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Nickel disulfide films synthesized by sulfidation of nickel oxide film
Solid State Sciences 13 (2011) 1375e1378
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Nickel disulfide films synthesized by sulfidation of nickel oxide film Huang Siyu a, *, Liu Xinyu b, Li Qingyu c, Meng Mianwu a, Long Tengfa a, Jiang Zhiliang a a
Guangxi Key Laboratory of Environmental Engineering, Protection and Assessment, School of Environment and Resource, Guangxi Normal University, 15 Yucai Road, Guilin 541004, China b Department of Materials and Engineering of Guilin University of Electronic Technology, Guilin 541004, China c School of Chemistry and Chemical Engineering of Guangxi Normal University, 15 Yucai Road, Guilin 541004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 August 2010 Received in revised form 28 March 2011 Accepted 14 April 2011 Available online 22 April 2011
Nickel Oxide films on gold substrates have been synthesized by solegel technique. Subsequently, the samples have been prepared by heat-treating the prepared nickel oxide films with sulfur in sealed quartz tubes at 400e800 C. The crystal structures and micrograph of the samples have been characterized by X-ray diffraction (XRD) and scanning electron microscopy respectively, the nickel contents of samples have been determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results show that: the crystal structures of the film samples prepared by heat-treating the nickel oxide films and sulfur at 400e600 C are nickel disulfide (NiS2) with the pyrite structure, the average value of the cell constant a is 5.69 Å calculated from the XRD peaks of the synthesized nickel disulfide films, and the average crystallite size of the nickel disulfide is 60 nm estimated from the Scherrer equation. After sulfurization of the NiO film at 700e800 C, there is loss of nickel contents from the Au substrate due to vaporization of the nickel sulfide. Ó 2011 Elsevier Masson SAS. All rights reserved.
Keywords: Solegel Film Nickel oxide Nickel disulfide Synthesis
1. Introduction The 3d transition metals disulfides with the pyrite structure, such as nickel disulfide (NiS2), cobalt disulfide (CoS2) and iron disulfide (FeS2), have received attention because of their electrochemical properties [1e4] and optical properties [5,6]. Nickel disulfide, cobalt disulfide and iron disulfide have already been used in thermal batteries as cathodes. Comparing nickel disulfide electrode with iron disulfide or cobalt disulfide electrode in thermal batteries, the nickel disulfide electrode shows comparatively small nucleation overpotentials and relatively simple polarization characteristics [1], so the nickel disulfide electrode is superior electrode in thermal batteries. There are several synthetic routes to prepare nickel disulfide in the form of powder, such as: gasesolid reaction of nickel and sulfur at 600 Ce1200 C in pressure cell [7], gasesolid reaction of nickel carbonate and sulfur at 400 C [8], reaction between anhydrous nickel sulfate and hydrogen sulfide [9,10] and low-temperature solventothermal synthetic route [11,12]. Being different from the bulk materials and the powder materials, two-dimensional films have special functional characteristics and are suitable for performance research, so films with two-
* Corresponding author. Tel.: þ86 773 5846141. E-mail address: [email protected] (H. Siyu). 1293-2558/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2011.04.006
dimensional structure have also been studied and applied extensively. However, there have not yet been any reports describing nickel disulfide in form of film. In this paper, nickel oxide films have been prepared by solegel method, the nickel disulfide films have been synthesized by heat-treating the prepared nickel oxide films in gaseous sulfur in sealed tubes, then the nickel disulfide films have been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), the nickel contents of prepared films have been determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). 2. Experimental A solution containing Ni(II) precursor was produced by dissolving 20 wt.% nickel chloride and 12 vol.% acetyl acetone in anhydrous ethanol. Then 3 vol.% chlorepoxy propone was added, after which the solution was heated to 50 C for 3 h while stirring. The solegel solution was clear and bottle green. Nickel oxide films were prepared using a dip-coating method in the above solegel followed by heat-treatment. The substrates used were pure Au foils. Prior to film coating, the substrates were degreased in a 1 M KOH solution, rinsed with distilled water and dried in air. The coating procedure was carried out at room temperature (25 C and humidity 70%). The substrates were dipped into the coating solution and then pulled up into the air at a rate of 8 cm min1. The gel films were dried for 15 min in air
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treated for 20 h at 400e800 C in a muffle furnace to change the nickel oxide films to nickel sulfide. The crystal structure of the films was determined by X-ray diffraction (XRD) with a D8 ADVANCE from BRUKER AXS using CuKa radiation. The film morphology was measured using a JSM5610LV scanning electron microscopy (SEM). The nickel was extracted from the nickel compounds films on Au foils (1 cm 1 cm) by reacting with 2 ml HNO3 (1:1), and then the nickel contents of prepared films were determined by Optima 2000DV inductively coupled plasma-atomic emission spectrometry (ICP-AES). The thickness of the prepared films was calculated by the nickel contents on Au foils (the density of nickel disulfide is about 4.8 gcm3). Fig. 1. XRD patterns of the prepared film containing nickel compound after heattreatment at 600 C for 30 min.
