Microwave drying oven

Evans, W.A., Rapid casting trials in a microwave drying oven. TSJ Brit Ceram Soc, 72 365-369, (1973). 

Mineralisation consists of the destruction of organic matter. Dry (oven) or humid (acid treatment) methods can be used for this purpose. Due to the absence of a universal method applicable to all mineral elements, it is necessary to adapt mineralisation to the sample being analysed. This stage, which is indispensable for the preparation of many types of samples, particularly those analysed by atomic absorption or emission, can be facilitated by the use of microwave digestion. 

Add the dry chemicals to the glycol at room temperature, heat in a microwave, conventional oven, or on a stovetop with continuous stirring until all of the chemicals have dissolved, then top up to the final volume. 

Moisture analyzers include a large variety of designs listed here. The list includes their inaccuracies (1) electrolytic hygrometer (2-5% FS), (2) capacitance (3% FS), (3) impedance (3% FS), (4) piezoelectric (10% AR or 2 ppm by volume), (5) heat of adsorption, (6) infrared (0.5-1% FS), (7) microwave (for a 1-15% moisture range, error is within 0.5%, less if corrected for density), (8) Karl Fischer titrator (0.5-1% FS), (9) drying oven (0.5-1% FS), (10) dipole, (11) cavity ring down, (12) fast neutron (0.2% in solid s density corrected), and (13) radio-frequency absorption (5 ppm). 

Microwave laboratory ovens are currently quite popular. Where applicable, these greatly shorten drying cycles. For example, slurry samples that require 12 to 16 hours for drying in a conventional oven are reported to be dried within 5 to 6 minutes in a microwave oven. The time needed to dry silver chloride, calcium oxalate, and barium sulfate precipitates for gravimetric analysis is also shortened significantly. ... 

The experiments were set up in such a way that the alkali/min-eral ratios, reaction times, drying temperature, and acid concentration were similar to those to be used later in the cleaning of coal with microwave irradiation. In the GE procedure described by Zavitsanos et al. (1-6), aqueous NaOH was added to coal to make a slurry with an alkali/coal ratio of 0.3 - 2.0. Their slurry had an initial moisture content of about 40% which was lowered to 20% by heating the slurry in a drying oven. Then the dried slurry was irradiated for 1 minute under inert atmosphere in a 2.45-GHz micro-wave apparatus at 1.0 or 2.0 kW. The mixture was then washed with water and acid (either 10% HCl or 10% SOj ) to remove NaOH and acid-soluble products. 

The clay mineral or mixture was reacted with NaOH for about 20 minutes and then placed in a drying oven at 105 for 5 to 30 minutes to reduce the moisture content. The sample was then removed from the oven, filtered, water washed, and air dried. In a few experiments the caustic-treated clay mixture was filtered to remove excess moisture and then placed in the drying oven the sample was again filtered and water washed. These two sets of experiments evaluated the effect of the treatment steps prior to microwave irradiation. 

This method has the disadvantage of a considerable drying time (usually 4-6 h) and many rapid techniques are now available. Infrared drying ovens and microwave ovens have been shown to produce comparable results to vacuum oven drying methods for various fruit products. Nondestructive techniques such as low-resolution nuclear magnetic resonance... 

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