Tacho
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pH indicator for portland cement.
I mixed phenolphtalein with a white portland cement mortar to study its pH. However, as the cement sets (about 2 hours) the mix, initially very pink,
turns almost white.
What is going on? The cement mix surely is very alkaline. Why the phenolphtalein loses it's indicator properties?
I'm studying a way to neutralize the mortar to use it with fiberglass reinforcement. I was planning to difuse phosphoric acid through the matrix. How
does that sound?
Any sugestions of books, articles, other indicators or ways to neutralize the cement are welcome.
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The_deadly_dustbin
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| Quote: | Originally posted by Tacho
I mixed phenolphtalein with a white portland cement mortar to study its pH. However, as the cement sets (about 2 hours) the mix, initially very pink,
turns almost white.
What is going on? The cement mix surely is very alkaline. Why the phenolphtalein loses it's indicator properties?
I'm studying a way to neutralize the mortar to use it with fiberglass reinforcement. I was planning to difuse phosphoric acid through the matrix. How
does that sound?
Any sugestions of books, articles, other indicators or ways to neutralize the cement are welcome. |
Good ídea but there was a lot of work done in the late 80s and beginning 90s by the big companies (at least in Europe) like LaFarge and Heidelberger
to do just that. The problem is that if you neutralize the concrete you throw off the whole chemistry of the hydrated phases like C2S and C2A
(concrete lingo for Calciumsilicate and Calciumaluminate) and the mix won't set anymore.
The only way out they found was to use different glass composition like high-zirkonia/alumina glasses that do not get seriously attacked by the
alkaline conditions.
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unionised
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In very alkaline conditions phenolphthalein loses another proton to give a doubly charged ion that is colourless.
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guy
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| Quote: | Originally posted by unionised
In very alkaline conditions phenolphthalein loses another proton to give a doubly charged ion that is colourless. |
Actually it needs to lose 2 protons to become colored. Adding excess base causes a nucleophilic attact destroying the resonance.
http://instruct.uwo.ca/chemistry/223b-98/colours.htm
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Tacho
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Thanks unionized, you were right on the spot. I did not know about this characteristic of phenolphthatein.
Since thymolphthalein is too expensive, I'll try to use red cabbage juice as an indicator. Red grape juice works( green=alkaline, violet=acid), but
the sugar prevents the setting of the cement. I guess we are going to have cabbage soup tonight.
dustbin: I am aware of the problems, but I have been reading a few patents who claim it can be done and I will try a solution that suits my special
needs.
[Edited on 26-9-2006 by Tacho]
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The_deadly_dustbin
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With the same mechanical properties? I do not say it can't be done, but I'd be interested to take a look at the patents. Could you be so kind to
provide me with a link??
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Tacho
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I will have to find out myself about mechanical properties.
Sorry not to link each patent individually, but I'm sure you won't mind cuting and pasting a few numbers.
http://patft.uspto.gov/netahtml/PTO/srchnum.htm
Some patents (US 5.690.729, 5.650.562, 5.518.540) claim that using CO2, dense-phase CO2 or supercritical CO2 (!) diffusion does the job reacting with
the calcium hydroxide generated by setting. This carbonation also happens naturally and is a problem to reinforced concrete because the higher pH
leaves the steel rebars unprotected against corrosion. I have some samples under CO2 and some under carbonated water.
Patent US 4.115.135 claim that some barium, zinc or lithium soluble salts would protect common glass. I tried zinc acetate and it certainly slows
down the setting. The strength is probably lower too. Many patents claim that zinc salts protect glass against alkalis in the bottle-washing industry.
Pat. US. 4.090.884 mentions a “scavenger” that would protect the glass fibers in the cement by “reacting first”.
I thought of phosphoric acid as a neutralizer because it usually produces insoluble salts or even some cements. ZnO+H3PO4 is a well known dental
cement. H3PO3 + lime makes a solid mass, not very hard, but solid anyway.
Phosphoric acid does not seem to lower the mortar resistance substantially if diffused after setting, but I can only check it’s diffusion with an
indicator. Hence this thread.
Since phosphoric acid is more expensive to me than polyester resin, I am willing to pay more for a less resistant material that is not commercially
viable, but will suit my special needs. The idea is a laminated shell with many thin fiberglass/cement layers. Each layer has to be neutralized,
adding labor and increasing costs. Not something LaFarge would consider.
[Edited on 26-9-2006 by Tacho]
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unionised
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"Actually it needs to lose 2 protons to become colored"
Bollocks!
Fermentation will remove the sugar from cabbage juice- then you need to dry the stuff to get rid of the alcohol
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guy
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| Quote: | Originally posted by unionised
"Actually it needs to lose 2 protons to become colored"
Bollocks!
