Working with Silica...

Are you trying to do foundry molding? here a Google doc with some ideas.

This book may give you something.

Without you providing more info "if you can" these are a shot in the dark.

Professional Sand Sculpture Stuff.

Ingredients: 10 parts sand. 1 part white glue. 3 parts water.

Ethyl Silicate is a very good binder. It again forms Silica-gel which has huge surface area.

interesting product. found this doc.I'll think about some uses for myself. With the refractory mix I could see a few uses i think.

Ethyl-silicate has to be dried very carefully and slowly not to crack.

Then firing to any temperature between 400 and 1500°C will give very soft binding after low temp firing and original quartz glass data after high temp firing.

Any mixture of oxides can be used that - if fired - give a glass may be used.

Which temperature, which strength requirements?

Some work was done in production of lightweight telescope mirrors, this can be found in the SPIE proceedings.

Simplest may be to switch from silica to alumina and buy a grinding wheel made from alumina?

RHABE

The good news is that nature has already solved this problem for you. Google "FULGURITE" to see how it's done. No chemicals or glue required.

and following your link, leads to methods to create them artifically.

chris

This is an important problem because disposal of coal fly ash (which is spherical silica) is unsolved. Right now it is impounded in lagoons, which are allegedly a danger to the water supply and certainly a danger to those living nearby when the containment is breached. Stringent EPA regulations are upcoming.

"Green bricks" made from fly ash have been done by drying the ash and compressing it. The drying step involves heat, which consumes energy and produces CO2. The OP wants to preserve the internal surface area of the ash aggregate. It is known that green bricks remove mercury from the air, so a high internal surface area is good.

In order to have a high internal surface area, the OP rules out glue and other binders, which blanket the grains. The fulgurite method, which depends on an arc fusing the grains, would be a big energy waste and the arc would pass through only a small portion of the grains along the path of least resistance.

It seems to me that the most promising path is heating the silica by friction to near the glass transition and then squeezing the grains together in some sort of sintering or forging process. You asked, so at the risk of getting yelled at here is my idea for dewatering the ash ponds and thickening the sludge so it extrudes as a paste suitable for molding into green bricks: http://www.freepatentsonline.com/7757866.pdf

"The fulgurite method, which depends on an arc fusing the grains, would be a big energy waste"

Seems to me that arc fusing is an energy efficient method for fusing grains of sand. It may require a lot of power, but because only the outer surface of the grains are heated by the arc, it may be exceedingly energy efficient. On the other hand, you may find a binder that is permeable to whatever it is you are trying to trap in the porous silica structure.

I think you're right. A diffuse arc, a corona, might be the key. When I saw the stuff about fulgurite, not knowing anything before, I assumed that lightning was state of the art. Diffuse arc fusion by "heating only the outer surface of the silica grains" would accomplish the same thing as grinding, maybe better.

or... put the raw material in a centrifuge, and 'write' with lightning electrode (on the inside) as the material spins, so that the fusing is as uniform as possible, and compressed as well. (controlling dust too, from)

just thinking...

Any time you bond grains you loos surface aria. The only way to bond something like this with out coating the entire surface of the grains is to sinter them. As soon as you make a 3D object out of the stuff every thing not on the surface of the object has limited access to reactants.

"The only way to bond..."

there may be other ways. it is too early in the game to make such a statement.

chris

Hi chrisg288

I also have a desire for specially connected silica particles to create high temp ceramics. Yesterday my photo/artist daughter showed us the fulgurite pictures as part of a photo project. The OP seems to want a silica product with a high surface to volume ratio, for some unstated use. Your caution regarding committing to any specific methodology is commendable, since any change in the surface to create adhesion could change the use for the high surface area desired. I have been toying with this for ca. 2 yr, and have some ideas. Perhaps if OP wants more details, we could have more details of desire.

You don't suppose we might actually achieve a functional solution here on CR4, or is that against site policy? I apologize for the personal communication, OP.

I view the set of solutions as a spectrum..(once more than one solution is found) and it simply suggests there are more.

and also I try not to forget such 'outside the conventional' as K. Eric Drexler's book "The Engines Of Creation" about future nano assembly. (potentially relevant here)

thank you.

Chris

One approach involves using glue, but a sophisticated glue, which can be assembled molecularly to customize the bonding of the silica particles. The book, K. Eric Drexler's book "The Engines Of Creation", as suggested by Chris, introduces this concept, though its been around at MIT since at least the early 70's. Blending design concepts, using regular code, helps cord.

interesting. :)

I was thinking also of using cyanacrylitic glue, and then possibly some form of etchant that would flow through the remaining matrix, and increasing surface area.. but I'm not sure how that would comparare to the original surface area.

Is it possible to spray or sputter melted silica, and condense it into a porous large surface area bonded matrix? (similar conditions to growing a crystal, but I think silica is amorphous) What is it really we want to create? What properties, shapes, strenths, conductivity, etc.?

In the current era, I think that all scientific research needs to be conducted towards specific (financially justifiable) goals, but to keep an open mind with regards to accidental or unexpected results, which may warrant further researches, with different goals.

Once a better economic situation exists, the budgeting can be increased and broadened in scope. I don't think anyone really wants to stop scientifice inquiry.. but I do think economic realities must be acknowledged by anyone who spends or receives a public dollar.

"Begin with the end in mind." Steven Covey... very appropriate.

Chris

I hope that cooperative problem-solving is not against site policy. The OP is on to a good project and I hope we can help him. It would have to be a continuous process, not batch, I guess.

Packing spheres leaves a quarter of the volume air, which would make the material light, insulating, and suitable as a substitute for metal screens or plastic membranes. A high surface to volume ratio would be good for adsorption of mercury or for evaporative cooling. It might be a new, improved cinder block.

Getting the spherical silica to bond need not involve melting it completely as with fulgurite. Only softening the outside of the grain would be enough because then the grains could be sintered so they would stick together. There is no need to heat up the inside of the grain.

The mineral content of coal emissions (fly ash) might thus be made into a useful product. Maybe it would be good for circuit boards, because it is thermally and electrically insulating and won't burn and offers high surface area for heat rejection to the air.

Capacitive coupling to soften the outside of the grains might be the way to go, maybe to finish the job of energy input begun by grinding the grains together to shear heat them. Preferably it would be a continuous process, not batch. I guess it is well known how to (1) squeeze the grains together to sinter them into a durable material once they are softened and (2) anneal the material so the grains won't break apart once they cool.