Uses of Chemistry in the Metallurgical Industry
Honors Project - Anthony Simpson
  Introduction
    In the metal working industry it is often necessary to identify different types or alloys of metal. Several metals are easily given general identifications by their physical appearance. In the example below, It is quite easy to perceive the difference between the sample of copper and the sample of brass. However the difference in appearance is not as defined between the samples of steel alloys. Depending on the surface texture even the aluminum could be mistaken for steel. Two pieces of metal can look and feel exactly the same yet be completely different in their properties; such as strength, hardness, or toughness of the alloy. Let us pause for a moment and define the word alloy. An alloy is an homogeneous mixture or solid solution of two or more metals, or a compound containing metal with certain nonmetals, (especially carbon) the atoms of one replacing or occupying the small spaces between the atoms of the other: Brass is an alloy of copper and zinc. By visual identification we would have never perceived the copper content in the brass, nor did we see any indication of tin. Brass therefore is not a “True Metal” i.e.- An elemental metal, but an Alloy metal. Steel too is an alloy metal. It is an alloy of Iron and other metal and non-metal elements. Since sight alone is not enough to accurately determine the identity of the type of metal, or indeed if the sample is a metal at all, we must find a more accurate way of identifying the sample.
 
 
 


    One major aid in metal identification, is the creation of set standards of metal alloys by organizations such as the American Society of Standards and Testing (ASTM). ASTM has set forth a coded listing of metal alloys and their physical requirements, such as strength, toughness, dimensional tolerances, and most importantly to our discussion chemical composition. This list of standards allows us to identify a specific sample of metal by it’s chemical composition. This identification can be achieved via several means.

    One of the methods by which we may chemically identify metal alloys is called chemical spot testing. A chemical spot test kit can provide adequate identification for combinations of metals. The test is accomplished by electrically removing a minute amount of surface metal and depositing it onto a moistened filter paper. Reagents are dropped onto the paper showing the distinct colors which are indicative of the presence of specific elements in the sample tested. A simple example of the use of color for identification in a chemical reaction is shown at right. In this example a solution of potassium iodide is added to a unknown solution suspected to contain lead. The reaction gives us a very visible yellow solid. Utilizing a set chart of previous reactions we determine that when potassium iodide is combined with lead nitrate that a yellow solid precipitate, lead iodide, is formed. The reason that the atoms of lead break their bond with the molecules of nitrate and reform with the iodine is as simple as what you see in this reaction. That this allows the lead iodide to form, a solid, which allows both the lead and the iodine to be much more stable in their new configuration. This is only one test and would not be absolute in identifying whether or not lead was present, more than one reaction could produce a yellow solid, but through a series of such test we could come to a reliable conclusion.
 
 
 

    Chemical spot testing can be accurately preformed in the field or the lab, but requires a skilled operator and a reasonably clean sample. A more useful test in the field is nitric acid testing. In chemical spot testing as many as twenty to thirty separate test are used to single out each elemental ingredient of an alloy. Such as all the elements in common mild steel (see below) you would use a reagent that would react only with the elements specific to this alloy of steel, so as to eliminate all other possible alloys. Nitric acid testing uses only one reagent, nitric acid, but as the chart below shows; allows for a fair indication of more common metal alloys when combined with a simple magnet and our original visual testing. While this is not a full analysis of the chemical composition of the alloy, these series of simple test will allow a worker with minimal training to obtain the proper material for a metal shop task.
 
Reactivity to
Reactivity to
Alloy or Metal
Visual Appearance
Fresh Surface
Magnet
Nitric Acid
Carbon Steel  Dark Gray  Bright Silvery Gray  Strong  Slow; Brown 
Stainless Steel (grade 304)  Dark Gray; Dull to Brilliant  Bright Silvery Gray  None  None 
Stainless Steel (grade 400)  Dark Gray; Dull to Brilliant  Bright Silvery Gray  Slight  Slow; Brown to Black 
Brass  Yellow to Green or Brown  Reddish Yellow to Yellowish White  None  Fast; Green 
Bronze  Red to Brown  Reddish Yellow to Yellowish White  None  Fast; Blue-Green 
Copper-Nickle  Dark Gray; Dull to Brilliant  Bright Silvery Gray  Slight  Fast; Green to Blue 

Composition of Alloys

Carbon Steel
Carbon 0.26%; Manganese 1.00%; Silicon 0.30%; Copper 0.20%; Iron- Balance
Stainless Steel (300 series)
Carbon 0.08%; Manganese 2.00%; Silicon 1.00%; Chromium 19.00%; Nickel 11.00%; Iron-Balance
Stainless Steel (400 series)
Carbon 0.70%; Manganese 1.00%; Silicon 1.00%; Chromium 19.00%; Molybdenum 0.79%; Iron-Balance
Brass
Copper 61.0%; Tin 0.9%; Lead 0.20%; Zinc- Balance
Bronze
Copper 78.0%; Tin 11.0%; Lead 9.0%; Zinc 1.0%; Nickel 2.0%
Copper-Nickel
Nickel 3.80%; Copper- Balance
 
 
 

Premise

Alloys of metals are made from a very specific formula or recipe, and can even be quantized to a molecular level. Therefore an alloy may be identified accurately via a series of controlled testing for individual characteristics, dependent upon the absence or presence of certain elements.
 

Laboratory Experiment
Purpose:
To confirm the identity of an unknown alloy sample, we will conduct visual inspection, magnetic reaction testing, and nitric acid reactivity testing to come to a dependable conclusion of the identity of the sample.

Apparatus:
(1) pipette, (1) metal file, (1) piece of 120 grit sandpaper, (1) magnet, (1) vial of 12 molar nitric acid, 30cm of string.

Procedure:
1. Obtain three unknown alloy samples.
2. Create a table and record the number of each sample across the top.
3. Observe and record the appearance of each sample.
4. Tie approximately 30cm of string to a magnet and allow the magnet to hang freely.
5. Hold the magnet approximately 10cm from the sample and slowly move it towards the sample.
6. Record whether or not there was a reaction to the magnet and how strong it was as a comparative measurement.
7. Using the metal file or sand paper, expose a fresh section of each sample. Observe and record the appearance
of the freshly exposed alloy.
8. Clean all sandpaper debris or metal filings from sample with a brush.
9. Utilizing a pipette, apply 1-2 drops of 16M nitric acid on fresh exposed portion of the sample.
Observe the reaction (if any) for 2 minutes.
10. Apply three to four drops of water one at a time to the sample and continue to observe the reaction.
11. Record a description of the observed reaction.
12. Using the chart below of given results, determine the identity of the three unknown samples.
 
 
Reactivity to
Reactivity to
Alloy or Metal
Visual Appearance
Fresh Surface
Magnet
Nitric Acid
Carbon Steel  Dark Gray  Bright Silvery Gray  Strong  Slow; Brown 
Stainless Steel (grade 304)  Dark Gray; Dull to Brilliant  Bright Silvery Gray  None  None 
Stainless Steel (grade 400)  Dark Gray; Dull to Brilliant  Bright Silvery Gray  Slight  Slow; Brown to Black 
Brass  Yellow to Green or Brown  Reddish Yellow to Yellowish White  None  Fast; Green 
Bronze  Red to Brown  Reddish Yellow to Yellowish White  None  Fast; Blue-Green 
Copper-Nickle  Dark Gray; Dull to Brilliant  Bright Silvery Gray  Slight  Fast; Green to Blue