J. Chem. Thermodynamics 71 (2014) 200–204

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J. Chem. Thermodynamics

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Thermochemical properties of two mixed alkali-alkaline earth metalborates as non-linear optical materials: NaSrBO3 and KSr4B3O9

0021-9614/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.jct.2013.11.033

⇑ Corresponding author. Tel.: +86 29 81530094.E-mail address: wangjunfengjy123@sina.com (J.-F. Wang).

Jun-Feng Wang ⇑, Xiao-Lan WangChemistry and Chemical Engineering, Shaanxi Xueqian Normal University, Xi’an 710062, PR China

a r t i c l e i n f o

Article history:Received 3 October 2013Received in revised form 2 November 2013Accepted 28 November 2013Available online 7 December 2013

Keywords:Mixed alkali-alkaline earth metal borateHigh-temperature solid state synthesisCharacterizationStandard molar enthalpy of formationSolution calorimetry

a b s t r a c t

Two mixed alkali-alkaline earth metal borates of NaSrBO3 and KSr4B3O9 have been synthesized by high-temperature solid state reaction, which were further characterized by XRD, FT-IR, DTA-TG techniques andchemical analysis. The molar enthalpies of solution of NaSrBO3(s) and KSr4B3O9(s) in 2.00 cm3 of1 mol � dm�3 HCl(aq), at T = 298.15 K were measured to be �(206.84 ± 0.43) kJ �mol�1 and�(494.59 ± 0.53) kJ �mol�1, respectively. The molar enthalpy of solution of NaCl(s) in 2.00 cm3 of{1 mol � dm�3 HCl + H3BO3 + Sr(OH)2 � 8H2O}(aq) mixed solvent at T = 298.15 K was measured to be(5.17 ± 0.02) kJ �mol�1. From these data and with the incorporation of the previously determined enthal-pies of solution of H3BO3(s) in HCl(aq) of Sr(OH)2 � 8H2O(s) in (HCl + H3BO3)(aq), and of KCl(s) in{HCl + H3BO3 + Sr(OH)2 � 8H2O}(aq), together with the use of the molar enthalpies of formation forNaCl(s)/KCl(s), Sr(OH)2 � 8H2O(s), H3BO3(s), HCl(aq) and H2O(l), the standard molar enthalpies of forma-tion of NaSrBO3(s) and KSr4B3O9 were calculated to be �(1653.1 ± 1.4) kJ �mol�1 and�(5071.1 ± 3.4) kJ �mol�1 on the basis of the designed thermochemical cycles, respectively.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The studies of alkali/alkaline earth metal borates have attractedconsiderable interest because some of these borates can be as non-linear optical (NLO) materials, such as CsLiB6O10, BaB2O4 (BBO) andBa2Be2B2O7 (TBO) [1,2]. The title two borates NaSrBO3 [3] andKSr4B3O9 [4] are also likely to be good candidates for futuredeep-UV NLO and birefringent materials [3].

Thermodynamic properties play very important roles in scientificresearch and industrial applications. Thermochemical data can pro-vide information on stabilities and reactivities of molecules that areused, and also are a key factor in the safe and successful scale-up ofchemical processes in the chemical industry. Until now, the standardmolar enthalpies of formation of several mixed alkali-alkaline earthmetal borates have been reported [5–9]. This paper reports thedetermination of the standard molar enthalpies of formation ofNaSrBO3 and KSr4B3O9 by using a heat conduction microcalorimeter.

2. Experimental

2.1. Synthesis and characterization of samples

All reagents and solvents employed in the synthesis werecommercially available and used without further purification.

Table 1 summarizes relevant information on sample materialpurities.

Polycrystalline NaSrBO3 sample was synthesized by high-tem-perature solid state reaction referring to literature [3]. A mixtureof 0.42 g Na2CO3, 1.18 g SrCO3 and 0.49 g H3BO3 was ground inan agate mortar and transferred to platinum crucible, which washeated in a furnace at T = 923 K for 4 h, then elevated to 1123 Kfor 72 h. The sample was cooled and then ground.

