TY  - JOUR
A1  - Laquai, Rene
A1  - Gouraud, Fanny
A1  - Müller, Bernd Randolf
A1  - Huger, Marc
A1  - Chotard, Thierry
A1  - Antou, Guy
A1  - Bruno, Giovanni
T1  - Evolution of Thermal Microcracking in Refractory ZrO2-SiO2 after Application of External Loads at High Temperatures
JF  - Materials
N2  - Zirconia-based cast refractories are widely used for glass furnace applications. Since they have to withstand harsh chemical as well as thermo-mechanical environments, internal stresses and microcracking are often present in such materials under operating conditions (sometimes in excess of 1700 °C). We studied the evolution of thermal (CTE) and mechanical (Young’s modulus) properties as a function of temperature in a fused-cast refractory containing 94 wt.% of monoclinic ZrO2 and 6 wt.% of a silicate glassy phase. With the aid of X-ray refraction techniques (yielding the internal specific surface in materials), we also monitored the evolution of microcracking as a function of thermal cycles (crossing the martensitic phase transformation around 1000 °C) under externally applied stress. We found that external compressive stress leads to a strong decrease of the internal surface per unit volume, but a tensile load has a similar (though not so strong) effect. In agreement with existing literature on β-eucryptite microcracked ceramics, we could explain these phenomena by microcrack closure in the load direction in the compression case, and by microcrack propagation (rather than microcrack nucleation) under tensile conditions.
KW  - electro-fused zirconia
KW  - microcracking
KW  - synchrotron x-ray refraction radiography (SXRR)
KW  - thermal expansion
Y1  - 2019
U6  - https://doi.org/10.3390/ma12071017
SN  - 1996-1944
VL  - 12
IS  - 7
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Chen, Cong
A1  - Müller, Bernd Randolf
A1  - Lebedev, Oleg I.
A1  - Giovannelli, Fabien
A1  - Bruno, Giovanni
A1  - Delorme, Fabian
T1  - Effects of impurities on the stability of the low thermal conductivity in Fe2TiO5 ceramics
JF  - Materials characterization
N2  - The stability of the low thermal conductivity in Fe2TiO5 pseudobrookite ceramics has been studied. An increase in thermal diffusivity is observed after only three cycles of measurement. X-ray refraction shows an increase in the mean value of specific surface after the thermal diffusivity measurements. By using scanning electron microscopy and high-angle annular dark-field scanning transmission electron microscope equipped with energy dispersive Xray spectroscopy, we observe a segregation of Ca- and F-rich nanocrystals at grain boundaries after three cycles of thermal diffusivity measurement. Therefore, impurities seem to be more efficient to scatter phonons as point defects in the pseudobrookite lattice rather than as nanocrystals at pseudobrookite grain boundaries. This emphasizes the importance of precursor purity and the influence of redistribution of impurities on thermoelectric properties: stability of micro-/nano-structures is a key point, and repeated thermoelectric measurements may allow detecting such metastable micro-/nano-structures and producing stable and reliable data.
KW  - Fe2TiO5
KW  - Impurity segregation
KW  - Thermoclectrics
KW  - X-ray refraction
KW  - Scanning transmission electron microscopy
KW  - Thermal conductivity
Y1  - 2019
U6  - https://doi.org/10.1016/j.matchar.2019.01.021
SN  - 1044-5803
SN  - 1873-4189
VL  - 149
SP  - 111
EP  - 117
PB  - Elsevier
CY  - New York
ER  - 
TY  - JOUR
A1  - Erdmann, Maren
A1  - Kupsch, Andreas
A1  - Müller, Bernd Randolf
A1  - Hentschel, Manfred P.
A1  - Niebergall, Ute
A1  - Böhning, Martin
A1  - Bruno, Giovanni
T1  - Diesel-induced transparency of plastically deformed high-density polyethylene
JF  - Journal of materials science
N2  - High-density polyethylene becomes optically transparent during tensile drawing when previously saturated with diesel fuel. This unusual phenomenon is investigated as it might allow conclusions with respect to the material behavior. Microscopy, differential scanning calorimetry, density measurements are applied together with two scanning X-ray scattering techniques: wide angle X-ray scattering (WAXS) and X-ray refraction, able to extract the spatially resolved crystal orientation and internal surface, respectively. The sorbed diesel softens the material and significantly alters the yielding characteristics. Although the crystallinity among stretched regions is similar, a virgin reference sample exhibits strain whitening during stretching, while the diesel-saturated sample becomes transparent. The WAXS results reveal a pronounced fiber texture in the tensile direction in the stretched region and an isotropic orientation in the unstretched region. This texture implies the formation of fibrils in the stretched region, while spherulites remain intact in the unstretched parts of the specimens. X-ray refraction reveals a preferred orientation of internal surfaces along the tensile direction in the stretched region of virgin samples, while the sample stretched in the diesel-saturated state shows no internal surfaces at all. Besides from stretching saturated samples, optical transparency is also obtained from sorbing samples in diesel after stretching.
Y1  - 2019
U6  - https://doi.org/10.1007/s10853-019-03700-8
SN  - 0022-2461
SN  - 1573-4803
VL  - 54
IS  - 17
SP  - 11739
EP  - 11755
PB  - Springer
CY  - New York
ER  -