A Better Understanding of Chemical Deicing Facts and Myths

11

A Better Understanding of Chemical Deicing

Providing Customers With Deicing Solutions Providing Customers With Deicing Solutions that Save Lives and enhance Commercethat Save Lives and enhance Commerce 11

Facts and Myths

Scott Koefod

Goals

• Take the mystery out of chemical deicers• How do deicers work?• What makes a deicer work better at lower

temperatures?

Providing Customers With Deicing Solutions Providing Customers With Deicing Solutions that Save Lives and enhance Commercethat Save Lives and enhance Commerce

p• What is the eutectic and what does it tell us?• What do deicer freezing point curves tell us?• How effective are corrosion inhibitors?

22

How do we make ice melt?

?


22

Method 1: Raise the ice temperature above the freezing point

Temp = 40 0FFreezing Point = 32 0F



Method 2: Lower the freezing point below the ice temperature!




All deicers work the same way

ice


• Deicer molecules “interfere” with water molecules• Makes it harder for them to lock together and freeze• Freezing point drops• The more deicer dissolves, the more the freezing point drops

66

ice water

33

How can we control how much we drop the freezing point?

• Easy! • More chemical dissolved = more

“interference” = lower freezing point


• Lowest freezing point is limited by how much chemical will dissolve

77

+

Freezing Point = 32 0F




+Freezing Point 12 F

+ Freezing Point = 2 0F

Sooner or later no more salt will dissolve – liquid is saturated

++


F.P. = - 6 0 F

The freezing point lowering from salt bottoms outSalt cannot possibly melt ice below -6 0 F

44

10

20

30

40Liquid NaCl


-10

0

10

-10 0 10 20 30 40 50% NaCl by Weight

Liquid is saturated23% NaCl @ -6 0F

Eutectic = lowestpossible freeze pointa deicer can give

Some chemicals can lower the freezing point more than others

20

0

20

Deicer Eutectic Temperatures

salt magnesium chloride

calcium chloride

Potassiumacetate


-80

-60

-40

-20

Not all deicers are created equal

5

6

7

8

Ice Melting Capacity

saltCaCl2


0

1

2

3

4

25 15 5 -5 -15 -25Temperature (degrees Fahrenheit)

55

Fact: deicers work by lowering the freezing point of water

• Myth: the lower the freezing point of a liquid deicer, the better it will work at low temperatures.


• From wikipedia: “Deicing fluids work best (surprisingly) when they are diluted with water.”

• An anti-freeze will work best when diluted, but not an ice-melter.

1313

+

1 tablespoon salt melts ~ ½ cup ice


+ +

Dissolve that salt in ½ cup water first,And the “liquid deicer” can’t melt any more ice.

+ +


So – we have to add more salt to our liquiddeicer to make it melt any ice

66

+ +


The more salt we add, the more ice it can melt

0

20

40

60

Calcium Chloride Solution


-60

-40

-20

0 10 20 30 40 50% Calcium Chloride

Best working concentration = 30%?

1

1.5

2

Ice Melting Capacities 15 degrees FAfter 60 Minutes

Eutectic dilution

Highest concentration providesmost ice melting capacity


0

0.5

44.5 35 29.6 20 10% Calcium Chloride

77

How do we understand this?

• Need to be careful with freezing point charts!• Important thing is freezing point of water (to

form ice)• Above eutectic concentration, the “freezing” is


not of water• It is excess deicer chemical crystallizing

because liquid is saturated!

1919

20

30

40

Liquid NaCl

Freezing point of

“freezing” is excesssalt crystallizing fromsaturated liquid


-10

0

10

-10 0 10 20 30 40 50% NaCl by Weight

Freezing point of water drops as more salt is dissolved

Liquid is saturatedno more salt can dissolve

f.p. of water no longer changing

saturated liquid

So what happens if we put “too concentrated” liquid on cold road?


Excess solid deicing chemical crystallizes outWill solid deicer still melt ice? Of course!

88

Deicer dilution can have some value

• Better low temperature storage stability– 26.4% salt brine “freezes” at 32 0F– 23.3% salt brine stable to – 6 0F

• But higher concentrations will always give


• But higher concentrations will always give more ice melting capacity

2222

Fact: certain additives can lower the freezing point of chloride deicer brines

Myth: this will make the brine melt


ice to lower temperatures

2323

-10

0

10

0.8

1

1.2

1.431% MgCl2 Brine + Organic Liquid Additive

Freezing Point Ice Melting Capacity


-40

-30

-20

0.2

0.4

0.6

-10 0 10 20 30 40 50 60

% Organic Liquid Additive

99

Why didn’t it work??• Some organic additives (e.g. sugars, glycols,

certain proteins) behave as “cryoprotectants”• Cryoprotectants inhibit the freezing of water


Used in ice cream to prevent ice crystals, they occur naturally in arctic fish, plants, etc.

Cryoprotectants do not work the same way as deicers

• Cryoprotectants inhibit freezing by slowing it down immensely

• They do not cause a true drop in the actual freezing point of water


freezing point of water• They have a “glass transition temperature”

rather than a freezing point• They can inhibit freezing, but can’t melt ice• They can “fool” the freezing point test

2626

How do we measure freezing points?

