Hydrofluoric acids

Fluoric acid.—This acid is obtained by the action of oil of vitriol on fluoride of calcium (fluor spar). The powdered mineral is gently heated with the acid in a retort of lead, silver, or platinum, as glass and porcelain are destroyed by the process, and the acid condensed in a receiver of the same metal, surrounded by a freezing mixture. The action is thus expressed— 

The acid appears as a very volatile liquid, strongly acid and corrosive, fuming in the air. A drop on the skin bums it like red-hot iron, and causes a painful sore, not easily healed. Even the vapours, if they are allowed to come much in contact with the hand, are apt to cause painful sores under the nails. The acid, even when much diluted, or in the form of vapour, rapidly corrodes glass, and may be used for etching on glass plates. 

With metallic oxides, hydrofluoric acid gives rise to water and metallic fluorides HF - - MO = HO -F MF. The afiinity of fluorine for silicon is such, that hydrofluoric acid decomposes all silicious compounds and this explains its corrosive action on glass and porcelain. Berzelius has employed this acid as a means of analysing silicious minerals. As the fluoride of silicium is gaseous, any such mineral, if digested with hydrofluoric acid, soon loses all its silica, and is dissolved, so that the other ingredients may be determined. 

No compound of fluorine with any of the preceding elements, except hydrogen, is yet known. Its compounds with silicon, boron, and the metals will come to be described in their natural places. 

Sulphur occurs, especially in volcanic districts, in a state of purity, often crystallised. It is also found in combination with o gen, as sulphuric acid, in gypsum, heavy spar, and many other minerals, with hydrogen as sulphuretted hydrogen, or mineral waters, and above all with metals, most abundantly with lead, iron, copper, c. c. Finally, it is an essential ingredient of vegetable and animal fibrine, albumen, and caseine, and as such is indispensable to vegetation and to animal life. Some essential oils, such as those of mustard, of horse-radish, of assafcetida, c., contain a large proportion of sulphur. 

Hydrofluoric acid is the most basic common precursor of most fluorochemicals. Aqueous hydrofluoric acid is prepared by reaction of sulfuric acid with fluorspar (CaF2). Because HF etches glass with formation of silicon tetrafluoride, it must be handled in platinum, lead, copper. Monel (a Cu-Ni alloy developed during the Manhattan Project), or plastic (e.g. polyethylene or PTFE) apparatus. The azeotrope contains 38 % w/w HF and it is a relatively weak acid (pfC 3.18, 8 % dissociation), comparable with formic acid. Other physicochemical properties of hydrofluoric acid are listed in Table 1.2. 

Anhydrous hydrofluoric acid (aHF) is obtained by heating Fremy s Salt (KF HF) as a liquid, boiling at 19.5 °C. Similar to water, aHF has a liquid range of approximately 100 K and a dielectric constant e of 83.5 (at 0°C). Associated by strong hy- 

The dark side of hydrofluoric acid is its toxicity and corrosiveness. Aqueous and anhydrous HF readily penetrate the skin, and, because of its locally anesthetizing effect, even in very small quantities can cause deep lesions and necroses [4, 5]. An additional health hazard is the systemic toxicity of fluoride ions, which interfere strongly with calcium metabolism. Resorption of HF by skin contact (from a contact area exceeding 160 cm ), inhalation, or ingestion leads to hypocalcemia with very serious consequences, for example cardiac arrhythmia. 

The most effective, specific antidote to HF and inorganic fluorides is calcium gluconate, which acts by precipitating fluoride ions as insoluble CaFj. After inhalation of HF vapor, treatment of the victim with dexamethasone aerosol is recommended, to prevent pulmonary edema. Even slight contamination with HF must always be taken seriously, and after the necessary first-aid measures a physician should be consulted as soon as possible. 

It should also be kept in mind that some inorganic (e. g. C0F3) and organic fluorinated compounds (e.g. pyridrne-HF, NEtj-lHF, DAST) can hydrolyze on contact with skin and body fluids, liberating hydrofluoric acid with the same adverse consequences. 

Hydrofluoric acid (melting point -83.1°C, boiling point 19.5°C) is produced by treating fluorspar (CaF2) with 20% oleum and heating it with sulfuric acid in a horizontal rotating drum. 

