grain but on thin side) then on test pieces coating was too thin (different steel). It is specially notable that when steel has low surface roughness then coating is extra thin.
I will try to mix MnCO3 and MnO2 solutions and see what it gives.
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The white sludge you ended up with in your last mix is similar to what i had and as far as i understand it needs to be filtered off. Your initial mix (the one that did not plate) had too much free acid. You should have FA around 4 and TA 24-40. The white sludge in my earlier experiments would actually partially dissolve when solution is heated up. Liquid would go from dull white/yellow to clear. Large sludge precipitate would settle.
Here are the baths parameters to play with:
PH between 1.5 and 4. Mine is 2.75
FA around 4
TA 6 to 10 times higher than FA
Iron content - around 0.2%. At 0.6% bath is about done.
I read that addition of Ni+ ions will help with grain structure, but i do not know quantity or preferred salt.
Nitrates are known as accelerators and bath stabilizers. Sodium nitrate as well as nitric acid are the sources of nitrates i read about.
Last night i started to try to dissolve MnO2 in dilute phosphoric acid. With some heating and active stirring (magnetic stirrer) i now have clear liquid with purple/violet tint to it; but most of MnO powder is still present. Hoping to use this as phosphoric acid replenishing tank.
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I did one additional test with MnCO3.
i took 70g MnCO3, 110g 85% H3PO4, 150ml h2o, 1,5g steel wool. Mixed togather, boiled until reaction stopped (took quite a while).
I let it sit and i extracted clear liquid. Settement (<-spelling?) remaining was light grey.
I added 100ml of this concentrate to 850ml water + ~0.2g NaNO3. For some reason white flaky settement appeared. https://imgur.com/tecwCGm
Added test piece and i left it there for 40 min. When i returned there was no bubbling remaining. Coating was very fine grain.
https://imgur.com/CPN2flw
PH was ~2,7 FA was ~4, TA 30 ratio 7,5. <- those are approx values i have 10y old uncalibrated Chinese ph meter.
Getting a closer look at your final piece i see some red tint in the middle. Iron phosphate is yellow-ish and Iron-oxide (Haematite) is red. I am wondering about the iron content in your final bath... Do a KMnO titration for iron content. Should be no greater than 0.6%.
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Now that i think about it i know where it came. When i was dissolving MNO3 in concentrated acid i added steel wool there too (should have added it later). In that strong concentrate it didn't dissolve completely. It turned red and that must have contaminated solution.
Regarding white flakes precipitate i noticed that it appears when PH increases.
pcm81 can you share how you prepare your solution + composition and what results you are getting?
Regarding source of Mn i found this:
The dissolved manganese cations required for necessary
component (A) may be obtained from any soluble manga
nese salt or from manganese metal itself or any manganese containing compound that reacts with aqueous acid to form
dissolved manganese cations. Normally preferred sources,
largely for economic reasons, are manganese carbonate and
manganese oxide. (If manganese oxide is used to prepare a
concentrate composition according to the invention, the
presence of reducing agent component (E) as defined above
is usually preferred, because without it the dissolution rate
of MnO in phosphoric acid is very slow. Reducing agents
appear to act in a catalytic or at least partially catalytic
manner to speed the dissolution process, inasmuch as the
amount of reducing agent needed to make the dissolution
rate of MnO practically fast is far less than the amount that
would be stoichiometrically required to react with all the
manganese present.)
Source: https://patentimages.storage.googleapis.com/6e/84/60/36a21d2dfe05b6/US5728235.pdf
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Regarding white flakes precipitate i noticed that it appears when PH increases.
Trivial - higher pH means converting more H3PO4 into dissociated forms (H2PO4-, HPO42-, PO43-), which form the precipitate.
Do you know what a solubility product is?
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Regarding white flakes precipitate i noticed that it appears when PH increases.
Trivial - higher pH means converting more H3PO4 into dissociated forms (H2PO4-, HPO42-, PO43-), which form the precipitate.
Do you know what a solubility product is?
I can confirm this. I got heavy precipitate after my initial addition of sodium nitrate and it increased ph to 2.75.
