Research On Microstructure And Properties Of Ceramics Prepared Under Oxygen-enriched Or Oxy-fuel Atmosphere

Oxygen-enriched combustion and oxy-fuel combustion are innovative technologies which belong to the area of engineering thermo-physics and applied in high temperature thermal equipment. The advantages attributed to oxygen-enriched or oxy-fuel combustion include increased productivity and energy efficiency, with reduced exhaust gas volume and pollutant emissions. The application of oxygen-enriched or oxy-fuel technology in the ceramic industry is beneficial to the energy-saving emission reduction. However, the influences of oxygen-enriched or oxy-fuel combustion on the microstructure and mechanical properties of sintered samples receive almost no research. In this paper, the effects of oxygen-enriched or oxy-fuel atmosphere on the microstructure and mechanical properties of ceramic specimens were investigated.In this paper, the condition of oxygen-enriched atmosphere, with different O2 concentration, was simulated by changing the volume proportion of CO2, H2 O and N2, which are combustion products of natural gas. The effects of sintering atmosphere, Al2O3 content, forming pressure and heating treatment- sintering temperature and firing time on the microstructure and mechanical properties of samples were investigated to acquire ceramics with improved microstructure and high mechanical properties prepared with optimized sintering procedure, also with substantial energy savings and emission reductions.TG-DSC, XRD, SEM and FT-IR were utilized to identify the microstructure of ceramic samples, and the mechanical properties of ceramics were measured with 3-point technique and Archimedes method. The thermal efficiency of sintering atmosphere, with different O2 concentration, was also calculated.According to the above experiments, the conclusions can be drawn as follows:Compared with conventional air, oxygen-enriched air or oxy-fuel atmosphere showed superior performances, leading to ceramic specimens with better mechanical properties and finer microstructure. An increase in O2 concentration in the simulated sintering atmosphere favors structure densification and mechanical properties enhancement.In the ceramic blank, increasing the Al2O3/SiO2 appropriately was beneficial to the crystallization, endowed ceramic specimens with superior mechanical properties. However, increasing the Al2O3 content excessively led to the degradation in the mechanical properties of the ceramics, mainly due to the blocking effect of AlO6 groups. The optimized Al2O3 content in this paper was 20.92 wt%, endowed ceramics with densest structure and optimal performance.The sintered ceramics with more compact structure were generated by increasing the forming pressure properly and the optimized pressure was 25 MPa in this paper. However, the pressing crack formed when the forming pressure increased from 25 MPa to 30 MPa, resulted in the degradation of mechanical properties. An increase in the sintering temperature and firing time was beneficial to the structure densification and performances enhancement. However, when increasing the sintering temperature or time inappropriately, the structure densification was hindered, resulted in the reduction of mechanical properties. When the oxy-fuel technology was employed in the ceramic sintering, the optimized sintering temperature or time, endowed ceramics with highest properties, is lower than that of ceramics prepared under ambient air, leading to substantial energy conservations.Taking the cost of O2 production and the mechanical properties of ceramic specimens sintered with different atmospheres into consideration, a simulated oxygen-enriched atmosphere with 25 %O2 represents a more economic and practical solution for the ceramic industry.