3. Results and discussion The NiO can be transformed into NiS2 by the following reaction:
at room temperature. The samples were pre-heated at 100 C for 30 min and then heat-treated at 600 C for 30 min in air. The samples were recoated 6 times to obtain suitable coatings. The samples of nickel oxide films and pure sulfur powder were sealed into evacuated quartz tubes. The samples were then heat-
Fig. 2. XRD patterns of the sample with NiO film on Au substrate after sulfurization for 20 h at different temperatures: A 400 C, B 500 C, C 600 C, D 700 C, E 800 C.
2NiO þ 5S ¼ 2NiS2 þ SO2
(1)
If both the pressure of the gaseous S and SO2 are 1 atm in a sealed reactor, the Gibbs free energies of reaction (1) are 1110 kJ mol1 at 400 C, 1001 kJ mol1 at 600 C and 890 kJ mol1 at 800 C [13]. The Gibbs free energy values are negative, which indicates that reaction (1) can occur spontaneously in the forward direction. Therefore, as long as the pressure of the gaseous S is not lower than 1 atm and the pressure of the gaseous SO2 is not greater than 1 atm, NiS2 can be synthesized from the reaction of NiO and S in a sealed reactor between 400 C and 800 C. The nickel oxide films on the Au substrate were prepared by dipcoating and heat-treating 6 times after being heat-treated at 600 C. The prepared oxide films adhered firmly to the gold substrates and did not peel off while being bent. Fig. 1 shows the XRD spectra of the prepared films containing nickel compound after heat-treatment at 600 C for 30 min. From these spectra, it can be seen that there are three XRD diffraction peaks, at 2q ¼ 37.26 , 43.30 and 62.91, which correspond to the (111), (200) and (220) diffraction planes of nickel oxide (ASTM card 44-1159), respectively.
Fig. 3. Analysis of nickel content (by ICP-AES) of the sample with the NiO film on an Au substrate after sulfurization for 20 h at different temperatures.
H. Siyu et al. / Solid State Sciences 13 (2011) 1375e1378
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Fig. 4. SEM pictures of the sample with NiO film on Au substrate after sulfurization for 20 h at different temperatures: A 400 C, B 500 C, C 600 C, D 700 C, E 800 C.
