Phase Transitions of Gypsum and Quartz Sand

Gypsum and quartz sand are, for example, used in plaster and mortar. The gypsum content of the sample shows a two-step release of H2O from CaSO4*2H2O (dihydrate) into CaSO4*1/2H2O (halfhydrate) and finally into CaSO4 (anhydrite). This requires an entire energy of 122 J/g. Quantitative analysis reveals that the sample contained 23.4% of pure dihydrate. Between approx. 300°C and 450°C, the exothermic formation of β-CaSO4 with a released energy of 18.3 J/g occurred. The endothermic effect at an extrapolated onset temperature of 573°C is due to the structural α→β transition of quartz (crystalline SiO2). (measurement with STA 449 F1 Jupiter®)

Thermal Expansion of Fired Tiles

Two colored tiles were simultaneously heated at 3K/min to 1100°C. The curves for the relative expansion of these fired tiles show significant differences in expansivity and quartz content (>567°C). The Proteus® software allows a graphic display of the expansion difference in a separate curve. (measurement with DIL 402 CD)

Sintering Behavior of a Porcelain Green Body

Porcelain is a ceramic material with variable composition mainly containing kaolinite, feldspar, and quartz. The formation of glass and mullite within the fired body at high temperatures (>1200°C) is responsible for the porcelain’s toughness, strength, and translucence.

During heating of the porcelain green body, dehydroxylation of the kaolinite occurs in the temperature range between 450°C and 570°C which leads to the formation of metakaolinite (peak at 467°C in the thermal expansion (blue curve), related to the peak at 517°C in the 1st derivative (red curve)). The temperature range indicates the release of chemically bound water of the clay crystal structure which involves shrinkage of approximately 0.4%. The peak at 572°C in the 1st derivative results from the α→β transition of quartz. A further effect can be observed at 961°C (blue curve), related to the peak at 985°C in the 1st derivative (red)) which can be attributed to the structural collapse of metakaolinite and the formation of γ-Al2O3 [1]. With the complete melting of feldspar and the formation of mullite, two-step sintering starts above 1159°C. The total shrinkage was determined to 10%.

[1] Classic and Advanced Ceramics: From Fundamentals to Applications, Robert B. Heimann, 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Measurement on a porcelain green body up to 1250°C at a heating rate of 5 K/min in a dynamic air atmosphere (20 ml/min), the contact force of the push rod was set to 0.01 NMeasurement on a porcelain green body up to 1250°C at a heating rate of 5 K/min in a dynamic air atmosphere (20 ml/min), the contact force of the push rod was set to 0.01 N

Thermal Decomposition of Dolomite

The mass loss steps during the thermal decomposition of dolomite [CaMg(CO3)2] overlap when the measurement is performed in a nitrogen atmosphere. By using CO2 as a purge gas, they can be clearly separated. The calculated DTA signal (c-DTA®) additionally yields the information that both effects are endothermal. (measurement with TG 209 F1 Libra®)

Thermal Conductivity of Glass Fiber Board

Here, a glass-fiber board (NIST-certified) standard reference material 1450c) was measured in the certified temperature range (0 … 60°C). The deviations between the literature values (taken from the NIST certificate) for the reference material and the measurement results are generally less than 1% and easily within the stated uncertainty of the reference material. This clearly reflects the outstanding performance of the GHP 456 Titan®.

Refractoriness Under Load (RUL) Test On A Fireclay Brick

The graph shows the result of an RUL test on a test piece taken from a fireclay brick (approx. 35% Al2O3);Test conditions: 0.2 N/mm2; 5 K/min; static air. At 960°C the test piece reaches its maximum expansion. Deformations of 0.5%, 1.0% and 2.0% have been achieved at 1210°C (T05), 1240°C (T1), and 1270°C (T2) respectively.

Creep In Compression (CIC) Test On A Fireclay Brick

A CIC test was performed on a test piece taken from a fireclay brick (approx. 35% Al2O3);Test conditions: 0.2 N/mm2; 5 K/min; 25h at 1190°C; static air. The double graph shows the dynamic heating phase and the time-scaled creep at constant temperature.

