Sciencemadness Discussion Board

DIY Low Temperature Refractory Plaster/Cement?

VeritasC&E - 11-7-2021 at 15:22


Hello,

I'd like to build a small but energetically efficient beaker heater aimed to run for several hours at a time at temperatures way under 350-400C.

The idea is to build NiCr wire into a first sort of plaster/cement (Type A) and then suround that with a second sort of paster/cement (Type B).

Both plasters/cements are to be made up of one or a mix of several cheap and readily available compounds that could be safely inhaled or eaten is small quantities (e.g. SiO2 / Ca/Mg/Zn Compounds) and simple to prepare (used as sorts of paste that is then dried or heated to hardness).

Type A Plaster/Cement is meant to conduct heat very well such as to minimize thermal gradient from the NiCr wire on the glass and instead provide a more uniform heating surface. It's also the one that needs to be most resistant to heat, and not conduct electricity as it's directly in contact with the heating wire.

Type B Plaster/Cement is meant to be as thermally insulative as possible and enough solid to make up the bulk of the heater body (and layer above a glass cap that comes on top of the heated beakers).

I've searched the forum and there's many threads about refractory materials but they all seem destined at much higher temperatures and/or involve Aluminum compounds or other stuff I'd like to avoid using.

Would you guys suggest a recipe/mix for making my type A and type B plasters/cements (making it easy enough for me to apply with my very limited skills)?

Twospoons - 11-7-2021 at 18:12

I'd start by looking at either phosphate bonded or silicate bonded systems. I dont have a recipe, but the net should be thick with them. For the type B, take the type A cement and mix in as much vermiculite as you can.

VeritasC&E - 12-7-2021 at 08:28

Thank you for your contribution Twospoons. Vermiculite contains aluminum but I'll retail the general idea of adding a low conductivity/density compound to the same cement mix for greater insulation.

For anyone interested / finding themselves confronted to the same issue, the solution I found online which I think I'll go with is called Parkhomov cement. It's a mix of MgO, ZnO and Sodium Silicate (water glass). It's left to dry and then heated at low temperature (i.e. 200-300C) for a few hours.

Here's a video outlining the very rudimentary preparation:

https://m.youtube.com/watch?v=eQf9sthFEUU

unionised - 12-7-2021 at 09:45

Quote: Originally posted by VeritasC&E  
Vermiculite contains aluminum

So does tea.


You can make an insulating material by sticking this stuff
https://en.wikipedia.org/wiki/Perlite
together with water glass.

SWIM - 12-7-2021 at 10:03

How big a beaker do you want this for?

I've got glas-col beaker heaters in a few sizes and will let them go mighty cheap.

Postage plus $10

I believe some of the are equipped with thermocouple wires if you want thermostatic heating control.

But these are glas-cols, so they don't come with power controllers or the electronics to control the heating with the thermocouple.

I'm in Calfornia, so if you're not in this part of the world postage and customs may be a consideration

VeritasC&E - 12-7-2021 at 10:27

Quote: Originally posted by unionised  
Quote: Originally posted by VeritasC&E  
Vermiculite contains aluminum

So does tea.


You can make an insulating material by sticking this stuff
https://en.wikipedia.org/wiki/Perlite
together with water glass.



True, as does tap water, but there's a few degrees of magnitude's difference in their content, a world of difference.

I take notes about using water glass as glue + anything refractory.

VeritasC&E - 12-7-2021 at 10:33

Quote: Originally posted by SWIM  
How big a beaker do you want this for?

I've got glas-col beaker heaters in a few sizes and will let them go mighty cheap.

Postage plus $10

I believe some of the are equipped with thermocouple wires if you want thermostatic heating control.

But these are glas-cols, so they don't come with power controllers or the electronics to control the heating with the thermocouple.

I'm in Calfornia, so if you're not in this part of the world postage and customs may be a consideration



Swim,

Thank you for your offer! I'd like to manufacture myself, not just for the precise heat control, but for the self-satisfaction of having acquired a small skill on the way.

I have to say though that I very much appreciate your generous offer to help a fellow chemist on his path, it is outmost noble of you.

SWIM - 12-7-2021 at 22:04

I can see where making your own would be much more interesting and gratifying.

Good luck.

unionised - 13-7-2021 at 04:16

Quote: Originally posted by VeritasC&E  




True, as does tap water, but there's a few degrees of magnitude's difference in their content, a world of difference.

I take notes about using water glass as glue + anything refractory.

Perlite (and vermiculite) a re full of air filled spaces so they are particularly good insulators.

