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Glucose-assisted combustion-nitridation synthesis of well-distributed CrN nanoparticles
Materials Research Bulletin 52 (2014) 74–77
Contents lists available at ScienceDirect
Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
Short communication
Glucose-assisted combustion-nitridation synthesis of well-distributed CrN nanoparticles Zhiqin Cao a,b, Mingli Qin a,*, Aimin Chu c, Min Huang a, Haoyang Wu a, Xuanhui Qu a a
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China School of resources and environmental engineering, Pan Zhihua University, Pan Zhihua 617000, China c School of Electromechanism Engineering, Hunan University of Science and Technology, Xiangtan 411201, China b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 September 2013 Received in revised form 1 January 2014 Accepted 7 January 2014 Available online 15 January 2014
Chromium nitride (CrN) nanoparticles were synthesized by nitridation of a glucose-assisted combustion synthesized precursor. Effects of glucose on the size and morphology of the precursors as well as synthesized CrN nanoparticles were studied. The results indicated that the precursor, synthesized from glucose (0.025 mol), was comprised of paper-thin flaky particles with high specific surface area (34 m2/g). Moreover, the product from glucose nitrided at 800 8C for 6 h exhibited single-crystalline structure of each cubic CrN nanocrystal, and consisted of well-distributed particles with an average size of about 20–50 nm. On the contrary, the product without glucose nitrided at 800 8C was agglomerated. Glucose was found to induce homogeneous and well-distributed nanoparticles. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Nitrides Nanostructures Chemical synthesis X-ray diffraction Microstructure
1. Introduction Chromium nitride (CrN) due to its excellent high chemical stability and functional physical properties such as high corrosion resistance and good wear resistance, has attracted considerable interest for their potential applications in electronic industry and high-temperature structural ceramics fields [1–4]. In addition, chromium nitride has been found to increase attention because of the pressure dependence of its mechanical properties through a phase transition from a paramagnetic cubic structure to an antiferromagnetic orthorhombic one [5]. Recent research showed that CrN nanocrystals of fcc structure exhibited attractive catalytic activity for cells [6–8]. Traditionally, many approaches have been developed for the preparation of CrN, such as ammonolysis [9], reactive sputtering [10], mechanically activated synthesis [11] and so on. Ammonolysis is widely used for nitridation. It is carried out by heating a reactive substance in a stream of ammonia gas to a temperature range between 700 8C and 1100 8C [12]. Because of high reactivity of ammonia (compared to nitrogen), it’s more likely to react with the reactants. Using ammonolysis to prepare nitrides
* Corresponding author at: School of Materials Science and Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, 100083 Beijing, China. Tel.: +86 10 82377286; fax: +86 10 62334311. E-mail address: [email protected] (M. Qin). 0025-5408/$ – see front matter ß 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2014.01.011
can significantly reduce the reaction temperature and gain smaller and higher purity products. Therefore, it was successfully used to synthesize nitrides [13–17]. Recently, low temperature combustion synthesis (LCS) has been introduced for the preparation of oxide powders with homogeneous nanocrystals [18–20]. This method involves exothermic chemical reaction between oxidizer and fuel, which are dissolved into a solution, providing high level molecular mixing of the components. The chemical energy released from the exothermic reaction provides self-sustained reaction. As a result, powder with high purity, better homogeneity and high surface area forms in a rapid, inexpensive single step operation. The fuels acted as complexing agents reacting with metal cations, and prevented selective precipitation at the heating stage of solution [21]. We have successfully synthesized nitrides by the combination of low temperature combustion and carbothermal reduction [20,22–24]. The use of glucose has various roles in materials synthesis [25]. In this work, glucose as an assisted additive, chromium nitrate as an oxidizer and chromium source, and glycine as fuel have been utilized. It is combination of low temperature combustion and ammonolysis to synthesis of CrN for the first time. Firstly, precursor has been prepared by LCS method. Subsequently, the CrN nanoparticle has been synthesized by ammonolysis of the prepared precursor. In addition, the effects of glucose on the particle size and morphology of the precursors as well as the synthesized CrN nanoparticles have been discussed.
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Fig. 1. DTA curves of the gel from glucose: (a) 0 mol glucose and (b) 0.025 mol glucose.
