subject: Stone Hardness And Absorbent Mechanism [print this page] The hardness of the stone is refers to the ability to resist other objects mechanical intrusion stone. It is related to the mineral composition, stone structure and construction, and is usually divided into the relative hardness and absolute hardness.
The relative hardness also referred Mohs hardness which chooses 10 kinds of minerals as the standard .And the relative hardness sizes are divided into 10. Such as iron Mohs hardness of 5 to 5.5, with a knife can not be carved in granite traces, most of marble mineral hardness is less than 4, which can be carved by knife.
Absolute hardness is the use of hardness meter for measuring. Depending on the load is applied in the measurement can be divided into static hardness and dynamic hardness. Static hardness can be divided into Knoop hardness and Vickers hardness, respectively, represented by symbol HK and HV. Dynamic hardness, also known as the Shore hardness notation HS. Stone is a brittle material, More suited to the determination of the Shore hardness. Usually, marble Shore hardness is between 35 to 55, Shore hardness of granite is usually between 70 to 95, and some can be up to 110 or more.
there are porous in the stone, and has a natural permeability. Keep the stone natural permeability is crucial. Stone has a tiny gap between the crystals, we called microporous. The pore size is different for different texture stone, Stone permeability level is usually determined by the size of these micropores. To maintain the smooth flow of these pores of the stone, the moisture at the bottom of the stone will be out of the volatile. Although there is less problem of stone in humid environments, it is the capillary action generated by the pores of the stone, so that the stone has a different water absorption. The amount of water absorption is proportional to time, within a period of time, the capillary water absorption amount is increased with the time of growth. In fact, in addition to the absorption of moisture through this capillary phenomenon, the gaseous water can also be absorbed by condensation mechanism. The condensation of vapor in the air which we are speaking is reduced by the temperature liquefied. At room temperature, if the heavier air humidity in the environment around us, temperature drops will cause air moisture condensation on the surface of the stone. The greater the relative humidity and the faster the cooling, the condensation phenomenon is more obvious. In addition, Stone moisture absorption phenomenon is also a stone absorbs moisture way, because the porous stone exist to varying degrees with some soluble salt. These salt have different degrees of hygroscopicity. In other words, the degree of moisture absorption is depend on the chemical nature of these salt, the salt content and the moisture in the air.
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