Effectiveness and Compatibility of a Novel Sustainable Method for Stone Consolidation Based on Di-Ammonium Phosphate and Calcium-Based Nanomaterials

External surfaces of stones used in historic buildings often carry high artistic value and need to be preserved from the damages of time, especially from the detrimental effects of the weathering. This study aimed to test the effectiveness and compatibility of some new environmentally-friendly materials for stone consolidation, as the use thereof has been so far poorly investigated. The treatments were based on combinations of an aqueous solution of di-ammonium phosphate (DAP) and two calcium-based nanomaterials, namely a commercial nanosuspension of Ca(OH)2 and a novel nanosuspension of calcite. The treatments were applied to samples of two porous stones: a limestone and a sandstone. The effectiveness of the treatments was assessed using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, ultrasound pulse velocity test, colour measurements, and capillary water absorption test. The results suggest that the combined use of DAP and Ca-based nanosuspensions can be advantageous over other commonly used consolidants in terms of retreatability and physical-chemical compatibility with the stone. Some limitations are also highlighted, such as the uneven distribution and low penetration of the consolidants

Failure Mechanism for Thermal Fatigueof Thermal Barrier Coating Systems

Thick thermal barrier coatings (TBCs), consisting of a CoNiCrAlY bond coat and yttria-partiallystabilized zirconia top coat with different porosity values, were produced by air plasma spray (APS). Thethermal fatigue resistance limit of the TBCs was tested by furnace cycling tests (FCT) according to thespecifications of an original equipment manufacturer (OEM). The morphology, residual stresses, andmicromechanical properties (microhardness, indentation fracture toughness) of the TBC systems beforeand after FCT were analyzed. The thermal fatigue resistance increases with the amount of porosity in thetop coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling; neverthelessthe increasing rate has a trend contrary to the porosity level of top coat. The data suggest that thespallation happens at the TGO/top coat interface. The failure mechanism of thick TBCs was found to besimilar to that of conventional thin TBC systems made by APS