Alkali aluminate

Alkali aluminate (5-calcium disilicate monosulfate), phase in Portland cement clinker, 5 472t Alkali aluminate (8-calcium disodium trialuminate), phase in Portland cement clinker, 5 472t Alkali belite, phase in Portland cement clinker, 5 472t Alkali blue toners, 14 318 Alkali borate glasses, 12 572, 573, 584 Alkali catalysed pad-dry-bake procedure, 9 485... 

The structure analysis of nitrites, however, shows that they contain isolated NO " groups in complexes of trivalent metals, e.g. in the alkali aluminates (KA102) that have the same bruto composition as the nitrites, the coordination, indeed, is higher. Here the AI3 ions are surrounded by six oxygen ions, a coordination number that is as to be expected for a really ionic compound. Hypochlorites ACIO, chlorites AC102, chlorates AG103, sulphites A2S03, etc., all have coordination numbers that are smaller than those to be expected in ionic compounds. 

Purified alumina2 is prepared in a similar way by neutralising crude alkali aluminate with sulphuric acid, and then placing the gelatinous mass in a space which is separated from anode and cathode by diaphragms. During electrolysis the alkali is expelled from the alumina and passes to the cathode. 

Aluminium Molybdates.—Simple molybdates of aluminium have not been prepared, but by dissolving aluminium hydroxide in solutions of alkali tri- or para-molybdates, and allowing to crystallise, salts of the type 3R 20.Al20g.l2Mo03.aq. are obtained. These may be represented as derivatives of the alkali aluminates thus R3Al Mo20,)3.aq. The following have been described ... 

Aluminum hydroxide adjuvant is prepared by the precipitation of a soluble aluminum salt by an alkali hydroxide, or the precipitation of an alkali aluminate by acid. 

The 90% alumina refractory showed a sharp drop in the amount of alpha-alumina present as the temperature was increased. The depletion of alpha-alumina does not occur unless excess soda is available and the temperature is above 2000°F, or unless the amount of SiOz present is not sufficient to tie up the soda as a sodium aluminum silicate. Finally, the free alumina existent in the lower silica-containing samples is depleted by the formation of beta-alumina and alkali aluminate. 

M en freshly precipitate, it is insoluble in H,0 soluble in acids and solutions of the fixed alkalies. When dried at a temperature above 50° (122° F ), or after 24 hours contact with the mother liquor, its solubility is greatly diminished. With acids it forms salts of aluminium and with alkalies, aluminates of the alkaline metal. Heated to near redness it is decomposed into A1,0, and H O. A soluble modification is obtained by dialysing a solution of ALH O in A1,C1 or by heating a dilute solution of aluminium acetate for 0 houra... 

C. Potassium hydroxide solution (0.1 molar aqueous) can be applied in single drop fashion or in a small puddle on a polished surface for 30 seconds. Rinse with an isopropyl alcohol spray and dry with forced warm air. C A and alkali-aluminate stain blue-brown, alkali sulfate darkens, and free lime turns brown. 

Alkali aluminate crystals clearly entrap alite and some belite, thus the aluminate crystals form later than some of the silicates, but this is not a new conclusion. Alkali aluminate rarely includes crystals of ferrite and appears to interrupt the continuity of ferrite, suggesting that the alkali aluminate crystallized first. 

Ono (1991) listed some of the characteristics of poorly burned clinker free lime greater than 4.5%, tightly packed large free lime nests, belite nests with a surrounding of small alites, high porosity, a loose framework of free lime and alkali aluminate, and a flow pattern of matrix into the free-lime nest. Well-burned clinker was said to contain small free lime and octahedral periclase from dolomite and coarse aluminate and ferrite, resulting from equilibrium crystallization. 

Photograph 7-62 Crushed clinkers with yellowish brown centers, produced in a kiln with a reducing environment. Examination at high magnification reveals belite coatings on alite, dull ferrite reflectivity, and alkali aluminate. (S A6682)... 

Alkali aluminate alkali-modified belite Excess alkali over equivalent sulfate (Long, 1983)... 

Alkali aluminate Alkalies, mainly sodium, in clinker (Hofmanner, 1973) more pronounced with NajO-bearing laboratory clinkers than in KjO-bearing clinkers negative effect on cement properties (Dreizier, Strunge, and Knofel, 1985)... 

Idiomorphous laminae or long staves (prismatic) aluminate Alkali aluminate and relatively high-alkali clinker (Gille and others, 1965)... 

Photograph 7-74 Prismatic alkali aluminate crystals in crushed clinker powder mount. High maximum temperature, long burning time, slow heating rate, moderately quick to moderately slow cooling rate. Gas- and coal-fired, wet-process kiln, 500 tons/day. (S A6692)... 

Photograph 7-77 Prismatic alkali aluminate (light tan) in matrix in which the ferrite displays a dull reflectivity. Thin belite coatings on many greenish blue alite crystals. Clinkers commonly exhibit brown areas. Moderately reducing conditions are inferred. Coal- and coke-fired, dry-process kiln. (S A6695)... 

Photograph 9-18 Alkali aluminate crystals in nital-etched clinker. (S A3458)... 

Affinities and antipathies of occurrence—for example, does alkali aluminate selectively occur in more porous zones or is free lime preferentially associafed with periclase ... 

Unlike Portland cement, hydrated aluminous cement pastes are resistant to diluted acid solutions with pH>4. This also includes natural waters containing dissolved CO2. One factor responsible for the good acid resistance of this cement is the absence of free calcium hydroxide among the formed hydrates, a phase that is easily soluble even in dilute acids. At the same time hydrous alumina is not dissolved at pH values down to 4. At very high pH values, such as those existing in alkah hydroxide solutions, corrosion of hardened aluminous cement may occur. Under these conditions AHj is dissolved in the liquid phase in the form of alkali aluminates. 

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