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Post by Donkey on May 25, 2012 6:21:56 GMT -8
I haven't personally used the silica.
I HAVE used quartz sand to poor effect. So I can warn against quartz sand use in high heat areas.
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Deleted
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Post by Deleted on May 25, 2012 7:00:34 GMT -8
Quartz is the most common crystaline form of silica in the nature. Very few sands eg. high alumina sands can beat the thermal properties of qartz sand, provided it is pure and does not contain flux. Clays are simply extremely fine sands. Fire clay contains roughly 50% to 90% silica (usually in the form of quartz crystals) en.wikipedia.org/wiki/Fireclay#Chemical_composition |
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Post by Donkey on May 26, 2012 14:35:01 GMT -8
Yes, quartz BY ITSELF can handle very high temperatures. The issue is that you have to consider ALL of the properties of EACH material in the mix. Do they play well together or not, are their heat expansion characteristics compatible and so on.
Clay isn't EXACTLY fine sand. Clay has properties that sand does not. Interestingly, the various sciences tend to classify clays to their particle sizes which is not particularly helpful outside those disciplines. Plasticity doesn't quite define clay's nature either. As usual, these disciplines define the material(s) in ways that make sense to them, but may not be useful to others and can obfuscate or confuse.
Silt (for instance) is essentially fine sand and can masquerade as clay. Trying to build with the two materials will quickly inform you of the difference. When dried, silt will no longer bind together and will crumble to dust easily, clay will stick together and stay that way. Mix the two with water, clay will bind (however loosely) with the water, holding onto it in solution. Silt will will quickly settle out of the water, leaving a layer of water on top (as will sand). The two materials have similar grain sizes, yet they have very different properties.
If you fire clay the chemical properties change, it stops being clay and it's properties will NOT be returned no matter how fine you grind it.
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Post by Deleted on May 27, 2012 5:04:12 GMT -8
That depends just on the way the stone ( sand, silt ) has been decomposed and separated by weathering and erosion. The forces between the particles will become stronger the more the particles have the shape of thin plates. If the particles have roughly the same size in all dimensions the forces will be weak. Clay: Large differences of size in the dimensions (thin plates). Silt: Roughly the same size in all dimensions. Aside of size and form the chemical composition of clays and silts is different. Silts contain large amounts of feldspars. Though silts including the feldspars can be degraded by weathering to clay too. No matter how fine you grind it, you will never get thin plates. Anyway even with a jet mill only a small percentage would be grinded to two microns or below. www.fluidenergype.com/ultra_fine_grinding_sizing.htmLeave it alone for a few million years and it may become clay again. |
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foz
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Post by foz on Aug 24, 2013 23:57:41 GMT -8
Hi, can i use hay in my cob? Straw is a little hard to come by and expensive, but hay there's lot here, also bracken would that work? with hay is there problems with the seed being in the mix?
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