Inorganic Fluorides: Comprehensive Overview

What Are Inorganic Fluorides?

Inorganic fluorides represent fluoride compounds that lack any carbon-hydrogen bonds. The structure of these compounds centers around fluoride ions (F^-), which pair with metal cations including sodium (Na⁺), calcium (Ca²⁺), and aluminum (Al³⁺) to create binary or complex salts. The extraordinary chemical stability and distinct physicochemical attributes of inorganic fluorides make them essential across diverse sectors such as metallurgy, electronics manufacturing, pharmaceutical development, and environmental management.

How Are Inorganic Fluorides Classified?

Inorganic fluorides exist in multiple forms that can be classified into three main categories based on their applications.

A. Basic fluorides

The fluorine chemical industry depends on these fundamental materials:

• Hydrofluoric acid (HF): Hydrofluoric acid serves as a fundamental precursor in fluorine chemistry while finding extensive applications in glass etching and metal refining alongside fluorine compound synthesis.
• Fluorite (CaF₂): Fluorite functions as a naturally occurring mineral which supplies fluorine for industrial applications particularly in steel production and hydrogen fluoride manufacturing.

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Catalog	Name
OFC7789755	Calcium fluoride

B. Fluoride salts for aluminum

The production of aluminum depends heavily on the use of various fluoride salts.

• Aluminum fluoride (AlF₃): Aluminum smelting processes benefit from aluminum fluoride because it serves as an electrolyte additive which boosts current efficiency while decreasing energy consumption and improving electrolysis conditions.
• Cryolite (Na₃AlF₆): Cryolite functions as a flux during aluminum electrolysis because it decreases alumina's melting point while optimizing the electrolyte's conductivity.

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Catalog	Name
OFC13462925	Aluminum Fluoride Monohydrate
OFC15098870	Aluminum fluoride trihydrate
OFC7784181	Aluminum fluoride, anhydrous
OFC12068552	Sodium Aluminum Fluoride (Chiolite)
OFC31794920	Strontium Aluminum Fluoride
OFC7784192	Ammonium hexafluoroaluminate

C. Electronic grade fluorides

High purity fluorides remain essential components for electronics manufacturing and production.

• Lithium hexafluorophosphate (LiPF₆): LiPF₆ functions as an essential component within lithium-ion batteries to increase conductivity and ensure thermal stability.
• Electronic Grade Hydrofluoric Acid: Semiconductor manufacturing depends on hydrofluoric acid to etch silicon wafers during microchip production.
• Nitrogen Trifluoride (NF₃): The semiconductor and display panel industries use NF₃ as a clean gas widely.

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Catalog	Name
OFC13821200	Lithium Hexafluoroaluminate
OFC17029162	Lithium Hexafluorostannate(IV)
OFC24389251	Lithium Difluorophosphate

D. Other Industry-Related Inorganic Fluorides

Representative inorganic fluorides that show promising application prospects include sodium fluoride, potassium fluoride, barium fluoride and boron trifluoride.

• Sodium fluoride functions as a bactericidal agent and finds application as an agricultural pesticide while also serving as a wood preservative and water treatment agent and can be used as a ceramic pigment and light metal fluoride salt treatment agent. This material finds applications in enameling and medicine as well as papermaking and building materials.
• The primary application of potassium fluoride is as welding flux for different alloys but it also finds uses in glass carving and food preservation. Potassium fluoride serves as a prevalent fluorinating agent throughout organic chemical manufacturing processes. Special optical glass production and other items like optical fiber and laser generators use barium fluoride in their manufacturing process.
• Boron trifluoride functions as a crucial acid catalyst across numerous organic synthesis and petrochemical processes. The compound serves multiple purposes in organic chemical reactions including alkylation along with polymerization, isomerization and both addition and condensation reactions and decomposition processes.

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Catalog	Name
OFC22554990	Sodium fluoride (Na18F)
OFC13455215	Potassium Fluoride Dihydrate
OFC53612912	Potassium fluoride (K18F)
OFC00024	Barium Hexafluorophosphate

Fig.1 Summary of the structures of inorganic fluorides^[1].

