ISSN 1067-8212, Russian Journal of Non-Ferrous Metals, 2017, Vol. 58, No. 6, pp. 600–607. © Allerton Press, Inc., 2017.

METALLURGY OF RARE AND NOBLE METALS

Preparation of V2O5 from Ammonium Metavanadate via Microwave Intensification1 Bingguo Liua, b, c, Jinhui Penga, b, c, Libo Zhanga, b, c, *, Junwen Zhoua, b, c, and C. Srinivasakannand aState

Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093 b Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093 cKey Laboratory of Unconventional Metallurgy, Ministry of Education, Kunming University of Science and Technology, Kunming 650093 d Chemical Engineering Department, the Petroleum Institute, Abudhabi, UAE *e-mail: [email protected] Received January 30, 2017

Abstract⎯Parameters of technique to prepare of V2O5 by microwave intensification from ammonium metavanadate were optimized using central composite design of response surface methodology. A quadratic equation model for decomposition rate was built and effects of main factors and their corresponding relationships were obtained. The microwave heating behavior indicated that ammonium metavanadate had weak capability to absorb microwave radiation, while V2O5 had good capability to absorb microwave radiation. The results of the statistical analysis showed that the decomposition rate of ammonium metavanadate was significantly affected by calcination temperature and calcination time in the range studied. The optimized conditions were as follows: calcination temperature 645.35 K, calcination time 9.66 min and 4.3 g, respectively. The decomposition rates of ammonium metavanadate were 99.13%, which coincided well with experiments values 99.33% under these conditions. These suggest that regressive equation fits the decomposition rates perfectly. XRD reveals that it is feasible to prepare the V2O5 by microwave intensification from ammonium metavanadate, which mixed with small amounts of V2O5. Keywords: response surface methodology, ammonium metavanadate, microwave intensification, vanadium pentoxide, rising behavior DOI: 10.3103/S1067821217060062

1. INTRODUCTION Vanadium pentoxide (V2O5) is widely used as a photocatalyst in photovoltaics, a gas sensor, a cathode for solid-state batteries, and a window for solar cells, electrochromic devices, and electronic and optical switches [1] due to its orthorhombic structure [2], which exhibits highly anisotropic electrical and optical properties. Furthermore, vanadium is the most important metal used in metal oxide catalysis [3–5] since vanadium atoms exist in different formal oxidation states varying from two to five. The capability of vanadium atoms to possess multiple stable oxidation states results in easy conversion between oxides with different stoichiometries via oxidation or reduction. This capability is also regarded as an important factor for oxides to function as catalysts in selective oxidation. Various methods are currently used to fabricate V2O5, such as vacuum evaporation [6, 7], sol-gel processes [8], sputtering [9], thermal decomposition [10], 1 The article is published in the original.

and chemical vapor deposition [11]. Among these methods, the thermal decomposition of ammonium metavanadate is commercially applied due to the simplicity of its process. However, the applicability of high rates to conventional processing is limited by heat transfer and thermal shock. In conventional heating, energy is absorbed on the surface of a material and must be transferred to its bulk via conduction. Temperature gradients exist in a sample until it achieves thermal equilibrium. The aforementioned conditions in conventional thermal decomposition procedures result in high energy consumption and long process duration. Microwaves are a form of electromagnetic radiation with frequencies ranging from 0.3 to 300 GHz. The internationally accepted and recognized frequency bands used for microwave heating are 915 and 2450 MHz. Microwave has the potential to overcome problems encountered in conventional heating processes. Uniform and rapid heating can be achieved within a shorter time and at lower temperatures than in conventional cases because energy is absorbed in the

600

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8000

3

7000

NH4VO3

6000 Intensity, a.u.

601

1

4

2

5000 4000 3000 7

2000 1000 5

0 20

40 2θ, deg

60

Fig. 2. Sketch of apparatus using microwave heating. (1) Oven door; (2) eye hole; (3) shielded thermocouple; (4) thermometric equipment; (5) heat insulating materials; (6) material; (7) power adjustment.