2. Experimental procedure Chromium nitrate (Cr(NO3)39H2O), glycine (C2H5NO2), and glucose (C6H12O6H2O) used for the synthesis can be purchased commercially and have the analytical reagent grade. In a typical sample preparation procedure, the starting solution was prepared by dissolving all materials with 150 ml distilled water. Among solution, the amount of chromium nitrate was 0.025 mol, and the molar ratio of glycine to chromium nitrate was fixed at 1, while the amount of glucose was 0.025 mol. The optimized amount of glucose in the initial solution was explored for the C/Cr molar ratio of 6. Each sort of solution was filled into a 500 ml glass, and subsequently the solution was heated in air on an electrical furnace whose temperature could be controlled to prepare the precursor. As heating continued, the solution evaporated and formed a gelatinous mass. Upon further heating, the resultant mass swelled suddenly accompanied by the release of a lot of gases. The whole process of swelling and combustion of gel appeared to undergo a selfpropagating and nonexplosive exothermic reaction and took several minutes, resulting in a fragile and foamy mass of precursor. Because carbon is not needed for the ammonolysis, the residual carbon in precursor was removed by heating at 700 8C in air for 90 min. The ammonolysis of precursor was performed in a tube furnace. A strict temperature program was followed in all runs, with heating at a constant rate of 10 8C min1 up to the plateau temperature, 600– 800 8C. The precursors were nitrided in a flowing NH3 at various temperatures for 6 h using a flow rate of 0.3 L min1. Differential thermal analysis of the gel collected prior to foam of the solution was performed in flowing air (20 ml min1) up to 600 8C at a heating rate of 10 8C min1 by using a thermal analyzer (DTA/TGA, Rigaku, DT-40, Tokyo, Japan). X-ray diffraction study of the precursor and the particles were carried out in an X-ray diffractometer using Cu Ka (l = 0.1542 nm) radiation [X-ray diffraction (XRD); Rigaku, D/max-RB12, TTRAX3 theta-theta gonio.]. The step is 0.028 and the time is 9 min from 108 to 1008. The morphology and particle size of the precursors and nitridation products were observed by scanning electron microscopy (SEM, JSM-5600) and field emission scanning electron microscopy (FESEM, JSM-6701F), respectively. The nitridation products were also observed by transmission electron microscopy (TEM, Tecnai G2 F30 S-TWIN). The specific surface area (SSA) of the precursors was determined by the BET method by using an Automated Surface Area & Pore Size Analyzer (QUADRASORB SI-MP, Quantachrome Instruments, Boynton Beach, FL).
(added 0 mol glucose), it is obvious that there is only one exothermic peak at 170 8C that can be attributed to redox reaction between chromium nitrate and glycine. Eq. (1) describes the exothermic reaction in a simple manner. Fig. 1b (added 0.025 mol glucose) shows an endothermic reaction that starts at approximately 100 8C and a sharp exothermic peak at 130 8C. In the temperature region of 100–120 8C, the endothermic peak is attributed to the vaporization of physically bound absorbed water and the dehydration reaction of gel sample. With respect to Fig. 1a (added 0 mol glucose), the drastic exothermic peak at 130 8C is ascribed to the thermally induced reaction between chromium nitrate and glycine and accompanied with the decomposition of glucose. Eq. (2) describes the decomposition reaction in a simple manner. As heating temperature is further increased, the exothermic peak, observed at 290 8C, corresponds to the oxidation of the carbon generated by decomposing of glucose, as shown in Eq. (3). When temperature surpasses 350 8C, the heat flow of the sample keeps nearly constant. It indicates the end of reaction. Compared to DSC curves of Fig. 1a, it indicates that Eqs. (2) and (3) do not occur without the glucose and the temperature of the exothermic reaction without the glucose is observed at higher temperature. 6CrðNO3 Þ3 þ 10C2 H5 NO2 ! 3Cr2 O3 þ 20CO2 þ 25H2 O þ 14N2
(1)
C6 H12 O6 ! 6C þ 6H2 O
(2)
C þ O2 ! CO2
(3)
3. Results and discussion Fig. 1 shows the results of differential scanning calorimetry (DSC) analysis of precursors prepared by the LCS. From Fig. 1a
Fig. 2. XRD patterns of the precursors prepared by LCS: (a) 0 mol glucose and (b) 0.025 mol glucose.
