Physical property: white crystal, easy to sublimate at normal temperature, high heat of vaporization, can rapidly reduce the ambient temperature when sublimating at normal pressure, so when dry ice sublimates in the air, it will liquefy or even further condense the water vapor in the air, and the formed water vapor droplets or small ice crystals attach to the dust in the air to form visible white smoke.The crystal structure of dry ice is simple cubic, belonging to molecular crystal[2]。Individual carbon dioxide molecules lie at the vertex and face center of the cube with different orientations, and form dry ice crystals.
Chemical properties: the chemical properties of dry ice are stable, tasteless, non-toxic, incombustible, and do not support combustion.However, if the content of carbon dioxide in the air is too high, it will stimulate the respiratory system and lead to the risk of suffocation (i.e., hypoxia).Carbon dioxide has high thermal stability (only 1.8% decomposition at 2000 ℃).Dry ice belongs toAcid oxide, with the commonness of acid oxide, it is generated by reacting with watercarbonic acid。
Chinese name
dry ice
Foreign name
dry ice; drikold; solid carbon dioxide
chemical formula
COtwo
molecular weight
forty-four point zero one
CAS login number
124-38-9
Melting point
-56.6 ℃[1]（527kPa）
Boiling point
-78.5 ℃[1](sublimation)
Water solubility
Soluble in water, partially generating carbonic acid
The liquid carbon dioxide is led out from the liquid carbon dioxide storage tank and injected into the chamber of the ice compression chamber of the dry ice machine.Throttling through the nozzle produces a large amount of gas carbon dioxide and snow like dry ice solids.When the solid dry ice reaches a certain amount, the hydraulic system starts, and the piston compacts the snowflake like dry ice into dry ice blocks and extrudes them from the die head end.At this time, the rotary blade at the end of the dry ice machine starts to break the long dry ice cylinder into dry ice particles of the required length.[3]
Precautions for use and storage
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1. It cannot be mixed with liquid;
2. It cannot be stored in a closed container;Do not use dry ice in a confined space, or it may cause suffocation and explosion;
3. Ice shall not be in direct contact with skin, otherwise frostbite may occur.
Schematic diagram of crystal structure of dry ice[2]
Application scenarios
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Artificial rainfall
In 1946, American Schaefer and Vonnegut found that dry ice and silver iodide could be used as efficient cold cloud catalysts. In April 1947, the test of aircraft seeding dry ice in clouds began[4]。Since then, dry ice has been increasingly used in the field of artificial rainfall.The principle of dry ice artificial rainfall is to put dry ice into the gun barrel and hit it to the designated area. Dry ice is scattered into the air to sublimate rapidly, absorb a lot of heat, and make the water vapor in the air liquefy and condense to form raindrops.
Schematic Diagram of Dry Ice for Artificial Rainfall
Cleaning industry
Dry ice cleaning mainly has the following three principles:
"Energy transfer":The dry ice hits the cleaned surface at high speed, and the impact kinetic energy dissipates. The dry ice particles and the cleaned surface undergo extremely rapid heat transfer. The carbon dioxide sublimates instantaneously, and the dirt shrinks and embrittles suddenly and is washed down.
"Low temperature cracking":The temperature difference between two different materials with different thermal expansion coefficients will destroy the combination between the two materials.Dry ice particles (- 78.5 ℃) impact the surface of the treated object to freeze the dirt to embrittlement and burst, resulting in "cracking", affecting the mechanical properties of adhering dirt and causing the dirt to fall off.
"Micro explosion":After drilling into the dirt cracks, dry ice particles sublimate in a few thousandths of a second, and their volume expands 600~800 times instantly, stripping the dirt off the surface of the object.
Dry ice cleaning equipment can generally be divided into two parts:
① Dry ice granulator.Put liquid COtwoMake dry ice particles of certain specifications, which are usually high-density dry ice particles with a diameter of 3 mm and a length of 2.5 mm - 10 mm.
② Dry ice high-pressure cleaning machine.The equipment generally needs more than 4.0 bar and 3 mthree/Clean compressed air source for more than min.Driven by compressed air, the high-density dry ice particles loaded into the cleaner are mixed and accelerated with the compressed air through a specially designed spray gun system and sprayed onto the surface of the object to be cleaned.
Jet photo of dry ice washer
Dry ice is widely used for cleaning such as metal[5], Mold[6]Production equipment[7], Ancient cultural relics[8]And other surface stains.The cleaning process does not require cooling and disassembly of the mold, which avoids the corrosion and damage of the mold caused by chemical cleaning, the mechanical damage and scratch of the mold caused by mechanical cleaning, and the decline in mold accuracy caused by repeated loading and unloading.Some examples are given below:
① Petrochemical industry: dry ice cleaning technology can be used to clean the rust and dust of the main fan, air compressor, flue gas turbine, steam turbine, blower and other equipment in the petrochemical process (it is not necessary to remove the blades, and the dynamic balance step of readjusting the blades is omitted);Removal of coking and carbon in various heating furnaces and reactors;Clean the PVC resin on the heat exchanger;Remove oil, rust and dust from compressor, storage tank, boiler, reaction kettle, condenser, complex machine body and other equipment;
② Power system: it can directly clean indoor and outdoor transformers, insulators, distribution cabinets, wires and cables with live load (below 37 kV);Generator, motor, rotor, stator and other parts shall be cleaned without damage;
③ Food production: dry ice cleaning can successfully remove the baking residues, gelatinous substances, oil stains and the mixture of fresh products before baking in the oven.Effectively clean ovens, mixing equipment, conveyor belts, molded products, packaging equipment, furnace racks, furnace trays, containers, rollers, refrigerator walls, biscuit bars and other equipment;
④ Automobile and ship industry: clean the car door, roof, carriage, underbody oil stain and other waterless residues, which will not cause water pollution;Car carburetor cleaning and car surface paint removal;Remove the carbon deposits on the engines of vehicles and ships (the chemical agent takes a long time to treat, at least more than 48 hours, and the agent is harmful to human health. Dry ice cleaning can completely solve the carbon deposit problem within 10 minutes, which saves time and reduces costs, and the scale removal rate can reach 100%);Clean the hull, seawater suction valve, seawater condenser and heat exchanger, engine room, machinery and electrical equipment, etc;
⑤ Aerospace field: pre processes of missile, aircraft painting and final assembly;Paint removal of composite mold and special aircraft;Engine carbon deposition cleaning;Maintenance and cleaning (especially in the landing gear wheel cabin area);Paint removal of aircraft shell;Jet engine conversion system.It can work directly on the machine body, saving time;
⑥ Printing industry: dry ice cleaning can remove various oil-based and water-based inks and varnishes, and clean oil stains, ink deposits and dyes on gears, guides and nozzles, which can not only effectively ensure the quality of printing products, but also ensure that printing equipment will not be worn.
⑦ Cultural relics cleaning: dry ice cleaning technology can efficiently and nondestructive clean the dirt, soluble salt, mold, deposition film and other pollutants attached to the surface of cultural relics.Compared with the traditional physical and chemical cleaning methods, it not only improves the cleaning efficiency and quality, but also is more friendly to the environment and staff health.
Cold chain transportation
① Low temperature transportation of plasma, vaccine and other special drugs;
② Long and short distance transportation of electronic cryogenic materials and precision components;
③ Preservation and transportation of high-grade beef, mutton, seafood and other high-end food.
Decorative special effects
Dry ice is widely used in the stage, theater, film and television, wedding, celebration, party and other production of cloud sea effect, as well as the smoke effect of table dishes.
