THERMAL SHOCK RESISTANCE OF A SODA LIME GLASS

We studied the thermal shock of a three millimeters thickness soda lime glass using the hot-cold thermal shock technique. The cooling was made by ambient air jet on previously warmed samples. The heat transfer coefficient was about 600 W/°C.m2 (Biot number β = 0.3). The thermal shock duration was fixed at 6 seconds. The hot temperature was taken between 100°C and 550°C while the cold temperature of the air flux was kept constant at 20°C. The acoustic emission technique was used for determining the failure time and the critical temperature difference (ΔTC). By referring to experimental results, thermal shock modelling computations are conducted. Our aim is especially focused on the fracture initiation moments during the cooling process and on the crack initiation sites. The used modeling is based on the local approach of the thermal shock during the experimental data treatment. For each test, the temperature profile and the transient stress state through the samples thickness are determined. By applying the linear superposition property of the stress intensity factors, evolution of the stress intensity factor KI in function of the pre-existing natural flaws in the glass surface is established. The size of the critical flaw is determined by the linear fracture mechanics laws. Computation results confirm the experimental values of the critical difference temperature obtained that is the source of the glass degradation

Thermomechanical behavior of a zircon-mullite composite

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Hybrid SiO2–ZrO2 coatings for restoring and repairing glasses damaged by sandblasting

The purpose of this work was to study the repairing of defect produced by sandstorms on the surface of car windshields and solar panels, by deposition of thin transparent sol-gel layers. Different silica-zirconia films (100-x SiO - x ZrO, x = (10, 15, 20, 25 and 30 mol %) were prepared by the sol–gel process using TEOS and MTES as silica precursors and incorporating two different colloidal suspensions with silica or zirconia nanoparticles. The silica-zirconia sols were deposited by dip coating on soda-lime glass samples previously eroded by sandblasting. Film thickness and homogeneity were evaluated by ellipsometry and AFM, and the optical and mechanical properties were studied by UV–vis spectroscopy, the hardness by microhardness, and the roughness by tactile profilometer. The sol-gel coatings present a good quality and are able to restore the optical and mechanical properties of sandblasted samples thus increasing the service life. The incorporation of zirconia particles to SiO coatings increases the refractive index, from 1.42 to 1.57. Moreover, optical transmission of coated samples increases from 91.4 to 93% for 90SiO–10ZrO coatings, and increases from 80% for eroded samples (Mp = 200 g) coated with SiO–ZrO films up to 91% while micro-hardness is greatly improved from 10.17 GPa for the raw material to 17.62 GPa for 70SiO–30ZrO coated sample.This work was supported by MINECO under projects MAT2017-87035-C2-1-P

Thermomechanical characterization of a fire clay refractory made of Algerian Kaolin

cited By 0International audienceThe thermomechanical behaviour of a mullitic refractory made of Algerian kaolin was investigated. Bending tests reveal that the behaviour was linear until 900 °C and became visco-plastic at 1000 °C. A maximum of strength (33 MPa) was reached at 900 °C where a crack bridging strengthening process was reported. The elaborated refractory presents a maximum elastic modulus of (8.21 GPa) at 700 °C due to the crack healing phenomenon. The calculated apparent activation energy for creep deformation is about 335 kJ/mole (T 1050 °C), an increase of the activation energy was recorded. Cyclic thermal shocks realized from 950 °C into a water bath kept at ambient temperature show that the elaborated refractory can be classified as a good thermal shock resistant material. © Lavoisier, Paris

Statistical analysis of a sodalime glass thermal shock resistance

cited By 1International audienceComparatively to the as received soda lime glass samples, the strength distribution after thermal shocks showed the appearance of a second branch in the Weibull curves. This branch is observed for temperature differences (δT) equal or higher than the critical temperature difference (δTc) for both water and motor oil cooling baths. The dispersion is more spread out in these two baths in comparison with the olive oil bath probably because of more pronounced slow crack growth effect. The Weibull modulus varies according to the used cooling bath and the considered temperature difference. In the case of thermal shock caused by air blast cooling at T = 20°C, a bimodal distribution is observed for only the critical state. The initial cracking time, obtained by acoustic emission, corresponds to the unstable propagation of the most critical defect. The number of cracks induced by thermal shock is proportional to the number of acoustic events

HF etching effect on sandblasted soda-lime glass properties

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Elaboration and characterization of mullite-zirconia composites from gibbsite, boehmite and zircon

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