Hydrofluoric acid is used for manufacture of fluorocarbons, including fluoropolymers, chlorofluorocarbons chemical intermediates including fluoroborates, surfactants, herbicides, and electronic chemicals aqueous hydrofluoric acid petroleum alkylation and uranium processing. 

Hydrogen (boiling point -252.8°C) is primarily manufactured by steamreforming natural gas (CH4) or hydrocarbons (C H2h+2). 

A variety of low-molecular-weight hydrocarbons can be used as feedstock in the steam-reforming process. The reaction occurs in two separate steps reforming and shift conversion. 

The reforming step makes a hydrogen-carbon monoxide mixture (synthesis gas) that is used to produce a variety of other chemicals. 

Anhydrous hydrogen fluoride has a very good solubility in water [8]. The resulting hydrofluoric acid is transported in drums, tank cars and rubber-lined railway tank wagons. Typical HF concentrations in water for technical applications are between 

Hydrofluoric acid is used to clean cast metals [9], copper and brass [10], It removes efflorescence from brick and stone and sand particles from metallic castings. Frosted daily products like clouded electric bulbs [11], [12] or other etched glass like polished crystal glass [13], [14], [15] and enamels [20] are well known to everybody. 

For the etching of silicon in photovoltaic and semiconductor industry [16], [17], [18] especially purified e-grade material is needed. Of minor importance is the decomposition of cellulose [19], the galvanizing of iron, the etching of porosity into ceramics [21], [22], specialty metal manufacture [24] as well as the use in laundry mixtures to substitute oxalic acid, in oil well acid stimulation [25], [26] and in the flotation of ores [27]. 

The manufacture of metal fluorides [23] by fluoride precipitation reactions between HF and metal oxides, -hydroxides or -carbonates is of great importance for Solvay Fluor. In 

Solvay Fluor s Bad Wimpfen plant the KHF2 and NaF processes consume hydrofluoric acid in amounts of several hundred tons per month. 

SERIOUS RISK OF POISONING BY INHALATION, SWALLOWING, OR SKIN CONTACT CAUSES SEVERE BURNS 

Colorless, fuming liquid with pungent smell, commonly available in concentrations of 47% and 53% HF.1 2 

Potassium Permanganate. Addition of solid potassium permanganate to concentrated hydrofluoric acid (60-90%) is violently exothermic.3 Sodium. Reacts explosively with sodium.4 

Gas severely irritates the respiratory system and eyes. It irritates the skin and painful burns may develop after an interval. The liquid causes severe, painful burns on contact with all body tissues. Swallowing results in immediate and severe internal irritation and damage. The treatment of hydrofluoric acid burns has been described.5 Prevent inhalation of gas. Prevent contact with skin, eyes, and clothing.2 TLV-STEL-C (as F) 3 ppm (2.6 mg/m3).6 

Instruct others to maintain a safe distance. Wear self-contained breathing apparatus, eye protection, butyl rubber gloves, and a laboratory coat. Cover the spill with a 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. When the hydrofluoric acid has been absorbed, scoop the mixture into a plastic pail and transport to the fume hood. Slowly add to a pail of cold water. Add an excess of calcium carbonate or calcium hydroxide. Let the precipitate settle for 24 hours. Decant the solution to the drain. Allow the solid residue (calcium fluoride and bentonite) to dry and package for disposal in accordance with local regulations.7,8 

Reactions with cyanides and sulfides generate hydrogen cyanide and hydrogen sulfide, respectively. Reaction with acetylene produces ethylene dichloride. Many chlorinated toxic compounds, such as dibenzodiox-ins and dibenzofurans, may be formed from HCl and phenol. However, such reactions may occur only at very high temperatures [550°C (1022°F)] during the incineration of wastes (Eklund et al. 1986) and not from inadvertent mixing of HCl and phenol. 

Hydrochloric acid or HCl gas is noncombustible. Contact of acid with alkali metals such as sodium or potassium can result in explosion. It reacts violently with alkaline-earth metals. Hydrogen is produced from the reaction of metals with HCl. Phosphine (flammable) is generated when a metal phosphide reacts with the acid. Its reaction with caustic alkalies is exothermic and can be vigorous to violent. Crowley and Block (1989) reported rupture of vessels resulting from the accidental introduction of HCl solution into hydrogen peroxide. 

Hydrogen chloride gas can ignite carbides of metals, alkali-metal silicides, and magnesium boride. Absorption of the gas over mercury sulfate above 125°C (257°F) can become violent (Mellor 1946, Suppl. 1956). 

