Limestone is the raw material for burnt and slaked lime. If the limestone is heated to more than 900 °C, carbon dioxide dissociates and burnt lime (CaO) is formed. This is done in shaft furnaces, rotary kilns or fluidized bed furnaces at a temperature range between 900 and 1,400 °C, depending on the quality requirements. The properties of burnt lime depend on the burning temperature and dwell time in the kiln. High temperatures and long dwell times lead to a low reactivity in burnt lime (dead-burned lime). In contrast, lime produced at lower temperatures is very reactive.