The aluminium in tea is in solution and is orders of magnitude more bioavailable than the stuff in a lump of rock or, for example, borosilicate glass.

VeritasC&E - 13-7-2021 at 06:53

Quote: Originally posted by SWIM  
I can see where making your own would be much more interesting and gratifying.

Good luck.



Thank you Swim!

VeritasC&E - 13-7-2021 at 07:07

Quote: Originally posted by unionised  
Quote: Originally posted by VeritasC&E  




True, as does tap water, but there's a few degrees of magnitude's difference in their content, a world of difference.

I take notes about using water glass as glue + anything refractory.

Perlite (and vermiculite) a re full of air filled spaces so they are particularly good insulators.

The aluminium in tea is in solution and is orders of magnitude more bioavailable than the stuff in a lump of rock or, for example, borosilicate glass.


We could make a thorough comprison of both, there's good arguments on both sides.

Tea
+++ Low Relative Aluminum Content
+++ Bioavailability may be strongly limited by simply adding milk or calcium carbonate
++ Low to no exposure from the environment after use
++ Aluminum passing the GI tract is rapidly excreted into urine (low half life in the body)
++ Household handling of tea is unlikely to result in much dust exposure
+ Contains fair amount of oxalic acid and phytic acid which possibly limit HCl solubilization of Al in the stomach, thus limiting bioavailability)
- - Routine/Chronic Exposure is more likely
- - Direct GI tract exposure (likely greater acute impact on bloodborn Aluminum)

Perlite
++ Only a small amount is directly acutely solubilized
++ Much less enters the GI tract vs tea
+ Routine/Chronic Exposure is less likely
- - Dusts are harder to quickly remove from the environment after use
- - Forms dust that gets into lungs, then very slowly released over time (long half life in the body)
- - - High Relative Aluminum Content

[Edited on 13-7-2021 by VeritasC&E]

VeritasC&E - 13-7-2021 at 10:06

Does anyone know if I can put two dimmers in series for more precise temperature control?

Twospoons - 13-7-2021 at 14:08

Quote: Originally posted by VeritasC&E  
Does anyone know if I can put two dimmers in series for more precise temperature control?


Unlikely. You'd do better to use one dimmer and replace the single turn control pot with a multi-turn one.

There are also 10 turn knobs that you could use instead, like this:
https://www.aliexpress.com/item/4000178399666.html.
No soldering, just need a screwdriver.


[Edited on 13-7-2021 by Twospoons]

Twospoons - 13-7-2021 at 15:42

Why are you so worried about aluminium? You know its everywhere - in rocks and soil, in most glazes, in concrete etc.
Alternate insulating fillers: softwood sawdust (eg pine), styrofoam beads. Both will need a bakeout to create the insulating voids. You can also use ceramic fiber blanket , which is readily available, but probably more dangerous than vermiculite.

VeritasC&E - 13-7-2021 at 15:56

Quote: Originally posted by Twospoons  
Quote: Originally posted by VeritasC&E  
Does anyone know if I can put two dimmers in series for more precise temperature control?


Unlikely. You'd do better to use one dimmer and replace the single turn control pot with a multi-turn one.

There are also 10 turn knobs that you could use instead, like this:
https://www.aliexpress.com/item/4000178399666.html.
No soldering, just need a screwdriver.


[Edited on 13-7-2021 by Twospoons]



Thank you!

I'm not too worried about Aluminum, as long as I don't risk exposing my inner self to it more than necessary. Cadmium, Arsenic, Lead, Mercury is also ubiquitous (in smaller amounts). If I can make refractory mortar without Aluminum compound dust, I'm happy, and I'd encourage you and anyone to do the same if it requires limited efforts and fits your requirements.

I'm a biologist.

Microtek - 10-8-2021 at 03:32

Do you have any sort of references documenting problems with Al-compounds? Al-salts are found in sea water (ca. 5 micrograms per liter) and therefore also in table salt made from evaporation of sea water.

macckone - 10-8-2021 at 08:53

Quote: Originally posted by VeritasC&E  
Does anyone know if I can put two dimmers in series for more precise temperature control?


Two dimmers in series won't have the desired effect because of how they work.

