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Article

Temperature-Induced Phase Transformations in Tutton Salt K2Cu(SO4)2(H2O)6: Thermoanalytical Studies Combined with Powder X-Ray Diffraction

by
João G. de Oliveira Neto
1,*,
Ronilson S. Santos
1,
Kamila R. Abreu
1,
Luzeli M. da Silva
1,
Rossano Lang
2 and
Adenilson O. dos Santos
1
1
Center for Sciences of Imperatriz, Federal University of Maranhão—UFMA, Imperatriz 65900-410, MA, Brazil
2
Institute of Science and Technology, Federal University of São Paulo—UNIFESP, São José dos Campos 12231-280, SP, Brazil
*
Author to whom correspondence should be addressed.
Physchem 2024, 4(4), 458-469; https://doi.org/10.3390/physchem4040032
Submission received: 27 September 2024 / Revised: 13 November 2024 / Accepted: 14 November 2024 / Published: 16 November 2024
(This article belongs to the Section Solid-State Chemistry and Physics)
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Versions Notes

Abstract

Tutton salts have received considerable attention due to their potential applications in thermochemical energy storage (TCHS) systems. This technology requires high-purity materials that exhibit reversible dehydration reactions, significant variations in dehydration enthalpy, and high-temperature melting points. In this study, K2Cu(SO4)2(H2O)6 Tutton salt in the form of single crystals was grown using the slow solvent evaporation method. Their structural, morphological, and thermal characteristics are presented and discussed, as well as temperature-induced phase transformations. At room temperature, the salt crystallizes in a monoclinic structure belonging to the P21/a space group, which is typical for Tutton salts. The lack of precise control over the solvent evaporation rate during crystal growth introduced structural disorder, resulting in defects on the crystal surface, including layer discontinuities, occlusions, and pores. Thermoanalytical analyses revealed two stages of mass loss, corresponding to the release of 4 + 2 coordinated H2O molecules—four weakly coordinated and two strongly coordinated to the copper. The estimated dehydration enthalpy was ≈ 80.8 kJ/mol per mole of H2O. Powder X-ray diffraction measurements as a function of temperature showed two phase transformations associated with the complete dehydration of the starting salt occurring between 28 and 160 °C, further corroborating the thermal results. The total dehydration up to ≈ 160 °C, high enthalpy associated with this process, and high melting point temperature make K2Cu(SO4)2(H2O)6 a promising candidate for TCHS applications.