This demonstrates that the prepared film on the Au substrate is single phase NiO. The nickel oxide film was found to contain 71 mg cm2 Ni (or contain 90 mg cm2 NiO) by inductively coupled plasma-atomic emission spectrometry (ICP-AES), the thickness of the prepared nickel oxide on Au substrate corresponded to 0.13 mm while the density of NiO is regarded as 6.7 g cm3. Fig. 2 shows the XRD patterns of the samples on gold substrates prepared by sulfurizing the NiO films over a temperature range 400e800 C for 20 h. From the spectra, it can be seen that the sulfurizing temperature has significant effects on the phase structure. The characteristic diffraction peaks of NiS2 (200), (210), (211), (220) and (311) (ASTM card 11-0099) appear after the NiO films have been sulfurized at 400e600 C for 20 h, and the diffraction peaks are more intense as the sulfurizing temperature is increased. Besides the XRD peaks mentioned above, the other diffraction peaks of the NiS2 crystal plane (222), (023) and (321) are distinct after the NiO films have been sulfurized at 600 C for 20 h. The average value of the cell constant a is calculated to be 5.69 Å from all the peaks, which is larger than the reported value 5.67 Å from ASTM card 11-0099. The average crystallite size of the nickel disulfide prepared at 400e600 C is 60 nm estimated from the Scherrer equation. After the NiO films have been sulfurized at 700 C for 20 h, all the characteristic diffraction peaks of NiS2 disappear, and five new XRD peaks of an unknown compound occur at 34.18 , 35.55 , 46.56 , 54.51 and 62.97 (Fig. 2D: a, b, c, d, e). For the NiO film sulfurized at 800 C for 20 h, there are no XRD peaks except for those of the Au substrate. Fig. 3 shows that the analysis of nickel content (by ICP-AES) of the sample formed from NiO films on Au substrate sulfurized for 20 h at different temperatures. This figure shows that the nickel contents of the sample sulfurized at 400e600 C were about 70 mg cm2 Ni which accords with that of the prepared NiO film. The thickness of the prepared nickel disulfide on Au substrate corresponded to 0.3 mm while the density of NiS2 is regarded as 4.8 g cm3. According to the nickelesulphur phase diagram [14], the lowest melting point of nickel sulfide is only 640 C, so if the sulfurizing temperature exceeds 640 C, the vapor pressure of nickel sulfide (as NimSn) may be high enough for it to vaporize. After the NiO film had been sulfurized for 20 h at 700 C and 800 C, the proportions of nickel in the Au substrate are 30 mg/cm2 and 0 mg/cm2, respectively. These suggested that about 40 mg/cm2 and 70 mg/cm2 Ni disappeared after the NiO films sulfurized at 700 C
and 800 C, respectively. From these results, we conclude that the sulfurization of the NiO film at 700e800 C can be pictured as follows: the NiO film is changed into nickel sulfide (as NimSn), then the nickel sulfide vaporizes. Finally, the temperature of the reactor wall falls faster than that of the Au substrate during the cooling stage and nickel sulfide is preferentially deposited on the reactor wall. So there is loss of nickel from the Au substrate after the NiO film has been sulfurized at 700e800 C. Fig. 4 shows SEM of the samples on gold substrates prepared by sulfurizing the NiO films over the temperature range 400e800 C for 20 h. For samples prepared at 400e600 C, the micrograph shows a dispersion of particle sizes, the phase structure of the films is determined to be bunsenite (NiS2) by XRD. After sulfurization of the NiO film at 700 C, a melted phase structure appears on the substrate, as a result of nickel sulfide melted at 700 C, according to the nickelesulfursulfur phase diagram [14]. When the sulfurizing temperature reaches 800 C, it shows only the micrograph of the Au substrate, which corresponds to the complete loss of nickel from the Au substrate after sulfurization at 800 C (Fig. 3). 4. Conclusions Nickel oxide (NiO) films have been deposited on Au substrates by a solegel method. After sulfurizing the prepared nickel oxide films and gaseous sulfur at 400e600 C for 20 h, the films samples were determined to be nickel disulfide (NiS2) with the pyrite structure by XRD, the average value of the cell constant a is 5.69 Å calculated from the XRD peaks of the synthesized nickel disulfide films, and the average crystallite size of the nickel disulfide is 60 nm estimated from the Scherrer equation. All the nickel contents of the nickel disulfide films synthesized at 400e600 C were about 70 mg cm2 Ni which accords with that of the prepared NiO film, the thickness of the prepared nickel disulfide on Au substrate corresponded to 0.3 mm. While sulfurization temperature exceeded 700 C, there is loss of nickel contents from the Au substrate due to vaporization of the nickel sulfide. Acknowledgment This work was supported by Fund of Guangxi Key Laboratory of Environmental Engineering, Protection and Assessment.
