Powder characterization bulk composition

Characterization. Ceramic bodies are characterized by density, mass, and physical dimensions. Other common techniques employed in characterizing include x-ray diffraction (XRD) and electron or petrographic microscopy to determine crystal species, stmcture, and size (100). Microscopy (qv) can be used to determine chemical constitution, crystal morphology, and pore size and morphology as well. Mercury porosknetry and gas adsorption are used to characterize pore size, pore size distribution, and surface area (100). A variety of techniques can be employed to characterize bulk chemical composition and the physical characteristics of a powder (100,101). 

Basic element of a sorber is metal hydride. Beside physicochemical characteristics, it has technical characteristics (fine or coarse powder, compound or composite). Freely filled powder has the certain bulk density and is characterized by porosity in the limits of e - 0.259 - 0.476 [1],... 

In essence, the test battery should include XRPD to characterize crystallinity of excipients, moisture analysis to confirm crystallinity and hydration state of excipients, bulk density to ensure reproducibility in the blending process, and particle size distribution to ensure consistent mixing and compaction of powder blends. Often three-point PSD limits are needed for excipients. Also, morphic forms of excipients should be clearly specified and controlled as changes may impact powder flow and compactibility of blends. XRPD, DSC, SEM, and FTIR spectroscopy techniques may often be applied to characterize and control polymorphic and hydrate composition critical to the function of the excipients. Additionally, moisture sorption studies, Raman mapping, surface area analysis, particle size analysis, and KF analysis may show whether excipients possess the desired polymorphic state and whether significant amounts of amorphous components are present. Together, these studies will ensure lotto-lot consistency in the physical properties that assure flow, compaction, minimal segregation, and compunction ability of excipients used in low-dose formulations. 

Not only is there a need for the characterization of raw bulk materials but also the requirement for process controled industrial production introduced new demands. This was particularly the case in the metals industry, where production of steel became dependent on the speed with which the composition of the molten steel during converter processes could be controlled. After World War 11 this task was efficiently dealt with by atomic spectrometry, where the development and knowledge gained about suitable electrical discharges for this task fostered the growth of atomic spectrometry. Indeed, arcs and sparks were soon shown to be of use for analyte ablation and excitation of solid materials. The arc thus became a standard tool for the semi-quantitative analysis of powdered samples whereas spark emission spectrometry became a decisive technique for the direct analysis of metal samples. Other reduced pressure discharges, as known from atomic physics, had been shown to be powerful radiation sources and the same developments could be observed as reliable laser sources become available. Both were found to offer special advantages particularly for materials characterization. 

The dispersion of components in the titania/silicas were characterized by X-ray powder diffraction. The results are shown in Figure 3. All precipitated titania/silicas showed patterns characteristic of anatase titania. However, sol-gel titania/silicas with Ti/Si ratios of less than 1 did not show clear diffraction peaks, indicative for their amorphous nature in spite of almost same bulk Si/Ti compositions. These results indicate that the crystallinity of the precipitated... 

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. 

Ceramic characterization 30-32 range from a process as simple as determining the bulk density of a green powder compact from its mass and dimensions, to a process as complicated as identifying the composition and structure of a submicron size crystal in a dense ceramic matrix using analytical electron microscopy (AEM). Some of the important characteristics evaluated during ceramic consolidation are outlined in Figure 5.2. 

As in a green ceramic body, important chemical characteristics of a powder compact during and after sintering include bulk chemical composition, chemical homogeneity, and the compositions and concentrations of impurities or undesired phases. Composition can be characterized by ICP, XRD, and XRF. ... 

Numerous research problems of practical and industrial importance and of theoretical and academic interest await solution in the preparation, characterization and application of ordered mixtures and composition-stable mixtures. Scant attention is paid here to these subjects because they are regarded as being outside the scope of bulk-solids mixing in the conventional sense, which usually is concerned with mixing and blending of free-flowing particles and powder in relatively large quantities. 

For powdered samples, mass-spectrometric (MS) analysis of the gas phase composition during isotope exchange is used for the estimation of parameters characterizing both the smface reaction and oxygen diffusion in the bulk. 

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