An upgraded version of the TGA/DTA analyzer Derivatograph 1100° is described. A linear variable differential transformer (LVDT) is used as a sensor of the balance movement to register changes in the sample mass. The furnace temperature measured by a Pt-PtRh10 thermocouple located in its original position is controlled using the temperature programmer TLK 38. Thermocouples for DTA and their connections are left in the original state. Electrical signals from LVDT and thermocouples are sent to multimeter AGILENT 34972A which is connected to a PC. The program records the time of the measurement, furnace temperature, difference between the temperatures of the measured and the reference samples, and mass of the sample. The program's output is a graph with continuous TGA and DTA curves.

No abstract

Mechanical behavior of the heatproof stove tile ceramic material Letovice, which consists of kaolinitic clays and quartz, and small amount of mica, calcite and feldspar, was studied using the non-destructive sonic resonant method mf-TMA. To find actual dimensions and the volume mass of the sample, thermodilatometry and thermogravimetry were carried out in the same temperature regime (201100°C, 5°C/min) as mf-TMA. It was found that liberation of the physically bounded water from the green mass makes Young's modulus higher. Dehydroxylation of phyllosilicates and the ¡ ¼ ¢ transformation of quartz affect Young's modulus to a lesser degree. The collapse of phyllosilicates structure above 900°C and the creation of mullite cause an increase in Young's modulus.

Brick clay from a locality Radobica, Central Slovakia, which was exploited for brick manufacturing in the past, was investigated for its possible reuse in the brick industry. The crystalline phases of the green sample were 48% of quartz, 37% of illite, 13%, of Na-feldspar and 2% of calcite. The measurements of Young's modulus of clay samples were performed during heating up to 1100°C and also at room temperature on samples preheated at temperatures from 100 to 1100°C. It was found during firing that 1) the physically bound water is released in 3 steps (up to 300°C) and reaches ³2.5 wt %. The thermal expansion is decelerated by setting the crystal closer at low temperatures. Young's modulus increases in its values (³36%) which is a result of the closer structure that is created via release of the physically bound water. 2) The mass loss during dehydroxylation (450750°C) is ³3 wt %. The superposition of dehydroxylation and ¡ ¼ ¢ transformation of quartz creates a step ³3% of the relative thermal expansion. Young's modulus slightly decreases in its values, the dehydroxylation does not influence this trend. 3) Above 900°C, the intensive contraction due to sintering is observed and a steep increase (250%) of Young's modulus takes place in this temperature interval. The irreversible changes of the Young's modulus measured at room temperature after firings at the temperatures from the interval 1001100°C give a different picture. Dehydroxylation affects Young's modulus very significantly decreasing its values from 7.8 GPa (at 400°C) to 4.3 GPa (at 700°C). After dehydroxylation, the sintering increases Young's modulus. Since the porosity remains relatively high (³30%) and a part of the glassy phase in the sample fired at 1100°C is relatively low (25%), the Young's modulus is low even after firing at 1100°C (9.3 GPa).

The paper deals with thermodilatometry of green and fired ceramic samples. Problems connected with the measurements in dilatometric practice are described in detail, namely a) the influence of the pressing force of the push-rod, b) the effect of an improperly placed sample and improper measuring range, c) the influence of the volume of a sample, d) the influence of the heating rate, and e) the influence of the grounding and AD transducer on the results of the thermodilatometric analysis.