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pcm81 can you share how you prepare your solution + composition and what results you are getting?
I am not sure if my solution qualifies as "a recipe worth sharing" I am still playing with chemistry of it, but basically I started with 80ml of 85% H3PO4 (my intention was to make 8L of solution). I diluted the 80ml of acid with about 800ml of water. I added about 15 grams of steel wool and 12 grams of MnO2 and let the solution sit for 24 hours. Grey precipitate formed. I decanted half of solution and dissolved in 4L of water. First set of test pieces turned out to be grey and non uniform. Ph of about 1.5-2 (going by memory) I added 92 grams on NaNO3, which pushed ph to 3.2. I then added more of the "acid steel wool solution" (the original 800ml mix) to get pH down to 2.6. This created grey coating. Interesting to note that prior to adding NaNO3 i could see allot of bubbles coming off the parts being treated. After adding NaNO3 bubbling stopped and new precipitate formed. My initial titration for iron of that bath revealed 0.06% concentration (but i was using uncalebrated KMnO solution for the titration. I weighed it out on a scale, but did not titrate to calibrate). I then added more steel wool to get iron content up to 0.22%. This is the solution I have now. I am considering this as a learning batch and playing with testing the iron as well as free vs total acid. At the moment my FA is 3.75 and my TA is 29.
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NaNO3 interacts with H2 formed on steel surface (H2 bubbles are interfering with phosphate deposition) that accelerates phopspating process as i understand.
Regarding playing with acidity am i on right track?:
If i want to increase PH i could dilute solution by adding water. It also reduces TA & FA but ratio stays same. If i add MnCO3, it would react with free acid thus reducing it and increasing TA also PH would increase. To lower PH i add concentrated solution.
Some pictures from pieces i made 24.06
I made 3 pieces in 10l tank (all were together and same time).
Regular test piece (i coated it with oil before taking photo): https://imgur.com/Locd55B regular S235 steel
1 key for some old lock i made. It's also oiled, but notice its dark grey not black. Altho coating is nice uniform but in thin side, should be similar S235 steel. https://imgur.com/Z1goFNx (not best photo).
Machinist square <- don't have picture atm, but that took very thin coating. Of course it's some sort of hardened alloy steel - what i've read is that phosphate coating works best with regular mild steel.
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If i want to increase PH i could dilute solution by adding water. It also reduces TA & FA but ratio stays same.
Generally speaking yes, diluting the solution will raise the pH by a tiny bit, but that's not an effective way of changing pH here. You have a phosphate buffer present in the solution, one of the properties of buffers is that their pH almost doesn't change during dilution.
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If i want to increase PH i could dilute solution by adding water. It also reduces TA & FA but ratio stays same.
Generally speaking yes, diluting the solution will raise the pH by a tiny bit, but that's not an effective way of changing pH here. You have a phosphate buffer present in the solution, one of the properties of buffers is that their pH almost doesn't change during dilution.
I've read that NaOH and KOH are used as pH adjusters to raise pH. Although NaNO3 did a good job raising pH in my bath all on its own.
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I did few more tests today. I took 500ml from MnCO3 based solution where i last made 3 pieces.
1) First i added 1g steel wool to it. It had hard time dissolving and it didn't dissolve completely. It looked like Mn phosphate coating formed on it (it was blackish). Since i last used like 1,5g to whole 9l patch then by adding 1g to 500ml iron content should be approx 0.2%. What i noticed is that light greysh deposition formed (iron phosphate?).
When i added test piece "2" to that solution there was active hydrogen formation. After 20min i saw no hydrogen formation so i took test piece out.
It lookes like bringing iron content up made Mn phosphate coating easier to adhere. Coating is even, nice black in color. On upper part of coating there are big crystals (notice them reflecting light back on photo). What i don't like about that is that they are relatively easy to scratch off. When coarse upper crystals are removed there seems to be even and strong coating of smaller crystals underneath.
