SAM4CH - 17-2-2006 at 13:51
1. How can I make mullite ceramic if I have a powder of sodium silicate and Alumina (Al2O3) "not fine powder", I searched at google but I need perfect
procedure and more about sodium silicate:aluminum oxide ratio with water..
2. If I need to increase the maximum operating temperature for my ceramic what is advised additive materials.
12AX7 - 17-2-2006 at 16:59
Mullite doesn't include sodium, it tends to make things melt. I'd keep it under 2%. You need silica. If you must use sodium silicate as a binder,
don't use much.
If you mean increase the operating temperature of a *mixture*, and not *already fired ceramic*, I would suggest increasing alumina content and if
possible reduce or remove flux content (soda, potash, lime and iron primarily). Silica is also refractory, but it tends to have more shrinkage (as a
result of forming quartz or crystobalite, rather than just glass) and is more prone to fluxing than alumina. If you have zirconia, chrome oxide or
other similar materials, they can be added to form a high melting phase that may or may not go into the surrounding glass "solution", but should, at
any rate, increase refractoriness.
In addition, if you are using nonoxide ceramics, excluding air might be a viable route, since most are prone to oxidation at temperatures under the
melting or decomposition point. That is, if you aren't already using a sealed apparatus, or can't exclude oxygen.
Tim
SAM4CH - 17-2-2006 at 17:13
I have TiO2, Al2O3 and I'd like to make ceramic which will use in my furnace (Temp. 1300-2000C).
What is the best ceramic in this and what is the best binder.
I need full instructions..!!
12AX7 - 17-2-2006 at 17:20
For mullite, you'd take about 40% clay (any refractory clay will suffice, a mixture of kaolin and ball clays preferred) and 60% alumina and blend with
enough water to make a workable dough, or if you desire a slip, a few drops of sodium silicate (or other deflocculant) and a bit more water. Fire to
maximum operating temperature and hold for an hour or two. Temp rise no faster than 500°F/hr (300°C/hr or so).
I don't know what you propose to do at 2000C, or if you're just throwing up a number at random. Besides being absurdly hot, no cheap, common
materials will handle this; you're better off purchasing a commercial zirconia refractory for that purpose.
Tim
SAM4CH - 17-11-2006 at 01:18
can I use silica gel "fused silica" as a clay and alumina to make mullite ceramic? I like full prucedure for making ceramic from alumina and sea
soil..
Maya - 17-11-2006 at 05:57
silica gel is not "fused silica" but sodium silicate instead..so the answer is no, you can't use it
12AX7 - 17-11-2006 at 13:44
Er...silica gel is silica gel. Whether or not it was made from sodium silicate or a more suitable medium depends.
If it has any (>1%) sodium in it, it's going to noticably affect the melting point (from "fucking high" to plain old "high"). Other than that,
silica and alumina of any particle size (depending on how long you want to fire the piece...) is fine. Mind the LOI and shrinkage when using gels....
Tim