What Are the Chemical Properties of Inorganic Fluorides?

Reactivity	Inorganic fluorides exhibit strong chemical activity, readily forming protective fluoride layers on metal surfaces. They serve as catalysts in organic reactions, such as alkylation, isomerization, and polymerization. Fluorides react vigorously with alkali metals to form stable fluoride salts.
Stability	Most fluorides possess high thermal and chemical stability. For instance, beryllium fluoride (BeF2) remains stable at elevated temperatures. Fluoride compounds used in metallurgy, such as cryolite (Na3AlF6), exhibit excellent resistance to decomposition under operational conditions.
Solubility and Hydrolysis	Solubility varies among fluorides; alkali metal fluorides (e.g., NaF, KF) are highly soluble in water, whereas fluorides like CaF2 are sparingly soluble. Some fluorides, such as silicon tetrafluoride (SiF4), react with moisture to form hydrofluorosilicic acid.
Special Properties	Fluorides in non-aqueous environments can function as strong bases, catalyzing unique organic transformations. Certain fluorides influence atmospheric fluoride levels, affecting environmental fluoride cycles.

What Are Fluorides Used for?

Metallurgy

• Aluminum Electrolysis: The melting point of alumina decreases when fluorides like AlF₃ and Na3AlF₆ are added, which improves electrolytic efficiency.
• Steel Production: Fluorides support desulfurization and slag formation, which enhances the quality of steel.

Electronics and Photonics

• Semiconductor Processing: HF is critical for silicon wafer etching.
• Optoelectronic Applications: Optical coatings, lenses, and infrared detectors make use of BaF₂ and MgF₂.
• Battery Technologies: Lithium-ion battery electrolytes contain LiPF₆ as a crucial element.

Pharmaceuticals and Healthcare

• Dental Care: Toothpaste and mouthwash use NaF and SnF₂ to protect against tooth decay.
• Pharmaceutical Formulations: Fluoride-based drugs exhibit improved stability and bioavailability.

Chemical Industry

• Catalysis: Petrochemical refining processes and organic synthesis operations commonly utilize BF₃ as a catalyst.
• Refrigerants: Refrigerant production relies on fluorinated compounds that originate from inorganic fluorides.

Environmental and Agricultural Applications

• Water Treatment: Controlled fluoridation through NaF usage helps to prevent dental caries.
• Pesticides and Fungicides: Certain fluoride compounds enhance crop protection.

Fig 2 The effect of inorganic fluorides on the morphology and PL property of large-sized InAs/InP/ZnSe/ZnS core/multishell QDs. (a) Scheme of shell evolution during the synthesis of InAs/InP/ZnSe/ZnS QDs without ZnF₂ (left half) and with ZnF₂ (right half). (b,c) Scanning TEM (STEM) images of InAs/InP/ZnSe/ZnS QDs without ZnF₂ (left half) and with ZnF₂ (right half). (d) HRTEM image^[2].

Comparative Properties of Selected Inorganic Fluorides

Fluoride Compound	Key Applications	Stability	Solubility	Special Properties
NaF	Water fluoridation, dental care	High	High	Antibacterial properties
AlF3	Aluminum production, ceramics	High	Low	Electrolyte additive
BaF2	Optical coatings, infrared optics	High	Low	High transparency in IR range
BF3	Catalysis, organic synthesis	Moderate	Reacts with water	Strong Lewis acid
LiPF6	Lithium-ion batteries	Moderate	Soluble in organic solvents	Electrolyte component

Inorganic fluorides are indispensable in various industries such as metallurgy, electronics, pharmaceuticals, and environmental applications. Alfa Chemistry provides numerous high-quality inorganic fluorides specifically designed for industrial and research purposes.

References

1. Achary S. N., et al. (2021). “Synthesis of Inorganic Fluorides.” Handbook on Synthesis Strategies for Advanced Materials. pp 93-135.
2. Li B., et al. (2024). “Over 20% external quantum efficiency in near-infrared quantum dot light-emitting diodes by using photo-crosslinked hole-transport layers.” PREPRINT (Version 1) available at Research Square.