Difference between pH and TBN
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In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
I dunno how one measures the pH of oil (as in "official" method) but I'd think you could get an idea by wetting indicator paper and then sticking it in an oil sample. I've never tried this but I'd expect the pH of the water phase to be altered by acids/bases diffusing from the oil phase, though some acid/base groups will remain oil bound, so it might not be a very accurate proxy for the oil's effective pH.
TBN is a measure of the remaining buffering capacity of the oil (its resistance to becoming acid) and will be determined by titration. I think I've seen a modified version of the "official" (ASTMS?) method in the online Machinery Lubrication magazine. Seemed within DIY scope, if one was sufficiently interested.
I dunno how one measures the pH of oil (as in "official" method) but I'd think you could get an idea by wetting indicator paper and then sticking it in an oil sample. I've never tried this but I'd expect the pH of the water phase to be altered by acids/bases diffusing from the oil phase, though some acid/base groups will remain oil bound, so it might not be a very accurate proxy for the oil's effective pH.
TBN is a measure of the remaining buffering capacity of the oil (its resistance to becoming acid) and will be determined by titration. I think I've seen a modified version of the "official" (ASTMS?) method in the online Machinery Lubrication magazine. Seemed within DIY scope, if one was sufficiently interested.
TBN is base number which means how much "stuff" is left to cancel out acid created in engine . acids can eat metals so the more of this , the less likely of having acid form in high concentration.
pH is how acidic ( or basic ) something is , theoretically the higher the TBN the lower the pH.
As TBN drops pH increases making the oil solution more acidic.
pH is how acidic ( or basic ) something is , theoretically the higher the TBN the lower the pH.
As TBN drops pH increases making the oil solution more acidic.
If you start with more buffering, like in a very heavy duty diesel oil, there'll be more of a spread. So a TBN of, say, 7 will be nearly used up vs brand new on a mediocre light duty passenger car oil.
Was reading about a specialty oil with TBN of, IIRC, 40, meant for high sulfur diesel fuel.
This site nerds it up with people trying to run the TBN down to 1 or 2 to get the most from their money. And worried b/c some oils drop quickly past that point while others hold steady.
Was reading about a specialty oil with TBN of, IIRC, 40, meant for high sulfur diesel fuel.
This site nerds it up with people trying to run the TBN down to 1 or 2 to get the most from their money. And worried b/c some oils drop quickly past that point while others hold steady.
Originally Posted By: Voltmaster
pH is how acidic ( or basic ) something is , theoretically the higher the TBN the lower the pH.
As TBN drops pH increases making the oil solution more acidic.
That's exactly what I was thinking. A new oil should have a high pH, which should become lower as acid cancelling additives are depleted. All this process should be very easily metered with a pH meter or just pH measuring strips.
Unless, of course, I am missing something, hence the initial question.
pH is how acidic ( or basic ) something is , theoretically the higher the TBN the lower the pH.
As TBN drops pH increases making the oil solution more acidic.
That's exactly what I was thinking. A new oil should have a high pH, which should become lower as acid cancelling additives are depleted. All this process should be very easily metered with a pH meter or just pH measuring strips.
Unless, of course, I am missing something, hence the initial question.
Found the article in Machinery Lubrication
http://www.machinerylubrication.com/Read/100/ph-test-tan-tbn
http://www.machinerylubrication.com/Read/100/ph-test-tan-tbn
Originally Posted By: Ducked
In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
Since motor oil doesn't contain water, it has no pH value.
In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
Since motor oil doesn't contain water, it has no pH value.
Originally Posted By: Gabe
Originally Posted By: Ducked
In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
Since motor oil doesn't contain water, it has no pH value.
That's why the article says that oil is dissolved in a special mixture that also contains water. The pH is read after that.
Originally Posted By: Ducked
In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
Since motor oil doesn't contain water, it has no pH value.
That's why the article says that oil is dissolved in a special mixture that also contains water. The pH is read after that.
Gabe is correct, it is difficult and mostly meaningless to measure pH in a nonaqueous mixture. There are nonaqueous pH probes and I have used them, but the consensus is that all you are measuring is the ionic concentration in the small amount of water present in the sample. Besides, even if you would get a reading what do you compare it against?
Originally Posted By: alexeft
Originally Posted By: Gabe
Originally Posted By: Ducked
In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
Since motor oil doesn't contain water, it has no pH value.
That's why the article says that oil is dissolved in a special mixture that also contains water. The pH is read after that.
