Calcium surface

D. E. Sandstrom, O.N. Antzutkin, W. Forsling, A spectroscopic study of calcium surface sites and adsorbed iron species at aqueous fluorapatite by means of 1H and 31P MAS NMR, Langmuir 22 (2006) 11060-11064. 

The commonly used electrolyte in the Ca-TC system is Ca(AlCl4)2. TC is reduced on the calcium surface as follows [447] ... 

Surface water Is usually undersaturated in calcium ions (Ca ). Where (even saturated) surface water mixes with sea water, mixing zone corrosion will dissolve calcium carbonate. Evidence of this occurring may be seen on islands. 

Brunauer and co-workers [129, 130] found values of of 1310, 1180, and 386 ergs/cm for CaO, Ca(OH)2 and tobermorite (a calcium silicate hydrate). Jura and Garland [131] reported a value of 1040 ergs/cm for magnesium oxide. Patterson and coworkers [132] used fractionated sodium chloride particles prepared by a volatilization method to find that the surface contribution to the low-temperature heat capacity varied approximately in proportion to the area determined by gas adsorption. Questions of equilibrium arise in these and adsorption studies on finely divided surfaces as discussed in Section X-3. 

Qualitative examples abound. Perfect crystals of sodium carbonate, sulfate, or phosphate may be kept for years without efflorescing, although if scratched, they begin to do so immediately. Too strongly heated or burned lime or plaster of Paris takes up the first traces of water only with difficulty. Reactions of this type tend to be autocat-alytic. The initial rate is slow, due to the absence of the necessary linear interface, but the rate accelerates as more and more product is formed. See Refs. 147-153 for other examples. Ruckenstein [154] has discussed a kinetic model based on nucleation theory. There is certainly evidence that patches of product may be present, as in the oxidation of Mo(lOO) surfaces [155], and that surface defects are important [156]. There may be catalysis thus reaction VII-27 is catalyzed by water vapor [157]. A topotactic reaction is one where the product or products retain the external crystalline shape of the reactant crystal [158]. More often, however, there is a complicated morphology with pitting, cracking, and pore formation, as with calcium carbonate [159]. 

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

If a compound has been recrystallised from petrol, benzene, etc.y some freshly cut shavings of clean paraffin wax should be added to the calcium chloride in (A) or to the sodium hydroxide in D, The surface of the wax absorbs organic solvent vapours (particularly the hydrocarbons) and the last trace of such solvents is thus readily removed from the recrystallised material. 

Place 0 5 ml. of the pyridine in a 200 ml. round- or flat-bottomed flask and add 34 ml. (30 g.) of benzene. Fit the flask with a reflux water-condenser, and then place it in a cold water-bath. If the experiment is conducted in a fume-cupboard, the top of the condenser can be closed with a calcium chloride tube bent downwards (as in Fig. 61, p. 105 or in Fig. 23(A), p. 45, where the outlet-tube A will carry the calcium chloride tube) and the hydrogen bromide subsequently allowed to escape if, however, the experiment is performed in the open laboratory, fit to the top of the condenser (or to the outlet-tube A) a glass delivery-tube which leads through a piece of rubber tubing to an inverted glass funnel, the rim of which dips just below the surface of some water... 

For this preparation, which must be performed in the fume-cupboard, assemble the apparatus shown in Fig. 67(A). C is a 150 ml. distilling-flask, to the neck of which is fitted a reflux single-surface water-condenser D, closed at the top E by a calcium chloride tube. The side-arm of C carries a cork F which fits the end E of the condenser for subsequent distillation. The side-arm of C is meanwhile plugged by a small rubber cork, or by a short length of glass rod. (Alternatively, use the ground-glass flask and condenser (Fig. 22 (a) and (c), p. 43), and... 

Figs. II, 13, 7 and II, 13, 8 depict various set-ups which involve tlio refluxing of a liquid the Liebig condenser may, of course, be replaced by a double-surface condenser. In Fig. II, 13, 7 a calcium chloride guard protects the contents of the flask from ingress of moisture. The... 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

Fit a 500 ml. round-bottomed flask with a dropping funnel and a double surface condenser alternatively, the flask may be provided with a two-way addition tube (Fig. II, 13, 9) and the dropping funnel and condenser inserted into the latter. Place 37 g. (46 ml.) of iso-butyl alcohol (b.p. 106-108°) and 40 g. (41 ml.) of pure pyridine in the flask and 119 g. (73 ml.) of redistilled thionyl chloride in the dropping funnel. Insert a cotton wool or calcium chloride guard tube into the mouth of the funnel. Introduce the thionyl chloride during 3-4 hours a white solid... 

Mix 40 g. (51 ml.) of isopropyl alcohol with 460 g. (310 ml.) of constant boiling point hydrobromic acid in a 500 ml. distilling flask, attach a double surface (or long Liebig) condenser and distil slowly (1-2 drops per second) until about half of the liquid has passed over. Separate the lower alkyl bromide layer (70 g.), and redistil the aqueous layer when a further 7 g. of the crude bromide will be obtained (1). Shake the crude bromide in a separatory funnel successively with an equal volume of concentrated hydrochloric acid (2), water, 5 per cent, sodium bicarbonate solution, and water, and dry with anhydrous calcium chloride. Distil from a 100 ml. flask the isopropyl bromide passes over constantly at 59°. The yield is 66 g. 

Allyl Bromide. Introduce into a 1-litre three-necked flask 250 g. (169 ml.) of 48 per cent, hydrobromic acid and then 75 g. (40-5 ml.) of concentrated sulphuric acid in portions, with shaking Anally add 58 g. (68 ml.) of pure allyl alcohol (Section 111,140). Fit the flask with a separatory funnel, a mechanical stirrer and an efficient condenser (preferably of the double surface type) set for downward distillation connect the flask to the condenser by a wide (6-8 mm.) bent tube. Place 75 g. (40 5 ml.) of concentrated sulphuric acid in the separatory funnel, set the stirrer in motion, and allow the acid to flow slowly into the warm solution. The allyl bromide will distil over (< 30 minutes). Wash the distillate with 5 per cent, sodium carbonate solution, followed by water, dry over anhydrous calcium chloride, and distil from a Claisen flask with a fractionating side arm or through a short column. The yield of allyl bromide, b.p. 69-72°, is 112 g. There is a small high-boiling fraction containing propylene dibromide. 

In a 1-litre three-necked flask, mounted on a steam bath and provided respectively with a separatory funnel, mechanical stirrer and double surface condenser, place 165 g. of bromoform (96 per cent.). Add 10 ml. of a solution of sodium arsenite made by dissolving 77 g. of A.R. arsenious oxide and 148 g. of A.R. sodium hydroxide in 475 ml. of water. Warm the mixture gently to start the reaction, and introduce the remainder of the sodium arsenite solution during 30-45 minutes at such a rate that the mixture refluxes gently. Subsequently heat the flask on the steam bath for 3-4 hours. Steam distil the reaction mixture (Fig. 11, 41, 1) and separate the lower layer of methylene bromide (79 g.). Extract the aqueous layer with about 100 ml. of ether a further 3 g. of methylene bromide is obtained. Dry with 3-4 g. of anhydrous calcium chloride, and distil from a Claisen flask with fractionating side arm. The methylene bromide boils constantly at 96-97° and is almost colourless. 

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