202 Section 3 Ferrous Metallurgy hardness, for example. Such boundaries are called phase boundaries. Each area in a phase diagram shows the conditions of concentration and temperature that form a single phase or a particular combination of two phases. A region with only one phase is called a phase domain. The graph in Figure 10-2 shows the percent of glycol in water (x-axis) versus the temperature of the fluid (y-axis). Any solution with glycol concentration and temperature that falls above and right of the red line will be liquid. Any solution below and left of the red line will be “slushy,” a mixture of liquid and solid ice. Solutions below –69°F (–53°C) will be completely solid. People who maintain their own vehicles need to read the table on the can and plan ahead for the coldest days in their area. Antifreeze—From Texas to North Dakota For people moving from Dallas, Texas, to Bismarck, North Dakota, knowledge of how temperature and composition affect their car’s cooling system become very important. In Dallas, the temperature might go as low as 15°F (–9°C) at the coldest point in a given winter. With 5 quarts of antifreeze in its 15-quart cooling system (a 33% glycol solution), their car has no trouble in the Dallas winter. According to the table on the antifreeze can and in Figure 10-3, the car could handle a temperature as low as 0°F (–18°C) with that solution. However, in Bismarck, North Dakota, the temperature in January can go as low as –44°F (–42°C). Without making changes and facing a winter in Bismarck, these car owners now have a problem! Most automobile engines have expansion plugs in the engine block that will pop out if the cooling fluid freezes. Confronting a temperature of –44°F (–42°C), the expansion plugs in the block would certainly pop out, and the engine block still might crack. PRACTICAL METALLURGY PRACTICAL METALLURGY Goodheart-Willcox Publisher Figure 10-3. A 33% antifreeze solution would be safe to 0°F (–18°C), so it could easily handle winter in Dallas. But a winter in Bismarck, North Dakota, reaching as low as –44°F (–42°C), would wreck the engine. Always be sure that the cooling system of your car is prepared for the area in which you are driving. 20 Safe temp: 0°F (–18°C) Dallas: 15°F (–9°C) Bismarck: –44°F (–42°C) –20 –40 –60 –80 20% 30% 40% 50% Percent glycol by volume 60% 70% –65 –51 –40 Liquid phase –29 Temperature, ° C Temperature, ° F –18 –7 0 Solid phase + liquid phase Completely solid phase Copyright Goodheart-Willcox Co., Inc.