Hydrofluoric-nitric acids

The elements of Group 5 are in many ways similar to their predecessors in Group 4. They react with most non-metals, giving products which are frequently interstitial and nonstoichiometric, but they require high temperatures to do so. Their general resistance to corrosion is largely due to the formation of surface films of oxides which are particularly effective in the case of tantalum. Unless heated, tantalum is appreciably attacked only by oleum, hydrofluoric acid or, more particularly, a hydrofluoric/nitric acid mixture. Fused alkalis will also attack it. In addition to these reagents, vanadium and niobium are attacked by other hot concentrated mineral acids but are resistant to fused alkali. 

Tungsten also forms hard, crystalline refractory borides, such as WB2, W2B and WB when heated with boron in an electric furnace. Tungsten also forms a group of silicides, hard refractory compounds of compositions WSi2, WSis and W2Si3. These silicides are attacked by hydrofluoric-nitric acid mixture or by fused alkalies. 

An older Be method, P CAM 121, discusses air, dust, ore, and swipe samples. More vigorous digestion procedures such as hydrofluoric nitric acid for filters or potassium fluoride sodium pyrosulfate fusion and nitric acid digestion for ores. A nitrous oxide/acetylene flame is suggested for this method rarely used (Table HI). 

Whole ash analyses were performed using flameless atomic absorption spectrophotometric techniques. The lithium metaborate—nitric acid fusion techniques was used in the preparation of the sample for analysis of Ca, Mg, Na and K. Hydrofluoric—nitric acid dissolution was employed in the preparation of the samples for measurement of Fe, Mn, Cu, Pb, Zn and Cd. 

Properties BIk. to gray cryst. or dk. brn. powd. (amorphous form) pract. insol. in water at. no. 14 m.w. 28.086 dens. 2.330 (20/4 C) m.p. 1420 C b.p. 2680 C hardness (Mohs) 7.0 sp. heat 0.162 cal/g/C dielec, const. 12 Toxicology ACGIH TLV/TWA 10 mg/m (total dust), when toxic impurities are not present LD50 (oral, rat) 3160 mg/kg mod. toxic by ing. nuisance dust eye irritant TSCA listed Precaution DOT Flamm. solid violent reactions with alkali carbonates, oxidants, etc. heated, reacts with water to produce H2 can react with oxidizers attacked by hydrofluoric or hydrofluoric/nitric acids burns in fluorine, chlorine... 

Isotropic etching of silicon is done with an aqueous mixture of HF-I-HNO3-F CH3COOH (hydrofluoric, nitric acid, and acetic acid). Often, the acetic acid is omitted. The etch rates are very high at room temperature 940 pm/min with 20-46% HNO3 (69% HNO3,31% H2O) complemented by H F (49% HF, 51% H2O). The quality of the silicon surface produced will depend on the solution used. Smoother surfaces are achieved with a higher proportion of nitric acid and a lower proportion of acetic add. 

Hydrofluoric-nitric acid 1-HF room rapid Nitric acid. - 252(122) <5.0(<127)... 

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. ... 

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). 

Hafnium is readily soluble in hydrofluoric acid and is slowly attacked by concentrated sulfuric acid. Hafnium is unaffected by nitric acid in all concentrations. It is resistant to dilute solutions of hydrochloric acid and sulfuric acid. Hafnium is attacked by all mineral acids if traces of fluorides are present. Hafnium is very resistant to attack by alkaUes. 

Lead Fluoride. Lead difluoiide, Pbp2, is a white oithorhombic salt to about 220°C where it is transformed into the cubic form some physical properties ate given in Table 1. Lead fluoride is soluble in nitric acid and insoluble in acetone and ammonia. It is formed by the action of hydrofluoric acid on lead hydroxide or carbonate, or by the reaction between potassium fluoride and lead nitrate. 

Direct attack by hot 70—80 wt % hydrofluoric acid, sometimes with nitric acid (qv), is effective for processiag columbites and tantalo-columbites. Yields are >90 wt%. This method, used in the first commercial separation of tantalum and niobium, is used commercially as a lead-in to solvent extraction procedures. The method is not suited to direct processiag of pyrochlores because of the large alkaU and alkaline-earth oxide content therein, ie, ca 30 wt %, and the corresponding high consumption of acid. 