The polycrystalline KSr4B3O9 sample was synthesized by high-temperature solid state reaction according to the literature [4]. Amixture of 0.55 g K2CO3, 1.25 g SrCO3 and 0.49 g H3BO3 wasground in an agate mortar and transferred to platinum crucible,which was heated in a furnace at T = 673 K for 5 h, then elevatedto 1173 K for 48 h. The sample was cooled to 673 K at a rate of0.2 K �min�1, followed by cooling to room temperature, and thenground.

The resulting colourless powders were collected, and washedwith deionized water and ethanol for three times, respectively.

The samples obtained were characterized by X-ray powder dif-fraction (Rigaku D/MAX-IIIC X-ray diffractometer with Cu target at8 min�1), FT-IR spectroscopy (recorded on a Nicolet NEXUS 670spectrometer with KBr pellets at room temperature), and TG-DTA(performed on a SDT Q600 simultaneous thermal analyser undera N2 atmosphere with a heating rate of 10 K �min�1). The chemicalcomposition of the sample was determined by EDTA titration forSr2+, and by NaOH standard solution titration in the presence ofmannitol for boron.

TABLE 1Chemical reagents used in this study.

Chemical name Provenance State Initial mole fraction CAS numbers

Na2CO3 Aladdin Reagent Co., Ltd Solid 0.998 497-19-8K2CO3 Aladdin Reagent Co., Ltd Solid 0.995 584-08-7SrCO3 Aladdin Reagent Co., Ltd Solid 0.99 1633-05-2H3BO3 Aladdin Reagent Co., Ltd Solid 0.998 10043-35-3NaCl Aladdin Reagent Co., Ltd Solid 0.998 7647-14-5KCl Aladdin Reagent Co., Ltd Solid 0.9998 7447-40-7

J.-F. Wang, X.-L. Wang / J. Chem. Thermodynamics 71 (2014) 200–204 201

2.2. Calorimetric experiment

The thermochemical cycles designed for the derivation of theDf Ho

m of NaSrBO3 and KSr4B3O9 are shown in figure 1. The1 mol � dm�3 HCl(aq) solvent can dissolve all components of de-signed reaction (6), and its concentration, 1.0004 mol � dm�3, wasdetermined by titration with standard sodium carbonate. Withthe use of its density of 1.019 g � cm�3 (taken from chemical hand-book [10]), its concentration can also be expressed as the form ofHCl 54.561H2O. All the enthalpies of solution were measured witha RD496-2000 heat conduction microcalorimeter (Mianyang CPThermal Analysis Instrument Co., LTD, China), which has been de-scribed in detail previously [11]. In all these determinations, strictcontrol of the stoichiometry in each step of the calorimetric cycle

(a)

KSr4B3O9(s) +(HCl·54.561H2O) 4+KCl(s)

K+(aq)+4Sr2+(aq) +9Cl-(aq) +3H3BO3(a

(1)

(6)

(b)

FIGURE 1. The designed thermochemica

has been observed, with the objective that the dissolution of thereactants give the same composition as those of the products.The total time required for the complete dissolution reaction ofNaSrBO3, KSr4B3O9 and NaCl(s) solutes in corresponding solventswas about 0.5 h for each compound. There were no solid residuesobserved after the reactions in each calorimetric experiment.

To check the performance of the calorimeter, the enthalpy ofsolution of KCl (mass fraction P 0.9998) in deionised water wasdetermined to be (17.54 ± 0.10) kJ �mol�1, which is in agreementwith that of (17.524 ± 0.028) kJ �mol�1 reported in the literature[12]. This shows that the device used for measuring the enthalpyof solution in this work is reliable.

