Nanostructured Ceramic Materials Research Articles

Mechanochemical synthesis of solid solutions based on ZrO2 and their electrical conductivity

Zirconia-and scandia-based complex solid solutions predominantly with a monoclinic structure are prepared by mechanochemical synthesis. The dense ceramic materials, which, for the most part, have a cubic structure with grain sizes of 250–400 nm and possess good mechanical properties, are produced by sintering submicron fractions of the powders under relatively mild conditions at temperatures of 1633–1653 K. It is revealed that the powders are characterized by nanostructuring due to the complex composition and the chemical inhomogeneity. This nanostructuring is partially retained upon rapid sintering of the ceramic powders. The nanostructured ceramic materials possess a high low-temperature conductivity, which decreases after annealing. Unlike conventional ceramic materials, the nanostructured ceramic materials have identical activation energies for bulk and grain-boundary electrical conduction. The high-temperature electrical conductivity of the nanostructured ceramic materials is rather low because of the small grain sizes and impurities of the monoclinic phase.

AFM Nanoindentations of Diatom Biosilica Surfaces

Diatoms have intricately and uniquely nanopatterned silica exoskeletons (frustules) and are a common target of biomimetic investigations. A better understanding of the diatom frustule structure and function at the nanoscale could provide new insights for the biomimetic fabrication of nanostructured ceramic materials and lightweight, yet strong, scaffold architectures. Here, we have mapped the nanoscale mechanical properties of Coscinodiscus sp. diatoms using atomic force microscopy (AFM)-based nanoindentation. Mechanical properties were correlated with the frustule structures obtained from high-resolution AFM and scanning electron microscopy (SEM). Significant differences in the micromechanical properties for the different frustule layers were observed. A comparative study of other related inorganic material including porous silicon films and free-standing membranes as well as porous alumina was also undertaken.

The Evolution of Advanced Mechanical Defenses and Potential Technological Applications of Diatom Shells

Diatoms are unicellular algae with silicified cell walls, which exhibit a high degree of symmetry and complexity. Their diversity is extraordinarily high; estimates suggest that about 10(5) marine and limnic species may exist. Recently, it was shown that diatom frustules are mechanically resilient, statically sophisticated structures made of a tough glass-like composite. Consequently, to break the frustules, predators have to generate large forces and invest large amounts of energy. In addition, they need feeding tools (e.g., mandibles or gastric mills) which are hard, tough, and resilient enough to resist high stress and wear, which are bound to occur when they feed on biomineralized objects such as diatoms or other biomineralized protists. Indeed, many copepods feeding on diatoms possess, in analogy to the enamelcoated teeth of mammals, amazingly complex, silica-laced mandibles. The highly developed adaptations both to protect and to break diatoms indicate that selection pressure is high to optimize material properties and the geometry of the shells to achieve mechanical strength of the overall structure. This paper discusses the mechanical challenges which force the development of mechanical defenses, and the structural components of the diatom frustules which indicate that evolutionary optimization has led to mechanically sophisticated structures. Understanding the diatom frustule from the nanometer scale up to the whole shell will provide new insights to advanced combinations of nanostructured composite ceramic materials and lightweight architecture for technological applications.

UV transmitters of aluminum polyphosphates prepared by high pressure technique at room temperature

