Experimental study on key factors of magnetic change of weakly caking coal during heating

Abstract

To study the magnetic change mechanism of weakly caking coal during the heating process, the mass magnetic susceptibility of coal samples during the heating process was measured in this paper. Compared with the burnt coal sample after heat treatment at the same temperature, the magnetic change process of coal during heating was divided into four stages. The experiments of programmed temperature rise, industrial analysis and X-ray diffraction of coal were conducted at different stages to explore the key factors that lead to changes in its magnetic properties in different heating stages. The experimental results show that the magnetic susceptibility of the coal sample changes from negative to positive and then slowly rises at room temperature to 200 ℃. The effect on the magnetic properties of the coal at this stage is due to the decrease of the diamagnetic carbon-containing compounds in the coal due to oxidative consumption. At 200 ℃ to 350 ℃, the magnetic susceptibility of the coal sample rises sharply, and the average growth rate is 10 times higher than that of the previous stage. This is because the trace minerals in the coal sample chemically react to produce more magnetic substances. When the temperature exceeds 350 ℃, the magnetic susceptibility begins to decrease rapidly, and the magnetic susceptibility stabilizes near 0 after the temperature is 500 ℃. The possible reason is that with the increase of temperature, the movement of particles inside the mineral intensifies and affects the orderly arrangement of the magnetic domain and magnetic moment. When the temperature rises to the Curie temperature, this influence reaches its limit and the change tends to be stable.

Keywords

• coal mine safety
• coal field fire
• magnetic detection
• coal and rock magnetism
• mass susceptibility