Efflorescence, Deliquescence

Nucleation is the science investigating the kinetics and thermodynamics of the formation of a new phase of a material at a size just sufficient to be stable. In addition to their role in new particle formation, nucleation processes are also critical to an accurate understanding of a number of other atmospheric events, including cloud droplet activation on CCN, ice formation, and the deliquescence/efflorescence of particles. In this section we focus on the nucleation of new particles through homogeneous nucleation, i.e., from gaseous precursors. The theoretical treatment of new particle nucleation, as well as field and laboratory measurements of nanoparticle formation, are addressed. 

Effect of sie on heterogeneous nucleation. Figure 17 shows an example of a mineral dust particle coated by hygroscopic salts. The deliquescence/efflorescence hysteresis cycle is reduced due to heterogeneous nucleation when foreign material, such... 

Deliquescence and efflorescence. A substance is said to deliquesce (Latin to become liquid) when it forms a solution or liquid phase upon standing in the air. The essential condition is that the vapour pressure of the saturated solution of the highest hydrate at the ordinary temperature should be less than the partial pressure of the aqueous vapour in the atmosphere. Water will be absorbed by the substance, which gradually liquefies to a saturated solution water vapour will continue to be absorbed by the latter until an unsaturated solution, having the same vapour pressure as the partial pressure of water vapour in the air, is formed. In order that the vapour pressure of the saturated solution may be sufficiently low, the substance must be extremely soluble in water, and it is only such substances (e.g., calcium chloride, zinc chloride and potassium hydroxide) that deliquesce. 

It must be emphasised that deliquescence and efflorescence are relative properties, since they depend upon the actual presence of water vapour in the atmosphere, which varies considerably with place and time. 

Cupric chloride [7447-39-4] M 134.4, m 498 , 630 (dec). Crystd from hot dilute aq HCl (0.6mL/g) by cooling in a CaCl2-ice bath. Dehydrated by heating on a steam-bath under vacuum. It is deliquescent in moist air but efflorescent in dry air. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

Here our interest is in the application of homogeneous nucleation theory to produce the comprehensive plots of meta-stable crystallization. Fig. 1 illustrates the meta-stable efflorescence paths(solid lines) of (NH4)2S04 and (NH4)3H(S04)2 particles as a function of RH with the decreasing rate of ARH = 0.005 min with the deliquescence paths(O). Fig. 2 shows the expectation time of the aqueous particle composed of (NH4)2S04 and H2SO4... 

When well-formed individual crystals have been obtained, filter them on a Witte plate, wash once with dilute nitric acid (1 3), pump as dry as possible, place the moist crystals in a suitable vessel, and put this in a desiccator over sulfuric acid. Watch the crystals carefully, with occasional stirring, and bottle them at once when they are dry. Do not touch them with the fingers, as this will discolor them. If they are allowed to overdry in the desiccator, they lose both crystal water and nitric acid and turn into a sticky mass of brownish-colored basic salt, which will not take up water from the air to reverse the reaction. Consequently, effloresced crystals cannot be used to complete the drying of the moist crystals. If the crystals are exposed to moist air, they deliquesce, undergo hydrolysis in the resulting solution, and form a basic salt. If they are bottled before they are dry, they will in time become discolored. If properly prepared, they will remain perfectly transparent and have a very pretty amethyst color, the intensity of which depends upon the size of the crystals. Crystals of iron alum have the same color. 

Jilulc HNO, and concentrating the solution. The compound deliquesces in moist air and effloresces in dry air. The pink anhydrous cobaltous nitrate cannot he formed by dehydrating Ihe hexahydrate but by treating Ihe salt with nitrogen pentoxide gas (or in solution in concentrated HNOi). The salt is used mainly in the preparation of catalysts. 

