Bulk solids properties

The engineering of novel deviees requires, in many eases, materials with finely seleeted and preestablished properties. In partieular, one of the most promising lines of synthetic materials research consists in the development of nanostructured systems (nanocomposites). This term describes materials with structures on typical length scale of 1-100 nm. Nanometric pieces of materials are in an intermediate position between the atom and the solid, displaying electronic, chemical and structural properties that are distinct from the bulk. The use of nanoparticles as a material component widens enormously the available attributes that can be realised in practice, which otherwise would be limited to bulk solid properties. 

The bulk properties of celluloses are generally influenced by adsorbed moisture. The effect of the change in bulk solid properties for microcrystalline cellulose has been demonstrated by a tableting operation in a very simplistic manner. Dry microcrystalline cellulose (%MC = 0.07) was compared with material with a moisture content above that associated with completion of the monolayer (%MC = 5.1). A thermodynamic picture of the character of water in these samples can be based on the adsorbate thermodynamic properties A// > 3.5kcal/mole (14.65 kJ/mole),... 

Johanson, J.R. (29 December 9%1) Bulk Solids Property Tester. U.S. Patent 4715212. 

The described problem in getting reliable X-values for design results from the fact that no simple, theoretical model exists which mbines known bulk solid properties like (pe, (pw or others with applicatiori in a satisfactory manner. As long as this relationship is not known the direct measurement in a special designed tester like the Lambdameter is the best solution. 

If no satisfactory and proven theoretical description exists between the measured bulk solid properties and the application it should be tried to measure the required parameter directly in an equivalent tester. 

The doming - no doming criterion was explained qualitatively with help of Fig. 7. For predicting the critical height h quantitatively the dependencies Oc = f(cTi) and 0 = f(oi) have to be known. Since doming is mainly a problem in the hopper section, only this part of the silo has to be considered, 0 and Oi can be calculated, a and 0 both increase linearly with distance from tire hopper apex and both are equal to zero at the apex. Therefore, the ratio of both, called flow factor ff = oi / cti, is a constant in the hopper, ff depends on the parameters (pe, cpx and 0, already used for the mass flow/funnel flow-decision in Fig. 5, and can be read from equivalent graphs in the literature [1]. The dependence o, = f(oi) is a bulk solid property, called flow function. It can be measured with help of shear testers (see chapter 5). 

Jansen H J F and Freeman A J 1984 Total-energy full-potential linearized augmented plane-wave method for bulk solids electronic and structural properties of tungsten Phys. Rev. B 30 561-9... 

Figure C2.17.13. A model calculation of the optical absorjDtion of gold nanocrystals. The fonnalism outlined in the text is used to calculate the absorjDtion cross section of bulk gold (solid curve) and of gold nanoparticles of 3 mn (long dashes), 2 mn (short dashes) and 1 mn (dots) radius. The bulk dielectric properties are obtained from a cubic spline fit to the data of [237]. The small blue shift and substantial broadening which result from the mean free path limitation are...

Equations la and lb are for a simple two-phase system such as the air-bulk solid interface. Real materials aren t so simple. They have natural oxides and surface roughness, and consist of deposited or grown multilayered structures in many cases. In these cases each layer and interface can be represented by a 2 x 2 matrix (for isotropic materials), and the overall reflection properties can be calculated by matrix multiplication. The resulting algebraic equations are too complex to invert, and a major consequence is that regression analysis must be used to determine the system s physical parameters. ... 

A useful property of liquids is their ability to dissolve gases, other liquids and solids. The solutions produced may be end-products, e.g. carbonated drinks, paints, disinfectants or the process itself may serve a useful function, e.g. pickling of metals, removal of pollutant gas from air by absorption (Chapter 17), leaching of a constituent from bulk solid. Clearly a solution s properties can differ significantly from the individual constituents. Solvents are covalent compounds in which molecules are much closer together than in a gas and the intermolecular forces are therefore relatively strong. When the molecules of a covalent solute are physically and chemically similar to those of a liquid solvent the intermolecular forces of each are the same and the solute and solvent will usually mix readily with each other. The quantity of solute in solvent is often expressed as a concentration, e.g. in grams/litre. 

These limitations, most urgently felt in solid state theory, have stimulated the search for alternative approaches to the many-body problem of an interacting electron system as found in solids, surfaces, interfaces, and molecular systems. Today, local density functional (LDF) theory (3-4) and its generalization to spin polarized systems (5-6) are known to provide accurate descriptions of the electronic and magnetic structures as well as other ground state properties such as bond distances and force constants in bulk solids and surfaces. 

In this brief review we illustrated on selected examples how combinatorial computational chemistry based on first principles quantum theory has made tremendous impact on the development of a variety of new materials including catalysts, semiconductors, ceramics, polymers, functional materials, etc. Since the advent of modem computing resources, first principles calculations were employed to clarify the properties of homogeneous catalysts, bulk solids and surfaces, molecular, cluster or periodic models of active sites. Via dynamic mutual interplay between theory and advanced applications both areas profit and develop towards industrial innovations. Thus combinatorial chemistry and modem technology are inevitably intercoimected in the new era opened by entering 21 century and new millennium. 

Test the bulk solid in a fluidization chamber to confirm both the Geldart (1973) classification and the material s air retention properties (i.e., by undertaking deaeration experiments). 

XPS has typically been regarded primarily as a surface characterization technique. Indeed, angle-resolved XPS studies can be very informative in revealing the surface structure of solids, as demonstrated for the oxidation of Hf(Sio.sAso.5)As. However, with proper sample preparation, the electronic structure of the bulk solid can be obtained. A useful adjunct to XPS is X-ray absorption spectroscopy, which probes the bulk of the solid. If trends in the XPS BEs parallel those in absorption energies, then we can be reasonably confident that they represent the intrinsic properties of the solid. Features in XANES spectra such as pre-edge and absorption edge intensities can also provide qualitative information about the occupation of electronic states. 

Evaluation of the morphology of a pharmaceutical solid is of extreme importance, since this property exerts a significant influence over the bulk powder properties of the material. In addition to providing insights into the micromeritic properties of the solid, microscopy can also be used to develop preliminary estimations of the particle-size distribution. A determination can be easily made regarding the relative crystallinity of the material, and it is often possible to deduce crystallographic information as well. Unknown particulates can often be identified solely on the basis of their microscopic characteristics, although it is useful to obtain confirmatory support for these conclusions with the aid of microscopically assisted techniques. 

In the present work, such a systematic approach to the physical characterization of pharmaceutical solids is outlined. Techniques available for the study of physical properties are classified as being associated with the molecular level (properties associated with individual molecules), the particulate level (properties pertaining to individual solid particles), and the bulk level (properties associated with an ensemble of particulates). Acquisition of this range of physical information yields a total profile of the pharmaceutical solid in question, whether it is an active drug, an excipient, or a blend of these. The development of a total profile is a requirement for successful manufacture of any solid dosage form. 

Here, we discuss in some detail the DFT implementation in our computer program, since only in the last few years DFT is becoming more familiar to the chemists community, as opposite to the physicists community, where it was used routinely for the last thirty years for obtaining structural and electronic properties of bulk solids and surfaces [19],... 

The scientific interest in solid surfaces whether in the context of heterogeneous catalysis, solid state electronics, or corrosion is a direct consequence of the fact that their properties are unique with relation to the corresponding properties of the bulk solid. This is not difficult to appreciate since at the surface there is a breakdown of translational symmetry, extreme gradients of chemical composition are feasible, and perturbation of both bulk structure and charge are possible. There are, therefore, formidable problems to overcome if we are to arrive at a situation where surface structure, electronic... 

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