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The XRD patterns for the precursors (before removing carbon) can be seen in Fig. 2. It is evident from Fig. 2a (added 0 mol glucose) that no obvious Bragg diffraction peaks have been detected in the precursor. It indicates that the precursor is amorphous in structure. It means that the energy generated from the Eq. (1) is not sufficient for the crystallization of Cr2O3. However, in Fig. 2b, the Cr2O3 crystallite has been formed. This may be ascribed to the higher energy of exothermic reaction and the energy generated from the Eq. (3). It also proves that glucose promotes the formation of Cr2O3 crystallites at lower temperature. The SEM images of the two precursors are shown in Fig. 3. The precursor added 0 mol glucose mainly consists of flaky particles with flocculent (Fig. 3a). Moreover, the SSA of this precursor is calculated to be 20 m2/g. The high SSA of this precursor is ascribed to the dispersant effect of gases generated during the Eq. (1). The glucose as an additive (0.025 mol) renders the flake-like particles more attenuated exhibiting the porous and paper-thin flaky
appearance (Fig. 3b and c). The SSA of this precursor (after being decarburized) is calculated to be 34 m2/g. It indicates that the SSA of the precursor from glucose (0.025 mol) is higher than that of the precursor added 0 mol glucose. This may be ascribed to the higher gas amount generated from both the Eqs. (2) and (3). However, the comprehension about the formation mechanism for the high SSA of the precursor from added glucose is still under investigation and will be published later. Fig. 4 presents the XRD patterns of the precursors nitrided at the temperature of 600–800 8C in flowing NH3 gas during 6 h. At the temperature of 600 8C, the product without glucose exhibits diffraction peaks of chromic oxide (Fig. 4a), indicating the crystallization process from amorphous to chromic oxide during heating. The product with glucose (Fig. 4b) exhibits no diffraction peaks of CrN. In Fig. 4a and b, the CrN has been observed at 700 8C but there is also chromic oxide. It indicates that CrN has been obtained by ammonolysis of chromic oxide, as shown in Eq. (4).
Fig. 3. SEM micrographics of the precursors prepared by LCS: (a) 0 mol glucose, (b) and (c) 0.025 mol glucose.
Fig. 4. XRD patterns of the products prepared by ammonolysis at different temperatures: (a) 0 mol glucose and (b) 0.025 mol glucose.
Fig. 5. FE-SEM micrographics of the products prepared by ammonolysis at 800 8C: (a) 0 mol glucose and (b) 0.025 mol glucose.
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Fig. 6. (a) TEM image and (b) SAED pattern of the product (0.025 mol glucose) prepared by ammonolysis at 800 8C.
The phase-pure cubic CrN has been obtained at 750 8C and well crystallized at 800 8C. Cr2 O3 þ 2NH3 ! 2CrN þ 3H2 O
(4)
Fig. 5 presents the FE-SEM images of the two products synthesized at 800 8C. It is obvious that the powder agglomerates consists of 30–80 nm particles (Fig. 5a). However, the product from glucose (0.025 M) is composed of well-distributed spherical particles varying from 20 to 50 nm (Fig. 5b), which may be ascribe to the dehydrated species of glucose and the carbon particles generated through the carbonization of glucose adsorbed on the as prepared particles hindering their crystal growth. Moreover, the product particles added glucose has exhibited much better spherical and homogenous morphology than that of product particles without glucose. The morphology of the prepared CrN nanoparticles from added glucose at 800 8C is investigated by TEM. The TEM image of the CrN particles is shown in Fig. 6a. It is obvious that the product powder consists of well-distributed spherical CrN particles varying from 20 to 50 nm, which is in good agreement with the FE-SEM images of the product (Fig. 5b). In order to get more information about the particles, the corresponding selected-area electron diffraction (SAED) is shown in Fig. 6b. The clear diffraction spots reveal CrN phase in agreement with the XRD results and further confirm the single-crystalline structure of each cubic CrN nanocrystal. 4. Conclusions Glucose has exhibited a significant effect on the morphology of the precursor prepared by LCS method. It has also been observed that the size and morphology of CrN nanoparticles, synthesized by nitridation of this LCS precursor, are affected by the glucose. The nitridation product with glucose is found to be finer than the products without glucose. Moreover, CrN powders yielded from glucose (0.025 mol) consisted of well distributed spherical particles of size 20–50 nm. Glucose was found to induce a homogeneous and well-distributed nanoparticles.
