The chrome-containing corundum castables specimens with different nano-CaCO3 additions （0-1.6 wt%） were prepared using tabular corundum,alumina powder,chrome oxide micropowder （average particle size 〈 5 μm）,calc...The chrome-containing corundum castables specimens with different nano-CaCO3 additions （0-1.6 wt%） were prepared using tabular corundum,alumina powder,chrome oxide micropowder （average particle size 〈 5 μm）,calcium aluminate cement （Secar71）,commercial nano-CaCO3 （average particle size 〈100 nm） as main starting materials and FS10 as water reducer. The specimens heat treated at 1 000 ℃ and 1 600 ℃ were characterized in terms of apparent porosity,bulk density,cold and hot strengths,and microstructure. The results show that,when the nano-CaCO3 addition is no more than 1.0 wt%,the apparent porosity of the castables increases with nano-CaCO3 addition increasing,both the cold and hot strengths are enhanced; however,when the nano-CaCO3 addition excesses 1.0 wt%,both the cold and hot strengths go down remarkably with nano-CaCO3 addition increasing; the thermal shock resistance is gradually improved with nano-CaCO3 addition increasing in chosen range.展开更多
The castables specimens were prepared using white fused alumina particle and powder, α-Al2O3 micropowder, hydrated alumina, nano calcium carbonate or calcium aluminate cement as starting materials. Effects of nano ca...The castables specimens were prepared using white fused alumina particle and powder, α-Al2O3 micropowder, hydrated alumina, nano calcium carbonate or calcium aluminate cement as starting materials. Effects of nano calcium carbonate addition on phase compositions, strength and microstructure of corundum based castables were studied. The calcium aluminate cement-containing corundum based castables with the same CaO amount was also tested for comparison. The results show that, when temperature is higher than 900 ℃ , the phase compositions of nano CaCO3-containing mixture and the calcium aluminate cement containing mixture are the same, but the forming mechanism, modality and distribution of new phases in the castables are different. With temperature rising, the hydration cement dehydrates and reacts inside cement forming calcium aluminate until the alumina in cement is not enough for the reaction （ternperature is 91 400 ℃ ） , then reacts with the surrounding alumina forming cluster CA6 in the castables. The change process of nano CaCO3 in corundum based enstables is that nano calcium carbonate decomposes to CaO after firing at 800℃ which reacts with Al2O3 forming amorphous calcium aluminate that causes an in-situ bonding. With temperature rising, the formed calcium aluminate reacts with Al2O3 in matrix and wholly forms tabular CA6 at 1 600 ℃ , which distributes uniformly in the castables. The cold and hot strength of the castables with nano calcium carbonate are obviously higher than those of the castables without nano calcium carbonate, especially at 800 -1 000 ℃ due to smaller size and higher dispersion of the nano calcium carbonate and its different reaction mechanism with Al2O3.展开更多
Calcium aluminate cement(CAC)bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials,CAC as the binder,zinc hydroxide(Zn(OH)_(2))and basic zinc carbonate(BZ...Calcium aluminate cement(CAC)bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials,CAC as the binder,zinc hydroxide(Zn(OH)_(2))and basic zinc carbonate(BZC)as the ZnO precursors.The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed,and the reasons affecting the hot performance of the castables were studied.The results show that Zn(OH)_(2) with a smaller particle size(d_(50)=1.26μm)is prone to agglomerate during sample preparation and generates ZnAl_(2)O_(4) spinel grains after firing,hindering the growth of CA_(6),thus decreasing the mechanical strength of the castables.BZC with a larger particle size(d_(50)=2.91μm),which shows a sound dispersity,in-situ generates nano-sized ZnO after firing,and ZnO or Zn^(2+)diffuses into calcium aluminates,promoting the sintering of CA_(2) and CA_(6),thereby enhancing the hot properties of the CAC-bonded corundum based castables.展开更多
文摘The chrome-containing corundum castables specimens with different nano-CaCO3 additions （0-1.6 wt%） were prepared using tabular corundum,alumina powder,chrome oxide micropowder （average particle size 〈 5 μm）,calcium aluminate cement （Secar71）,commercial nano-CaCO3 （average particle size 〈100 nm） as main starting materials and FS10 as water reducer. The specimens heat treated at 1 000 ℃ and 1 600 ℃ were characterized in terms of apparent porosity,bulk density,cold and hot strengths,and microstructure. The results show that,when the nano-CaCO3 addition is no more than 1.0 wt%,the apparent porosity of the castables increases with nano-CaCO3 addition increasing,both the cold and hot strengths are enhanced; however,when the nano-CaCO3 addition excesses 1.0 wt%,both the cold and hot strengths go down remarkably with nano-CaCO3 addition increasing; the thermal shock resistance is gradually improved with nano-CaCO3 addition increasing in chosen range.
文摘The castables specimens were prepared using white fused alumina particle and powder, α-Al2O3 micropowder, hydrated alumina, nano calcium carbonate or calcium aluminate cement as starting materials. Effects of nano calcium carbonate addition on phase compositions, strength and microstructure of corundum based castables were studied. The calcium aluminate cement-containing corundum based castables with the same CaO amount was also tested for comparison. The results show that, when temperature is higher than 900 ℃ , the phase compositions of nano CaCO3-containing mixture and the calcium aluminate cement containing mixture are the same, but the forming mechanism, modality and distribution of new phases in the castables are different. With temperature rising, the hydration cement dehydrates and reacts inside cement forming calcium aluminate until the alumina in cement is not enough for the reaction （ternperature is 91 400 ℃ ） , then reacts with the surrounding alumina forming cluster CA6 in the castables. The change process of nano CaCO3 in corundum based enstables is that nano calcium carbonate decomposes to CaO after firing at 800℃ which reacts with Al2O3 forming amorphous calcium aluminate that causes an in-situ bonding. With temperature rising, the formed calcium aluminate reacts with Al2O3 in matrix and wholly forms tabular CA6 at 1 600 ℃ , which distributes uniformly in the castables. The cold and hot strength of the castables with nano calcium carbonate are obviously higher than those of the castables without nano calcium carbonate, especially at 800 -1 000 ℃ due to smaller size and higher dispersion of the nano calcium carbonate and its different reaction mechanism with Al2O3.
文摘Calcium aluminate cement(CAC)bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials,CAC as the binder,zinc hydroxide(Zn(OH)_(2))and basic zinc carbonate(BZC)as the ZnO precursors.The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed,and the reasons affecting the hot performance of the castables were studied.The results show that Zn(OH)_(2) with a smaller particle size(d_(50)=1.26μm)is prone to agglomerate during sample preparation and generates ZnAl_(2)O_(4) spinel grains after firing,hindering the growth of CA_(6),thus decreasing the mechanical strength of the castables.BZC with a larger particle size(d_(50)=2.91μm),which shows a sound dispersity,in-situ generates nano-sized ZnO after firing,and ZnO or Zn^(2+)diffuses into calcium aluminates,promoting the sintering of CA_(2) and CA_(6),thereby enhancing the hot properties of the CAC-bonded corundum based castables.
