A Better Understanding of Chemical Deicers Cargill, Incorporated All Rights Reserved. A Better Understanding of Chemical Deicers

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1 A Better Understanding of Chemical Deicers Scott Koefod, Ph.D. Cargill Deicing Technology October 17, The Challenge Many factors affect deicer/anti-icer performance Precise prediction of field performance very difficult Improved tests to predict field performance are in development Best approach at present is to understand the basic performance characteristics of different chemicals 2 1

2 Basic factors that affect deicer function Ability to melt ice Ability to prevent freezing Ability to prevent ice from bonding to pavement Very little salt is required to prevent ice from bonding! 1 Concentration of NaCl Required to Prevent Freezing and Bonding at 5 degrees F prevent freezing prevent bonding 2

3 Ability to Melt Ice? 5 All deicers work the same way ice water 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 6 3

4 Common Points of Confusion A liquid with a lower freezing point does not predict better ice melting capacity Lower eutectic often (but not always) indicates better ice melting at lower temperatures Organic additives which lower the apparent freezing point of a liquid do not necessarily lower the eutectic temperature 6 Calcium Chloride Solution Best working concentration = 3%? % Calcium Chloride 8 4

5 2 Ice Melting Capacities 15 degrees F After 6 Minutes 1.5 Highest concentration provides most ice melting capacity Eutectic dilution % Calcium Chloride 9 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! 1 5

6 Liquid NaCl Freezing point of water drops as more salt is dissolved freezing is excess salt crystallizing from saturated liquid Liquid is saturated no more salt can dissolve f.p. of water no longer changing % NaCl by Weight 11 Freezing Point Ice Melting Capacity 31% MgCl2 Brine + Organic Liquid Additive % Organic Liquid Additive 12 6

7 Why didn t it work?? Some organic additives (e.g. sugars, glycols, certain proteins) behave as cryoprotectants Cryoprotectants inhibit the freezing of water They act as an anti-freeze not the same function as an ice melter 13 Potential Organic Additive Value Corrosion inhibition Leaching inhibition in treated salt Possibly improved residual effect Possibly improved anti-icing Probably not improved ice melting 14 7

8 14 12 Leaching Test Deicing Salt + 8 gal/t Liq MgCl2 8-9% RH Visc = 25 cp Visc = 63 cp Visc = 72 cp Visc = 146 cp Time (days) Visc = 25 cp (7.5 gal/t) Visc = 235 cp (7.5 gal/t) Visc = 235 cp (1 gal/t) Leach Test 8% RH, 75 F Deicing Salt + Liq MgCl Time (days) 8

9 Hot Deicers Calcium chloride is a well known hot deicer How important is the heat released for ice melting? 17 8 Heat Released by 1 Pound Solid Deicer Magnesium Chloride (pure) 6 4 Calcium Chloride (pure) 2 Magnesium Potassium Chloride Acetate (flake) salt urea

10 How Important is the Heat Released? 8 Ice Melting Capacity at 25 degrees F 7 salt 6 5 Calcium Chloride Time (minutes) 19 The ice melting advantage of CaCl2 or MgCl2 starts at about 15 F or colder salt CaCl2 8 Ice Melting Capacity Temperature (degrees Fahrenheit) 2 1

11 How much boost in ice melting capacity do we get by in a hot mix? Is there a synergistic boost between salt and calcium chloride or mag chloride? 11

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13 Grams Ice Melted Ice Cube Titration Test at 5 F 4 grams of Liquid Deicer NaCl Brine MgCl2 Brine 2/8 hot mix (theoretical) Ice Melting in hot mix is additive No indication of synergism between MgCl2 and NaCl 2/8 hot mix (experimental) What is Residual Effect? How long does a deicer or anti-icer treatment continue to be effective? How well does effectiveness resist dilution by precip? How well does effectiveness resist being lost by traffic action? How might we measure this? 13

14 Precipitation endurance Test Method How long will a deicer treatment resist being exhausted when exposed to freezing precipitation? Precipitation endurance a standard performance test for aircraft deicer fluids Modify test to better simulate roadway/parking lot/sidewalk deicing Test development work between Cargill and Anti-Icing Materials Laboratory (AMIL) Treat asphalt coated plates with deicer liquids Expose plates to controlled freezing precipitation at controlled temperature Plates with no deicer treatment immediately form a layer of rime ice minutes 17 min 3 min 4 min 12 min 14

15 Plates treated with Salt brine go through a series of stages minutes 2 min 6 min 8 min 1 min 14 min fluid film non-adherent rime ice layer glaze ice layer begins Does the onset of rime ice formation signal exhaustion of the deicer by Precipitation? Some brine additives appear to delay the onset of rime ice formation meaning? 15

16 Deicer Corrosion and Corrosion Inhibitors all chloride deicers will be relatively corrosive Non-chloride deicers relatively non-corrosive Corrosion inhibited deicers provide a middle ground At best corrosion tests provide a relative ranking of corrosiveness for a specific exposure condition 31 7 Corrosion Rates of Deicer Solutions (.513 M) PNS Test Method H2O 1 NaCl 2 CaCl2 3 MgCl2 4 KCl 5 urea 6 KAc

17 PNS Corrosion Tester PNS Corrosion Test Two Commercial MgCl2 + OBPE Products Meets PNS Spec Meets PNS Spec 6 4 Fails PNS Spec Fails PNS Spec 2 Liquid Treated Salt Liquid Treated Salt 17

18 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 ~ 7% less corrosive than salt wet with plain salt brine 35 Questions? Feel free to contact me with any technical deicer questions Scott Koefod, Principal Scientist Cargill Deicing Technology Phone: scott_koefod@cargill.com 18