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Kinetics and Mechanism of Thermal Dehydration of KMnPO4 · H2O in a Nitrogen Atmosphere Pittayagorn Noisong and Chanaiporn Danvirutai* Department of Chemistry, Center of Excellence for InnoVation in Chemistry, Faculty of Science, Khon Kaen UniVersity, Khon Kaen 40002, Thailand

The potassium manganese phosphate monohydrate (KMnPO4 · H2O) was confirmed to dehydrate in a single step process. Therefore, the thermal transformation of this compound is an ideal case for testing the kinetic models and calculation procedures. The kinetics of thermal dehydration of this compound was studied using thermogravimetry (TG) at four heating rates by Ozawa and KAS methods. The calculated activation energy values from both methods are very close to each other. Four calculation procedures based on a single TG curve and the isoconversional method, as well as 26 mechanism functions were carried out. The mechanism function of dehydration with the integral form g(R) ) 1 - (1 - R)1/3 and the differential form f(R) ) 3(1 - R)2/3 can be suggested to be the mechanism of phase boundary reaction (spherical symmetry) for the title compound. In this work, the kinetic parameters and the transition state thermodynamic functions for the dehydration process of KMnPO4 · H2O are reported for the first time. 1. Introduction The thermal dehydration and decomposition routes of inorganic compounds are well-established in the literature.1–3 Nonetheless, studies on KMnPO4 · H2O are by far less common. The potassium manganese phosphate monohydrate (KMnPO4 · H2O) is in the dittmarite series MIMIIPO4 · H2O (MI ) K+, NH4+; MII ) Mg2+, Mn2+, Fe2+, Co2+, Ni2+), which are reported to be a biomineral and found (rather infrequently) in urinary calculi.1 Its synthetic analogue is used in the production of fertilizers, fireproof materials as well as for the extraction of divalent cations from seawater.4,5 The phosphates in the dittmarite series are a good source for macro- and micronutrients required by plants. Recently, more attention has been paid to potential applications in ionic conductivity, catalyst, and ion exchange for these type of compounds with a layered or tunnel structure.6 Although, there are some reports on the structure,7 magnetic,4,8 and spectroscopic4,9,10 properties of these compounds, to our knowledge, little or no kinetic and thermodynamic data are available. Recently, the thermal analysis (TG/DTG/DTA and DSC) methods have been widely used for scientific and practical purposes.3,11,12 The results obtained from these methods can be directly applied in materials science for the preparation of various metal and alloys, cements, ceramics, glasses, enamels, glazes, polymer, and composite materials.3 Nonisothermal methods are becoming more widely used because they are more convenient than the classical isothermal methods. In our previous papers,13,14 the kinetic and thermodynamic properties of a manganese hypophosphite compound were studied using nonisothermal method in various equations. The nonisothermal method is based on multiple heating rate data by setting the assumption that the parameters of the model are identical for all heating rates measurements. Various equations of kinetic analyses are known such as the Kissinger15 (differential method), Ozawa,16 Kissinger-Akahira-Sunose (KAS),17 Coats-Redfern,18 and Van Krevelen et al.19 methods (integral methods). Especially, the Ozawa and KAS equations were well described and widely * To whom correspondence should be addressed. Tel.: +66-43202222to 9 ext 12243. Fax: +66-43-202373. E-mail address: [email protected].

