Clays, chamottes and ceramics are used in various applications and must therefore comply with different levels of quality standards. In recent years, quality standards have gained in significance for the processing industry—and therefore for manufacturers of chamottes and ceramics as well.

Raw materials and finished products must be more precisely analyzed in order to meet these constantly increasing quality standards. Classic chemical and physical variables must be considered, as well as the technological data of crude materials and finished parts, such as:

• Geochemical and mineralogical composition
• Thermal endurance
• Heat conductance and coefficient of thermal expansion
• Breaking resistance and flexural strength

Based on the very inhomogeneous composition of clays, sample preparation in a clay and ceramics laboratory for further analytical use is necessary since the chemical composition of the crude materials has a decisive influence on the technical abilities of the finished products. Typical methods include X-ray fluorescence, atomic absorption spectrometry and inductively coupled plasma emission spectrometry.

Case in Point

Based in the Westerwald region in Germany, Goerg & Schneider is a leading producer of crude clays, milling clays, chamottes and ceramic bodies. The company recently chose a FRITSCH PULVERISETTE 6 classic planetary mono mill with an agate grinding set for efficient and time-saving sample preparation.

The PULVERISETTE 6 classic line is mainly used for the fine grinding of milling clays, particularly pre-broken pieces of firing clays. The basic sample size ranges between 0.2-5 mm. Bentonite is added as a bonding clay to finely ground chamottes in order to produce models for the determination of the thermal expansion coefficient. The approximately 100-g sample size that is obtained in this manner is used for the disintegration of a fusion tablet during X-ray fluorescence analysis in order to determine the finished product’s chemical composition.

The selection of the comminution tools is mainly based on the chemical composition of the material (see Table 1), as well as the physical and mechanical characteristics of agate (see Table 2). Due to the relative chemical neutrality of the composition (99.9 % SiO₂), no other elements from the agate (respectively from the preparation) influence the material characteristics (e.g., firing color, heat conductance or the flexural strength of the finished products). The Mohs hardness of the agate (6.5-7) is also sufficient for fulfilling the required tasks.

Figure 1 shows that the insertion of SiO₂ as an indicator for the emerging abrasion during mechanical comminution of the agate grinding set can, despite the clearly higher application of energy of the planetary mill compared to the previous preparation with the mortar principle, be almost completely masked out. An additional decisive criterion for the purchase of the equipment was the efficient preparation and associated time savings achieved during sample preparation with this mill type. Due to the use of the planetary mill, Goerg & Schneider saw time savings of 90% compared to the previously used mechanical preparation.

For additional information, call (49) 6784-700, email info@fritsch.de or visit www.fritsch.de. Goerg & Schneider can be found online at www.goerg-schneider.de/en.