ANHYDROUS SODIUM DICHROMATE IN FLAKE FORM

• Main Author: DIEGO PERRONE
• Format: Patent
• Language: English
• Published: 18.05.1988
• Edition: 4
• Subjects: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOIDCHEMISTRY; CHEMISTRY; COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSESC01D OR C01F; INORGANIC CHEMISTRY; METALLURGY; PERFORMING OPERATIONS; PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL; THEIR RELEVANT APPARATUS; TRANSPORTING

A new anhydrous sodium dichromate in flakes, Na2Cr2O7, m.p. 356 DEG C. (dec. 400 DEG C.) is described, characterized in that it comes in flakes with an area of approx. 1 cm2, thickness 0.5 mm and apparent specific gravity 1.10 (absolute 2.748) at 25 DEG C.; it is not deliquescent, nor does it become powdery. It is prepared from dihydrate sodium dichromate or aqueous solutions thereof using a new process in two stages, namely (a) evaporation-melting of the dihydrate salt or concentrated aqueous solution at a strictly controlled temperature of around 380 DEG C. and no higher, and (b) flaking of the melted mass obtained thereby, as it is being rapidly cooled to 150 DEG -160 DEG C. The apparatus for carrying out the process is also claimed; said apparatus consisting essentially of a dehydrator-melter oven, a flaker rotating at 10-20 revs per minute and a heat recovery system. The thermic contribution, respectively positive and negative in the two stages, is provided by means of a particular eutectic mixture of melted salts, which melts at 139 DEG C. Said mixture is composed of KNO3 52.2%, NaNO3 7.0%, NaNO2 39.4%, K2Cr2O7 1.4%.