Acknowledgements This work is financially supported by the National Natural Science Foundation Program of China (50802006) and (51172017), Program for New Century Excellent Talents in University (NCET10-0226), and the Fundamental Research Funds for the Central Universities (FRF-TP-11-004A) and National 863 Program. References [1] H. Chen, P.Q. Wu, C. Quaeyhaegens, K.W. Xu, L.M. Stals, J.W. He, J.P. Celis, Wear 253 (2002) 527–532. [2] L. Cunha, M. Andritschky, K. Pischow, Z. Wang, A. Zarychta, A.S. Miranda, A.M. Cunha, Surf. Coat. Technol. 153 (2002) 160–165. [3] C. Liu, A. Leyland, Q. Bi, A. Matthews, Surf. Coat. Technol. 141 (2001) 164–173. [4] P. Engel, G. Schwarz, G.K. Wolf, Surf. Coat. Technol. 112 (1999) 286–290. [5] F. Rivadulla, M. Banobre-Lopez, C.X. Quintela, V. Pardo, D. Baldomir, M.A. LopezQuintela, J. Rivas, C.A. Ramos, C.H. Salva, J.S. Zhou, J.B. Goodenough, Nat. Mater. 8 (2009) 947–951. [6] H.X. Zhong, X.B. Chen, H.M. Zhang, M.R. Wang, S.S. Mao, Appl. Phys. Lett. 911 (2007) 63103. [7] Q. Sun, Z.-W. Fu, Electrochem. Solid St. 10 (2007) A189–A193. [8] M. Yang, R. Guarecuco, F.J. DiSalvo, Chem. Mater. 25 (2013) 1783–1787. [9] Y.G. Li, L. Gao, J.G. Li, D.S. Yan, J. Am. Ceram. Soc. 85 (2002) 1294–1296. [10] I. Miloˇsev, B. Navinˇsek, J. Electrochem. Soc. 140 (1993) L30–L32. [11] P. Cai, J. Zhu, Z. Yang, Y. Qian, Mater. Chem. Phys. 95 (2006) 1–4. [12] Y. Kim, J. Li, J.-P. Zhang, R. Seshadri, Solid State Sci. 13 (2011) 216–223. [13] A.W. Jackson, O. Shebanova, A.L. Hector, P.F. McMillan, J. Solid State Chem. 179 (2006) 1383–1393. [14] D. Choi, G.E. Blomgren, P.N. Kumta, Adv. Mater. 18 (2006) 1178–1182. [15] S. Kaskel, K. Schlichte, G. Chaplais, M. Khanna, J. Mater. Chem. 13 (2003) 1496– 1499. [16] T. Aarthi, G. Madras, Catal. Commun. 9 (2008) 630. [17] G. Cao, Y. Li, Q. Zhang, H. Wang, J. Am. Ceram. Soc. 95 (2012) 2478–2480. [18] J. Kishan, V. Mangam, B.S.B. Reddy, S. Das, K. Das, J. Alloys. Compd. 490 (2010) 631. [19] F.A. Rabuffetti, J.S. Lee, R.L. Brutchey, Chem. Mater. 24 (2012) 3114–3116. [20] A. Chu, M. Qin, Rafi-ud-din, B. Jia, H. Lu, X. Qu, J. Am. Ceram. Soc. 95 (2012) 2510– 2515. [21] S.R. Nair, R.D. Purohit, A.K. Tyagi, P.K. Sinha, B.P. Sharma, Mater. Res. Bull. 43 (2008) 1573–1582. [22] M. Qin, X. Du, Z. Li, I.S. Humail, X. Qu, Mater. Res. Bull. 43 (2008) 2954–2960. [23] A. Chu, M. Qin, X. Jiang, L. Zhang, B. Jia, H. Lu, Y. Chen, X. Qu, Mater. Charact. 81 (2013) 76–84. [24] A. Chu, M. Qin, Rafi-ud-din, B. Jia, H. Lu, X. He, X. Qu, Mater. Res. Bull. 47 (2012) 2475–2479. [25] M.K. Naskar, J. Am. Ceram. Soc. 93 (2010) 1260–1263.
