coefficient is represented by the symbol alpha (), L signifies the change in length, L_0 denotes the original length, and D_t is the change in temperature. It is ideal to have two metals having like coefficients of linear expansion, because it will allow for the expansion and retraction of both to be similar. For example, if a metal with a high coefficient has another metal wrapped around it with a low coefficient, the metal inside expands faster and could cause a fracture to the metal surrounding it. However, there are situations in which you may need to join two metals having unlike coefficients of linear expansion. For example, preparing an alloy requires combining metals with two different coefficients. The four metals being tested have theoretical coefficients of:

Table [1]. Theoretical Coefficient of Linear Expansion for 4 materials (Toolbox 2003)
Material Linear Temperature Expansion Coefficient
(10-6 m/ (m K))
Brass 18-19
Copper 16-16.7
Aluminum 21-24
Stainless Steel 11-12.5

These theoretical values are important because they will be a baseline example to compare our coefficients with from our experiment. We will be able to calculate our error percentage based off these values.

Another factor in determining the best material for the vessel is cost. Each material is listed with its cost per foot of pipe below. In terms of optimal price for the piping, the ranking would go as follows from lowest cost to highest: Aluminum, Brass, Copper, then Stainless Steel.

Table [2]. Cost per Foot of Piping Material (Kauffman)

Material Cost/Foot of Pipe
Brass $2.65
Copper $2.76
Aluminum $1.24
Stainless Steel $4.65

In addition to these factors in determining the best material for the piping, corrosion resistance is a key factor. It is brought into consideration, because hydrochloric acid is an extremely corrosive substance and higher temperatures increase the rate of corrosion. Given the chemical formula of each metal, they must be compared to hydrogen on the reactivity series to see how they will react.

Figure [2]. Reactivity Series for Metal (Chinmayi)

The metal that will react the most with the HCl will be the aluminum since it is located above hydrogen. This makes it the most corrosive and not a suitable choice for the pipe. The next most corrosive will be the common brass since it is composed of around 62-65% zinc and around 37% copper. (Bell) Almost the least corrosive, but still not corrosive resistant would be stainless steel. It is an alloy composed of chromium, nickel, iron and carbon. Given stainless steel’s carbon makeup, some corrosion will occur, however, it will occur at a very minimal rate. The least corrosive element will be copper, because it is located well below hydrogen. Being that this pipe will be solely composed of copper, the pipe will never corrode since the reaction cannot occur. This makes copper the optimal choice in terms of corrosion.

Experimental Methods