Influence of dry coated nano-additives on Ca SiO … EA.pdf · Influence of dry coated...
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Influence of dry coated nano-additives on Ca2SiO4 formation Sanat Chandra Maiti, Nishtha Rathore, Chinmay Ghoroi * DryProTech Lab, Chemical Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, Gujarat 382355, India. 1. Introduction Among various types of cement, Ordinary Portland Cement (OPC) is the most common type of cement used in highest percentage for general use around the world[1].The manufacturing of OPC produces about 0.83 tons of CO2 per ton of cement. In contrast, belite cement has been reported as environment friendly materials which reduces almost 10% CO2 [2]. Though it has low hydration rate, still it is being used extensively for construction of dams and lining of oil wells[2]. Therefore, kinetics of di-calcium silicate formation has huge importance in belite cements industry. Reactivity of CaO- SiO2-Al2O3-Fe2O3 system has been extensively studied in presence of several micron size additives[3] (MnO2, CuO, V2O5, PbO, CdO,ZrO2, Li2O, MoO3, Co2O3, NiO, WO3, ZnO, Nb2O5, CrO3, Ta2O5, TiO2, BaO2 and H3BO3).Similarly,reactivity of tri-calcium silicate in presence of micron size additives (TiO2 and BaO) is also well documented[4,5]. However, in all of these studies, wet method is used for mixing the additives with raw materials. Thus, implementation of those innovations in real dry process cement manufacturing remains questionable.Also, the effect of nano-additives such as TiO2 and Fe2O3 on reactivity of di-calcium silicate is not reported so far. The present work aims to enhance the Ca2SiO4 formation using dry coated calcium carbonate (CaCO3) with nano-additives on its surface. Dry-coated CaCO3 with silica reacted at different temperatures for different time intervals. Phase formation was studied using qualitative as well as quantitative analysis of X-ray diffraction. 2. Materials and method AR grade CaCO3 was obtained from SRL, Mumbai and nano-additives (TiO2 and Fe2O3) and SiO2 were purchased from Sigma Aldrich. Required amount of nano-additives were mixed with CaCO3 in V-blendor followed by Prism Co-mill for effectively coating over CaCO3. The details of dry coating technique is given in literature[6]. The coated and uncoated calcium carbonate were mixed with SiO2 at the ratio of 1.8:1 and pressed in to a pellet under 1 ton load. The pellets were placed in the furnace at different temperatures (1100, 1200 and 1350 o C) for different hours. After the reaction, samples were quenched in air and grounded in mortar and pestle and stored in desiccator for further characterization. For the surface morphological features, uncoated and nano-coated samples were analyzed by using field emission scanning electron microscope (FESEM) (JEOL JSM 7600 F, USA).Quantitative phase analyses were determined by Rietveld refinement with the help of Topas 4.2, Bruker. 3. Results and Discussion The micrograph of coated and uncoated calcium carbonate is shown in Fig. 1. Fig. 1A represents the pure CaCO3 and Fig. 1B and C represent the samples coated with nano-Fe2O3 and TiO2 respectively. From the Fig. 1, it is observed that additives are distributed over the surface of calcium carbonate after passing through co-mill. Fig. 2 described the mass percentage of free lime (CaOf) after the reaction at different temperatures with different time intervals. Fig. 2A, B and C represent the mass percentage of CaOf at 1100 o C, 1200 o C and 1350 o C respectively. It can be seen from the graph that with addition of nano-additives, the amount of free lime decreases in the mixture i.e. increases the reactivity of reaction mixture. In addition, the effect of Fe2O3 is more as compared to TiO2 in all the temperatures. The effect is decreased with increasing the temperature and higher time interval. The results indicated that the nano-additives play key role to increase the reactivity of mixture. In Fig. 3 we can see the mass percentage of di-calcium silicate at different temperature with different time intervals.
Transcript of Influence of dry coated nano-additives on Ca SiO … EA.pdf · Influence of dry coated...
Influence of dry coated nano-additives on Ca2SiO4 formation
Sanat Chandra Maiti, Nishtha Rathore, Chinmay Ghoroi*
DryProTech Lab, Chemical Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gandhinagar, Gujarat 382355, India.
1. Introduction
Among various types of cement, Ordinary Portland Cement (OPC) is the most common type of cement used in highest percentage for general use around the world[1].The manufacturing of OPC produces about 0.83 tons of CO2 per ton of cement. In contrast, belite cement has been reported as environment friendly materials which reduces almost 10% CO2 [2]. Though it has low hydration rate, still it is being used extensively for construction of dams and lining of oil wells[2]. Therefore, kinetics of di-calcium silicate formation has huge importance in belite cements industry. Reactivity of CaO-SiO2-Al 2O3-Fe2O3 system has been extensively studied in presence of several micron size additives[3] (MnO2, CuO, V2O5, PbO, CdO,ZrO2, Li2O, MoO3, Co2O3, NiO, WO3, ZnO, Nb2O5, CrO3, Ta2O5, TiO2, BaO2 and H3BO3).Similarly,reactivity of tri-calcium silicate in presence of micron size additives (TiO2 and BaO) is also well documented[4,5]. However, in all of these studies, wet method is used for mixing the additives with raw materials. Thus, implementation of those innovations in real dry process cement manufacturing remains questionable.Also, the effect of nano-additives such as TiO2 and Fe2O3 on reactivity of di-calcium silicate is not reported so far. The present work aims to enhance the Ca2SiO4 formation using dry coated calcium carbonate (CaCO3) with nano-additives on its surface. Dry-coated CaCO3 with silica reacted at different temperatures for different time intervals. Phase formation was studied using qualitative as well as quantitative analysis of X-ray diffraction.