The standard molar enthalpies of formation of NaSrBO3 andKSr4B3O9 were obtained by solution calorimetry in combination

[Sr(OH)2·8H2O](s) +3H3BO3(s) + 14.561H2O

HCl(aq)

3H3BO3(aq)+HCl(aq)

4Sr2+(aq) + 8Cl-(aq) + 3H3BO3(aq) +HCl(aq)

q) +HCl(aq)

(5)

(4)

(3)

(2)HCl

l cycles: (a) NaSrBO3, (b) KSr4B3O9.

40

50

60

70

80

90

100

110

Tra

nsm

ittan

ce/%

(a)

(b)

202 J.-F. Wang, X.-L. Wang / J. Chem. Thermodynamics 71 (2014) 200–204

with the standard molar enthalpies of formation of NaCl(s)/KCl(s),Sr(OH)2 � 8H2O(s), H3BO3(s), HCl(aq) and H2O(l).

3. Results and discussion

3.1. Characterization of the synthetic samples

Figures 2 and 3 contain the powder XRD pattern of as-synthe-sized samples and the simulated patterns on the basis of crystalstructures of NaSrBO3 and KSr4B3O9, respectively. The diffractionpeaks on patterns corresponded well in position, indicating thephase purity of the as-synthesized samples.

10 20 30 40 50 60 70

2θ / °

(a)

(b)

FIGURE 2. X-ray powder diffraction patterns of synthetic NaSrBO3 sample: (a)simulated, (b) experimental.

(a)

10 20 30 40 50 60 70

2θ / °

(b)

FIGURE 3. X-ray powder diffraction patterns of the synthetic KSr4B3O9 sample: (a)simulated, (b) experimental.

4000 3500 3000 2500 2000 1500 1000 50010

20

30

Wave numbers/cm–1

FIGURE 4. The FT-IR spectra of synthetic samples: (a) NaSrBO3, (b) KSr4B3O9.

TABLE 2Molar enthalpies of solution of NaSrBO3(s) and KSr4B3O9(s) samples in 1 mol � dm�3

HCl(aq) at T = 298.15 Ka and atmospheric pressure.

No. m/mg DsolH/mJ DsolHm/(kJ �mol�1)

NaSrBO3(s)1 3.13 �3809.9 �206.882 3.42 �4174.8 �206.813 3.66 �4484.5 �207.584 3.39 �4127.4 �206.275 3.25 �3964.4 �206.66Mean �206.84 ± 0.43b

KSr4B3O9(s)1 4.45 �3890.2 �494.802 4.84 �4224.3 �494.003 5.35 �4678.3 �494.944 4.35 �3708.9 �493.945 4.65 �4068.9 �495.27Mean �494.59 ± 0.53b

a In each experiment, 2.00 cm3 of HCl(aq) was used.b The uncertainty is estimated to be twice the standard deviation of the mean.

TABLE 3Molar enthalpies of solution of NaCl(s) in (H3BO3 + HCl + Sr(OH)2�8H2O)(aq) atT = 298.15 Ka and atmospheric pressure.

No. m/mg DsolH/mJ DsolHm/(kJ �mol�1)

1 5.54 486.6 5.132 6.79 604.5 5.203 5.68 500.6 5.154 4.98 441.0 5.185 5.14 454.3 5.17Mean 5.17 ± 0.02b

a In each experiment, 2.00 cm3 of HCl(aq) was used.b The uncertainty is estimated to be twice the standard deviation of the mean.