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References [1] S.K. Preto, Z. Tomczuk, S.V. Winbush, et al., J. Electrochem. Soc. 130 (1983) 264e273. [2] J.M. Patrick, A.G. Ronald, J. Power Sources 178 (2008) 456e466. [3] M. Berrettoni, R. Tossici, S. Zamponi, et al., J. Electrochem. Soc. 140 (1993) 969e973. [4] J.M. Patrick, A.G. Ronald, J. Power Sources 177 (2008) 595e609. [5] M. Wang, Y.L. Min, Y.C. Chen, Mater. Lett. 62 (2008) 3280e3283. [6] L.Y. Huang, F. Wang, Z.J. Luan, L. Meng, Mater. Lett. 64 (2010) 2612e2615. [7] Q. Li, Y.Q. Cheng, Y.Q. Liu, Patent CN1240765 (1999).
[8] G.J. An, C.G. Liu, Y.D. Hou, X.L. Zhang, Y.Q. Liu, Mater. Lett. 62 (2008) 2643e2646. [9] P.B. Bonneau, R.K. Shibao, R.B. Kaner, Inorg. Chem. 29 (1990) 2511e2514. [10] X.M. Zhang, X.F. Qian, C. Wang, Y. Xie, et al., Mat. Sci. Eng. B-Solid 57 (1999) 170e173. [11] X.H. Chen, R. Fan, Chem. Mater. 13 (2001) 802e805. [12] X.F. Qian, Y.D. Li, X. Yi, Y.T. Qian, Mater. Chem. Phys. 66 (2000) 97e99. [13] I. Barin, Thermochemical Data of Pure Substances. Science Press, Beijing, 2003, pp. 1198e1221. [14] N. Jacinto, M. Nagamori, H.Y. Sohn, Trans. Inst. Min. Metall. C 92 (1983) 225e228.
Contents lists available at ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Nickel disulfide films synthesized by sulfidation of nickel oxide film Huang Siyu a, *, Liu Xinyu b, Li Qingyu c, Meng Mianwu a, Long Tengfa a, Jiang Zhiliang a a
Guangxi Key Laboratory of Environmental Engineering, Protection and Assessment, School of Environment and Resource, Guangxi Normal University, 15 Yucai Road, Guilin 541004, China b Department of Materials and Engineering of Guilin University of Electronic Technology, Guilin 541004, China c School of Chemistry and Chemical Engineering of Guangxi Normal University, 15 Yucai Road, Guilin 541004, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 August 2010 Received in revised form 28 March 2011 Accepted 14 April 2011 Available online 22 April 2011
Nickel Oxide films on gold substrates have been synthesized by solegel technique. Subsequently, the samples have been prepared by heat-treating the prepared nickel oxide films with sulfur in sealed quartz tubes at 400e800 C. The crystal structures and micrograph of the samples have been characterized by X-ray diffraction (XRD) and scanning electron microscopy respectively, the nickel contents of samples have been determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results show that: the crystal structures of the film samples prepared by heat-treating the nickel oxide films and sulfur at 400e600 C are nickel disulfide (NiS2) with the pyrite structure, the average value of the cell constant a is 5.69 Å calculated from the XRD peaks of the synthesized nickel disulfide films, and the average crystallite size of the nickel disulfide is 60 nm estimated from the Scherrer equation. After sulfurization of the NiO film at 700e800 C, there is loss of nickel contents from the Au substrate due to vaporization of the nickel sulfide. Ó 2011 Elsevier Masson SAS. All rights reserved.
