Marble, corrosion

Sulfur dioxide emissions may affect building stone and ferrous and nonferrous metals. Sulfurous acid, formed from the reaction of sulfur dioxide with moisture, accelerates the corrosion of iron, steel, and zinc. Sulfur oxides react with copper to produce the green patina of copper sulfate on the surface of the copper. Acids in the form of gases, aerosols, or precipitation may chemically erode building materials such as marble, limestone, and dolomite. Of particular concern is the chemical erosion of historical monuments and works of art. Sulfurous and sulfuric acids formed from sulfur dioxide and sulfur trioxide when they react with moisture may also damage paper and leather. 

Magnesium oxychloride cements are widely used for the fabrication of floors. They find application for this purpose because of their attractive appearance, which resembles marble, and also because of their acoustic and elastic properties and their resistance to the accumulation of static charge. They have also been used for plastering walls, both interior and exterior for exterior walls the cement often includes embedded stone aggregate (Sorrell Armstrong, 1976). However, there have been problems with this latter application, since the base cement has been found to be dimensionally unstable and, in certain circumstances, to release corrosive solutions and show poor weather resistance. 

Sulfuric acid is a stronger acid than sulfurous [pAa(l) < 0, p7fa(2) = 1.99 at 25 °C and infinite dilution] rain as acidic as pH 2.1 has been recorded at Hubbard Brook, New Hampshire, and the pH of water droplets in clouds can be as low as 1.5 (for comparison, the pH of rainwater saturated with atmospheric CO2 is about 5.6 at 15 °C). Acid rain destroys building materials (especially marble), kills fish and vegetation, accelerates metallic corrosion (Sections 16.5 and 16.7), and can be directly harmful to humans (e.g., it causes the alligator skin condition reported in Cubatao, Brazil). Sulfate rain is not completely without redeeming features, as many soils (e.g., in southern Alberta, Canada) are sulfur-deficient. On balance, however, its acidity is unacceptable, and sulfur oxide emissions must be controlled at the source. Several control measures are possible ... 

In addition it has led to the increased corrosion of exposed metals and to damage to buildings and statues made from limestone or marble (Figure 12.4). The sulfurous acid in rainwater oxidises to sulfuric acid. The sulfuric acid reacts with the limestone, which is eaten away by the chemical process. 

Acid rain causes corrosion of some metals, erosion of marble (limestone), mortar etc. It is responsible for the destruction of softwood forests and for the pollution of ground water. 

A wad of glass wool in the bottom of a glass funnel may sometimes be used to filter corrosive liquids. Another method which can be used in separating crystals from a corrosive liquid consists in putting a glass marble into a funnel. The crystals form a mat in the small space between the marble and the sides of the funnel and the liquid can be removed by suction. 

In the atmosphere, sulfur oxides can combine with water and oxygen to form sulfurous and sulfuric acids. The deposition of these acids causes corrosion or decomposition of materials such as limestone, marble, iron, and steel. The deterioration of building facades and monuments is one result of this worldwide problem. Flushing of the sulfur oxides from the air by precipitation (acid rain) can lead to acidification of lakes and sods, weakening or killing plants and animals. 

Many examples of acid-base reactions can be found in cooking, such as the soda-sour cream reaction in Little Men. In addition, the unfortunate result of acid rain (the formation of which we will discuss later) is that the acid in the rain reacts with the carbonates found in limestone and marble, which causes the deterioration of statues, some of which had managed to survive without corrosion for thousands of years before the advent of the industrial age. (But before one completely condemns the industrial age, it should be remembered that the bacteria of Black Death, smallpox, and syphilis also managed to survive for thousands of years before modem technology brought them to bay.) This ability of acid rain to dissolve marble brings up another property common to all acids and bases they are corrosive. 

The full methodology of retrospective analysis was applied for the case of marble tombstone deterioration in an urban and a remote cemetery near New York City (8,9). In this exercise it was found that our technique may estimate rural SO2 concentrations acceptably well, but it does not reproduce detailed structure of urban concentrations adequately. The main reasons are uncertainty about the effective release heights of sources and a lack of detailed local emission Information. For the purposes of metal corrosion, the current state of the retrospective reconstruction of environmental histories is not sufficiently quantitative to warrant extraction of damage functions. 

Close the tube by placing a marble on the top. Digest the sample on heating blocks set at 180°C for 1 h (Caution Hot perchloric acid is highly corrosive and potentially explosive. This procedure should be carried out in a suitable fumehood behind a blast shield). 

As the theoretical calculation does not always result in entirely correct results, practical corrosion tests are carried out. Aggressivity towards CaC03 is experimentally determined by the so-called Heyer s test (marble test). In these experiments water is brought in contact with CaC03 and after achieving equilibrium the increase or the loss of calcium or hydrogen carbonates is determined. 

Because acids react with metals and with carbonates, add rain is corrosive both to metals and to stone building materials. Marble and limestone, for example, whose major constituent is CaC03, are readily attacked by acid rain ( FIGURE 18.8). Billions of dollars each year are lost because of corrosion due to SO2 pollution. 

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