The FT-IR spectra of synthetic samples (figure 4) exhibited thefollowing absorption bands and they were assigned referring tothe literature [3,4,13]. For the NaSrBO3 sample: The bands at(1410 and 1390) cm�1 might be the asymmetric stretching modeof BO3. The bands observed at (1180, 1110, and 1020) cm�1 shouldbe assigned to the B–O stretching mode of triangular [BO3]3�

groups, while the bands at about (752,780 and 818) cm�1 shouldbe attributed to the B–O out of plane bending. The bands at (606and 579) cm�1 are the bending mode of B(3)–O. For KSr4B3O9 sam-ple: The bands at (1460 and 1380) cm�1 and (1180 and 880) cm�1

TABLE 4Thermochemical cycle and results for the derivation of Df He

m (NaSrBO3, 298.15 K).a

No. Reaction DrHem/

(kJ �mol�1)

(1) NaSrBO3(s) + 94.38(HCl � 54.561H2O) = Na+(aq) + Sr2+(aq)+ 3Cl�(aq) + H3BO3(aq) + 91.38 (HCl � 56.35H2O)

�206.84 ± 0.43b

(2) 93.38 (HCl � 55.04H2O) = 93.38(HCl � 54.561H2O)+ 44.561H2O

0.84 ± 0.04

(3) H3BO3(aq) + 93.38 (HCl � 55.03H2O) = H3BO3(s)+ 93.38 (HCl � 55.03H2O)

�21.83 ± 0.08

(4) Sr2+(aq) + 2Cl�(aq) + H3BO3(aq) + 91.38(HCl � 56.35H2O) = Sr(OH)2 � 8H2O(s)+ H3BO3(aq) + 93.38 (HCl � 55.03H2O)

51.69 ± 0.15

(5) K+(aq) + Sr2+(aq) + 3Cl(aq) + H3BO3(aq) + 91.38(HCl � 56.35H2O) = NaCl(s)+ Sr2+(aq) + 2Cl�(aq) + H3BO3(aq) + 91.38 (HCl � 56.35H2O)

�5.17 ± 0.02

(6) 1/2H2(g) + 1/2Cl2(g) + 54.561H2O(l) = (HCl � 54.561H2O) �165.42 ± 0.1(7) NaCl(s) = Na(s) + 1/2Cl2(g) 411.15 ± 0.10(8) Sr(OH)2 � 8H2O(s) = Sr(s) + 5O2(s) + 9H2(g) 3352.2 ± 0.4(9) H3BO3(s) = B(s) + 3/2H2(g) + 3/2O2(g) 1094.8 ± 0.8(10) 10H2(g) + 5O2(g) = 10H2O(l) �2858.3 ± 0.4(11) NaSrBO3(s) = Na(s) + 4Sr(s) + 3B(s) + 9/2O2(g) 1653.1 ± 1.4b

a Equation (11) = equation (1) + equation (2) + equation (3) + equation (4) + equa-tion (5) + equation (6) + equation (7) + equation (8) + equation (9) + equation (10).b The uncertainty of the combined reaction is estimated as the square root of thesum of the squares of uncertainty of each individual reaction.

TABLE 5Thermochemical cycle and results for the derivation of Df He

m (KSr4B3O9, 298.15 K).a

No. Reaction DrHem/

(kJ �mol�1)

(1) KSr4B3O9(s) + 235.93(HCl � 54.561H2O) = K+(aq) + 4Sr2+(aq) + 9Cl�(aq)+ 3H3BO3(aq) + 163.24 (HCl � 56.86H2O)

�494.59 ± 0.53

(2) 234.93 (HCl � 54.62H2O) = 234.93(HCl � 54.561H2O) + 14.561H2O

0.29 ± 0.04

(3) 7H3BO3(aq) + 163.24(HCl � 56.83H2O) = 7H3BO3(s) + 163.24 (HCl � 56.83H2O)

�152.81 ± 0.56

(4) 4Sr2+(aq) + 8Cl�(aq) + 7H3BO3(aq) + 163.24(HCl � 56.84H2O) = 4Sr(OH)2 � 8H2O(s)+ 7H3BO3(aq) + 163.24 (HCl � 56.83H2O)

206.76 ± 0.6

(5) K+(aq) + 4Sr2+(aq) + 9Cl(aq) + 3H3BO3(aq) + 163.24(HCl � 56.86H2O) = KCl(s)+ 4Sr2+(aq) + 8Cl�(aq) + 7H3BO3(aq) + 163.24(HCl � 56.84H2O)