Keywords: Solegel Film Nickel oxide Nickel disulfide Synthesis
1. Introduction The 3d transition metals disulfides with the pyrite structure, such as nickel disulfide (NiS2), cobalt disulfide (CoS2) and iron disulfide (FeS2), have received attention because of their electrochemical properties [1e4] and optical properties [5,6]. Nickel disulfide, cobalt disulfide and iron disulfide have already been used in thermal batteries as cathodes. Comparing nickel disulfide electrode with iron disulfide or cobalt disulfide electrode in thermal batteries, the nickel disulfide electrode shows comparatively small nucleation overpotentials and relatively simple polarization characteristics [1], so the nickel disulfide electrode is superior electrode in thermal batteries. There are several synthetic routes to prepare nickel disulfide in the form of powder, such as: gasesolid reaction of nickel and sulfur at 600 Ce1200 C in pressure cell [7], gasesolid reaction of nickel carbonate and sulfur at 400 C [8], reaction between anhydrous nickel sulfate and hydrogen sulfide [9,10] and low-temperature solventothermal synthetic route [11,12]. Being different from the bulk materials and the powder materials, two-dimensional films have special functional characteristics and are suitable for performance research, so films with two-
* Corresponding author. Tel.: þ86 773 5846141. E-mail address: [email protected] (H. Siyu). 1293-2558/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.solidstatesciences.2011.04.006
dimensional structure have also been studied and applied extensively. However, there have not yet been any reports describing nickel disulfide in form of film. In this paper, nickel oxide films have been prepared by solegel method, the nickel disulfide films have been synthesized by heat-treating the prepared nickel oxide films in gaseous sulfur in sealed tubes, then the nickel disulfide films have been characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), the nickel contents of prepared films have been determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). 2. Experimental A solution containing Ni(II) precursor was produced by dissolving 20 wt.% nickel chloride and 12 vol.% acetyl acetone in anhydrous ethanol. Then 3 vol.% chlorepoxy propone was added, after which the solution was heated to 50 C for 3 h while stirring. The solegel solution was clear and bottle green. Nickel oxide films were prepared using a dip-coating method in the above solegel followed by heat-treatment. The substrates used were pure Au foils. Prior to film coating, the substrates were degreased in a 1 M KOH solution, rinsed with distilled water and dried in air. The coating procedure was carried out at room temperature (25 C and humidity 70%). The substrates were dipped into the coating solution and then pulled up into the air at a rate of 8 cm min1. The gel films were dried for 15 min in air
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treated for 20 h at 400e800 C in a muffle furnace to change the nickel oxide films to nickel sulfide. The crystal structure of the films was determined by X-ray diffraction (XRD) with a D8 ADVANCE from BRUKER AXS using CuKa radiation. The film morphology was measured using a JSM5610LV scanning electron microscopy (SEM). The nickel was extracted from the nickel compounds films on Au foils (1 cm 1 cm) by reacting with 2 ml HNO3 (1:1), and then the nickel contents of prepared films were determined by Optima 2000DV inductively coupled plasma-atomic emission spectrometry (ICP-AES). The thickness of the prepared films was calculated by the nickel contents on Au foils (the density of nickel disulfide is about 4.8 gcm3). Fig. 1. XRD patterns of the prepared film containing nickel compound after heattreatment at 600 C for 30 min.
3. Results and discussion The NiO can be transformed into NiS2 by the following reaction:
at room temperature. The samples were pre-heated at 100 C for 30 min and then heat-treated at 600 C for 30 min in air. The samples were recoated 6 times to obtain suitable coatings. The samples of nickel oxide films and pure sulfur powder were sealed into evacuated quartz tubes. The samples were then heat-
Fig. 2. XRD patterns of the sample with NiO film on Au substrate after sulfurization for 20 h at different temperatures: A 400 C, B 500 C, C 600 C, D 700 C, E 800 C.