used in the literature; therefore, these methods are selected for studying the kinetics of thermal decomposition of the title compound. The aim of this paper was to report the nonisothermal decomposition kinetics of KMnPO4 · H2O in a nitrogen atmosphere by the isoconversional method of Ozawa16 and KAS.15,17,20 The mechanism model of dehydration and thermodynamic and kinetic parameters will be suggested and discussed. The calculated thermodynamic functions of transition state complexes (∆Hq, ∆Sq, ∆Gq) and kinetic (A, E) parameters in the dehydration process of KMnPO4 · H2O will be reported. The synthesized KMnPO4 · H2O and its dehydration product (KMnPO4) were characterized by thermogravimetry/differential thermogravimetry/differentail thermal analysis (TG/DTG/DTA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). 2. Experimental Section 2.1. Preparation and Characterization. The KMnPO4 · H2O was synthesized as described in the literature.21 The manganese and water contents of this compound were determined by using atomic absorption spectrophotometry (AAS, Perkin-Elmer, Analyst 100) and thermal analysis (TG/DTG/DTA, Pyris Diamond Perkin-Elmer), respectively. About 10 mg of the synthesized compound was used for the TG/DTG/DTA experiments and carried out at four heating rates of 5, 15, 20, and 25 °C min-1 over the temperature range from 50 to 250 °C in a N2 atmosphere with the flow rate of 100 mL min-1. The thermogram of a sample was recorded in an open aluminun pan using R-Al2O3 as the standard reference material. The synthesized KMnPO4 · H2O was calcined in a thermal analyzer at 300 °C in a N2 atmosphere, and the thermal transformation product was further characterized. The FTIR spectra of the synthesized compound and its calcined samples were recorded in the range of 4000-370 cm-1 using the KBr pellet technique (KBr, Merck, spectroscopy grade) on a Perkin-Elmer spectrum GX FTIR/FT Raman spectrophotometer with 16 scans and the resolution of 4 cm-1. The structures of the prepared hydrate and its calcined product were characterized by X-ray powder diffraction using a D8

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Advanced powder diffractometer (Bruker AXS, Karlsruhe, Germany) with Cu KR radiation (λ ) 0.15406 Å). The Scherrer method was used to evaluate the crystallite size (i.e., D ) Kλ/ (β cos θ), where λ is the wavelength of X-ray radiation, K is a constant taken as 0.89, θ is the diffraction angle, and β is the full width at half-maximum (fwhm)).22 2.2. Kinetics Studies. All kinetics studies are assumed to be based on the following equations: dR ) kf(R) dt

(1) Figure 1. TG/DTG/DTA curves of the synthesized KMnPO4 · H2O at a heating rate of 5 °C min-1 in a N2 atmosphere.

and k ) Ae-E/RT

(2)

where R is the extent of conversion and is equal to (Wo - Wt)/ (Wo - Wf); Wo, Wt, and Wf are the initial mass of sample, current mass of sample at temperature t, and final mass at a temperature at which the mass loss is approximately unchanged, respectively. f(R) is a function depending on the particular decomposition mechanism and is referred to as the differential form. The preexponential factor A (min-1) is assumed to be independent of temperature, E is the activation energy (kJ mol-1), R is the gas constant (8.314 J mol-1 K-1), and k is the rate constant. Combination of eqs 1 and 2 gives dR ) Af(R)e-E/RT dt

(3)

Figure 2. FTIR spectra of (a) synthesized KMnPO4 · H2O and (b) the calcined KMnPO4 · H2O at 300 °C in a N2 atmosphere.

Equation 3 can be modified, when β is the heating rate (β ) dT/dt, T is temperature (K), and t is time), and the following equation is obtained: dR dR dT dR )β ) Af(R)e-E/RT ) dt dt dT dT

(4)

Equation 4 can be rearranged to eq 5 as follows: dR A ) e-E/RT dT f(R) β

(5)

The solution of the left-hand side integral depends on the explicit expression of the function f(R) and is denoted as g(R). Various scientists suggested different ways to solve the right-hand side of eq 5. Thus, the kinetics of solid state reactions can be described by various equations taking into account the special features of their mechanisms. In kinetic study of KMnPO4 · H2O, Ozawa and KAS equations were used to determine the activation energy (E) and pre-exponential factor (A) of the dehydration reaction. These methods are well described and widely used in the literature, which provides reliable results. Therefore, these methods are selected for the kinetic analysis of the dehydration. The equations used for E calculation are

Figure 3. XRD patterns of (a) the calcined KMnPO4 · H2O at 300 °C in a N2 atmosphere and (b) the synthesized KMnPO4 · H2O.

on the reaction mechanism. According to the above-mentioned equations, the plots of ln β versus 1000/T (eq 6) and ln(β/T2) versus 1000/T (eq 7) corresponding to different extents of conversion R can be obtained by a linear regression of the leastsquares method. The activation energies ER and pre-exponential factor A can be evaluated from the slopes and intercepts of the straight lines with better linear correlation coefficients (r2), respectively. The activation energies were calculated at the heating rates of 5, 15, 20, and 25 °C min-1 via these methods in the R range of 0.1-0.9. 3. Results and Discussion

