Yes they are. This is were they used to make sinter. Wiki: Sintering is a method for making objects from powder, by heating the material in a sintering furnace below its melting point (solid state sintering) until its particles adhere to each other. Sintering is traditionally used for manufacturing ceramic objects, and has also found uses in such fields as powder metallurgy.
The word "sinter" comes from the Middle High German Sinter, a cognate of English "cinder".