Aluminium (III) nitrate

Aluminium Nitrate

Other Names: Aluminium(III) nitrate, Aluminium trinitrate, Nitric acid aluminium salt
Chemical Formula: Al(NO₃)₃
Molar Mass: 213.00 g/mol
CAS Number: 13473-90-0
Appearance: White crystalline solid
SMILES: [N+](=O)([O-])[O-].[N+](=O)([O-])[O-].[N+](=O)([O-])[O-].[Al+3]

Aluminium nitrate is an inorganic salt composed of Al³⁺ cations and nitrate anions. It is highly compatible with aqueous processing and is extensively used in inorganic and materials chemistry as a soluble aluminium precursor. In laboratory and materials-science applications, aluminium nitrate is also frequently encountered as aluminium nitrate nonahydrate, Al(NO₃)₃·9H₂O. Its high water solubility, hydrolytic behaviour and thermal conversion to aluminium oxide make it particularly useful for preparing alumina and other aluminium-containing materials through sol-gel, precipitation, electrospinning and solution-combustion techniques.

Chemical and physical properties

Anhydrous aluminium nitrate has a molar mass of approximately 213.00 g/mol and is described as a white crystalline inorganic solid. The compound is an oxidizing nitrate salt and dissolves readily in water.

In aqueous solution, Al³⁺ does not remain as a free isolated ion but becomes strongly hydrated. The aluminium ion is commonly represented as the hexaaqua complex [Al(H₂O)₆]³⁺. Polarization of coordinated water molecules promotes hydrolysis, giving aqueous aluminium nitrate solutions acidic characteristics. This hydrolytic behaviour plays an important role in sol-gel and precipitation processes used to form aluminium hydroxide, oxyhydroxide and oxide structures.

The hydrated form, aluminium nitrate nonahydrate, has been studied extensively by thermal analysis. Its decomposition occurs through several stages involving initial dehydration, subsequent hydrolysis and progressive elimination of nitrate groups. Thermal treatment ultimately produces amorphous aluminium oxide, which can undergo further structural transformations to crystalline alumina phases depending on temperature and processing conditions.

Crystallographic studies of aluminium nitrate nonahydrate have shown that the hydrated compound crystallizes in the monoclinic system. Its structure contains strongly hydrated aluminium centres and an extended hydrogen-bonding network involving water molecules and nitrate ions.

Applications

Aluminium nitrate is widely used as a precursor for the synthesis of aluminium oxide materials. Sol-gel processing of hydrated aluminium nitrate can produce amorphous and mesoporous alumina, with pore structure and particle morphology influenced by precursor concentration, hydrolysis conditions and subsequent calcination.

It is used in the preparation of nanocrystalline alumina. Scientific studies have employed aluminium nitrate in polymeric sol-gel routes to obtain γ- and α-Al₂O₃ nanoparticles, with the crystalline phase, particle dimensions and surface properties controlled through complexing agents and thermal-treatment conditions.

Aluminium nitrate is also used as a precursor for alumina fibres and nanofibres. Sol-gel and electrospinning methods based on aluminium nitrate solutions have produced aluminium oxide fibres that transform through amorphous and transitional alumina phases before forming crystalline α-Al₂O₃ at elevated temperatures.

In solution-combustion synthesis, aluminium nitrate serves simultaneously as an aluminium source and as the nitrate-containing oxidizing component. This approach has been investigated for preparing high-purity, fine and nanostructured alumina powders with properties that depend strongly on the reaction composition and subsequent calcination.

Aluminium nitrate is additionally employed in the preparation of alumina catalyst supports and other aluminium-containing ceramic and catalytic materials. Because nitrate species can be removed during thermal processing, aluminium nitrate is particularly useful when high-purity oxide products and homogeneous distribution of aluminium in precursor solutions are required.

Scientific references

1. PubChem, National Center for Biotechnology Information. Aluminum nitrate, CID 26053. Molecular formula, molecular mass, CAS number, chemical structure and SMILES.
2. Pacewska, B.; Keshr, M. Thermal transformations of aluminium nitrate hydrate. Thermochimica Acta, 2002, 385(1-2), 73-80. DOI: 10.1016/S0040-6031(01)00703-1.
3. Herpin, P.; Sudarsanan, K. Structure cristalline du nitrate d'aluminium hydraté. Bulletin de la Société Française de Minéralogie et de Cristallographie, 1965, 88(4), 595-601. DOI: 10.3406/bulmi.1965.5899.
4. Hao, Z.; Liu, H.; Guo, B.; Li, H. et al. Sol-Gel Synthesis of Alumina Using Inorganic Salt Precursor. Acta Physico-Chimica Sinica, 2007, 23(3), 289-294. DOI: 10.1016/S1872-1508(07)60021-7.
5. Rajaeiyan, A.; Bagheri-Mohagheghi, M. M. Comparison of Urea and Citric Acid Complexing Agents and Annealing Temperature Effect on the Structural Properties of γ- and α-Alumina Nanoparticles Synthesized by Sol-Gel Method. Advances in Materials Science and Engineering, 2013, 2013, 791641. DOI: 10.1155/2013/791641.
6. Toniolo, J. C.; Lima, M. D.; Takimi, A. S.; Bergmann, C. P. Synthesis of alumina powders by the glycine-nitrate combustion process. Materials Research Bulletin, 2005, 40(3), 561-571. DOI: 10.1016/j.materresbull.2004.07.019.
7. Fabrication of α-alumina fibers by sol-gel and electrospinning of aluminum nitrate precursor solutions. Results in Physics, 2019, 12, 193-204. DOI: 10.1016/j.rinp.2018.11.068.
8. Vorakitkanvasin, S.; Kunjara Na Ayudhya, S.; Suriye, K.; Praserthdam, P.; Panpranot, J. Enhanced metathesis activity of low loading Re₂O₇/Al₂O₃ catalysts for propylene production by using aluminum nitrate as Al₂O₃ precursor. Applied Catalysis A: General, 2016, 517, 39-46. DOI: 10.1016/j.apcata.2016.01.008.

Safety Data:

• Hazard Statement(s) (H):

  • H272: May intensify fire; oxidizer.
  • H314: Causes severe skin burns and eye damage.
  • H335: May cause respiratory irritation.

• Precautionary Statement(s) (P):

  • P210: Keep away from heat/sparks/open flames/hot surfaces. No smoking.
  • P220: Keep/Store away from clothing and other combustible materials.
  • P280: Wear protective gloves/protective clothing/eye protection/face protection.
  • P305+P351+P338: IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do. Continue rinsing.
  • P310: Immediately call a POISON CENTER or doctor/physician.
  • P403+P233: Store in a well-ventilated place. Keep container tightly closed.

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