Originally Posted By: alexeft
Originally Posted By: Gabe
Originally Posted By: Ducked
In principle (from my hazy memory of school physics) pH is the negative log of the hydrogen ion concentration, and is measured with a pH meter, or an indicator dye, perhaps on a paper carrier, as in litmus or universal indicator paper.
Since motor oil doesn't contain water, it has no pH value.
That's why the article says that oil is dissolved in a special mixture that also contains water. The pH is read after that.
Originally Posted By: alexeft
Found the article in Machinery Lubrication
http://www.machinerylubrication.com/Read/100/ph-test-tan-tbn
Very interesting article.
I was hoping for graphs showing measured pH vs. TAN & TBN for various samples.
Found the article in Machinery Lubrication
http://www.machinerylubrication.com/Read/100/ph-test-tan-tbn
Very interesting article.
I was hoping for graphs showing measured pH vs. TAN & TBN for various samples.
To answer you both, and as the article says, I would condemn the oil when I saw pH drop faster than usual, which would mean that reserve alkalinity is depleted and/or that there other factors introducing acids in the oil at a pace faster than usual.
The above requires regular testing and recording of the results.
The article also states some pH condemnation limits.
The above requires regular testing and recording of the results.
The article also states some pH condemnation limits.
Originally Posted By: alexeft
Originally Posted By: Voltmaster
pH is how acidic ( or basic ) something is , theoretically the higher the TBN the lower the pH.
As TBN drops pH increases making the oil solution more acidic.
That's exactly what I was thinking. A new oil should have a high pH, which should become lower as acid cancelling additives are depleted. All this process should be very easily metered with a pH meter or just pH measuring strips.
Unless, of course, I am missing something, hence the initial question.
I doubt that its quite as simple as that, and if it was "As TBN drops pH increases making the oil solution more acidic." would be exactly wrong, since an acid solution has a low pH, it being a negative scale.
IIRC, in general “wet chemistry” (which, as has been pointed out, isn’t exactly what we are discussing here), pH does not initially change much as you add acid to a base, until you get close to the equivalence point, where most of the base is neutralized by the acid. This is even more true where acid is being added to a buffer solution, which I’d think would be analogous to the situation with motor oil.
I should perhaps have made it clearer that using wet indicator paper was my speculative suggestion, and I havn’t seen or heard any industry endorsement of it. My rationale would be that changes in the wet paper might be analogous to what happens in the water-phase of water-contaminated oil (which I’d guess is relevant for machinery corrosion), and I’m assuming that the separate water phase would prevent oil infiltration into the paper (which might interfere with “wet chemistry” colour development and visualization) but I’m also assuming that the diffusion path is short enough for the water in the paper to equilibrate with oil-bourne but water soluable acids/bases in the oil on a practical timescale.
“Official” TBN and TAN methods use isopropyl alcohol as a “bridging solvent”, in an effort to apply traditional “wet chemistry” titration methods to oil analysis, so that’s a different approach. The Machinery Lubrication article I mentioned (but didn’t have time to cite) “Total Acid Number Titration Method” (it covers TBN as well) gives a detailed description of a (modified) titration method, but doesn’t say much about the significance of the results.
http://www.machinerylubrication.com/Read/4/tan-titrations
This article “Optimizing Drain Intervals Using TBN vs. TAN” http://www.machinerylubrication.com/Read/2170/oil-drain-interval-tan-tbn
shows a graph depicting the relationship between them. It has some puzzling features (that “clear wedge” with no TAN points, for example) and apparently the authors never been told to label his X-axis, (tsk tsk!) but the basic inverse relationship is pretty much what you’d expect.
This article A Comprehensive Look At the Acid Number Test goes a bit further into the significance of the acid number and additive depletion.
http://www.machinerylubrication.com/Read/1052/acid-number-test
This author has apparently never been told to label his X-axis and he hasn’t been told not to use locally undefined acronyms either.(RUL stands for Remaining Useful Life, apparently, which I suppose his specialist audience would know.) but he does explain some differences between AN and pH.
Beyond that, the picture is rather complex, and perhaps the main take-home message is that accuracy and reproducibility are low, and results from different laboratories can’t be reliably compared.
Originally Posted By: Voltmaster
pH is how acidic ( or basic ) something is , theoretically the higher the TBN the lower the pH.
As TBN drops pH increases making the oil solution more acidic.
That's exactly what I was thinking. A new oil should have a high pH, which should become lower as acid cancelling additives are depleted. All this process should be very easily metered with a pH meter or just pH measuring strips.
Unless, of course, I am missing something, hence the initial question.
I doubt that its quite as simple as that, and if it was "As TBN drops pH increases making the oil solution more acidic." would be exactly wrong, since an acid solution has a low pH, it being a negative scale.