1. Introduction

Inorganic salt hydrates have significantly influenced various research fields, including physics, chemistry, and crystallography [1]. These compounds have attracted considerable attention due to their potential to store energy in the form of heat through temperature-induced changes, making them suitable for space heating and domestic hot tap water supply [2].
Thermal energy storage can be achieved in three forms: sensible, latent, and thermochemical. In sensible heat storage, a storage material is heated and kept in an insulated environment until the heat is required. In latent heat storage, the energy is stored in the heat of a phase transition, like a compound that may turn from solid to liquid after absorbing heat and revert to the solid state as heat is removed. Thermochemical storage involves heat stored in a reversible chemical reaction that consumes energy (heat) during the charging phase (dehydration of a salt hydrate) and releases it during the discharging phase (the salt undergoes hydration) [3,4,5]. In this context, Tutton salts have been studied in recent years for their suitability in heat storage applications through thermochemical processes [6,7].
Tutton salts are an isomorphic class of hexahydrate salts that crystallize in a monoclinic system, specifically in the P21/a space group, with two formulas A2B(XO4)2(H2O)6 per unit cell (Z = 2) [8,9,10]. In such compounds, A represents a monovalent cation (K+, Rb+, Cs+, or NH4+), B a divalent cation (Mg2+, Mn2+, Fe2+, Co2+, Cu2+, Ni2+, Zn2+, or another divalent ion from the 3d group of the periodic table), and X an atom with a high oxidation state, such as S or Se [11,12]. The unit cell dimensions and molecular structures of the Tutton salts family are very similar [9,13,14]. Each unit cell contains two [B(H2O)6] hexahydrate octahedral complexes, where H2O molecules surround the divalent cations at symmetrical inversion sites (Ci) [8]. In the primitive cell, the divalent ions are located at atomic positions (0,0,0) and (½,½,0), while the remaining components occupy general positions [15,16,17].
Under room temperature conditions, all crystals of the Tutton salt family share similar cell dimensions and molecular layers. Rb2Cu(SO4)2(H2O)6 [18], Cs2Cu(SO4)2(H2O)6 [19], K2Cu(SO4)2(H2O)6 [20], and (NH4)2Cu(SO4)2(H2O)6 [21], for instance, exhibit the Cu2+ metal ion hexacoordinated by H2O molecules [Cu(H2O)6] in a slightly distorted octahedral geometry due to the Jahn–Teller effect. Furthermore, the H2O molecules stabilize the crystal lattice through intermolecular contact with A2 and (XO4)2 groups [22].
Among the various copper Tutton salts, the K2Cu(SO4)2(H2O)6 crystal was first obtained in 1996 by Rauw et al. [23], who determined its structure, evaluated the effects of pressure on the crystal structure and intermolecular interactions, and analyzed its electron paramagnetic resonance spectrum. In subsequent years, research was focused on investigating the [Cu(H2O)6] complex in various Tutton salt matrices with the evaluation of the disordering effects of Cu2+ ions in these crystals [24,25]. Additionally, temperature effects on crystal lattice and some physicochemical properties were reported [4,26]. More recently, Abdulwahab S. et al. [27] conducted a thermal study on K2Cu(SO4)2(H2O)6 crystals using thermogravimetry (TG) and differential thermal analysis (DTA), observing that the release of H2O molecules occurs in two stages.
Despite previous studies, the thermostructural properties of K2Cu(SO4)2(H2O)6 (here called KCuSOH) above room temperature, such as the thermal expansion coefficient, phase change temperatures, determination of high-temperature crystalline phases, and the crystallinity degree, need to be better investigated. This study aims to fill these gaps and address open questions regarding the structural arrangement of Tutton salts under changing temperatures.
Here we present a comprehensive study of the structural and thermal properties of KCuSOH using TG, DTA, differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD) as a function of temperature. The approach allowed access to the structural transformations of KCuSOH during heating up to 200 °C. Tracking the dehydration temperature ranges is considered valuable for TCHS applications, as well as the possible phase transformations of a thermochemical material.

2. Materials and Methods

2.1. Crystal Growth

KCuSOH single crystals were synthesized using the slow solvent evaporation method. This technique involves the gradual evaporation of the solvent from the saturated solution, facilitating the nucleation of the solid phase from the dissolved solute. For that, K2SO4 (Vetec, >99%) and CuSO4∙5H2O (Synth, >99%) were used as starting reagents in a 1:1 (0.1 mol/L) equimolar ratio.
The materials were weighed on a digital analytical balance and transferred to a beaker containing 50 mL of deionized water. The compounds were homogenized using a magnetic stirrer at 360 RPM for 5 h with a controlled temperature of 35 °C. The final solution, with a pH of 4.12, was stored under temperature (28 °C) and ambient pressure. The chemical reaction between the reagents is shown in Equation (1).
K2SO4(s) + CuSO4·5H2O(s) + H2O(l) → K2Cu(SO4)2·6H2O(s)
After five days, KCuSOH single crystals were successfully grown. The opaque blue solids were collected from the mother solution, washed with acetone, and air-dried for 24 h. Acetone was chosen for cleaning the crystals due to its effectiveness in removing surface residues (mother solution), not dissolving the crystal, and its high volatility at room temperature. Figure 1 depicts an image of a synthesized KCuSOH crystal with an average size of 0.60 × 0.73 × 0.33 mm3.