2) I added 3g of NaNO3 to this 500ml solution where i just made test piece "2". When i added test piece "1" there was noticeably less hydrogen formation and bubbles were very small. After 20 min i took it out. Coating is dark grey, it's thinner then previous. What i've read about NO3 accelerators it that disadvantage is: "Reduction of FePO4 increases the iron content of the coating." Hence the grey color? Also more NO3 is added thinner the coating will be (i cant find source atm).
Picture: https://imgur.com/NhrYXGm
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I did few more tests today. I took 500ml from MnCO3 based solution where i last made 3 pieces.
1) First i added 1g steel wool to it. It had hard time dissolving and it didn't dissolve completely. It looked like Mn phosphate coating formed on it (it was blackish). Since i last used like 1,5g to whole 9l patch then by adding 1g to 500ml iron content should be approx 0.2%. What i noticed is that light greysh deposition formed (iron phosphate?).
When i added test piece "2" to that solution there was active hydrogen formation. After 20min i saw no hydrogen formation so i took test piece out.
It lookes like bringing iron content up made Mn phosphate coating easier to adhere. Coating is even, nice black in color. On upper part of coating there are big crystals (notice them reflecting light back on photo). What i don't like about that is that they are relatively easy to scratch off. When coarse upper crystals are removed there seems to be even and strong coating of smaller crystals underneath.
2) I added 3g of NaNO3 to this 500ml solution where i just made test piece "2". When i added test piece "1" there was noticeably less hydrogen formation and bubbles were very small. After 20 min i took it out. Coating is dark grey, it's thinner then previous. What i've read about NO3 accelerators it that disadvantage is: "Reduction of FePO4 increases the iron content of the coating." Hence the grey color? Also more NO3 is added thinner the coating will be (i cant find source atm).
Picture: https://imgur.com/NhrYXGm
Adding NO3 will increase pH of the bath, effectively decreasing your free acid. I am GUESSING that this also decreased solubility of iron phosphate + Mn-phosphate in the solution, resulting in slower deposition rate. What pH was your bath at after adding sodium nitrate?
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I did some testing with knife blades (shiny smooth surface) as phosphate has harder time adhering there.
27.06
I used my MnCO3 based solution from earlier.
https://imgur.com/lNss3g3
"1" was only cleaned with acetone.
"2" cleaned with acetone, phosphated, phosphate removed with H3PO4 diluted solution, rinsed with water and phosphated again.
"3" Cleaned with acetone and half was kept in ~10% H3PO4 for approx 10 min (wanted to keep for minute but forgot). From acid straight to phosphate path.
28.06
500ml MnCO3 solution from 10l tank + 500ml i had from earlier combined + added 6g MnCO3 to reduce some acidity.
When solution was hot PH was 2.2 ish.
https://imgur.com/lu3uawX
left - cleaned with acetone.
middle - acetone + few minutes in dilute h3po4
right - acetone + half in dilute h3po4 but here i rised hot solution PH to 3 with NAOH.
Surface activation/preparation has big role in end result.
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Received some metallic Mn today ($12/lb). As expected the reaction with dilute phosphoric acid is much more vigorous than MnO2 had. Observing the quantity of MnO2 which i had in dilute phosphoric acid for almost a week i am questioning the quantity of Mn that actually gets picked up by phosphoric acid from MnO2 in phosphating bath. I am going to try to run a bath with metallic Mn as the donor of Mn. More specifically i am dissolving Mn and steel wool in dilute phosphoric acid, will add nitrate before adding additional water and using it in phosphating bath.
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(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fmagicmrv.com%2FPictures%2FDPR%2Fph.JPG&hash=6c1eb718c96c32b441982c6c74f5af0126ffbf1b)
Did a very quick test just to compare MnO2 vs mettlic Mn as the source of Mn. The top nail is hot black oxide (so its true black) the middle nail is mangenese being sourced from MnO2 while the bottom nail is Mn being sourced from Mn metal. I believe that using MnO2 as a source of Mn is difficult and often we fool ourselves into thinking that we are depositing more Mn that the bath actually does.
