Precipitates, heating temperatures

Precipitation Heat Treatment. The supersaturated solution produced by the quench from the solution temperature is unstable, and the alloys tend to approach equiUbrium by precipitation of solute. Because the activation energies required to form equiUbrium precipitate phases are higher than those to form metastable phases, the soHd solution decomposes to form G-P zones at room temperature (natural aging). Metastable precursors to the equihbrium phases are formed at the temperatures employed for commercial precipitation heat treatments (artificial aging). 

This ester (70 g) and diethyl carbonate (250 mg) were stirred at 90°C to 100°C while a solution of sodium ethoxide [from sodium (7.8 g) and ethanol (1 54 ml)] was added over 1 hr. During addition, ethanol was allowed to distill and after addition distillation was continued until the column heat temperature reached 124°C. After cooling the solution to 90°C, dimethyl sulfate (33 ml) was followed by a further 85 ml of diethyl carbonate. This solution was stirred and refluxed for 1 hr and then, when Ice cool, was diluted with water and acetic acid (10 ml). The malonate was isolated in ether and fractionally distilled to yield a fraction boiling at 148°C to 153°C/0.075 mm, identified as the alpha-methyl malonate. This was hydrolyzed by refluxing for 1 hr at 2.5N sodium hydroxide (350 ml) and alcohol (175 ml), excess alcohol was distilled and the residual suspension of sodium salt was acidified with hydrochloric acid to give a precipitate of the alpha-methyl malonic acid. This was decarboxylated by heating at 180°C to 200°Cfor 30 minutes and recrystallized from petroleum ether (BP 80°C to 100°C) to give 2-(2-fluoro-4-biphenylyl)propionic acid, MP 110°C to 111°C. 

Elevated heat exchangers, 19 508 Elevated tank, 24 280-281 Elevated temperature precipitation heat treatment, aluminum alloys, 2 333 Elevator furnace, 12 288 Elgonidipine, 5 131... 

Room temperature precipitation heat treatment aluminum alloys, 2 332-333 Room-temperature vulcanizable silicone rubber, 25 129... 

In contrast to the silicates, most carbonate and many sulfate minerals dissolve exothermically (AW ° < 0). This makes them most soluble at low temperatures and gives them a tendency to precipitate as temperature increases (Fig. 1.7). (Compare log versus /T curves for calcite and quartz in Fig. 1,7.) Thus, calcite (AW° = -2.30 kcal/mol) can be a troublesome precipitate on the walls of boiler systems where its thermal insulating properties prevent heat exchange and can seriously damage boiler performance. 

Factors causing low colloid formation (low specific activity) are primarily related to pH, incorrect order of mixing, low heating temperature, heating a large volume, inadequate boiling time, or a defect of kit formulation. Tc eluate used for colloid preparation should be obtained from a generator by daily elution in order to minimize Tc carrier (Ponto et al. 1987). A flocculent precipitate is formed in the presence of cation (1 pg/ml) (Haney et al. 1971 Ponto et al. 1987). 

It forms soft, flexible, lemon-yellow crystals, permanent in air at ordinary temperatures. They begin to lose Aq at 60° (140° F.), and become anhydrous at 100° (213° F.). Soluble in HaO insoluble in alcohol, which precipitates it from its aqueous solution. When calcined with KHO or KaCOs, potassium cyanid and cyanate are formed, and Fe is precipitated. Heated with dilute HaSOi, it yields an insoluble white or blue salt, potassium sulfate, and hydrocyanic acid. Its solutions form with those of many of the metallic salts insoluble ferrocyanids those of Zn, Pb, and Ag are white, cupric ferrocyanid is mahogany-colored, fer-... 

An isopleth is a line of constant composition such as hijk in Fig. 15.7. At h, the system is entirely liquid. As the system cools, solid antimony appears at i as the antimony crystallizes out, the saturated liquid becomes richer in lead, and the liquid composition moves along the curve ice. At j the solution has the eutectic composition e and is saturated with respect to lead also, so lead begins to precipitate. The temperature remains constant even though heat flows out since, in this condition, the system is invariant. The amount of liquid diminishes and the amounts of solid lead and antimony increase. Finally the liquid solidifies, and the temperature of the mixed solids decreases along the line jk. If the process is done in reverse, heating a mixture of solid lead and solid antimony from /c, the state point moves from k to j. At j, liquid forms having the composition e. Note that the liquid formed has a different composition than the solid mixture. The system is invariant, so the... 

Artificial Aging (Elevated Temperature Precipitation Heat Treatments). Most precipitation hardenable alloy products are usually... 

Z20 sample was still amorphous of pre-heated at 900 C. When increase the temperature up to 1000"C, the small amount of t-Zr02 was precipitated firstly. When the temperature increases up to llOO C, the mullite, cristobalite, m-Zr02 were precipitated. When the heating temperature was higher than 1150, for all samples there are no more new phases generated. The main phases were t-Zr02, mullite, cristobalite, m-Zr02 and a trace of cordierite. 

The chromium-free alloys include nickel itself and copper alloys such as Monel. The success of nickel in strong alkalis depends on development of a passive hydroxide film. It is fairly resistant to many acids but is unsuitable in strong oxidizing environments. The most common grades are nickel 200 and nickel 201. The former contains up to 0.1 % carbon. On prolonged heating, the carbon can precipitate at temperatures as low as 315°C. Nickel 201, with a carbon content less than 0.02%, therefore is preferred at least in first-stage evaporators and in molten anhydrous caustic service. 

Using a solution of AICI3 (in acid), neutralize and precipitate the A1 as A1(0H)3 by the addition of NH4OH. Filter the precipitate. Obtain the TGA thermal curve of the precipitate. Heat the precipitate until no change in mass occurs (to at least 1000°C). Could this precipitate be dried to a constant weight at any temperature below 1000°C ... 

The carbides of these elements are more stable than those of chromium and precipitate at temperatures where chromium remains in solution. By a heat treatment above the sensitizing region one can thus precipitate the dissolved carbon and prevent the formation of chromium carbide at the grain boundaries. 

T5. Cooled from an elevated temperature-shaping process and artificially aged. Applies to products that are not cold worked after an elevated temperature-shaping process such as casting or extrusion and for which mechanical properties, dimensional stability, or both have been substantially improved by precipitation heat treatment. 

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