| Steel slag is the most solid wastes in the steel production. The utilization ratio of steel slag in China is very lower because of its characteristics of composition complex, poor grindability, low activity and poor stability of volume, and steel slag resulted in many serious environmental problems. Because the steel slag contains a high silicate composition and has certain cementitious properties, it can be used as raw material for cement,glass-ceramic and ceramics and other building materials. Noise pollution is becoming much severer issues and more urgent to be controled. The use of inorganic non-metallic materials such as porous ceramics and foam glass in controlling noise pollution get more and more attention. Therefore, the preparation of porous absorption material using steel slag is studied to develop new ways and fields of utilizing steel slag and improve its utilization ratio, which is significant for the enterprises to save resources, protect environment and improve economic benefits.In this paper, the high temperature sintering method was selected to prepare steel slag porous sound absorption material. In preparing process, the raw material formula, moulding and pore-forming method were gradually improved according to the change of the key material parameters and performance indexes. By comparing the characteristics of the base materials formula and moulding and pore-forming process of steel slg-fly ash system, steel slag-clay-feldspar-quartz system and steel slag-fly ash-clay-rice husk ash system, the preparation process of the steel slag porous sound absorption material was determined, and the mechanism of pore-forming and sintering process of the porous material was discussed, and the sintering process model of steel slag absorption material was established. The main conclusions of this paper are as follows:(1) The main chemical compositions of steel slag included calcium oxide, silicon dioxide, aluminium oxide, iron sesquioxide, magnesium oxide, etc. The common minerals in steel slag were dicalcium silicate, tri-calcium silicate, dicalcium ferrite, an RO phase (CaO-FeO-MnO-MgO solid solution), dicalcium ferrite, and tricalcium aluminate, etc. The early strength of steel slag cementitious material prepared by cold state was very low, and the strength of the specimen at 28 days reached 18.36MPa. The compressive strength of the samples sintered at high temperature reached 90.86MPa. Thus, comparing with the method of preparing cementitious material, steel slag porous material sintered at high temperature would have better mechanical properties.(2) The mechanical properties of the sample could be obtained and the sintering temperature range could be widened gradually by adding different silica materials to improve the raw material formulation. The porosity of steel slag sound-absorbing material could be improved and the mechanical properties could be well maintained by adjusting the type of pore forming agent, shaping and pore forming method. The porosity of the steel slag sound-absorbing material prepared by using three kinds of base materials formula and its moulding and pore-forming process reached more than 50%. The compressive strength of the steel slag sound-absorbing material reached up to 3.0MPa, and the average absorption coefficien of porous material with 2.5-3.0cm thickness could reach 0.40-0.48. As the preparation process with the steel slag-fly ash-clay-rice husk ash system and composite pore-forming mathod of particle stacking and pore former had some advantages such as high waste utilization rate, simple process, and wide sintering temperature range, and good mechanical properties and sound absorption performance of porous material and so on, it was chosen as the preparation process of steel slag porous material.The optimum preparation conditions for the steel slag sound-absorbing material were a proportion of steel slag, fly ash, clay, and rice husk ash of 12:3:2:3, 10% dolomite, the particle size of 1.2-2.8mm, a forming pressure of 1.0-1.5MPa, sintering temperature range of 1130-1180℃, the appropriate sintering temperature of 1150℃, and a sintering time of 4.0 h.(3)Based on the pore forming mechanism of steel slag porous material, it was found that the rice husk ash and dolomite cloud be used as multifunctional pore forming agent, but also good additive. The porosity of the sintered body with them was more than 50% and flexural strength could reach about 44.7MPa under the appropriate sintering temperature. In the control of sintering temperature, the addition of the raw materials such as rice husk ash, dolomite and feldspar could change the the sintering reaction temperature, the rice husk ash and feldspar could decrease the reaction temperature for 20-30℃ and 10℃ respectivly, but the sintering temperature range would be reduce. The dolomite could broaden the temperature range, while sintering temperature would be improved. Therefore, the addition of the rice husk ash and dolomite should be controled, and the feldspar would not be mixed. The sintering temperature was the main factor affecting the material preparation of steel slag porous material. The porosity forming process of the material was mainly in the low temperature stage, and the heating rate should not be too fast. The sintering reaction mainly occurs in the high temperature stage. Extending the sintering time could promote the sintering reaction and make the crystal grow well; The porous material would obtain good mechanical properties, but the porosity of the material decreased and the sound absorption performance should be affected. The sintering time should be controlled in 2.5-4.Oh. Increasing the molding pressure could increase the density of the body, and promote the sintering reaction, but the porosity of the sample would be obviously decreased. The sample with lower molding pressure had high porosity, but the degree of densification was low. Thus, The molding pressure of the sample should be 1.0-1.5MPa.The sintering process could be divided into the initial, middle and late stages, and included the process of the pore forming agent decomposition reaction and sintering reaction process. The initial stage of sintering was about 0-1100℃, the sintering reaction was slow and the shrinkage was about 1%, and a small amount of andradite was produced, which was the process of pore forming reaction. The middle stage of sintering was about 1100-1150℃, the sintering shrinkage accelerated and the shrinkage reached about 5%, which the sintering neck expanded gradually and the pores shape changed accordingly. The mineral phase changed from intermediate minerals to the stable mineral phase sunch as diopside and a small amount of RO. The final stage of sintering was about 1150-1200℃, the shrinkage reached above 10%, which was the process of rapid change of pore morpholohy, size and quantity, and the process of crystal formation, growth, and the formation of a stable mineral phase. The mass transfer mode was changed due to the high temperature liquid phase. The main process of the sintering reaction was in the intermediate stage and the final stage.The sintering kinetics results showed that the rate constant of the body increased rapidly with the increase of sintering temperature. The value of the sintering time relation index (n) was gradually from 0.221 to 0.342, which indicated that the mass transfer in the body was changed from the surface diffusion to the crystal boundary diffusion. At 1190℃, the n value was reduced to 0.195, which indicated that the liquid phase was produced and the mass transfer mode had been changed. The sintering activation energy was 32.88 kJ/mol at 1150-1190℃.(5) The parameters of the material such as porosity, average pore size, thickness and volume density had obvious effect on the absorption property of steel slag porous material. Increasing the porosity, thickness, pore size and reducing the volume density of the porous material could improve the average sound absorption coefficient; Especially, the effect of increasing the thickness of material on the low frequency absorption coefficient was significant, and the average sound absorption coefficient of the specimen with thickness of 5.1cm reached 0.55. The result of steel slag porous sound absorption material comparing with other commonly porous materials showed that the absorption performance of steel slag porous sound absorption material was better than that of most commonly materials, and the sound absorption coefficient reached 0.74 after the absorption coefficient of the standing wave tube of the porous material was converted into a reverberation chamber method. The sound absorption properties of porous materials were grade Ⅱ, which belongs to the sound absorption products with good absorption properties. |
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