Nonoxidizing acids

Hydrogen chloride and the aqueous solution, muriatic acid, find appHcation in many industries. In general, anhydrous HCl is consumed for its chlorine value, whereas aqueous hydrochloric acid is often utilized as a nonoxidizing acid. The latter is used in metal cleaning operations, chemical manufacturing, petroleum well activation, and in the production of food and synthetic mbber. 

Nickel—Copper. In the soHd state, nickel and copper form a continuous soHd solution. The nickel-rich, nickel—copper alloys are characterized by a good compromise of strength and ductihty and are resistant to corrosion and stress corrosion ia many environments, ia particular water and seawater, nonoxidizing acids, neutral and alkaline salts, and alkaUes. These alloys are weldable and are characterized by elevated and high temperature mechanical properties for certain appHcations. The copper content ia these alloys also easure improved thermal coaductivity for heat exchange. MONEL alloy 400 is a typical nickel-rich, nickel—copper alloy ia which the nickel content is ca 66 wt %. MONEL alloy K-500 is essentially alloy 400 with small additions of aluminum and titanium. Aging of alloy K-500 results in very fine y -precipitates and increased strength (see also Copper alloys). 

MetaUic arsenic is not readily attacked by water, alkaline solutions, or nonoxidizing acids. It reacts with concentrated nitric acid to form orthoarsenic acid [7778-39-4] H AsO. Hydrochloric acid attacks arsenic only in the presence of an oxidant. 

Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

A number of cement materials are used with brick. Standard are phenolic and furan resins, polyesters, sulfur, silicate, and epoxy-based materials. Carbon-filled polyesters and furanes are good against nonoxidizing acids, salts, and solvents. Silica-filled resins should not be used against hydrofluoric or fluosihcic acids. Sulfur-based cements are limited to 93°C (200°F), while resins can be used to about 180°C (350°F). The sodium silicate-based cements are good against acids to 400°C (750°F). 

Unplasticized polyvinyl chlorides (type I) have excellent resistance to oxidizing acids other than concentrated and to most nonoxidizing acids. Resistance is good to weak and strong alkahne materials. Resistance to chlorinated hydrocarbons is not good. Polyvinyhdene chloride, known as Saran, has good resistance to chlorinated hydrocarbons. 

Access of oxygen to steel surfaces during corrosion influences the wastage process in nonoxidizing acids. Fluid velocity can influence the amount of oxygen reaching the metal surface and, therefore, the corrosion rate. In deaerated acid solutions, steel corrosion rate is constant with fluid velocity. If dissolved oxygen is present, however, the corrosion rate is proportional to fluid velocity. 

Acidic attack on stainless steels differs from corrosion on nonsteunless steels in two important respects. First, nonoxidizing acid corrosion is usually more severe in deaerated solutions second, oxidizing acids attack stainless steel far less strongly than carbon steel. Hence, nitric acid solutions at low temperatures cause only superficial damage, but hydrochloric acid causes truly catastrophic damage. 

Alloys whose corrosion resistance depends on forming a protective oxide layer, such as stainless steel, are susceptible to severe localized attack when pH falls as a result of nonoxidizing acid excursions. How-... 

Corrosion involving nonoxidizing acids can be highly sensitive to flow. Thus regions of high flow and turbulence are often more severely attacked than more quiescent regions. Weirs, lips, and other flow obstructions increase turbulence and thus corrosion. Pipe elbows, tees, and joints are frequently attacked. Outer curves at pipe bends often are more severely wasted than inner bends. 

In the construction of plants, titanium with 0.2% Pd is mainly used. It can be employed with advantage in nonoxidizing acid media and also has increased resistance to pitting and crevice corrosion because of its more favorable pitting potential [40]. 

Furnace mortars are used over a very wide range of conditions. They are resistant to nonoxidizing acids, alkalis, and solvents up to 190°C. Carbon fillers should be used for conditions involving strong alkalis and compounds containing fluorine. 

When active, as in a pit or a crevice or when depassivated by mechanical damage of oxide film or chemical removal in nonoxidizing acid. 

Iron is quite reactive and corrodes in moist air. It is passivated by oxidizing acids such as HNO, (Section 12.14) but reacts with nonoxidizing acids, evolving hydrogen and forming iron(II) salts. The colors of these salts vary from pale yellow to dark green-brown. Iron(II) salts are readily oxidized to iron(III) salts. 

Chemical Resistance. TaC oxidizes rapidly in air at 800°C. Otherwise it is one of the most chemically stable carbides. It decarburizes when heated in hydrogen at very high temperatures (3000°C). It does not react with nitrogen up to 2700°C. It reacts at high temperature with Nb, Ta, and Mo. It is stable in nonoxidizing acids, but is attacked easily by HNO3 and HF and by melts of oxidizing salts. 

Nonoxidizing acids dissolve some insoluble sulfides, including MnS and CuS. The H+ ions react with S2 ions to form gaseous H2S, which bubbles out of the solutions. The Qsp of the sulfide becomes less than the... 

Coordination complexes of zinc, cobalt, and platinum show a stability similar to complexes involving copper and iron. They are stable to concentrated, nonoxidizing acids and bases. The fact that such complexes sublimate at 550 to 600°C without decomposing points to their extreme heat stability [7],... 

Milling the pigment in the presence of salts or solvents, possibly in the presence of surfactants, or in the presence of strong, nonoxidizing acids (with a pK below 2.5). 

PMMA is resistant to nonoxidizing acids, bases, and salts at ordinary temperatures but is attacked by oxidizing acids at room temperature. It is resistant to highly polar solvents, such as ethanol, but is soluble in less polar solvents, such as toluene. 

Iron dissolves in mineral acids. In nonoxidizing acids, such as HCl or H2SO4, and in the absence of air or oxidizing agents, the metal is oxidized to ferrous state (Fe2+) liberating hydrogen ... 

Unlike the trioxide, molybdenum dioxide is stable towards nonoxidizing acids, alkalies or fused salts. 

In dilute aqueous solution, sulfuric acid is a nonoxidizing acid. However, when concentrated and hot, it is an oxidizing agent. Thus, hot and concentrated sulfuric acid oxidizes copper to Cu2+, hherating sulfur dioxide. The net ionic equation is ... 

TPX has a coefficient of linear expansion of 11.7 X 10 s cm/cm C, which is similar to that of water, and hence it is useful for calibrating containers such as laboratory graduated cylinders. TPX is resistant to nonoxidizing acids, alkalis, and salts but is not resistant to oxidizing acids, such as nitric acid. Because of the presence of tertiary carbon atoms, TPX, like PP, is readily oxidized and cannot be used outdoors in the absence of antioxidants. 

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