Ozawa equation. E - 1.0516( ) ( 0.0048AE g(R)R ) RT

(6)

E AR β ) ln 2 g(R)E RT T

(7)

ln β ) ln KAS equation. ln

All other parameters are the same as given in eqs 1 and 2. The Arrhenius parameters, together with the reaction model, are sometimes called the kinetic triplet. g(R) ) ∫0R dR/f(R) is the integral form of f(R), which is the reaction model that depends

3.1. TG/DTG/DTA. The theoretical mass loss for the formula (KMnPO4 · H2O) is 7.90% which agrees well with the observed mass loss of 8.45% (Figure 1) and corresponds to the mass loss of water molecule. DTA curves of the synthetic potassium manganese phosphate monohydrate at four heating rates (5, 15, 20, and 25 °C min-1) show a single peak for every case, which is attained at higher temperatures for a faster heating rate. The peaks of the DTA curves of this compound agree with DTG peaks at 162.68, 183.45, 187.98, and 192.26 °C for the heating rates of 5, 15, 20, and 25 °C min-1, respectively. The decomposition (dehydration)

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Table 1. Average Particle Sizes and Lattice Parameters of KMnPO4 · H2O and Calcined KMnPO4 · H2O at 300 °C in N2 Atmospheres Calculated from XRD Data compound KMnPO4 · H2O KMnPO4 (calcined KMnPO4 · H2O at 300 °C) a

method

a/Å

b/Å

c/Å

PDF no. 802360 this work DIF. PDF-this work PDF#890333 this work DIF. PDF-this work

5.676 5.680 -0.004 5.481

8.335 8.333 0.002 8.627

4.905 4.904 0.001 8.886

-a

-a

-a

average particle sizes/nm 103.4 ( 0.19 34.3 ( 0.23

Not available.

Table 2. Twenty-six Types of Mechanism Functions g(r) and f(r) Used for the Present Analysis no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

symbol F1/3 F3/4 F3/2 F2 F3 P3/2 P1/2 P1/3 P1/4 E1 A1, F1 A3/2 A2 A3 A4 R1, F0, P1 R2, F1/2 R3, F2/3 D1 D2 D3 D4 D5 D6 D7 D8

mechanism function name

g(R)

f(R)

one-third order three-quarters order one and a half order second order third order Mampel power law Mampel power law Mampel power law Mampel power law exponential law Arami-Erofeev equation Arami-Erofeev equation Arami-Erofeev equation Arami-Erofeev equation Arami-Erofeev equation power law power law power law parabola law Valensi equation Jander equation Ginstling-Brounstein equation Zhuravlev, Lesokin, Tempelman equation anti-Jander equation anti-Ginstling-Brounstein equation anti-Zhuravlev, Lesokin, Tempelman equation

1 - (1 - R) 1 - (1 - R)1/4 (1 - R)-1/2 - 1 (1 - R)-1 - 1 (1 - R)-2 - 1 R3/2 R1/2 R1/3 R1/4 ln R -ln(1 - R) [-ln(1 - R)]2/3 [-ln(1 - R)]1/2 [-ln(1 - R)]1/3 [-ln(1 - R)]1/4 R 1 - (1 - R)1/2 1 - (1 - R)1/3 R2 R + (1 - R) ln(1 - R) [1 - (1 - R)1/3]2 1-2R/3 - (1 - R)2/3 [(1 - R)-1/3 - 1]2 [(1 + R)1/3 - 1]2 1 + 2R/3 - (1 + R)2/3 [(1 + R)-1/3 - 1]2

3/2(1 - R) 4(1 - R)3/4 2(1 - R)3/2 (1 - R)2 1/2(1 - R)3 (2/3)R-1/2 2R1/2 3R2/3 4R3/4 R (1 - R) 3/2(1 - R)[-ln(1 - R)]1/3 2(1 - R)[-ln(1 - R)]1/2 3(1 - R)[-ln(1 - R)]2/3 4(1 - R)[-ln(1 - R)]3/4 (1 - R)0 2(1 - R)1/2 3(1 - R)2/3 1/2R [-ln(1 - R)]-1 3/2(1 - R)2/3[1 - (1 - R)1/3]-1 3/2[(1 - R)-1/3 - 1]-1 3/2(1 - R)4/3[1 - R)-1/3 - 1]-1 3/2(1 + R)2/3[(1 + R)1/3 - 1]-1 3/2[(1 + R)-1/3 - 1]-1 3/2(1 + R)4/3[(1 + R)-1/3 - 1]-1

reaction of this compound is suggested to be as the following:23 KMnPO4 · H2O f KMnPO4 + H2O