2.2. Characterization Techniques

Temperature-dependent powder X-ray diffraction (PXRD) patterns were collected using a PANalytical Empyrean diffractometer with an Anton Paar TTK450 temperature chamber attached to the system, measuring with CuKα (λ = 1.5418 Å) radiation and operating at 40 kV and 40 mA. The diffractograms were obtained in the 2θ angular range between 10–40°, with a 0.02° step size and acquisition time of 2 s. The temperature range used in this study was 28 to 200 °C. The PXRD patterns were further analyzed using the Rietveld refinement method [28] with EXPGUI-GSAS [29] software (version 3.0).
The crystal surface morphology and elementary analysis were examined using a scanning electron microscope (JEOL microscope, model JSM-7100F operating at 20 kV) with an integrated energy-dispersive X-ray spectroscopy analyzer (EDX). The sample was placed in aluminum stubs under carbon tape and coated with Au film.
To further investigate the thermal stability and evaluate the physical-chemical events associated with heat variation in the crystal, simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) measurements were performed using a Shimadzu DTG-60 analyzer in the 25–900 °C temperature range. Experimental conditions were dry N2 atmosphere, 100 mL/min gas flow rate, 10 °C/min heating rate, and powder sample weighing ≈ 4 mg.
Differential scanning calorimetry (DSC) measurement was performed in a DSC 60 Shimadzu thermal analyzer, under a 10 °C/min heating rate, in the 25–200 °C temperature range under a dry N2 atmosphere (100 mL/min), with a powder sample weighing ≈ 2 mg.

3. Results and Discussion

3.1. Crystal Phase Identification and Molecular Structure

Figure 2a shows the PXRD pattern at 28 °C and the calculated pattern (using the Rietveld method and Inorganic Crystal Structure Database (ICSD) under the number 81463) for the KCuSOH. The refined data indicate that the crystal belongs to the Tutton salts class, crystallizing in a monoclinic system of P21/a space group with two formulas per unit cell (Z = 2). The following refined lattice parameters were obtained: a = 9.076(7) Å, b = 12.105(6) Å, c = 6.146(9) Å, α = γ = 90.0°, and β = 104.4(5)°. The results are consistent with previously published data [23]. The quality of the structural refinement is reflected in the goodness of fit indicator and R-factors, which are S = 1.84, Rwp = 9.92%, and Rp = 8.21%, respectively.
Figure 2b illustrates the primitive unit cell of KCuSOH with intermolecular contacts. The crystal structure consists of a copper atom in a coordination sphere hexacoordinated by six H2O molecules in a [Cu(H2O)6] complex with octahedral geometry slightly distorted by the Jahn–Teller effect. In addition, the [SO4] tetrahedra and [KO8] polyhedra interact with the H2O units through hydrogen bonds, as shown.

3.2. Crystal Surface and Elemental Analysis

Figure 3 shows a SEM micrograph of a KCuSOH crystal. The surface morphology reveals growth defects, such as layer discontinuity, occlusion, and pores, resulting from the lack of precise control of the solvent evaporation rate during the crystal growth process [30]. The EDX semiquantitative analysis has confirmed the presence of the K, S, O, and Cu elements. The respective atomic percentages were ≈ 13.5, 14.6, 64.8, and 7.1%, respectively. Light elements, such as H, were not detected due to their low atomic weight and the reduced sensitivity of the EDX method for this specimen. Despite this, the elemental distribution indicates high purity and uniformity in the crystallized phase.

3.3. Thermal Properties via TG-DTA and DSC

The TG-DTA and DSC thermograms are shown in Figure 4a,b, respectively. The TG curve indicates that the KCuSOH thermal decomposition occurs in three stages. Initially, the material remains stable up to approximately 57 °C, followed by a mass loss of 16.51% (0.592 mg) between 58 and 110 °C. This mass loss is attributed to the release of four H₂O molecules coordinated to the metallic center. The endothermal events observed in the DTA (at 71 °C) and DSC (at 63 °C) curves suggest a phase transformation due to the partial dehydration of the system. Such a phase transformation could be confirmed through temperature-dependent PXRD.
In the second stage, a smaller mass loss corresponding to 8.09% (0.290 mg) was registered in the 110–175 °C temperature range. Endothermal peaks in the DTA (140 °C) and DSC (121 °C) curves were also observed in this interval. The data show that the mass loss in this second stage is associated with the release of two remaining H2O molecules. The difference between the dehydration temperatures in the TG-DTA and DSC curves implies that four H2O molecules are weakly bonded to the copper. Hence, they need less energy to break the bonds. However, two H2O molecules are more strongly coordinated; a higher temperature and energy are required to break through and release from the structure. The thermoanalytical studies (TG-DTA and DSC) thus suggest that the KCuSOH Tutton salt undergoes two consecutive phase transformations until 200 °C: hexahydrate → dihydrate and dihydrate → anhydrous. Furthermore, the endothermal peak at 528 °C in the DTA curve suggests a solid–solid phase transition of K2SO4 in the anhydrous K2Cu(SO4)2 structure, where the orthorhombic β-K2SO4 phase transforms into the trigonal α-K2SO4 phase, similar to what was reported by Morales et al. [26] and by Souamti et al. [31]. Table 1 summarizes temperature ranges, mass loss, event peaks, and chemical reactions related to heating the KCuSOH.
Additionally, from the two endothermal peaks recorded in the DSC curve, it was possible to estimate the dehydration enthalpy values in the two processes: 321.4 kJ/mol (63 °C) + 163.5 kJ/mol (121 °C). Therefore, the average enthalpy of each H2O unit around the copper atom is ≈ 80.8 kJ/mol H2O. This value is considered high and superior to other similar Tutton salts, such as (NH4)2Cu(SO4)2(H2O)6 (61 kJ/mol H2O) and Cs2Cu(SO4)2(H2O)6 (50 kJ/mol H2O) [4]. Therefore, KCuSOH is another promising material for thermochemical heat storage system applications. Besides, when compared with other materials suggested for such purposes, Tutton salts stand out due to their thermal stability, low toxicity, reaction reversibility, low cost, and easy synthesis [5,32]. However, further investigations, including structural reversibility and cyclability tests, should be conducted to validate the potential of the KCuSOH salt.

