Heat of volatilisation

The heats of volatilisation of polymers have been determined. Values obtained for polymethyl methacrylate (PMMA) agreed well with calculated values [34]. Chemically crosslinked and oriented LDPE have been investigated using differential photocalorimetry and DSC [35, 36]. 

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The heat absorbed when a mol of the solvent is evaporated at a constant temperature T from a volume of solution so large that no perceptible change of concentration occurs during the process, is called the heat of volatilisation A (x, T). From (7) ... 

The heat of volatilisation of the pure solvent under its saturated vapour pressure, tt, at the temperature T is similarly ... 

Because of its low vapour tension, dichloroethyl sulphide evaporates very slowly, in spite of its low specific heat (0-330 calories) and low latent heat of volatilisation (80 calories). It is thus highly persistent, especially on terrain covered with bushes and shrubs (see p. 12). 

Its heat of formation from sulphur trioxide and hydrochloric acid is 14,400 calories, its heat of solution in water is 40,300 calories, and its heat of volatilisation is 12,800 calories per gm. molecule. It has a vapour density of 4 0. 

The specific heat is 0-268 calorie and the heat of volatilisation 54-8 calories. 

H O. Heat of volatilisation 54-8 Cal. H O —cheny-red col. AsCIg —> green sol. HaO gives slowly phenarsazine oxide. 

Various thermal material properties (as opposed to thermal stability. Chapter 9) are discussed in Chapter 16. These include coefficient of expansion, melting temperature, Vicat softening point, heat deflection/distortion temperature by thermomechanical analysis, also brittleness temperature, minimum filming temperature, delamination temperature, meltflow index, heat of volatilisation, thermal conductivity, specific heat and ageing in air. 

To determine the exact Si02 content of the residue, moisten it with 1 mL water, add two or three drops of concentrated sulphuric acid and about 5 mL of the purest available hydrofluoric acid. (CARE ) Place the crucible in an air bath (Section 3.21) and evaporate the hydrofluoric acid in a fume cupboard (hood) with a small flame until the acid is completely expelled the liquid should not be boiled. (The crucible may also be directly heated with a small non-luminous flame.) Then increase the heat to volatilise the sulphuric acid, and finally heat with a Meker-type burner for 15 minutes. Allow to cool in a desiccator and weigh. Re-heat to constant weight. The loss in weight represents the weight of the silica (Note 2). 

Tellurium melts at 452° C.1 and boils near 1390° C. under ordinary pressure,2 but volatilises at as low a temperature as 430° C. in a cathode-ray vacuum the vapour is yellow in colour.3 Like the density, the specific heat of the solid is inconstant, ranging from 0-0475 for the distilled element to 0-0524 for the precipitated amorphous substance.4 It has been observed 5 that exposure to X-rays increases the specific heat of tellurium by about 8 per cent., possibly owing to a change in the structure of the element. 

When heated, the dioxide fuses at an incipient red heat, giving a clear, deep yellow liquid, the colour being lost on cooling. On account of its considerable latent heat of fusion, the mass becomes feebly incandescent during solidification. Appreciable volatilisation occurs at 400° to 500° C., the oxide, however, being mueh less volatile than tellurium itself. 

Mercuric arsenide forms microscopic mamellated crystals. When dry it oxidises readily in the air to arsenious oxide and mercury. On heating it volatilises without melting, forming a sublimate of arsenic and mercury and a little arsenious oxide. The arsenide is therefore dried under diminished pressure. When heated with an alkyl iodide, a diarsonium mercuriodide of the type As2R6I2.2HgI2 is formed.8... 

When heated, arsenious sulphide readily sublimes and fusion occurs, according to Borgstrom,8 at 320° C. Earlier determinations have put the melting point at 310°,9 300°10 and 325° C.11 Air must be excluded or oxidation occurs. Some degree of volatilisation may be observed at the ordinary temperature.12 According to Schuller,13 when... 

When arsenic trisulphide is exposed to dry hydrogen chloride or hydrogen bromide, it liquefies at the ordinary temperature and on heating complete volatilisation occurs.9 It is not readily attacked by halogen acids. When boiled with concentrated hydrochloric acid it is decomposed, but with great difficulty, and the hydrogen sulphide and arsenious chloride evolved reproduce arsenious sulphide in the receiver.10 A similar reaction occurs when heated with a chloride in the presence of concentrated sulphuric acid, but the decomposition is incomplete.11 The reaction is facilitated by the presence of cuprous chloride or ferric chloride. Only a slight reaction is observed with dilute acid,12 and the... 

Another possibility is the volatilisation of 210Po from soil or vegetation. In the laboratory, polonium is notorious for its ability to transfer from one surface to another. Abe Abe (1969) found that 60% of 210Po collected on a filter paper volatilised on heating to 200°C for one hour. The inventory of 210Po in topsoil is about 5000 times the inventory in air, when both are expressed per unit area of ground, so only a small degree of volatilisation or resuspension would materially increase the concentration in air. 

Crookes2 had in 1911 already studied the relative volatilities of the metals of the platinum group at temperatures ranging from 900° C. upwards. The metals were heated in still air in an Herseus furnace, the order of volatilisation proving to be as follows Ru, Ir, Pd, Pt, and Rh, the last named being the least volatile. 

The acid appears as a transparent, vitreous, tough mass, which usually is deliquescent and dissolves in water with much heat. At a red heat it volatilises without decomposition 8 giving a vapour with a density corresponding to a molecular weight of 76-8 to 78-2, the theoretical value for (HP03)2 being 80.9... 

Anhydrous chromic chloride forms large, lustrous, unctuous plates of the colour of peach blossom, of density 2-757 at 15° C. It has a specific heat of 0-143. Its vapour density just above 1065° C., at w hieh temperature it volatilises, is 6-135 (air=l), whilst at 1200° C. it approximates to the theoretical value, 5-478, required by the formula C1CI3. At much higher temperatures partial decomposition takes place, with consequent diminution of the vapour density. ... 

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