Contents lists available at ScienceDirect
Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
Short communication
Glucose-assisted combustion-nitridation synthesis of well-distributed CrN nanoparticles Zhiqin Cao a,b, Mingli Qin a,*, Aimin Chu c, Min Huang a, Haoyang Wu a, Xuanhui Qu a a
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China School of resources and environmental engineering, Pan Zhihua University, Pan Zhihua 617000, China c School of Electromechanism Engineering, Hunan University of Science and Technology, Xiangtan 411201, China b
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 September 2013 Received in revised form 1 January 2014 Accepted 7 January 2014 Available online 15 January 2014
Chromium nitride (CrN) nanoparticles were synthesized by nitridation of a glucose-assisted combustion synthesized precursor. Effects of glucose on the size and morphology of the precursors as well as synthesized CrN nanoparticles were studied. The results indicated that the precursor, synthesized from glucose (0.025 mol), was comprised of paper-thin flaky particles with high specific surface area (34 m2/g). Moreover, the product from glucose nitrided at 800 8C for 6 h exhibited single-crystalline structure of each cubic CrN nanocrystal, and consisted of well-distributed particles with an average size of about 20–50 nm. On the contrary, the product without glucose nitrided at 800 8C was agglomerated. Glucose was found to induce homogeneous and well-distributed nanoparticles. ß 2014 Elsevier Ltd. All rights reserved.
Keywords: Nitrides Nanostructures Chemical synthesis X-ray diffraction Microstructure
1. Introduction Chromium nitride (CrN) due to its excellent high chemical stability and functional physical properties such as high corrosion resistance and good wear resistance, has attracted considerable interest for their potential applications in electronic industry and high-temperature structural ceramics fields [1–4]. In addition, chromium nitride has been found to increase attention because of the pressure dependence of its mechanical properties through a phase transition from a paramagnetic cubic structure to an antiferromagnetic orthorhombic one [5]. Recent research showed that CrN nanocrystals of fcc structure exhibited attractive catalytic activity for cells [6–8]. Traditionally, many approaches have been developed for the preparation of CrN, such as ammonolysis [9], reactive sputtering [10], mechanically activated synthesis [11] and so on. Ammonolysis is widely used for nitridation. It is carried out by heating a reactive substance in a stream of ammonia gas to a temperature range between 700 8C and 1100 8C [12]. Because of high reactivity of ammonia (compared to nitrogen), it’s more likely to react with the reactants. Using ammonolysis to prepare nitrides
* Corresponding author at: School of Materials Science and Engineering, University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, 100083 Beijing, China. Tel.: +86 10 82377286; fax: +86 10 62334311. E-mail address: [email protected] (M. Qin). 0025-5408/$ – see front matter ß 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.materresbull.2014.01.011
can significantly reduce the reaction temperature and gain smaller and higher purity products. Therefore, it was successfully used to synthesize nitrides [13–17]. Recently, low temperature combustion synthesis (LCS) has been introduced for the preparation of oxide powders with homogeneous nanocrystals [18–20]. This method involves exothermic chemical reaction between oxidizer and fuel, which are dissolved into a solution, providing high level molecular mixing of the components. The chemical energy released from the exothermic reaction provides self-sustained reaction. As a result, powder with high purity, better homogeneity and high surface area forms in a rapid, inexpensive single step operation. The fuels acted as complexing agents reacting with metal cations, and prevented selective precipitation at the heating stage of solution [21]. We have successfully synthesized nitrides by the combination of low temperature combustion and carbothermal reduction [20,22–24]. The use of glucose has various roles in materials synthesis [25]. In this work, glucose as an assisted additive, chromium nitrate as an oxidizer and chromium source, and glycine as fuel have been utilized. It is combination of low temperature combustion and ammonolysis to synthesis of CrN for the first time. Firstly, precursor has been prepared by LCS method. Subsequently, the CrN nanoparticle has been synthesized by ammonolysis of the prepared precursor. In addition, the effects of glucose on the particle size and morphology of the precursors as well as the synthesized CrN nanoparticles have been discussed.
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Fig. 1. DTA curves of the gel from glucose: (a) 0 mol glucose and (b) 0.025 mol glucose.
