Aqueous sodium silicate, unspecified concentration and modulus, goes for US$2/kg.
Bentonite (“bentonita sodica”) goes for US$0.30/kg (AR$1260/25kg). It’s the binder in greensand. Other vendors sell it in adulterated form as clumping cat litter for US$0.55/kg.
Ground coal (“carbon mineral molido para fundicion”) goes for US$0.70/kg (AR$2941/25kg).
They sell a product called “tierra de Junín” for aluminum casting for US$0.20/kg (AR$1346/40kg). I’m guessing this is a substitute for quartz sand; people say you need to add bentonite.
Low-temperature (1100°) kaowool-type ceramic fiber blanket, density unspecified, goes for US$0.60/ℓ (AR$1565/2.5cm/61cm/1m, which is 15 liters and US$9.60).
Fiberglass is good to much lower temperatures but far cheaper at US$0.026/ℓ (AR$13583 for 3 × 1.2 mm × 18 m × 50 mm = 3240 ℓ for US$83). Typically it has trouble above 230°. “High density” is evidently 14kg/m³ and normal values are 7.7–12.1 kg/m³ so this is probably in that ballpark; if it were 10 kg/m³ that would be almost US$3/kg.
Fiberfrax 1260° 96 kg/m³ ceramic fiber blanket costs US$0.40/ℓ (AR$7000 for 7200 mm × 610 mm × 25mm).
Solid firebrick (advertised as 1300°, 38% alumina) costs US$1.10/brick (23 cm × 11.5 cm × 6 cm, 3.6 kg).
Insulating 1480° firebricks (“K26”) cost US$3 (23 cm × 11.5 cm × 6 cm).
1000° refractory mortar costs US$0.80/kg, premixed.
1750° refractory mortar (SURECAST 80, 80% alumina) costs US$0.90/kg, premixed, but comes in a 30kg bucket.
Alumina in 100-μm grains (325 mesh) is US$3/kg.
Red clay is US$0.30/kg (“temp max 1180°”, which I doubt it reaches.)
Ball clay (?) is US$0.30/kg (AR$1240/25kg). 200 mesh, 1150° firing.
200-mesh quartz is US$0.30/kg (AR$1120/25kg). Quartz sand (“molido tipo azúcar o sal fina”, so probably about 150 μm) is US$0.35/kg, while quartz flour (200-mesh, but “impalpabale”?) is US$0.27/kg.
200-mesh talc is US$0.40/kg (AR$1550/25kg). Talc is very interesting; see Firing talc.
200-mesh calcite is US$0.20/kg (AR$790/25kg).
200-mesh potassium feldspar is US$0.30/kg (AR$1240/25kg).
325-mesh infusorial earth is US$0.40/kg (AR$1390/20kg).
Calcined metakaolin is US$0.35/kg (AR$1160/20kg). Uncalcined “super white” kaolin is US$1/kg.
Sparkly 30/80-mesh wet-milled mica is US$2.30/kg.
Alumina sold as abrasive (polvo abrasivo para pulir) is US$7/kg, regardless of whether it’s 80-grit, 120-grit, or 220-grit. I'm assuming it’s alumina; it's gray, so it’s hard to tell.
There’s this guy in San Juan who sells graphite crucibles at prices from US$52 to US$58 to US$100, depending on the size. A different vendor they’re good to 1600°, but I don’t know if that’s because the graphite is bonded with clay or something or because graphite burns too fast in air above that temperature.
These guys sell natural zeolite clay as an insecticide for US$7/kg; otherwise they mostly sell cosmetics supplies (ti tree oil, cetyl alcohol, castor oil, cocoa butter, bentonite, etc.)
Zirconia abrasive wheels are widely available but I haven’t been able to find zirconia in bulk.
Astonishingly, high-pressure sodium lucalox bulbs are also widely available; this 250W bulb costs US$12.
You can get construction sand for US$0.03/kg, which is pretty much pure quartz, alabaster for US$0.30/kg, and slaked lime for US$0.11/kg.
