Brittle Behaviour in Aspirin Crystals: Evidence of Spalling Fracture

<div> <div> <div> <p>Single crystals of aspirin form I were cleaved and indented on their dominant face. Upon inspection, it was possible to observe strongly anisotropic shallow lateral cracks due to the extreme low surface roughness after cleavage. Atomic Force Microscopy (AFM) imaging showed spalling fractures nucleating from the indent corners, forming terraces with a height of one or two interplanar spacings d100. The formation of such spalling fractures in aspirin was rationalised using basic calculations of attachment energies, showing how (100) layers are poorly bonded when compared to their relatively higher intralayer bonding. An attempt at explaining the preferential propagation of these fractures along the [010] direction is discussed. </p> </div> </div> </div>

Brittle Behaviour in Aspirin Crystals: Evidence of Spalling Fracture

<div> <div> <div> <p>Single crystals of aspirin form I were cleaved and indented on their dominant face. Upon inspection, it was possible to observe strongly anisotropic shallow lateral cracks due to the extreme low surface roughness after cleavage. Atomic Force Microscopy (AFM) imaging showed spalling fractures nucleating from the indent corners, forming terraces with a height of one or two interplanar spacings d100. The formation of such spalling fractures in aspirin was rationalised using basic calculations of attachment energies, showing how (100) layers are poorly bonded when compared to their relatively higher intralayer bonding. An attempt at explaining the preferential propagation of these fractures along the [010] direction is discussed. </p> </div> </div> </div>

Ethylene Glycol Accelerated Weathering Test: An Improved, Objective Aggregate Durability Test Method

Ethylene glycol has been used extensively by the concrete and road construction industries to identify rock durability issues associated with smectite clay minerals. The presence of these clay minerals is synonymous with rock degradation under normal environmental wetting and drying cycles. However, such historical test methods are predominately based on a subjective visual interpretation, describing the observed degradation of individual rock pieces at fixed time intervals during the soaking process. In addition, some test methods include complex equations with multiple weighting factors applied to nominated degradation descriptors (e.g., spalling, fracture, and disintegration) used to calculate a single durability indicator. This paper describes the development and implementation of an alternative, nonsubjective accelerated weathering test that also uses ethylene glycol. The research included metamorphic and volcanic rock types used extensively in New Zealand for road construction. The greatest benefit of the proposed new test method is the ability to eliminate the subjective visual assessment described in historical test methods and adequately quantify results to specify contractual acceptance and rejection criteria. The test method also shows that good repeatability is possible from duplicate test samples. However, rock quality and quarry production consistency will influence the ability of the test method to report the same “percentage change in fines” over a prolonged test period. This phenomenon was particularly evident with problematic and lower quality rock. The test findings are well supported by observed field performance, thus giving confidence in the new method’s usefulness.

Microstructure and Abrasive Wear Properties of Plasma Sprayed Nanostructured Al2O3-TiO2-ZrO2-CeO2 Coatings

Al2O3-TiO2-ZrO2-CeO2 coatings formed via a plasma spray approach. The optimal spray parameters of plasma sprayed nano-structured coating were determined by orthogonal experimental design, based on porosity, bond strength of the coatings and the partly melted(PM) zone percentage. Microstructure of the plasma sprayed nanostructured Al2O3-TiO2-ZrO2-CeO2 coating sprayed on the optimal spray parameters was analyzed. Wear map was established by wear experiments. The results show, nanostructured coating contains fully melted (FM) zone and PM zone, the increasing of the critical plasma spray parameter (CPSP) promote the decreasing of the PM zone percentage and the increasing of the bond strength of the coatings. The composition phases of the powder reacted to each other during the plasma spraying process. FM and PM zone resulted from fully melted droplets and partly melted particles respectively. Nanosized crystals and amorphous particles exist in the PM zone, liquid phase sintering is taken place in the PM zone. The main wear mechanism of plasma spraying coatings are plastic deformation and microplow, microfracture and grain spalling, fracture and delamination at different normal load and sliding speed in dry friction.