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Pretty good write up on Mn phosphating bath here: http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1870-249X2013000400010
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(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fmagicmrv.com%2FPictures%2FDPR%2Fph.JPG&hash=6c1eb718c96c32b441982c6c74f5af0126ffbf1b)
Did a very quick test just to compare MnO2 vs mettlic Mn as the source of Mn. The top nail is hot black oxide (so its true black) the middle nail is mangenese being sourced from MnO2 while the bottom nail is Mn being sourced from Mn metal. I believe that using MnO2 as a source of Mn is difficult and often we fool ourselves into thinking that we are depositing more Mn that the bath actually does.
How did you prepare nails prior to phosphating? I assume you did abrasive cleaning but anything chemically to activate surface? I've found that placing items prior to phosphating to dilute H3po4 solution and from there straight to phosphating path results better Mn adhesion.
Can you also make some tests with carbon steels? I've found that i can make satisfactory coating with mild steel test piece but some other stuff i need to coat get's poor uneven coating.
Better thing to test on is utility knife blade: https://images.homedepot-static.com/productImages/e97155cb-129f-4999-b0b0-fb13ac13de87/svn/olfa-replacement-blades-9281-64_1000.jpg - you can still use them after :)
If you can make good coating on that with pure Mn based solution i'm going to buy it also. But as i need to order it from other country i would wait for your results first.
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My cleaning process consists of mechanical cleaning, followed by acid etch in a mixture of sulphuric/phosphoric acids at pH of 1.2, followed by a cleaning in citric acid at ph of 2.2. Then a rinse in water. I need to do a better / proper job of surface activation prep, but so far i have not established a full process, just playing with some basic steps. The sulphuric acid is doing all of the heavy lifting in cleaning process, with citric acid cleaning up the sulphate deposits from sulphuric acid bath.
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Every time i try to post with an embedded image with or without IMG tags the post does not go through...
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This one:
http://www.magicmrv.com/Pictures/DPR/blade.JPG
That I resized and attached:
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Thanks for your help. I'd never figure out what was bugging it down.
Here is the funny part: that 2MB image is the reduced size version. Just checked the file on cameras card and the original jpg is 17.3MB.
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It's made with metallic Mn solution (bottom nail and blade)?
It looks thin and uneven, even nail. Previous nail with metallic Mn looks better.
But how does it looks when it's wet? Imo when it's wet you get best visual info.
If i'm not mistaken proper thickness Mn coating is only in bottom left corner of blade 0.5mm x 15mm strip.
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It's made with metallic Mn solution (bottom nail and blade)?
It looks thin and uneven, even nail. Previous nail with metallic Mn looks better.
But how does it looks when it's wet? Imo when it's wet you get best visual info.
If i'm not mistaken proper thickness Mn coating is only in bottom left corner of blade 0.5mm x 15mm strip.
This is almost the same solution with metallic Mn as was used on previous nail. Actually this one has more Mn dissolved, 1g/L. The image with the blade is before oiling, so it is grey-ish. oil makes it darker almost black.
Here is a side note: the digital cameras will alter colour depending on lighting conditions (energy spectrum of incident light). White balance is meant to compensate for it, but does poor job. That is why i am including the black oxide coated nail to serve as a "true black" reference point in every image.
These images were straight out of the tank after they were rinsed in water and allowed to dry the goal was to see if the blade will receive phosphate, which it did. Still need to play with cooking time, this was 30 minutes., iron content and pH to optimise this bath. The purpose of this bath mixture was to see if darker coating can be achieved using metallic Mn than using Mn-Oxide; which it did, confirming that Mn-Oxide as a source of Mn, may be lacking in its capacity as Mn donor.
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Here is a side note: the digital cameras will alter colour depending on lighting conditions (energy spectrum of incident light).
It is not a problem with digital cameras, actually it is a problem with our sight. Cameras show reasonably accurately real colors present. We are accustomed to see them after they pass through adaptive filtering applied by our brains, so we prefer to modify the picture so that it looks as if it was taken in a daylight.
White balance is meant to compensate for it, but does poor job.
