Terms Of Grain Size Distribution Research Articles

Ethanol and Water Processing of Submicrometer Cemented Carbide Powders

The processing of submicrometer hardmetal grades using water and ethanol was compared. Powder dispersion was first studied in terms of electrokinetic experiments. Higher repulsive charges are generated in powders surfaces when immersed in water, which tends to decrease suspensions viscosity and to improve milling efficiency. Using water, suspensions with higher solids loading, shorter milling times can be achieved without affecting the microstructural homogeneity. Sintered samples with Co contents of 5.5 and 3.5 wt% were also prepared using both liquids. Higher quality microstructures in terms of grain size distribution, Co dispersion, porosity, and fracture toughness were obtained in water milling. This better Co distribution results in significant differences in terms of sintering behavior. Water processing of hardmetals can therefore bring substantial improvements to the production of these submicrometer grades with low Co contents, known for their processing difficulties. On the other hand, water technology is also environmental friendlier, requires lower investments related with equipment safety and maintenance costs, and hence it is a very promising step toward hardmetal green fabrication.

Polysilicon Films Formed On Alumina By Aluminium Induced Crystallization Of Amorphous Silicon

AbstractWe investigated the structural quality of polysilicon films fabricated by the aluminium induced crystallization (AIC) of amorphous silicon on alumina substrates. We analyzed the overall crystallographic quality of the poly-Si films in terms of grain size distribution and grain orientation versus crystallization temperature. For these studies, we used extensively the orientation imaging micrograph (OIM) technique, a very powerful tool that allows elucidating the inner-grain structure, the grain boundaries, the grain orientation. From our analysis, we may conclude that the polysilicon films formed by AIC on alumina substrates have the following features: (i) for all investigated temperatures, most of the silicon grains have a deviation angle from (100) crystallographic orientation between 5 and 25°; (ii) increasing the annealing temperature tends to decrease the (100) preferred orientation; (iii) the angular boundary distribution revealed that the main defects are those that have been observed inside isolated dentrites, namely low angle boundaries (<2°) and coincident site lattice boundaries such as Σ3, Σ9 and Σ27.

X-ray microdiffraction: local stress distributions in polycrystalline and epitaxial thin films

When investigated by X-ray microdiffraction, the stress states in thin metal films are found to be more complex than as assumed by the simple models that have been formulated to describe their behavior. In this paper, the local differences in stress have been measured in a polycrystalline Al(0.5 wt% Cu) film on Si and an epitaxial Cu film on Al 2O 3. Significant differences in stress state are apparent between grains, but also within grains. While both types of film display a local variation in residual stress state, the width of the distribution is much broader in the polycrystalline film. The reasons for this are discussed in terms of grain size distribution and dislocation nucleation.

Transmission Electron Microscopy Observation of Microstructure of Plasma-Sprayed Nanostructured Zirconia Coating

Nanostructured zirconia coatings deposited by plasma spraying technique were observed using transmission electron microscopy (TEM). It was found that the as-sprayed nanostructured zirconia coating had bimodal microstructures in terms of grain size distribution in the direction parallel to substrate surface. One was in the range 30–120 nm, which was the dominative structure of the coating, and the other was about 150–400 nm. The cross-section micrograph of the plasma sprayed nanostructured zirconia coating revealed that the coating still exhibited lamellar structure with columnar grains extending through its thickness. In conjunction with partially molten zirconia grains, amorphous regions were found. Domain structure and superlattice structure were observed in the plasma-sprayed nanostructured zirconia coating. The formations of the domain and superlattice structures are discussed in this paper.

Influence of Yttrium Oxide Doping on the Microstructures of Alumina-Niobium Carbide Composites

Ceramic cutting tools have been developed as an alternative material to cemented carbides based ones with the goal of improving cutting speeds and productivity. Among the vast variety of ceramics considered for prospective use as cutting tools materials the preference is given to the composites containing carbides as a second component, i.e., such materials as Al 2 O 3 -SiC, and A1 2 O 3 -TiC. In the present work, the influence of Y 2 O 3 additives on microstructure of Al 2 O 3 -NbC composite is studied in order to evaluate the applicability of this material for as ceramic cutting tools manufacturing. The amount of Y 2 O 3 additives varied in the ranged, 0 - 3 wt% in the Al 2 O 3 -NbC 20 wt% composition. Specimens were produced by consequent uniaxial and isostatic pressing followed by pressureless sintering in the flowing argon at 1750 °C for 15 min in a graphite resistance furnace. The achieved densities were up to 99% TD. Microstructure evaluation in terms of grain size distribution were achieved by mean of QUANTIKOV software applied to scanning electron microscope (SEM) micrographs. Optimization of the materials composition in regard of achieving the high densities without compromising the microstructure formation are discussed.

Formation of tough interlocking microstructures in silicon nitride ceramics by dynamic ripening.

Ceramics based on Si(3)N(4) have been comprehensively studied and are widely used in structural applications. The development of an interlocking microstructure of elongated grains is vital to ensure that this family of ceramics have good damage tolerance. Until now this has been accomplished by heating the appropriate powder compacts to temperatures above 1,700 degrees C for extended periods. This procedure involves a necessary step of controlling the size and population of seeds added ex situ or formed in situ to ensure selective grain growth. Here we report the very fast (within minutes) in situ formation of a tough interlocking microstructure in Si(3)N(4)-based ceramics. The microstructures are obtained by a dynamic ripening mechanism, an anisotropic Ostwald ripening process that results from the rapid heating rate. The resulting microstructures are uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics. This process is very efficient and opens up new possibilities to optimize mechanical properties and cost-effectively manufacture ceramics.

Long Term Sorption Kinetics of Phenanthrene in Aquifer Materials

Most aquifer materials are heterogeneous in terms of grain size distribution and petrography. To understand sorption kinetics, homogeneous subfractions, either separated from heterogeneous sands and gravels (lithocomponents) or fragments of fresh rocks, have to be studied. In this paper we present data on long-term sorption kinetics of phenanthrene for homogeneous samples consisting of one type of lithocomponents or fresh rock fragments in different grain sizes. Diffusion rate constants were determined in batch experiments using a numerical model for retarded intraparticle pore diffusion and correlated to grain size and intraparticle porosity of the lithocomponents. Sorption isotherms were nonlinear for all samples investigated (Kleineidam et al. (1)). The numerical model described the sorption kinetics very well for coarse sand and gravels. Tortuosity factors, which were obtained as final fitting factors, agreed with Archie's law predictions based on the intraparticle porosity. The dependency of sorptive uptake on grain size revealed that for smaller grains intrasorbent diffusion may become significant. This is attributed to relatively large particulate organic matter (POM) within the sedimentary rock fragments. Specifically, charcoal and coal particles, which were found in some of the sandstones, controlled the sorptive uptake rates.