Hydrofluoric acid (HF) dissolves glass, concrete, many metals, most ceramics, and even bone. What makes it unusual among acids is its ability to attack silicon-based materials that shrug off other strong acids, plus its fluoride ions penetrate deep into organic tissue in ways no other common acid can. Here’s a closer look at what HF breaks down and why.
Glass, Quartz, and Silicate Materials
The most well-known property of hydrofluoric acid is its ability to dissolve glass. Glass is primarily silicon dioxide, and HF breaks it apart through a multistage reaction. First, fluoride ions attack the silicon atoms in the glass surface. Then additional fluoride bonds to the silicon, eventually producing silicon tetrafluoride and water. The fluoride ion reacts with silicon dioxide 2,000 to 3,000 times faster than the intact HF molecule does, which is why even dilute solutions eat through glass quickly.
This reactivity extends to every material containing silica: quartz, concrete, ceramic tiles, fiberglass, and natural silicate minerals like feldspar and mica. In geology and environmental labs, HF is the only acid that can fully dissolve soil and rock samples for chemical analysis. Without it, silicate grains remain stubbornly intact no matter how much nitric or hydrochloric acid you throw at them. Even quartz powder, one of the most chemically resistant common minerals, dissolves when digested with HF under microwave heating.
Metals HF Attacks (and Those It Doesn’t)
HF corrodes many common metals, but not all of them equally. Oak Ridge National Laboratory tested several alloys in HF and found dramatic differences. Stainless steel 316, a workhorse alloy in many industries, fared the worst. Coupons of it lost roughly 60% of their mass in four weeks, with corrosion rates of 1,600 to 1,800 mils per year during the first week. That’s aggressive enough to eat through typical equipment walls in months.
A nickel-chromium alloy (alloy 600) held up somewhat better, averaging 128 mils per year over four weeks but turning completely black from vapor exposure. Gold plating offered only temporary protection: one gold-plated coupon lost most of its plating by day four. Nickel-copper alloy (alloy 400) performed much better, averaging 29 mils per year. But the clear winner was a nickel-molybdenum-chromium alloy (C-276), which ended testing at just 5 mils per year and appeared virtually unaffected.
Temperature matters enormously. Projections to 200°C estimated that the nickel-copper alloy would corrode at nearly ten times the rate of C-276. So while several metals can tolerate brief HF contact at room temperature, only specialized high-nickel alloys survive prolonged exposure, especially at elevated temperatures. Notably, HF does not dissolve lead, platinum, or gold in bulk form under normal conditions, which is why platinum crucibles are sometimes used in HF chemistry.
How It Dissolves Bone and Tissue
What makes HF uniquely dangerous compared to other acids is the fluoride ion’s ability to penetrate deep into living tissue. According to the CDC, fluoride passes through intact skin and binds to calcium and magnesium inside cells. This destroys cells directly and strips calcium from bone, a process called demineralization. The result is tissue death that extends far beneath the skin surface, well beyond what you’d expect from an acid burn.
The systemic effects can be even more dangerous than the local ones. As fluoride locks up calcium in the bloodstream, the resulting calcium deficiency can trigger muscle spasms, weakened heart contractions, and cardiovascular collapse. At the same time, potassium levels rise, which can cause fatal heart rhythm disturbances. Concentrated solutions (50% or higher) cause immediate pain and visible tissue destruction, but dilute solutions below 20% are deceptively dangerous. Pain and redness may not appear for up to 24 hours, during which the fluoride is already deep in the tissue doing damage.
Plastics and Rubbers: What Survives
Because HF destroys glass, it has to be stored in plastic containers. Polyethylene (PE) and polypropylene are the standard choices, as HF doesn’t react with their carbon-hydrogen molecular structure. PTFE (the material in Teflon) is also fully resistant and is used for labware in analytical chemistry. PVC and neoprene resist HF well enough for protective gloves.
Rubber, on the other hand, is attacked by HF, especially formulations containing silica fillers. Many coatings and sealants also break down on contact. The general rule: if a material contains silicon or silica in any form, HF will find it and react with it.
Semiconductor Manufacturing
HF’s precision in dissolving silicon dioxide is the backbone of computer chip manufacturing. Every silicon wafer naturally grows a thin oxide layer when exposed to air, and that layer must be removed at specific steps during production. A quick dip in 5% HF strips this native oxide in about 30 seconds, leaving a clean, water-repelling silicon surface ready for the next processing step.
For thicker oxide layers, concentrated 40% HF removes material at roughly 833 nanometers per minute. When more control is needed, engineers use a buffered oxide etch (BOE), which is HF mixed with ammonium fluoride. This slows the etch rate to 30 to 80 nanometers per minute, allowing precise removal of oxide without damaging delicate photoresist patterns on the wafer. Critically, HF etches silicon dioxide selectively. It attacks pure silicon and silicon nitride only at extremely slow rates, making it possible to remove one layer while leaving the others intact.
What HF Cannot Dissolve
For all its destructive reach, HF has clear limits. It does not dissolve polyethylene, polypropylene, or PTFE plastics. Wax and paraffin are also unaffected. Among metals, high-nickel alloys like C-276 resist it well, and noble metals like platinum hold up under normal laboratory conditions. Pure silicon and silicon nitride survive HF exposure with minimal damage, which is exactly why they’re useful as structural layers in chip manufacturing while the oxide around them gets etched away.
Carbon-based materials without silica fillers, including graphite and certain carbon composites, also resist HF. The acid’s superpower is highly specific: it targets silicon-oxygen bonds and calcium in biological tissue. Materials built on different chemistry can often withstand it.