2. Experimental procedure Chromium nitrate (Cr(NO3)39H2O), glycine (C2H5NO2), and glucose (C6H12O6H2O) used for the synthesis can be purchased commercially and have the analytical reagent grade. In a typical sample preparation procedure, the starting solution was prepared by dissolving all materials with 150 ml distilled water. Among solution, the amount of chromium nitrate was 0.025 mol, and the molar ratio of glycine to chromium nitrate was fixed at 1, while the amount of glucose was 0.025 mol. The optimized amount of glucose in the initial solution was explored for the C/Cr molar ratio of 6. Each sort of solution was filled into a 500 ml glass, and subsequently the solution was heated in air on an electrical furnace whose temperature could be controlled to prepare the precursor. As heating continued, the solution evaporated and formed a gelatinous mass. Upon further heating, the resultant mass swelled suddenly accompanied by the release of a lot of gases. The whole process of swelling and combustion of gel appeared to undergo a selfpropagating and nonexplosive exothermic reaction and took several minutes, resulting in a fragile and foamy mass of precursor. Because carbon is not needed for the ammonolysis, the residual carbon in precursor was removed by heating at 700 8C in air for 90 min. The ammonolysis of precursor was performed in a tube furnace. A strict temperature program was followed in all runs, with heating at a constant rate of 10 8C min1 up to the plateau temperature, 600– 800 8C. The precursors were nitrided in a flowing NH3 at various temperatures for 6 h using a flow rate of 0.3 L min1. Differential thermal analysis of the gel collected prior to foam of the solution was performed in flowing air (20 ml min1) up to 600 8C at a heating rate of 10 8C min1 by using a thermal analyzer (DTA/TGA, Rigaku, DT-40, Tokyo, Japan). X-ray diffraction study of the precursor and the particles were carried out in an X-ray diffractometer using Cu Ka (l = 0.1542 nm) radiation [X-ray diffraction (XRD); Rigaku, D/max-RB12, TTRAX3 theta-theta gonio.]. The step is 0.028 and the time is 9 min from 108 to 1008. The morphology and particle size of the precursors and nitridation products were observed by scanning electron microscopy (SEM, JSM-5600) and field emission scanning electron microscopy (FESEM, JSM-6701F), respectively. The nitridation products were also observed by transmission electron microscopy (TEM, Tecnai G2 F30 S-TWIN). The specific surface area (SSA) of the precursors was determined by the BET method by using an Automated Surface Area & Pore Size Analyzer (QUADRASORB SI-MP, Quantachrome Instruments, Boynton Beach, FL).
(added 0 mol glucose), it is obvious that there is only one exothermic peak at 170 8C that can be attributed to redox reaction between chromium nitrate and glycine. Eq. (1) describes the exothermic reaction in a simple manner. Fig. 1b (added 0.025 mol glucose) shows an endothermic reaction that starts at approximately 100 8C and a sharp exothermic peak at 130 8C. In the temperature region of 100–120 8C, the endothermic peak is attributed to the vaporization of physically bound absorbed water and the dehydration reaction of gel sample. With respect to Fig. 1a (added 0 mol glucose), the drastic exothermic peak at 130 8C is ascribed to the thermally induced reaction between chromium nitrate and glycine and accompanied with the decomposition of glucose. Eq. (2) describes the decomposition reaction in a simple manner. As heating temperature is further increased, the exothermic peak, observed at 290 8C, corresponds to the oxidation of the carbon generated by decomposing of glucose, as shown in Eq. (3). When temperature surpasses 350 8C, the heat flow of the sample keeps nearly constant. It indicates the end of reaction. Compared to DSC curves of Fig. 1a, it indicates that Eqs. (2) and (3) do not occur without the glucose and the temperature of the exothermic reaction without the glucose is observed at higher temperature. 6CrðNO3 Þ3 þ 10C2 H5 NO2 ! 3Cr2 O3 þ 20CO2 þ 25H2 O þ 14N2
(1)
C6 H12 O6 ! 6C þ 6H2 O
(2)
C þ O2 ! CO2
(3)
3. Results and discussion Fig. 1 shows the results of differential scanning calorimetry (DSC) analysis of precursors prepared by the LCS. From Fig. 1a
Fig. 2. XRD patterns of the precursors prepared by LCS: (a) 0 mol glucose and (b) 0.025 mol glucose.