Fig. 1. XRD patterns of ammonium metavanadate.

volume of the heating object rather than conducted outside [12, 13]. In addition, microwave heating provides good control of the heating process and minimizes energy cost [14, 15]. Microwave calcination is an attractive technique for processing materials, and thus, has been adopted by several researchers [16–18]. However, the microwave calcination of ammonium metavanadate has not yet been fully explored. This technique can be possibly applied to processing materials. Therefore, the main objective of this study is to determine the microwave heating behavior of ammonium metavanadate and related materials. V2O5 is then prepared from ammonium metavanadate via microwave intensification using the response surface methodology (RSM). RSM is a collection of mathematical and statistical techniques that are useful for modeling and analyzing problems with numerous variables influencing the response and with the objective of optimizing the response [19–22]. Moreover, a central composite design (CCD) is selected to optimize the decomposition rate responses of ammonium metavanadate. 2. EXPERIMENTAL 2.1. Materials The chemically pure ammonium metavanadate used in the present study, which had a particle size of less than 100 μm, was obtained from Tianjin Chemical Reagent Co., Ltd. All reagents were of analytical grade and used without further purification. The mineralogical content of the material was analyzed as shown in Fig. 1. 2.2. Equipment for Microwave Heating The microwave reactor used in the present study was built by the Key Laboratory of Unconventional RUSSIAN JOURNAL OF NON-FERROUS METALS

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Metallurgy, Ministry of Education, Kunming University of Science and Technology. This reactor is capable of altering power intensity from 0 to 3000 W and can operate at a frequency of 2.40 GHz. The crucible that held the sample was made of a ceramic material, and temperature was measured using a type K thermocouple placed inside the thermo well. The schematic and digital photograph of the microwave heating system are shown in Fig. 2. 2.3. Microwave Calcination Experiments The mixture of ammonium metavanadate containing 15% V2O5 was used to study microwave calcination processes at different temperatures, calcination times, and sample masses based on the heating behavior of ammonium metavanadate and related materials. The sample was initially weighed and placed inside a ceramic crucible, which was then positioned at the center of the microwave reactor. During the reaction, temperature was monitored with a temperature controller system that used a proportional-integral-derivative controller. Sample temperature was measured using the type K thermocouple. The experiment was stopped after a fixed duration for each cycle. The products were removed from the microwave reactor and immediately placed in a drier. They were then allowed to cool naturally to room temperature. The final mass (M) of a sample was weighted subsequently. The decomposition rate was calculated based on the following equation:

γ=

M0 − M , M 0W t

(1)

where M and M 0 are final mass and initial mass of the sample, respectively; W t is the theoretical value of mass loss; and γ is the decomposition rate of the sample.

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100 95

Mass loss, %

90

DTG, %/min

5 K/min 10 K/min 15 K/min 20 K/min

85 80 75 70 65 300

400

500 600 Temperature, K

700

0.5 0 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 –4.0 –4.5 –5.0 –5.5 –6.0 –6.5 –7.0 –7.5 300

5 K/min 10 K/min 15 K/min 20 K/min 400

500 600 Temperature, K

700

Fig. 3. TG curves of ammonium metavanadate at the heating rate of 5, 10, 15, and 20 K/min.

Fig. 4. DTG curves of ammonium metavanadate at the heating rate of 5, 10, 15, and 20 K/min.

2.4. Designing an Experiment Using RSM

and IV is attributed to the decomposition of ammonium metavanadate. The mass loss of ammonium metavanadate is significant within the range of 450– 550 K, which indicates that decomposition reaction occurs quickly. Furthermore, weight change eases beyond 700 K. On the basis of the obtained results, the thermal decomposition mechanism of ammonium metavanadate can be shown as [25]

A three-variable, two-level central composite design was adopted to optimize the decomposition condition and obtain a high decomposition rate [23]. The effects of the following factors on decomposition rate were studied: χ1 (calcination temperature), χ 2 (calcination time), and χ 3 (sample mass). A quadratic equation was utilized to relate the experimental variables to the response variable, as expressed in Eq. (4) [24]. n

