Thermite - Revision history

NebarnixWikiSysop: /* Hope Appears! Ceramics Quality Red Iron Oxide */

2018-04-25T18:11:51Z

Hope Appears! Ceramics Quality Red Iron Oxide

NebarnixWikiSysop: /* Hope Appears! Ceramics Quality Red Iron Oxide */

2018-04-25T18:09:55Z

Hope Appears! Ceramics Quality Red Iron Oxide

NebarnixWikiSysop: /* Kiln wash and Grog 50/50 */

2018-04-10T15:22:39Z

Kiln wash and Grog 50/50

NebarnixWikiSysop: /* Furnace Cement */

2018-04-10T15:17:22Z

Furnace Cement

NebarnixWikiSysop: /* Furnace Cement */

2018-04-10T15:17:09Z

Furnace Cement

NebarnixWikiSysop: /* Lessons Learned */

2018-04-10T15:15:26Z

Lessons Learned

NebarnixWikiSysop at 15:14, 10 April 2018

2018-04-10T15:14:28Z

NebarnixWikiSysop: /* Lessons Learned */

2018-04-10T15:13:14Z

Lessons Learned

NebarnixWikiSysop: /* Plaster and Dextrin */

2018-04-10T15:11:29Z

Plaster and Dextrin

NebarnixWikiSysop at 15:10, 10 April 2018

2018-04-10T15:10:42Z

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 Creating iron oxide in the lab is a large effort low yield process when going directly to an Iron Hydroxide Gel. The density of the gel is quite low, 8 oz is only a gram or so. Asking around it seems the local ceramic supply store carries multiple 'colors' of Iron Oxide for $6 a pound. The red stuff was VERY red, which is a great sign. It also extremely 'cakey' which indicates very fine particle sizes, also a good sign. Sure enough, a 50g test yield was about 12g of the possible 26g theoretical which is not as good as the lab grade, but certainly better than using dirt based ores.
-A 200g test using the ceramic store red iron oxide and 50/50 lab grade aluminum and internet 5 micron aluminum was conducted. A natural clay from my backyard was used to form a funnel in the bottom of a flower pot. It was not fired, only dried at 200 degrees F overnight. The thermite was packed solid with an espresso tamper and ignited with a sparkler. The kiln wash based mold was filled with 55.6g of iron. 66.3g total was recovered (some spilled outside of the mold). This is 64% of the maximum possible yield!
+A 200g test using the ceramic store red iron oxide and 50/50 lab grade aluminum and internet 5 micron aluminum was conducted. A natural clay from my backyard was used to form a funnel in the bottom of a flower pot. It was not fired, only dried at 200 degrees F overnight. The thermite was packed solid with an espresso tamper and ignited with a sparkler. The kiln wash based mold was filled with 55.6g of iron. 61.2g total was recovered (some spilled outside of the mold). This is 58% of the maximum possible yield. Not as good as the lab grade, but significantly better yield than the ore, and at a price point that makes the difference irrelevant.
 == Mold Process Progression ==

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 Creating iron oxide in the lab is a large effort low yield process when going directly to an Iron Hydroxide Gel. The density of the gel is quite low, 8 oz is only a gram or so. Asking around it seems the local ceramic supply store carries multiple 'colors' of Iron Oxide for $6 a pound. The red stuff was VERY red, which is a great sign. It also extremely 'cakey' which indicates very fine particle sizes, also a good sign. Sure enough, a 50g test yield was about 12g of the possible 26g theoretical which is not as good as the lab grade, but certainly better than using dirt based ores.
-A 200g test using the ceramic store red iron oxide and 50/50 lab grade aluminum and internet 5 micron aluminum was conducted. A natural clay from my backyard was used to form a funnel in the bottom of a flower pot. It was not fired, only dried at 200 degrees F overnight. The thermite was packed solid with an espresso tamper and ignited with a sparkler. The kiln wash based mold was filled with 55.6g of iron. This is 75% of the maximum possible yield!!
+A 200g test using the ceramic store red iron oxide and 50/50 lab grade aluminum and internet 5 micron aluminum was conducted. A natural clay from my backyard was used to form a funnel in the bottom of a flower pot. It was not fired, only dried at 200 degrees F overnight. The thermite was packed solid with an espresso tamper and ignited with a sparkler. The kiln wash based mold was filled with 55.6g of iron. 66.3g total was recovered (some spilled outside of the mold). This is 64% of the maximum possible yield!
 == Mold Process Progression ==

