Non-metallic inclusions are classified according to their chemical composition

Classification of Non-Metallic Impurities According to their Chemical Composition

Non-metallic impurities are substances present in small amounts in foods, consumed in trace amounts and may be considered essential or detrimental to human health, depending on the quantity consumed. They are usually inorganic and are divided according to their chemical composition into three main groups.

The first group includes alkali and alkaline earth metals, as well as some trace elements such as selenium, iodine, chromium and manganese. These elements increase the alkalinity in foods, which can lead to an increase in acidity, leading to corrosion and the deterioration of flavor. They also interfere with enzymatic reactions that take place in the digestion process.

The second group of non-metallic impurities consists of silicates and silicate minerals, which are found in trace amounts in some foods. Silicates are not very soluble in water, and can accumulate in the small intestine, thus blocking absorption of essential nutrients. If too large an amount is consumed over time, it can lead to gastrointestinal issues, including constipation and abdominal pain.

The third group of non-metallic impurities consists of insoluble phosphates, which are highly insoluble and mostly present in animal-based foods. They increase the phosphorus content of foods, leading to the formation of calcium-phosphate complexes. This can lead to the hardening of tissues and organs, as well as the deposit of insoluble plaque onto the teeth, causing tooth decay.

Some non-metallic impurities, such as arsenic, mercury and lead, are toxic when consumed in large amounts. Arsenic is found in certain fruits, vegetables and grains, and in some water supplies, as well as arsenic-containing additives used in certain foods. Mercury is present in animal-based foods, as well as in certain fish. Lead is mainly present in household dusts, as well as in lead-containing paints and water pipes.

The amount of impurity present in foods is regulated by various national and international authorities, who set the maximum allowable levels. It is therefore important to ensure that foods comply with these regulations, and to choose healthy foods, as some non-metallic impurities can cause serious health problems when consumed in large amounts.

Non-metallic inclusions can be classified into oxides, sulfides, silicates, nitrides, and borides based on their chemical composition.

Oxides are the most common type of non-metallic inclusion. These comprise of a large, diverse category of materials such as alumina (Al2O3), silica (SiO2), and magnesia (MgO). These constituents are produced by oxidation of manual processing and heating. They generally exist in a passive or protective environment, sometimes containing pure or combined forms of iron and/or other metals, and titanium compounds. Oxides are very heat resistive, and can affect the microstructure and properties of the steel by modifying its microstructure and oxidation behavior.

Sulfides are thermodynamically unstable, and usually penetrate into the steel more deeply than oxides. Sulfides can be formed due to the presence of sulfur-containing feedstock or during the manufacturing process. They can remain in the interstitial matrix when the steel is in a molten state. Sulfide inclusions can have an effect on the transformation and precipitation behavior of alloyed materials.

Silicates are divided into two groups: alkaline and alkaline earth. Alkaline silicates are formed by the reaction of magnesium and oxygen, while alkaline earth silicates are primarily composed of calcium and magnesium. These inclusions have very strong refractory characteristics and can often have a detrimental effect on steel performance.

Nitrides can form when nitrogen-containing compounds are added to the steel or through an internal gas exchange process during high temperature heat treatment cycles. Nitride inclusions are usually formed as cubic, acicular, or agglomerated particles in the as-cast state. They can cause embrittlement, reduced fatigue strength, and a decrease in impact strength.

Borides are usually formed by reaction between boron and other metal atoms in the steel. Borides can form at high temperatures, and can produce an effect on the strength and ductility of the material. They are usually found in steels containing relatively high levels of boron.

In summary, non-metallic inclusions in steel can have a wide range of effects on material properties and processing. It is important to take into account the chemical composition of the inclusions when evaluating their potential effects.