Micronized powders

Some mechanical air classifiers are designed so that the fine product must pass radially inward through rotor blades instead of spirally moving across them as with whizzer blades. Examples are the Mikron separator Hosokawa Micron Powder Systems Div.), Sturtevant Side Draft separator, and the Majac classifier shown attached to the Majac jet mill (Fig. 20-55). 

There are several mechanical air classifiers designed to operate in the superfine 10- to 90- Im range. Two of these are the Mikroplex spiral air classifier MP T Hosokawa Micron Powder Systems Div.) and the classifier which is an intregal part of the Hurricane pulverizer-classifier ABB Raymond Div, Combustion Engineering Inc.) described under Hammer Mills. Others are the Majac classifier Hosokawa Micron Powder Systems Div.), the Sturtevant Superfine Air Separator, and the Bradley RMC classifier. These also use a vaned rotor, but operate at higher speed with higher power input and lower throughput. 

FIG. 20-46 Mikro-Piilverizer hammer mill. (Hosokawa Micron Powder Systems Div.)... 

The Majac jet pulverizer (Ho.sokawa Micron Powder Sy.stems Div.) is an opposed-jet type with a mechanical classifier (Fig. 20-55). Fineness is controlled primarily by the classifier speed and the amount of fan air dehvered to the classifier, but other effects can be achieved by variation of nozzle pressure, distance between the muzzles of the gun barrels, and position of the classifier disk. These pulverizers are available in 30 sizes, operated on quantities of compressed air ranging from approximately 0.6 to 13.0 mVmin (20 to 4500 ftV min). In most apphcations, the economics of the use of this type of jet pulverizer becomes attractive in the range of 98 percent through 200 mesh or finer. 

Fluidized-bed opposed-jet mills Hosokawa Micron Powder Systems Div.) differ from the Majac mill in that powder is not fed into the jets, but the jets impinge into a chamber mich contains suspended powder. The powder is entrained into the jets. This ehminates wear on the nozzles, and reduces contamination. Otherwise, construction and appheations are similar to the Majac mill. The fluidized-bed level is maintained a few inches above the jets. The Fluidized-bed mill is available in 13 sizes with air volumes ranging from. 50 to 11,000 mVh. One application is for toner grinding. 

The importance of particle size is directly proportional to the sub-sample size recommended by the analytical method. The larger the sub-sample size the larger the acceptable particle size. For sub-sample sizes of ig or greater a soil sieved through a imm screen is generally acceptable. Therefore if the sample is relatively coarse, e.g up to 2mm particles and the matrix CRM is an uniform sub-micron powder, it may be necessary to use a much larger sample from the material under test than for the CRM. 

Based on these data, particle-liquid Reynolds numbers were calculated to range from Re = 25 (50 rpm) to Re = 90 (150 rpm) for coarse grade particles with a median diameter of 236 pm. In contrast, Reynolds numbers for a batch of micronized powder of the same chemical entity with a median diameter of 3 pm were calculated to be significantly lower (Re < 1), indicating less sensitivity towards convective hydrodynamics [(10), Chapter 12.3.8]. Based on the aforementioned considerations for spheres, bulk Reynolds numbers of about Re > 50 appear to be sufficient to produce the laminar-turbulent transition around a rough drug particle of coarse grade dimensions. 

Micronized powders are added at the 5-15% level in new adapted formulations to replace mineral fillers. The density is slightly inferior and the performances are in a similar range. 

Drugs can be sprayed in aerosol form onto mucosal surfaces of body cavities accessible from the outside (e.g., the respiratory tract [p. 14]). An aerosol is a dispersion of liquid or solid particles in a gas, such as air. An aerosol results when a drug solution or micronized powder is reduced to a spray on being driven through the nozzle of a pressurized container. 

The micronized powder gives much higher concentration in blood as compared to ordinary powder and tablets. 

Ion Engines. Saunders (Ref 6a) reports successful usage of porous W platelets for ionizing the N2 working medium in exptl ion-powered rocket engines. Thin, porous W platelets were developed by sintering compacted 1-micron powder at 2750°F for 20 hrs in a H2 atm... 

Acetyl, phthalyl 6 CAP (Eastman Comp.) Aquateric (Lehmann Voss) Organic solution Aqueous dispersion (pseudolatices) Sensitive to hydrolysis, 5-30% plasticizer required Micronized powder (0.05-3 pm)... 

Figure 8.1 Pin mill internals. (Photo courtesy of Hosokawa Micron Powder Systems.)...

GENERAL ISSUES IN THE PHYSICAL CHARACTERIZATION OF MICRONIZED POWDERS USED IN LOW-DOSE FORMULATIONS... 

So, our investigations allow us to establish the correlation between physico-chemical properties of the crystallization media (capillary properties of the diamond-metal melt interface, carbon supersaturation in the melt with respect to diamond) and adsorption-structure and energy proreties of the produced diamond powders. Our findings permit us to extend scientific and technological potentialities for production of diamond grinding and micron powders having unique properties. 

Inhalation in the form of an aerosol, a gas, or a mist permits drugs to be applied to the bronchial mucosa and, to a lesser extent, to the alveolar membranes. This route is chosen for drugs intended to affect bronchial smooth muscle or the consistency of bronchial mucus. Furthermore, gaseous or volatile agents can be administered by inhalation with the goal of alveolar absorption and systemic effects (e.g., inhalational anesthetics, p.216). Aerosols are formed when a drug solution or micronized powder is converted into a mist or dust, respectively. 

Laboratory tests confirmed that in the absence of effective corrosion inhibitors molybdenum disulphide could cause corrosion in humid environments. Kay ° showed in tests with different steels that corrosion was accelerated in the presence of loose molybdenum disulphide powder, especially ball-milled or micronated powder. Her test conditions were realistic, namely 20 C and 90% relative humidity for six days, but the use of loose powder was not representative of practical use, and it subsequently became clear that burnished films were less active in promoting corrosion. Calhoun et al also showed that molybdenum disulphide in a bonded film actively promoted corrosion, although their test conditions were severe, consisting of salt fog and salt spray tests. They found that corrosion was more severe when graphite was present, but that molybdenum disulphide also clearly caused corrosion. 

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