Inorganic Chemicals

Formula AlH3; MW 30.005; Structure: polymeric, containing residual ether;

Uses
It is used as a reducing agent, and also as a catalyst for polymerization reaction.

Physical and Thermochemical Properties
Colorless cubic crystal; very unstable; decomposes in water; ΔΗ°ƒ −11.0 kcal/mol (-46.0kJ/mol)

Preparation
Aluminum hydride is prepared by the reaction of lithium hydride with aluminum chloride in diethyl ether

Chemical Reactions
Aluminum hydride decomposes in air and water. Violent reactions occur with both. It forms a complex, aluminum diethyl etherate with diethyl ether. The product decomposes in water releasing heat.

AlH3 + (C2H5)2O ——›H3Al•O(C2H5)2

Similar complexes are likely to form with other lower aliphatic ethers. It also forms a 1:1 complex with trimethyl amine, H3Al•N(CH3)3 which reacts explosively with water (Ruff 1967).
Aluminum hydride reduces CO2 to methane under heating:

Reaction with lithium hydride in ether produces lithium aluminum hydride,

Safety
Many reactions of aluminum hydride or its complexes may proceed with explosive violence, especially with water or moist air.

Formula: Al(NO3)3; MW 213.00; the anhydrous salt is covalent; also occurs as hydrated salts, Al(OH)(NO3)2, Al(OH)2NO3, and the more stable nonahydrate, Al(NO3)3 •9H2O [7784-27-2]

Uses
The nonahydrate and other hydrated aluminum nitrates have many applications. These salts are used to produce alumina for preparation of insulating papers, in cathode tube heating elements, and on transformer core laminates. The hydrated salts are also used for extraction of actinide elements.

Physical Properties
White or colorless crystalline solid (nonahydrate – rhombic crystal); deliquescent; refractive index 1.54; melts at 73.5°C; decomposes at 150°C; highly soluble in cold water (63.7% at 25°C), decomposes in hot water, soluble in polar organic solvents.

Preparation
The nonahydrate is prepared by treating aluminum, aluminum hydroxide, aluminum oxide, or aluminous mineral with nitric acid. The nitrate is crystallized from the solution.

Reactions
Since Al(NO3)3 or its salt hydrates dissociates to Al3+ and NO3– ions in the aqueous solution, its reactions in solutions are those of Al3+ . It is partially hydrolyzed, producing H3O+ and thus accounting for the acidity of its solution in water. The products constitute a complex mixture of mono- and polynuclear hydroxo species.
Aluminum nitrate is soluble in bases, forming aluminates, [Al(OH)4(H2O)2]–. It decomposes to Al2O3 when heated at elevated temperatures.

Chemical Analysis
Elemental composition: Al 12.67%, N 19.73%, O 67.60%. Al may be analyzed by various instrumental techniques, including atomic absorption or emission spectroscopy, or colorimetry (see under Aluminum). The nitrate anion in aqueous phase may be measured by the NO3– ion selective electrode, ion chromatography, or reduction with cadmium or hydrazine, followed by colorimetric tests.

Formula: AlN; MW 40.99

Uses
Aluminum nitride is used in manufacturing of steel and in semiconductors.

Physical Properties
White crystalline solid, hexagonal; odor of ammonia in moist air; sublimes at 2000°C; melts in N2 atmosphere over 2200°C; density 3.26 g/cm3 ; decomposes in water, alkalies and acids

Thermochemical Properties

ΔH°ƒ(s)          –76.0 kcal/mol
ΔG°ƒ(s)          –68.6 kcal/mol
S°                  4.82 cal/degree mol
Cρ                 7.20 cal/degree mol

Preparation
Aluminum nitride may be prepared in the laboratory by heating powdered aluminum metal with nitrogen.

Commercially, it is made by heating an aluminous mineral, such as, bauxite with coal in a stream of nitrogen.

Chemical Reactions
The nitride reacts with water forming aluminum hydroxide and ammonia.

AlN + 3H2O ——›Al(OH)3 + NH3

The compound decomposes in alkalies and acids forming products of complex stoichiometry.

Analysis
Elemental composition: Al 65.82%, N 34.18%, the metal is determined by wet analysis or AA spectroscopy. NH3 liberated on hydrolysis may be determined by titration or colorimetry (see under Ammonia).

