Solid subdivision

Vanadium pentoxide, vanadium(V) oxide, V2O5, is the most important compound in this oxidation state. It is a coloured solid (colour due to charge transfer, p. 60), the colour varying somewhat (red -> brown) with the state of subdivision it is formed when vanadium (or some of its compounds) is completely oxidised, and also by heating ammonium vanadate)V) ... 

External Conditions The principal external variables involved in any drying study are temperature, humidity, air flow, state of subdivision of the solid, agitation of the solid, method of supporting the solid, and contact between hot surfaces and wet solid. Alf these variables will not necessarily occur in one problem. 

In terms of the two-phase system which comprises dispersions of solids in liquids, the minimum energy requirement is met if the total interfacial energy of the system has been minimized. If this requirement has been met, chemically, the fine state of subdivision is the most stable state, and the dispersion will thus avoid changing physically with time, except for the tendency to settle manifest by all dispersions whose phases have different densities. A suspension can be stable and yet undergo sedimentation, if a true equilibrium exists at the solid-liquid interface. If sedimentation were to be cited as evidence of instability, no dispersion would fit the requirements except by accident—e.g., if densities of the phases were identical, or if the dispersed particles were sufficiently small to be buoyed up by Brownian movement. 

State of subdivision. The smaller the pieces of a solid reactant—the smaller the state of subdivision—the faster the reaction. Wood shavings burn faster than solid wood, for example, because they have more surface area in contact with the oxygen with which they are combining (for a given mass of wood). In a sense, this is also a corollary of factor 4. 

As the state of subdivision of a solid increases, the surface area of the solid available to react becomes greater. Because reactions take place at the surface of a solid, the rate of reaction increases. This explains why solid chemicals are often supplied in powder form rather than in large lumps. 

A major subdivision of processes is possible on the basis of the principal phase in which the reactions take place. This clearly cannot be a clear-cut division since many processes have a number of steps which involve, in turn, the gas phase, the liquid or solution phase, and the solid phase. By and large, however, the principal characteristic step of each process is associated with either the gas phase or solution, and on this basis a significant subdivision can be made. 

Most chemical reactions occur in solutions. This is because a substance dissolved in a solvent, the solute, will be in its smallest state of subdivision, existing as individual molecules or ions that will increase their ability to react with other molecules or ions. Most chemistry in the body takes place in solution in the absence of the solution, much of the chemistry of life would not take place. You are familiar with solutions that are liquid, like iced tea and sea water, but solutions can also be gases, like the atmosphere, or solids, like a gold ring, which is a mixture of silver dissolved in gold. 

Inflammability or Flammability (latter is preferred in modern usage). The ease with which a material (gas, liquid or solid) will ignite, either spontaneously (pyrophoric), from exposure to a high-temperature environment (autoignition), or to a spark or open flame. It also involves the rate of spreading of a flame once it has started. The more readily ignition occurs, the more flammable the material less easily ignited materials are said to be combustible, but the line of demarcation is often indefinite, and depends on the state of subdivision of the material as well as on its chemical nature... 

A large number of oxides which are commonly solid insulators at room temperature (e.g., A1203) yield highly conducting (specific conductance > 10 ohm-1 cm-1) melts on fusion. Some of these melts are undoubtedly ionic conductors whereas others are electronic conductors. It is, however, not always possible to differentiate between these two general types since both mechanisms may be operative to comparable extents at a particular temperature. Relatively few experiments have been reported in which reliable estimates of the transport numbers of either ions or electrons could be made. The subdivision in this section into the two general types of conductors is thus not to be interpreted as rigid. 

Levigating agents substances that aid in reducing another substance to an extremely fine state of subdivision after that other substance has been made into a paste with some suitable liquid in which it is insoluble also, nonsolid vehicles used to disperse a solid substance to a paste. 

In the case of two-ion systems, the coupled species is placed into the grouping that corresponds to that ion which has been sensitized. That is, in a system in which energy pumped into, say, gadolinium is fluoresced by, say, terbium, the system is placed into the terbium section. A further subdivision into crystalline solid, glass, and liquid hosts is also made. 

Slurry Pipelines. Finely divided solids can be transported in pipelines as slurries, using water or another stable liquid as the suspending medium. Flow characteristics of slurries in pipelines depend on the state of subdivision of the solids and their distribution within the fluid system. 

If the colouring matter is insoluble in caustic soda, its solubility in boiling 95% alcohol is tested. For further subdivision, use is made, for colouring matters soluble in alcohol, of the test with zinc dust and acetic add, and for those insoluble in alcohol, of the tests with stannous chloride and with sodium hydrosulphite. The latter test is carried out by heating a little of the substance for 5-10 minutes at about 8o° with about an equal amount of solid sodium hydrosulphite and a little 1% caustic soda solution the substance is dissolved and reduced to the leuco-derivative, the colour of this being observed. 

An important parameter of the API to investigate prior to excipient studies is the ability of the compound to gain and/or lose water when exposed to environments having variable humidity because it is known that water will equilibrate and redistribute in solid-state mixtures. Additionally, solid-state photochemical assessment should be considered as it can be dramatically different than solution-state photoreactivity (8). These brief studies will provide early warnings on preparation, storage, and subdivision precautions. 

Colloidal dispersions can be formed either by nucleation with subsequent growth or by subdivision processes [12,13,16,25,152,426], The nucleation process requires a phase change, such as condensation of vapour to yield liquid or solid, or precipitation from solution. Tadros reviews nucleation/condensation processes and their control [236], Some mechanisms of such colloid formation are listed in Table 7.1. The subdivision process refers to the comminution of particles, droplets, or bubbles into smaller sizes. This process requires the application of shear. Some of the kinds of devices used are listed in Table 7.2 [228]. 

Suspensions can be formed either by nudeation or by subdivision and dispersion. The nudeation process requires a phase change, such as condensation of vapour to yield solid, or precipitation of a salt from a supersaturated solution. In the latter case a supersaturated solution must be formed. The supersaturation condition is then alleviated by condensation on nudei (which need not be composed of the same material) already present, or else by formation of nuclei with subsequent condensation. The nudei eventually grow to microscopic, or macroscopic, size. Additional details of this process are discussed elsewhere [49,320],... 

A bioreactor is a vessel in which biochemical transformation of reactants occurs by the action of biological agents such as organisms or in vitro cellular components such as enzymes. This type of reactor is widely used in food and fermentation industries, in waste treatment, and in many biomedical facilities. There are two broad categories of bioreactors fermentation and enzyme (cell-free) reactors. Depending on the process requirements (aerobic, anaerobic, solid state, immobilized), numerous subdivisions of this classification are possible (Moo-Young, 1986). 

Any of six factors can affect the rate (1) the nature of the reactants, (2) the temperature, (3) the presence of a catalyst, (4) the concentration of reactants in solution, (5) the pressure of gaseous reactants, and (6) the state of subdivision of solid reactants. For a reaction to occur, the atoms, molecules, or ions must come into contact with one another with enough energy to rearrange chemical bonds in some way. Increased concentration, gas pressure, or surface area of a solid tends to get the particles to collide more frequently, and increased temperature tends to get them to collide more frequently and with greater energy to accomplish more effective collisions. Catalysts work in very many different ways. 

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