| China is one of the countries with the most abundant coal resources in the world.Coal consumption occupies a dominant position in the production and consumption of disposable energy in China.However,there are serious coal spontaneous combustion disasters in the process of mining,storage,and transportation,which cause a lot of waste of resources,casualties and property losses.On this basis,the technology of polymorphic foam has been studied in order to provide technical support for more effective prevention and control of coal spontaneous combustion.In order to explain the performance of polymorphic foam in restraining coal spontaneous combustion,a systematic analysis is made on its preparation methods and thermal characteristics.Polymorphic foam is mainly composed of foaming liquid and organic acid.The foaming liquid is composed of surfactant,thickener,inhibitor,and silicate.In order to determine the optimum concentration of each component of the polymorphic foam,the fluorescence spectra and Zeta potential were studied.It was found that when the surfactant,thickener,inhibitor,and silicate concentrations were 20g/L,1g/L,0.7g/L and 20g/L,respectively,the surface tension and viscoelasticity of the mixed solution were the best,when the silicate and organic acid uniformly mixed with 8:1,with injected gas,the polymorphic foam performance is the best.In order to analyze the mechanism from a macroscopic perspective,the physical and chemical reactions and energy changes at different time points were analyzed through three samples: coal,polymorphic foam and coal,and polymorphic foam,by thermogravimetric differential scanning calorimeter.The alkyl side chains,oxygen-containing functional groups,and bridge bonds in coal-based macromolecules undergo thermal cracking,releasing small molecule active radicals to react with oxygen.The polymorphic foam has the adsorption of moisture in the air,improves the surface humidity of coal,absorbs the heat produced by coal oxidation,and blocks the pores and fissures of coal by heat fusion.In order to analyze the mechanism from the microscopic perspective,three kinds of samples were analyzed by the means of XPS,XRD and FTIR to analyze the species,atoms form and functional groups of the samples.The results showed that the surface of the polymorphic foam was mainly composed of amorphous silica and sodium sulfate and it can cover the contact between coal and oxidation and interrupt the free radical reaction of coal.A large number of hydrogen ions in the polymorphic foam can reduce the content of hydroxyl and alkyl in the process of coal oxidation,thus inhibiting the low-temperature oxidation of coal. |
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