Standard method for deicers is ASTM D1177


Cool liquid at a steady rate

Look for break in cooling curve

1010

Well defined freezing 40

50

60

70

Plain Deicer BrineNo Additive


gpoint = 19 0F

10

20

30

-5 0 5 10 15 20 25 30Time (minutes)

20

40

60

80

ASTM D1177 Cooling Curves

plain brinebrine + 25% organic liquid

freezing point = 19 0F


-40

-20

0

-5 0 5 10 15 20 25 30Time (minutes)

freezing point = -35 0F??

Freezing Point vs. “Glass Transition”

Normalf.p. curve is“V” shaped

“glass transition”Curve has no “V”


1111

0

20

40Deicer Freezing Point Curves

MgCl2 Brine + 25% Organic LiquidMgCl2 Brine + No Additive


-60

-40

-20

0 5 10 15 20 25 30 35% Magnesium Chloride

Plain MgCl2 brine showswell defined eutectic “V”shaped curveAddition of organic

liquid causes typicalglass transition curve

Potential Organic Additive Value

• Improved residual effect• Corrosion inhibition• Leaching inhibition• Lower temperature ice melting???

– Unlikely


y– Must be verified by a performance test – Lower liquid “freezing point” does not indicate

lower temp ice melting– ASTM D1177 is not accurate for f.p. of liquids

containing cryoprotectant type additives

3232

“Exothermic Deicers”

• Calcium chloride is a well known “hot” deicer

• How does it work?• How important is the heat released for


pice melting?

3333

1212

When chemicals dissolve, they either release heat (get hot)


Or they absorb heat (get cold)

+


urea

400

600

800

Heat Released by 1 Pound Solid Deicer

Magnesium Chloride (pure)

CalciumChloride (pure)


-200

0

200

(pure)

PotassiumAcetate

Magnesium Chloride (flake)

salt urea

1313

How Important is the Heat Released?

5

6

7

8

Ice Melting Capacity at 25 degrees F

salt

CalciumChloride


2

3

4

5

0 10 20 30 40 50 60 70Time (minutes)

Heat Released in Perspective

• Calcium chloride is an excellent ice melter• The “hot” contribution is relatively unimportant• Remember – the environment is an enormous heat

sink– Like trying to heat an entire house with a candle!


y g– Heat released by deicer dissipates very quickly!

• Also – liquid deicers have no heat to release– Once dry chemical dissolves, heat is quickly lost

3838

Fact: corrosion inhibitors reduce the corrosiveness of chloride deicers

• Caution: this must also be understood in perspectiveI t t t d t d i t t


• Important to understand corrosion tests• At best corrosion tests provide a relative

ranking of corrosiveness for a specificexposure condition

3939

1414

40

50

60

70

Corrosion Rates of Deicer Solutions (0.513 M)PNS Test Method


0

10

20

30

1 2 3 4 5 6 7H2O NaCl CaCl2 MgCl2 KCl urea KAc

Current Industry Corrosion Standard

• PNS Test Method• Simulates a moderately aggressive exposure

condition– 10 minutes wet/50 minutes “aeration” cycle– Simulates repeated deicer brine “splash” on


Simulates repeated deicer brine splash on exposed mild steel

– Cannot be extrapolated to other metals– Cannot be extrapolated to concrete rebar

• Standard spec is at least 70% less corrosive than salt

4141

PNS Corrosion Tester


1515

PNS Corrosion Tester


Distinguishing PNS Categories 1,2, and 4

• PNS categories 1 and 2 are for liquidmagnesium and calcium chloride.– These are commonly used to pre-wet salt

• PNS category 4 is for corrosion inhibited solid


g ysalt

• Pre-wetting liquid specs generally require meeting PNS specs 1 or 2

• Blending a PNS 1 liquid with salt does not necessarily make a PNS 4 deicer!

4444

Meets PNSSpec

Meets PNSSpec

F il PNS Fails PNS

60

80

100

PNS Corrosion TestTwo Commercial MgCl2 + OBPE Products


Liquid LiquidTreatedSalt

TreatedSalt

Fails PNSSpec

Fails PNSSpec

0

20

40

1616

“Simulated Equipment Corrosion” Test

• We have developed our own test to estimate equipment corrosion

• Steel coupons directly immersed in piles of treated salt


• Salt pre-wetted with corrosion inhibited liquid ~ 70% less corrosive than salt wet with plain salt brine

Corrosion Conclusions

• All chlorides will be aggressive to mild steel –not a huge difference between them

• Corrosion inhibited chlorides probably always more corrosive than non-chloridesC i i hibit d d i ff iddl


• Corrosion inhibited deicers offer a middle ground option

• Corrosion protection of standard pre-wetted products is probably primarily restricted to equipment

Questions?• Feel free to contact me with any

technical deicer questions• Scott Koefod, Principal Scientist• Cargill Deicing Technology


g g gy• Phone: 952-742-5670• Email: [email protected]

Documents

A Better Understanding of Chemical Deicing Facts and Myths