TECHNICAL NOTES:
Grinding the sample- The larger the particle size, the more difficult it becomes for moisture to diffuse, and the greater the risk of
carbonization, as the outside heats quicker than the inside. It has been noted that during grinding, especially with hygroscopic materials, moisture and volatile loss can occur. In most applications the amount of miscellaneous loss through sample grinding
can be accounted for, by weighing the sample before and after grinding, and wiping any residue from the grinder with glass fiber pads, then incorporating the glass fiber pads in to the test. Glass fiber pads are also recommended to help prevent surface burn, as well as to eliminate the effects of sample color on heat absorption.
Automatic settings- While most moisture balances have an automatic setting, when dealing with sample types that are subject to carbonization and/or loss of volatiles while heating, we recommend comparing results obtained at lower temperatures for longer time frames (105 c for two hours is a good place to start), to results obtained with the automatic setting. Compare the results as well as the characteristics of the sample, ie... color, etc...
If the automatic setting results in a carbonized sample, or notably different moisture results, revert to the lower temperature protocol, and gradually raise the temperature and decrease the time on the tests, as much as you can, without altering the end result. It often helps to plot the time and percent moisture and visualize the drying curve Below are examples of drying curves showing the characteristics of carbonization, volatile burn off, and temperature resistant samples. Many moisture balances allow for programming the drying process in steps, so that the drying parameters can be optimized for the samples characteristics at different stages.
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