Effect Of Nano Alumina Powder On Hydration Of Calcium Aluminate Cement And Sintering Of Castable Matrix

The strength of the calcium aluminate cement bonded castables is low at intermediate temperatures.During the first heating process,the castables appear easily pelling phenomenon.which greatly reducing the high temperature using reliability.The introduction of nano alumina powders with high surface activity can promote the sintering of the castable matrix,which may improve the strength of castables at medium and high temperature.At present,there are few researches on the sintering behavior of castables containing nano alumina powders.Moreover,the effect of nano alumina powders on hydration rateof calcium aluminate cement,the flowability and the working time of castables has not been reported.Therefore,this work studied the effect of nano alumina powders on the hydration behavior of calcium aluminate cement at different temperatures and on the sintering properties of alumina powders and castable matrix.The results showed that:(1)at 10~40°C,alumina gel powders and alumina nano powders promoted the hydration of calcium aluminate cement.Alumina gel powders did not change the anomalous setting behavior of calcium aluminate cement at 10~30°C,whilethe hydration rate accelerated significantly at 30°C.The anomalous setting behavior ofthe samples with alumina nano powders disappeared at 30~40°C.Then,alumina nano powders changed anomalous setting behavior.The reason is that alumina nano powders and alumina gel powders provide more nucleation areas,which promote the hydration of calcium aluminate cement.(2)At 10~40°C,the alumina gel powders and the alumina nano powders promoted the hydration of calcium aluminate cement,which were conducive to the formation of hydration products,and the amount of hydration products were more.The effect of alumina nano powders was more stronger,and the hydration products had better crystallinity.Because the alumina nano powders have better dispersion and provide more nucleation areas to promote the hydration of calcium aluminate cement than the alumina gel powders.(3)When the curing temperature was40°C,the time of thepeak of hydration exotherm of the sample of pure calcium aluminate cement was 3 h.The time of thepeak of hydration exotherm of the sampleswith 5% alumina gel powders and 5% alumina nano powderswas40 min and 30 min,respectively.The alumina nano powders and the alumina gel powders greatly promoted the hydration of calcium aluminate cement,so the setting time of the castables was too short to working.Therefore,when the environment temperature is high(40°C),it is not suitable for adding alumina nano powders and alumina gel powders.(4)Both alumina gel powders and alumina nano powders with the large surface areas and high activity promoted sintering of the alumina powders at 1200~1500°C.Different specific surface areas and degree of agglomerate resulted in the different best amount of addition.The content of alumina gel powders was 5%,the modulus of rupture of the samples was the best,which was 88.67 MPa.And the alumina gel powders is easier to agglomerate,the strength of the sample decreases when adding a large amount of alumina gel powders.While the content of alumina nano powders was 30%,the modulus of rupture of the samples was the best,which was 86.67 MPa.It shows that the dispersion of alumina nano powders is better than alumina gel powders.(5)The alumina gel powders and the alumina nano powders were favorable for the sintering of castable matrix.At 1600°C.The modulus of rupture of samples of castable matrix was 100 MPa.The addition of alumina gel powders should not be relatively high due to the larger specific surface areas and degree of agglomerate.When the content of alumina gel powders was 5%,the modulus of rupture of samples was the largest,which was 118.25 MPa.However,with the content addition the alumina gel powders are seriously agglomerate,the strength of the sample decreased.Alumina nano powders presented excellent dispersion so the addition could be increased appropriately.When the content of alumina nano powders was 30%,the modulus of rupture of samples was the largest,which was 120 MPa.