Objective:
To demonstrate the way crystals grow and how they affect the behavior of material. A comparison can also be made between the growth of the crystals in metals and non-metals.
Equipment:
Hot plates, glass plates, beakers, glass rods, scale to weigh out the salt, graduated flask for water, furnace, crucibles, sand, tongs, safety glasses and gloves. Starting materials: Epsom salts, water, 50% Aluminum - 50% Copper alloy (previously alloyed).
Safety:
Whenever you are dealing with hot liquids, there is the potential for burns and spills. Protect yourself from the possible risks, especially around the hot metal. Make sure you know where any potential spillage will go and place something in the way to protect yourself. In part ‘B’ be especially careful of the hot metal. Remember, it will still be very hot, even when it has changed back into a solid.
Procedure:
Part A: A supersaturated solution of salt will separate out into crystals on cooling. The size of the crystals is a function of the rate of cooling, the amount of impurities present and the degree of supersaturation (concentration of salt present in the solution). 1. Dissolve 25 grams of Epsom salts in 25 ml of water. Heat the water until all the salt dissolves, but keep the water below the boiling point. If all the salt will not dissolve, add water in small quantities until it does. Pour some of the solution onto a clean glass plate so as to form a thin film and watch it solidify. If it solidifies too rapidly, return it to your beaker and add more salt. Again, keep track of how much additional salt is added. When you achieve the proper mixture you should be able to observe the crystals start to form at the edge and slowly “grow” toward the center. 2. Record the ratio of salt vs. water you used and sketch the crystals you observed. Pay particular attention to the area where two crystals meet or join. Part B: If an alloy of two metals forms an eutectic (from the Greek word “eutoctos”=easily fused; an alloy with eutectic composition has the lowest melting temperature) and a solid solution (or intermetallic compound) on cooling, the eutectic can be poured off and crystals formed by the solid solution will be exposed. This part of the experiment lends itself best to a demonstration. An alloy has been prepared by melting equal weights of pure copper and aluminum in one crucible, and holding the materials overnight in the furnace. An intermetallic compound, Al2Cu and a eutectic are formed. The compound takes the form of large needles if slowly cooled from the molten phase. 1. Heat the Copper-Aluminum alloy up to approximately 750℃ and pour it into a hollowed out firebrick resting on a metal tray full of sand or a hollow made in dry sand contained in a metal tray. SAFETY IS EXTREMELY IMPORTANT DURING THIS OPERATION. 2. As the liquid cools, you will first observe small bubbles on the surface. Next, you may be able to see a hint of motion just under the surface, as the crystals of metal are forming. Tilt the pan slightly to see this structure. When there seems to be some rigidity or structure inside the liquid, tip the pan to pour off the liquid eutectic phase. Depending on when you decide to tip the pan, you will see large crystals that have formed throughout the system. Note the size of the crystals in the liquid that was poured out as compared to those left behind.

Conclusion In this experiment the crystals grow because it the temperature increased while it was a solution. The water molecules are farther apart which provides room for solid substance to dissolve. As the solution cools after being heated the water molecules move closer together so there are less room for the solid. Therefore the crystals begin to form due to the excess solute in the water. They grow like that because it is growing from a saturated solution.Almost all the metallic crystals will grow in a familiar fashion as the Epsom salts. The cooling rate affects it because it moves the water molecules closer. The molecules will tend to move into the center so there is little room in the middle. Therefore the salt crystals grow from the outside and then work its way to the center. The composition does have an effect on crystal formation because the crystal shape is an expression of the mineral’s atomic structure. The ductility of the Al-Cu alloy is lower than aluminum. The ductility changes a lot based on the temperature. The mixture is brittle because the ductility is decreased. The ductility is low if the temperature is not high.It is brittle because there are different sized atoms in the alloy which makes the metal less malleable. It is less malleable because of the different sized atoms which prevents the atoms from sliding. The pure metals are malleable because atoms can slide past each other which losing structural strength.