Non-Metallic Impurities in Metals
Metals are naturally occurring materials that have many important uses in everyday life such as manufacturing, construction, jewelry and even currency. Because of their diverse applications, metals are highly sought after and come in a variety of forms, including alloys and raw forms such as ingots and slabs.
Metals that are produced or processed from ore often contain other substances or impurities, some of which are harmful or toxic. Examples of these impurities include non-metallic inclusions. Non-metallic impurities in metals can adversely affect their physical and chemical properties, making them unsuitable for certain applications or unsafe for people to use.
Non-metallic inclusions come in many forms, including slag, graphite, oxides, nitrides, carbides, nitrates, sulfides, phosphides and other compounds. They can be introduced into a metal during the casting, welding, forging or machining of the metal and can affect the properties of the metal after it is formed.
Non-metallic impurities can have a number of adverse effects on the performance and strength of the metal. They can reduce its ductility, making it more brittle, decrease its corrosion resistance and impact its resistance to fatigue and thermal cracking. In extreme cases, non-metallic impurities can reduce the strength of the metal by as much as half, hindering its usability for certain applications.
Non-metallic impurities can also lower the melting point of the metal, causing it to melt or deform during processing or thermal treatments. During gas welding, for example, non-metallic impurities can react with the flame and create bubbles or porosity in the weld. These defects can result in a weakened weld, increasing the risk of failure during use.
Non-metallic impurities are often difficult to detect and can be found in metals through the use of specific tests such as optical or electron microscopy or spark spectral analysis. The amount of non-metallic inclusions should be kept to a minimum, as even trace amounts can have a negative impact on the properties of the metal.
In summary, non-metallic impurities are unwanted intrusions that can have a detrimental effect on the performance and strength of metals. They can be introduced during the processing of the metal, and can be difficult to detect. To ensure that metals are of the highest quality, tests should be conducted to ensure that non-metallic impurities are not present.
