Sublimation definition

In both these continuous processes medium to high energy disperse dyes should be used to avoid the risk of dye subliming to contaminate the atmosphere of the fixation unit and then staining the print by vapor-phase dyeing, or to produce a loss of definition of the printed mark due to diffusion from the appHed thickened paste. 

The atoms of any metal adhere together to form a crystal because of the forces of attraction between them to remove an atom from the surface requires a definite amount of work, characteristic of the metal this is called the sublimation energy. ... 

Many solid substances (camphor, iodine, naphthalene, etc.), are known which are appreciably volatile at ordinary temperatures. Others, such as the metals, are apparently quite fixed, but they probably possess a definite, although very small vapour-pressure, even at ordinary temperatures. Thus, if magnesium is heated to 550° for a few hours in a magnesia boat enclosed in a vacuous tube it sublimes in beautiful crystals on the cool part of the tube. The vaporisation of a solid without previous fusion is called sublimation the vapour-pressure (like the vapour-pressure of a liquid), is definite for each temperature, is independent of i the volume of the vapour space, and increases with rise of temperature. 

The thermal decomposition of a solid, which necessarily (on the above definition) incorporates a chemical step, is sometimes associated with the physical transformations to which passing reference was made above melting, sublimation, and recrystallization. Aspects of the relationships between physical transitions and decomposition reactions of solids are discussed in a book by Budnikov and Ginstling [1]. Since, in general, phase changes exert significant influence upon concurrent or subsequent chemical processes, it is appropriate to preface the main survey of the latter phenomena with a brief account of those features of melting, sublimation, and recrystallization which are relevant to the consideration of thermal decomposition reactions. 

This definition of the process shows that it differs essentially from sublimation and distillation. A chemical-transport reaction is necessarily reversible a concentration gradient is induced, e.g., by means of a tem-... 

We define the cohesive energy Ecoh (Johansson, Skriver ) as the difference between the energy of an assembly of free atoms in their ground state (see Table 1 of Chap. A) and the energy of the same assembly in the condensed phase (the solid at 0 °K), (this definition yields a positive number for Ecoii). It coincides with the enthalpy of sublimation AHj (see Chap. A) (which is usually extrapolated at room temperature). 

Unlike the carbonates, ammonium carbamate does not fuse when heated, but, as was observed by J. Davy, it is converted into a gas at 60°. F. E. C. Scheffer was unable to establish a definite relation between the press, and the sublimation temp, for ammonium carbamate since the results were very irregular and dependent upon a variety of circumstances—rate of rise of temp., etc. The hypothesis suggested by W. D. Bancroft, and by C. van Rossem is that the observed results are produced by the superposition of two phenomena dependent on (i) the speed of vaporization, and (ii) the speed of dissociation. J. H. van t Hoff half filled a... 

The alkaline earths, particularly the lighter ones, have more definite water coordination, and a probable coordination number of 4. The heats of sublimation (Table I) of the magnesium salts are about 50 kcal/mole or higher, those for the calcium halides are over 60 kcal/mole, and for the heavier alkaline earths they run over 70 kcal/mole. For the beryllium halides other than the fluoride, however, the values are 30 to 33 kcal/mole. In... 

Sublimation. Accdu to definition ziven in Perry (Ref 13, p660), it covers the physical changes encountered by a substance in passing from a solid phase to a gas and back to a solid phase. It is characterized by the absence of the liquid phase and is used for purification of volatile substances like iodine, camphor, etc. Detailed description of the process is given in Refs 12, 13, 15 18). 

This material is sufficiently pure for most purposes. If a purer product is desired, the crude material is dissolved in 300 ml. of dimethylformamide, 10 g. of activated alumina (48-100 mesh) is added, and the mixture is filtered. The filtrate is heated to 80-90° on a steam bath, then 1 1. of boiling water is added immediately (Note 2). The resultant mixture is cooled in an ice bath, and the light buff crystals of 2,5-diamino-3,4-dicyanothio-phene that separate are collected on a Buchner funnel and thoroughly washed with 500 ml. of acetone weight 26-28 g. (79-85%). The product has no definite melting point but sublimes with some decomposition when heated above 250°. 

A tellurium di-iodide has been described by Berzelius as obtained when tellurium and iodine are sublimed together, but its existence as a definite compound appears doubtful.2 Damiens 3 has shown that the so-called tellurium di-iodide is a mixture of the tetra-iodide and a solid solution of tellurium with the tetra-iodide. 

A triple point is a point where three phase boundaries meet. For water, it occurs at 4.6 Torr and 0.01°C (see Fig. 8.5). At the triple point, all three phases (ice, liquid, and vapor) coexist in dynamic equilibrium. Under these conditions, water molecules leave ice to become liquid and return to form ice at the same rate liquid vaporizes and vapor condenses at the same rate and ice sublimes and vapor condenses directly to ice again at the same rate. The location of the triple point of a substance is a fixed property of that substance and cannot be changed by changing the conditions. The triple point of water is used to define the size of the kelvin by definition, there are exactly 273.16 kelvins between absolute zero and the triple point of water. The normal freezing point of water is found to lie 0.01 K below the triple point, so 0°C corresponds to 273.15 K. 

---