Volatile Matter Crucibles - Parr Instrument Company - #2

have all of the solvent removed before they are heated in a VM Crucible, since chlorinated solvents will attack the crucible and cause cracking. These cru­cibles also are not suitable for procedures involving second­ary treatment with acids, as is sometimes practiced with precipitates of lead, iron, mag­nesium phosphate and the like. They also are not suitable for alkali fusions in silicate analy­ses, or for the volatilization of silica with hydrofluoric acid, and they are not recommended for ashing flours where calcium acetate is employed.

In some cases Parr VM Crucibles have been used as sample holders in oxygen combustion bombs, but this practice is not recommended. These thin wall crucibles may ignite under the high tempera­ture and extreme oxidizing con­ditions developed in an oxygen bomb, causing dangerous pressures and possible serious damage to the bomb. Other metal sample holders with heavier walls are made espe­cially for oxygen bomb tests.

Parr VM Crucibles and insert covers are fabricated from a special nickel-chromium alloy selected for its specific resistance to oxidation when heated repeatedly to 1000 °C. Both crucibles and covers have uniform walls and bottoms approximately 0.5 mm thick with sidewall tapers designed so that the insert cover fits snugly in the top of the crucible as required in the standard test method. Each crucible is electro-polished to obtain a smooth, matte finish which will readily take and hold a passive oxide film.

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rr VM Crucibles with sert covers have been eveloped especially for

25.5 mm 17.0 mm 34.0 mm* 14.9 g 13.0 mL

25.5 mm 23.0 mm 11.0 mm

7.0 g

determining volatile matter in coal and coke according to the standard ASTM test method D3175*. They meet all require­ments of the ASTM method except they are made of a special nickel-chromiurn alloy instead of platinum. In this test volatile matter is determined by heating a coal sample in a metal crucible with a closely fitting cover for seven minutes at 950 °C. Parr VM Crucibles will withstand the severe con­ditions imposed by this test, maintaining a remarkably con­stant tare weight and offering an attractive substitute for the expensive platinum crucibles specified in the ASTM method. The wide acceptance and gen­eral use of these special alloy crucibles over the past sixty years will attest to their ability to perform satisfactorily in rou­tine volatile matter determina­tions. In addition, their superior strength and light weight, com­bined with uniform thickness and excellent resistance to oxi­dation, make them equally suit­able for other ignition purposes where working temperatures do not exceed 1000 °C.

Parr VM Crucibles will ordi­narily withstand the corrosive conditions produced when working with many different materials and precipitates, but it must be emphasized that their corrosion resistance is not equivalent to that of a noble metal such as platinum. Coal samples that have been treated with chlorinated solvents must

Volume with insert cover 11.5 mL

To establish normal constant weight, each new VM Crucible should be given a preliminary heating. This will produce a hard, dull, grey-green oxide coating which will resist fur­ther oxidation. To develop this coating the crucible should be heated for one hour, either in an electric muffle furnace at 950 °C or over the full flame of a Meker type gas burner. This procedure should be repeated during the life of the crucible whenever it has been cleaned or whenever the oxide coating has been destroyed. Do not use coarse or sharp abrasives on these crucibles as they will remove the oxide coating which provides resistance to oxidation and produces stabil­ity in the tare weight.

VM Crucible with insert cover VM Crucible without cover Insert cover for VM Crucible

3101

3102

3103

211 53rd Street, Moline, Illinois 61265 USA Phone: 309-762-7716 or 800-872-7720 Fax: 309-762-9453 Email: parr@parrlnst.com http://www.parrinst.com

Bulletin 3100 2000 0308 Printed in US