Ceramic powder characterization sampling

This chapter has described the various techniques of ceramic powder characterization. These characteristics include particle shape, surface area, pore size distribution, powder density and size distribution. Statistical methods to evaluate sampling and analysis error were presented as well as statistical methods to compare particle size distributions. Chemical analytical characterization although veiy important was not discussed. Surface chemical characterization is discussed separately in a later chapter. With these powder characterization techniques discussed, we can now move to methods of powder preparation, each of which 3uelds different powder characteristics. 

To characterize a ceramic powder, a representative sample must be taken. Methods of sampling and their errors therefore are discussed. Powder characteristics, including shape, size, size distribution, pore size distribution, density, and specific surface area, are discussed. Emphasis is placed on particle size distribution, using log-normal distributions, because of its importance in ceramic powder processing. A quantitative method for the comparison of two particle size distributions is presented, in addition to equations describing the blending of several powders to reach a particular size distribution. 

Various techniques have been developed to characterize the surface properties of ceramic powders [43 5]. Generally, the principles of surface characterization techniques are to use the interactions of the samples with atomic particles, such as atoms, ions, neutrons, and electrons, or radiations, such as X-rays and ultraviolet rays. Various emissions are produced during the interactions, which are collected as signals to analyze the samples. Figure 4.8 shows the principal emissions caused by the interactions of an electron beam with solid particles. 

The quality of a ceramic sample is a function of the degree to which it consists of the desired product. An essential tool for the characterization of a polycrystalline sample is powder X-ray diffraction. The powder pattern is a fingerprint of the sample. For a sample to be declared single phase, all low angle peaks (below 60 20 for CuKq radiation) which are above the noise must be accounted for. Powder X-ray diffraction is often unable to see impurity phases present below the 5% level. Visual inspection (using a microscope)... 

The driving force behind the rapid development of powder diffraction methods over the past 10 years is the increasing need for structural characterization of materials that are only available as powders. Examples are zeolite catalysts, magnets, metal hydrides, ceramics, battery and fuel cell electrodes, piezo- and ferroelectrics, and more recently pharmaceuticals and organic and molecular materials as well as biominerals. The emergence of nanoscience as an interdisciplinary research area will further increase the need for powder diffraction, pair-distribution function (PDF) analysis of powder diffraction pattern allows the refinement of structural models regardless of the crystalline quality of the sample and is therefore a very powerful structural characterization tool for nanomaterials and disordered complex materials. 

For further characterization of the material, a high-temperature DTA/TG has been carried out. The ceramic material, obtained from 3P and pyrolyzed at 1000 °C, shows only a weight loss of 2% up to 2000 °C. Powder X-ray diffraction analysis as well as HRTEM investigations of the sample indicates the crystallization of Si3N4 and SiC at the mentioned temperatures. 

Abstract Ceramic samples of LaSr2Fe3.yCry08+g are characterized with X-ray powder... 

In order to characterize SiC powders and sintered ceramics the total oxygen and nitrogen content as well as the contents of metallic impurities are analyzed. Total oxygen and nitrogen contents are usually determined by an inert gas fusion method (Leco TC 436) using powdered samples, whereas metallic impurities (Na, K, Ca, Mg, V, Fe, Ti, Al, Cr and Ni) and boron content are determined in acidic solutions by inductive plasma emission (ICP) spectroscopy [240-242],... 

The main objective of the project, ie. to study the reaction bonding technique as an effective way to produce porous silicon carbide ceramics, has been successfully achieved. This includes the colloidal processing of the precursor powders, compaction through slip-casting, and finally sintering to achieve the muilitization reaction. Characterization of the sintered and polished samples using SEM and XRD have confirmed the formation of the muliite phase. 

While INAA has an excellent track record in archaeology, bulk techniques like INAA have inherent limitations. In bulk analysis, powdered, homogenized whole samples are characterized, so contributions from individual components of a composite material, such as a ceramic, cannot be separated. One reason to characterize individual components in ceramics is that patterned elemental variation may arise not only from provenance differences, but also from paste preparation and diagenesis [5]. Microprobe techniques, either electron microprobes [5] or LA-ICP-MS [1,40], offer a means to identify where within the ceramic fabric the important elements are concentrated or diluted. Microprobes can also be targeted at ceramic slips, glazes, and pigments, as discussed in greater detail below. 

Similar experiments were performed in La2-xStxCu04 doped with Mn ". The Mn ion is substituted for the Cu ion and hence, the Mn ESR allows one to probe the spin fluctuations in the Cu02 planes (Kochelaev et al. 1994). Ceramic samples with Sr concentrations 0 < X < 0.3 were doped with up to 6% Mn. The samples were characterized by measuring the electrical resistivity and the dc susceptibility, as Mn doping suppresses superconductivity. The Mn-ESR experiments were performed at X-band frequencies for temperatures 4 < r <300 K. The powder spectrum revealed a pure Lorentzian profile. AH(T) exhibits a peculiar temperature dependence with decreasing temperatures, AH decreases, passes through a minimum and increases towards low temperatures. It is essentially the same... 

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