Determination of the Content of Organic Material in Clay

Introduction 

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.

Experimental Details

The measurements described here were performed using a TGA/SDTA851e thermobalance. Care was taken to make sure that samples were as representative as possible. The sample material was homogenized before it was added to the crucible.

In view of the fact that a combustion process cannot occur in the absence of oxygen and that at 600 ºC the water of crystallization can be eliminated from most clay minerals, the optimized final method (Method 2) was:

1. isothermal at 25 °C for 10 min in nitrogen
   
2. heating to 600 °C at 10 K/min in nitrogen
   
3. isothermal at 600 °C for 20 min in nitrogen
   
4. isothermal at 600 °C for 15 min in air.

Conclusions

Both this study and values based on measurements of numerous industrial samples show that the results obtained with the TGA/SDTA 851e using the method described above with gas switching are suitable for determining small differences in the content of organic material in clays.

_{Determination of the Content of Organic Material in Clay | Thermal Analysis Application No. UC 245 | Application published in METTLER TOLEDO Thermal Analysis UserCom 24}