Effects Of Heat Treatment On Properties And Its Mechanism For Carbon-Containing Refractory

The service properties of the carbon-containing refractory are determined by the compositions and processes. The heat-treatment process (curing and firing) has a great effect on the properties. The essence of heat-treatment is complex physical and chemical changes of the binder phenolic resin, while the remaining ingredients don’t obviously change. Effects of heat treatment on properties and its mechanism for carbon-containing refractory were studied in this thesis. Changes of heat, mass and structure of binder by methods of Differential Scanning Calorimetry (DSC), Thermogravimetry-Differential Thermogravimetry (TG-DTG), Infrared Spectroscopy (IR) and X-Ray Diffraction (XRD), were mainly analysised. In addition, the firing temperature was optimized. The main contents in this thesis are as follows:(1) The curing mechanism of carbon-containing refractories has been studied.The essence of curing is physical and chemical changes of phenolic resin for the binder. Before130℃, solvent absorbs heat and quickly rules out, the mass quickly reduces. A less activation energy can finish beyond50%rate of mass change. The binder gradually hardens between100～110℃, carbon-containing refractory is prone to deformation at this temperature. Between130～200℃, dehydration condensation reaction occurs. The heat, mass and structure of the binder dramatic change in the process; methylene and ether linkages are generated, methylene is the main product; the heating rate should be slow in this process. Between200～270℃, cure gradually completes, the heat, mass and structure of the binder gradually tend to stabilize, the process requires a higher activiation energy, the heating rate should be faster. Between270-300℃, the mass, heat, and structure are almost constant, the carbon-containing refractory curing reaction has been completed.(2) Effects of the firing temperature on the properties and its mechanism for carbon-containing have been studied.Firing temperature mainly affects the properties of carbon-containing refractory, such as the strength and porosity. Before700℃, the strength of carbon-containing refractory is lower at approximate7MPa, the porosity is high at about8.7%, which is due to pyrolysis of phenolic resin binder excluding a great number of gases in firing process. Between700～800℃, the strength sharply increases to about8.5MPa, the porosity becomes down to about7.8%, this is due to the shrinkage of binder. Between800～950℃, the strength is higher and has a smaller change, the porosity is lower and has a smaller change, the fire of carbon-containing refractory has been completed.The firing temperature has effects on the properties of carbon-containing refractory through the pyrolysis behavior of the binder. Before600℃, the main cleavage reaction of binder occur, more heat is released, excluding a large number of gases makes the quality rapidly decrease and make the prosity become higher. Between600～750℃, heat change tends to smooth, the quality gradually decreases, this is the deep pyrolysis of the binder, the peak (002) c-axis correlation mean crystallite size Lc of pyrolysis product gradually increases from0.72nm to0.84nm, the changes of the strength and porosity are small. Between750～800℃, obvious endothermic occurs, reduced quality is small, Lc sharp increases to.095nm, the binder quickly shrink, the porosity becomes down, the strength sharp increases. Between800～950℃, the changes of the mass, heat and structure are smaller, the strength is higher and the porosity is lower, the firing rection has been completed.(3) Firing temperature of carbon-containing refractory sensor for molten steel temperature measurement has been optimized.On the basis of the study on the effects of the firing temperature on the properties and its mechanism, the firing temperature has been agjusted from950℃to800℃,950℃is the regular temperature. The sensor temperature response continues to heat up and without fluctuation, the response time is less than5min, which are the same with regular sensor. The service life is about24h (SPHC steel) and hasn’t obvious difference with regular sensor. According to the properties of the sensor, the firing temperature of the carbon-containing sensor can be adjusted to800℃, which will save20%energy and improve15%production efficiency.