Apparently pumice is sold for US$0.14/ℓ under the brand name “Pometina” as an aggregate for lightweight concrete (“la roca natural mas liviana con un peso de 0,4 Kg / dm3 (menos que el agua)”), or at US$0.17/ℓ, which I guess would be US$0.42/kg, in 1-4 cm stones; they say it has no compressive strength, as a substitute for LECA. (At a slightly later date, it turns out the garden store down the street sells it for AR$370/10ℓ when US$1 = AR$180, thus US$2.10 or US$0.21/ℓ.) LECA itself (1200°?) is mostly sold for hydroponics these days, for US$0.29/ℓ or US$0.12/ℓ for construction, and is about three times as dense; perlite (1150°) goes for US$0.38/ℓ at 0.128 kg/ℓ, so US$3/kg; rock wool (maybe 700–850°?) growth medium for US$0.31/ℓ at 0.1 kg/ℓ, so also US$3/kg; and vermiculite (1100°) for US$0.23/ℓ, at 0.06-0.16 kg/ℓ.
Unspecified broken-rock aggregate for concrete is more like US$0.08/kg, same price as ornamental 1–4 cm landscaping rocks. Even better, round 1–3 cm river rocks are only US$0.09/kg. However, these rocks probably don’t have reliable refractory properties.
Gravel for fishtanks goes for US$0.19/kg (2–4 mm I guess) while gravel (“cascote”) for concrete is US$0.016/ℓ, so probably US$0.008/kg, and construction gravel “6/20” (I think that means “6-20 mm”) is US$0.03/ℓ, which is probably close to US$0.01/kg. Pure white marble pebbles (700°, say) is pricier at US$0.14/ℓ, which is at 1.25 kg/ℓ US$0.12/kg. Quartz gravel aggregate for concrete is sold as one type of “nonmetallic hardener”; for example, US$0.15/kg for an 8/20 grade (which I think is 8–20 mm); as ornamental stone another vendor sells it for US$0.021/kg, 6 tonnes minimum order.
Commercial castable insulating refractories sell for prices around US$1/kg.
[Other solid firebricks] go for prices depending on their alumina content. 23 cm × 8 cm × 11 cm bricks go for US$1.50 used, US$2 new if 45% alumina; US$2.50 new if 60% alumina; US$3.50 new or US$4.30 used (?) if 90% alumina.
This guy Ariel Weston is evidently marketing carborundum (“carburo de silicio”) as “esmeril” at US$1.80/kg up to 220 mesh.
Phosphate is a crucial ingredient in many refractory cements. Previously I found that the cheapest way to buy it is as diammonium phosphate fertilizer, which is now US$1.00/kg and not very pure. By comparison, food-grade 85% phosphoric acid is US$3.40/kg; the pure substance is 98 g/mol of which 30.97 is phosphorus, so the liquid is thus 26.9% phosphorus by weight and US$13 per kg of phosphorus, while the fertilizer is nominally 132.06 g/mol and thus 23.4% phosphorus by weight and US$4.30 per kg of phosphorus. Either of the two might be more convenient, depending on circumstances. Trisodium phosphate goes for about US$2/kg.
Químico Cotton Fields sells boric acid for US$2.90/kg, but Planeta Verde sells it for US$1.70/kg; borax is sold by others for sealing ceramic crucibles for US$10/kg. Planeta Verde also sells aluminum sulfate for US$1.50/kg as a swimming pool clarifier; this is a potentially useful soluble aluminum salt for making either aluminum phosphate or foam of hydrated alumina. Many vendors also sell potassium alum, a soluble double sulfate of aluminum, for about US$3.50/kg, and MG Química also sells ammonium alum for US$8/kg, along with a bunch of food and cosmetics ingredients like borax, menthol, glycerin, turpentine, sodium lauryl sulfate, triethanolamine, sodium hyposulfite, silicone lubricant, lye, colophony, polyethylene glycol, carboxymethylcellulose, etc.
(Unrelatedly, Cotton Fields sells the pharmaceutical grade of the nontoxic wide-temperature-range coolant propylene glycol at US$6/kg, as well as triethanolamine, oxalic acid, naphthalene, isopropanol, sorbitol, povidone (polyvinylpyrrolidine), etc.)
Silica gel in particular goes for about US$5/kg. Other vendors sell it as silica cat litter for US$1.54/ℓ, which seems cheaper.
Someone is selling a lot of 5 carborundum globars for US$12 (brand: “Delta”). Someone else is selling what claims to be Kanthal A-1 for a variety of prices, such as US$0.72/m for 1-mm diameter, as well as 1-mm-diameter 80/20 nichrome for US$1.20/m. Thinner nichrome is naturally cheaper per meter; it’s largely marketed for making and fixing segelines.
My efforts to find abrasives
welding blankets
zirconia
carborundum
alumina