(8)

The dehydration temperature at about 162 °C was observed from TG/DTG/DTA experiments (Figure 1). The water molecules can be classified as crystal water or water of crystallization, because the water was eliminated at 150 °C and below, whereas the water molecules that were eliminated at 200 °C and above indicate coordination by the metal cation atom. Water molecules eliminated at intermediate temperatures can be coordinately linked water as well as crystal water.24 In this studied hydrate, it can be suggested that the water molecules are considered to be coordinately linked water as well as crystal water. The thermal dehydration of the KMnPO4 · H2O is an ideal case for testing kinetic models and calculation procedures for the well observed single stage of dehydration. 3.2. FTIR Spectroscopy. The FTIR spectra of KMnPO4 · H2O and its calcined product at 300 °C are presented in Figure 2. Three components with ν1(A1), ν2(A1), and ν3(B2) symmetries are expected under the C2V factor group symmetry and Csyz site symmetry for H2O molecule internal vibrations. In Figure 2a, one band in the 3481-3223 cm-1 region corresponds to the O-H stretching vibration. The band at 1655 cm-1 is attributed to the ν2(A1) mode of the water molecule, while the band at 1423 cm-1 is attributed to the very low bending vibration of water molecules, which is expected to be involved in the water-cation interactions with a tendency to

2/3

1/3

be more pronounced when the cation size is small and its charge is high as suggested by Falk.25 The vibrational bands of phosphate anion in both KMnPO4 · H2O (Figure 2a) and its calcined product at 300 °C in a N2 atmosphere (Figure 2b) appear in the 1100-400 cm-1 region. The characteristic vibrational bands were found in the range 1008-931, 500-375, 1176-1015, and 630-510 cm-1 and are assigned to ν1(A1), ν2(E), ν3(F2), and ν4(F2), respectively. Four bands around 550 cm-1 were observed in both compounds and agree with those observed by Koleva.26 These bands were assigned to the rocking libration modes (hindered rotation) of the water molecule. In this region, we found the different vibrational behaviors of the phosphate ion. It is suggested to be influential by two factors, namely: (i) the repulsion potential of the lattices and (ii) the weakening of the intramolecular P-O bonds owing to both the interionic M2+-O and M+-O interactions.27 3.3. XRD. The XRD patterns of the synthesized KMnPO4 · H2O and its calcined product at 300 °C in a N2 atmosphere are shown in Figure 3. All detectable peaks of KMnPO4 · H2O and its calcined product at 300 °C in a N2 atmosphere are indexed as the synthesized KMnPO4 · H2O, KMnPO4 structures. KMnPO4 · H2O is identified using the standard data of PDF no. 802360, this result indicated that KMnPO4 · H2O crystallizes in the orthorhombic system with space group Pmn21 or C2V7 (Z ) 2). In the case of KMnPO4, the corresponding PDF standard file is PDF no. 890333 with space group P1 bar or Ci1 (Z ) 2). The average crystallite sizes and lattice parameters of the synthesized compound and its calcined product calculated from XRD patterns are tabulated

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-1

2 kJ mol ). Hence, it can be concluded that the activation energy of nonisothermal decomposition of KMnPO4 · H2O is reliable. However, the studies on KMnPO4 · H2O are by far less common. Some calculations (kinetic compensation effect (KCE)) were suggested to check the activation energy value and the appropriate mechanistic function. 3.4.2. Determination of the Most Probable Mechanism Function and Pre-exponential Factor. The kinetic results reported in the literature3,18,28–30 showed that the kinetic parameters depend strongly on the selection of a proper mechanism function for the process. Therefore, the determination of the most probable mechanism function is highly essential. The results in Table 4 reveal that the activation energy (E) is independent of alpha (R). Thus, the following equation will be used to estimate the most probable reaction mechanism:

Figure 4. Ozawa plots for the dehydration process of KMnPO4 · H2O at four heating rates at various conversions (R ) 0.1-0.9, with 0.1 increment).