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 === Kiln wash and Grog 50/50 ===
-Mulcoa 200 Grog seemed promising to cut the kiln wash with to keep the shrinkage down. The process works extremely well for aluminum and other lower temperature metals. It almost works for the thermite process, but seems to plastic deform at temperature leading to a low pass filtered look on mold details. No 3D print lines are visible in the final distorted product, but also no boiling or glassing is observed either. Progress.
+Mulcoa 200 Grog seemed promising to cut the kiln wash with to keep the shrinkage down. The process works extremely well for aluminum and other lower temperature metals. It almost works for the thermite process, but mullite, the major component, melts around 1800 C. The mix seems to plastic deform at temperature leading to a blobby low pass filtered look on mold details. No 3D print lines are visible in the final distorted product, but also no boiling or glassing is observed either. Progress, though not really good enough.
 === Kiln wash and Fired Kiln Wash 50/50 ===
 Kiln wash cut with 50% pre-fired kiln wash seems to be the next logical step. Pre firing half of the material will keep the shrinkage under control, but the ultimate mold strength may be less. A binder such as sodium silicate might be the answer, but might also act as a flux to lower the melting point. A higher firing temperature may be necessary with an oil based binder to maintain mold integrity during the dehydration temperatures <500 C.

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 === Furnace Cement ===
-Furnace cement seemed promising at first, but it seems that even the 2700 degree cement decomposes to gassy and glassy byproducts at thermite temperatures, and plastic deforms like modeling clay at red hot temperatures. It is not a good material for coming into direct contact with the thermite reaction or the molten metal itself. It is a good last layer for structural support during the other parts of the process.
+Furnace cement seemed promising at first, but it seems that even the 2700 degree cement decomposes to gassy and glassy byproducts at thermite temperatures, and plastic deforms like modeling clay at red hot temperatures. It is not a good material for coming into direct contact with the thermite reaction or the molten metal itself. '''It is a good last layer for structural support during the other parts of the process.'''
 === Pure Kiln Wash ===

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 === Furnace Cement ===
-Furnace cement seemed promising at first, but it seems that even the 2700 degree cement decomposes to gassy and glassy byproducts at thermite temperatures, and plastic deforms like modeling clay at red hot temperatures. It is not a good material for coming into direct contact with the thermite reaction or the molten metal itself.
+Furnace cement seemed promising at first, but it seems that even the 2700 degree cement decomposes to gassy and glassy byproducts at thermite temperatures, and plastic deforms like modeling clay at red hot temperatures. It is not a good material for coming into direct contact with the thermite reaction or the molten metal itself. It is a good last layer for structural support during the other parts of the process.
 === Pure Kiln Wash ===

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 == Lessons Learned ==
 * '''Brown dirt''' is mostly not Iron Oxide, and is basically useless for casting. If your thermite burns for more than ~1-2 seconds, it won't work.
 * A mix of fine ($$) '''aluminum''' and a mix of less fine ($) aluminum works OK in at least a 50/50 mix. Using only cheap 5 micron aluminum seems to impact the yield as the burn time is too long and heat is allowed to escape.

