Microporous Regulations Technology Of Fly-ash Sintering Product

This paper is from the sub-project of the national technology support program of China(project No.2006BAF02A29,named Green Manufacturing Processing Technology and Equipment of New Style Wall Material),Green Manufacturing Technology and Equipment of New Style Self-heat Insulation and Load-bearing Product with High Porosity.Major studying content included four parts:optimal selection of the ratio and sintering system of fly-ash product,sintering mechanism of fly-ash product at high temperature,the effect of different pore former on the characteristic of fly-ash and shale sintering product,the effect of pore former on porosity and thermal conductivity.The main achievements are listed as follows:1.Matrix selection of fly-ash sintering product for pore former and fly-ash sintering mechanism at high temperature(1) With the increasing of agglutinant,shale and sodium base bentonite,there comes out more and more liquid-phase during the procedure of sintering,and the density is much higher,which resist oxygen penetrate into interior of the specimens, so the sample is sintered without enough oxygen,which affects the coherence of the sample.On the other hand,sintering temperature and time affect the properties of the sintering product.(2) The specimens of A70a30,which take 30%of shale(by weight) as agglutinant,sintering at 1050℃for 2h,has the compress strength of 26.81MPa, higher than the sample of A70b30(take 30%sodium base bentonite as agglutinant) 9.82MPa.The porosity of A70a30 is 35.49%,lower than A70b30's 48.08%,and its density is up to 1.58 g·cm^-3.Comparing with A70a30,the best sintering time for A70b30 is 4h,which use up more time and energy.(3) The best raw material proportion and sintering system for fly-ash system is, sample A70a30,sintered by the system of:＜400℃,2℃/min;≥400℃,3℃/min; holding at 1000℃for 2h;cooling down with the furnace.(4) Shale added into fly-ash powder can decrease the sintering temperature,and enhance the ability of fireproofness.Small particle of shale filled into the bigger gaps of fly-ash particles,which increases the bulk density.Minerals in shale turn to flowing liquid phase at a lower temperature,and make the second part of sintering procedure ended ahead of time,which make the pure fly-ash samples' shrinkage at the sintering temperature higher than those added with shale.The increasing amount of liquid phase also increases the viscosity of the sample,which has the positive effect of making samples to maintain their appearance.The fluent of the liquid phase is increasing along with temperature's elevation.So,samples added with shale melt with the shape of semi spherical,the diameter of the bottom increases obviously,and the top is decreases.Pure fly-ash expands irregularly along its vertical axis.(5) Mullite and SiO₂ are the main outcome of the fly-ash sintering product. Fly-ash particle is glass-state material after high temperature.In XRD pattern,the characteristic peaks of its mineral are vague,which proves its glass state.There are Na₂CO₃ in shale,which can react with mullite at high temperature and make the mullite decomposes into nepheline.(6) Shale particles fill the gaps among fly-ash,increase the bulk density,promote solide-solide reaction,increase the amount of liquid phase in high temperature, reduce the sintering temperature,and they benefit the samples' compressive strength.2.The effect of different mechanism pore former on the characteristic of fly-ash sintering product(1) Pore former added within the sintering product can decrease the shrinkage ratio of the specimens when sintering;because of different pore former mechanism the compress strength losing ratio is distinct from each other,so are the porosity increasement and density decreasement.(2) There are no differences among biological pore formers(such as PF,R,and S) in controlling the sintering shrinkage ratio;Pore formers' density and ash content after burning make the mass loss ratio different.Specimens added with S have the best property of compress strength,porosity and volume density than those added with other biological pore formers.The strength of specimens S10 is 12.26MPa,much higher than those added with PF10 and S10; the porosity ratio is 42.43%,2%higher than the other two samples;and the volume density is 1.32 g·cm^-3 lower than the rest samples. (3) Mineral-internal-burning pore formers(such as M) can decrease the strength losing percentage,samples M10 still get the strength of above 20MPa,with the porosity of 43.1%,which is higher than those with biologic pore former,the volume density is 1.38 g·cm^-3,higher than other specimens.(4) Thermal decomposition pore formers(such as L) have a better effect in controlling the sintering shrinkage,both diameter and height shrinkages decrease obviously along with the pore former volume increasement,and the shrinkage of L15 decreased to about 2%.L pore former has an equal affection on the compress strength with the biological pore former,sample L10's strength is about 12MPa,with the porosity of 45%.(5) Added with pore formers of different mechanism,there is a consistency of specimens' pore size distribution at each interval.Specimens,added with a better effect pore former can increase the number of pores much better at each interval.(6) The thermal conductivity has a nearly linear relationship between porosity and volume density in similar kind of product.In sintering products,the linear relationship between thermal conductivity y(W/m·k) and porosity x(%) is y=-0.0326x+1.872,while that between y and volume density z(g·cm^-3) is y=0.4999z-0.1851.