I. Chemical cleaning methods Cleaning methods can be divided into physical cleaning and chemical cleaning. Physical cleaning can be divided into mechanical cleaning, hydraulic cleaning, steam cleaning, ultrasonic cleaning and laser cleaning. Chemical cleaning can be divided into surfactant, chemical solvent, acid, alkali, complex reaction and biochemical cleaning. Because most pollutants in stone materials reside in the micropores of stone materials, general physical cleaning is either difficult to achieve or expensive, so chemical cleaning has become the main means of stone cleaning at present. (1) Surfactant is a common method to clean the dirt on the ground surface of terrazzo, marble and other stones. There are two kinds of surfactants: ionic and nonionic. Their molecules contain polar and nonpolar genes. The principle of cleaning is to use the properties of surfactant such as reducing interfacial tension, wetting, adsorption, emulsification, solubilization and dispersion to make dirt molecules fall off and disperse, so as to achieve the cleaning effect. (2) Alkaline washing is to use saponification and emulsification of alkaline chemicals to make dirt loose and dispersed. The commonly used alkaline solution is an aqueous solution with sodium hydroxide and sodium carbonate as the main components, which is mainly used to eliminate oil pollution. Oil pollution can be divided into saponification and unsaponification. Saponifiable oil pollution is animal and plant oil pollution, which can form soap when it meets alkali and is soluble in water, so it is easier to remove. Non-saponified oil pollution is mineral oil pollution. To clean this kind of oil stains, it is necessary to use emulsifier to reduce the binding force between oil stains and attachments and fall off. Common emulsifiers include trisodium phosphate and sodium silicate. (3) Pickling is widely used in stone cleaning, especially granite. Hydrochloric acid, sulfuric acid, nitric acid and hydrofluoric acid are commonly used in inorganic acids; Organic acids are mostly citric acid, oxalic acid and sulfamic acid. If rust is removed with sulfuric acid, sulfuric acid reacts with iron oxide to produce ferric sulfate, which can be dissolved in water, so rust can be removed. However, the corrosion problem of inorganic acid cleaning deserves great attention, especially for carbonate stones such as marble, the acid or acid radical left in its micropores may harm the stone for a long time, and it is difficult to avoid the corrosion problem even if buffering agent is added, so foreign countries have tended to use organic acids or other organic substances with low corrosiveness and easy purification. (4) Complexing agent cleaning is the cleaning of complexing or chelating various scale-forming metal ions with complexing agents to generate soluble complexes. Commonly used organic chelating agents are EDTA, DTPA and NTA. For example, EDTA (ethylenediamine tetraacetic acid) can generate multi-sodium salts, such as disodium salt or trisodium salt, which has strong complexing ability to various scaling metal ions. In recent years, the United States, Western Europe and Japan have developed some more effective chelating cleaning methods. (5) Electrochemical cleaning is to make the ions or polar molecules in the dirt move according to a certain law or promote electrochemical reaction by means of the electric field force (including DC, alternating current and pulse electricity) between the two plates, so as to make the pollutants desorb, move or undergo chemical changes, so as to achieve the purpose of cleaning. For example, current can reduce the adsorption force of iron ions in granite micropores, increase the diffusion coefficient and produce electric pulses. Remove rust from granite surface and a certain depth below the surface. (6) The ability of solvent cleaning to dissolve pollutants. If the composition of pollutants is known, it is very effective to choose a specific solvent. For example, many organic solvents, such as toluene, xylene, butyl acetate, etc. It has strong solubility in grease or oil stains. It is generally faster to remove oil stains with organic solvents than with alkali liquor, and its disadvantage is that the volatilization of organic solvents is easy to cause environmental impact. (7) Biochemical cleaning is mainly aimed at biological pollutants. People have long discovered the erosion and pollution of stone by microorganisms, and the effective cleaning method is to choose a biochemical cleaning agent with targeted killing, dissolution, decomposition and stripping to clean it. The biggest feature of stone cleaning is that most pollutants reside in the tiny pores of stone (mostly micron-sized pores). Cleaning agent needs to penetrate into the pores of stone and