Clay-water mixtures drying properties

Three main properties render clay suitable for making ceramic materials its plasticity when wet, its hardness when dry, and the toughness, increased hardness, and stability that it acquires when fired. The addition of water to dry clay produces a clay-water mixture that, within a narrow range of water content, has plastic properties it is deformed, without breaking or cracking, by the application of an external stress, and it retains the acquired shape when the deforming stress is removed. Wet clay mixtures can, therefore, be modeled, molded, or otherwise made to acquire a shape that will be retained after the forming operations. Water-poor mixtures are not plastic, however, and excess water results in mixtures, known as slips, that are too fluid to retain a shape, as shown in Table 56. 

As for the drying properties of clay-water mixtures when wet clay dries at ambient temperature, the water of plasticity that surrounds the particles... 

The idea that, if a single available material cannot fulfill a set of desired properties, then a mixture or a compound of that material with another one might be satisfactory is likely as old as mankind. Adobe, likely the oldest building material, is made by blending sand, clay, water and some kind of fibrous material like straw or sticks, then molding the mixture into bricks and drying in the sun. It is surely one of the oldest examples of reinforcement of a "plastic" material, moist clay, with natural fibers that was already in use in the Late Bronze Age, nearly everywhere in the Middle East, North Africa, South Europe and southwestern North America. In a sense, the basic principle of reinforcement, i.e., to have a stiffer dispersed material to support the load transmitted by a softer matrix, is already in the adobe brick. Therefore, the "discovery" of natural rubber reinforcement by fine powdered materials, namely carbon black, in the dawn of the twentieth century surely proceeded from the same idea. 

Clay and mineral fillers have been used for reducing production costs and improving the comprehensive water absorbing properties of superabsorbent materials For example, a poly(acrylic acid)/mica superabsorbent has been synthesized with water absorbency higher than 1100 g H20/g In a typical method of preparation, acrybc acid monomer is neutralized at ambient temperature with an amount of aqueous sodium hydroxide solution to achieve 65% neutralization (optimum) Dry ultrafine (<0.2 tm) mica powder (10 wt%) is added, followed by cross-linker N,N-methylene-bisacrylamide (0.10 wt%) and radical initiator, potassium persulfate The mixture is heated to 60-70°C in a water bath for 4 h. The product is washed, dried under vacuum at 50°C, and screened. 

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