Propellants, Protective Gases

Food sensitive to oxidation and/or microbial spoilage can be stored in an atmosphere of protective gas or a gas mixture (N2, CO2, CO, etc. modified or controlled atmosphere storage). This is often a suitable method for lengthening the shelf life of food. 

Liquid food can be filled into pressurized containers and, when needed, using a propellant, discharged in the form of a cream or paste (e.g. cream cheese, ketchup), a foam (whipping cream) or a mist (herb or spice extracts in oil liquid barbecue smoke). Propellants used are N2, N2O, and CO2. 

Due to its low solubility in water, fat and oil, N2 is used preferentially as a propellant when foam formation is not desired (ketchup). On the other hand, gases such as N2O and CO2 are preferred for foam formation (whipped cream) due to then-good solubility in water. 

Ariyoshi, Y., Kohmura, M., Hasegawa, Y.,Ota, M., Nio, N. Sweet peptides and proteins Synthetic studies. ACS Symposium Series 450, p. 41 (1991) 

Borrego, F., Castillo, J., del Rio, J. A. Neo-hesperidin dihydrochalcone Properties and applications. Lebensm. Wiss. Technol. 23, 371 (1990) 

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Another tool the interstates use to maintain their pipelines is a device known as an intelligent pig. Propelled through the pipeline with the gas stream, these devices, taking thousands of measurements with electronic sensors that can be analyzed later by computers, can inspect pipeline interior walls for corrosion or other defects and remove accumulated debris from a section of pipeline. Pipelines also use state-of-the-art coating and cathodic protection to battle corrosion. 

Triple-based propellants are mixtures of nitroguanidine, nitrocellulose, and nitroglycerine. The mixture reduces the muzzle flash observed with double-based propellants, reduces the burn temperature, which protects the gun barrel, and increases the gas volume. Triple-based propellants are used in tank guns, large caliber guns, and some naval weapons. 

The burning surface is sometimes destroyed by a mechanical action, e.g. shock or vibration, which strips off the burning layer from the composition to stop the combustion. Such an accident often occurs in the case of shooting stars the burning surface is dug off by the propellant gas. To protect the surface from the mechanical action, we use a punched metal... 

Ignition surface is protected against wind and propellant gas. 

Dichlorodifluoromethane and dichlorotetrafluoroethane are usually encountered as a liquefied gas and appropriate precautions for handling such materials should be taken. Eye protection, gloves, and protective clothing are recommended. These propellants should be handled in a well-ventilated environment. Chlorofluorocarbon vapors are heavier than air and do not support life therefore, when cleaning large tanks that have contained chlorofluorocarbons, adequate provisions for supply of oxygen in the tanks must be made in order to protect workers cleaning the tanks. 

Butane and the other hydrocarbon propellants are liquefied gases and should be handled with appropriate caution. Direct contact of liquefied gas with the skin is hazardous and may result in serious cold burn injuries. Protective clothing, rubber gloves, and eye protection are recommended. 

The principle of all aerosols is that a liquefied gas in a pressurised container will provide a constant pressure while the container is being emptied. The essential components of an aerosol beside the container itself are the product, propellant, and valve assembly. The valve is designed to dispense the product in the required manner while maintaining both the product and propellant hermetically sealed until the product is expended. The fact that the product is sealed in the container and protected from air and other outside contaminants has obvious advantages in the field of pharmaceuticals. The intimate mixture of propellant and product in a true aerosol results in a rapid expansion of the propellant as it leaves the valve orifice. This breaks up the product into small particles giving a fine mist, coarse spray, foam, or dust according to the nature and relative quantity of the product and the propellant and the type of valve. 

Reasonably, the corrosion form is typical at relatively high velocities between the material surface and flie fluid, and it is particularly intensive in cases of two-phase or multiphase flow, i.e. hquid-gas and liquid-solid particle flow. Components often liable to erosion corrosion are propellers, pumps, turbine parts, valves, heat exchanger tubes, nozzles, bends, and equipment exposed to liquid sputter or jets. Most sensitive materials are those normally protected by corrosion products with inferior strength and adhesion to flie substrate, e.g. lead, copper and its alloys, steel, and under some conditions aluminium/aluminium alloys. Stainless steel, titanium... 

The type of primary packaging also has an influence on product protection during use by the consumer. Aerosols generally provide good product protection. Filled into the can and pressurized with propellant gas, the very nature of its packaging protects the product from exposure to potential contamination. Nevertheless, even this... 

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