First, the principle of ultraviolet sterilization
Ultraviolet sterilization is to destroy and change the DNA (deoxyribonucleic acid) structure of microorganisms by ultraviolet radiation, so that bacteria can die immediately or not to breed, and achieve the purpose of sterilization. The true bactericidal effect is UVC ultraviolet light, because the C-band ultraviolet ray is easily absorbed by the DNA of the living body, especially the ultraviolet ray of about 253.7 nm.
Ultraviolet sterilization is a pure physical disinfection method. It has the advantages of simple and convenient, broad spectrum and high efficiency, no secondary pollution, easy management and automation. With the introduction of various new designs of UV lamps, the application range of UV sterilization is constantly expand.
Second, the structure of ultraviolet germicidal lamps
Ultraviolet germicidal lamps (UV lamps) are actually low-pressure mercury lamps that, like ordinary fluorescent lamps, are excited by low-pressure mercury vapor (<10-2Pa) to emit ultraviolet light. The difference is that the tube of the fluorescent lamp is made of ordinary glass, and the ultraviolet light of 254 nm cannot be penetrated, and can only be absorbed by the phosphor of the inner wall of the tube to excite visible light. If you change the composition and proportion of the phosphor, it can emit light of different colors that we usually see.
Generally, the lamps of the germicidal lamps are made of quartz glass, because quartz glass has a high transmittance for each wavelength band of ultraviolet rays, which is 80% to 90%, and is the best material for germicidal lamps.
The germicidal lamp has several structures such as hot cathode low-pressure mercury vapor discharge lamp and cold cathode low-pressure mercury vapor discharge lamp, which can be divided into various types according to the shape and power.
Quartz glass and ordinary glass have great differences in performance, mainly due to different thermal expansion coefficients. Generally, aluminum caps cannot be sealed, so the material of germicidal lamps is made of bakelite, plastic or ceramic.
Third, the lamp of the ultraviolet germicidal lamp
Due to the difference in cost and use, it is also possible to replace quartz glass with a high borax glass tube with a UV transmittance of <50%. The production process of high-boron glass is the same as that of energy-saving lamps, so the cost is very low, but its performance is far less than that of quartz germicidal lamps, and its sterilization effect is quite different.
The ultraviolet light intensity of the high-boron lamp is easily attenuated, and the ultraviolet intensity drops to 50% to 70% at the initial time after lighting for hundreds of hours. After the quartz lamp is ignited for 2000 to 3000 hours, the ultraviolet intensity is only reduced to 80% to 70% of the initial time, and the degree of light decay is much smaller than that of the high boron lamp.
It is also a kind of ordinary glass with high ultraviolet light, which is much higher than that of high boron glass and slightly lower than quartz glass. However, the light decay is larger than the quartz germicidal lamp and does not produce ozone. The lamp on a germicidal lamp produced by Philips is made from this glass.
Fourth, the type of ultraviolet germicidal lamp
The spectrum of the ultraviolet germicidal lamp has two main lines of 254 nm and 185 nm. 254nm ultraviolet light kills bacteria by illuminating the DNA of microorganisms. 185nm ultraviolet light can change O2 in the air into O3 (ozone). Ozone has strong oxidation effect, which can effectively kill bacteria. The dispersion of ozone can just make up for Dissemination along the straight line, disinfection has the disadvantage of dead angles.
When quartz glass is refining, if a sufficient amount of titanium (Ti) is added, the ultraviolet light passing through it can be cut off below 200 nm, and the ultraviolet light transmission at 254 nm is substantially unaffected. By properly controlling the amount of titanium added, the amount of ultraviolet light at 185 nm can be effectively controlled. According to this feature, we can produce three kinds of ultraviolet germicidal lamps with low ozone (no ozone), ozone and high ozone.
Five, ultraviolet germicidal lamp precautions
1. Each microorganism has its specific UV killing and death dose standard, and its dose is the product of the irradiation intensity and the irradiation time (bactericidal dose = irradiation intensity, irradiation time / K = I · t), that is, ultraviolet radiation The dose depends on the intensity of the ultraviolet light and the length of the irradiation time. The effect of the high intensity short time and the low intensity long time irradiation is the same.
2. After using the quartz lamp for a period of time, it will gradually age, and the ultraviolet radiation intensity will decline. To achieve the effect of thorough disinfection, the illumination intensity of the quartz lamp should be checked regularly, and it should be replaced immediately if the strength is insufficient.
3. Ultraviolet light can only travel in a straight line, and the penetration ability is weak. Any paper, lead glass and plastic will greatly reduce the irradiation intensity. Therefore, when disinfecting, the disinfection site should be fully exposed to ultraviolet light, and the lamp should be wiped regularly to avoid affecting the ultraviolet transmittance and the irradiation intensity.
4. Ultraviolet rays can cause great damage to the skin of the human body. Do not use UV lamps in some places. Do not use the eyes to look directly at the lighted tubes. Since short-wave ultraviolet rays cannot pass through ordinary glass, wearing glasses can be avoided. The eyes are hurt.
5. In places where there are personnel activities, ozone lamps cannot generally be used, because ozone promotes the hemoglobin condensation of the human body, causing insufficient oxygen supply to the human body, causing dizziness and nausea, affecting the health of the body, especially when the ozone concentration reaches >0.3ppm. (mg/m2) will cause serious damage to the human body.
6. The purple-blue ray in the low-pressure discharge lamp is the mercury vapor pressure. Although the intensity of the mercury vapor pressure is still related to the ultraviolet ray, it does not directly represent the intensity of the ultraviolet ray, which means that the intensity of the ultraviolet ray cannot be used with the naked eye. To judge.
7, the lamp plus reflector can ensure the concentration of ultraviolet energy, in addition to avoid damage to the staff. The reflector must be made of a material that absorbs less reflection with 253.7nm ultraviolet material. The surface oxidized and polished aluminum has the largest reflection coefficient for short-wave ultraviolet rays, so the reflective system of general ultraviolet lamps is made of aluminum.
(Content Source Food Laboratory Service)
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