Thermal Properties of Illite-Zeolite Mixtures up to 1100 °C.

Illitic clays are the commonly used material in building ceramics. Zeolites are microporous, hydrated crystalline aluminosilicates, they are widely used due to their structure and absorption properties. In this study, illitic clay (Füzérradvány, Hungary) was mixed with natural zeolite (Nizný Hrabovec, Slovakia) with up to 50 wt.% of zeolite content. The samples were submitted to thermal analyses, such as differential thermal analysis, differential scanning calorimetry, thermogravimetry, and dilatometry. In addition, the evolution of thermal diffusivity, thermal conductivity, and specific heat capacity in the heating stage of firing were measured and discussed. The amount of the physically bound water in the samples increased along with the amount of zeolite. The temperature of the illite dehydroxylation (peak temperature) was slightly shifted to lower temperatures, from 609 °C to 575 °C (for sample IZ50). On the other hand, the mass loss and the shrinkage of the samples significantly increased with the zeolite content in the samples. Sample IZ50 reached 10.8% shrinkage, while the sample prepared only from the illitic clay contracted by 5.8%. Nevertheless, the temperature of the beginning of the sintering (taken from the dilatometric curves) decreased from 1021 °C (for illitic clay) to 1005 °C (for IZ50). The thermal diffusivity and thermal conductivity values decreased as the amount of zeolite increased in the samples, thus showing promising thermal insulating properties.

Determination of Time Domain Reflectometry Surface Sensors Sensitivity Depending on Geometry and Material Moisture.

The article concerns the electric techniques of moisture detection that are based on the evaluation of the apparent permittivity of the tested medium. The main goal of the research was to evaluate the non-invasive Time Domain Reflectometry (TDR) sensors' sensitivity by measuring the span of elements and material moisture. To that aim, two non-invasive sensor designs were investigated for their sensitivity in the evaluation of the apparent permittivity value of aerated concrete. Sensors A and B were characterized by the spacing between the measuring elements equal to 30 mm and 70 mm, respectively. The tested samples differed in moisture, ranging between 0 and 0.3 cm3/cm3 volumetric water content. Within the research, it was stated that in the case of the narrower sensor (A), the range of the sensor equals about 30 mm, and in the case of the wider design (B), it equals about 50 mm. Additionally, it was stated that material moisture influences the range of sensor influence. In the case of the dry and low-saturated material, it was not possible to evaluate the range of sensor sensitivity using the adopted method, whereas the range of sensor signal influence was visible for the moist material.

Young's Modulus of Different Illitic Clays during Heating and Cooling Stage of Firing.

Dynamical thermomechanical analysis of 5 illite-based clays from deposits in Slovakia, Estonia, Latvia, and Hungary is presented. The clays consist of illite (37-80 mass%), quartz (12-48 mass%), K-feldspar (4-13 mass%), kaolinite (0-18 mass%), and calcite (0-3 mass%). Young's modulus is measured during the heating and cooling stages of firing (25 °C → 1100 °C → 25 °C). The liberation of the physically bound water increases Young's modulus by ∼70% for all studied clays. By increasing the temperature, dehydroxylation and the α → ß transition of quartz take place without a significant effect on Young's modulus. Sintering, which starts at 800 °C, leads to an intensive increase in Young's modulus up to the highest temperature (1100 °C). The increase remains also in the early stage of cooling (1100 °C → 800 °C). This increase of Young's modulus is also the result of solidification of the glassy phase, which is finished at ∼750 °C. A sharp minimum of Young's modulus is observed at around the ß â†’ α transition of quartz. Then, Young's modulus still decreases its value down to the room temperature. The physical processes observed during heating and cooling do not differ in nature for the studied clays. Values of Young's modulus vary at around 8 GPa, up to 800 °C. During sintering, Young's modulus reaches values from 30 GPa to 70 GPa for the studied clays. The microstructure and composition given by the origin of the clay play a cardinal role for the Young's modulus of the final ceramic body.

Many-particle surface diffusion coefficients near first-order phase transitions at low temperatures.

We analyze the chemical and jump surface diffusion coefficients, D(c) and D(J), near a first-order phase transition at which two phases coexist and the surface coverage, θ, jumps between single-phase values θ(-)(*) and θ(+)(*). Contrary to other studies, we consider temperatures that are sufficiently subcritical. Using the local equilibrium approximation, we obtain approximate analytical formulas for the dependences of D(c) and D(J) on the coverage and system size, N, near such a transition. In the two-phase regime, when θ ranges between θ-* and θ+*, the diffusion coefficients behave as the sums of two hyperbolas, D(c) ≈ A-/N|θ-θ(-)(*)| + A+/N|θ-θ(+)(*)| and D(J) ≈ A(-)|θ-θ(+)(*)|/θ+A(+)|θ-θ(-)(*)|/θ. This behavior rapidly changes as the system goes from the two-phase regime to either of the single-phase regimes (when θ goes below θ(-)(*) or above θ(+)(*)). The crossover behavior of D(c)(θ) and D(J)(θ) between the two-phase and single-phase regimes is described by rather complex formulas involving the Lambert function. We consider a lattice-gas model on a triangular lattice to illustrate these general results, applying them to four specific examples of transitions exhibited by the model.

Chiral segregation in three microscopic statistical-mechanical models.

We consider three microscopic model molecular systems, each containing an equimolar mixture of a chiral molecule and its nonsuperimposable mirror image. The molecules in each model are assumed to lie on a thin film in such a way that they occupy the sites of a honeycomb lattice. Although neither enantiomorph is externally favored at low temperatures, we prove that for one range of interactions, chiral segregation into ordered phases containing a single enantiomorph occurs for two of the models and, in a second range of interactions, ordered racemic phases (containing equal numbers of each enantiomorph) occur for the two models. For a third range of interactions, each of the two models has an infinite number of ground-state configurations and, moreover, an associated residual entropy. In all three ranges of interactions considered, the third model has an infinite number of ground-state configurations and a residual entropy.

Low temperature phases of the Andelman-de Gennes model of chiral discrimination: rigorous results.

We determine the ordered low temperature phases of the Andelman-de Gennes model of chiral discrimination, using rigorous statistical mechanical methods. The system is considered in the close-packed regime, equivalent to placing the molecules at every site of a honeycomb lattice. If the system contains an equimolar mixture of each of a pair of enantiomers, we prove in general that a heterochiral phase (disfavoring enantiomeric segregation) as well as a homochiral phase (favoring the segregation) is possible, depending on the types of intermolecular interactions. We apply our general results to the specific examples of the interactions considered by Andelman and de Gennes and provide a comparison with their conjectures that were based on two-molecule partition functions.