2NiO þ 5S ¼ 2NiS2 þ SO2
(1)
If both the pressure of the gaseous S and SO2 are 1 atm in a sealed reactor, the Gibbs free energies of reaction (1) are 1110 kJ mol1 at 400 C, 1001 kJ mol1 at 600 C and 890 kJ mol1 at 800 C [13]. The Gibbs free energy values are negative, which indicates that reaction (1) can occur spontaneously in the forward direction. Therefore, as long as the pressure of the gaseous S is not lower than 1 atm and the pressure of the gaseous SO2 is not greater than 1 atm, NiS2 can be synthesized from the reaction of NiO and S in a sealed reactor between 400 C and 800 C. The nickel oxide films on the Au substrate were prepared by dipcoating and heat-treating 6 times after being heat-treated at 600 C. The prepared oxide films adhered firmly to the gold substrates and did not peel off while being bent. Fig. 1 shows the XRD spectra of the prepared films containing nickel compound after heat-treatment at 600 C for 30 min. From these spectra, it can be seen that there are three XRD diffraction peaks, at 2q ¼ 37.26 , 43.30 and 62.91, which correspond to the (111), (200) and (220) diffraction planes of nickel oxide (ASTM card 44-1159), respectively.
Fig. 3. Analysis of nickel content (by ICP-AES) of the sample with the NiO film on an Au substrate after sulfurization for 20 h at different temperatures.
H. Siyu et al. / Solid State Sciences 13 (2011) 1375e1378
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Fig. 4. SEM pictures of the sample with NiO film on Au substrate after sulfurization for 20 h at different temperatures: A 400 C, B 500 C, C 600 C, D 700 C, E 800 C.
This demonstrates that the prepared film on the Au substrate is single phase NiO. The nickel oxide film was found to contain 71 mg cm2 Ni (or contain 90 mg cm2 NiO) by inductively coupled plasma-atomic emission spectrometry (ICP-AES), the thickness of the prepared nickel oxide on Au substrate corresponded to 0.13 mm while the density of NiO is regarded as 6.7 g cm3. Fig. 2 shows the XRD patterns of the samples on gold substrates prepared by sulfurizing the NiO films over a temperature range 400e800 C for 20 h. From the spectra, it can be seen that the sulfurizing temperature has significant effects on the phase structure. The characteristic diffraction peaks of NiS2 (200), (210), (211), (220) and (311) (ASTM card 11-0099) appear after the NiO films have been sulfurized at 400e600 C for 20 h, and the diffraction peaks are more intense as the sulfurizing temperature is increased. Besides the XRD peaks mentioned above, the other diffraction peaks of the NiS2 crystal plane (222), (023) and (321) are distinct after the NiO films have been sulfurized at 600 C for 20 h. The average value of the cell constant a is calculated to be 5.69 Å from all the peaks, which is larger than the reported value 5.67 Å from ASTM card 11-0099. The average crystallite size of the nickel disulfide prepared at 400e600 C is 60 nm estimated from the Scherrer equation. After the NiO films have been sulfurized at 700 C for 20 h, all the characteristic diffraction peaks of NiS2 disappear, and five new XRD peaks of an unknown compound occur at 34.18 , 35.55 , 46.56 , 54.51 and 62.97 (Fig. 2D: a, b, c, d, e). For the NiO film sulfurized at 800 C for 20 h, there are no XRD peaks except for those of the Au substrate. Fig. 3 shows that the analysis of nickel content (by ICP-AES) of the sample formed from NiO films on Au substrate sulfurized for 20 h at different temperatures. This figure shows that the nickel contents of the sample sulfurized at 400e600 C were about 70 mg cm2 Ni which accords with that of the prepared NiO film. The thickness of the prepared nickel disulfide on Au substrate corresponded to 0.3 mm while the density of NiS2 is regarded as 4.8 g cm3. According to the nickelesulphur phase diagram [14], the lowest melting point of nickel sulfide is only 640 C, so if the sulfurizing temperature exceeds 640 C, the vapor pressure of nickel sulfide (as NimSn) may be high enough for it to vaporize. After the NiO film had been sulfurized for 20 h at 700 C and 800 C, the proportions of nickel in the Au substrate are 30 mg/cm2 and 0 mg/cm2, respectively. These suggested that about 40 mg/cm2 and 70 mg/cm2 Ni disappeared after the NiO films sulfurized at 700 C