Chlorine is generated when concentrated HCl reacts with oxidizing substances such as permanganates, chlorates, and dichromates  

EPA Designated Toxic Waste, RCRA Waste Number U134 DOT Label Corrosive Material, UN 1052, UN 1790 Formula HE MW 20.01 CAS [7664-39-3] Composition The acid is an aqueous solution of hydrogen fluoride gas, commercially available in varying strengths 47, 53, and 79% concentrations. 

Ga were obtained with low levels of 68(je breakthrough. At this 

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

In the area of bifunctional chelates, the method of Krejcarek and Tucker (J ) has been utilized to attach galllum-68 to proteins (51). In this approach DTPA is coupled to proteins by the formation of an amide bond. It has been shown that 

Ga-protelns can be formed and that the labeled protein is stable for a time period of several hours. The same type of linkage has also been used to attach galllum-68 to human serum microspheres (51). 

When galllum-67 is injected into the bloodstream as either chloride or citrate, it rapidly becomes bound to serum proteins, especially transferrin (5 53 54). Although the gallium-transferrin interaction is weaker than that of iron and 

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Other kinds of liquid-liquid equilibria are encountered in processes such as alkylation, where anhydrous hydrofluoric acid (HF) is partially soluble in hydrocarbons. 

All silicon compounds on oxidation yield silica or silicates these are difficult to detect but silica (given by silicates after acid treatment) is insoluble in all acids except hydrofluoric acid. 

The ability to form hydrogen bonds explains the formation of complex ions such as HFJ and HjFj when a fluoride salt, for example potassium fluoride, is dissolved in aqueous hydrofluoric acid ... 

Anhydrous hydrogen fluoride (as distinct from an aqueous solution of hydrofluoric acid) does not attack silica or glass. It reacts with metals to give fluorides, for example with heated iron the anhydrous iron(II) fluoride is formed the same product is obtained by displacement of chlorine from iron(II) chloride ... 

In addition to the abnormal properties already discussed, aqueous hydrofluoric acid has the properties of a typical acid, attacking metals with the evolution of hydrogen and dissolving most metallic hydroxides and carbonates. 

The complexes of manganese(III) include [Mn(CN)g] (formed when manganesefll) salts are oxidised in presence of cyanide ions), and [Mnp5(H20)] , formed when a manganese(II) salt is oxidised by a manganate(VII) in presence of hydrofluoric acid ... 

If it is desired to employ fluoboric acid HBF4, it can be prepared by adding 100 g. of A.R. boric acid in small proportions to 325 g. of A.R. hydrofluoric acid (40 p>er cent. HF) cooled in ice the hydrofluoric acid is contained in a Bakelite beaker, a beaker coated with wax or in a lead vessel. A simple container may also be prepared by cutting of the neck of the wax bottle (in which the hydrofluoric acid is supplied) with a large e.g., a butcher s ) knife which has been slightly warmed. One-third of the above solution should be employed in the preparation. Handle unth great care. 

The fluoboric acid may be prepared by adding 92 g. of A.R. boric acid slowly and with constant stirring to 250 g. of hydrofluoric acid (40-48 per cent.) in a copjier, lead or a waxed-lined beaker. A lead rod may be used for stirring. All operations should be carried out in a fume cupboard. 

Fluorine and its compounds are used in producing uranium (from the hexafluoride) and more than 100 commercial fluorochemicals, including many well known high-temperature plastics. Hydrofluoric acid etches the glass of light bulbs, etc. Fluorochlorohydrocarbons are extensively used in air conditioning and refrigeration. 

Tantalum is a gray, heavy, and very hard metal. When pure, it is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals such as aluminum. Tantalum is almost completely immune to chemical attack at temperatures below ISOoC, and is attacked only by hydrofluoric acid, acidic solutions containing the fluoride ion, and free sulfur trioxide. Alkalis attack it only slowly. At high temperatures, tantalum becomes much more reactive. The element has a melting point exceeded only by tungsten and rhenium. Tantalum is used to make a variety... 

Until the late 1950s chemists generally considered mineral acids, such as sulfuric, nitric, perchloric, and hydrofluoric acids, to be the strongest acid systems in existence. This has changed considerably as extremely strong acid systems—many billions or even trillions of times stronger than sulfuric acid—have been discovered. 