�19.90 ± 0.18

(6) 1/2H2(g) + 1/2Cl2(g) + 54.561H2O(l) = (HCl � 54.561H2O) �165.42 ± 0.1(7) KCl(s) = k(s) + 1/2 Cl2(g) 436.75 ± 0.10(8) 4Sr(OH)2 � 8H2O(s) = 4Sr(s) + 20O2(s) + 36H2(g) 13408.8 ± 1.6(9) 3H3BO3(s) = 3B(s) + 9/2H2(g) + 9/2O2(g) 3284.4 ± 2.4(10) 40H2(g) + 20O2(g) = 40H2O(l) �11433.20 ± 1.6(11) KSr4B3O9(s) = K(s) + 4Sr(s) + 3B(s) + 9/2O2(g) 5071.1 ± 3.4b

a Equation (11) = equation (1) + equation (2) + equation (3) + equation (4) + equa-tion (5) + equation (6) + equation (7) + equation (8) + equation (9) + equation (10).b The uncertainty of the combined reaction is estimated as the square root of thesum of the squares of uncertainty of each individual reaction.

J.-F. Wang, X.-L. Wang / J. Chem. Thermodynamics 71 (2014) 200–204 203

might be the asymmetric and symmetric stretching mode of B(3)–O. The bands at (741 and 623) cm�1 should be attributed to out ofplane bending of B(3)–O. The band at 590 cm�1 is the bendingmode of B(3)–O. These assignments are consistent with their struc-tures containing BO3 group.

The TG curves shows that NaSrBO3 and KSr4B3O9 samples haveno weight loss from at temperatures from (303 to 1073) K, which

are consistent with both borates having no water or OH group,indicating their good thermal stability.

The chemical analytical data of synthetic samples are (found/calcd, %), SrO (60.98/61.16), B2O3 (20.68/20.55) for NaSrBO3 andSrO (73.43/73.23), B2O3 (18.32/18.45) for KSr4B3O9. The chemicalanalytical results are consistent with the theoretical values.

All of above results indicate that the synthetic samples are pureand suitable for the calorimetric experiments.

3.2. Results of calorimetric experiments

The molar enthalpies of solution of NaSrBO3 and KSr4B3O9 sam-ples in 1 mol � dm�3 HCl(aq) at T = 298.15 K are listed in table 2respectively, and the molar enthalpies of solution of NaCl(s) in2 cm3 of {1 mol � dm�3 HCl + H3BO3 + Sr(OH)2 � 8H2O}(aq) atT = 298.15 K are listed in table 3, in which m is the mass of sample,DsolH is the enthalpy of solution, and DsolHm is the molar enthalpyof solution of solute. The uncertainty is estimated as twice thestandard deviation of the mean.

Tables 4 and 5 give the thermochemical cycles used for the deri-vation of the standard molar enthalpies of formation of NaSrBO3 andKSr4B3O9, in which Df He

m is the standard molar enthalpy of formationand the DrH

em is the enthalpy of reaction. The molar enthalpy of solu-

tion of H3BO3(s) of (21.83 ± 0.08) kJ �mol�1 in 1 mol � dm�3 HCl(aq)was taken from literature [14]. The molar enthalpy of solution ofSr(OH)2 � 8H2O(s) of �(51.69 ± 0.15) kJ �mol�1 in (HCl + H3BO3)(aq)was taken from the literature [8]. The molar enthalpy of solution ofKCl(s) of (19.90 ± 0.18) kJ �mol�1 in {Sr(OH)2 � 8H2O + H3BO3 +HCl}(aq) was also taken from the literature[8]. The standard molarenthalpy of formation of HCl(aq) and the enthalpy of dilution ofHCl(aq) were calculated from the NBS tables [15]. The standard mo-lar enthalpies of formation of H3BO3(s) and H2O(l) were taken fromthe CODATA Key Values [16], namely �(1094.8 ± 0.8) kJ �mol�1,and�(285.830 ± 0.040) kJ �mol�1, respectively. The standard molarenthalpies of formation of Sr(OH)2 � 8H2O(s), NaCl(s) and KCl(s) wastaken from the NBS tables [15], which are�(3352.2 ± 0.4) kJ �mol�1,�(411.15 ± 0.10) kJ �mol�1, and�(436.75 ± 0.10) kJ �mol�1, respec-tively. From these values, the standard molar enthalpies of forma-tion were calculated to be �(1653.1 ± 1.4) kJ �mol�1 for NaSrBO3