[

ln g(R) ) ln

Table 3. Most Probable Mechanism Functions g(r), Slopes, and the Correlation Coefficients of Linear Regression (r2) at 165 and 170 °C during the Dehydration Process of KMnPO4 · H2O temperature/°C

mechanism no.

slope

r2

dehydration

165

2 6 17 18 26 2 6 17 18 26

-1.05931 -1.17835 -0.95934 -1.02499 -1.22779 -1.07859 -1.02867 -0.9266 -1.0254 -1.02588

0.9946 0.9991 0.9964 0.9953 0.9999 0.9954 0.9997 0.9980 0.9963 0.9984

170

(9)

Where, x is E/RT and h(x) is expressed by the fourth Senum and Yang approximation as described in refs 3 and 31. The plots of ln(g(R)) vs ln(β) were carried out by using a linear regression of the least-squares method. To determine the most probable mechanism function, the degrees of conversion R corresponding to four heating rates taken at the same temperature (we selected at 165 and 170 °C) were substituted into the left side of eq 9 for all 26 types of mechanism functions as presented in Table 2.3 If the mechanism function g(R) according to eq 9 exhibits the slope and the linear correlation coefficient r2 closest to -1.0000 and unity, respectively, then the function g(R) is the most probable mechanism function. The results of the most probable mechanism functions during the dehydration process at 165 and 170 °C are tabulated in Table 3. According to Table 3, the slopes determined from the function nos. 17 and 18 are the closest to -1.000 and the correlation coefficients r2 were suited best. The mechanism function no. 18 was selected as the most probable mechanism function, because the slopes and correlation coefficients r2 were nearly constant at two temperatures. In addition, the slope from this function shows the best value. Therefore, it can be stated that the mechanism function with the integral form g(R) ) 1 - (1 - R)1/3 and differential form f(R) ) 3(1 - R)2/3 belongs to the mechanism of phase boundary reaction (spherical symmetry). This type of mechanism is assumed that the nucleation occurs rapidly on the surface of the crystal. The rate of dehydration is controlled by the resulting reaction from the interface progresses toward the center of the crystal.32 The pre-exponential factor A can be estimated from the intercept of the plots from Ozawa (eq 6) and KAS (eq 7) equations by inserting the most probable function g(R) and the

Figure 5. KAS plots for the dehydration process of KMnPO4 · H2O at four heating rates at various conversions (R ) 0.1-0.9, with 0.1 increment).

stage

]

e-x AE + ln 2 + ln h(x) - ln β R x

in Table 1. The lattice parameters of KMnPO4 · H2O and its calcined product are compared with that reported standard data and found to agree well. 3.4. Kinetic Studies. 3.4.1. Calculation of Activation Energy. The Ozawa and KAS analysis results from four TG measurements are presented in Figures 4 and 5, respectively. The activation energies E from these methods are listed in Table 4. According to Table 4, the activation energy values of dehydration step calculated from Ozawa and KAS methods were found to be 99.87 and 97.85 kJ mol-1, respectively, which reveal that they agree well with each other. The difference of this value in both methods can be observed in a very small range (about

Table 4. Activation Energy Values (E), Pre-exponential Factor (A), and Correlation Coefficient (r2) Calculated by Ozawa and KAS Methods for the Dehydration of KMnPO4 · H2O in an N2 Atmosphere Ozawa method R 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 average

E/kJ mol-1 104.03( 4.04 104.59 ( 3.90 102.96 ( 4.02 101.42 ( 3.70 100.01 ( 3.42 98.51 ( 3.21 97.13 ( 3.08 96.08 ( 2.93 94.13 ( 2.65 99.87 ( 3.10

r2 0.9970 0.9972 0.9970 0.9973 0.9977 0.9979 0.9980 0.9981 0.9984 0.9976

KAS method A/min-1

E/kJ mol-1

r2

× × × × × × × × × ×

102.52 ( 4.23 102.93 ( 4.08 101.12 ( 4.20 99.41 ( 3.87 97.86 ( 3.57 96.22 ( 3.35 94.72 ( 3.22 93.56 ( 3.05 91.43 ( 3.76 97.75 ( 4.07

