ABSTRACT
Dense (>98 th%) and homogeneous ceramic/metal composites were obtained by spark plasma sintering (SPS) using ZrO2 and lamellar metallic powders of tantalum or niobium (20 vol.%) as starting materials. The present study has demonstrated the unique and unpredicted simultaneous enhancement in toughness and strength with very high flaw tolerance of zirconia/Ta composites. In addition to their excellent static mechanical properties, these composites also have exceptional resistance to fatigue loading. It has been shown that the major contributions to toughening are the resulting crack bridging and plastic deformation of the metallic particles, together with crack deflection and interfacial debonding, which is compatible with the coexistence in the composite of both, strong and weak ceramic/metal interfaces, in agreement with predictions of ab-initio calculations. Therefore, these materials are promising candidates for designing damage tolerance components for aerospace industry, cutting and drilling tools, biomedical implants, among many others.
ABSTRACT
Alumina-zirconia nano-composites were recently developed as alternative bearing materials for orthopedics. Previous, preliminary reports show that such alumina-zirconia nanocomposites exhibit high crack resistance and low wear rate. In this paper, additional information is given in terms of wear, crack resistance and ageing behaviour: femoral heads are inspected after 7 million cycles of wear testing on a hip simulator, crack resistance is measured and compared to other ceramics used today in orthopedics, slow crack growth is reported under static and cyclic fatigue, and aging resistance is assessed. We also report on the load to failure of femoral heads prototypes during compression tests. This overall reliability assessment ensures a potential future development for these kinds of new nanocomposites in the orthopedic field.
Subject(s)
Materials Testing/methods , Nanocomposites , Orthopedics , Aluminum Oxide/chemistry , Ceramics/chemistry , Hip Joint/surgery , Hip Prosthesis , Luminescent Measurements , Microscopy, Atomic Force , Microscopy, Electron, Scanning , Prosthesis Failure , Stress, Mechanical , Time Factors , Zirconium/chemistryABSTRACT
A low melting point soda-lime glass powder containing copper nanoparticles with high antibacterial (against gram-positive and gram-negative bacteria) and antifungal activity has been obtained. Sepiolite fibres containing monodispersed copper nanoparticles (d(50) approximately 30 +/- 5 nm) were used as the source of the copper nanoparticles. The observed high activity of the obtained glass powder, particularly against yeast, has been explained by considering the inhibitory synergistic effect of the Ca(2+) lixiviated from the glass on the growth of the colonies.
Subject(s)
Anti-Bacterial Agents/pharmacology , Antifungal Agents/pharmacology , Calcium Compounds/chemistry , Copper/pharmacology , Glass/chemistry , Nanoparticles/chemistry , Oxides/chemistry , Sodium Hydroxide/chemistry , Escherichia coli/drug effects , Escherichia coli/ultrastructure , Microbial Sensitivity Tests , Nanoparticles/ultrastructure , Particle Size , Spectrophotometry, Ultraviolet , X-Ray DiffractionABSTRACT
The antibacterial and antifungal activity of a low melting point soda-lime glass powder containing silver nanoparticles has been studied. Nano-Ag sepiolite fibres containing monodispersed silver nanoparticles (d(50) approximately 11 +/- 9 nm) were used as the source of silver. This powder presents a high antibacterial (against gram-positive and gram-negative bacteria) as well as antifungal (against I. orientalis) activity. The observed high activity against yeast has been explained by considering the inhibitory effect of the Ca(2+) lixiviated from the glass on the growth of the yeast colonies.
Subject(s)
Anti-Bacterial Agents/administration & dosage , Antifungal Agents/administration & dosage , Ascomycota/drug effects , Calcium Compounds/chemistry , Escherichia coli/drug effects , Micrococcus luteus/drug effects , Nanoparticles/administration & dosage , Oxides/chemistry , Silver/administration & dosage , Sodium Hydroxide/chemistry , Ascomycota/cytology , Escherichia coli/cytology , Glass/chemistry , Materials Testing , Micrococcus luteus/cytologyABSTRACT
Isolated tungsten nanoparticles (α-W and ß-W phase) were synthesized and epitaxially grown on alumina and spinel particle surfaces with an average tungsten size of ≤20 nm for a low tungsten content (of ≤1.5 vol%). Using tungsten (VI) ethoxide alcoholic solutions, tungsten trioxide hydrated precursors were attached to a ceramic grains surface as a nanoparticle coating. High-resolution transmission electron microscopy (HRTEM) micrographs showed epitaxial interfaces between alumina, spinel and metallic tungsten. This epitaxial growth is assumed to be due to the effect of water vapour on the sublimation of ortho-tungstic acid during the reduction process in a hydrogen atmosphere. The planes involved in the epitaxy were found to be [Formula: see text] and [Formula: see text].
ABSTRACT
Oxide ceramics are sensitive to slow crack growth because adsorption of water can take place at the crack tip, leading to a strong decrease of the surface energy in humid (or air) conditions. This is a major drawback concerning demanding, long-term applications such as orthopaedic implants. Here we show that a specific nanostructuration of ceramic oxides can lead to a crack resistance never reached before, similar to that of covalent ceramics.
