Hydrogen fluoride uses by industry, and why the use, not the name, sets the grade

A refinery topping up its alkylation unit and a wafer fab ordering 49% electronic-grade acid for oxide etch can send the same line on a request for quotation (RFQ): hydrofluoric acid, CAS 7664-39-3. The refinery needs anhydrous hydrogen fluoride; the fab needs a water solution held to trace-metal limits. Almost nothing else on the two orders should match. If your order names only the chemical, the supplier has to guess form, strength, impurity limits and paperwork, and all four follow the use, not the name.

What is hydrogen fluoride used for?

Hydrogen fluoride (HF) is used anhydrous as a refinery alkylation catalyst and as a fluorinating agent for fluorochemicals, aluminum fluoride and uranium fluorides. Hydrofluoric acid, its water solution, is used to etch and frost glass, etch oxide on silicon wafers, pickle stainless steel, purify quartz and extract metals, each use at its own strength.

The two names describe one compound in two forms. Hydrogen fluoride is the compound and the name of its anhydrous form, a colorless gas or fuming liquid that boils at 19.51 °C (HSDB). Hydrofluoric acid is the same compound dissolved in water. ICSC keeps separate cards for the two: 0283 for anhydrous hydrogen fluoride and 1777 for the 70% aqueous solution. The comparison of hydrofluoric acid and hydrogen fluoride sets the two forms side by side.

Broadly, the solutions are bought for what fluoride does to silica and metal oxides, and the anhydrous form for its acidity and as a fluorine source. HSDB calls anhydrous hydrogen fluoride one of the most acidic substances known, which suits its role as one of the two alkylation catalysts OSHA’s refining manual names. Formula and density data are in hydrofluoric acid properties, chemical formula and density; the sections below follow each use to the figure the sources give for it, where they give one.

Hydrofluoric acid uses, and the figure each source gives

Only a few industrial uses of hydrofluoric acid carry a figure in the sources cited here, and each figure describes something different. Haz-Map’s 49% is a use concentration with no stated basis, the buffered oxide etch application gives a feedstock strength by mass, OSHA’s alkylation figures describe acid inside a running unit, and the pickling figure is the dissolved iron at which a bath is renewed. Where the sources cited here give no figure, the table says so rather than guess.

The patent and patent-application figures are published data, not a recommendation to practice the compositions they claim.

Semiconductors: 49% acid, bought on its impurity profile

Haz-Map, quoted in PubChem from a semiconductor-industry safety handbook, gives 49% as the standard concentration at which HF is used as a wet etchant in semiconductor manufacturing. Many etch steps dilute the acid with high-purity water or buffer it with ammonium fluoride into buffered oxide etch, so one fab can run several strengths from the same purchase. Published patent application CN119685022A, for a buffered oxide etch with high etching uniformity, specifies its hydrofluoric acid feedstock as electronic grade at a mass concentration of 48-50%.

What the fab pays for is the impurity profile. Metal carried in the acid can stay behind on the wafer, so electronic grade is sold against limits for trace metals, anions and particles that the fab sets in its own qualification. Name the grade, strength, basis and the fab’s specification number, require a certificate of analysis (CoA) on every lot, and treat a change of production site as a requalification. The comparison of 49% and 70% hydrofluoric acid grades covers how the two strengths differ.

Glass, enamel and quartz: uses built on the silicon-oxygen bond

Fluoride breaks the silicon-oxygen bond. HSDB records that hydrofluoric acid dissolves silica, silicic acid and glass, and ICSC that it attacks glass, which is why one acid serves a frosting shop, a crystal polisher and a quartz plant. NIOSH’s emergency-response database lists etching, polishing and frosting glass among its uses, and HSDB’s use list adds etching enamel, removing sand from metal castings and the analytical determination of silicon dioxide.

The sources cited here give no working strength for frosting or polishing baths. Shops dilute a stock solution to their own recipe, so the RFQ names the stock: aqueous hydrofluoric acid at a stated percent HF by weight, with the assay tolerance the recipe can absorb. The glass etching and frosting post covers bath practice.

Quartz purification is on EPA’s list of aqueous uses. Patent CN110182814B, for high-purity quartz sand, describes a high-temperature, high-pressure step in which fluoride cuts the silicon-oxygen bond and frees aluminum sitting in silicon’s lattice sites, with other metal ions then removed as fluoride and sulfate salts. That is one patent’s step, not general practice, but the logic carries: the acid is there to take metals out, so the metals it brings in belong on the RFQ.

