Hot-stage accessories

The theory involved in the operation of a hot-stage/DSC accessory is presented. The material under investigation is placed into a transparent crucible and then into the hot-stage accessory, which has a DTA/DSC sensor. A second transparent crucible, which is similar to the sample crucible, is positioned in the hot stage for use as a reference. Upon initiation of the heating program, the sample equilibrates for a moment to allow the crucibles to reach the temperature of the furnace. Once the... 

In some samples, a difference between the melt-onset temperatures collected from the DSC and the hot-stage accessory may be observed. These differences may be as small as tenths of °C, or as large as 10 to 20°C. In general, the finer particles melt initially, followed by the larger particles. 

The optical microscope is a valuable tool in the laboratory and has numerous applications in most industries. Depending on the type of data that is required to solve a particular problem, optical microscopy can provide information on particle size, particle morphology, color, appearance, birefringence, etc. There are many accessories and techniques for optical microscopy that may be employed for the characterization of the physical properties of materials and the identification of unknowns, etc. Utilization of a hot-stage accessory on the microscope for the characterization of materials, including pharmaceutical solids (drug substances, excipients, formulations, etc.), can be extremely valuable. As with any instrument, there are many experimental conditions and techniques for the hot-stage microscope that may be used to collect different types of data. Often, various microscope objectives, optical filters, ramp rates, immersion media, sample preparation techniques, microchemical tests, fusion methods, etc., can be utilized. 

FIGURE 7.6 Mettler FP84HT hot-stage accessory. (From Rapid and Automatic Determination of Thermal Values Product Brochure, Mettler-Toledo Company, Hightstown, NJ, 1996. With permission.)... 

Once this initial characterization has been completed, continuation of the microscopic analysis using the hot-stage accessory may proceed. As an initial analysis, the ramp rate utilized for the DSC experiment should also be used for the hot-stage analysis. Use of a consistent ramp rate permits direct comparison of the data previously collected by DSC and TGA. If transitions are observed in the thermal data up to 300°C, the hot-stage experiment should also be run to that temperature. Ultimately, the assay should be conducted to generate confirmatory data on all transitions of interest. If available, the color camera should be utilized so that images may be collected as documentation of the transitions observed. Once the experiment is completed, the analyst may be able to compare the DSC, TGA, XRD, optical, and HSM data and develop a comprehensive characterization of the material. 

The hot stage has not only been applied to optical and atomic force microscopes, but also to scanning electron microscopes. Hot-stage accessories are available on environmental SEMs that can collect ESEM images at elevated temperatures. Applications to the electronics industry include fluxless soldering, intermetallic growth studies, and copper thick-film sintering studies (92-94). 

---