γ = β0 +

n

n

∑β χ + ∑β χ + ∑β χ χ , i

i =1

i

ii

i =1

2 i

ij

i

j

(2)

i〈 j

where γ is the predicted response, β 0 is a constant, β i is the ith linear coefficient, β ii is the ith quadratic coefficient, β ij is the ijth interaction coefficient, and χ ij is the independent variable. 3. RESULTS AND DISCUSSION 3.1. Thermal Decomposition Behavior of Ammonium Metavanadate The thermal decomposition behavior of ammonium metavanadate was investigated at heating rates of β = 5, 10, 15, 20 K/min via thermogravimetric (TG) analysis. The TG and derivative TG (DTG) curves for non-isothermal decomposition at various heating rates are presented in Figs. 3 and 4, respectively. The results show that the TG curves have four mass loss stages that correspond to the four peaks in the DTG curves. For the TG curves, when β = 10 K/min, free moisture removal is initiated at 300 K and the water removal rate increases until a maximum value is achieved at a temperature of 325 K. The free water is completely removed at 350 K and accompanied by a weight loss of 7.36%. The occurrence of Stages II, III,

2NH 4 VO 3 → V 2O 5 ⋅ 1 2 NH 3 ⋅ 1 3 H 2O + 3 2 NH 3 + 2 3 H 2O,

(3)

V 2O 5 ⋅ 1 2 NH 3 ⋅ 1 3 H 2O → V2O 5 ⋅ 1 6 NH 3 ⋅ 1 9 H 2O + 1 3 NH 3 + 2 9 H 2O,

(4)

V 2O 5 ⋅ 1 6 NH 3 ⋅ 1 9 H 2O → V2O 5 + 1 6 NH 3 + 1 9 H 2O.

(5)

3.2. Microwave Heating Behavior of Ammonium Metavanadate and Related Materials

The interaction degree of microwaves with a material depends on the dielectric and magnetic properties of the medium. To assess the heating behavior of ammonium metavanadate and related materials, 10 g the mixture of ammonium metavanadate containing 5, 10, 15, 20, 25, 30, 35% V2O5, respectively and vanadium pentoxidewere prepared for experimentation by mixing the calculated quantities of ammonium metavanadate and V2O5 then grinding the mixture in a stainless steel ball mill for 1 h. The mixture was then placed in a ceramic crucible and heated. The effect of microwave irradiation time on heating behavior, with microwave power at 800 W, is presented in Fig. 5. Ammonium metavanadate exhibits a weak capability to absorb microwave energy, whereas V2O5 demon-

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strates a strong capability to absorb microwave energy. The reason is that the imaginary part of the complex permittivity ε" increased with an increase mixture ratio of V2O5 and the order of increase can be as fol" < ε15% " < ε "20% < lows, ε "ammonium metavanadate < ε "5% < ε10% ε "25% < ε "30% < ε "35% < ε "V2O5 [26, 27]. During the microwave irradiation process, the sample temperature rises rapidly with an increase in the mixture ratio of V2O5. A maximum temperature of approximately 329 K is reached within a radiation time of 110 s, with a V2O5 addition of approximately 15% mass. Consequently, the addition of a material with good microwave absorbing capacity to a material with poor microwave absorbing capacity can significantly affect the microwave absorption characteristics of the poor absorber [28, 29]. This finding indicates the feasibility of preparing V2O5 from ammonium metavanadate via calcination. In particular, ammonium metavanadate is mixed with small amounts of V2O5 under microwave fields. 3.3. Data Analysis and Evaluation of the Model Using RSM Response surface optimization is more advantageous than the traditional single parameter optimization because it saves time, space, and raw materials. All 20 designed experiments were conducted to optimize the 3 individual parameters in the CCD experimental design with 6 replicates and 6 axial points, as shown in Table 1. The decomposition rate of ammonium metavanadate ranges from 65.43 to 99.84%. Runs 15–20 at the center point were used to determine the experimental error. The data obtained from the experiments were analyzed using linear multiple regression software. The corresponding second-order response model for Eq. (2), which was found after regression analysis, was

γ = − 178.4 + 0.0731χ1 + 2.972χ 2 − 0.109χ 3 + 3.486χ1χ 2 + 7.361χ1χ 3 − 0.381.83χ 2χ 3

(6)

− 5.338χ1 − 0.236χ 2 − 0.031χ 3. 2

2

2

The experimental data were analyzed through ANOVA, which is also part of RSM, to assess “goodness of fit.” The results are listed in Table 2. The fit quality of models is generally judged based on their coefficient of determination ( R 2 ) [28, 29]. ANOVA was applied to estimate the effects of the main variables and their potential interaction on decomposition rates. The statistical significance test was based on the total error criterion with a confidence level of 95%. Confirmatory experiments were performed to validate the equation using combinations of variables at different levels. To determine whether the quadratic model is significant, ANOVA should be conducted. P-values were RUSSIAN JOURNAL OF NON-FERROUS METALS

