Muffle furnace method

In a fire-assay method used at the smelters, a weighed quantity of concentrate is mixed with sodium cyanide in a clay or porcelain cmcible and heated in a muffle furnace at red heat for 20—25 min. The tin oxide is reduced to metal, which is cleaned and weighed. Preliminary digestion of the concentrate with hydrochloric and nitric acids to remove impurities normally precedes the sodium cyanide fusion. 

Various methods of heating are required in the analytical laboratory ranging from gas burners, electric hot plates and ovens to muffle furnaces. 

As CaC03 by heating at 475-525 °C in an electric muffle furnace. This is the most satisfactory method, since calcium carbonate is non-hygroscopic. 

Dry sediment (0.15-0.2g) was ignited in a muffle furnace in a porcelain crucible (550°C for lh). After cooling, the residue was washed into a 100ml Erlenmeyer flask with 25ml mol L-1 hydrochloric acid and boiled for 15min on a hot plate. The sample was diluted to 100ml and orthophosphate was determined as in the perchloric acid method. Standards and blanks were not ignited. 

In the test method (ASTM D4422), a sample of petroleum coke is dried, ground, and ashed in a muffle furnace at 700 to 775°C (1292 to 1427°F). The noncarbonaceous residue is weighed and reported as the percent by weight ash. As already noted, the ash must not be understood to be the same as the mineral content of the petroleum coke. 

Method (a).—500 gms. of wire-form and 100 gms. of powder CuO are placed in separate fireclay basins. The first is heated to a dull red heat in a muffle furnace, and the second over a Bunsen flame. While they are being heated the combustion tube is prepared. 

The glass content was determined by resin bum-off of ring segments in crucibles in a muffle furnace. The void content was determined by a method of optical microscopy previously reported (6). Horizontal shear was measured by the Short Beam method (1). 

In the thermal-catalytic method a peroxide catalyst is usually used to initiate the free radical chain reaction. The main disadvantages are the higher temperatures required for carrying out the polymerizations, the potential hazard of explosion on addition of catalyst to the monomer, and disposal of excess catalyzed monomer after impregnating. Combinations of heat, radiation, and catalyst have been experimented with to reduce the radiation and catalyst requirements and to increase the rate of polymerization. In thermal polymerization a muffle furnace, infrared heating, and microwave heating can be used to provide the thermal energy. 

Ash content was determined as follows At least 1 g of dry stems, ground to 60 mesh, was ashed in a muffle furnace at 650°C for 18-24 h. Ash content was calculated by weight difference. Carbohydrate and lignin compositions of untreated and treated straw samples were determined by quantitative saccharification using the method of Saeman et al. 

The DM content of the samples was determined by drying duplicate samples for 16 h in an oven at 105°C according to the National Renewable Energy Laboratory (NREL) standard method for determination of total solids in biomass, LAP-001 (11). Total ash content was determined by ashing samples in triplicate at 575°C in a muffle furnace according to the NREL standard method for ash in biomass, LAP-005 (12). 

The major drawbacks of the method are the possible loss of some elements by volatilization, contamination of the sample by airborne dust, as it must be left open to the atmosphere, and irreversible sorption of analyte into the walls of the vessel. It is important to do blanks with each batch of samples. Particles generated within the muffle furnace may be the cause of high or variable blanks. In this case the applicability of the method will depend on the level of analyte expected in the samples. A variable blank can be tolerated when the analyte level is substantially higher than the blank but not when the concentration analyte found in the blank and the sample are similar. 

Dry ashing is simple and inexpensive. Large numbers of samples can be treated at the same time and the quantity of the sample is not limited. Usually the sample is heated in a crucible of platinum, silica or pyrex to a relatively high temperature, between 400°C and 700°C, in a muffle furnace. Dry ashing is not recommended for samples with trace metal contents unless special furnaces, and very accurate temperature control methods are employed. The more volatile metals such as lead, mercury, and cadmium may be partially lost at even low temperatures. 

Sampling procedures are often dependent on the method of sample preparation as well as the physical and chemical properties of the analyte For most analytes that are collected by the above method the usual procedure is to ash the filter in either a low temperature plasma asher or a muffle furnace, disperse the residue in a suitable liquid such as isopropanol using ultrasonic agitation, and filter the suspension through a silver membrane filter. In addition, if the internal standard method is used, the chosen standard must be added to the residue suspension prior to filtration ... 

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