Substances that are ordinarily deliquescent are sulfuric add (concentrated), glycerol, calcium chloride crystals, sodium hydroxide (solid), and 100% ethyl alcohol. In an enclosed space, these substances deplete the water vapor present to a definite degree. Other substances are used to accomplish this end by chemical reaction, e.g.. phosphorus pentoxide (forming phosphoric acid), and boron trioxide (forming boric acid). Water is absorbed from nonmiscible liquids by addition of such substances as anhydrous sodium sulfate, potassium carbonate, anhydrous calcium chloride. and solid sodium hydroxide. The converse phenomenon is known as efflorescence. 

With some substances, not necessarily salt hydrates, the reverse of efflorescence occurs. For example, if anhydrous calcium chloride is left in the air, it absorbs water vapour and eventually forms a very concentrated solution. This process is called deliquescence, and substances which behave like this are said to be deliquescent. Solid sodium hydroxide will deliquesce. 

Sodium carbonate decahydrate effloresces quite readily. With some substances, such as solid sodium hydroxide, the reverse of efflorescence occurs - they deliquesce. There are some substances, such as concentrated sulfuric acid, which when left open to the atmosphere are diluted - they are hygroscopic. 

Appearance Colorless, odorless crystals or granules efflorescent in dry air, deliquescent in moist. Very soluble in water freely soluble in alcohol. 

In the second column the behavior of the crystallized salt when it is exposed to the air of the laboratory is indicated s = stable, i.e. unchanged by exposure to atmosphere e = efflorescent d = deliquescent d, e = deliquescent or efflorescent, according as to whether the humidity is above or below the average C02 = absorbs carbon dioxide and falls to a white powder Ox - compound is oxidized, especially in presence of moisture Hyd = hydrolyzed, even by the water vapor of the air. 

Selected physical properties of sodium thiosulfate pentahydrate are shown in Table 1. The crystals are relatively stable, efflorescing in warm, dry air and deliquescing slightly in moist air. They melt in their water of hydration at 48°C and can be completely dehydrated in a vacuum oven at this temperature, or at atmospheric pressure at 105°C. Anhydrous sodium thiosulfate can also be crystallized direcdy from a 72% solution above 75°C. It decomposes at... 

A solution of cobaltous nitrate in water is readily prepared by dissolving the oxides or carbonate in dilute nitric acid. Slow evaporation yields red, monoclinic prisms of the hexahy rate, Co(N03)2.6H20, of density 1-83.3 The crystals are very slightly deliquescent in moist air over concentrated sulphuric acid they effloresce. They melt at 56° C.4 to a red liquid which, at higher temperatures, thickens, becoming... 

The hexahydrate, Ni(N03)2.6H20, is dimorphous. It is obtained as green monoclinic crystals by concentration of a solution of nickel hydroxide or carbonate in dilute nitric acid at temperatures below 55° C.—most advantageously at about 40° C. Density 6 2-065 at 14° C. At low temperatures the salt separates out in crystalline lamellae. The crystals deliquesce in moist air and effloresce in the dry. Their solubility in water is as follows 7 ... 

General Properties.—The evaporated solution prepared as above deposited crystals of the hydrate H2P03.H20 which had the form of four-sided rectangular plates and melted at 70° C.1 They were very deliquescent, but when kept over sulphuric acid effloresced giving the anhydrous acid, which melted at 55° C. A half-hydrate, HaPO . HaO, which melted at about 80° C. was also obtained by evaporation over sulphuric acid. 

Tight Container A tight container protects the contents from contamination of extraneous liquids, solids, or vapors from loss of the chemical and from efflorescence, deliquescence, or evaporation under the ordinary or customary conditions of handling, shipment, storage, and sale, and is capable of tight reclosure. 

Sodium Thiosulfate occurs as large, colorless crystals or as a coarse, crystalline powder. It is deliquescent in moist air and effloresces in dry air at a temperature above 33°. Its solutions are neutral or faintly alkaline to litmus. One gram dissolves in 0.5 mL of water. It is insoluble in alcohol. 

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