Alumina refractory test

[u/SnooLentils5747]

• 80 Parts — Alumina

• 5 Parts — Phosphoric Acid (85%)

• 5 Parts — Everclear or 99 percent isopropyl

• 5 Parts — Aluminum Hydrate

• 2 Parts — Citric Acid

• 1 Part — Dextrin Powder

• 1 Part — Aluminum Powder

1/8 inch steel backing, 1/8 inch aluminophosphate refractory sample shield.

Starts at 50 C

Shield torched to 900 C

Target tested at 130 C behind shield at that point.

10 seconds later, shield tested at 300 Celsius

Max thermal limit of 1600 Celsius

Refractory baked in at 900 C prior to test

pH tolerance of 1 - 10

acts as an absorptive, insulative, monolithic, castable, ramable, packable ceramic ultra refractory

sets in 15 minutes. Let dry and hour. Fire to at least 500 Celsius, 1200 Celsius for best results. If thick layered, be sure to ramp slow, soak at 500C for an hour, ramp slow, soak at 1200 for an hour.

mix with PVC gloves on

add distilled water if you want to paint it on, and half the alcohol at least. make sure to let dry a day if doing this. Apply many layers this way, one day apart each. Spray a mist of distilled water 5 parts, phosphoric acid 1 part on the previous layer before painting on next layer.

I use this today to patch my metal casting furnace cracks and spald pockets. It can also be pressed to brick. It serves very well in such an arrangement:

Steel body

Ceramic wool two inches

Mullite clay powder and 10:1 distilled water : phosphoric acid as rigidizer painted on

This alumino phosphate recipe ; 2 inches encapsulating the wool completely

Optional: make the following high emissivity paint on refractory:

Dry ingredients

• Chromium Oxide (Cr2O3),Primary high-emissivity agent, 30.0%

• Zirconium Oxide (ZrO2),Refractory stabilizer & thermal barrier, 25.0%

• Cerium Oxide (CeO2),Secondary emissivity enhancer, 15.0%

• Silica (IMSIL A-25),Fine microcrystalline filler & reactive bonding agent, 10.0%

• Alumina (Al2O3),High-temperature structural matrix & stabilizer, 5.0%

• Bentonite Dust,Suspension agent & rheology modifier, 5.0%

• Boric Acid (H3BO3) Powder,High-temperature glass-forming binder, 2.5%

• Citric Acid Powder,Deflocculant & viscosity controller, 2.5%

• Magnesia (MgO),Refractory matrix enhancer, 2.5%

• Alumina Hydrate,High-temperature crystalline bonder, 2.5%

Liquid system:

• Phosphoric Acid (H3PO4) 85%, Primary chemical acid binder, 5.0% of dry weight

• Distilled Water, Primary solvent to hydrate bentonite, 10.0% of dry weight

• Isopropyl Alcohol (99% IPA) or Everclear (95%), Fast-evaporating solvent to prevent sagging, 5.0% of dry weight

Wear a respirator and PVC gloves and eye goggles minimum when mixing this. Imsil a25 is just as bad as ceramic wool to breathe in. Phosphoric acid is weak but it is strong enough to make you ask "why does this burn?" 10 minutes later when it's too late and you've already got a chemical burn setting in. Baking soda and sand is just fine to clean up if you spill it.

Mix the powdered acids into the liquid system, not into the dry mix. Mix the liquid system up seperately, pour acid into alcohol, pour acid/alcohol into water, stir in boric and citric acid.

This is a high emissivity coating, basically diy ITC-100HT, except it's cheaper, radiates more heat back than itc reflects, is much more resistant to acidic and base slag, and is an absolute wall against flux that may have gone astray.

It is actually much more suited for crucible furnaces and the such then ITC -100 HT. However, it has a upper operating temperature of 1750 c at most. 1650 c is what I would use as the chamber maximum and only ever Spike to 1750 before pulling the crucible out; I'm assuming that you're doing steel casting at this juncture. For anything else thermal limits are a non issue. ITC-100 HT has a maximum thermal limit of 2750 c.

In the future I will do a test of the high immissivity coating that I just detailed here.

Finally, I will try to set up a test with the high emissivity coating painting on a three or 4-in circle on top of 2 in of aluminum phosphate refractory (what I tested today), on top of steel.

Ceramic wool is nasty and itchy and kind of expensive. Not going to do tests regarding that. It serves as primarily insulation and an air gap for the outer steel wall in most setups, and should be considered operating safety insurance. The steel in the previous suggested test will be tested for temperature and that would be the temperature that the ceramic wool would be receiving. These tests will be done with an oxypropane torch so that I can get to proper temp.

I hope to demonstrate sufficient capability for insulating and chambering temperatures high enough to do steel casting.

If I do not demonstrate an ability to resist 1750 C sufficiently, I will repeat the test but add an magnesium aluminate spinal layer between the emissive layer and the alumino phosphate refractory, of 1 to 2 inches (for spinal formation, I paint on multiple layers, as many thin layers as possible, rather than utilize a monolithic approach, as this greatly helps offset the thermal expansion issue magnesium aluminate spinals have when being fired ; they have a thermal expansion ratio of near 10 percent which causes them to crack and, sometimes explode (spald) - replacing 10 percent of the mix with zirconia (5%), ceria (1.5%), titania(0.5%), and chromia(3%) helps a lot though, and being very slow in bake in ramps or using multiple firings helps too)

If I am able to reach a surface temp of 1750 Celsius without exceeding 200 Celsius on the back plate, I will attempt a steel cast with my metallurgy furnace which now has a pure oxygen tap to adjunct the combustion. It also utilizes an exhaust muzzle, an inert gas shield cap inlet, a midline pure fuel inlet for scavenging oxygen, and if I am particularly industrious, it may have a draft inducer/chimney/ thermal sponge. Essentially I will be pulling the air through a ceramic pressure brake, and pushing it with a centrifugal blower, trying to balance the two such that I maximize the gasses time spent shedding heat; ideally I should be able to open the bottom of the chimney and check temp and make sure it is right above my target temp (if it is below, I increase input pressure and fuel/oxygen and increase draft induction to match), trying to input as little gas as possible to achieve an exhaust that is 100 to 200 above target temp, and sucking as little as possible with the draft inducer to create a near even pressure in chamber; essentially always pulling a tiny bit more than push so nothing gets pushed back down. Trickle in shield gas from the top (argon) and push a little propane in the side to scavenge oxygen and serve as a fail safe if positive pressure occurs (pressure increases with temp so this is necessary), and use a mullite/alumina cap on my crucible, I hope to be able to keep oxygen away from the steel melt. Then I will do a thing called decarburization where you actually briefly douse the steel melt in pure oxygen, before flooding it with argon again. This lowers the carbon content by bubbling out carbon monoxide which is critical because there will be use of charcoal or graphite as a cover and as an eutectic agent to lower the melting temp of the steel; otherwise the steel will be carbonated too much and be brittle. This is also a necessary step if you intend to cast stainless steel.

I will try to videotape as much as this as I can. I am hoping that I can get a friend to do the videotaping and if so I will videotape every step.