Search Results (2)

The combination of biocompatible polymers and ceramics shows great promise in the development of composites with suitable mechanical properties for dental applications. In an attempt to further expand this research line, Al₂O₃ commercial powders (Vitro-ceram, Alglass, In-ceram) were sintered at 1400 °C for 2 h and infiltrated with poly(methyl methacrylate) for potential use in dental prostheses. The infiltration was performed using a homemade apparatus under a pressure of 7 bar for 6 and 12 h. The microstructure (studied using a scanning electron microscope), Archimedes density, 3-point bending flexural strength and Vickers hardness of the prepared composites were assessed and quantitatively compared. In general, microstructural analyses showed ceramic- and polymer-based interpenetrating network in all materials. The preforms infiltrated for 12 h showed superior properties; among them, the Vitro-ceram-based composite also demonstrated a near-zero open porosity and optimum mechanical characteristics. Specifically, its density, strength and hardness were 2.6 ± 0.07 g/cm³, 119.3 ± 5.0 MPa and 1055.1 ± 111.0 HV, respectively, passing the acceptance criteria of ISO 6872 and making it suitable for consideration as a metal-free structure for dental crowns and fixed partial prostheses until three anterior units. Full article

Magnesium-based composites reinforced with open-celled carbon foams (C_of) of porosity approx. 97 vol % and three cell sizes (20, 45 and 100 ppi) were examined to characterize the influence of foam cell size on the microstructure and properties when pure magnesium and two cast alloys AZ31 and RZ5 were used as matrices. All composites were fabricated by pressure infiltration under the same conditions (temperature, pressure, time). For each matrix composition, two main factors due to the presence of the foam determined the composite microstructure—the efficiency of foam penetration and different conditions of metal crystallization. The lowest porosity was obtained when C_of45ppi was used and was independent of the applied matrix composition. The metallic component microhardness increased with a decrease in the carbon cell size as well as a decrease in the α-Mg grain size; both of those results should be taken into account during theoretical calculations. Compression and three-point bending strength measurements showed increases as the carbon cell size decreased, but reinforcing effectiveness relative to the matrix material depended on the metal matrix composition. At the fractured surface, different structural effects in the foam and matrix as well as at the interface were observed and depended on the foam geometry, metal composition and mechanical test type. In glassy carbon foam, those effects occurred as cracking across walls, fragmentation, and delamination, while in the matrix, shear bands and intergranular cracking were observed. On the delaminated foam surface, the microareas of a thin oxide layer were detected as well as dispersed phases characteristic for the applied matrix alloys. The accumulation of intermetallic phases was also observed on the metal matrix surface in microareas delaminated from the carbon foams. Mechanical property results indicated that among the tested, open-celled, carbon foams a 45 ppi porosity was the most useful for pressure infiltration and independent of magnesium-based matrix composition. Full article