Fluxes and Fillers Questions and Answers

Answer: A

Producing a liquid at a workable temperature is what allows a body to vitrify without approaching the melting point of its refractory constituents. Without one the firing temperature would be far beyond what industrial kilns can reach economically.

Answer: B

The sodium form gives a more fluid melt that begins sooner, while the potassium form gives a more viscous one over a wider interval. Potash is generally preferred where firing range matters, which is most of the time in production.

Answer: C

Both are true and the reason gives the practical advantage: a kiln cannot hold every piece at exactly the same temperature, so a body that tolerates a spread of twenty or thirty degrees is far easier to fire successfully.

Answer: D

A wide range means variations across the kiln can be tolerated, while a narrow one means part of the load is underfired and part deformed. Widening it is one of the main objects of body formulation. A wide range forgives the unavoidable variation across a kiln load.

Answer: A

It means the acceptable window is small and any temperature variation in the kiln produces rejects. A wide range is what a production body needs, since no kiln is uniform to within a few degrees. Kiln temperature always varies from front to back and top to bottom.

Answer: B

Correct answer: melts at a lower temperature for the same effect

Nepheline syenite carries a higher total alkali content than feldspar and almost no free quartz, so it forms its melt some 50 to 100 degrees lower. Substituting it lets the same degree of vitrification be reached at a lower temperature, saving fuel and kiln time - which is why it is used wherever a fast, low firing cycle is wanted.

Answer: C

Both are true and the reason gives the chemistry: more alkali per unit mass means more melt at a given temperature, which is what allows the peak to be reduced or the quantity of flux to be cut back. The saving in fuel is weighed against the narrower firing range.

Answer: D

Correct answer: magnesia to the composition

Talc is a hydrated magnesium silicate, so what it brings to a body is magnesia. In a wall tile it acts as a flux and gives a low thermal expansion; in a cordierite body it is the essential magnesia source. It supplies no plasticity and no alumina, and its iron content is a contaminant to be minimised rather than a purpose.

Answer: A

Being a calcium silicate rather than a carbonate it contributes lime without evolving carbon dioxide, which suits fast-fire tile production. Its needle-like particles also reduce drying shrinkage and raise green strength.

Answer: B

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Calcium carbonate decomposes around 800 to 900 degrees and releases carbon dioxide, which must escape through the body before the surface seals or it causes bloating and black coring. A fast fire does not allow the time. Wollastonite is already a calcium silicate, so it supplies lime with no gas evolution at all.