and �(5071.1 ± 3.4) kJ �mol�1 for KSr4B3O9.

4. Conclusions

Through the appropriate thermochemical cycles, the standardmolar enthalpies of formation of NaSrBO3 and KSr4B3O9 have beenobtained from measured enthalpies of solution, together with thestandard molar enthalpies of formation of NaCl(s)/KCl(s), Sr(OH)2

� 8H2O(s), H3BO3(s), HCl(aq) and H2O(l).

Acknowledgments

Project supported by the National Natural Science Foundationof China (No. 21173143). We thank Prof. Zhi-Hong Liu in ShaanxiNormal University for his support and guide in this work.

References

[1] Y.F. Zhou, M.C. Hong, Y.Q. Xu, B.Q. Chen, C.Z. Chen, Y.S. Wang, J. Cryst. Growth276 (2005) 478–484.

[2] H. Qi, C.T. Chen, J. Synth. Cryst. 30 (2001) 63–66.[3] L. Wu, X.L. Chen, Y. Zhang, Y.F. Kong, J.J. Xu, Y.P. Xu, J. Solid State Chem. 179

(2006) 1219–1224.[4] W.W. Zhao, S.L. Pan, Y.J. Wang, Z.H. Yang, X. Wang, J. Han, J. Solid State Chem.

195 (2012) 73–78.[5] R.Y. Chen, J. Li, S.P. Xia, S.Y. Gao, Thermochim. Acta 306 (1997) 1–5.[6] Y.Z. Jia, J. Li, S.Y. Gao, S.P. Xia, Thermochim. Acta 335 (1999) 1–4.[7] H.S. Huang, D.H. Lin, Z.H. Liu, J. Chem. Eng. Data 53 (2008) 1163–1166.[8] H.S. Huang, Z.S. Chen, Z.H. Liu, Thermochim. Acta 459 (2007) 130–132.

204 J.-F. Wang, X.-L. Wang / J. Chem. Thermodynamics 71 (2014) 200–204

[9] N. Li, R.B. Zhang, Z.H. Liu, Thermochim. Acta 5 (2013) 62–66.[10] K. Tao, Soviet Chemical Handbook (III), Science Press, Beijing, 1963.[11] M. Ji, M.Y. Liu, S.L. Gao, Q.Z. Shi, Instrum. Sci. Technol. 29 (1) (2001) 53–57.[12] R. Rychly, V. Pekárek, J. Chem. Themodyn. 9 (1977) 391–396.[13] J. Li, S.P. Xia, S.Y. Gao, Spectrochim. Acta 51A (1995) 519–532.[14] J. Li, S.Y. Gao, S.P. Xia, B. Li, R.Z. Hu, J. Chem. Thermodyn. 29 (1997) 491–497.

[15] D.D. Wagman, W.H. Evans, V.B. Parker, R.H. Schumm, I. Halow, S.M. Bailey, K.L.Chumey, R.L. Nuttall, J. Phys. Chem. Ref. Data 11 (Supple. 2) (1982).

[16] J.D. Cox, D.D. Wagman, V.A. Medvedev, CODATA Key Values forThermodynamics, Hemisphere, New York, 1989.

JCT 13-571