Melting point, and particle size

Softening or melting points and particle size distribution of suspended drug (suppositories). 

The PLM can be used in a reflection or a transmission mode. With either mode, light of various wavelengths from ultraviolet to infrared, polarized or unpolarized, is used to yield a wide variety of physical measurements. With just ordinary white light, a particle or any object detail down to about 0.5 p.m (500 nm) in diameter can be observed to detect shape, size, color, refractive index, melting point, and solubiUty in a group of solvents, all nondestmetively. Somewhat larger particles yield UV, visible, or IR absorption spectra. 

Any refractory material that does not decompose or vaporize can be used for melt spraying. Particles do not coalesce within the spray. The temperature of the particles and the extent to which they melt depend on the flame temperature, which can be controlled by the fueLoxidizer ratio or electrical input, gas flow rate, residence time of the particle in the heat zone, the particle-size distribution of the powders, and the melting point and thermal conductivity of the particle. Quenching rates are very high, and the time required for the molten particle to soHdify after impingement is typically to... 

Figure 10 Size-dependence of the melting point and diffusion coefficient of silica-encapsulated gold particles. The dotted curve is calculated by the equation of Buffat and Borel. The bulk melting temperature of An is indicated by the double arrow as (oo). The solid curve (right-hand side axis) is a calculated An self-diffusion coefficient. (From Ref. 146.)...

By the time the clinical program has entered phase 3, the sponsor should provide a full description of the physical, chemical, and biological characteristics of the drug substance. For example, most of the following should be evaluated and submitted solubility and partition coefficient, pKa, hygroscopicity, crystal properties/morphology, thermal evaluation, X-ray diffraction, particle size, melting point, and specific rotation stereochemical consideration. Proof... 

The authors have described some fundamental procedures to evaluate the solid-liquid phase relations of nano-sized particles in binary alloys from the calculation of the surface properties as well as the phase equilibira on the basis of thermodynamic databases, which are usually used for the calculation of phase diagrams of the bulk materials. In order to obtain quantitatively precise values of the melting points and liquidus temperatures in alloys, we should carry out further investigation as follows ... 

The important properties of aluminum oxide ceramics are their high temperature stability (melting point of AI2O3 2050°C), their good thermal conductivity, their high electrical resistivity and their high chemical resistance. Their mediocre thermal shock resistance is a disadvantage. All these properties are dependent upon the chemical purity and particle size distribution of the oxide powder and the density, structure and pore size di.stribution of the ceramic. 

Size affects the stmcture of nanopartides of materials such as CdS and CdSe, and also their properties such as the melting point and the electronic absorption spectra. In Figures 1.4 and 1.5, we show such size effects graphically. It should be noted that even metals show nonmetallic band gaps when the diameter of the nanocrystals is in the 1-2 nm range. Hg dusters show a nonmetallic band gap which shrinks with increase in cluster size. It appears that around 300 atoms are necessary to dose the gap. It is also noteworthy that metal partides of 1-2 nm diameter also exhibit unexpected catalytic activity, as exemplified by nanocatalysis by gold particles. 

Small supported particles (nanoparticles) differ from bulk, for example, in having lower melting points, and are thermodynamically unstable, that is, they have a tendency to oxidise the size of the most stable particle is defined by a compromise between stability as size decreases, and metal-support interactions.36,37... 

When the various solid forms exhibited by a drug substance have been found and characterized, important properties of each form should be determined and compared. Some properties, such as melting point and hygroscopicity, will have been obtained in the form characterization process. Investigations of other properties will require directed research efforts. We will limit our discussion to selected properties that reflect internal arrangement (thermodynamic stability, solubility, and dissolution rate), and will not cover bulk properties which may be greatly affected by both solid form and particle morphology (flowability, particle size, etc.). 

Magnesium oxide particles in the 2- to 7-p.m median particle size range deposit in the convection pass preferentially, while finer sized particles are not deposited and tend to get carried into the back end of the boiler. When an MgO of 2-p.m median particle size is fed into the fuel at treatment rates of 0.5-1.0 parts by weight Mg to 1.0 part V in the oil, the quantity of MgO deposited on the superheater tubes is 2-3 times that of the V and Na. This treatment rate results in a high Mg V ratio, which is needed to raise the ash-melting point and reduce tube deposits. 

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