Milestone Temperatures in Ceramics

50-250C - Hygroscopic water removed in clay bodies
80C-250C - Calcium Sulphate decomposition
120C - Borax
150C - Epsom salts decompose to lose water
180C - Boric Acid expels water
185C - Copper hydroxide decomposes to CuO
200C - Manganese Carbonate decomposes to MnO
200C-1000C - Decarbonation
200C-450C - Alumina Hydrate Decomposition
210C-280C - Cristobalite inversion (alpha/beta)
250C-370C - Organic burnout
260C - Bismuth Subnitrate decomposes
290C - Copper Carbonate decomposes to CuO
300C-330C - Copper carbonate basic decomposes
300C - Boron from Boric Acid melts
370-950C - Carbon / iron oxidation
400C-600C - Dehydroxylation of Kaolin
400C - Colemanite reacts to water loss
425C-650C - Sulfur evolution
480C-600C - Dehydroxylation in clays
500C-600C - Magnesite decomposition
512C - Hydrated lime decomposes (25% H2O)
535C - Manganese dioxide decomposes to MnO
540C-600C - Quartz inversion (alpha-beta)
650C-900C - Dolomite decomposition
700F - Sodium Carbonate Dehydrates
750C-1000C - Calcium carbonate decomposition
750-850 - Amorphous cargon burns from Texas Talc
800C-1100C - Strontium carbonate decomposition
850-950 - Zinc oxide boils and volatilizes
850C - Sodium Carbonate decomposes
850C+ - Sintering and densification
900-1000 - Talc crystalline water vaporizes
900C - Co3O4 decomposes
990C - Chrome oxide decomposes
1025-1325 - Copper Oxide breakdown
1025C+ - Decomposition of Barium Carbonate
1050C - Copper carbonate basic breakdown
1050C - Metakaolin converts to mullite
1082C - Spodumene converts to beta phase
1100C+ - Antimony volatilizes
1100C - Mullite converts to cristobalite
1100C - Strontium carbonate melts
1300C - Li2O Decomposes
1325C - Copper oxide melts
1330C - Fluorspar melts
1360C - Barium carbonate melts
1400F - Gerstley Borate stops gassing
1400F - Common frits begin melting
1418C-1428C - Spodumene melts
1420C - Talc melts
1500F - Calcium carbonate, talc finished gassing
1550C - Zircon melts, slowly dissolves
1565C - Iron oxide red decomposes
1600F-1650F - Gerstley Borate Melts Suddenly
1650F - Talc has finished gassing
1785C - Manganese oxide melts
1800F - Densification
1950F-2050F - Body decomposition causes glaze bubbles
1990C - Chrome oxide melts
2300C - Praseodymium oxide decomposes
2320C - Neodymium oxide melts
2750F - Kyanite decomposes to Mullite and Silica


Many ceramic problems relate to a lack of understanding about what is happening at each stage of a firing, there are just so many materials that are doing so many things. This part of the database will help solve that problem. In a material-centric ceramic information universe it quickly becomes evident that each material has its own way to decomposing and melting. Many materials (especially ground minerals) have multiple decomposition events where they change crystal structure (accompanied by volume and state changes), release gases (e.g. CO2, H2O), soften and melt. This area of the knowledge base brings together all of the events in the thermal decomposition that have been defined for individual materials or minerals (however there are obviously interactions, see paragraph below). The result is a master temperature line that can be examined for any specific range to see what is happening there and specific temperature events that are linked to other parts of the database that relate to them.

One key thing to remember about studying the thermal history of how a material decomposes, alters and melts is this: In glazes and clay bodies materials interact, often they do not evolve in the same way when they are part of a mixture of other materials that is being heated. For example, barium carbonate decomposes at 1450C by itself, but in a glaze it readily dissolves in the glass melt. The story is the same with calcium and magnesium carbonate. Kaolin by itself has a very high melting temperature, but dissolves readily into active melts at low temperatures. When low melting materials are part of a glaze recipe, for example, they act as catalysts that accelerate the reactions of other materials. Also, if these catalysts create a glass phase that actively dissolves materials that normally go through complex phase and crystal changes during heatup, none of these changes ever get a change to happen because the particles have dissolved. In addition, another level of complexity arises: the product of a mix of many material will often have its own complex thermal history that exists only as that mix. For example, certain crystal species only grow where the chemistry is just right, no material may have that chemistry, but a mix can.


Articles Reducing the Firing Temperature of a Glaze From Cone 10 to 6
Moving a cone 10 high temperature glaze down to cone 5-6 can require major surgery on the recipe or the transplantation of the color and surface mechanisms into a similar cone 6 base glaze.
Articles A Low Cost Tester of Glaze Melt Fluidity
This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems.
Articles Firing: What Happens to Ceramic Ware in a Firing Kiln
Understanding more about changes are taking place in the ware at each stage of a firing and you can tune the curve and atmosphere to produce better ware
Glossary Decomposition
In ceramic manufacture, knowing about the how and when materials decompose during firing is important in production troubleshooting and optimization
Glossary Melt Fluidity
Ceramic glazes melt and flow according to their chemistry and mineralogy. Observing and measuring the nature and amount of flow is important in understanding them.
Glossary Water Smoking
In ceramics, this is the period in the kiln firing where the final mechanical water is being removed. The temperature at which this can be done is higher than you might think.
Minerals Limestone

By Tony Hansen

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