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Yttrium aluminium garnet (YAG) is a promising topcoat material for thermal barrier coatings due to its high temperature stability and better CMAS (calcium-magnesium-alumino-silicate) resistance. YAG topcoats were deposited by suspension and solution precursor high-velocity oxy-fuel (HVOF) thermal spray. The relationships between processing, microstructure and final properties were studied through a range of characterization techniques and thermal cycling tests. The microstructure of the as-sprayed YAG topcoat from stoichiometric solution precursor (SP-YAG) had distributed pores and inter-splat boundaries, while the as-sprayed topcoat produced from suspension (S-YAG) had vertical and branched micro cracks, pores, and inter-splat boundaries. Both as-sprayed coatings were composed of amorphous phase, hexagonal yttrium aluminium perovskite (YAP) and cubic YAG. In thermal cycling tests, 20% of SP-YAG failure was reached after the 10th cycle; whereas, S-YAG reached the failure criteria between the 60th and 70th cycle. The failure of both the SP-YAG and the S-YAG topcoats occurred due to thermal stresses during the thermal cycling.

Calcium carbonate is widely used as a filler material in the production of polymer matrix composites and studies have shown that eggshell contains about 94% calcium carbonate. The effect of calcium carbonate from eggshell particles in polypropylene was studied in this work and the result compared with unreinforced polypropylene. Industrially synthesized calcium carbonate/eggshell particles were used as filler in polypropylene matrix with varying mass fractions from 5 to 20 wt. % at 5 wt. % increment. The produced samples were mechanically characterized for indentation hardness and uniaxial tensile properties using a Rockwell hardness tester and universal mechanical testing machine respectively. These properties were measured at different compositions to determine its compositional dependence. Microstructural analysis of the composites top and fracture surface was also carried out using scanning electron microscope to examine possible failure mode. The results were compared to measure the effect of reinforcement and the replacement criteria for the conventional calcium carbonate. The results obtained showed that calcium carbonate reinforced polypropylene has its highest tensile strength, elastic modulus and modulus of rupture at 5 wt. %, ductility and modulus of resilience at 10 wt. %, and hardness at 15 wt. %. The results also showed that granulated eggshell can provided appreciable improvement in the mechanical properties of polypropylene as obtainable in mineral calcium carbonate reinforced polypropylene.

The nature and magnitude of residual stresses in thermal-sprayed coatings determine their lifetime and failure mechanisms. The residual stresses of suspension high-velocity oxy-fuel (SHVOF) thermal sprayed alumina (Al2O3) coating were measured with hole-drilling and x-ray diffraction. The coating is dense and consists of amorphous and two crystalline phases: alpha and gamma. The residual stresses measured by hole-drilling in the Al2O3 coating was − 162 MPa (compression) in the longitudinal direction and − 104 MPa (compression) in the transverse direction. This is due to the peening stress and the high substrate–coating CTE ratio of ~ 2.1. The nature of the residual stress through the coating is related to the microstructure build-up shown from the cross section and the fracture surfaces of the coating.

This paper provides a succinct and simplified account of desalination techniques. The techniques are categorized as membrane-based, thermal-based, combined membrane/thermal-based and miscellaneous techniques. Essential features of membrane-based, thermal-based and combined membrane/thermal-based techniques are presented, while their associated limitations are equally highlighted. Reverse Osmosis (RO) remains the state-of-the-art technology in seawater desalination with the highest installed capacity of 65% globally. Whereas, solar desalination potentially shows as a cost and energy-effective means of ensuring steady supply of potable water in off-grid arid-coastal environments, where freshwater reserves are non-existing. In general, if the world is to aim for global freshwater sustainability, seawater desalination must be considered crucial, and a good understanding of its techniques will further drive the vision closer to reality.

International audience; Turtle shells comprising of cortical and trabecular bones exhibit intriguing mechanical properties. In this work, compression tests were performed using specimens made from the carapace of Kinixys erosa turtle. A combination of imaging techniques and mechanical testing were employed to examine the responses of hierarchical microstructures of turtle shell under compression. Finite element models produced from microCT-scanned microstructures and analytical foam structure models were then used to elucidate local responses of trabecular bones deformed under compression. The results reveal the contributions from micro-strut bending and stress concentrations to the fractural mechanisms of trabecular bone structures. The porous structures of turtle shells could be an excellent prototype for the bioinspired design of deformation-resistant structures.Statement of SignificanceIn this study, a combination of analytical, computational models and experiments is used to study the underlying mechanisms that contribute to the compressive deformation of a Kinixys erosa turtle shell between the nano-, micro- and macro-scales. The proposed work shows that the turtle shell structures can be analyzed as sandwich structures that have the capacity to concentrate deformation and stresses within the trabecular bones, which enables significant energy absorption during compressive deformation. Then, the trends in the deformation characteristics and the strengths of the trabecular bone segments are well predicted by the four-strut model, which captures the effects of variations in strut length, thickness and orientation that are related to microstructural uncertainties of the turtle shells. The above results also suggest that the model may be used to guide the bioinspired design of sandwich porous structures that mimic the properties of the cortical and trabecular bone segments of turtle shells under a range of loading conditions.

Suspension high-velocity oxy-fuel (SHVOF) thermal spray is an emerging spray technology that enables the processing of nanometric feedstock. Although SHVOF thermal sprayed alumina coatings prepared from alpha alumina feedstock have been widely reported, a metastable δ-θ Al2O3 feedstock has yet to be investigated despite its low cost and commercial availability. In this study, an aqueous δ-θ Al2O3 suspension was sprayed on to a stainless steel (SS 304) substrate via SHVOF thermal spraying using an internal injection UTP TopGun. X-ray diffraction (XRD) of the as-sprayed coating showed δ-θ Al2O3 to γ-Al2O3 transformation upon spraying, along with amorphous/nanocrystalline phase formation. Furthermore, post-spray heat treatment of the coatings was performed at 600–750 °C for 6 and 48 h. The microhardness and indentation fracture toughness of the heat treated coatings increased by a factor of two compared to the as-sprayed coatings: due to grain refinement, pore consolidation and phase transformation of amorphous and γ-Al2O3 to δ-Al2O3. Unlubricated sliding wear tests were conducted at room temperature (~25 °C, relative humidity ~60%) using α-Al2O3 balls (O 9.5 mm) as the counter body at a normal load of 16.8 N to study the wear performance of the coatings. The wear rate of the as-sprayed coating and the coating heat treated at 600 °C for 6 h is of the order of 10−9 mm3 (Nm)−1, a noticeable improvement over conventional alumina coatings. The coatings heat treated at 750 °C for both 6 and 48 h failed abruptly by severe wear due to their pre-cracked surface.