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 == Lessons Learned ==
-* Brown dirt is mostly not Iron Oxide, and is basically useless for casting. If your thermite burns for more than ~1-2 seconds, it won't work.
+* '''Brown dirt''' is mostly not Iron Oxide, and is basically useless for casting. If your thermite burns for more than ~1-2 seconds, it won't work.
-* A mix of fine ($$) aluminum and a mix of less fine ($) aluminum works OK in at least a 50/50 mix. Using only cheap 5 micron aluminum seems to impact the yield as the burn time is too long and heat is allowed to escape.
+* A mix of fine ($$) '''aluminum''' and a mix of less fine ($) aluminum works OK in at least a 50/50 mix. Using only cheap 5 micron aluminum seems to impact the yield as the burn time is too long and heat is allowed to escape.
-* A single sparkler stabbed into the mix works well for ignitition. If a sparkler won't ignite it, it is probably crap thermite, and won't work for casting.
+* '''A single sparkler''' stabbed into the mix works well for ignitition. If a sparkler won't ignite it, it is probably crap thermite, and won't work for casting.
-* Air trapped in the thermite is bad. Incrementally hard pack as much as possible to decrease atmospheric oxygen losses. Do not use a binder.
+* Air trapped in the thermite is bad. Incrementally '''hard pack''' as much as possible to decrease atmospheric oxygen losses. Do not use a binder.
-* Natural clay is OK as a funnel inside a flower pot crucible, in fact, the decomposition probably acts as a lubricant to keep iron globules from sticking and not exiting the mold.
+* '''Natural clay is OK as a funnel''' inside a flower pot crucible, in fact, the decomposition probably acts as a lubricant to keep iron globules from sticking and not exiting the mold.
-* Use a lid on the crucible to contain the splatter. Not only is it safer, it redirects splatter back into the melt and increases yield.
+* '''Use a lid''' on the crucible to contain the splatter. Not only is it safer, it redirects splatter back into the melt and increases yield.
-* A few layers of aluminum foil or aluminum tape on the bottom of the crucible works well as a final exit gate for the molten iron.
+* A few layers of '''aluminum foil or aluminum tape''' on the bottom of the crucible works well as a final exit gate for the molten iron.
-* Mold materials matter. Firing of the mold materials beforehand matters. A blowtorch is not a kiln, and will not remove all of the PLA or water from the mold.
+* '''Mold materials matter'''. Firing of the mold materials beforehand matters. A blowtorch is not a kiln, and will not remove all of the PLA or water from the mold.
-* Playground sand works OK as a support structure for the mold, but one must take care to avoid getting sand into the mold.
+* '''Playground sand works OK''' as a support structure for the mold, but one must take care to avoid getting sand into the mold.
-* Once the mold cools to ~300C, shock using a water bath or the mold will be nearly impossible to remove. Re-heating with a blow torch before dunking is probably fine.
+* Once the mold cools to ~300C, '''shock using a water bath''' or the mold will be nearly impossible to remove. Re-heating with a blow torch before dunking is probably fine.
 ==Problem Statement==

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 == Log of Experiments ==
-=== Plaster and Dextrin ===
+=== Plaster and Dextrin (fail) ===
 Initially and naively I created a mold from plaster. I used a 3D printed calibration cat as the test piece, and added three vents by welding 1.75mm PLA filament to the high points of the print. I submerged the print into 50% plaster and 50% playground sand. I used a pen to create the main sprue about 0.5" long. The PLA was removed by placing the cured plaster mold upside down in the oven at 500 degrees F with a ramp rate of 50 degrees every 10 minutes.
 g of thermite using laboratory grade Fe2O3 and laboratory grade purified atomized aluminum was mixed with 2% dextrin and pressed into a 3" flower pot with a pencil sized central vertical cavity. An aluminum foil diaphragm covered the bottom of the terracotta pot. The dextrin was added in an attempt to create a solid 'brick' without air as well as a source of carbon for the creation of steel in stead of raw iron. A small amount of metal poured into the mold, but it was clear that the mold was mostly empty, so a second batch of 100g of the same mixture, but not moistened, was placed into a second flower pot and ignited. The mold was still not full, but was destroyed to asses the yield. A total of 35 grams of iron made it into the mold, and it was clear that the inlet was too small and several droplets of iron sat on top of the main sprue.
 The lower half of the calibration cat's shape was apparent, but massive amounts of frothing in the iron were observed as well as an extreme sulfur stench similar to the smell of a used ested model rocket engine tube. The sulfur was a byproduct of the plaster decomposing due to temperature, over twice the decomposition point. It was clear that plaster was not an appropriate mold material.
 === Thermite Yield Experiments ===