Preparation
Pure alumina, needed to produce aluminum by the Hall process, is made by the Bayer process. The starting material is bauxite (Al2O3 • nH2O). The ore contains impurities, such as, SiO2, Fe2O3, TiO2, and Na2O. Most impurities are removed following treatment with caustic soda solution. Bauxite is dissolved in NaOH solution. Silica, iron oxides and other impurities are filtered out of the solution. CO2 is then bubbled through this solution. This precipitates out hydrated alumina, which is heated to remove water and produce Al2O3. These impurities are removed. Calcinations of bauxite produce alumina of abrasive and refractory grades. Activated aluminas of amorphous type, as well as the transition aluminas of γ, η, χ, and ρ forms, are obtained from various aluminum hydroxides, such as, α- and β-trihydrates, α-monohydrate and alumina gel. Such chemicals are obtained from bauxite by the Bayer process also.

Chemical Reactions
Alumina exhibits amphoteric behavior. It is soluble both in acids and bases. With acids, it produces their corresponding salts. It froms Al2(SO4)3, Al(NO3)3 and AlCl3 upon reactions with H2SO4, HNO3, and HCl, respectively. In acid medium, it exists as a solvated aluminum ion, in which water molecules are hexacoordinated to trivalent Al3+, as shown below:

Al2O3 + 6H3O+ + 3H2O ——› 2[Al(H2O)6]3+

(Rollinson, C. L., 1978., Aluminum Compounds. In Kirk-Othmer Encyclopedia <of Chemical Technology, 3rd ed. Vol 2, pp 188-97. NY,: Wiley Interscience)

Alumina forms hydroxide in aqueous alkaline solution. The reaction is slow. The products, aluminum hydroxides (hydrated aluminas), contain hexacoordinated aluminohydroxide anion:

Al2O3 + 2OH– + 7H2O → 2[Al(OH)4(H2O)2]–

In its dry state, alumina exhibiting basicity reacts with silica, forming aluminum silicate

Al2O3 + 3SiO2 → Al2(SiO3)3

Similarly, with basic CaO or MgO aluminate salts are formed

MgO + Al2O3 → Mg(AlO2)2
CaO + Al2O3 → Ca(AlO2)2

It forms aluminum nitride, AlN when heated with coal in a stream of nitrogen; and aluminum borate, Al2O3 •B2O3 when heated with B2O3 at 1000°C.

Analysis
Elemental composition: Al 52.91%, O 47.08%. Al may be anlayzed by atomic absorption or emission spectrophotometry or by colorimetric methods after acid digestion. Different forms of alumina may be identified by x-ray diffraction analysis. The X-ray crystallogaphic data for the mineral corundum are as follows:

crystal system: rhombohedral symmetry
space group     R3c
αο                    4.7591
χο                    12.9894
z                      6
x-ray density  3.9869 g/cm3

Toxicity
Chronic inhalation of Al2O3 dusts may cause lung damage.

Formula: AlPO4; MW 121.95

Synonym: Aluminum orthophosphate

Occurrence and Uses
The compound occurs in nature as the mineral, berlinite. Also, it occurs in nature in minerals, amblygonite, [NaAl(PO4)(OH)]; augelite, [Al2(PO4)(OH)3]; lazulite, [(Mg,Fe)Al2(PO4)2(OH)2]; variscite [(Al,Fe3+)(PO4)•2H2O]; and wavellite, [Al3(OH)3•(PO4)2•5H2O]. It is used as flux for ceramics; as cement in combination with calcium sulfate and sodium silicate; and in the manufacture of special glasses. It is also used in dried gel and therapeutically as an antacid.

Physical Properties
White powdery solid (rhombic plate); the mineral berlinite (AlPO4) has hexagonal quartz-like structure; refractive index 1.546; mp > 1,500°C; density 2.566 g/cu3; insoluble in water and alcohol; Ksp 9.83×10–10 very slightly soluble in HCl or HNO3.

Thermochemical Properties

ΔH°ƒ(s)      –414.4 kcal/mol
ΔG°ƒ(s)      –368.7 kcal/mol
S°             166.6 cal/degree mol
Cρ            22.27 cal/degree mol

Preparation
It is prepared by treating sodium aluminate with phosphoric acid.

NaAlO2 + H3PO4 ——›AlPO4 + NaOH + H2O

 It may be prepared by slowly adding (with stirring) ammonium phosphate (0.2M) to a solution of aluminum sulfate (0.1M).

Al2(SO4)3 + 2(NH4)3PO4 ——› 2AlPO4 +3(NH4)2SO4

The compound may, alternatively, be prepared by the reaction of aluminum sulfate with sodium phosphate.

Al2(SO4)3 + 2Na3PO4 ——› 2AlPO4 +3Na2SO4