| China is a country with rich mineral resources, but per capita relative shortage ofresources. Low utilization rate of the ore resource lead to a serious waste of resources. Highvalue-added development and utilization of mineral resources are important for releasing thecontradiction between economic growth and resource shortages. Inorganic hollow sphere is anew type of light industrial base material, with its unique characteristics, such as low density,high strength, low thermal conductivity, low water absorption, high dispersion, electricalinsulation and good thermal stability, et al.In this paper, natural mineral powders were used as raw materials to fabricate hollowsphere by particle stabilized foamed slurry and spray drying technology, then hollow sphereswere used to fabricate hollow sphere porous ceramics with low density and high strength bysintering at a low temperature. The microstructure and mechanical properties of hollow sphereceramics were investigated. The main research conclusions are as follows:The effect of sintering temperature on porosity formation mechanism and properties ofporous ceramics was investigated. The results show that porous ceramics can be prepared atlow sintering temperatures (650-860oC). With the increase of sintering temperature, thecompressive strength and apparent density of sample were first decreased and then increased,the size of the pores was increased. After reaching a certain temperature, the individualbubbles oversize and apparent density of the samples became higher. The apparent densityvalue rapidly decreased from0.61to0.36g/cm3and the compressive strength decreased from11.46to1.91MPa when the sintering temperature was increased from780oC to820oC.In order to improve the mechanical properties of porous ceramics, the effect of alumina(Al2O3) content on the properties of porous ceramics was investigated. The results are shownthat the minimum compressive strength and the minimum apparent density were increased with the increase of Al2O3content at the same sintering temperature. The softeningtemperature was significantly affected by Al2O3content. The more Al2O3content, the higherthe sintering temperature. When Al2O3content is5,6,7and8wt.%, the apparent density is0.37,0.74,0.84and1.22g/cm3, compressive strength is1.10、6.21、15.09and25.58MPa,respectively.In order to reduce the apparent density of porous ceramics, the effect of additive on theproperties of porous ceramics was investigated. Compared with the two kinds of preparationmethods of porous ceramics:(1) Process1: the zeolite powder was added to the raw materialin the preparation processing of hollow sphere.(2) Process2: mixing zeolite powder withhollow sphere. The results shown that: these two different processes could significantlyreduce the apparent density of porous ceramics. With the sintering temperature increased, theapparent density of the hollow sphere porous ceramics via process2decreased more. The airbubbles are small and the pores are intercommunicated. The apparent density of the sampleprepared by process1is0.90g/cm3, the apparent density of the sample prepared by process2is1.21g/cm3sintered at650oC. The size of the pores was increased and the porous structuregradually became closed pore structure in porous ceramics samples, the apparent density ofthe sample prepared by process1is0.30g/cm3, the apparent density of the sample preparedby process2is0.21g/cm3, compressive strength of0.59MPa sintered at800oC.The effect of MgCO3additive on the properties of porous ceramics was investigated.MgCO3was added in process2. The results shown that with the increase of sinteringtemperature, MgCO3additive lead to the apparent density of the sample decreased and thesize of the pores in porous ceramics samples is gradually increased. The apparent density ofsample sintered at650oC was1.22g/cm3. However, when the sintering temperature wasincreased to800oC, the apparent density of sample was0.21g/cm3, compressive strength was1.27MPa, the water absorption was5.81%. Compared to the samples adding zeolite powderand MgCO3by process2, the apparent density of two samples are0.21g/cm3at800oC, butthe sample containing MgCO3in process2had more bubbles, smaller pore sizes,well-distributed pore size and higher compressive strength. |
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