Importance of thermal gradient in the bitumen bees genesis

Abstract

International audienceBitumen can be regarded as a complex colloidal suspension. Indeed, the heaviest molecules in bitumen, the asphaltenes, are known to self-associate to form solid particles suspended in a fluid called maltenes. Bitumen is also composed of a crystallizable fraction that partitions between asphaltenes and maltenes. This complex colloidal system exhibits peculiar patterns at their surface called ‘‘bees.’’ By varying the bitumen formulation and also tuning process parameters such as the temperature cooling rate, we demonstrate the role of the various components: asphaltenes, maltenes, and the crystallizable fraction on thebee existence and we evidence that the bee formation results from a complex coupling between different physico-chemical phenomena such as phase separation, crystallization, and buckling. We then propose a mechanism of bee genesis based on the thermal properties of the various fractions and especially on the heat capacity of both asphaltenes and maltenes. We demonstrate that a thermal gradient in the sample is required for the formation of bees and put into evidence the importance of kinetic aspects. We also discuss the bitumen general bulk properties

Thermomagnetically Responsive γ‐Fe2O3@Wax@SiO2 Sub‐Micrometer Capsules

“…In this configuration, the γ‐Fe 2 O 3 nanoparticles trapped within the wax volume bearing a lower heat capacity than the surrounding matrix might act as hot spots that will lower the crystallization temperature of the wax in their vicinity, cancelling the DLS peak observed at 38 °C. This effect has already been observed elsewhere with wax and asphaltens when dealing with bitumen‐bees morphosyntheses . Effectively at the intrinsic wax melting temperature (35.9 °C), we observed the same effect by heating the wax either macroscopically or by magnetic field where γ‐Fe 2 O 3 nanoparticles can behave as “hot spots” but have no interplay on the wax melting temperature.…”

“…This effect has already been observed elsewhere with wax and asphaltens when dealing with bitumen-bees morphosyntheses. [49] Effectively at the intrinsic wax melting temperature (35.9 °C), we observed the same effect by heating the wax either macroscopically or by magnetic field where γ-Fe 2 O 3 nanoparticles can behave as "hot spots" but have no interplay on the wax melting temperature. All observations made over the wax microstructure evolution with temperature by the DSC experiments are not direct.…”

Morphology and kinetics of asphalt binder microstructure at gas, liquid and solid interfaces

“…Since initial conditioning temperature and cooling rate influence bee formation [17,18], control samples with an air-binder interface were fabricated with the same thermal history as the glycerol-binder interface samples. Specifically, one sample in each experimental set was placed in the glycerol bath with the binder right side up and above the surface of the glycerol, then subjected to the same thermal treatment as submerged samples.…”

Bitumen surface microstructure evolution in subzero environments

“…After exposure to high temperatures, the surface composition of bitumen can change (Isacsson & Zeng, 1997; Petersen, 2009; Das et al ., 2014; Cavalli et al ., 2018). The so‐called ‘surface microstructures’ (Masson et al ., 2007; Schmets et al ., 2010; Pauli et al ., 2011; Lyne et al ., 2013; Nahar et al ., 2013; Hung & Fini, 2015; Mercé et al ., 2015) and the properties of bitumen are also affected by temperature. Bitumen behaves like a Newtonian fluid above its melting point and as a viscoelastic material below it (Lesueur et al ., 1996; Lesueur, 2009).…”