0.9966 0.9969 0.9966 0.9970 0.9973 0.9976 0.9977 0.9979 0.9982 0.9973

3.95 4.34 2.70 1.76 1.20 7.99 5.54 4.19 2.49 1.77

1011 1011 1011 1011 1011 1010 1010 1010 1010 1011

A/min-1 2.31 2.44 1.43 8.79 5.70 3.62 2.40 1.75 9.73 9.45

× × × × × × × × × ×

1011 1011 1011 1010 1010 1010 1010 1010 109 1010

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Table 5. Values of ∆Sq, ∆Hq, and ∆Gq for the Dehydration Step of KMnPO4 · H2O Calculated According to the Ozawa and KAS Equations parameter

Ozawa

KAS

∆Sq/J mol-1 K-1 ∆Hq/kJ mol-1 ∆Gq/kJ mol-1

-41.60 96.00 115.36

-46.82 93.88 115.67

4. Conclusions

activation energy into the intercepts of these plots. The obtained pre-exponential factors A from Ozawa and KAS calculations are tabulated in Table 4. It can be seen that the values of preexponential factor A regularly decrease with an increasing degree of conversion R for both the Ozawa and KAS models. These A values are the measure of the collision frequencies and were found to be 1.77 × 1011and 9.45 × 1010 min-1, respectively. The average pre-exponential factors from the Ozawa method agree well with the KAS method. 3.4.3. Estimation of the Transition State Thermodynamic Functions. The pre-exponential factor or Arrhenius constant (A) can be calculated by both Ozawa and KAS methods. The related transition state thermodynamic functions can be calculated by using the activated complex theory (transition state) of Eyring.33–35 The following general equation can be written:35 A)

(

) ( )

eχkBT0 ∆Sq exp h R

(10)

where e is the Neper number (e ) 2.7183), χ is the transition factor, which is unity for the monomolecular reaction, kB is the Boltzmann constant (kB ) 1.3806 × 10-23 J K-1), h is Planck’s constant (h ) 6.6261 × 10-34 J s), T0 is the peak temperature of the DTA curve (corresponding stage at the highest heating rate), R is the gas constant (R ) 8.314 J K-1 mol-1), and ∆Sq is the entropy change of transition state complex or entropy of activation. Thus, the entropy of activation may be calculated as follows: ∆Sq ) R ln

Ah eχkBT0

state thermodynamic functions ∆Sq, ∆Hq, and ∆Gq by the Ozawa method are close to those evaluated by the KAS method.

(11)

The enthalpy change of transition state complex or heat of activation (∆Hq) and Gibbs free energy of activation (∆Gq) of decomposition were calculated according to eqs 11 and 12, respectively. ∆Hq ) Eq - RT0

(12)

∆Gq ) ∆Hq - T0∆Sq

(13)

where, Eq is the activation energy E of the Ozawa and KAS methods. Transition state thermodynamic functions were calculated from eqs 11-13 and summarized in Table 5. The negative values of ∆Sq from two methods for the dehydration step reveals that the activated state is less disordered compared to the initial state. These ∆Sq values suggest a large number of degrees of freedom due to rotation and vibration which may be interpreted as a “slow” stage35,3,14 in this step. The positive values of ∆Gq at all studied methods are due to the fact that, the dehydration processes are not spontaneous. The positivity of ∆Gq is controlled by a small activation entropy and a large positive activation enthalpy according to the eq 13. The endothermic peaks in DTA data agree well with the positive sign of the activation enthalpy (∆Hq). The estimated transition

