Thermal Analysis UserCom 24
Thermal Analysis UserCom 24; Table of Contents:
- Influence of absorbed moisture on the mechanical properties of Polyamide 6
New in our sales program
- Thermosets booklet
- TGA-FTIR-MS Interface
- Microscope hot-stage cooling system
- Certified reference materials for thermal analysis from LGC
- TA precision weights (0.2 g, 1 g and 5 g)
- Evaluation and interpretation of peak temperatures of DSC curves. Part 2: Examples
- Curie temperature measurements on nanocrystalline iron-based mechanically alloyed materials
- Thermal characterization of food products
- Determination of the content of organic material in clay
Evaluation and interpretation of peak temperatures of DSC curves. Part 2: Examples
With the aid of practical examples, different approaches are shown for obtaining thermodynamically relevant temperatures or at least comparable characteristic temperatures from the measured peak temperatures of melting peaks. This is especially important for materials with wide melting ranges or for the determination of phase diagrams. Furthermore, it is shown how reorganization processes can be identified by means of peak evaluation. Finally special points are discussed concerning peaks that originate from other events such as chemical reactions, second order phase transitions, vaporization, and so on.
Curie temperature measurements on nanocrystalline iron-based mechanically alloyed materials
During the past decades, weakly magnetic materials such as amorphous Fe(Ni)-based alloys containing α-Fe nanocrystallites with the body-centered cubic (bcc) structure have been the subject of increasing interest. Their magnetic properties make them suitable for use in magnetic parts and devices such as low and high frequency transformers, alternating current machines, generators, induction coils, sensors and motors.
For such applications, it is important to determine the correct value of the Curie temperature (Tc) of materials, that is, the temperature at which the transition from ferromagnetic to paramagnetic behavior occurs. This characteristic temperature is often determined using thermoanalytical techniques .
This article describes how a METTLER TOLEDO TGA/SDTA851e thermobalance was modified to measure the Curie temperature of materials by incorporating a small magnet.
 M.E. McHenry, M.A. Willard and D.E. Laughlin, Progress in Materials Science 44 (1999) 291–433.
 G. Luciani, A. Constantini, F. Branda, P. Scardi and L. Lanotte, J. Therm. Anal. Calorim. 72 (2003) 105–111.
Thermal characterization of food products
The thermal properties of a candy were completely characterized using “jelly bears” as an example. The glass transition temperature, composition, and the creep-, flow-, swelling- and frequency-behavior of two different commercial products were analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA).
“Jelly bears”, the well-known German “Gummibären”, are similar to the English “jelly baby” sweets in appearance, taste and consistency.
They are ideal products with which to demonstrate the potential applications of thermal analysis in the food industry. Between their production date and the time when they are finally eaten, jelly bears are exposed to widely different conditions such as temperature fluctuations, different frequencies, mechanical stress and different media.
These changing conditions can be simulated using thermal analysis instrumentation and the properties of the product determined from the measurement results.
Jelly bears consist mainly of gelatin, a protein product, and different types of sugar. The carbohydrate content can be up to 78 percent by weight.
Due to the fact that the raw mass is obtained by heating the different ingredients and that the mechanical properties of the finished products contribute decisively to their enjoyment and taste, thermal analysis can provide an important contribution to maintaining constant quality and for the optimization of the production and the product properties.
Determination of the content of organic material in clay
This study looks at an analytical method for the determination of the content of organic material in clay using differential scanning calor - imetry (DSC) and thermogravimetry (TGA). The results are compared with those obtained from the coulometric determination of the carbon content in the same samples.
Clays are raw materials that are often used in different applications in ceramics and in the glass industry. In some of these applications, the content of organic materials in the clay is a factor that must be monitored because it influences the rheological properties and material behavior of the ceramic parts.
An accurate determination of the carbon content can be performed using a carbon analyzer. The sample is subjected to a combustion cycle and the liberated carbon is determined by coulometry.
In a thermal analysis experiment (Method 1) in which the clay is subjected to a combustion cycle of 25−1200 ºC at a heating rate of 25 K/min in an air atmosphere, an mass loss is observed in some cases between 200 ºC and 500 ºC, which can be traced to the oxidation of organic substances (Fig. 1, Process 2).
In general, the end of the process coincides with the loss of water of crystallization of the clay minerals (Fig. 1, Process 3), which makes an accurate determination of the content of organic substances more difficult, especially with small amounts.
Figure 1. Properties of clay at a constant heating rate up to 1200 ºC in an air atmosphere.