Selfmade ceramic slurry for high-temp applications

Hi all,

for fabbing with high-temp materials at room-temp i'm testing with different filler-materials and fluids.

My last test was a mixture of eccospheres ( [www.trelleborg.com] - hollow glass-spheres, around 50 microns in size) and waterglass.

The mixture is slurry-like but because of the spheric particles with the same waterglass-amount more fluid than with glass- or ceramic-dust, so it didn't clogg up thin needles - but it's viscous/thixotropic enough for forming trays with nearly 4:3 aspect ratio.

In thin trays it's drying and hardening at open air in some minutes, so it's good for fabbing continuously without waiting or special curing the slices.

By heating in an oven you can make it more stable - here i have to test when running with my repstrap.

As the spheres are hollow, it's an extreme lightweigt material - comparable to styrofoam or forex - and a bit brittle (i think the thin-walled hollow spheres are braking too when applying forces).

I hope to receive some samples of solid glass-spheres (from [www.sil-trade.de] ) with average sizes smaller 0,1mm and some samples of rock-spheres too - the resulting material should be harder/stronger/heavier than with eccospheres but heavier too - around 1.5 kg/liter.

I think this materials are ideal candidates for high-temp (up to 1000°C) applications like metal-casting, sensor-housings and covering or isolating heat spots (e.g. nicro-wire).

The hollow spheres cost around 50 Euros per kg (with a density of 100g to 160g per liter, so one kg should give up to 10 litres), the solid glass-spheres are something below 6 Euros per kg and the stone-spheres around 9 Euros per kg - here you'll receive around 0,7 litres per kg - so it's expensiver than the hollow spheres per volume.

I'll post some more infos and maybe some images too when getting stable results ...

Viktor

Edited 1 time(s). Last edit at 03/05/2009 05:06PM by Viktor.

Have you considered sand-blasting sand? It is very inexpensive (~$20/10kg) and is available down to sand so fine that it appears to be powder.

Edited 1 time(s). Last edit at 03/05/2009 06:19PM by Annirak.

Hi Annirak,

... i tried with several dusts and powders and noticed that the sharp-edged particles tend to clogg when applying pressure.

For this i ordered marble-blasting glass-spheres with average size of 0,1mm but found size-distribution from 0,0001mm to 1mm, so i had to filter and sort (what i really did some times ).

Here the uniform sizes from sil-trade and trellborg are much better and more than equals the higher costs ...

Viktor

Viktor, would love to see some images of your tests!

Viktor, you might look into using colloidal silica, IE silica with particle sizes on the order of nanometers. Though if you use colloidal silica, you might have to dilute it a bit, as colloidal silica solutions behave as shear thickening fluids and are actually being investigated for use in body armor. Though, I've heard of it being shot through inkjet printer cartridges just fine.
[www.jgreer.com]

Viktor,
I have done some lost wax casting successfully with a mixture of portland cement, silica sand and chopped glass fibres. It was nasty to get off the finished article though ! I think less glass fibres might have helped... I put them in to keep the structure intact if there was any cracking, but with preheat, I has no problems with cracking whatsoever.

Graham.

... actually i'm busy with making slurries for highgrade temperature insulation by mixing the hollow spheres or aerogels with different self-hardening or curable fluids.

This sort of material isn't very hard or structural stable - but when building walls out from massive rock-spheres-paste and filling with the isolation material i can make some nice ceramic-objects with hard/stable walls, good temperature isolation and low specific weight too ...

Viktor

For changing the structure of particles, the problem of sharp edged particles can be relatively easily solved with a little more processing. These rules work for sub millimeter rock processing in my experiance (from mining) and are probably applicable here.

The basic rule with shaping particles is:

Impacting the particles (crushing them)=sharp elongated shapes.
Milling the particles (ie running them in a rotating drum like a rock tumbler)=ball like particles.

The problem with milling is that it can take for ever to mill down to the smallest sizes.

Dear friends
How are you and everything goes well .This is John From ohio .Im stydying metal casting in university.
I have a question about ceramic shell casting from you please send for me your answer.
1. yellow mgcl2 uses in shell castig and whats this matrial?
2. i want to learn how to make mold and core from yellow Magnesium chloride ?
please send for me more pictures or useful links About above question .thanks.

Looking forward to your kind reply.

Yours sincerely
Best wishes
John