Microencapsulated Phase Changing Materials for Gypsum Plasters: A Practical Approach

Several studies have shown the feasibility and thermal potential of gypsum plaster with microspheres of PCM, but very few of them investigated an approach with practical and standards concern. In this work, different characterizations are performed according to European standards on a standard gypsum plaster and two different gypsum plasters formulated with 20 wt.% of PCM microspheres. A material is experimentally made by mixing conventional gypsum and PCM microspheres, whereas the other is an already prepared commercial mix. For the laboratory material, the addition of PCM increases the consistency of the fresh paste of plaster. In order to reach a consistency in agreement with the standards more water is required. This higher amount of water causes further issues on the densification and cohesion properties. In contrary, the properties of the commercial mix are closer to a common plaster. It is therefore assumed that the commercial material incorporates thinner additives. In view of these results, it is assumed that most of the drawbacks due to the addition of PCM microspheres in gypsum plasters could effectively be encountered by adequate addition of additives in order to reduce the amount of water, and binding resins in order to improve the adhesion and mechanical properties.

Molecular Dynamics Simulations on the Thermal Effect of Interfacial Friction During Asperity Shearing

To explore the thermal effect of interfacial friction at the nano/microscale, a solid-solid contact model of a rough surface with a single peak was established to research single-crystal Fe. The friction characteristics, stress distributions, temperature changes, and energy changes under different indentation depths and lattice orientations during the shearing process were analyzed. From the perspective of temperature and energy, the mechanism of the thermal effect was revealed. The relationship between the friction force, temperature, and energy at the atomic scale was clarified. The results showed that the temperature of the asperities gradually increased during the shearing process, and a stress concentration formed in the shearing zone. After contact, the asperities had undergone unrecoverable plastic deformation, and there was wear at the contact interface accompanied by the loss of atoms from the asperity. At each indentation depth, as the rotation angle of the crystal increased, the friction force, average temperature, and the sum of the changes in thermal kinetic and thermal potential energy all first increased and then decreased; the trends of the three parameters changing with the rotation angle of the crystal were consistent. The average decreases in the friction force, average temperature, and the sum of the changes in thermal kinetic and thermal potential energy were 52.47%, 30.91%, and 56.75%, respectively, for a crystal structure with a rotation angle of 45° compared to a crystal structure with a rotation angle of 0°. The methods used in this study provide a reference for the design of frictional pairs and the reduction of the thermal effect of interfacial friction.

Measurements of Aluminum-Annealed Pyrolytic Graphite Composite Baseplates with Improved Thermal Conductivity

Annealed pyrolytic graphite (APG) is a material with thermal conductivity of about 1500 W/(m·K). This property may enable the usage of APG’s thermal potential to develop highly thermally conductive composites for devices requiring effective thermal management. In this paper, APG has been encapsulated in aluminum by brazing, and the thermal properties of Al-APG composite baseplates were measured. The results show that the thermal conductivity of the Al-APG composite baseplates is about 620 W/(m·K), which is four times higher than the pure aluminum plate (152 W/(m·K)).