Acid mixtures containing nitric acid and a strong acid, eg, sulfuric acid, perchloric acid, selenic acid, hydrofluoric acid, boron trifluoride, or an ion-exchange resin containing sulfonic acid groups, can be used as the nitrating feedstock for ionic nitrations. These strong acids are catalysts that result in the formation of nitronium ions, NO" 2- Sulfuric acid is almost always used industrially since it is both effective and relatively inexpensive. 

Acid Treatment. The treatment of petroleum products with acids has been in use for a considerable time in the petroleum industry. Various acids such as hydrofluoric acid, hydrochloric acid, nitric acid, and phosphoric acid have been used in addition to the most commonly used sulfuric acid, but in most instances there is Httie advantage in using any acid other than sulfuric. 

Titanium carbide is resistant to aqueous alkaU except in the presence of oxidising agents. It is resistant to acids except nitric acid, aqua regia, and mixtures of nitric acid with sulfuric or hydrofluoric acid. In oxygen at 450°C, a nonprotecting anatase coating forms. The reaction... 

Hydrolysis of solutions of Ti(IV) salts leads to precipitation of a hydrated titanium dioxide. The composition and properties of this product depend critically on the precipitation conditions, including the reactant concentration, temperature, pH, and choice of the salt (46—49). At room temperature, a voluminous and gelatinous precipitate forms. This has been referred to as orthotitanic acid [20338-08-3] and has been represented by the nominal formula Ti02 2H20 (Ti(OH). The gelatinous precipitate either redissolves or peptizes to a colloidal suspension ia dilute hydrochloric or nitric acids. If the suspension is boiled, or if precipitation is from hot solutions, a less-hydrated oxide forms. This has been referred to as metatitanic acid [12026-28-7] nominal formula Ti02 H2O (TiO(OH)2). The latter precipitate is more difficult to dissolve ia acid and is only soluble ia concentrated sulfuric acid or hydrofluoric acid. 

Qua.driva.Ient, Zirconium tetrafluoride is prepared by fluorination of zirconium metal, but this is hampered by the low volatility of the tetrafluoride which coats the surface of the metal. An effective method is the halogen exchange between flowing hydrogen fluoride gas and zirconium tetrachloride at 300°C. Large volumes are produced by the addition of concentrated hydrofluoric acid to a concentrated nitric acid solution of zirconium zirconium tetrafluoride monohydrate [14956-11-3] precipitates (69). The recovered crystals ate dried and treated with hydrogen fluoride gas at 450°C in a fluid-bed reactor. The thermal dissociation of fluorozirconates also yields zirconium tetrafluoride. 

Zirconium tetrafluoride dissolves in dilute acid without hydrolysis, and can be recovered as the monohydrate [14956-11-3] by crystallization from nitric acid solutions. If the solution is acidified with hydrofluoric acid, ZtF 3H20 [14517-16-9] crystallizes at 10—30 wt % HF HZtF 20 [18129-16-9] crystallizes at 30—35 wt % HF, and at higher HF concentrations H2ZtF -2H20 [12021 -95-3] can be recovered. 

Nitric acid oxidizes antimony forming a gelantinous precipitate of a hydrated antimony pentoxide (8). With sulfuric acid an indefinite compound of low solubihty, probably an oxysulfate, is formed. Hydrofluoric acid forms fluorides or fluocomplexes with many insoluble antimony compounds. Hydrochloric acid in the absence of air does not readily react with antimony. Antimony also forms complex ions with organic acids. 

BeryUium reacts readUy with sulfuric, hydrochloric, and hydrofluoric acids. DUute nitric acid attacks the metal slowly, whereas concentrated nitric acid has Httle effect. Hot concentrated alkaUes give hydrogen and the amphoteric beryUium hydroxide [13327-32-7] Be(OH)2. Unlike the aluminates, the beryUates are hydrolyzed at the boU. 

Hydrobromic, hydrochloric, hydrofluoric and hydroiodic acids Methacrylic acid Nitric acid... 

Mineral acid Hydrobromic acid Hydrochloric acid Hydrofluoric acid Nitric acid Sulphuric acid... 

Aqueous hydrofluoric acid catalyzes such reactions as nitration and oxidation. Thus anthraquinone can be nitrated easily with nitric acid in 80-98% aqueous hydrofluoric acid [10]... 

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