Method powder

Although powder methods dominate ceramic forming, ceramics can also be formed by glass-ceramic and gelation methods. 

Gelation methods are analogous to the glass-crystallization method in that processing starts with a metastable system. With this method, soluble 

One of the major attributes of the gelation method is that multielement, metastable systems (intimately mixed at the molecular level) can be produced at low temperatures. Phase partitioning from these metastable systems can be used to control microstructures by heat treatment at higher temperatures. 

Gelation methods are generally limited to the processing of thin films, fibres and powders. 

Powder methods are used to fabricate most advanced ceramics. They involve powder manufacture, preparation of the powder for consolidation, consolidation of the powder into a shape and densification (elimination of 

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As a rule, in practice, the surface defects are revealed by the magnetic-powder and capillary methods. However, in the case of nonmagnetic materials the magnetic-powder methods are not applicable and the capillary ones do not detect the subsurface defects or defects filled with the lubricant after the grinding, wire-drawing and so on. 

Ceramics High E, CTy Low kjj Stiff (E = 200 GPo) Very high yield, hardness a > 3 GPo) High MP (Tm = 2000°C) Corrosion resistant Moderate density Very low toughness (kj = 2 MPa m ) T-shock (AT = 200°C) Formobility —> powder methods... 

At and near room temperature, metals have well-defined, almost constant, moduli and yield strengths (in contrast to polymers, which do not). And most metallic alloys have a ductility of 20% or better. Certain high-strength alloys (spring steel, for instance) and components made by powder methods, have less - as little as 2%. But even this is enough to ensure that an unnotched component yields before it fractures, and that fracture, when it occurs, is of a tough, ductile, type. But - partly because of their ductility - metals are prey to cyclic fatigue and, of all the classes of materials, they are the least resistant to corrosion and oxidation. 

Stearic acid (5 wt%) was compounded with a linear polymer prepared from 3,9-bis(ethylidene-2,4,8,10-tetraoxaspiro[5,5]undecane) and a 30 70 mole ratio of 1,6-hexanediol and trans-cyclohexanedi-methanol by thermal, solvent, or powder methods (Table 4). The thermal method (flux mixer and roller mill) resulted in good stearic... 

FIGURE 27.2 Debye-Scherrer powder method. Cones of reflected and transmitted radiation are produced. In this example the pattern is recorded with photographic film. Alternatively,... 

We recognize that there are applications in two- and three-dimensional waveguides (12,13) which do not have the same criteria of phase-matching as in simple crystals or that one may just as well be interested in screening these materials for the related electrooptic performance by the simple SHG powder method. (It has been shown for several organic materials that although the electro-optic and SHG x tensors are in principle unequal, due to dispersion and due to the possible contribution of atomic and molecular distortions... 

Jenkins, R. (2002). X-ray powder methods. In McGraw-Hill Encyclopedia of Science and Technology 19, New York, McGraw-Hill, pp. 668-673. 

Six comments are appropriate at this point. Firstly, it is the experience of the reviewer that chemically-similar compounds with very similar infrared and Raman spectra in factor-group split regions are isomorphous. This method is probably at least as reliable as X-ray powder methods when there is a significant change in scattering factors between the two compounds studied (e.g. bromo-derivatives of... 

As with neutron powder methods, both monochromatic and time-of-flight (Laue) techniques have been used for single-crystal neutron studies. Such studies are much less numerous, however, as a result of the difficulty of compressing suitably sized (>1 mm ) single-crystal sample to the required pressure while maintaining the crystal quality. The piston cylinder cell design of Me Whan and others [128] has been used at the ILL reactor source for a number of neutron structural studies to... 

The difficulty in the powder method lies in deciding which planes are responsible for each reflection this is known as indexing the reflections (i.e., assigning the correct hkl index to each reflection). Although this is often possible for simple compounds in high... 

Originally, the cause of this phenomenon was unknown. In all the countries producing smokeless powder methods for improving the stability of the powder were sought. Similar research was also initiated by Vieille but in spite of systematic... 

The thin-section methods of the petrologist may be used for artificial specimens which are in the form of large aggregates—specimens of such materials as refractories, bricks, and boiler scales. Instead of powdering them and using immersion methods, it is possible to grind thin sections and examine them. When it is simply a question of distinguishing between a few possible constituents of known characteristics, this is a useful method. But in unfamiliar systems the powder method is likely to be more useful for identification purposes the principal function of the thin-section method in such circumstances is to provide information on the distribution, orientation, or size of the crystals of the different constituents. 

Degree of pseudosymmetry is given in parentheses, (a) Deviation from maximum symmetry readily observable (even by powder methods), (b) Deviation not so pronounced but in any case detectable by conventional single-crystal techniques, (c) Deviation only observable when suitable samples and special techniques are used, (d) Extreme cases of suspected pseudosymmetry based on slight indications only. 

The random orientation of the crystalline order in typical Shirakawa polyacetylene means that diffraction studies are limited to powder methods. For such studies, and many others, it would be very useful to have much more oriented polymers and many attempts have been made to orient polyacetylene, either by mechanical treatment of the polymer or by appropriate modifications to the polymerization reaction. These have been reviewed earlier. 

We thank Mr. I. Ando for SHG measurement with the powder method and Dr. T. Hori and Dr. M. Furukawa in Rigaku Corp. for X-ray crystallography. 

Eu-Cu-Sb. EuCuSb was found to crystallize with the ZrBeSi type structure with lattice parameters of a = 0.4512, c = 0.8542 (Tomuschat and Schuster, 1981 X-ray photographic powder method). 

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