Hardness of Metals Chart
- Thread starter mdengraver
- Start date
AllenClapp
Elite Cafe Member
I found the following discussion on the Mineral Society of America website. It explains a key difference between the Moh's hardness scale and Brinell and other scales typically used to determine hardness in metals. What it doesn't say is if all the scales give a similar relative result.
The Mohs' hardness scale was developed in 1822 by Frederich Mohs. This scale is a chart of relative hardness of the various minerals (1 - softest to 10 - hardest). Since hardness depends upon the crystallographic direction (ultimately on the strength of the bonds between atoms in a crystal), there can be variations in hardness depending upon the direction in which one measures this property. One of the most striking examples of this is kyanite, which has a hardness of 5.5 parallel to the 1 direction ( c-axis), while it has a hardness of 7.0 parallel to the 100 direction ( a-axis). Talc (1), the softest mineral on the Mohs scale has a hardness greater than gypsum (2) in the direction that is perpendicular to the cleavage. Diamonds (10) also show a variation in hardness (the octahedral faces are harder than the cube faces). For further information see articles from the American Mineralogist on microhardness, the Knoop tester, and diamonds.
Mohs' hardness is a measure of the relative hardness and resistance to scratching between minerals. Other hardness scales rely on the ability to create an indentation into the tested mineral (such as the Rockwell, Vickers, and Brinell hardness - these are used mainly to determine hardness in metals and metal alloys). The scratch hardness is related to the breaking of the chemical bonds in the material, creation of microfractures on the surface, or displacing atoms (in metals) of the mineral. Generally, minerals with covalent bonds are the hardest while minerals with ionic, metallic, or van der Waals bonding are much softer.
When doing the tests of the minerals it is necessary to determine which mineral was scratched. The powder can be rubbed or blown off and surface scratches can usually be felt by running the fingernail over the surface. One can also get a relative feel for the hardness difference between two minerals. For instance quartz will be able to scratch calcite with much greater ease than you can scratch calcite with fluorite. One must also use enough force to create the scratch (if you don't use enough force even diamond will not be able to scratch quartz - this is an area where practice is important). You also have to be careful to test the material that you think you are testing and not some small inclusion in the sample. This is where using a small hand lens can be very useful to determine if the test area is homogenous.
MOHS' SCALE OF HARDNESS |
Mohs' hardness is a measure of the relative hardness and resistance to scratching between minerals. Other hardness scales rely on the ability to create an indentation into the tested mineral (such as the Rockwell, Vickers, and Brinell hardness - these are used mainly to determine hardness in metals and metal alloys). The scratch hardness is related to the breaking of the chemical bonds in the material, creation of microfractures on the surface, or displacing atoms (in metals) of the mineral. Generally, minerals with covalent bonds are the hardest while minerals with ionic, metallic, or van der Waals bonding are much softer.
When doing the tests of the minerals it is necessary to determine which mineral was scratched. The powder can be rubbed or blown off and surface scratches can usually be felt by running the fingernail over the surface. One can also get a relative feel for the hardness difference between two minerals. For instance quartz will be able to scratch calcite with much greater ease than you can scratch calcite with fluorite. One must also use enough force to create the scratch (if you don't use enough force even diamond will not be able to scratch quartz - this is an area where practice is important). You also have to be careful to test the material that you think you are testing and not some small inclusion in the sample. This is where using a small hand lens can be very useful to determine if the test area is homogenous.
AllenClapp
Elite Cafe Member
I can see why you would want to use the Moh's test, instead of Brinell, et. al, for crystals that might fracture under pressure.
mdengraver
~ Elite 1000 Member ~
Interesting Allen! The information could be useful for engraving and inlay, inlaying the softer metal into the harder metal!
AllenClapp
Elite Cafe Member
The thing that concerned me about this particular test was that copper, bronze, and brass all had the same rating. I am not sure that this is the case. Because the Moh's test is a scratch test, rather than an impact or penetration test, I can see them being very close, but I am not sure that they are the same when considering could you inlay one into the other or not. You have peaked my interest in this subject. I have looked online for a similar chart that is based upon Brinell or one of the other impact/penetration methodologies, but no luck so far. Hopefully one of us can find one and report back.
AllenClapp
Elite Cafe Member
Here is the Wikipedia page on hardness of ELEMENTS, so it doesn't have alloys in it, like brass and copper.
https://en.wikipedia.org/wiki/Hardnesses_of_the_elements_(data_page)
Notice that many of the tests have quite a range of values. I have seen some other charts of Moh's info that also had a range, rather than a single number. I suspect that you might be able to inlay brass into copper, because zinc is not as hard as copper. However, sometimes other things are mixed into brass--and particularly into bronze-- that may make them harder than copper. I suspect that trial and error is required for some metals.
https://en.wikipedia.org/wiki/Hardnesses_of_the_elements_(data_page)
Notice that many of the tests have quite a range of values. I have seen some other charts of Moh's info that also had a range, rather than a single number. I suspect that you might be able to inlay brass into copper, because zinc is not as hard as copper. However, sometimes other things are mixed into brass--and particularly into bronze-- that may make them harder than copper. I suspect that trial and error is required for some metals.
mdengraver
~ Elite 1000 Member ~
I generally feel copper is softer than brass or bronze in the hardened state or when all are annealed. And generally hardened or annealed bronze is harder than hardened or annealed copper and brass. But then again the alloys in the metals can change all this, and that could make all the difference.
AllenClapp
Elite Cafe Member
I found a good discussion that covers copper, brass, and bronze. https://www.sequoia-brass-copper.com/blog/metal-alloy-comparison-guide/
The alloy makes a huge difference. I.e., one brass is not necessarily the same as another.
The alloy makes a huge difference. I.e., one brass is not necessarily the same as another.
mdengraver
~ Elite 1000 Member ~
Thanks Allen all interesting stuff! Thanks for sharing!
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