# Young’s Modulus of Different Illitic Clays during Heating and Cooling Stage of Firing

^{1}

^{2}

^{3}

^{4}

^{5}

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## Abstract

**:**

## 1. Introduction

#### 1.1. Quartz and Illite

_{α}(20 °C) = 2.65 g/cm

^{3}and ρ

_{β}(590 °C) = 2.53 g/cm

^{3}[17]. Other physical properties of quartz also show anomalous behavior around its α ↔ β transition. For example, Young’s modulus and Poisson’s ratio pass through a sharp V-shape minimum in their temperature dependences [18,19]. A steep decrease in the value of specific heat capacity was also obtained [17]. The α ↔ β transition of quartz takes place in a narrow temperature interval around 573 °C, and the enthalpy of this transition is ∼45.4 kJ/mol [20].

#### 1.2. Illite-Based Ceramics

## 2. Materials and Methods

_{0}/d

_{0}< 20. Quantities m

_{0}, l

_{0}are the initial mass and the length of the sample, d

_{0}is the initial diameter of the circular cross-section or side of the square cross-section, and Δl(t)/l

_{0}and Δm(t)/m

_{0}, are the relative linear thermal expansion and relative mass change of the sample measured by thermodilatometer and TG analyzer. The resonant frequency f is continuously measured during heating/cooling with the sonic resonant method [41] or the impulse excitation technique [42] using the apparatus made in the Thermophysical laboratory, CPU Nitra [41,42]. Cylindrical samples with dimensions ∅10 × 130 mm

^{2}and prismatic samples with dimensions 10 × 10 × 130 mm

^{3}were used for D-TMA, which was performed with a heating/cooling rate of 5 °C/min in the firing cycle 20 °C → 1100 °C → 20 °C. The maximum relative expanded uncertainty of the Young’s modulus is ∼2% [42].

^{2}and 10 × 10 × 20 mm

^{3}were used for TG. Samples for TDA had dimensions ∅10 × 30 mm

^{2}and 10 × 10 × 30 mm

^{3}. All measurements were done in a static air atmosphere. The high similarity of the sample dimensions and identical thermal regimes permit a comparison of the results obtained on different clays.

_{0}is the bulk density of the green sample at room temperature.

## 3. Results and Discussion

#### 3.1. Mass Changes

_{2}is released from them due to the calcite decomposition above 700 °C. This is more significant for Arumetsa clay, which contains 3 mass% of calcite. Kunda clay also contains a small amount of pyrite, which decomposes in two steps, the second of them at temperatures above 740 °C [45]. The escape of SO

_{2}, which was confirmed by evolved gas analysis (EGA) [11], causes a mass loss of the Kunda clay above 750 °C.

#### 3.2. Volume Changes

#### 3.3. Bulk Density

^{3}to 1.9 g/cm

^{3}, depended on the sample preparation. The composition did not play a significant role because of the densities of crystals (illite 2.7 g/cm

^{3}, kaolinite 2.6 g/cm

^{3}, montmorillonite 2.5 g/cm

^{3}, chlorite 2.8 g/cm

^{3}, quartz 2.6 g/cm

^{3}, and feldspar 2.6 g/cm

^{3}) differ only slightly. The initial values of bulk density were: 1.66 g/cm

^{3}for Füzérradvány, 1.85 g/cm

^{3}for Radobica, Kunda, and Liepa, and 1.90 g/cm

^{3}for Arumetsa.

_{f}/ρ

_{g}, where ρ

_{f}is the bulk density of the fired sample and ρ

_{g}of the green (unfired) sample.

#### 3.4. Young’s Modulus during Heating

#### 3.5. Young’s Modulus during Cooling

_{final}– ρ

_{initial}are given in Table 4.

## 4. Conclusions

- The release of the physically bound water increases Young’s modulus by ∼70%.
- The influence of the α → β quartz transition and dehydroxylation of illite on Young’s modulus is negligible during heating.
- The intensive sintering, which takes place at ∼800 °C → 1100 °C → 800 °C increases Young’s modulus.
- Solidification of the glassy phase is finished at ∼750 °C. Cooling from this temperature, the creation of cracks begins due to differences between the thermal expansions of quartz, glassy phase, and other mineral phases.
- At around the β → α quartz transition, a partial recovery of Young’s modulus occurs as the result of the thermal stresses reversal.
- Young’s modulus lowers its values down to the room temperature as the consequence of cracking.
- The results of Young’s modulus indicate that the mineral composition and character of the clay particles, determined by the clay’s origin, play an important role for Young’s modulus, with the final values varying between 15 GPa to 68 GPa.
- Only the Kunda clay from Estonia keeps its Young’s modulus values after the β → α quartz transition. To explain this anomalous behavior, a new set of experiments should focus on studying the microstructure, composition, and granulometry of the Kunda clay.

