james manning

Brian,

I hope you're right! I don't mean to sound like a negative nancy... I've just worked with these refractories for years, please note I'm not saying an IFB/ fiber core won't work (they're great insulators) rather I'm just curious as to the lifespan vs the cost of an IFB/ fiber core vs the lifespan vs cost of an SiC/ fiber core. For shits and giggles I've fired a soft brick next to a hard brick in a wood kiln a few years back... the soft brick eroded by half its volume in one firing, while the hard brick was slightly bigger from an accumulation of melted ash without having worn away or eroded. I am still interested in this project though and would be interested in helping track the life cycle and total run hours of any configuration as I believe that we will do more with data to push UL standards and bring this tech into the mainstream.

P.s. have you checked out Kacheloffens/ Masonry stoves? They seem like the big brother to rocket mass heaters but prettier!

P.P.s if the cost is less than 50 bucks count me in on your project.

I don't think think the expense is in the casting. There shouldn't be any reason why the draft angles to make it in one or two pieces would get in the way. It's really about spreading the cost of setup, design, and tooling over enough units to bring that cost down. Additionally, my thoughts for SiC were that people use it in wood fired kilns over 2600 f for decades and they're still serviceable. That's why I'm curious to track life vs cost/ energy required to fabricate. My thoughts are that a SiC core insulated with ceramic fiber would out last an IFB core by an order of magnitude of thousands... My basis for this is that no one uses soft brick in anything wood-fired because the alkalis degrade it very quickly (wood firings typically go to over 2500 f and will stay there while accumulating caustic ash deposits for hours) while SiC lasts in these conditions for decades. That being said, if the short run time of a rocket stove limits exposure at temps that melt ash maybe it's not an issue, but then wouldn't said ash be a particulate concern?

Hey Brian, I hope that works. There is a castable version of IFB (soft brick refractory) called Greenlite (they have different grades, the increasing number corresponds to tougher stuff) A monolithic interior should last longer and ship easier. I do wonder if this may end up being a more cost effective version than the Silicon Carbide? The advantage of the SiC is that is non-porous and more resistant as a whole to the erosion/abrasion of combustion gasses in regards to the flow (think wind erosion) and chemical attack (wood ash has a high alkali/alkaline content). When do you expect a prototype? I work with a company out of the Boston area that has a fast turnaround time... Have you thought about building it outside and running it nonstop (sleep depending) in order to ascertain lifecycle? A shared google sheet with all owners could allow an aggregation of data (spall, hot face wear, cracking) to be tracked over time to factor in the price of the riser vs life and factor that into the overall efficacy... How much does one cost?

Regards, James

How's this coming? I've heard mention of it on the podcast and was wondering what the difficulty is... Is it scale? If there were enough interest we could have saint gobain make a custom SiC core about a 3/8 inch thick that could then be insulated with ceramic fiber wool... The SiC is expensive (relatively) but is specifically made for extreme heat (its strongest over 2200 f), thermal shock, and corrosion. The fiber is the best insulator you can buy for these temps. The whole thing should be less than 25lbs and should last for years.

Hey guys some info for wood fired kilns. The following books not only give good info but also plans and some material lists.

Wood fired stoneware and porcelain by Jack troy
Kiln book by Fred Olsen
Japanese wood fired ceramics by kusakabe and Lancet

Also, I make a living working in combustion and refractories hit me up if you hit a snag! manningceramics @gmail.com

Hi folks. I was asked to weigh in on this thread a while back so I apologize for the delay but the wide range of topics required some sort of organizing my response. As I see it there seem to be several concerns and I think that I’ll address them in increasing complexity so ya’ll can bail out when I start sounding like a martian.

So first off ceramics is a field that has a fairly high capital outlay and embodied energy cost, which is fine if this is your business but maybe not quite as practical for a project or two. Add this to the rather specialized skillsets needed to make pots or tiles and you’re probably better off getting them elsewhere for a better ROI (most novices find it hard enough to make something over three inches and keep it roundish). That being said anyone interested in ceramics should give it a go but just be aware that you may be more in the having fun category and it probably will cost more than you could ever save, but if you have fun it’s not my place to say how you spend your money.

As for the durability of wares in low fire… they just aren’t and quite frankly anyone who thinks something fired at 1300 F is vitreous either doesn’t know the what vitrification is or is full of shit.

There are three ranges (broadly speaking) that we fire to: low, medium, and high fire. Vitrification is directly related to body maturity and therefore absorption rates, earthenware will have 5-15% absorption, stonewares 0.5-1.5% and porcelains less than 0.5%. As you fire hotter you get more vitrification. This isn’t to say that there isn’t a long tradition of cooking in low fired wares, cooking a pot does the same thing as cooking food… It kills germs. However those germs won’t stay above the critical 140 degrees for long enough on wares one eats off.

That brings us to testing standards. Unless someone can show you the documentation for acid and alkali(ne) leach testing of lead and cadmium don’t use the piece for food or drink. This testing should be at the cone it’s typically fired to as well as one cone up and down to ensure safety within a margin of temperature fluctuation. Technically there are ppm standards for both of these materials, however both will bioaccumulate as the body has difficulty dealing with inorganic compounds that aren’t needed. Crazing is the crackling pattern seen on some wares… It should be avoided on any food contact surface that is not on vitreous clay as the cracks go all the way to the clay body and if it is porous it will absorb material.

Microwave safety is mostly subjective with the exception of metallic lustre type finishes, depending on the user's tolerance for heat. Once again performance in regard to the heat transferred to a mug handle will improve (less heat felt in grabbing handle) as vitrification increases with higher firings. Use a potholder and you’ll likely have no problem here.

Few potters indeed, actually test their wares but most will tell you that it’s microwave and food safe, combine this with a tendency of potters to use glaze recipes they have found without knowing how to test or correct for faults and you have a tricky ricky situation.

In practical terms, anyone with enough interest can take up and do just about anything to a certain skill level. But there will always be an associated cost to learning.

Hey folks. I lurk on here quite a bit and thought I might be able to help in this regard. I am a working potter and industry glaze chemist and can shed some light here. First, as noted earlier toxicity is a matter of exposure rates... However there is also the format of an exposure to consider. For instance silica, one of the dangers in my line of work is mostly harmless ingested but harmful if inhaled. Also we must look at the nature of the compound you're exposed to, and example here is Barium oxide and carbonates that are used as rat poisons and Barium Sulfate which is used to provide contrast in an MRI this is possible because unlike the oxide and/or carbonate formats are soluble while the sulfate is not.

Now to the point of alumina (which is what we call Al2O3 in the ceramic industry)... The difference between glass and ceramic is alumina. So litterally every single piece of ceramic you have ever encountered has exposed you to alumina. Everything you drink out of or eat off of, unless you use paper or plastic (in which case we can't be friends). The oxidized form of alumina is highly stable, insoluble, and largely non toxic. Compare the melting points here with metallic aluminum melting just over 1200 F and alumina melting at over 3700 F. As a final note while you never need a brick with that alumina rating for an oven, any firebrick would be pretty damn stable at even high pizza oven temps of 1000 or so degrees... cook the shit out of them pizzas and rest easy.