Fermentation will remove the sugar from cabbage juice- then you need to dry the stuff to get rid of the alcohol |
Cabbage juice doesn't contain phenophthalein.
http://en.wikipedia.org/wiki/Phenolphthalein
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unionised
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So?
I'ts not as if anyone said it did.
Your assertion was still bollocks and that trick to get a low sugar indicator still works.
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The_deadly_dustbin
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| Quote: | Originally posted by Tacho
I will have to find out myself about mechanical properties.
Some patents (US 5.690.729, 5.650.562, 5.518.540) claim that using CO2, dense-phase CO2 or supercritical CO2 (!) diffusion does the job reacting with
the calcium hydroxide generated by setting. This carbonation also happens naturally and is a problem to reinforced concrete because the higher pH
leaves the steel rebars unprotected against corrosion. I have some samples under CO2 and some under carbonated water.
I thought of phosphoric acid as a neutralizer because it usually produces insoluble salts or even some cements. ZnO+H3PO4 is a well known dental
cement. H3PO3 + lime makes a solid mass, not very hard, but solid anyway.
Phosphoric acid does not seem to lower the mortar resistance substantially if diffused after setting, but I can only check it’s diffusion with an
indicator. Hence this thread.
Since phosphoric acid is more expensive to me than polyester resin, I am willing to pay more for a less resistant material that is not commercially
viable, but will suit my special needs. The idea is a laminated shell with many thin fiberglass/cement layers. Each layer has to be neutralized,
adding labor and increasing costs. Not something LaFarge would consider.
[Edited on 26-9-2006 by Tacho] |
Thanks for the links.......
Interesting stuff with the CO2 but nothing someone would do easily in the home-lab (especially supercritical)
If you do not use the concrete for construction the phosphoric acid might be the way to go. Another thing to consider is to go for high alumina
specialty concrete compositions. Might get some samples for cheapo from e.g. LaFarge. Another thing you might wanna try is to get rovings from a
supplier for the plastics industry. Those fibers are coated with some polymer to increase the adhesion between glass and e.g. PA This coating might
also help to slow down the alkaline attack on the glass
[Edited on 27-9-2006 by The_deadly_dustbin]
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Tacho
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Yesterday I made red cabbage inidicator for the first time. I was pleasantly surprised by it! Quick to make, cheap and accurate. I could easily tell 4
different colors depending on pH. With some practice one could tell pH changes within a couple of units.
But the cement mixed with it doesn't seem to be setting. Maybe something from the cabbage or the flavonoids themselves. Probably sugars.
unionized: Fermenting it souds too messy. I read your flavonoid extraction thread anb I think I'll try to extract the flavonoids with acetone or IPA
from a MgSO4 or CaCl2 saturated solution, if I can get a 2 phase system. Did you try that?
Edit:
Or maybe ethanol and ammonium sulphate, check this link:
http://www.ajevonline.org/cgi/content/abstract/12/1/1
Access to the full article would be useful. Anyone?
[Edited on 27-9-2006 by Tacho]
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unionised
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The paper on ethanol/ ammonium sulphate looks interesting and my best guess is that it would work for this indicator.
I got the idea for the fermentation from a reference that used beetroot as the dyestuff but I can't see why it wouldnt work. I agree it's messy and a
bit slow.
You might want to look at flowers as a source of indicators- they tend to have relatively low sugar contents. Extraction with ethanol or acetone shoud
work.
All of this is interesting enough but I think you will still have difficulty getting cement anywhere near neutral without seriously changing its
properties.
I know it's not very strong, but did you consider plaster of Paris rather than cement?
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pantone159
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| Quote: | Originally posted by Tacho
Yesterday I made red cabbage inidicator for the first time. I was pleasantly surprised by it! Quick to make, cheap and accurate. I could easily tell 4
different colors depending on pH. With some practice one could tell pH changes within a couple of units.
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I also like red cabbage, cuz I'm a fan of bright colors. I notice, however, that the basic colors are not very stable. Meaning, I add some indicator
to a solution around pH 8-9, and it will turn one color (say blue) but in a few minutes this changes to e.g. green. (I forget the details.)
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Tacho
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Extraction of flavonoids with acetone or IPA from a solution saturated (or almost saturated) with MgSO4 or Ammonium Sulfate works very well. Both
solvents bring most of the pigments to their organic layer with a single small portion, leaving an almost clear water layer behind.
Ammonium Sulfate has the extra advantage of precipitating some impurities, probably proteins.
Calcium chloride did NOT work for me.
Have to test on cement now...
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