KMnPO4 · H2O decomposes in single step process and the final product is KMnPO4 at the temperature not higher than 300 °C. The kinetic study of thermal dehydration of this compound was carried out by using Ozawa and KAS methods, which reveal that the calculated activation energy values are close to each other. Kinetic analysis results from the nonisothermal TG curves applying the model-fitting method provide a single value of E for different extents of conversion R and lead to the conclusion that the dehydration process is a single step reaction. The mechanism of the dehydration process is the phase boundary reaction (spherical symmetry), by which the rate of this process is controlled by the resulting reaction interface progresses toward the center of the crystal. The activation entropy ∆Sq, enthalpy ∆Hq, and Gibbs free energy ∆Gq of transition state for KMnPO4 · H2O from two methods can be calculated through kinetic parameters. The transition state thermodynamic functions agree well with the thermal analysis data. The discussion about the activation energy, pre-exponential factor in relation to the change of activated entropy enthalpy, and Gibbs free energy of the dehydration of the title compound is reported for the first time. Acknowledgment We thank the Department of Chemistry, Faculty of Science, and Department of Environmental Engineering, Faculty of Engineering (For XRD), of Khon Kaen University for providing research facilities. The financial support from the Development and Promotion in Science and Technology Talents Project (DPST) and the Center of Excellence for Innovation Chemistry (PERCH-CIC), Commission on Higher Education, Ministry of Education, is gratefully acknowledged. Literature Cited (1) Hevroni, L.; Shamish, Z.; Danon, A. Thermal dehydration and decomposition of copper selenate pentahydrate. J. Therm. Anal. Calorim. 2009, 98, 367. (2) Paulik, J.; Paulik, F.; Arnold, M. Dependence of the thermal decomposition of CuSO4 · 5H2O on the experimental conditions. J. Therm. Anal. 1988, 34, 1455. (3) Vlaev, L.; Nedelchev, N.; Gyurova, K.; Zagorcheva, M. A. Comparative Study of Non-Isothermal Kinetics of Decomposition of Calcium Oxalate Monohydrate. J. Anal. Appl. Pyrol. 2008, 81, 253. (4) Sˇoptrajanov, B.; Stefov, V.; Kuzmanovski, I.; Jovanovski, G.; Lutz, H. D.; Engelen, B. Very Low H-O-H Bending Frequencies. IV. Fourier Transform Infrared Spectra of Synthetic Dittmarite. J. Mol. Struct. 2002, 613, 7. (5) Lapina, L. M. Metal Ammonium Phosphates and Their New Applications. Russ. Chem. ReV. 1968, 37, 693. (6) Yuan, A.; Wu, J.; Bai, L.; Ma, S.; Huang, Z.; Tong, Z. Standard Molar Enthalpies of Formation for Ammonium/3d-Transition Metal Phosphates NH4MPO4 · H2O (M ) Mn2+, Co2+, Ni2+, Cu2+). J. Chem. Eng. Data 2008, 53, 1066. (7) Carling, S. G.; Day, P.; Visser, D. Crytal and Magnetic Structures of Layer TransitionMetal Phosphate Hydrates. Inorg. Chem. 1995, 34, 3917. (8) Visser, D.; Carling, S. G.; Day, P.; Deportes, J. Magnetic Structure of KMnPO4 · H2O. J. Appl. Phys. 1991, 69, 6016. (9) Sˇoptrajanov, B.; Jovanovski, G.; Pejov, L. Very low H-O-H Bending Frequencies. III. Fourier Transform Infrared Study of Cobalt Potassium Phosphate Monohydrate and Manganese Potassium Phosphate Monohydrate. J. Mol. Struct. 2002, 613, 47. (10) Sˇoptrajanov, B.; Pejov, L.; Jovanovski, G.; Stefov, V. Very Low HOH Bending Vibrations. V. Quantum Chemical Study of Water Bending Vibrations in MgKPO4 · H2O. J. Mol. Struct. 2004, 706, 101.

