Particle sizes control

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

The processing of diatomite is unique, since its particle-size control is effected by calcination treatments and air classification. 

Finch at (28), show three "stratifying polymerizers" rather than the design combinations described earlier by Ruffing et al (27). The reactors operate at inlet and outlet temperatures respectively of 120 to 135°C, 135 to 145°C, and 145 to 170 C. The first reactor effluent contains 18 to 20% polystyrene and a portion of this stream is recirculated back to the reactor inlet such that the inlet stream polystyrene concentration is as high as 13.5%. This recirculation is claimed to improve rubber phase particle size control and end use properties. 

In the polymer industry, post-reaction product treatment processes such as liquid-solid separation, drying, precipitation, particle size control, and polymer purification are very complex and costly. Future polymer plants should be designed such that process equipment can be easily and quickly converted to making new products at minimal cost and with... 

In this section we will discuss two studies that were performed to investigate factors which may effect particle size control (1) the type of support material and (2) the weight loading. 

Our Chemical Engineering colleagues had developed an elegant impinging jet crystallization which provided excellent particle size control for the finasteride process [13]. In the final pilot plant campaign just before the factory start-up, the crystallization suddenly started producing a different particle size distribution and lower recovery. The problem was traced to a new finasteride solvate which reduced the solubility in the crystallization solvent system. Fortunately, only relatively... 

Where there are existing pharmacopeial specifications for active ingredients in the Ph Eur or the pharmacopeia of a member state, these will be expected to apply. Other pharmacopeial specifications or in-house specifications may be used in other cases. The same is true for excipients where harmonized specifications are mentioned. Particular quality requirements related to a particular application are discussed, e.g., particle size control requirements. 

There are two EPARs for eyedrops. Specific issues considered for these include container composition and tamper evidence, the optimization of the formulation and manufacture, preservative and preservation issues, and justification for the use of nonterminal sterilization processes. Many of the points concerning active ingredients and excipients are similar to those discussed above. Changes in formulation during the development process (e.g., for carbomers or surfactants) are mentioned. Particle size controls for suspension products are discussed. 

Villegas, J.C., Garces, L.J., Gomez, S., Durand, J.P. and Suib, S.L. (2005) Particle size control of cryptomelane nanomaterials by use of H202 in acidic conditions. Chemistry of Materials, 17, 1910-1918. 

Bastress, E. K., Modification of the Burning Rates of Ammonium Perchlorate Solid Propellants by Particle Size Control, Ph.D. Thesis, Department of Aeronautical Engineering, Princeton University, Princeton, NJ (1961). 

When suspensions are formulated to provide a stable system, the particle size becomes critical. Flocculated suspensions also require careful particle size control either in the process of manufacturing or in the starting material. Equally important is the crystal habit — the outward appearance of an agglomeration of crystals. Crystal structure can be altered during the manufacturing process, particularly if the product is subject to temperature cycling, and this can alter the stability of suspensions. 

Particle size control can also be afforded by constraining the colloid to vesicles , membranes or zeolites An intriguing recent report achieves size limitation of semiconductor electrodes by preparing them by photolithography techniques... 

In any case, the ability to tune their luminescence characteristics by particle size control, combined with relatively high quantum yields, narrow fluorescence emission, very broad absorption spectra and photostability provide new solutions to many of the problems associated with traditional luminescence sensors and hold a strong promise for a completely new set of analytical applications with QDs.18... 

Particle size control of the API is often an important development strategy to consider, particularly when considering the impact of particle size on the quality attributes of the final chug product or the chug product manufacturing process. The physical properties of the API can affect the chug product quality in several ways ... 

Collins PC, Roginski RT. 2006. Feed-forward modeling approach to particle size control in milling operations. AIChE Annual Meeting, San Francisco, CA, November. 

Microemulsions Particle-size control High consumption of solvents... 

Flame pyrolysis Particle-size control Nonporous primary particles... 

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