3.4. PXRD as a Function of Temperature

The PXRD analysis as a function of temperature was carried out to investigate phase stability and phase transformation (dehydration) in more detail. Figure 5 shows the diffractograms measured at several temperatures. The PXRD patterns recorded between 28 and 57 °C exhibit only the monoclinic phase (P21/a) associated with the hexahydrate Tutton salt. Even though the Tutton phase remains stable up to ≈ 57 °C, small peak shifts are observed due to changes in the lattice parameters. For example, the (121) reflection at 2θ = 24.80° shifted with increasing temperature, evidencing change in the cell parameters due to heating. A similar behavior was observed by Diniz et al. [33] in a thermostructural study of bis (L-glutaminato) copper (II) semi-organic crystals, where an expansion in the a lattice parameter was noticed because of a shift of the (200) peak to lower angles.
Rietveld refinement was performed for all diffractograms recorded up to 57 °C to probe the stability of Tutton phase lattice parameters. Figure 6a illustrates the refined lattice parameter values as a function of temperature. It is possible to observe that b and c parameters increase while a parameter decreases. The refinement also reveals that the monoclinic β angle decreases slightly from 104.4(5)° (28 °C) to 104.1(7)° (57 °C). This behavior indicates a thermal expansion of the KCuSOH structure with increasing temperature, further confirmed by the dilation effect on the unit cell volume shown in Figure 6b. However, it is important to highlight the non-linearity of the lattice parameters and, consequently, volume with the temperature increase between 28 and 57 °C. It is well known that materials with metallic centers exhibit thermal–structural properties dependent on the crystallographic direction, showing positive thermal expansion in one direction and negative thermal expansion in another [34].
The thermal expansion coefficients of KCuSOH were estimated from the refined unit cell parameters up to 57 °C. Figure 6c exhibits the temperature dependence of the relative changes in length (ΔL/L0) and the thermal expansion coefficients for each crystallographic axis. The linear fittings to the data were carried out from 28 to 57 °C. The data show a decrease in the a-axis, with an α[001] coefficient ≈ –16.17(1) × 10–6 °C−1. As the temperature increases, the b-axis remains practically unchanged with a value of α[010] = 2.01(1) × 10−6 °C−1, while the c-axis increases with α[001] = 40.75(2) × 10−6 °C−1. KCuSOH crystal in the monoclinic phase (P21/a) thus has a thermal expansion markedly anisotropic. Such a structural effect can be related to differences in the angles and distances in the hydrogen-bond lattice [35].
A remarkable structural change occurs at temperatures above 59 °C (see Figure 5). Shifts in the diffraction peaks at 11.42°, 14.60°, 17.76°, 19.09°, 22.43°, 25.35°, and 27.40° can be observed. The PXRD pattern changes between 59 and 61 °C, indicating the onset of phase transformation associated with the loss of four coordination H2O molecules. From 73 °C to 150 °C, the KCuSOH crystal transforms from the hexahydrate state to the dihydrate ones: K2Cu(SO4)2(H2O)2. It is worth mentioning that phase transformations in salt hydrates occur when an external variable, such as temperature, is applied to the salt, potentially causing changes in its internal structure, necessarily leading to mass loss (partial or total dehydration). Conversely, a phase transition usually refers to a change between distinct macroscopic states of material or phases (such as from solid to liquid) or from one amorphous → crystalline or even one crystalline structure to another, without mass loss. Therefore, only phase transformations were observed in the investigated PXRD temperature range.