Temperature, K

600

603

0% 5% 10% 15% 20% 25% 30% 35% 100%

550 500 450 400 350 300 0

20

40

60 Time, s

80

100

120

Fig. 5. Curve of increasing temperature of ammonium metavanadate and relative materials in microwave field (P = 800 W). (1) Ammonium metavanadate; (2–8) the mixture of ammonium metavanadate containing 5, 10, 15, 20, 25, 30 and 35% vanadium pentoxide, respectively; (9) V2O5.

used to check the significance of each coefficient, which indicated the interaction strength of each parameter. When P-values are small, the significance of the corresponding coefficient is considerable. The ANOVA result of the quadratic model for decomposition rate is presented in Table 2. The model with a P-value of less than 0.0001 is statistically significant in the present experiment, thereby indicating that the model is suitable for this experiment. Meanwhile, the “lack of fit” of this model, with a P-value of less than 0.0001, is significant. The R 2 2 and adjusted R 2 ( Radj ) are 0.964 and 0.932, respectively, which implies that the accuracy and general availability of the polynomial model are adequate. A model F-value of 29.92 implies that the model is significant and the probability that such a high model F-value can occur due to noise is only 0.01%. An inadequate fit indicates poor or misleading results. Therefore, checking model adequacy is an important step in the data analysis procedure [30]. Multivariable linear regression was used to calculate the coefficients of the second-order polynomial equation. The obtained regression coefficients, whose significance was determined using P-values, are summarized in Table 3. The regression analysis of the experimental design demonstrates that the linear model terms (χ1 and χ 2 ) and the quadratic model terms (χ12 and χ 22 ) are significant (P < 0.05). However, the linear model term (χ 3 ), the quadratic model term (χ 32 ), and the interactive model terms (χ1 χ 2, χ 2 χ 3, and χ1 χ 3, ) are insignificant (P > 0.05).

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Table 1. Experimental design matrix and results for the response surface of decomposition rate of ammonium metavanadate Calcination variables Run

calcination temperature χ1, K

calcination time χ 2, min

mass of sample χ 3 , g

Decomposition rate γ, %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

523 703 523 703 523 703 523 703 462 764 613 613 613 613 613 613 613 613 613 613

4.00 4.00 10.00 10.00 4.00 4.00 10.00 10.00 7.00 7.00 2.00 12.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00

4.00 4.00 4.00 4.00 10.00 10.00 10.00 10.00 7.00 7.00 7.00 7.00 2.00 12.00 7.00 7.00 7.00 7.00 7.00 7.00

72.89 89.41 79.89 99.12 71.44 87.70 76.03 97.11 65.43 99.84 79.22 98.49 95.78 92.35 92.26 92.41 92.67 92.19 92.21 92.82

Table 2. Analysis of variance (ANOVA) for response surface quadratic model for decomposition rate

Source Model Residual Lack of fit Pure error Cor total

Sum of squares

Degrees of freedom

1884.41 69.98 69.63 0.34 1954.38

9 10 5 5 19

Mean square

F-value

Prob > F

209.38 7.00 13.93 0.07

29.92

<0.0001

201.87

<0.0001

2 = 0.932; adequate precision = 20.316 > 4 R 2 = 0.964, Radj

Table 3. Regression coefficient of polynomial function of response surface of decomposition rate of ammonium metavanadate

Term Intercept

Regression coefficient

P-value

χ1

92.56 9.59

<0.0001 <0.0001

χ2

4.62

<0.0001

χ3

–1.08

0.1610

0.94

0.3379

χ1χ 2 χ1χ 3

0.20

0.8360

χ 2χ3

–0.34

0.7247

χ12

–4.32

0.0001

χ 22

–2.12

0.0123

χ 32

–0.28

0.6939

3.4. Response Surface Analyses The graphical representations of the models (Eq. (6)) facilitate an examination of the effects of the experimental factors on the responses. The 3D surface graphs of the factors were obtained using the DesignExpert software and presented in Figs. 6, 7. The 3D surface graph in Fig. 6 shows that the decomposition rate significantly increases with increasing microwave calcination temperature at a fixed sample mass of 7 g. This result is probably caused by the thermal decomposition of ammonium metavanadate, which is an endothermic reaction; ammonium metavanadate will occur as an acceleration reaction with increasing temperature [31]. Moreover, a long microwave calcination time results in complete calcination reaction. Thus, the decomposition rates increase with increasing calcination temperature and calcination time. In addition, the figure shows that the effect of cal-