2. Materials and method
AR grade CaCO3 was obtained from SRL, Mumbai and nano-additives (TiO2 and Fe2O3) and SiO2 were purchased from Sigma Aldrich. Required amount of nano-additives were mixed with CaCO3 in V-blendor followed by Prism Co-mill for effectively coating over CaCO3. The details of dry coating technique is given in literature[6]. The coated and uncoated calcium carbonate were mixed with SiO2 at the ratio of 1.8:1 and pressed in to a pellet under 1 ton load. The pellets were placed in the furnace at different temperatures (1100, 1200 and 1350oC) for different hours. After the reaction, samples were quenched in air and grounded in mortar and pestle and stored in desiccator for further characterization. For the surface morphological features, uncoated and nano-coated samples were analyzed by using field emission scanning electron microscope (FESEM) (JEOL JSM 7600 F, USA).Quantitative phase analyses were determined by Rietveld refinement with the help of Topas 4.2, Bruker.
3. Results and Discussion The micrograph of coated and uncoated calcium carbonate is shown in Fig. 1. Fig. 1A represents the pure CaCO3 and Fig. 1B and C represent the samples coated with nano-Fe2O3 and TiO2 respectively. From the Fig. 1, it is observed that additives are distributed over the surface of calcium carbonate after passing through co-mill. Fig. 2 described the mass percentage of free lime (CaOf) after the reaction at different temperatures with different time intervals. Fig. 2A, B and C represent the mass percentage of CaOf at 1100oC, 1200oC and 1350oC respectively. It can be seen from the graph that with addition of nano-additives, the amount of free lime decreases in the mixture i.e. increases the reactivity of reaction mixture. In addition, the effect of Fe2O3 is more as compared to TiO2 in all the temperatures. The effect is decreased with increasing the temperature and higher time interval. The results indicated that the nano-additives play key role to increase the reactivity of mixture. In Fig. 3 we can see the mass percentage of di-calcium silicate at different temperature with different time intervals.
Figure1. Scanning electron micrograph of uncoated and coated samples (A) uncoated CaCO3 (B) with 1 wt. % Fe2O3(C) with 1 wt. % TiO2 Fig. 3A,B and C represent the mass percentage of di-calcium silicate at 1100oC, 1200oC and 1350oC respectively. It is observed that nano-additives boost the formation of di-calcium silicate. The efficiency of Fe2O3 is more as compared to TiO2, which is also observed in the Fig.2.
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Figure 2: Mass percentage of free lime (CaOf) at different temperature at different time intervals (A) at 1100oC (B) at 1200oC (c) at 1350oC.
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Figure 3: Mass percentage of di-calcium silicate (C2S) at different temperatures at different time intervals (A) at 1100oC (B) at 1200oC (c) at 1350oC. Overall the reactivity of the CaO-SiO2 system is improved by presence of nano-additives. This could be explained by the crystal defect introduced by the diffusion of nano-additives in to the CaO crystal at high temperature. From the Fig. 4 it can be seen that with addition of nano-additives the peak shifts
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at 1100oC for different time intervals, which indicate that there exists strain inside the CaO crystal with nano-additives. This improves the reactivity of reaction mixture.
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Figure 4: Effect of doping at 1100 0C for different time intervals. Conclusions: The influence of dry coating of nano-Fe2O3 and TiO2 on reactivity of C2S phase formation is investigated. Nano-Fe2O3 has significant effect on C2S phase formation as compared to TiO2. The strain/defect due to diffusion of additive ions inside the crystals is responsible for higher reactivity of the system. References
[1] P.C. Hewlett, Lea’s Chemistry of Cement and Concrete, Fourth Edi, Elsevier, 1998.
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[3] K. Kolovos, S. Tsivilis, G. Kakali, The effect of foreign ions on the reactivity of the Part II : Cations, 32 (2002) 463–469.
[4] N.K. Katyal, S.C. Ahluwalia, R. Parkash, Effect of barium on the formation of tricalcium silicate, Cem. Concr. Res. 29 (1999) 1857–1862. doi:10.1016/S0008-8846(99)00172-6.
[5] N.K. Katyal, R. Parkash, S.C. Ahluwalia, G. Samuel, Influence of titania on the formation of tricalcium silicate, Cem. Concr. Res. 29 (1999) 355–359. doi:10.1016/S0008-8846(98)00231-2.
[6] V. Karde, C. Ghoroi, Influence of surface modification on wettability and surface energy characteristics of pharmaceutical excipient powders, Int. J. Pharm. 475 (2014) 351–363. doi:10.1016/j.ijpharm.2014.09.002.