play a role in it, sucking out or diluting the residual liquid after cleaning. It is difficult to clean the stone because of the limitation and shielding effect of micropores in the stone. In short, finding out the structure and nature of stone dirt, understanding the characteristics of stone itself, and choosing the appropriate cleaning method or compound method are the most important links in cleaning work, just like seeing a doctor. Second, chemical cleaning formula In recent years, some patents for chemical cleaning of stone materials have been published, many of which are compound formulas. Here are a few: (1) China patent (CN 1055 198) is a marble surface cleaning agent. It is made of sodium citrate, triethanolamine, oleic acid, white oil, methyl silicone oil and water. It is said that it can clean inorganic and organic dirt, save water, have certain polishing function and have low cost. (2) China Patent (CN 1064886), a decontamination paste for dirt, sludge and rust spots on the stone surface. It consists of sodium tripolyphosphate, calcite powder sulfuric acid, sodium silicate, sodium hydroxymethyl cellulose, liquid paraffin, liquid caustic soda and ionized water. It is said that it can clean granite monuments, buildings and related products of wind erosion, organic microorganisms and stains. (3) U.S. Patent (U.S. Pat.No. US48972 13), granite cleaning agent, the formula is: mixed solution of NF4HF, ethanol or modified ethanol. It is said that it can clean granite monuments, granite buildings and granite products from wind erosion, organic microorganisms and stains. (4) Japanese patent (JP903 1493A), detergents for stone, concrete, brick, etc. Its formula is phosphoric acid, hydrochloric acid, formic acid, diethanol fatty amide, polyoxyalkyl ether, ammonium chloride or ammonium sulfate; It is said that dirt on concrete, stones, mortar and bricks can be cleaned. (5) Japanese Patent (JP6322398A), an oil stain remover for hard surfaces such as stone, is prepared from various amphoteric surfactants, fatty acid salts, metal ion flocculants, solvents, etc. According to the author, it can remove oil stains attached to hard surfaces such as stone. (6) The world patent (WO9722679A) is suitable for the surface cleaning of high-gloss marble, and its formula contains at least one anionic surfactant, which is mixed into a neutral solution, and divalent cations to form a saturated decontamination mixture. It is said that it has the function of decontamination and light protection. (7) American patents. No.5780111), a marble surface cleaning and polishing agent, the formula is ZnSO4, abrasive, thickener, penetrant, fluorosilicate, etc. It can react chemically with the surface of marble, and it is said that it can clean marble and restore its luster, and improve its durability, wear resistance and anti-cracking and anti-fouling performance. (8) The stone floor cleaning agent of patent (JO3 182-596A) has the formula of anionic surfactant (alkylbenzene sulfonate, etc.). ) nonionic surfactant (polyoxyethylene sulfonate, etc. ) hydroxyalkyl cellulose (hydroxymethyl cellulose, etc. ) general alcohol substances (isopropanol, alcohol, etc. ) and adjust the PH value to 9- 12. It is said that after washing, the detergency is high and the surface gloss is good. (9) U.S. Patent (U.S. PatentNo. US46 13378), a method for cleaning hard surfaces such as marble. Dissolve cellulose, phosphate, etc. First put it into boiling water, then add talcum powder and sucrose and stir it into a paste. During processing, these pastes are directly coated on the surface to be cleaned with a brush, or the surface to be cleaned is covered with a cloth, and then the mixture is sprayed on the surface of the cloth, then covered with a plastic film and cured, and finally washed with water or steam. It is said that this method can remove stubborn dirt. (10) China patent (CN 107 1452) is a hard surface oil stain cleaner, which consists of surfactant and absorbent mineral powder (diatomite, bentonite, bentonite, bleaching soil, zeolite or expanded perlite powder, etc.). It is said that this method is very effective in cleaning oil stains on hard surfaces. In the past 20 years, great progress has been made in chemical cleaning technology, and various cleaning methods and formulas have emerged constantly, providing a new means for the maintenance and renovation of stone materials. But generally speaking, the natural micropores of stone bring great difficulty to the cleaning work. After some dirt on the stone surface is treated, after a period of time, the dirt will ooze or adsorb from the micropores. Therefore, stone cleaning should be coordinated with stone maintenance in addition to exploring scientific cleaning methods.
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