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The XRD patterns for the precursors (before removing carbon) can be seen in Fig. 2. It is evident from Fig. 2a (added 0 mol glucose) that no obvious Bragg diffraction peaks have been detected in the precursor. It indicates that the precursor is amorphous in structure. It means that the energy generated from the Eq. (1) is not sufficient for the crystallization of Cr2O3. However, in Fig. 2b, the Cr2O3 crystallite has been formed. This may be ascribed to the higher energy of exothermic reaction and the energy generated from the Eq. (3). It also proves that glucose promotes the formation of Cr2O3 crystallites at lower temperature. The SEM images of the two precursors are shown in Fig. 3. The precursor added 0 mol glucose mainly consists of flaky particles with flocculent (Fig. 3a). Moreover, the SSA of this precursor is calculated to be 20 m2/g. The high SSA of this precursor is ascribed to the dispersant effect of gases generated during the Eq. (1). The glucose as an additive (0.025 mol) renders the flake-like particles more attenuated exhibiting the porous and paper-thin flaky
appearance (Fig. 3b and c). The SSA of this precursor (after being decarburized) is calculated to be 34 m2/g. It indicates that the SSA of the precursor from glucose (0.025 mol) is higher than that of the precursor added 0 mol glucose. This may be ascribed to the higher gas amount generated from both the Eqs. (2) and (3). However, the comprehension about the formation mechanism for the high SSA of the precursor from added glucose is still under investigation and will be published later. Fig. 4 presents the XRD patterns of the precursors nitrided at the temperature of 600–800 8C in flowing NH3 gas during 6 h. At the temperature of 600 8C, the product without glucose exhibits diffraction peaks of chromic oxide (Fig. 4a), indicating the crystallization process from amorphous to chromic oxide during heating. The product with glucose (Fig. 4b) exhibits no diffraction peaks of CrN. In Fig. 4a and b, the CrN has been observed at 700 8C but there is also chromic oxide. It indicates that CrN has been obtained by ammonolysis of chromic oxide, as shown in Eq. (4).
Fig. 3. SEM micrographics of the precursors prepared by LCS: (a) 0 mol glucose, (b) and (c) 0.025 mol glucose.
Fig. 4. XRD patterns of the products prepared by ammonolysis at different temperatures: (a) 0 mol glucose and (b) 0.025 mol glucose.
Fig. 5. FE-SEM micrographics of the products prepared by ammonolysis at 800 8C: (a) 0 mol glucose and (b) 0.025 mol glucose.
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Fig. 6. (a) TEM image and (b) SAED pattern of the product (0.025 mol glucose) prepared by ammonolysis at 800 8C.
The phase-pure cubic CrN has been obtained at 750 8C and well crystallized at 800 8C. Cr2 O3 þ 2NH3 ! 2CrN þ 3H2 O
(4)
Fig. 5 presents the FE-SEM images of the two products synthesized at 800 8C. It is obvious that the powder agglomerates consists of 30–80 nm particles (Fig. 5a). However, the product from glucose (0.025 M) is composed of well-distributed spherical particles varying from 20 to 50 nm (Fig. 5b), which may be ascribe to the dehydrated species of glucose and the carbon particles generated through the carbonization of glucose adsorbed on the as prepared particles hindering their crystal growth. Moreover, the product particles added glucose has exhibited much better spherical and homogenous morphology than that of product particles without glucose. The morphology of the prepared CrN nanoparticles from added glucose at 800 8C is investigated by TEM. The TEM image of the CrN particles is shown in Fig. 6a. It is obvious that the product powder consists of well-distributed spherical CrN particles varying from 20 to 50 nm, which is in good agreement with the FE-SEM images of the product (Fig. 5b). In order to get more information about the particles, the corresponding selected-area electron diffraction (SAED) is shown in Fig. 6b. The clear diffraction spots reveal CrN phase in agreement with the XRD results and further confirm the single-crystalline structure of each cubic CrN nanocrystal. 4. Conclusions Glucose has exhibited a significant effect on the morphology of the precursor prepared by LCS method. It has also been observed that the size and morphology of CrN nanoparticles, synthesized by nitridation of this LCS precursor, are affected by the glucose. The nitridation product with glucose is found to be finer than the products without glucose. Moreover, CrN powders yielded from glucose (0.025 mol) consisted of well distributed spherical particles of size 20–50 nm. Glucose was found to induce a homogeneous and well-distributed nanoparticles.