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99.0 Decomposition rate, %

102.0 Decomposition rate, %

605

94.5 87.0 79.5 72.0

93.5 88.0

10.00

703 8.50 658 613 Tim 7.00 e, K tur e, m 5.50 568 a r in pe 4.00 523 Tem

82.5 77.0 10.00

703 658 8.50 Ma 613 ss o 7.00 e, K 568 tur f sa 5.50 a r mp pe le, 4.00 523 Tem g

Fig. 7. Response surface plot of effect of the decomposition rate (γ) versus the temperature (χ1 ) and mass of sample (χ 3 ).

Fig. 6. Response surface plot of effect of the decomposition rate (γ) versus the temperature (χ1 ) and time (χ 2 ).

feature of the Design-Expert software based on the proposed models. The experiments were conducted under these conditions, and the experimental results were compared with the predicted results from the model. The maximum decomposition rates were selected as the optimum values. The results demonstrated that the model prediction from Eq. (6) agreed reasonably with the experimental data. Thus, the optimum values of the process variables were calcination temperature (645.35 K), calcaination time (9.66 min), and sample mass (4.3 g). The predicted decomposition value was 99.13%, whereas the experimental value under these conditions was 99.33%, thereby indicating that the experimental value agrees with the predicted value.

cination temperature on the decomposition rate is significantly higher than that of calcination time. Figure 7 shows the 3D display of the response surface plot of the function of the decomposition rate versus calcination temperature and sample mass, with calcination time set at 7 min. The decomposition rate decreases with an increase in sample mass within the experimental range. Furthermore, gas diffusion becomes increasingly difficult with increasing sample mass, thereby decreasing the decomposition rates. The decomposition rate decreases with an increase in sample mass within the studied experimental range due to the rapid conduction of heat away from the interior of the sample [16]. 3.5. Optimal Conditions and Verification of the Model

3.6. X-ray Diffraction (XRD) Analysis The results of the XRD studies of the products under optimization conditions are shown in Fig. 8. The results indicate that V2O5 was the only identified solid product whose diffraction pattern satisfactorily

To verify the developed model, additional experiments on decomposition rate were performed (as shown in Table 4) by using the numerical optimization

Table 4. Model validity of the response surface of decomposition rate of ammonium metavanadate under the optimal conditions Variables

Decomposition rate

calcination temperature χ1, K

calcination time χ 2, min

mass of sample χ 3, g

predicted, %

experimental, %

645.35

9.66

4.3

99.13

99.33

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Intenisty, a.u

4000

V2O5

3000 2000 1000 0 20

40

60

80

2θ, deg Fig. 8. The XRD Pattern for the decomposition final solid products under the optimization conditions.

matched the V2O5 pattern. Thus, preparing V2O5 from ammonium metavanadate via microwave intensification under optimum conditions is feasible. 4. CONCLUSIONS Ammonium metavanadate exhibited weak capability to absorb microwave energy, whereas V2O5 demonstrated strong capability, and the sample temperature increased rapidly with an increase in the mixture ratio of V2O5. The calcination parameters were optimized using RSM under microwave fields based on TG analyses. The decomposition rate of ammonium metavanadate was significantly affected by calcination temperature and calcination time compared with sample mass. The optimized intensification conditions were as follows: calcination temperature (645.35 K), calcination time (9.66 min), and sample mass (4.3 g). The decomposition rate of ammonium metavanadate was 99.13%, which coincided well with the experiment value of 99.33% under these conditions. The aforementioned results suggest that the regressive equation perfectly fits the decomposition rates. Preparing V2O5 from ammonium metavanadate via microwave intensification is feasible by mixing small amounts of V2O5.

