【Weekly Topic】(34) July 4, 2015: What is hardness? Into how many categories?

The ability of a material to resist the penetration of a hard object into its surface is called hardness. Hardness is classified into: ① Scratch hardness. It is mainly used to compare the hardness of different minerals. The method involves using a rod with one end hard and the other end soft, and sliding the material to be tested along this rod; the hardness of the material is determined by the position where scratches appear. Qualitatively, scratches made by hard objects are long, while those made by soft objects are short. ②Indentation hardness. It is mainly used for metal materials; the method involves applying a certain load to press a specified indenter into the material under test, and the hardness of the material is determined by comparing the extent of local plastic deformation on its surface. Due to differences in the indenter, load, and load duration, there are various types of indentation hardnesses, mainly including Brinell hardness, Rockwell hardness, Vickers hardness, and microhardness. ③Rebound hardness. It is mainly used for metal materials, by causing a specially designed small hammer to fall freely from a certain height and impact a specimen of the material under test; the hardness of the material is determined by the amount of strain energy stored (and then released) by the specimen during the impact, as measured by the rebound height of the hammer.

Water hardness originally referred to the ability of calcium and magnesium ions in water to precipitate soapy solutions. Carbonate hardness: It is primarily the hardness resulting from bicarbonates of calcium and magnesium, with a small amount of carbonate hardness as well. Bicarbonate hardness decomposes into precipitates upon heating and is removed from water, which is why it is also known as temporary hardness. Non-carbonate hardness: It is the hardness resulting mainly from salts such as sulfates, chlorides, and *ao oxalates of calcium and magnesium. This type of hardness cannot be removed by heating and decomposition; therefore, it is also known as permanent hardness. Examples include CaSO4, MgSO4, CaCl2, MgCl2, Ca(NO3)2, Mg(NO3)2, etc. The sum of carbonate hardness and non-carbonate hardness is called total hardness ； The content of Ca2+ in water is referred to as calcium hardness ； The content of Mg2+ in water is referred to as magnesium hardness ； When the total hardness of water is less than its total alkalinity, the difference between them is called negative hardness.

Water hardness refers to the concentration of calcium and magnesium ions in water, expressed in PPM. Classification: calcium hardness, magnesium hardness, carbonate hardness, non-carbonate hardness.

1. Water hardness (also known as mineralization) refers to the amount of calcium and magnesium salts dissolved in water. 2. Hardness can be divided into temporary hardness and permanent hardness

Water hardness refers to the total amount of calcium and magnesium ions in the water; therefore, hardness denotes the total hardness. Total hardness is composed of temporary hardness and permanent hardness. Temporary hardness: When water contains a certain amount of carbonates such as Ca(HCO3) and Mg(HCO3)2, these carbonates decompose and precipitate upon heating, being removed from the water. This is what we refer to as temporary hardness. Permanent hardness: This refers to the situation where water contains not only a certain amount of carbonates but also a certain amount of sulfates such as CaSO4 and MgSO4, as well as chlorides like CaCl2 and MgCl2. These substances do not precipitate out of the water even when it is heated to boiling point; they will only precipitate when the water continues to evaporate, causing their concentration to exceed the saturation limit. The substance that precipitates is called scale, and we refer to this type of hardness as permanent hardness. The higher these two levels of hardness, the greater the total hardness of the water.

What is water hardness? Into how many categories? Answer: Water hardness mainly refers to the content of soluble calcium and magnesium salts in water. Water hardness is classified as follows: temporary hardness (carbonate hardness), magnesium bicarbonate (calcium): a type of hardness that can be removed by heating. Permanent hardness (non-carbonate hardness): calcium sulfate (chloride, *ao acid); Indelible hardness: magnesium sulfate (chloride, *ao acid)

Water hardness refers to the total amount of calcium and magnesium ions in the water. It is divided into temporary hardness and permanent hardness.

Water hardness refers to the total amount of calcium and magnesium ions in the water. It is divided into temporary hardness and permanent hardness.

Water hardness refers to the total amount of calcium and magnesium ions in the water; therefore, hardness denotes the total hardness. Total hardness is composed of temporary hardness and permanent hardness. Temporary hardness: When water contains a certain amount of carbonates such as Ca(HCO3) and Mg(HCO3)2, these carbonates decompose and precipitate upon heating, being removed from the water. This is what we refer to as temporary hardness. Permanent hardness: This refers to the situation where water contains not only a certain amount of carbonates but also a certain amount of sulfates such as CaSO4 and MgSO4, as well as chlorides like CaCl2 and MgCl2. These substances do not precipitate out of the water even when it is heated to boiling point; they will only precipitate when the water continues to evaporate, causing their concentration to exceed the saturation limit. The substance that precipitates is called scale, and we refer to this type of hardness as permanent hardness. The higher these two levels of hardness, the greater the total hardness of the water.

Water hardness refers to the total amount of calcium and magnesium ions in the water; therefore, hardness denotes the total hardness. Total hardness is composed of temporary hardness and permanent hardness. Temporary hardness: When water contains a certain amount of carbonates such as Ca(HCO3) and Mg(HCO3)2, these carbonates decompose and precipitate upon heating, being removed from the water. This is what we refer to as temporary hardness. Permanent hardness: This refers to the situation where water contains not only a certain amount of carbonates but also a certain amount of sulfates such as CaSO4 and MgSO4, as well as chlorides like CaCl2 and MgCl2. These substances do not precipitate out of the water even when it is heated to boiling point; they will only precipitate when the water continues to evaporate, causing their concentration to exceed the saturation limit. The substance that precipitates is called scale, and we refer to this type of hardness as permanent hardness. The higher these two levels of hardness, the greater the total hardness of the water.