Orthorhombic particle

The effective thermal conductivity of the packed bed expressed in Eq. (126) includes two terms, the conductivity term with no gas flow, k°, and the convective term. The factor 0.1 was recommended by Yagi and Kunii (1957) for spherical particles. The conductivity term with no gas flow can be calculated below, following that suggested by Swift (1966) for orthorhombic particle packing with a voidage of 0.395. 

Texture. All limestones are crystalline, but there is tremendous variance in the size, uniformity, and arrangement of their crystal lattices. The crystals of the minerals calcite, magnesite, and dolomite are rhombohedral those of aragonite are orthorhombic. The crystals of chalk and of most quick and hydrated limes are so minute that these products appear amorphous, but high powered microscopy proves them to be cryptocrystalline. Hydrated lime is invariably a white, fluffy powder of micrometer and submicrometer particle size. Commercial quicklime is used in lump, pebble, ground, and pulverized forms. 

A special group of particles that are often produced are the icosahedral (I5) and decahedral (D5) structures shown in Fig. 9. These particles have a fivefold symetry axis which is forbidden for infinite crystals. Yang (1 0) has described these particles using a non-Fcc model. The particles are composed by five (D5) and twenty (I5) tetrahedral units in twin relationship. However the units have a non-Fcc structure. The decahedral is composed by body-centered orthorhombic units and the icosahedral by rhombohedral... 

Fig. 11.21 shows the results of TG and DTA measurements on mixtures of AP particles and catalysts. The endothermic peak observed at 513 K is caused by the crystal structure transformation of AP from orthorhombic to cubic. A two-stage exothermic decomposition occurs in the range 573-720 K. The decomposition of the AP is seen to be drastically accelerated by the addition of catocene. The exothermic peak accompanied by mass loss occurs before the AP crystal transformation. Although the AP is sensitized by the addition of carborane, no effect is seen on the AP decomposition. The results indicate that carborane acts as a fuel component in the gas phase but does not catalyze the decomposition of AP. Thus, the critical friction energy is lowered due to the increased reaction rate in the gas phase. The results imply that the initiation of ignition by friction is caused by the ignition of the gaseous products of the AP pyrolants.PI... 

Precipitation conditions determine crystal structure. Lemon chrome yellows are precipitated hot with excess lead to form the monclinic crystal. Primrose yellow is preciptated at a lower temperature to form the orthorhombic crystal. Chrome oranges are precipitated under alkaline conditions. The higher the alkalinity, the larger the particle. The precipitation of molybdate orange is complicated by the polymorphic nature of two of the components of the solid solution precipitate lead chromate and lead sulfate. As with primrose yellow, the crystal is stabilized after precipitation to prevent conversion. 

A comparison of Y123 powders produced by SHS (SHS-Jl and SHS-J2) with those produced by furnace synthesis is shown in Table X. The oxygen content, transition temperature, orthorhombic phase Y123 content, basic impurities, and mean particle sizes of SHS powders compare favorably with those produced by furnace synthesis. However, the time of Y,23 production for a conventional fur-... 

The retarding of traTisformaJtion of one crystalline form into another for instance, the retardation of transformation of clino-riiombic sulphur into orthorhombic sulphiur at ordinary temperature, retardation stopped by contact with a piece of rhombic sulphur the retardation of transformation of orthorhombic sulphur into clinorhombic sulphur, at temperatures above 97. 2 retardation ceasing by contact with a clinorhombic particle. 

Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO)6 in diphenylmethane (DPhM) in the presence of an Ar (80%) and O2 (20%) gaseous mixture at 90 °C [137]. Heating this amorphous powder at 550 °C under Ar yields snowflake-like dendritic particles consisting of a mixture of monodinic and orthorhombic WO2 crystals. Annealing... 

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