IIRC, in general “wet chemistry” (which, as has been pointed out, isn’t exactly what we are discussing here), pH does not initially change much as you add acid to a base, until you get close to the equivalence point, where most of the base is neutralized by the acid. This is even more true where acid is being added to a buffer solution, which I’d think would be analogous to the situation with motor oil.
I should perhaps have made it clearer that using wet indicator paper was my speculative suggestion, and I havn’t seen or heard any industry endorsement of it. My rationale would be that changes in the wet paper might be analogous to what happens in the water-phase of water-contaminated oil (which I’d guess is relevant for machinery corrosion), and I’m assuming that the separate water phase would prevent oil infiltration into the paper (which might interfere with “wet chemistry” colour development and visualization) but I’m also assuming that the diffusion path is short enough for the water in the paper to equilibrate with oil-bourne but water soluable acids/bases in the oil on a practical timescale.
“Official” TBN and TAN methods use isopropyl alcohol as a “bridging solvent”, in an effort to apply traditional “wet chemistry” titration methods to oil analysis, so that’s a different approach. The Machinery Lubrication article I mentioned (but didn’t have time to cite) “Total Acid Number Titration Method” (it covers TBN as well) gives a detailed description of a (modified) titration method, but doesn’t say much about the significance of the results.
http://www.machinerylubrication.com/Read/4/tan-titrations
This article “Optimizing Drain Intervals Using TBN vs. TAN” http://www.machinerylubrication.com/Read/2170/oil-drain-interval-tan-tbn
shows a graph depicting the relationship between them. It has some puzzling features (that “clear wedge” with no TAN points, for example) and apparently the authors never been told to label his X-axis, (tsk tsk!) but the basic inverse relationship is pretty much what you’d expect.
This article A Comprehensive Look At the Acid Number Test goes a bit further into the significance of the acid number and additive depletion.
http://www.machinerylubrication.com/Read/1052/acid-number-test
This author has apparently never been told to label his X-axis and he hasn’t been told not to use locally undefined acronyms either.(RUL stands for Remaining Useful Life, apparently, which I suppose his specialist audience would know.) but he does explain some differences between AN and pH.
Beyond that, the picture is rather complex, and perhaps the main take-home message is that accuracy and reproducibility are low, and results from different laboratories can’t be reliably compared.
Normally, when people think of stuff, they think that if they need to make something that is +2 become equal to zero, you need to add a -2...brain easy.
An example of why pH and the ability to resist acid is when we did a fish pond last spring.
Filled the tank with rainwater, and had the children there with a pH test kit, some acetic acid, and some bicarbonate. Trying to bring the bicarbonate/carbonate up to something useful.
A few drops of vinegar, in clean water, and the pH dropped quickly, and a lot. A few grains of bicarbonate and it rose quickly and a lot.
After adding more of each, and still reading 7, a few drops of either made not much difference at all.
The wildly swinging pH was acid/base, and levels of acisity.
The end result was water that could take a fair hit of either acid or base without changing pH to a great degree...
TBN is a bit like that. The ability to absorb acids, without becoming "acidic".
An example of why pH and the ability to resist acid is when we did a fish pond last spring.
Filled the tank with rainwater, and had the children there with a pH test kit, some acetic acid, and some bicarbonate. Trying to bring the bicarbonate/carbonate up to something useful.
A few drops of vinegar, in clean water, and the pH dropped quickly, and a lot. A few grains of bicarbonate and it rose quickly and a lot.
After adding more of each, and still reading 7, a few drops of either made not much difference at all.
The wildly swinging pH was acid/base, and levels of acisity.
The end result was water that could take a fair hit of either acid or base without changing pH to a great degree...
TBN is a bit like that. The ability to absorb acids, without becoming "acidic".
Thanks to all for your answers.
I think a viable practice could be to monitor the pH of oil solved in a solution of isopropyl alcohol, toluene and water (thus adding the necessary water to have a pH measurement).
One could start from brand new oil and graph the results. When pH rate of change increases dramatically, it would be time to change the oil, assuming that its other quality aspects are within limits.
To take the pH measurements, pH strips would be inaccurate, whereas a cheap pH meter could be enough.
I intend to try it. I will post the results.
I think a viable practice could be to monitor the pH of oil solved in a solution of isopropyl alcohol, toluene and water (thus adding the necessary water to have a pH measurement).
One could start from brand new oil and graph the results. When pH rate of change increases dramatically, it would be time to change the oil, assuming that its other quality aspects are within limits.
To take the pH measurements, pH strips would be inaccurate, whereas a cheap pH meter could be enough.