If you want precise heat control you are going to need to go with something more expensive. You can get relatively inexpensive PID controllers that work on K type thermocouples. Getting ones that work with pt100 RTDs is usually more. The nice ones have solid-state relays and can provide really accurate temperature control.

andy1988 - 10-8-2021 at 10:17

No aluminum in Superwool (or maybe <1%). Materials say it is much safer to handle than other ceramic blankets, mask not required [1][2]. Something about the particle size distribution being non-irritant and non-toxic composition IIRC. I'd wear a mask and vacuum the area after handling anyway. A roll is ~$100 and people sell smaller sections for a markup on ebay and etc. Something to consider instead of the refractory material you're thinking about. Cut and shape the wool to fit your apparatus.
Quote:

Superwool Plus blanket Chemical composition, %:
SiO2 62 - 68
CaO 26 - 32
MgO 3 - 7
Other oxides <1 [3]


I thought this [4] was a good paper on aluminum toxicity. Excerpts:
Quote:

[...]dose for the oral rouse is dependent upon additional conditions such as the presence of citrate.
[...]These data confirm clinical observations that renal compromise aggravates Al accumulation. As individuals age, renal function decreases.


Aluminum is not well absorbed by the GI tract... it typically does a good job keeping it out. So... maybe not the best routine to consume orange juice with aluminum-containing food products? Maybe an explanation for dementia/alzheimer's...

When examining the literature you must keep in mind many rodent species are exceptionally resilient to aluminum toxicity in comparison to humans and other mammals [5].

You can also find aluminum salts in food stuffs, like pre-cooked tortillas, and macaroni and potato salad from the deli. Used as a leavener in flatbreads, also some processed cheeses. I don't know why alum is used in those deli products, it may have something to do with tradition or extending shelf-life through the inhibition of replication of organisms causing spoilage. However the aluminum is also harmful to humans if it is absorbed, through mechanisms like mitochondrial damage [4], disruption of intracellular Ca+ homeostasis [4], and more unknowns.


References:
[4] Jeffery, E. H., Abreo, K., Burgess, E., Cannata, J., & Greger, J. L. (1996). Systemic aluminum toxicity: effects on bone, hematopoietic tissue, and kidney. Journal of Toxicology and Environmental Health Part A, 48(6), 649-666.
[5] Foulkes, E. C. (1990). Biological effects of heavy metals.

[Edited on 10-8-2021 by andy1988]

macckone - 10-8-2021 at 14:07

aluminum is a common element in soil.
everything contains some amount and it is easily excreted since the vast majority of it's salts are soluble.
renal issues impact a lot more than aluminum excretion.
I have renal issues and have for 20 years. If that was the cause of alzheimers, I would have it.
I also have genetic markers for predisposition. I also have inherited mitochondrial issues.
Those genetic markers may be related but they have nothing to do with aluminum.

Now back to our original discussion.
Super wool is not as heat resistant as kaowool.
The HT is only good to 1300C.
Kaowool 3000 is good to 1650C.

For really refractory requirements you have to use pure alumina or pure magnesia.
With magnesia based refractories being the primary type used in blast furnaces.
Silica based refractories also break down with heat cycling unlike kaolin based refractories.

As for the requirements the OP requested, most low binder fiberglass will work.
Example welding cloth: https://www.amazon.com/ZYAMY-Hands-Free-Resistant-Fiberglass...

For under $50 you can get fire resistant mineral wool insulation that will work up to 1000C and somewhat beyond.
It is often made from slag from blast furnaces and your mileage will vary above 1000C.
The following product supposedly uses a non-flammable binder (suspect sodium silicate/phosphate or similar)
https://www.homedepot.com/p/Owens-Corning-R-15-Thermafiber-U...

happyfooddance - 11-8-2021 at 11:51

I've been using finely ground vermiculite + waterglass to make firebricks with great success.

I've wanted to post more about it but I've been extremely busy lately, but y'all can figure it out, I'm sure...

Edit: Also, there's the MgCl2 + MgO + H20 refractory, though it doesn't insulate nearly as well as verm/waterglass

O.P.: The serious difficulty I see with your idea is you are going to need plasters that have the same or similar thermal expansion coefficients both during construction (while drying) and operation
[Edited on 8-11-2021 by happyfooddance]

[Edited on 8-12-2021 by happyfooddance]

Fyndium - 13-8-2021 at 10:48

LECA aggregate is good insulator, owing it's high air content and low thermal mass. I suppose it could be glued together with silicate based refractory caulk.

I prefer ceramic wool, because it is lightweight, it has near zero thermal mass, meaning very little energy wasted heating the oven itself, and it cools rapidly and can be readily cut and formed into any desired shape with steel mesh backing and steel wire. To be honest, I would never ever touch any masonry after getting into wools, heavy duty refractories are good for sustained production environments like production kilns that retain the heat and are in constant use without thermal cycling. What I failed to do with high mass refractories in three years, I succeeded in a week with a wool made raku type kiln.

[Edited on 13-8-2021 by Fyndium]