Engine coolants solution

After 32 days at 88°C in 33% Prestone II (a commercial engine coolant solution that contains silicate inhibitors), ZA-8 and Alloy 3, either as-cast or polished, showed no corrosion. Dynamic tests confirmed the suitability of ZA-8 at 118°C. ZA-27 displayed intergranular attack when tested as-cast but not when its surface was polished before testing. Possibly, the soft, zinc-rich phase had been smeared over the whole surface during polishing. 

Solutions are addressed specifically and in more detail in Chapter 7. At this point, however, it is useful to have some imderstanding of the quantitative expression of the amount of solute dissolved in a specified amount of solution. In a relative sense, a solution that has comparatively little solute dissolved per unit volume of solution is called a dilute solution, whereas one with an amount of solute of the same order of magnitude as that of the solvent is a concentrated solution. Water saturated with air at 25 °C contains only about 8 milligrams of oxygen dissolved in 1 liter of water this composes a dilute solution of oxygen. A typical engine coolant solution contains about as much ethylene glycol (antifreeze) as it does water, so it is a concentrated solution. A solution that is at equilibrium with excess solute so that it contains the maximum amount of solute that it can dissolve is called a saturated solution. One that can still dissolve more solute is called an unsaturated solution. 

Laws have been enacted in many states in an attempt to prevent the sale and distribution of deleterious antifreeze products, such as salt solutions or petroleum coolants. Even ethylene glycol engine coolants must be evaluated by testing and comparison of test results with specifications for engine coolant concentrate, such as ASTM D 3306. These tests ensure desired levels of antifreeze coolant concentrate and inhibitor are available to adequately protect cooling systems against freezing, boilover and corrosion (Fig. 2). 

Check Accuracy of Tester. Test the instrument with solutions of known freezing protection. A 33% solution of ethylene glycol engine coolant in water protects to 0°F (—18°C) and a 50% solution should indicate —34°F (—37°C) protection. 

Car manufacturers recommend that the factory-fill coolant be used for one to two years. Previous surveys [7] on the performance of coolants in automotive service indicated that about one third showed appreciable loss of freezing protection, loss of inhibitor reserve, and rust in solution at the end of one year. Before two full years, most coolants require change. Based on these data, major engine coolant manufacturers recommend that their products be used for one year, preferably changing each Spring or Fall. 

Air-cooled heat exchangers eliminate the need for water treatment and the need for disposal or recycling of solutions of antifreeze.82 The Volkswagen beetle uses an aircooled engine. Texaco is marketing an Extended Life Anti-Freeze/Coolant for cars and light trucks that lasts for 100,000 miles. Engine coolants can be recycled profitably.83... 

Antifreeze Solution - A fluid, such as methanol or ethylene glycol, added to vehicle engine coolant, or used in solar heating system heat transfer fluids, to protect the systems from freezing. 

The salt-water corrosion test is used to evaluate submarine splice closures. For this test a spUce closure tuid its outer housing are immersed in aerated 3.5 % sodium chloride solution for 180 days. The test is described in TA-TSY-041 [17]. The same closures are also exposed to a similar test using artificial fresh water (ASTM D 2570, Method for Simulated Service Corrosion Testing of Engine Coolants). 

L.H. Han, X.Y. Nie, H. Hu, Electrochemical behaviour of squeeze cast AJ62 magnesium alloy in salt solution and engine coolant . Mater. Technol. 24 (2009) 170-173. 

R.L. Chance, Electrochemical corrosion of an aluminium alloy in cavitating ethylene glycol solutions , in W.H. Ailor (ed). Engine Coolant Testing State of the Art, ASTM STP 705, American Society for Testing and Materials, Philadelphia (1980) pp. 270-283. 

RI,. Chance, Electrochemical Corrosion of an Alu-minum Alloy in Cavitating Ediylene Glycol Solutions, p r presented at the Intemational Sympo-sium on State of the Art Engine Coolant Testing, April 1979, (Atlanta, GA), ASTM... 

HOCHj CHjOH. Colourless, odourless, rather viscous hygroscopic liquid having a sweet taste, b.p. 197 C. Manufactured from ethylene chlorohydrin and NaHC03 solution, or by the hydration of ethylene oxide with dilute sulphuric acid or water under pressure at 195°C. Used in anti-freezes and coolants for engines (50 %) and in manufacture of polyester fibres (e.g. Terylene) and in the manufacture of various esters used as plasticizers. U.S. production 1979 1 900 000 tonnes. 

Laboratory tests used in the development of inhibitors can be of various types and are often associated with a particular laboratory. Thus, in one case simple test specimens, either alone or as bimetallic couples, are immersed in inhibited solutions in a relatively simple apparatus, as illustrated in Fig. 19.34. Sometimes the test may involve heat transfer, and a simple test arrangement is shown in Fig. 19.35. Tests of these types have been described in the literatureHowever, national standards also exist for this type of test approach. BSl and ASTM documents describe laboratory test procedures and in some cases provide recommended pass or fail criteria (BS 5117 Part 2 Section 2.2 1985 BS 6580 1985 ASTM 01384 1987). Laboratory testing may involve a recirculating rig test in which the intention is to assess the performance of an inhibited coolant in the simulated flow conditions of an engine cooling system. Although test procedures have been developed (BS 5177 Part 2 Section 2.3 1985 ASTM 02570 1985), problems of reproducibility and repeatability exist, and it is difficult to quote numerical pass or fail criteria. 

FIG. 6—Insufficient antifreeze coolant protection, or incomplete mixing of solution, may result in slush-ice freezeup in the radiator, stoppage of circulation, loss of coolant through the overflow, and serious engine overheating. 

Magnesium Chromate. [CAS 13423-fil-5. MgCiCC SH.o, small readily soluble, yellow cryslals. formed by reaction ol magnesium carbonate and chromic acid solution. Use Since it does not produce a fusible alkaline residue when thermally decomposed, it is used as a corrosion inhibitor in the water coolant of gas turbine engines. Insoluble basic magnesium chromates also arc available. Their potential applications arc in the treatment of light metal surfaces. 

Another colligative property of solutions is the lowering of the freezing point. (As mentioned before, a 1 M NaCl solution freezes at approximately -1 °C.) This property is particularly important in cold areas of the world where salt is applied to icy roads. When the applied salt dissolves in the thin layer of water on the surface of ice, forming a very concentrated solution, it causes the ice to melt (it lowers the freezing point of water). The same property is also used to protect automobile engines. The coolant used... 

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