I intend to try it. I will post the results.
Last edited:
Originally Posted By: alexeft
Thanks to all for your answers.
I think a viable practice could be to monitor the pH of oil solved in a solution of isopropyl alcohol, toluene and water (thus adding the necessary water to have a pH measurement).
One could start from brand new oil and graph the results. When pH rate of change increases dramatically, it would be time to change the oil, assuming that its other quality aspects are within limits.
To take the pH measurements, pH strips would be inaccurate, whereas a cheap pH meter could be enough.
I intend to try it. I will post the results.
If you try it, then I'd say it MIGHT be of value if you also tested universal indicator paper, both against the semi-aqueous pH-reading cocktail, and wet, tested against oil in the manner I suggest above.
Various ranges of universal indicator paper are available. They MAY be less accurate than a pH meter (without trying it its rather difficult to say) but they may be accurate enough for a condemnation limit, which is all that is required.
Very cheap digital pH meters are available. They may be OK, dunno, but the cost of the reagents and the volume of sample required might still give indicator paper a practical edge.
Thanks to all for your answers.
I think a viable practice could be to monitor the pH of oil solved in a solution of isopropyl alcohol, toluene and water (thus adding the necessary water to have a pH measurement).
One could start from brand new oil and graph the results. When pH rate of change increases dramatically, it would be time to change the oil, assuming that its other quality aspects are within limits.
To take the pH measurements, pH strips would be inaccurate, whereas a cheap pH meter could be enough.
I intend to try it. I will post the results.
If you try it, then I'd say it MIGHT be of value if you also tested universal indicator paper, both against the semi-aqueous pH-reading cocktail, and wet, tested against oil in the manner I suggest above.
Various ranges of universal indicator paper are available. They MAY be less accurate than a pH meter (without trying it its rather difficult to say) but they may be accurate enough for a condemnation limit, which is all that is required.
Very cheap digital pH meters are available. They may be OK, dunno, but the cost of the reagents and the volume of sample required might still give indicator paper a practical edge.
I already bought a pH meter, this one http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190863408370
It already contains plenty of calibrating solutions, so, no problem there. It also automatically compensates for temperature differences, which would have to be done by hand in the case of strips.
I found these strips http://www.amazon.com/dp/B0007RSD0A
They also have an accuracy of +- 0.2, same as the pH meter above. Not much of an issue there really.
It already contains plenty of calibrating solutions, so, no problem there. It also automatically compensates for temperature differences, which would have to be done by hand in the case of strips.
I found these strips http://www.amazon.com/dp/B0007RSD0A
They also have an accuracy of +- 0.2, same as the pH meter above. Not much of an issue there really.
pH and TAN (Total Acid Number) are both used as indicators of the amount of acid in an lubricant.
As oils break down - acids are produced. The simple, and common, way to measure this in the industry is to determine the total acid number - following ASTM D664-2011a. The rule of thumb is that once your TAN goes above the 2-3 mark, the fluid needs to be replaced.
Basically - your take your used oil and put some Phenolphthalein in it as your marker. You then titrate KOH into the oil until it's neutral. If you have a gram of oil your testing and you had to put a milligram of KOH into it to neutralize it - your oil has a TAN of 1.0.
TBN is another way of classifying the TAN.
As oils break down - acids are produced. The simple, and common, way to measure this in the industry is to determine the total acid number - following ASTM D664-2011a. The rule of thumb is that once your TAN goes above the 2-3 mark, the fluid needs to be replaced.
Basically - your take your used oil and put some Phenolphthalein in it as your marker. You then titrate KOH into the oil until it's neutral. If you have a gram of oil your testing and you had to put a milligram of KOH into it to neutralize it - your oil has a TAN of 1.0.
TBN is another way of classifying the TAN.
Are you saying that rule of thumb is change oil after TAN increases 2-3x the original/clean value? Or, do you mean after TAN increases to a numerical value above 2-3? There is a big difference since many oils start out clean with a TAN above 2-3 numerically.
I personally like to use 2x TAN from original value. Not that that is a harmful scenario...just that TBN is no longer effective at controlling acids, no matter what the TBN number is.
I personally like to use 2x TAN from original value. Not that that is a harmful scenario...just that TBN is no longer effective at controlling acids, no matter what the TBN number is.
It can vary from lubricant to lubricant. the 2x original TAN value can also be used, especially if you are starting w/ a fluid w/ a virgin TAN above 2.0. Most of what I deal with starts in the .1 range, so a TAN of 2.0 is time to recommend my user to switch it out. Acids can be bad news in some systems if they are uncontrolled.
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