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Here both the chemical and physical blowing are used in tandem to balance each other out with respect to thermal energy released and absorbed, minimizing temperature rise. Otherwise excessive exothermic heat because of high loading of a physical blowing agent can cause thermal degradation of a developing thermoset or polyurethane material.
Physical weathering, also called mechanical weathering or disaggregation, is the class of processes that causes the disintegration of rocks without chemical change. Physical weathering involves the breakdown of rocks into smaller fragments through processes such as expansion and contraction, mainly due to temperature changes.
The international pictogram for chemicals that are sensitising, mutagenic, carcinogenic or toxic to reproduction. In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level.
Incapacitating agent is a chemical or biological agent which renders a person unable to harm themselves or others, regardless of consciousness. [ 1 ] Lethal agents are primarily intended to kill, but incapacitating agents can also kill if administered in a potent enough dose, or in certain scenarios.
Natural weathering of rocks by physical and chemical agents can mobilize lead in soils. Mobilized lead can react to form oxides or carbonates. It can co-precipitate with other minerals by being occluded through surface adsorption and complexation [4]
DNA may be modified, either naturally or artificially, by a number of physical, chemical and biological agents, resulting in mutations. Hermann Muller found that "high temperatures" have the ability to mutate genes in the early 1920s, [2] and in 1927, demonstrated a causal link to mutation upon experimenting with an x-ray machine, noting phylogenetic changes when irradiating fruit flies with ...
The defined agents reflect and systematise the main chemical and physical deterioration pathways to which most physical material is subject. They are a major influence on the applied practice of conservation, restoration , and collection management , finding particular use in risk management for cultural heritage collections.
Mutagen – Physical or chemical agent that increases the rate of genetic mutations; Pesticide – Substance used to destroy pestss; Polychlorinated biphenyl – Highly carcinogenic chemical compoundss; Radon – chemical element with the atomic number of 86 and other natural sources of radioactivity