hardness


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hardness,

property of matter commonly described as the resistance of a substance to being scratched by another substance. The degree of hardness is relative, different substances being compared with one another. Mohs's scale of hardness (named for Friedrich Mohs), used commonly in mineralogy, lists certain minerals in order of hardness: talc, 1; gypsum, 2; calcite, 3; fluorite, 4; apatite, 5; orthoclase, 6; quartz, 7; topaz, 8; corundum, 9; diamond, 10. The listing indicates merely that gypsum (hardness=2) is harder than—i.e., capable of scratching—talc (hardness=1). The listing does not indicate that gypsum (2) is twice as hard as talc (1). The hardness of many minerals falls between those included in the list. For example, the hardness of barite is 3.3. Hardness may differ with the direction of the scratch made on the substance. Thus the mineral kyanite has a hardness of 5 parallel to the length of its crystals and of 7 at right angles to this direction. There are several other methods based on the resistance to indentation for testing engineering materials. The solid elements have been thus classified: diamond (an allotropic form of carbon) is hardest and listed as 10, with cesium the softest, rated as 0.2, the same degree of hardness as wax (hardness=0.2 at 0°C;). The hardness numeral of the Brinell scale is based upon the indentation produced when pressure is exerted by a sphere on the substance. The value thus obtained has a direct relation to the tensile strength of the substance. The hardness of a material may be modified by the presence of small quantities of another substance, as in metallic alloys, or by impurities in minerals.

hardness

[′härd·nəs]
(chemistry)
The amount of calcium carbonate dissolved in water, usually expressed as parts of calcium carbonate per million parts of water.
(electromagnetism)
That quality which determines the penetrating ability of x-rays; the shorter the wavelength, the harder and more penetrating the rays.
(engineering)
Property of an installation, facility, transmission link, or equipment that will prevent an unacceptable level of damage.
(materials)
Resistance of a metal or other material to indentation, scratching, abrasion, or cutting.

hardness

1. The resistance of wood, rubber, sealant, plastic, or metal to plastic deformation by compression or indentation; in wood, hardness is generally related to density. Common methods of measurement include the Rockwell, Brinell, Scleroscope, and Vickers tests.
2. A property of a paint or varnish film that is a measure of its ability to withstand damage from marring, abrasion, etc.
3. The degree of hardness, applied to water, based on the amount of calcium and magnesium salts in the water, expressed as grains per gallon or parts per million of calcium carbonate.
References in periodicals archive ?
Hardness is the resistance of a material to deformation, particularly permanent deformation, indentation or scratching.
Hardness Testing, which is based on comparative knowledge, is often performed as the first step in evaluating materials.
The pH, ammonia concentration, level of microbial contamination and the hardness of water used in scald tanks, washers and chiller tanks can influence the ability of sanitizing procedures to remove microorganisms from carcasses during processing.
These include increased early and final mar resistance, lower color, higher scratch resistance, and hardness.
While common testing of (macro) hardness according to Vickers is done by means of load of 10 N to 1200 N, the forces weaker than 10 N were used first in 1932, when such testing was done at the National Physical Laboratory in UK.
According to Teter, there simply may not be a material that can rival the hardness of diamond.
The recognized tests for hardness of materials, Brinell, Rockwell, Vickers, etc, consist of applying known weights and specific indentor shapes to the surface of material samples and measuring the resulting permanent indentations.
Whereas they would previously have needed to stock many different grades of silicone if they wanted to make products of different hardness, they now have in Silpuran 2410 A/B a product whose hardness can be flexibly adjusted to suit the intended application.
In order to determine the hardness of materials on the principle of force measurement the invention proposal A00/873/2010, entitled ,,Apparatus for testing and characterization of advanced materials", authors Gutt S, et.
A more common hardness would be 70-75 in sand casting and 85+ in permanent mold casting.
Hardness also is one indicator of chemical structure and degree of crosslinking and is useful for establishing structure-property relationships.
Hardness was measured by nano-hardness tester, which was Triboinddenter root position nano-mechanic testing system produced by Hysitron Company (U.