M M0 Wt

NOMENCLATURE final mass (g) initial mass (g) theory value of mass loss

β β0 βi

Greek Symbol heating rates constant the ith linear coefficient

β ii β ij

the ith quadratic coefficient the ijth interaction coefficient

χ ij γ χ1 χ2 χ3

the independent variable the predicated response decomposition rate calcination temperature calcination time mass of sample

ACKNOWLEDGMENTS Financial support for this work from the National Technology Research and Development Program of China (863Program) (2013AA064003), The National Natural Science Foundation of China (no. 51564033), Yunnan Applied Basic Research Project (no. 2016FA023) and State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology (no. CNMRCUXT1403) are gratefully acknowledged. REFERENCES 1. Bahgat, A.A., Ibrahim, F.A., and El-Desoky, M.M., Electrical and optical properties of highly oriented nanocrystalline vanadium pentoxide, Thin Sol. Films, 2005, vol. 489, no. 1–2, pp. 68–73. 2. Losurdo, M., Barreca, D., Bruno, G., and Tondello, E., Spectroscopic ellipsometry investigation of V2O5 nanocrystalline thin films, Thin Sol. Films, 2001, vol. 384, no. 1, pp. 58–64. 3. Weckhuysen, B.M. and Keller, D.E., Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis, Catal. Today, 2003, vol. 78, no. 1–4, pp. 25–46. 4. Ertl, G., Knozinger, H., and Weitkamp, J., Eds., Handbook of Hetero-Geneous Catalysis, Weinheim: Wiley-VCH, 1997. 5. Hagen, J, Industrial Catalysis, A Practical Approach, Weinheim: Wiley-VCH, 1999. 6. Guan, Z.S., Yao, J.N., Yang, Y.A., and Loo, B.H., Electrochromism of the annealed vacuum-evaporated V2O5 films, J. Electroanal. Chem., 1998, vol. 443, no. 2, pp. 175–179. 7. Rajendra Kumar, R.T., Karunagaran, B., Venkatachalam, S., Mangalaraj, D., Narayandass, Sa.K., and Kesavamoorthy, R., Influence of deposition temperature on the growth of vacuum evaporated V2O5 thin films, Mater. Lett., 2003, vol. 57, no. 24–25, pp. 3820–3825. 8. Ozer, N., Electrochemical properties of sol gel deposited vanadium pentoxide films, Thin Sol. Films, 1997, vol. 305, no. 1–2, pp. 80–87. 9. Cazzanelli, Mariotto, G., Passerini, S., Smyrl, W.H., Gorenstein, A., Energymater, Sol., Raman and XPS characterization of vanadium oxide thin films deposited by reactive RF sputtering, Energy Mater. Sol. Cells, 1999, vol. 56, no. 3–4, pp. 249–258. 10. Bing Guo Liu, Jin Hui Peng, and Li Bo Zhang, Optimization of preparing V2O5 by calcination from ammo-

RUSSIAN JOURNAL OF NON-FERROUS METALS

Vol. 58

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11.

12.

13. 14.

15.

16.

17.

18.

19.

20.

21. 22.

