Aluminum oxide melting point

Gallium (eka-Aluminum) Density Melting point Formula of oxide 5.9 g/cm Low X203 5.91 g/cm3 29.8°C Ga2C>3... 

Molten cryohte dissolves many salts and oxides, forming solutions of melting point lower than the components. Figure 1 combines the melting point diagrams for cryolite—A1F. and for cryohte—NaF. Cryohte systems ate of great importance in the HaH-Heroult electrolysis process for the manufacture of aluminum (see Aluminumand ALUMINUM alloys). Table 5 Hsts the additional examples of cryohte as a component in minimum melting compositions. 

Aluminum nitrate is available commercially as aluminum nitrate nonahydrate [7784-27-2], A1(N02)3 9H20. It is a white, crystalline material with a melting point of 73.5°C that is soluble in cold water, alcohols, and acetone. Decomposition to nitric acid [7699-37-2], HNO, and basic aluminum nitrates [13473-90-0], A1(0H) (N03) where x + = 3, begins at 130°C, and dissociation to aluminum oxide and oxides of nitrogen occurs above 500°C. 

Examination of the metallic product (regulus) of such aluminothermically produced vanadium metal reveals the presence of oxide phases in the metal matrix. This suggests that there is a decreasing solubiHty for aluminum and oxygen below the melting point. To date, no purification processes have been developed that take advantage of the purification potential of this phenomenon. 

Aluminum is the liighest melting point metal (660°C) applied by hot dipping. Aluminized steel can be used at temperatures up to SSO C without appreciable oxidation. Tliis steel has very good resistance to gases and vapors containing small quantities of sulfur dioxide and hydrogen sulfide [41,42,43]. 

Aluminum metal is produced from aluminum oxide by electrolysis using the Hall-Heroult process, whose story is detailed in our Chemical Milestones Box. The melting point of AI2 O3 is too high (2015 °C) and its electrical conductivity too low to make direct electrolysis commercially viable. Instead, AI2 O3 is mixed with cryolite (Na3 AlFfi) containing about 10% CaF2. This mixture has a melting point of 1000 °C, still a high temperature but not prohibitively so. Aluminum forms several complex ions with fluoride and oxide, so the molten mixture... 

The excess aluminum in the charge compensates for the loss of aluminum due to nonreductive air oxidation, and also provides aluminum for alloying with the niobium metal produced in the reduction. As mentioned earlier, the liquidus temperatures of niobium-aluminum alloys are lower than the melting point of niobium. The melting of this alloy and the alumina slag is achieved even with the reduced amount of heat available from the reaction implemented without preheating in the open reactor. 

Sodium is a soft, wax-like silver metal that oxidizes in air. Its density is 0.9674 g/cm, and therefore it floats on water as it reacts with the water releasing hydrogen. It has a rather low melting point (97.6°C) and a boiling point of 883°C. Sodium is an excellent conductor of heat and electricity. It looks much like aluminum but is much softer and can be cut with a knife like butter. Its oxidation state is +1. 

Vanadium is a silvery whitish-gray metal that is somewhat heavier than aluminum, but lighter than iron. It is ductile and can be worked into various shapes. It is like other transition metals in the way that some electrons from the next-to-outermost shell can bond with other elements. Vanadium forms many complicated compounds as a result of variable valences. This attribute is responsible for the four oxidation states of its ions that enable it to combine with most nonmetals and to at times even act as a nonmetal. Vanadiums melting point is 1890°C, its boiling point is 3380°C, and its density is 6.11 glam . 

Cobalt s Curie point is 1,121°C, and its melting point is 1,495°C. About 25% of all cobalt mined in the world is used as an alloy with other metals. The most important is the alloy alnico, which consists of nickel, aluminum, and cobalt. Alnico is used to make powerful permanent magnets with many uses, such as CT, PET, and MRl medical instruments. It is also used for electroplating metals to give a fine surface that resists oxidation. 

FIG. 5.4 The potassium nitrate /sulfur /aluminum system. Endo-therms for sulfur can be seen near 105° and 119 c, followed by the potassium nitrate phase transition near 130 C. As the melting point of potassium nitrate is approached (334 C), an exotherm is observed. A reaction has occurred between the oxidizer and fuel, and ignition of the mixture evolves a substantial amount of heat. 

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