It does a poor job if the camera has to guess, but there are ways of making it work great (it requires uniform lighting and a white reference on the picture, no guessing needed then).
That is why i am including the black oxide coated nail to serve as a "true black" reference point in every image.
True black (0,0,0) is identical no matter what the white balance is so I don't see how it is going to help.
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Here is a side note: the digital cameras will alter colour depending on lighting conditions (energy spectrum of incident light).
It is not a problem with digital cameras, actually it is a problem with our sight. Cameras show reasonably accurately real colors present. We are accustomed to see them after they pass through adaptive filtering applied by our brains, so we prefer to modify the picture so that it looks as if it was taken in a daylight.
White balance is meant to compensate for it, but does poor job.
It does a poor job if the camera has to guess, but there are ways of making it work great (it requires uniform lighting and a white reference on the picture, no guessing needed then).
That is why i am including the black oxide coated nail to serve as a "true black" reference point in every image.
True black (0,0,0) is identical no matter what the white balance is so I don't see how it is going to help.
Generally i do not like to tell smart people that they are wrong, but in this case you are very wrong on many points. I have spent several years working with photography and fully calibrated work flow, here is how it actually works:
Camera uses a Bayer sensor, which is a collection of RGB cells with R, G or B filter (little prisms) on top of each pixel. Each pixel measures intensity of one of those 3 colours and the other 2 get interpolated from neighbouring pixels. This is what is called a RAW image. It has no "colours" on each pixel, just intensities of RGB. When the camera or your computer processing the raw file, creates the jpg file a particular "colour" is assigned to each pixel. This particular colour can be in one of many colour spaces (sRGB, aRGB, Lab etc) and the algorithm that generates the colours can take into account the white balance, which is an attempt to compensate for energy spectrum of incident light when picture was taken, or it can be a full fledge colour profiling using something like a colour checker passport from x-rite (yes I have one). While balance is meant to correct for energy spectrum of incident light via a colour adjustment to a true grey scene, while colour calibration also adjusts for any bias present in the sensor.
Your monitor has an RGB colour space (well close to it, many monitors can't display full RGB space), which is known as additive space, because you add all colours to make white and a printer uses CYMK or the more tone equivalent of CYMK which is known as subtractive space, because you mix CYM to make the black while you start from white paper and subtract from it to make black. Going from RGB space of the stored file to RGB space of the monitor or CYMK space of the printer is know as rendering intent and it determines what happens to colours that exist in the file, but cannot be dsplayed on the output device (screen or printer). YOu often see on expansive monitors statements like "full 10-bit RGB". This means each pixel can have 1024 levels of intensity. In comparison a consumer DSLRs have 12-bit sensors, while pro DSLRs have 14 bit sensors. So each pixel can recognize 2^12 or 2^14 unique intensity levels.
In something like photo-shop you can use tools like "curves" to try and correct for colour shifts by "selecting" a black, grey and white colours. This is why having a black nail is useful as a colour reference point since manganese phosphate itself supposed to be almost black. Of course, even if i took a picture with my x-rite colour checker in the frame and actually adjusted the colours so that the image is colour accurate on my colour calibrated monitor and actually prints colour accurately on my colour calibrated epson 3880, i have no way of predicting how it will display on your uncalibrated monitor. which is why having a black reference point in the picture is useful.
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Camera uses a Bayer sensor, which is a collection of RGB cells with R, G or B filter (little prisms) on top of each pixel. Each pixel measures intensity of one of those 3 colours and the other 2 get interpolated from neighbouring pixels. This is what is called a RAW image. It has no "colours" on each pixel, just intensities of RGB. When the camera or your computer processing the raw file, creates the jpg file a particular "colour" is assigned to each pixel. This particular colour can be in one of many colour spaces (sRGB, aRGB, Lab etc) and the algorithm that generates the colours can take into account the white balance, which is an attempt to compensate for energy spectrum of incident light when picture was taken, or it can be a full fledge colour profiling using something like a colour checker passport from x-rite (yes I have one). While balance is meant to correct for energy spectrum of incident light via a colour adjustment to a true grey scene, while colour calibration also adjusts for any bias present in the sensor.