Mass-Loss Steps of Porcelain Raw Material

This STA measurement on porcelain raw material shows three mass-loss steps. Below approx. 250°C, the evaporation of humidity occurred. At temperatures between 250°C and 450°C, the burn-up of organic content was observed, during which 156 J/g of energy was released. The dehydration of kaolin occurred above 450°C and required 262 J/g. The mass spectrometer signals for mass numbers 18 and 44 reflect the corresponding release of H2O and CO2. The exothermic DSC peak at 1006°C with an enthalpy of -56 J/g is due to an solid-solid transition. (measurement with STA 449 F3 Jupiter®)

Sintering of an Alumina Green Body

An alumina green body was tested with the DIL 402 C employing the NETZSCH Rate Controlled Sintering (RCS) software. The measurement was carried out at a heating rate of 10 K/min. The start/stop mode of the RCS software was used. The threshold value was 10 µm/min (0.046 %/min). The heating rate was reduced by RCS during sintering to achieve a constant shrinkage rate. The influence of additives (e.g. organic binder, clays) was measured up to 1150°C. The main sintering step occured between 1150°C and 1350°C.

Thermal Expansion of Silicon Nitride

Because of its excellent thermal and mechanical properties, silicon nitride is used more and more for high-tech applications (e.g. valves in automobile engines). Of course, the properties of the final parts are heavily influenced by the production/sintering process. Depicted in this figure is the thermal expansion of a silicon nitride green body. The sintering step starting at 1201°C is due to the influence of the sintering additives. The main shrinkage step occured at 1424°C (extrapolated onset). The effect above 1760°C is most probably due to evaporation of additives. (measurement with DIL 402 C)

Thermal Expansion of Polycrystalline Alumina

Presented in the figure is a comparison of three test runs (lines) on a polycrystalline alumina (aluminum oxide) with the corresponding literature values (crosses) between room temperature and 1575°C. No visible deviations exist between the individual curves. Evaluation of the thermal expansion values at 500°C, 1000°C and 1500°C clearly shows that the measurement results are within 1% of the corresponding literature values. This test proves the outstanding reproducibility and accuracy of the dilatometer. (measurement with DIL 402 PC)

Thermal Expansion of Glassy Carbon

The thermal expansion of the glassy carbon sample shows a linear range up to 2300°C and subsequently a strong increase of the expansion coefficient up to 2700°C. The sharp bend in the expansion curve at 2326°C shows the maximum sintering temperature which was applied in the manufacturing process of this carbon product. (measurement with DIL 402 E)

Glass Transition, Structural Change and Specific Heat
of Phosphate Glass Powder

A fine grained phosphate glass powder was measured between room temperature and 1100°C. Typical for such glass types, the glass transition was measured at 483°C (midpoint). At 632°C, an exothermal effect was obtained. This effect is most probably caused by structural changes in the material and/or agglomeration of the powder particles above the softening point. The large surface of the powder is reduced causing a slight energy release. The energy release superimposes the true specific heat values between 600°C and 900°C. (measurement with DSC 404 F3 Pegasus®)

Thermal Expansion, Glass Transition and Softening of Glass

Coefficients of thermal expansion (CTE), glass transition temperatures and softening points are crucial parameters for the characterization of glass materials. Presented in the figure are three tests on the same type of glass but from different batches. It can clearly be seen that the coefficients of thermal expansion are in good agreement within the instrument’s uncertainty boundaries. The glass transition temperature and the softening point of sample #3 (blue curve) show slightly lower values, indicating a slightly different composition. (measurement with DIL 402 PC)

Firing of Cordierite Ceramic

Cordierite is a popular magnesia-alumina-silica ceramic used in various kinds of industrial applications. It is used, for example, as a carrier for catalysts in the automotive industry. During the production of this ceramic, various raw materials are ground and mixed to form a green body. During firing under oxidizing atmospheres, the organic additives are burned out and the cordierite phase is formed at high temperatures. Using the DIL 402 PC in combination with the c-DTA® software, the production process can be analyzed in detail.

Sintering of Zirconia

During the production of high-tech ceramics, a ceramic powder is mixed with a binder and pressed to a green body. By thermal treatment the binder is removed (burned out) and the ceramic is sintered to the final part. In order to determine the quality of the final part, the binder burnout and sintering temperatures as well as the shrinkage during sintering have to be known. These properties can be measured quickly and easily using pushrod dilatometry. Presented in the figure are tests on an yttria-stabilized zirconia green body and on the sintered ceramic. (measurement with DIL 402 PC)

Thermal Expansion of Glass Ceramic Zerodur

Zerodur is a glass ceramic produced by Schott Glas in Mainz, Germany. It is designed for zero thermal expansion around room temperature. This material is often used for high performance terrestrial telescopes. The figure shows the linear thermal expansion between -150°C and 100°C. The sample was measured twice at a heating rate of 3 K/min in a helium atmosphere. The measured CTEs between 0°C and 50°C are in excellent agreement with the literature values (Schott brochures). (measurement with DIL 402 C)