Hydrofluoric acid reactivity

Chemical Reactivity - Reactivity with Water Dissolves and forms a weak solution of hydrofluoric acid Reactivity with Common Materials In presence of moisture will corrode glass, cement and most metals. Flammable hydrogen gas may collect in enclosed spaces Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water, rinse with dilute solution of sodium of sodium bicarbonate or soda ash Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Chemical Reactivity - Reactivity with Water Dissolves and forms dilute solution of hydrofluoric acid Reactivity with Common Materials May corrode glass, cement and most metals Stability During... 

Hydrofluoric Acid Reactivity with Bone. Students are presented with an exposure story regarding hydrofluoric acid. A description of skin absorption, lack of burning sensation and bone composition (calcium carbonate) is provided. Students are then asked to balance a simple neutralization reaction between the acid and the bone suing proper nomenclature and stoichiometry. Discussion of why hydrofluoric is not rated as corrosive is facilitated, as well as a prediction of what will happen at the tissue level (bone) when this exposure occurs. MSDSs are a good source of reactivity information for this exercise. 

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... 

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. 

Two well-known salts of ammonia (qv) are the normal ammonium fluoride [12125-01 -8] NH F, and ammonium bifluoride [1341 -49-7] NH4HF2 the latter is sometimes named ammonium acid, or hydrogen difluoride. Much of the commercial interest in the ammonium fluorides stems from their chemical reactivity as less ha2ardous substitutes for hydrofluoric acid. 

Properties. Lithium fluoride [7789-24-4] LiF, is a white nonhygroscopic crystaUine material that does not form a hydrate. The properties of lithium fluoride are similar to the aLkaline-earth fluorides. The solubility in water is quite low and chemical reactivity is low, similar to that of calcium fluoride and magnesium fluoride. Several chemical and physical properties of lithium fluoride are listed in Table 1. At high temperatures, lithium fluoride hydroly2es to hydrogen fluoride when heated in the presence of moisture. A bifluoride [12159-92-17, LiF HF, which forms on reaction of LiF with hydrofluoric acid, is unstable to loss of HF in the solid form. 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

The reactivity of titanium dioxide toward acid is dependent on the temperature to which it has been heated. Freshly precipitated titanium dioxide is soluble iu concentrated hydrochloric acid. However, titanium dioxide that has been heated to 900°C is almost iusoluble iu acids except hot concentrated sulfuric, iu which the solubiUty may be further iucreased by the addition of ammonium sulfate to raise the boiling poiut of the acid, and hydrofluoric acid. Similarly, titanium dioxide that has been calciued at 900°C is almost iusoluble iu aqueous alkahes but dissolves iu molten sodium or potassium hydroxide, carbouates, or borates. 

It is common practice to refer to the molecular species HX and also the pure (anhydrous) compounds as hydrogen halides, and to call their aqueous solutions hydrohalic acids. Both the anhydrous compounds and their aqueous solutions will be considered in this section. HCl and hydrochloric acid are major industrial chemicals and there is also a substantial production of HF and hydrofluoric acid. HBr and hydrobromic acid are made on a much smaller scale and there seems to be little industrial demand for HI and hydriodic acid. It will be convenient to discuss first the preparation and industrial uses of the compounds and then to consider their molecular and bulk physical properties. The chemical reactivity of the anhydrous compounds and their acidic aqueous solutions will then be reviewed, and the section concludes with a discussion of the anhydrous compounds as nonaqueous solvents. 

Attention is drawn to the extremely inert character of Teflon, which is so lacking in reactivity that it is used as the liner in pressure digestion vessels in which substances are decomposed by heating with hydrofluoric acid, or with concentrated nitric acid (see Section 3.31). 

Columbium (also known as niobium) and tantalum metals are produced from purified salts, which are prepared from ore concentrates and slags resulting from foreign tin production. The concentrates and slags are leached with hydrofluoric acid to dissolve the metal salts. Solvent extraction or ion exchange is used to purify the columbium and tantalum. The salts of these metals are then reduced by means of one of several techniques, including aluminothermic reduction, sodium reduction, carbon reduction, and electrolysis.19-21 Owing to the reactivity of these metals, special techniques are used to purify and work the metal produced. 

Retarded acids are primarily applicable to sandstone acidizing. Fluoroboric acid slowly hydrolyzes to form the more reactive hydrofluoric acid (109,110). The time required for this hydrolysis process may enable deeper penetration of the HF into the formation although one report contradicts these findings (111). Na TiF and similar salts also slowly generate HF in acid media (112). Phosphorous acid addition to hydrochloric acid has been used to reduce the HC1 reaction rate with limestone (113). 

The fiber bundles used for the electronic nose platform are polished and chemically etched with hydrofluoric acid to create an ordered array of micrometer sized wells on the tip of the fiber (Figure 3)4. The etching process takes advantage of the difference in reactivity of the core and the... 

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