The PXRD pattern at 120 °C was selected for crystallographic structure analysis using DASH 3.4.5 software [36] for peak indexing. The data suggest that the dihydrate phase belongs to a monoclinic system of the P21/c space group. Using the Le Bail method [37] implemented in EXPGUI-GSAS software (version 3.0) [29], the lattice parameters at 120 °C were determined, as shown in Figure 7. The least-squares refinement (Rwp = 5.4%, Rp = 2.2%, and S = 1.2) provided the following cell parameters: a = 12.035(2) Å, b = 10.133(1) Å, c = 7.722(1) Å, and β = 92.91(3)°.
At 160 °C, PXRD patterns display differences compared to those at lower temperatures. The change is caused by the total dehydration of the KCuSOH crystal, as determined by the TG-DTA and DSC data. Releasing the last two H2O molecules causes a second phase transformation: dihydrate to anhydrous. The anhydrous material was identified as a low-crystallinity K2Cu(SO4)2 phase (PDF index 17-0485). This can be explained by the increase in entropy that occurs when the sample is subjected to elevated temperatures. Several hydrogen bonds break between 150 and 160 °C, but new chemical bonds form at 160 °C, favoring the formation of anhydrous K2Cu(SO4)2 salt.
The crystallinity profile between 28 and 200 °C is shown in Figure 6d, where a decrease in crystallinity degree can be observed with increasing temperature. The crystallinity degree in percentage was evaluated using the following equation [38]:
Crystallinity   [ % ] = area   of   crystalline   peaks area   of   all   peaks   ( crystalline + amorphous )
The calculated percentages suggest that the K2Cu(SO4)2 structure is the most disordered, with increasingly higher temperatures up to 200 °C. The diffractograms corroborate this observation, showing increasingly broad and low-intensity peaks.
An overview of the structural evolution can be seen in the mapping (Figure 8) established from the 2θ positions and diffraction intensities as a function of temperature. K2Cu(SO4)2(H2O)6 starts with 6 H2O molecules. The crystal loses four H2O molecules during heating, forming K2Cu(SO4)2(H2O)2. At temperatures higher than 160 °C, K2Cu(SO4)2(H2O)2 loses its two H2O molecules and transforms into anhydrous K2Cu(SO4)2.
Summing up, the PXRD data show two phase transformations due to dehydration, in which the atomic disorder increases proportionally with the temperature increase. However, the temperature of the phase transformations can decrease or increase depending on the heating rate of the sample [39].

4. Conclusions

In this paper, KCuSOH single crystals were successfully grown using the slow solvent evaporation method. At room temperature, the structure of monoclinic symmetry (P21/a) was confirmed by PXRD and Rietveld refinement. The surface morphology by SEM micrograph revealed growth defects, such as layer discontinuity, occlusion, and pores, resulting from the lack of precise control of the solvent evaporation rate during the crystal growth process. Thermal results showed that KCuSOH undergoes dehydration in two steps: the first between 58 and 110 °C with the release of four H2O molecules and the second in the 110–175 °C interval with the release of the remaining two H2O molecules. Considering the two processes, the estimated dehydration enthalpy was ≈ 80.8 kJ/mol H2O. PXRD patterns as a function of temperature exhibited two phase transformations consistent with TG-DTA and DSC results. During the heating process, the K2Cu(SO4)2(H2O)6 loses four H2O molecules (T > 58 °C), forming K2Cu(SO4)2(H2O)2. At temperatures higher than 160 °C, K2Cu(SO4)2(H2O)2 loses its two H2O molecules and transforms into K2Cu(SO4)2. In addition, it was observed that as the temperature increases, the structural disorder increases. The anhydrous K2Cu(SO4)2 phase has a lower crystallinity than the hydrate phases. The findings improve understanding of the effects of temperature on the K2Cu(SO4)2(H2O)6 Tutton structure, aiming for potential applications in thermochemical heat energy storage systems.