Ind. Eng. Chem. Res., Vol. 49, No. 7, 2010 (11) Wendland, W. W. Thermal Methods of Analysis; John Wiley & Sons Inc: New York, 1974. (12) Sˇesta´k, J. Thermodynamical Properties of Solids; Academia: Prague, 1984. (13) Noisong, P.; Danvirutai, C.; Srithanratana, T.; Boonchom, B. Synthesis, Characterization and Non-isothermal Decomposition Kinetics of Manganese Hypophosphite Monohydrate. Solid State Sci. 2008, 10, 1598. (14) Noisong, P.; Danvirutai, C.; Boonchom, B. Thermodynamic and Kinetic Properties of the Formation of Mn2P2O7 by Thermal Decomposition of Mn(H2PO2)2 · H2O. J. Chem. Eng. Data 2009, 54, 871. (15) Kissinger, H. E. Reaction Kinetics in Differential Thermal Analysis. Anal. Chem. 1957, 29, 1702. (16) Ozawa, T. A. New Method of Analyzing Thermogravimetric Data. Bull. Chem. Soc. Jpn. 1965, 38, 1881. (17) Akahira, T.; Sunose, T. Transactions of the 1969 Joint ConVention of Four Electrical Institutes; Paper No. 246, 1969;Res Report Chiba Inst. Technol. (Sci. Technol.) 1971, 16, 22. (18) Coats, A. W.; Redfern, J. P. Kinetic Parameters from Thermogravimetric Data. Nature 1964, 20, 68. (19) Van Krevelens, D. W.; Hoftijzer, P. J. Kinetics of Gas-Liquid Reaction-General Theory. Trans. Inst. Chem. Eng. 1954, 32, 5360. (20) Liqing, L.; Donghua, C. Application of Iso-temperature Method of Multipled Rate to Kinetic Analysis: Dehydration for Calcium Oxalate Monohydrate. J. Therm. Anal. Calorim. 2004, 78, 283. (21) Basset, H.; Bedwell, W. L. Studies of Phosphates. Part I. Ammonium Magnesium Phosphate and Related Compounds. J. Chem. Soc. 1933, 137, 854. (22) Cullity, B. D. Elements of X-ray Diffraction, 2nd ed.; AddisonWesley Publishing company: New York, 1978. (23) Xuehang, W.; Wenwei, W.; Sen, L.; Yanjin, F.; Shushu, L. Preparation Via Solid-State Reaction at Room Temperature and Characterization of Layered Nanocrystalline KMnPO4.H2O. J. Alloys Compd. 2009, 497, 541. (24) Gabal, M. A.; El-Bellihi, A. A.; Ata-Allah, S. S. Effect of Calcination Temperature on Co(II) Oxalate Dihydrate-Iron(II) Oxalate

3151

Dihydrate Mixture: DTA-TG, XRD, Mo¨ssbauer, FT-IR and SEM Studies (Part II). Mater. Chem. Phys. 2003, 81, 84. (25) Falk, M. The Frequency of the HsOsH Bending Fundamental in Solids and Liquids. Spectrochim. Acta 1984, 40A, 43. (26) Koleva, V. G. Vibrational Behavior of the Phosphates Ions in Dittmarite-Type Compounds MIMIIPO4 · H2O (MI ) K+, NH4+; MII ) Mn2+, 2+ Co , Ni2+). Spectrochim. Acta 2007, 66, 413. (27) Sˇoptrajanov, B. Very Low HOH Bending frequencies. I. Overview and Infrared Spectra of NiKPO4 · H2O and Its Deuterated analogues. J. Mol. Struct. 2000, 555, 21. (28) Price, D.; Dollimore, D.; Fatemi, N.; Whitehead, R. Mass Spectrometric Determination of Kinetic Parameters for Solid State Decomposition Reactions. Part 1. Method; Calcium Oxalate Decomposition. Thermochim. Acta 1980, 42, 323. (29) Tanaka, H.; Ohshima, S.; Ichiba, S.; Negita, H. Kinetics and Mechanism of the thermal Dehydration of Calcium Oxalate Monohydrate. Thermochim. Acta 1981, 48, 137. (30) Ninan, K. N. Thermal Decomposition Kinetics. Part XIV. Kinetics and Mechanism of Isothermal Decomposition of Calcium Oxalate Monohydrate and Correlation with Sample Mass. Thermochim. Acta 1986, 98, 221. (31) Senum, G. I.; Yang, R. T. Rational approximations of the integral of the Arrhenius function. J. Therm. Anal. Calorim. 1977, 11, 445. (32) Khawam, A.; Flanagan, D. R. Solid-State Kinetic Models: Basics and Mathematical Fundamentals. J. Phys. Chem. B. 2006, 110, 17315. (33) Yong, D. Decomposition of Solids; Academia: Prague, 1984. (34) Rooney, J. J. Eyring Transition-State Theory and Kinetics in Catalysis. J. Mol. Catal. A: Chem. 1995, 96, L1. (35) Boonchom, B. Kinetics and Thermodynamic Properties of the Thermal Decomposition of Manganese Dihydrogenphosphate Dihydrate. J. Chem. Eng. Data 2008, 53, 1533.

ReceiVed for reView June 19, 2009 ReVised manuscript receiVed February 9, 2010 Accepted February 16, 2010 IE900993F