Any Chemists here?

[pwd72s]

This morn's paper gave the names of ingrediants in a non salt spray used on Oregon road surfaces during frozen spells: "Calcium Magnesium Acetate" and Portland also uses "Magnesium Chloride". No salt used on Oregon roads for envrionmental reasons. Concerns about fish habitat and roadside vegetation. My question: Are the above chemicals corrosive to cars? If so, how would they compare to salt in corrosion ability? For those in Washington state, be warned. The article also says: "Washington State, which also doesn't use salt, is experimenting with brine-a combination of salt and water..."

[Zeke]

Originally posted by pwd72s
"Washington State, which also doesn't use salt, is experimenting with brine-a combination of salt and water..."

Intelligent, eh?

[thabaer]

Heard on the radio just this morning that the Denver region public transportation dept are having to retire vehicles because of excessive corrosion caused by magnesium chloride.

Just did a quick look at some Colo. DOT sites and they cited multiple studies and reports on the various compounds, of course there were no links to the content of those reports They did show multple flavors of de-icers:

– Magnesium chloride (used above 16 degrees pavement temperature)
– Cold temperature magnesium chloride (used below 16 degrees pavement temperature) – Includes a corn bi-product to lower the freezing point

What it definitely DOES do is reduce traction on both the snow it is sprayed over as well as the clear pavement. Be careful if your area starts using it, you'll find yourself slipping on it days after the snow is gone.

[arcsine]

In a previous life I was a chemist so I may be of some help. My understanding is that corrosion is a manifestaion of oxidation/reduction (redox) reactions between elemental iron (Fe) in the car body and chloride (Cl) in salt eventually creating iron oxides which we call rust. Calcium Magnesum Acetate I would not be too concerned about as none of the elements has a particularly high redox potential. But Magnesium Chloride I do not imagine would have any less of a corrosive effect than Sodium Chloride.

[masraum]

I have a question, isn't Magnesium Chloride a salt? Maybe not THE salt, but a salt? I hated chemistry.

[Jerome Ryals]

Magnesium chloride is the source of magnesium metal, also used in the manufacture of paper, common road dust-laying compounds and floor sweeping compounds as well. It is precipitated from seawater or brines, yes it is salt and would have basically the same effect as THE salt.

[banjomike]

don't know about calsium magnesium acetate, but while magnesium chloride is not Table Salt (NaCl) it is a salt.

Rust is the result of a chemical reaction. And the reaction works much better in the presence of water (snow) with lots of electrolytes (salts). It doesn't really matter if the water has NaCl or MgCl, they both serve the same purpose. Both NaCl and MgCl when dissolved in water, dissasociate into ions Na+ and Cl- or Mg+ and Cl- (I may thave the +- backwards) so the same about of Salt and this magnesium salt will likely have roughly the same effect on your car.

just my $0.02


oh then I went and googled and found this

http://www.peterschemical.com/Calcium%20Magnesium%20Acetate.htm

seems that CMA is a corrosion inhibitor when used with salt for de-icing...

[anh911]

um, this might be a stupid question but isn't magnesium extremely dangerous if exposed to combustion, i.e, fire?

[jpnovak]

Yes NaCl is table salt. Yes, MgCl(2) is a salt. Many places use it since it gives more bang for the buck. Freezing point depression is a factor of the number of ions in a solution. Each NaCl molecule will yeild 2 ions (Na+) and (Cl-). [you were correct Mike]. Each MgCl2 molecule yields 3 ions. (Mg 2+) and 2 (Cl-). They will both rust your car.

Rust happens in the presence of oxygen. Electrons are "stolen" from iron metal (Fe is oxidized) to reduce oxygen to form water. This process occurs faster in the presence of water and especially salts. The salt and water provide a pathway for electrons to be transferred from Fe to O2.

All of these salts will likely rust out the car. The chloride salts will do it much faster. The CMA salts may do an effective job of corrosion protection. Ca and Mg will oxidize much easier than Fe. The difference is the lack of Cl ions. The Cl has a much different and less favorable electrode potential than an acetate salt.

Now the question is... Would you subject that nice 72S to the white stuff on the road without knowing which salt is truly is?

[ischmitz]

All the stuff you guy are talking about are salts. Table salt is NaCl as mentioned earlier with is the salt of HCl (chloric acid and sodium). But any other anion can form salts as well such as SO4(2-) (sulfates) NO3(1-) (nitrates). Some are more soluble(Cl, SO4, NO3) other less (some carbonates, sufides).

