Khob fiber yug nyob rau hauv lub 1930s. Nws yog ib yam ntawm cov inorganic tsis-metallic khoom ua los ntawm pyrophyllite, quartz xuab zeb, limestone, dolomite, calcite, brucite, boric acid, dej qab zib tshauv thiab lwm yam tshuaj raw cov ntaub ntawv. Nws muaj lub teeb yuag, siab zog, siab thiab tsawg kub tsis kam, corrosio ...
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