Your monitor has an RGB colour space (well close to it, many monitors can't display full RGB space), which is known as additive space, because you add all colours to make white and a printer uses CYMK or the more tone equivalent of CYMK which is known as subtractive space, because you mix CYM to make the black while you start from white paper and subtract from it to make black. Going from RGB space of the stored file to RGB space of the monitor or CYMK space of the printer is know as rendering intent and it determines what happens to colours that exist in the file, but cannot be dsplayed on the output device (screen or printer). YOu often see on expansive monitors statements like "full 10-bit RGB". This means each pixel can have 1024 levels of intensity. In comparison a consumer DSLRs have 12-bit sensors, while pro DSLRs have 14 bit sensors. So each pixel can recognize 2^12 or 2^14 unique intensity levels.
I feel like you talk apples, I talk oranges. I don't see where any of what you wrote here contradicts what I wrote, and it seems to me like most of these things are unrelated to the problem at hand. I can agree I used rather sloppy language when talking about colors.
Have you ever used yellow goggles while skiing? World is initially yellow, but after some time the colors become "normal", exactly as you would expect them without goggles. When you take goggles off, world becomes yellowish again for some time. That's our brain compensating so that we "see" the "same" colors always. Camera measures reasonably well RGB intensities (in an "objective" way), and doesn't compensate (well, almost) so when we look at pictures even on perfectly calibrated output device they often look wrong to us, for physiological reasons - our brain takes into account ambient light and does some tricks to the observed colors. Yes, there are many fine points and details when it comes to exact conversion/calibration/color spaces - but they don't change the fact they are designed to fool our physiology.
I am taking pictures for over 40 years and I worked in desktop publishing for some time, while I don't consider myself to be an expert it is not like these things are completely alien to me.
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Camera uses a Bayer sensor, which is a collection of RGB cells with R, G or B filter (little prisms) on top of each pixel. Each pixel measures intensity of one of those 3 colours and the other 2 get interpolated from neighbouring pixels. This is what is called a RAW image. It has no "colours" on each pixel, just intensities of RGB. When the camera or your computer processing the raw file, creates the jpg file a particular "colour" is assigned to each pixel. This particular colour can be in one of many colour spaces (sRGB, aRGB, Lab etc) and the algorithm that generates the colours can take into account the white balance, which is an attempt to compensate for energy spectrum of incident light when picture was taken, or it can be a full fledge colour profiling using something like a colour checker passport from x-rite (yes I have one). While balance is meant to correct for energy spectrum of incident light via a colour adjustment to a true grey scene, while colour calibration also adjusts for any bias present in the sensor.
Your monitor has an RGB colour space (well close to it, many monitors can't display full RGB space), which is known as additive space, because you add all colours to make white and a printer uses CYMK or the more tone equivalent of CYMK which is known as subtractive space, because you mix CYM to make the black while you start from white paper and subtract from it to make black. Going from RGB space of the stored file to RGB space of the monitor or CYMK space of the printer is know as rendering intent and it determines what happens to colours that exist in the file, but cannot be dsplayed on the output device (screen or printer). YOu often see on expansive monitors statements like "full 10-bit RGB". This means each pixel can have 1024 levels of intensity. In comparison a consumer DSLRs have 12-bit sensors, while pro DSLRs have 14 bit sensors. So each pixel can recognize 2^12 or 2^14 unique intensity levels.
I feel like you talk apples, I talk oranges. I don't see where any of what you wrote here contradicts what I wrote, and it seems to me like most of these things are unrelated to the problem at hand. I can agree I used rather sloppy language when talking about colors.
Have you ever used yellow goggles while skiing? World is initially yellow, but after some time the colors become "normal", exactly as you would expect them without goggles. When you take goggles off, world becomes yellowish again for some time. That's our brain compensating so that we "see" the "same" colors always. Camera measures reasonably well RGB intensities (in an "objective" way), and doesn't compensate (well, almost) so when we look at pictures even on perfectly calibrated output device they often look wrong to us, for physiological reasons - our brain takes into account ambient light and does some tricks to the observed colors. Yes, there are many fine points and details when it comes to exact conversion/calibration/color spaces - but they don't change the fact they are designed to fool our physiology.