Acknowledgements This work is financially supported by the National Natural Science Foundation Program of China (50802006) and (51172017), Program for New Century Excellent Talents in University (NCET10-0226), and the Fundamental Research Funds for the Central Universities (FRF-TP-11-004A) and National 863 Program. References [1] H. Chen, P.Q. Wu, C. Quaeyhaegens, K.W. Xu, L.M. Stals, J.W. He, J.P. Celis, Wear 253 (2002) 527–532. [2] L. Cunha, M. Andritschky, K. Pischow, Z. Wang, A. Zarychta, A.S. Miranda, A.M. Cunha, Surf. Coat. Technol. 153 (2002) 160–165. [3] C. Liu, A. Leyland, Q. Bi, A. Matthews, Surf. Coat. Technol. 141 (2001) 164–173. [4] P. Engel, G. Schwarz, G.K. Wolf, Surf. Coat. Technol. 112 (1999) 286–290. [5] F. Rivadulla, M. Banobre-Lopez, C.X. Quintela, V. Pardo, D. Baldomir, M.A. LopezQuintela, J. Rivas, C.A. Ramos, C.H. Salva, J.S. Zhou, J.B. Goodenough, Nat. Mater. 8 (2009) 947–951. [6] H.X. Zhong, X.B. Chen, H.M. Zhang, M.R. Wang, S.S. Mao, Appl. Phys. Lett. 911 (2007) 63103. [7] Q. Sun, Z.-W. Fu, Electrochem. Solid St. 10 (2007) A189–A193. [8] M. Yang, R. Guarecuco, F.J. DiSalvo, Chem. Mater. 25 (2013) 1783–1787. [9] Y.G. Li, L. Gao, J.G. Li, D.S. Yan, J. Am. Ceram. Soc. 85 (2002) 1294–1296. [10] I. Miloˇsev, B. Navinˇsek, J. Electrochem. Soc. 140 (1993) L30–L32. [11] P. Cai, J. Zhu, Z. Yang, Y. Qian, Mater. Chem. Phys. 95 (2006) 1–4. [12] Y. Kim, J. Li, J.-P. Zhang, R. Seshadri, Solid State Sci. 13 (2011) 216–223. [13] A.W. Jackson, O. Shebanova, A.L. Hector, P.F. McMillan, J. Solid State Chem. 179 (2006) 1383–1393. [14] D. Choi, G.E. Blomgren, P.N. Kumta, Adv. Mater. 18 (2006) 1178–1182. [15] S. Kaskel, K. Schlichte, G. Chaplais, M. Khanna, J. Mater. Chem. 13 (2003) 1496– 1499. [16] T. Aarthi, G. Madras, Catal. Commun. 9 (2008) 630. [17] G. Cao, Y. Li, Q. Zhang, H. Wang, J. Am. Ceram. Soc. 95 (2012) 2478–2480. [18] J. Kishan, V. Mangam, B.S.B. Reddy, S. Das, K. Das, J. Alloys. Compd. 490 (2010) 631. [19] F.A. Rabuffetti, J.S. Lee, R.L. Brutchey, Chem. Mater. 24 (2012) 3114–3116. [20] A. Chu, M. Qin, Rafi-ud-din, B. Jia, H. Lu, X. Qu, J. Am. Ceram. Soc. 95 (2012) 2510– 2515. [21] S.R. Nair, R.D. Purohit, A.K. Tyagi, P.K. Sinha, B.P. Sharma, Mater. Res. Bull. 43 (2008) 1573–1582. [22] M. Qin, X. Du, Z. Li, I.S. Humail, X. Qu, Mater. Res. Bull. 43 (2008) 2954–2960. [23] A. Chu, M. Qin, X. Jiang, L. Zhang, B. Jia, H. Lu, Y. Chen, X. Qu, Mater. Charact. 81 (2013) 76–84. [24] A. Chu, M. Qin, Rafi-ud-din, B. Jia, H. Lu, X. He, X. Qu, Mater. Res. Bull. 47 (2012) 2475–2479. [25] M.K. Naskar, J. Am. Ceram. Soc. 93 (2010) 1260–1263.