石油气燃烧的温度比乙炔火焰温度低,丙烷在氧气中燃烧的温度为2000℃~2850℃,用于气割时,金属预热时间需稍长。()
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氧气不能燃烧,但能助燃,是强氧化剂,与可燃气体混合燃烧 可以得到高温火焰。所以氧气广泛应用于气焊气割行业。()
使用氧气时,操作人员应站在出气口的侧面,缓慢开启阀门;乙炔瓶必须直立放置,不准卧放。()
气焊、气割用的新橡皮管在首次使用时,要先把橡皮管内的滑石粉吹干净,以防焊炬内部的通道被堵塞。()
Modern agriculture is criticized as unsustainable because _____.
A. it promotes the erosion of topsoil
B. it cannot provide a long-term planning
C. 300 years is not long enough for the development
D. the lost topsoil is irreplaceable