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 5.**Fracture surface with quartz grain and circumferential crack around it. Abraded, not etched sample (adopted from [9]).

**Figure 6.**Development of the radial stress and the tangential stress on the quartz grain surface during cooling for 30% part of quartz in the double sphere model. The tensile stress has positive value, the compressive stress is negative.

Minerals | Füzérradvány | Radobica | Kunda | Arumetsa | Liepa |
---|---|---|---|---|---|

Illite | 80 | 51 | 54 | 43 | 37 |

Kaolinite | – | – | 8 | 18 | 15 |

Montmorillonite | 4 | – | – | – | – |

Chlorite | – | – | 5 | – | – |

Quartz | 12 | 34 | 28 | 25 | 35 |

Feldspar | 4 | 13 | 5 | 11 | 13 |

Calcite | – | 2 | – | 3 | – |

Oxides | Füzérradvány | Radobica | Kunda | Arumetsa | Liepa |
---|---|---|---|---|---|

SiO_{2} | 58.4 | 56.7 | 61.4 | 57.8 | 62.7 |

Al_{2}O_{3} | 23.9 | 23.1 | 17.8 | 18.7 | 15.9 |

Fe_{2}O_{3} | 0.6 | 6.3 | 5.7 | 7.0 | 7.2 |

TiO_{2} | – | 0.5 | – | – | 1.9 |

CaO | 0.4 | 0.4 | 0.4 | 1.6 | 0.9 |

MgO | 1.7 | 2.4 | 2.3 | 2.6 | 1.5 |

K_{2}O | 7.7 | 5.0 | 5.6 | 4.8 | 4.3 |

Na_{2}O | 0.1 | – | 0.1 | 0.6 | 0.1 |

SO_{2} | – | – | 1.7 | – | – |

L.O.I | 7.2 | 5.6 | 5.0 | 6.9 | 5.5 |

Minerals | Füzérradvány | Radobica | Kunda | Arumetsa | Liepa |
---|---|---|---|---|---|

Quartz | 11 | 34 | 23 | 24.3 | 35 |

Feldspar | 6 | 10 | 7 | 4.6 | 5 |

Hematite | – | 4 | 2 | 3.0 | 4 |

Spinel | 4 | 7 | – | 2.8 | – |

Amorphous | 79 | 45 | 68 | 62.0 | 56 |

**Table 4.**The final values of Young’s modulus, the bulk densities, and the difference between the final and initial bulk density.

Quantity | Füzérradvány | Radobica | Kunda | Arumetsa | Liepa |
---|---|---|---|---|---|

E_{final} (GPa) | 39 | 17 | 68 | 30 | 15 |

ρ_{final} (g/cm^{3}) | 1.84 | 1.95 | 2.27 | 2.17 | 1.94 |

Δρ (g/cm^{3}) | 0.18 | 0.1 | 0.44 | 0.28 | 0.08 |

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**MDPI and ACS Style**

Húlan, T.; Štubňa, I.; Ondruška, J.; Csáki, Š.; Lukáč, F.; Mánik, M.; Vozár, L.; Ozolins, J.; Kaljuvee, T.; Trník, A.
Young’s Modulus of Different Illitic Clays during Heating and Cooling Stage of Firing. *Materials* **2020**, *13*, 4968.
https://doi.org/10.3390/ma13214968

**AMA Style**

Húlan T, Štubňa I, Ondruška J, Csáki Š, Lukáč F, Mánik M, Vozár L, Ozolins J, Kaljuvee T, Trník A.
Young’s Modulus of Different Illitic Clays during Heating and Cooling Stage of Firing. *Materials*. 2020; 13(21):4968.
https://doi.org/10.3390/ma13214968

**Chicago/Turabian Style**

Húlan, Tomáš, Igor Štubňa, Ján Ondruška, Štefan Csáki, František Lukáč, Marek Mánik, Libor Vozár, Jurijs Ozolins, Tiit Kaljuvee, and Anton Trník.
2020. "Young’s Modulus of Different Illitic Clays during Heating and Cooling Stage of Firing" *Materials* 13, no. 21: 4968.
https://doi.org/10.3390/ma13214968