8. Procedure
8.1 Heat the evaporating dish or crucible that is to be used fo the test at 700 to 800°C for a minimum of 10min. Cool to room temperature in a suitable container, and weigh to the nearest 0.1mg.
NOTE 3 - The container in which the dish or crucible is cooled can be a desiccator not containing a desiccating agent. In addition, all weighings of the crucibles should be performed as soon as the crucibles have cooled. If it should be necessary that the crucibles remain in the desiccator for a longer period, then all subsequent weighings should be made after allowing the crucibles and contents to remain in the desiccator for the same length of time.
8.2 When the sample is sufficiently mobile, mix thoroughly before weighing. The mixing is necessary to distribute catalyst fines and other particulate material throughout the sample. Satisfactory mixing can usually be achieved by 10 min of manual shaking or 10min using a mechanical shaker. Examine the sample for homogeneity before proceeding with 8.3. Continue mixing the sample if it is not homogeneous.
8.2.1 When it is evident that the sample is not homogenized after repeated mixings, or there is a reasonable doubt, a non-aerating, high-speed shear mixer can be used. Such a device is described in Annex A1 of Test Methods D4928.
8.2.2 When the sample cannot be satisfactorily homogenized, reject the sample and acquire a new sample.
8.2.3 When the sample is viscous or solid at room temperature, heat the container carefully until the sample is entirely liquid and mix carefully. An oven at an appropriatete mperature can be used.
8.2.4 The sample can contain water. After heating in an oven, the water can boil causing splattering or foaming. The operator shall proceed cautiously with the heating step, wearing appropriate personnel protective equipment, such as safety goggles and gloves. Mixing this type of sample shall be done carefully. Stirring, rather than shaking, is an option.
8.3 The quantity of test specimen taken for testing will depend upon the ash content expected in the sample. Refer to Table 1. The weighing procedure will also depend upon whether the sample requires heating or not, and whether more than one portion has to be weighed.
8.4 Using a top-loading balance, weigh into the dish or crucible sufficient test specimen to the nearest 0.1g to yield no more than 20 mg of ash. Determine the mass of the test specimen used in the analysis at ambient temperature. One way to do this is to take the difference between the initial and final masses of the sample container weighed at ambient temperatures. If one weighing is sufficient, as determined from Table 1, or experience, proceed with steps 8.6-8.11.
8.5 If more than one addition of test specimen is required, proceed only through 8.6 (noting 8.6.1 and 8.7) and allow the dish or crucible to cool to ambient temperature before adding more sample as outlined in 8.4. Proceed with steps 8.6-8.11.
8.6 Carefully heat the dish or crucible with a Meeker burner or equivalent until the contents can be ignited by the flame. Maintain the dish or crucible at such a temperature that the sample continues to burn at a uniform and moderate rate leaving only a carbonaceous residue when the burning ceases. A hot plate can be used at this stage.
8.6.1 The test sample may contain water that can cause spattering.The operator shall heat the test portion cautiously while wearing appropriate personnel protective equipment, such as safety goggles and gloves. If spattering is very severe, so that material escapes the confines of the dish or the crucible, discard the test portion. If the first test portion is discarded, add 2 more or less 1mL of propan-2-ol (Warning - Flammable) to a second test portion while stirring with a glass rod and warming the test portion gently to liquefy if it is solid or near solid. Proceed as described in 8.6. If this is unsuccessful, repeat on a third test portion using a 10 more or less 1mL mixture of 50 more or less 5% by volume toluene (Warning - Flammable. Vapor harmful) and 50 more or less 5% by volume of propan-2-ol. In either case, any test specimen that adheres to the glass rod can be returned to the dish using a strip of ashless filter paper. Continue burning as outlined in 8.6.
8.7 Vigilance by the operator is mandatory; burning samples shall never be left unattended.
8.8 Some test specimens will require extra heating after the burning has ceased, particularly heavy samples such as marine fuels which form crusts over the unburned material. The crust can be broken with a glass rod. Any crust that adheres to the glass rod can be returned to the dish using a strip of ashless filter paper. Burn the remaining test specimen.
8.9 The heavier material tends to foam, therefore the operator shall exercise considerable care. Overheating shall be avoided so that neither the test specimen nor the dish are heated to a red hot appearance, as this can result in loss of ash. Likewise, the flame shall never be higher than the rim of the dish to avoid superheating the crust, thereby producing sparks that can result in considerable loss of ash.
8.10 Heat the residue in the muffle furnace at 775 more or less 25°C until all carbonaceous material has disappeared. Cool the dish to room temperature in a suitable container (Note 3), and weigh to the nearest 0.1mg.
8.11 Reheat the dish at 775 more or less 25°C for at least 20min, cool in a suitable container (Note 3), and reweigh. Repeat the heating, cooling, and weighing process until consecutive weighings differ by not more than 0.5mg.
