Heating methods aluminum block

In the closed reflux spectrophotometric method (Standard Method 5220 D), a standardized colorimetric reagent, based on dichromate, is provided in a sealed vial. Test samples are added to the vial and heated to 150 °C for 2 h in an aluminum block with appropriate holes to accommodate the vials. After cooling, the... 

The second boundary condition to be considered is that in which the sample surface is subjected to a linear rate of temperature rise. A method based on this has been developed by Shoulberg [47] for diffusivity measurements on polymer melt.s. He used two discs of his material with a thermocouple sandwiched between them the diameter-to-thickness ratio was such that the sample sandwich could be regarded as an infinite flat slab. The sample completely filled the cavity in an aluminum block and was melted in the apparatus. The aluminum block was heated electrically, and the power was adjusted to give an approximate linear rate of temperature rise. Under his experimental conditions this Lusted for about 30 C. 

The methods described previously may be used over a range of about 50°C to over 200°C. A hot water bath, however, may be a suitable alternative for temperatures below 80°C. A beaker (250 mL or 400 mL) is partially filled with water and heated on a hot plate. A thermometer is clamped into position in the water bath. You may need to cover the water bath with aluminum foil to prevent evaporation, especially at higher temperatures. The water bath is illustrated in Figure 6.6. A mixture can be stirred with a magnetic spin vane (Technique 7, Section 7.3). A hot water bath has some advantage over an aluminum block or a sand bath in that the temperature in the bath is uniform. In addition, it is sometimes easier to establish a lower temperature with a water bath than with other heating devices. Finally, the temperature of the reaction mixture will be closer to the temperature of the water, which allows for more precise control of the reaction conditions. 

Finally, a method that is used to determine pitch volatility (ASTM D-4893) might also be used, on occasion, to determine the nonvolatility of mineral oil. In the method, an aluminum dish containing about 15 g of accurately weighed sample is introduced into the cavity of a metal block heated and maintained at 350°C (662°F). After 30 min, during which the volatiles are swept away from the surface of the sample by preheated nitrogen, the residual sample is taken out and allowed to cool down in the desiccator. Nonvolatility is determined by the sample weight remaining and reported as % w/w residue. 

The sustained burning test was originally developed for British Standard BS-3900 and adapted by ASTM. The purpose of the test is to determine the sustained burning characteristics of solvents by direct experiment rather than by deducing characteristics from flash point data. Mixtures of some flammable liquids (e.g., alcohol and water) are classified as flammable based on the closed-cup flash point method. Some mixtures may be classed as flammable even though they do not sustain burning. The test is performed in a block of aluminum with a concave depression called a well. The liquid under test is heated to a temperature of 49 C and a flame is passed over the well and held in position for 15 s. The specimen is observed to determine if it can sustain burning. 

A convenient water bath suitable for microscale methods can be constructed by placing the aluminum collars, which are generally used with aluminum heating blocks into a 150-mL beaker (Figure 7.17A). In some cases, it may be necessary to round off the sharp edges of the collars with a file in order to allow them to fit properly into the beaker. Held by the aluminum collars, the conical vial will stand securely in the beaker. This assembly can be filled with water and placed on a hot plate for use in the evaporation of small amounts of solvent. 

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