Rotation – Maintenance of laboratory equipment

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The maintenance of laboratory instruments is crucial. Proper protection of these instruments facilitates the smooth progress of experiments, enables the adoption of new experimental methods, and helps improve the quality of experiments. It helps to prevent experimental accidents, expands the range of applications for these instruments, and prolongs their service life. This is equivalent to an increase in production volume and an improvement in quality for such instruments. (II) Erosion of instruments and equipment: Instruments and equipment are made up of either metallic or non-metallic materials. Studying the erosion process of instruments actually involves studying the erosion of metallic and non-metallic materials. The difference lies in the fact that instruments have special structural forms and application scenarios, which gives rise to certain specific issues related to instrument erosion. Wear of the flexure tester and balance blade edges – this is mechanical damage resulting from stress ； The plastic seal ring deforms and swells when immersed in a solvent; this is physical swelling of the plastic caused by the solvent ； Metal components are corroded by the medium, and the rubber lining layer becomes brittle and cracks over time due to chemical corrosion of the materials by the medium ； The dielectric properties of insulated materials that have developed mold are reduced, as this is a result of microbial invasion by mold in those insulating materials. The phenomenon of degradation in the properties of these metallic and non-metallic materials under mechanical, physical, chemical, and microbial effects is collectively referred to as material erosion. The corrosion of metals can be divided into chemical corrosion and electrochemical corrosion. Chemical corrosion is a process in which a gas or liquid medium reacts chemically with the metal surface to form compounds, thereby damaging the metal surface. The process by which metal materials are corroded by corrosive agents such as oxygen, water vapor, and carbon dioxide at high temperatures is known as high-temperature oxidation. The ability to resist corrosion in high-temperature oxidizing atmospheres is known as oxidation resistance. Electrochemical corrosion refers to the occurrence of electric current during the corrosion process. The metal materials commonly used are all alloys composed of multiple elements. Even pure metal materials contain a certain amount of impurities; therefore, on a microscopic level, the composition and structural arrangement of various tiny regions within the material are never exactly the same. As a result, their electrode potential values also differ. When such metal materials come into contact with corrosive substances, countless tiny galvanic cells are formed, leading to the corrosion of the metal material. The composition and structural state of non-metallic materials differ from those of metallic materials; therefore, the erosion of non-metallic materials also differs from that of metallic materials. The erosion of polymer compound materials is manifested as softening upon heating or charring and carbonization ； Swelling or dissolution occurs under the action of a solvent ； It may change color, become sticky, become hard and brittle, develop cracks, and experience a decrease in mechanical strength under the effects of heat, light, electricity, oxygen, and corrosive substances. Silicate materials such as ceramics, glass, and enamel can also become corroded, thin out, or turn porous when exposed to corrosive substances such as hydrofluoric acid, hot carbonic acid, concentrated alkalis, and molten alkalis. For example, when glass composed of Na2O and SiO2 is placed in acidic media such as hydrochloric acid, Na2O reacts with the acid and is leached out, leaving behind SiO2 which forms a porous structure, thereby significantly reducing the mechanical strength of the glass. When glass interacts with water, the water can dissolve the alkali metal oxides in the glass, turning the water into an alkaline solution. This alkaline solution then reacts with SiO2 in the glass, causing corrosion of the glass; of course, this corrosion process is very slow and goes unnoticed. ; There are many factors that affect instrument erosion, and temperature changes can also cause erosion. Thermal expansion and contraction, brittleness at low temperatures, softening at high temperatures, melting, or burning are common phenomena. Rubber with weak elasticity becomes very hard at low temperatures ； Soft plastic becomes very brittle at low temperatures ； Some metals, such as ordinary carbon structural steel (body-centered cubic lattice), exhibit a pronounced tendency to become brittle at temperatures below –40°C, whereas