I am taking pictures for over 40 years and I worked in desktop publishing for some time, while I don't consider myself to be an expert it is not like these things are completely alien to me.
Thanks for clarification of your experience. This information however does not provide any means for colour accuracy without a reference point. A hot caustic blued nail is a true black colour, and even if it looks yellow on someone’s monitor, they know that is what true black is. Hence they can determine how close to true black the phosphated objects are. Its a reference point nothing more. A reference point is needed because unless I want to teleport to every visitors of this page house and colour calibrate their monitor, they have no means of knowing how close to black the Mn phosphated objects are.
Furthermore, most of what you wrote about mind tricks is irrelevant. Is the dress white and gold or purple and black? https://www.nytimes.com/interactive/2015/02/28/science/white-or-blue-dress.html
This is mind tricks and that rabbit hole is waaaaaaay deeeper than anything i want to get into. Objectively, the best we can home for is colour accuracy, not how people interpret colours. And giving people a true black reference point is the simplest way i can think of to have some amount of colour accuracy across the internets.
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Few pictures from things i covered with phosphate coating( few weeks ago). Small stuff is hardened steel that i hardened myself.
https://imgur.com/a/829nOY2
https://imgur.com/a8MLLa2
https://imgur.com/WwkEf9W
Areas that are not black are not uncoated. Imo it's coated with iron phosphate. I've been unable to figure out why and how to improve it. Atm i don't have much time to play with experiments, maybe in few weeks.
If you have any breakthrough let us know.
To clarify my previous post regarding photo vs real life. It's just that imo best visual about coating is when you took it out of phosphating solution and it's still vet, then defects are best seen. If it has dried it lookes more pleasing to eye (but defects are still there). But what i noticed is that lot of pictures part looks lot better when in actual real life inspection. Maybe it's because of 3d (real life) vs 2d (photo) or angles etc.
Pcm81 i assume you have also done caustic black? Can you share your recipe and process?
I've used Potassium hydroxide (KOH) 1200 g/l + potassium nitrate (KNO3) 250 g/l. Boiling @140c +-3c. Recipe from http://www.substech.com/dokuwiki/doku.php?id=black_oxide_coating
Works more less OK, but what i've noticed is that solution "dies" quickly. It would be good to know what happens in chemical level and how to prolong solutions life.
What iv'e found is that adding fresh water (to reduce boiling temp as water evaporates) kills solution. https://patentimages.storage.googleapis.com/e3/7d/84/c3070be986057c/US2148331.pdf
It writes also that instead of adding pure water when 10% alkaline + nititre solution is added instead solution won't die quickly. I haven't tried it myself.
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Pcm81 i assume you have also done caustic black? Can you share your recipe and process?
I've used Potassium hydroxide (KOH) 1200 g/l + potassium nitrate (KNO3) 250 g/l. Boiling @140c +-3c. Recipe from http://www.substech.com/dokuwiki/doku.php?id=black_oxide_coating
Works more less OK, but what i've noticed is that solution "dies" quickly. It would be good to know what happens in chemical level and how to prolong solutions life.
What iv'e found is that adding fresh water (to reduce boiling temp as water evaporates) kills solution. https://patentimages.storage.googleapis.com/e3/7d/84/c3070be986057c/US2148331.pdf
It writes also that instead of adding pure water when 10% alkaline + nititre solution is added instead solution won't die quickly. I haven't tried it myself.
I am using 5lb sodium hydroxide plus 2lb sodium nitrate per gallon of water solution. The key parameter for caustic black is the temperature. What I understood is that solution has to be boiling and the best results i got were in temperature range of 270 to 290 degrees F. Higher temperature will deposit more haematite than magnetite. At 315f you are mostly depositing haematite. I've added plenty of fresh water to control the boiling point and it did not kill the solution.