As soon as water and soluble salts come into contact the conductivity of water increases dramatically allowing redox reactions such as corrosion to take place. The corrosion of metal is when iron get oxidized to Fe2+ or Fe3+ in the presence of oxygen or other oxidizers that in the process get reduced O2 -> O (2-)

Ingo

[HarryD]

Originally posted by pwd72s
This morn's paper gave the names of ingrediants in a non salt spray used on Oregon road surfaces during frozen spells: "Calcium Magnesium Acetate" and Portland also uses "Magnesium Chloride". No salt used on Oregon roads for envrionmental reasons. Concerns about fish habitat and roadside vegetation. My question: Are the above chemicals corrosive to cars? If so, how would they compare to salt in corrosion ability? For those in Washington state, be warned. The article also says: "Washington State, which also doesn't use salt, is experimenting with brine-a combination of salt and water..."

Paul,

My chmistry is a bit rusty ( ), but the magnesium stuff (as others noted) is a salt and since it is the chloride that does the damage, you should be careful.

The other stuff is acetic acid nuetralized with tums and phillips MOM (errr.. calcium and magnesium ). If the water used to wash the stuff off the roads has an acid pH (less than 6, and rain is slightly acidic by the way), you will have your metal attacked by a weak acid and you can watch your metal disappear.

Personally, my '73 will be in the garage until after a few good rains when this snow/ice removal stuff passes.

Regards.

[JTO]

Chemist here,

Hi Paul. A couple of the posters hit it on the head regarding oxidation and how its facilitated by anions and cations. The thing about Cl-, like Harry said, it is excellent at promoting corrosion to to its ability to move a negative charge.

Troy

[arcsine]

Originally posted by anh911
um, this might be a stupid question but isn't magnesium extremely dangerous if exposed to combustion, i.e, fire?

Elemental or solid metal magnesium burns (oxidizes) very well but cationic magnesium (Mg2+) will not.

[Randy Webb]

"roughly the same effect on your car"

The dissociation constants will differ, so the rust promoting effect will not be the same. How rough? I dunno. Maybe you shold write an inquiry letter to ODOT. Also, I wonder what it does to fish? For listed fish species (listed under the ESA), ODOT should have consulted with the feds. on the effects.

We could just go back to using volcanic grit -- won't cause rust, but does a great job at abrading paint.

[arcsine]

I was under the impression that ionic compounds such as NaCl and MgCl2 would dissociate completely in an aqueous environment. Where is that Merck index when you need it?

[arcsine]

Solubilities:
NaCl 35.7g/100ml cold water
MgCl2 54g/100 ml cold water

Not only do they both completely disssociate but MgCl2 is more soluble in water and as it contains two chloride molecules, each dissociation will release twice as much Cl- as the NaCl would. Oh boy.

[nostatic]

http://www.peterschemical.com/Magnesium%20Chloride.htm

http://www.peterschemical.com/Calcium%20Magnesium%20Acetate.htm

Ksp should be fairly large for both these (can't find them in Zumdahl, and I don't have my CRC in my office), meaning they dissolve completely. You get Ca2+, Mg2+, Cl- and OAc- (acetate, the conjugate base of acetic acid).

What you're worried about is redox potential of the ions.

Fe -> Fe2+ + 2e- E= 0.44V


meaning it is spontaneous (ie downhill...releases energy). But you need something to take up the electrons, otherwise the reaction slows (Le Chatlier's principle). So with water:

O2 + 2H2O + 4e- -> 4OH- E=0.40V

So this is downhill by 0.84V

Cl- helps things becuase it forms a stable complex with Fe3+ ions (that can form when Fe2+ loses another e-. Acetate does not form as stable a complex, hence is "less corrosive" than the Cl- ion.

[pwd72s]

Thanks all for the responses. When ODOT first started using the materials listed, a "suzy shallow" on Portland TV nightly "news" assured her audience that these sprays wouldn't rust cars like salt could. Riggght! I agree with Randy...ODOT should just go back to Volcanic grit...but they don't ask P-car drivers, do they? I think my car will stay in the garage for a while...until our heavy rains have had plenty of time to wash the stuff off the road surfaces, so the fish & the vegetation can worry about it.

[Randy Webb]

Hey, I'm sure Suzy had great hair...

I'm going to take my car out today but not on county roads. Eugene uses grit.

You know, Paul, you could always file an ESA Law suit over the fish protection issue (assuming they haven't consulted) -- even if your real motivation is to protect your car.

BTW, if you fish -- go way upstream & hope Weyerhauser hasn't sprayed anything nasty recently...