copper, aluminum, and austenitic stainless steels (face-centered cubic lattice) do not become brittle at such low temperatures. As the temperature rises, the mechanical strength of materials decreases; cast iron and medium-carbon steel undergo creep at temperatures above 350°C, while alloy steel does so at temperatures above 400°C. Some plastics can experience internal creep under long-term loading at room temperature, and non-ferrous metals can also undergo creep at room temperature. As the temperature rises, the resistance of conductive materials increases, while the insulating properties of insulating materials decline, potentially leading to cracking, melting, charring, or thermal breakdown. Furthermore, when metal materials come into contact with media, corrosion occurs, resulting in the formation of corrosion products; for example, a dense protective film is formed to prevent further corrosion of the metal. Water is an excellent solvent; it can dissolve corrosive gases such as oxygen, ammonia, chlorine, and sulfur dioxide present in industrial atmospheres, turning them into corrosive solutions. The moisture adsorbed on the surfaces of instruments and meters forms a continuous film of water or condenses into droplets; these droplets contain corrosive gases from the industrial atmosphere, and as a result, the neutral water turns into a corrosive solution that erodes the instruments. $ V1 H5 g, ^! O2 W _4 v2 | For example, an iron screw screwed onto a copper solenoid valve forms a water film when in contact with humid air, generating hydrogen ions and hydroxide ions; as a result, the iron screw is continuously corroded. 8 L7 i; M; f3 S. }2 ] 5 H; h! Insulating materials such as glass and fine porcelain have a dense surface, so moisture can only adhere to the surface and does not penetrate into the material. However, insulating materials such as cotton yarn and silk have a loose, porous structure, possess strong moisture absorption capacity, and water will diffuse inward. The moisture adsorbed on the surface of insulating materials will dissolve corrosive gases, forming a conductive medium that reduces electrical insulation properties. This leads to leakage and breakdown, affecting the proper operation of the equipment. 0 j! ^& }* q7 `2 w$ R 4 ]" ?' U. P, q; x+ p& ] The growth conditions for molds are essentially three basic factors: moisture, nutrients, and temperature. The nutrients required by molds include carbon, hydrogen, oxygen, nitrogen, magnesium, phosphorus, sulfur, potassium, calcium, iron, and others. It can grow and reproduce in the temperature range of 3 to 45°C. In materials that have developed mold, the mold often uses them as a nutrient source to grow and reproduce, thereby damaging the material itself. Substances secreted by molds also have a corrosive effect, corroding the material they infest. For example, molds use the film-forming substances in paint as food, destroying these substances and causing the coating to lose its protective properties. Mold also reduces the electrical insulation properties of insulating materials, leading to phenomena such as electric leakage. It is very common for instruments and equipment to suffer from atmospheric corrosion. Atmospheric corrosion is essentially the result of the combined effect on instruments by water, oxygen, nitrogen, carbon dioxide, sulfur dioxide, sodium chloride, ammonia, chlorine, hydrogen chloride in industrial atmospheres, as well as microorganisms and dust. These corrosive substances intensify the corrosion effect when combined with climate conditions such as heat, light, and wind. Silicate materials such as glass and ceramics have good resistance to atmospheric corrosion. Polymer materials such as plastics and rubbers are prone to aging under the combined action of oxygen, heat, and light. The corrosion of metals in a dry atmosphere is a pure chemical reaction, while the corrosion of metals in a humid atmosphere is an electrochemical reaction. The corrosion rate of metals in a humid atmosphere is naturally much higher than in a dry atmosphere. ! d% p9 b! B# z: ^" X7 ~2 q0 X$ k Many components of testing instruments and equipment come into direct contact with the working medium, and as a result are subject to corrosion by that medium. There are many types of working media, including inorganic or organic substances such as acids, bases, salts, and solvents. It exists in gaseous, liquid, and particulate states. Media with different chemical properties can cause varying degrees of corrosion to the components of instruments. The pH value is an indicator of the hydrogen ion concentration in an electrolyte solution; it reflects an important chemical property related to the corrosiveness of the solution. For example, a medium with a pH of 7 is neutral, while a medium with a pH greater than 7 is alkaline. pH