nium metavanadate using response surface methodology, Trans. Nonferrous Met. Soc. China, 2011, vol. 21, no. 3, pp. 673–678. Ghanashyam Krishna, M., Debauge, Y., and Bhattacharya, A.K., X-ray photoelectron spectroscopy and spectral transmittance study of stoichiometry in sputtered vanadium oxide films, Thin Sol. Films, 1998, vol. 312, no. 1–2, pp. 116–122. Pickles, C.A., Microwave heating behaviour of nickeliferous limonitic laterite ores, Miner. Eng., 2004, vol. 17, pp. 775–780. Mujundar, Handbook of Industrial Drying, vol. 1/2, New York, USA: Marcel Dekker Inc., 1995. Keysona, D., Volantic, D.P., and Cavalcanteb, L.S., Domestic microwave oven adapted for fast heat treatment of Ba0.5Sr0.5(Ti0.8Sn0.2)O3 oowders, J. Mater. Process. Technol., 2007, vol. 189, no. 1, pp. 316–319. Zhang, P., Ling, X.L., Xu, M.X., and Liu, L., The new red luminescent Sr3Al2O6:Eu2+ phosphor powders pynthesized via sol-gel route by microwave-assisted, J. Alloys Compd., 2008, vol. 456, no. 1, pp. 216–219. Menzies, D.B., Qing Dai, Yi-Bing Cheng, Simon, G.P., and Leone Spiccia, One-step microwave calcination of ZrO2-coated TiO2 electrodes for use in dye-sensitized solar cells, C. R. Chimie, 2006, vol. 9, pp. 713–716. Selmi, F., Guerin, F., Yu, X.D., and Varadan, V.K., Microwave calcination and sintering of barium strontium titanate, Mater. Lett., 1992, vol. 12, pp. 424–428. Guo Shenghui, Peng Jinhui, Fan Xingxiang, and Zhang Libo, Calcination of ZnCO3 ⋅ 2Zn(OH)2 · H2O by microwave heating, Nonferrous Met., 2002, vol. 54, no. 4, pp. 53–55. Venter, G., Non-Dimensional Response Surfaces for Structural Optimization with Uncertainty, University of Florida, USA, 1998. Shweta Sharma, Anushree Malik, and Santosh Satya, Application of response surface methodology (RSM) for optimization of nutrient supplementation for Cr(VI) removal by Aspergillus lentulus AML05, J. Hazard. Mater., 2009, vol. 164, no. 2–3, pp. 1198–1204. Myers, R.H. and Montgomery, D.C., Response Surface Methodology, USA: John Wiley & Sons, Inc., 2002. Chen, M.J., Chen, K.N., and Lin, C.W., Optimization on response surface models for the optimal manufacturing conditions of dairy tofu, J. Food Eng., 2005, vol. 68, no. 4, pp. 471–480.

RUSSIAN JOURNAL OF NON-FERROUS METALS

607

23. Azargohar, R. and Dahai, A.K., Production of activated carbon from luscar char: Experimental and modeling studies, Micropor. Mesopor. Mater., 2005, vol. 85, no. 3, pp. 219–227. 24. Bingguo Liu, Jinhui Penga, Libo Zhang, Rundong Wan, and Shenghui Guo, Optimization of preparation for Co3O4 by calcination from cobalt oxalate using response surface methodology, Chem. Eng. Res. Design, 2010, vol. 88, pp. 971–976. 25. Zhang Mei, Lin Qin, and Xu Ai-Ju, Application of thermal analysis in study of mechanism of thermal decomposition of NH4VO3, Modem. Sci. Instrum., 2007, no. 3, pp. 98–100. 26. Huang, Mengyang, Jinhui Peng, and Ying Lei, The temperature rise behavior and microwave-absorbing characteristics of ilmenite concentrate in microwave field, J. Sichuan Univ., 2007, vol. 39, pp. 111–115. 27. Bingguo Liu, Jinhui Peng, Libo Zhang, et al., Coupling and absorbing behavior of microwave irradiation on the Co(C2O4) · 2H2O:Co3O4 system, J. Taiwan Inst. Chem. Eng., 2011, vol. 42, pp. 92–96. 28. Pickles, C.A., Microwave heating behaviour of nickeliferous limonitic laterite ores, Miner. Eng., 2004, vol. 17, pp. 775–784. 29. Zhang Libo, Ma Aiyuan, Liu Chenhui, et al., Dielectric properties and temperature increase characteristics of zinc oxide dust from a fuming furnace, Trans. Nonferrous Met. Soc. China, 2014, vol. 24, no. 12, pp. 4004– 4011. 30. Istadi, I. and Amin, N.A.S., Optimization of process parameters and catalyst compositions in carbon dioxide oxidative coupling of methane over CaO–MnO/CeO2 catalyst using response surface methodology, Fuel Proc. Technol., 2006, vol. 87, pp. 449–459. 31. Ahmadi, M., Vahabzadeh, F., Bonakdarpour, B., Mofarrah, E., and Mehranian, M., Application of the central composite design and response surface methodology to the advanced treatment of olive oil processing wastewater using Fenton’s peroxidation, J. Hazard. Mater. B, 2005, vol. 123, pp. 187–195. 32. Korbahti, B.K. and Rauf, M.A., Determination of optimum operating conditions of carmine decoloration by UV/H2O2 using response surface methodology, J. Hazard. Mater., 2009, vol. 161, no. 1, pp. 281– 286. 33. Selim, S.A., Philip, Ch.A., and Mikhail, R.Sh., Thermal decomposition of ammonium metavanadate, Thermochim. Acta, 1980, vol. 36, pp. 287–297.

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