Powder mixtures direct method

The majority of formulations that are filled into capsules are dry powder mixtures. The methods of measuring the dose can be divided up into two groups dependent and independent. The dependent machines use the capsule body directly to measure the dose of powder, whereas the independent machines use a separate device. The literature available on the mechanics of capsule filling is limited when compared to that available for tabletting. Part of the reason for this is that tablets, unlike capsules, are used in a wide range of industries outside the health-care sector, and thus there have been many more workers in the field. 

In a variant of the second method described earlier the premixed metallic powders (or pulverized ingots) are milled under hydrogen atmosphere to directly form an intermetallic hydride. It can be also viewed as hydrogen alloying of metal powders and powder mixtures in hydrogen alloying mills. This method is called a reactive mechanical alloying (RMA) or mechanochemical synthesis (MCS). 

Direct compression is a simpler alternative tablet manufacturing method. With direct compression, tablets are compressed directly from a powder mixture of an API and appropriate excipients. Like granulation methods, this approach is also based on the required flow, compressibility, and compactibility of a formulation. Direct compression offers both time and economic advantages by eliminating intermediate granulating and drying steps. 

Starting from fine boron and carbon powders, the direct synthesis of stoichiometric boron carbide is possible -, either under vacuum at 2073K in an electric furnace, or at 2273 K by hot pressing under Ar. This method is inefficient economically and finds no practical application. The compositions in the phase homogeneity range B10.4C-B4C can be obtained by hot pressing mixtures of B C with boron . The diffusion diagram between B and C is established. ... 

Wendlandt (45) used a microscopic method for the determination of the reflectance of the sample. The apparatus, as shown in Figure 9.28, consisted of a low-power (100 x, generally) reflection-type microscope, A, which is illuminated by means of a monochromator, B. The reflected radiation is detected by a photomultiplier tube, C, and amplifier, D, and recorded on either an X-Y recorder, E, or a strip-chart recorder, F. In order to heat the sample to 250°C, a Mettler Model FP-2 hot stage, G, is employed. Either isothermal ( 1CC) or dynamic sample temperatures may be attained by this device. The sample is moved through the illuminated optical field by means of the reversible motor, H. The motor is reversed at preset intervals by a relay circuit and timer, J. Thus, it is possible to scan the reflectance from the sample, which may consist of a single crystal or a powdered mixture. Powdered samples may be placed directly on the heated microscope slide or... 

This process is very. similar to the conventional spray drying. However, the slaked lime slurry is directly fed into the ductwork. A moderate degree of desulfurization is possible by using this method. A dry powdered mixture of calcium compounds is produced as the final product. 

The only way to apply chemically bonded thin perfluorosulfonic acid layer onto the surface of an inert support is to graft perfluorinated functional monomers onto perfluorinated polymers. Some features of radiation-induced graft copolymerization of PFAVESF onto fluoropolymers were investigated. The studies showed that neither irradiation of a fluoropolymer-PFAVESF mixture (direct grafting) or interaction of PFAVESF with previously irradiated fluoropolymers (preirradiation grafting) yielded the grafted copolymers. It was assumed that this is connected with the low activity of PFAVE in radical polymerization. A special method has been developed for the synthesis of grafted copolymer. Previously irradiated fluoropolymer powders were used to prevent waste of PFAVESF. 

As an addition to the general method of preparation of a powder mixture, for capsules some specific directions apply. Capsules are filled by volume, therefore, the powder mixture should be prepared to obtain a specific volume. The correct volume depends on the capsule size and the number of capsules to be filled (Table 4.3). 

Tablets are prepared by compression of uniform volumes of particles (powder mixtures) or granules. The choice of excipients depends on the preparation method wet granulation or direct compression.

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