Darvan is a deflocculant and used to disperse ceramic suspensions to minimize their water content. It is a liquid alternative to the long popular sodium silicate. About twice as much is required typically (0.4-0.5%) however Darvan does offer a number of advantages. Typically soda ash is not needed as a complement and Darvan does not attack plaster molds. In addition slurries are much less sensitive to over deflocculation and are more stable. It is thus easier to reprocess scrap. However a number of engineers still prefer using a sodium silicate:soda ash mix to control thixotropic properties better, especially if little scrap is being added. Darvan 811 is a low molecular weight short chain polymer for use in vitreous and semivitreous bodies and glazes. In comparison to the conventional soda ash-sodium silicate system, these polyelectrolytes produce slips with longer casting range, higher solids content, improved viscosity stability, fewer "soda" or "hard spots", and significantly increased mold life. Slips also tend to reclaim better without the need for constant adjustments with more deflocculant. The active agent in Darvan is polyacrylic acid. Its molecules are negatively charged along their length. They attach to clay particles and cause them to repel each other. There are two cautions with this material: -It has a shelf life of two years -Some types cannot go below 40 degrees F without detrimental effects on their performance. Darvan definitely cannot be frozen. In either of these cases, it will simply not disperse your slurry as expected.
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