Stainless steel pickling: buy on assay, run on dissolved iron

EPA names stainless steel pickling and metal coatings among the uses of aqueous hydrofluoric acid. In a nitric-hydrofluoric pickling bath, the nitric acid is the oxidizer and the fluoride dissolves the oxide scale and holds the dissolved iron and chromium in solution, so the bath is spent by the metal it picks up. In the base process that patent JP3225880B2 describes, a continuous pickling method for stainless steel, the bath is renewed once dissolved iron exceeds 4% by weight.

That is a published patent condition, not a universal rule, but it frames the purchase: acid use follows the iron a line dissolves, so log the bath’s iron next to the acid bought. If the bath is made up by volume, a lot with a different assay moves its fluoride, so put an assay range on the order and check each CoA against it. The stainless steel and superalloy pickling post covers bath make-up.

Refining, fluorochemicals and uranium: the anhydrous uses

EPA’s notebook names anhydrous hydrogen fluoride as a catalyst in petroleum alkylation, a process that raises octane rating. OSHA’s refining manual describes alkylation as combining light olefins, mainly propylene and butylene, over a sulfuric or hydrofluoric acid catalyst to make alkylate, a premium, clean-burning blending stock; the other reactant is isobutane. In the HF process OSHA describes, the acid settles out of the hydrocarbon and returns to the reactor, while propane carrying trace HF goes to a stripper and is then defluorinated before storage.

Water is the variable to watch. OSHA’s manual advises keeping the in-process acid above 65% and moisture below 4% to prevent corrosion, and drying the unit thoroughly after any shutdown that used water. Those are conditions inside the unit, not a supply specification, but they set the purchase line: the water content of each anhydrous makeup lot. CAMEO’s reactivity profile adds that HF diluted below 65% with water may react with iron and steel to generate flammable hydrogen gas.

Two standard chemical dictionaries reproduced in PubChem list hydrogen fluoride gas as a fluorinating agent and a raw material for fluorine, aluminum fluoride, other fluorides and fluorine-containing plastics. Fluorocarbon refrigerants come from the same chemistry, with fluorine from HF replacing chlorine on a chlorinated feedstock.

EPA describes hydrogen fluoride in uranium processing, where uranium oxide refined from yellow cake is converted to uranium tetrafluoride ahead of further fluorination. The sources cited here give no strength for these uses, so the plant’s own specification for the anhydrous product goes on the RFQ.

What should the RFQ say for each use?

1. Form first. Anhydrous hydrogen fluoride or aqueous hydrofluoric acid. Both carry CAS 7664-39-3, so the CAS number alone does not tell a supplier which to quote.

2. Strength with its basis. State percent HF by weight on the order and require the same basis on the CoA.

3. Impurities by use. The fab’s limits for electronic grade; metal limits for high-purity quartz; an assay range for pickling and glass; a water limit for alkylation makeup.

4. One regulatory line the strength crosses. Under 40 CFR 68.130 (eCFR, 2026), hydrogen fluoride or hydrofluoric acid at 50% or greater is listed for EPA’s Risk Management Program with a threshold quantity of 1,000 lb. Coverage turns on how much HF at that strength a process holds, so no single lot’s certificate settles it. Anhydrous HF and the 70% solution sit inside the entry. A 48-50% specification reaches the line at its top end, so your EHS lead needs the assay on each CoA for the coverage determination.

5. Release reporting. Under 40 CFR 302.6(a), a release at or above the 100 lb (45.4 kg) CERCLA reportable quantity listed in 40 CFR 302.4, within any 24-hour period and other than a federally permitted release, requires immediate notification of the National Response Center (PubChem’s regulatory summary, 2026). For a release of a solution such as a 49% grade, read 40 CFR 302.6 with your regulatory lead before assuming the dilution keeps it below that quantity.

6. Safety documents before the first shipment. Take the hazard statements, exposure controls and first aid for each form and strength from the current Safety Data Sheet (SDS) for that exact grade, not from a uses summary; the safety section of the hydrofluoric acid product page points to the same document. Get the SDS to your EHS lead before the first lot arrives.

For qualifying the source itself, see hydrofluoric acid suppliers for industrial uses in the USA.

Methodology: uses and physical data come from PubChem’s hydrogen fluoride record (CID 14917) and the HSDB, Haz-Map, NIOSH, ATSDR, ICSC and CAMEO entries it aggregates, plus EPA’s Health Effects Notebook for hydrogen fluoride (2016), OSHA’s Technical Manual on petroleum refining processes, 40 CFR 68.130 on eCFR (2026), two granted patents (JP3225880B2 and CN110182814B) and one published patent application (CN119685022A). Statements without a figure are standard acid and materials chemistry.