The possibility to obtain nanostructured ceramic materials from nanometric powders has been studied over the last few years. Such interest was motivated by the promise of potential improvement in optical and mechanical properties, like transparency, ductility, hardness and strength, among other potentially interesting properties [1–4]. These enhanced properties have been related to the nanostructure of these materials [5]. However, it is very difficult to retain the nanocrystalline grain size during the sintering process in order to produce a high-density bulk nanostructured ceramic. Therefore, it is necessary to find favorable conditions to enhance densification and limit grain grow. The high pressure technique has been used successfully to obtain nanostructured ceramic or composite materials with the desired properties [6–10]. Aluminum polyphosphate nanostructured systems have been used extensively as pigment for painting [11, 12], as matrix for composite materials [13], as well as ceramic foams [14]. However, as far as we know, there is no report in the literature concerning the preparation of aluminum polyphosphate ceramic materials by using the compaction of nanometric powders. In this work, we studied the required conditions to produce bulk ceramic materials from nanometric powders of aluminum polyphosphate, using a special high pressure cell configuration with a highly hydrostatic pressure transmitting medium and at room temperature. The samples were analyzed by Vickers microhardness, density, UV-VIS spectroscopy and X-ray diffraction. Nanocrystalline aluminum polyphosphate with P:Al mol ratio = 0.60 ± 0.01 in the reaction admixture, was obtained by precipitation from solutions of sodium polyphosphate, aluminum nitrate, and ammonium hydroxide, under strong stirring and at room temperature. Particle diameters were in the 2–6 nm range. The powder obtained was dried at 600 ◦C [15]. For the high pressure experiment the aluminum polyphosphate powder was initially pre-compacted in a piston-cylinder type die to approximately 0.1 GPa.

Nanostructured ceramic and hybrid materials via electrodeposition

Electrodeposition is unique in that it can be used for processing metals, ceramics, and polymers. Electrochemical strategies offer important advantages and unique possibilities in the development of nanomaterials and nanostructures. Novel electrodeposition methods have evolved into an important branch of nanotechnology. This paper presents a brief overview of recent developments in the application of electrochemical methods for synthesis of nanostructured ceramic and hybrid materials.

Thermal Plasma Processing of Nanostructured Si-based Ceramic Materials

A novel thermal plasma process, based on Thermal Plasma Chemical Vapor Deposition (TPCVD) for producing nanostructured ceramics from liquid precursors is described. The process combines the rapid thermal decomposition of low-cost liquid precursors injected into an Inductively Coupled Plasma (ICP) with a fast gas phase condensation due to the high cooling rate and short residence time existing in such a plasma. Examples of synthesis of Si-based nanostructured ceramic materials (SiC, Si3N4) as powders or coatings are given. Deposition rates of up to 10 μm/min can be achieved by the present technique.

Formation Mechanism of Molybdenum and Molybdenum Oxide Nanoparticles by Electron Irradiation

ABSTRACTThe mechanism of molybdenum and molybdenum oxide nanoparticles formation from molybdenum oxide microparticles by electron beam irradiation using a high-resolution transmission electron microscope on a room-temperature stage have been investigated. It is found that, the microsized molybdenum oxide particles disintegrated to form nanosized molybdenum oxide particles by electron beam irradiation with an intensity of approximately 1021e/cm2 · sec. The molybdenum nanoparticles were formed from molybdenum oxide nanoparticles upon further electron irradiation. During the electron irradiation process, the surfaces and interfaces of molybdenum oxide nanoparticles suffered damage and defects, such as vacancy arrays showing hole like spots and a moire-like fringes in the lattice image due to oxygen loss, followed by a gradual change from molybdenum oxide to molybdenum nanoparticles. The phenomenon of molybdenum metal nanoparticle formation from nanosized molybdenum oxide is considered to be due to desorption of oxygen as a result of electron stimulation and atomic displacement via the knock-on effect. It is suggested that electron irradiation is a powerful technique to create nanostructured metal, ceramic and semiconductor materials by atomic-scale control.

Nanostructured Oxide Ceramic Materials of High Density

The paper deals with the nanostructured oxide ceramic materials of high density only. In the first part of the paper the structure of nano-materials was briefly discussed. The nanostructured ceramics have specific properties as a consequence its specific structure which contains about 50% of its atoms at the grain boundary. That structure and its properties are the result of the processing routs which are generally rewived. In some length the superplastic properties of the studied ceramics systems (alumina, zircona and titania) were discussed. The experimental results of colloidal processed alumina, zirconia and titania are presented and the problems solving in achieving the super-plasticity are discussed.