Nitronium tetrafluoroborate was first prepared by adding a mixture of anhydrous hydrofluoric acid and boron trifluoride to a solution of dinitrogen pentoxide in nitromethane. Nitric acid can be used in place of dinitrogen pentoxide, and by replacing boron trifluoride by other Lewis-acid fluorides Olah and his co-workers prepared an extensive series of stable nitronium salts. ... 

Aluminous and siliceous residues A 2% hydrofluoric acid solution followed by concentrated sulfuric acid rinse immediately with distilled water followed by a few milliliters of acetone. Repeat rinsing until all trace of acid is removed. 

Hydrofluoric acid, H2F2—48% solution use as purchased, and keep in the special container. Hydrogen peroxide, H2O2—3% solution use as purchased. 

Ammonia, anhydrous Mercury, halogens, hypochlorites, chlorites, chlorine(I) oxide, hydrofluoric acid (anhydrous), hydrogen peroxide, chromium(VI) oxide, nitrogen dioxide, chromyl(VI) chloride, sulflnyl chloride, magnesium perchlorate, peroxodisul-fates, phosphorus pentoxide, acetaldehyde, ethylene oxide, acrolein, gold(III) chloride... 

This is a reasonable result since we expect the concentration of hydrofluoric acid s conjugate base, F , to increase as the pH increases. Similar reasoning shows that the concentration of HE exceeds that of F when... 

Hydrofluoric acids Hydrofluoroboric acid Hydrofluorocarbon Hydrofluorocarbons... 

FLUORINECOMPOUNDS,ORGANIC - FLUORINATED ALIPHATIC COMPOUNDS] (Vol 11) -for hydrofluoric acid burns [FLUORINE COMPOUNDS, INORGANIC - ALDTONIUT (Volll)... 

In 1973 the Semiconductor Equipment and Materials Institute (SEMI) held its first standards meeting. SEMI standards are voluntary consensus specifications developed by the producers, users, and general interest groups in the semiconductor (qv) industry. Examples of electronic chemicals are glacial acetic acid [64-19-7] acetone [67-64-17, ammonium fluoride [12125-01 -8] and ammonium hydroxide [1336-21 -6] (see Ammonium compounds), dichloromethane [75-09-2] (see Cm.OROCARBONSANDcm.OROHYDROCARBONs), hydrofluoric acid [7664-39-3] (see Eluorine compounds, inorganic), 30% hydrogen peroxide (qv) [7722-84-1] methanol (qv) [67-56-1] nitric acid (qv) [7697-37-2] 2-propanoI [67-63-0] (see Propyl alcohols), sulfuric acid [7664-93-9] tetrachloroethane [127-18-4] toluene (qv) [108-88-3] and xylenes (qv) (see also Electronic materials). 

Water. Fluorine reacts with water to form hydrofluoric acid [7664-39-3] HF, and oxygen difluoride [7783 1-7] OF2. In dilute (<5%) caustic solutions, the reaction proceeds as follows ... 

Raw Material. The principal raw material for fluorine production is high purity anhydrous hydrofluoric acid. Each kilogram of fluorine generated requires ca 1.1 kg HE. Only a small portion of the hydrofluoric acid produced ia the United States is consumed ia fluorine production. The commercial grade is acceptable for use as received, provided water content is less than 0.02%. Typical specifications for hydrofluoric acid are... 

Price. The 1993 U.S. price for fluorine in cylinders was 109/kg for 2.2 kg and 260/kg for 0.7 kg cylinders. The price in large volumes is determined by (/) the price of hydrofluoric acid (2) power costs, ca 4.5 kWh electricity is required for each kilogram of fluorine produced (J) labor costs (4) costs to maintain and rebuild cells and (5) amortization of fixed capital. Fluorine production is highly capital intense. In addition, purification, compression, packaging, and distribution in cylinders increase the cost significantly. 

Fluorine, the most reactive element known, is a dangerous material but may be handled safely using proper precautions. In any situation where an operator may come into contact with low pressure fluorine, safety glasses, a neoprene coat, boots, and clean neoprene gloves should be worn to afford overall body protection. This protection is effective against both fluorine and the hydrofluoric acid which may form from reaction of moisture in the air. 

Burns. Skin bums resulting from contact with pure fluorine gas are comparable to thermal bums and differ considerably from those produced by hydrogen fluoride (114). Fluorine bums heal much more rapidly than hydrofluoric acid bums. 

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