and 800 C, respectively. From these results, we conclude that the sulfurization of the NiO film at 700e800 C can be pictured as follows: the NiO film is changed into nickel sulfide (as NimSn), then the nickel sulfide vaporizes. Finally, the temperature of the reactor wall falls faster than that of the Au substrate during the cooling stage and nickel sulfide is preferentially deposited on the reactor wall. So there is loss of nickel from the Au substrate after the NiO film has been sulfurized at 700e800 C. Fig. 4 shows SEM of the samples on gold substrates prepared by sulfurizing the NiO films over the temperature range 400e800 C for 20 h. For samples prepared at 400e600 C, the micrograph shows a dispersion of particle sizes, the phase structure of the films is determined to be bunsenite (NiS2) by XRD. After sulfurization of the NiO film at 700 C, a melted phase structure appears on the substrate, as a result of nickel sulfide melted at 700 C, according to the nickelesulfursulfur phase diagram [14]. When the sulfurizing temperature reaches 800 C, it shows only the micrograph of the Au substrate, which corresponds to the complete loss of nickel from the Au substrate after sulfurization at 800 C (Fig. 3). 4. Conclusions Nickel oxide (NiO) films have been deposited on Au substrates by a solegel method. After sulfurizing the prepared nickel oxide films and gaseous sulfur at 400e600 C for 20 h, the films samples were determined to be nickel disulfide (NiS2) with the pyrite structure by XRD, the average value of the cell constant a is 5.69 Å calculated from the XRD peaks of the synthesized nickel disulfide films, and the average crystallite size of the nickel disulfide is 60 nm estimated from the Scherrer equation. All the nickel contents of the nickel disulfide films synthesized at 400e600 C were about 70 mg cm2 Ni which accords with that of the prepared NiO film, the thickness of the prepared nickel disulfide on Au substrate corresponded to 0.3 mm. While sulfurization temperature exceeded 700 C, there is loss of nickel contents from the Au substrate due to vaporization of the nickel sulfide. Acknowledgment This work was supported by Fund of Guangxi Key Laboratory of Environmental Engineering, Protection and Assessment.
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References [1] S.K. Preto, Z. Tomczuk, S.V. Winbush, et al., J. Electrochem. Soc. 130 (1983) 264e273. [2] J.M. Patrick, A.G. Ronald, J. Power Sources 178 (2008) 456e466. [3] M. Berrettoni, R. Tossici, S. Zamponi, et al., J. Electrochem. Soc. 140 (1993) 969e973. [4] J.M. Patrick, A.G. Ronald, J. Power Sources 177 (2008) 595e609. [5] M. Wang, Y.L. Min, Y.C. Chen, Mater. Lett. 62 (2008) 3280e3283. [6] L.Y. Huang, F. Wang, Z.J. Luan, L. Meng, Mater. Lett. 64 (2010) 2612e2615. [7] Q. Li, Y.Q. Cheng, Y.Q. Liu, Patent CN1240765 (1999).
[8] G.J. An, C.G. Liu, Y.D. Hou, X.L. Zhang, Y.Q. Liu, Mater. Lett. 62 (2008) 2643e2646. [9] P.B. Bonneau, R.K. Shibao, R.B. Kaner, Inorg. Chem. 29 (1990) 2511e2514. [10] X.M. Zhang, X.F. Qian, C. Wang, Y. Xie, et al., Mat. Sci. Eng. B-Solid 57 (1999) 170e173. [11] X.H. Chen, R. Fan, Chem. Mater. 13 (2001) 802e805. [12] X.F. Qian, Y.D. Li, X. Yi, Y.T. Qian, Mater. Chem. Phys. 66 (2000) 97e99. [13] I. Barin, Thermochemical Data of Pure Substances. Science Press, Beijing, 2003, pp. 1198e1221. [14] N. Jacinto, M. Nagamori, H.Y. Sohn, Trans. Inst. Min. Metall. C 92 (1983) 225e228.