Author Contributions

Conceptualization, J.G.d.O.N., L.M.d.S., R.L. and A.O.d.S.; methodology, J.G.d.O.N., R.S.S. and K.R.A.; software, J.G.d.O.N., R.S.S. and K.R.A.; validation, J.G.d.O.N., L.M.d.S., R.L. and A.O.d.S.; formal analysis, J.G.d.O.N., L.M.d.S., R.L. and A.O.d.S.; investigation, J.G.d.O.N., R.S.S. and K.R.A.; resources, L.M.d.S., R.L. and A.O.d.S.; data curation, J.G.d.O.N., L.M.d.S., R.L. and A.O.d.S.; writing—original draft preparation, J.G.d.O.N., R.S.S. and K.R.A.; writing—review and editing, J.G.d.O.N., L.M.d.S., R.L. and A.O.d.S.; visualization, J.G.d.O.N., R.S.S., K.R.A., L.M.d.S., R.L. and A.O.d.S.; supervision, J.G.d.O.N., L.M.d.S., R.L. and A.O.d.S.; project administration, L.M.d.S., R.L. and A.O.d.S.; funding acquisition, L.M.d.S., R.L. and A.O.d.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA), grant number BPD-12643/22; the National Council for Scientific and Technological Development (CNPq), grant numbers 312926/2020-0, and 317469/2021-5; and the Coordenação de Aperfeicoamento de Pessoal de Nível Superior (CAPES), grant number 001.

Data Availability Statement

Data are contained within the article.

Acknowledgments

All authors thank the Postgraduate Program in Materials Science at the Federal University of Maranhão.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Physchem 04 00032 g001
Figure 1. Image of an as-grown KCuSOH single crystal obtained using the slow evaporation technique.
Figure 1. Image of an as-grown KCuSOH single crystal obtained using the slow evaporation technique.
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Figure 2. (a) PXRD pattern at 28 °C of the K2Cu(SO4)2(H2O)6 crystal and refined by the Rietveld method. The theoretical pattern extracted from the ICSD 81463 is shown for comparison purposes. (b) Unit cell in monoclinic symmetry with labels and intermolecular contacts along the c-axis.
Figure 2. (a) PXRD pattern at 28 °C of the K2Cu(SO4)2(H2O)6 crystal and refined by the Rietveld method. The theoretical pattern extracted from the ICSD 81463 is shown for comparison purposes. (b) Unit cell in monoclinic symmetry with labels and intermolecular contacts along the c-axis.
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Figure 3. SEM image of a KCuSOH single crystal.
Figure 3. SEM image of a KCuSOH single crystal.
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Figure 4. (a) Simultaneous TG-DTA and (b) DSC thermograms of KCuSOH Tutton salt.
Figure 4. (a) Simultaneous TG-DTA and (b) DSC thermograms of KCuSOH Tutton salt.
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Figure 5. Evaluation of the PXRD pattern as a function of temperature for K2Cu(SO4)2(H2O)6.
Figure 5. Evaluation of the PXRD pattern as a function of temperature for K2Cu(SO4)2(H2O)6.
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Figure 6. (a) Lattice parameters as a function of temperature. (b) Unit cell volume as a function of temperature. (c) Thermal expansion coefficients on the monoclinic phase K2Cu(SO4)2(H2O)6. (d) Crystallinity degree in the 28–200 °C temperature range.
Figure 6. (a) Lattice parameters as a function of temperature. (b) Unit cell volume as a function of temperature. (c) Thermal expansion coefficients on the monoclinic phase K2Cu(SO4)2(H2O)6. (d) Crystallinity degree in the 28–200 °C temperature range.
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Figure 7. PXRD pattern at 120 °C and refined by the Le Bail method.
Figure 7. PXRD pattern at 120 °C and refined by the Le Bail method.
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Figure 8. Mapping of diffraction intensities as a function of temperature for the KCuSOH crystal.
Figure 8. Mapping of diffraction intensities as a function of temperature for the KCuSOH crystal.
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Table 1. Fragmentation events observed for KCuSOH powder in TG-DTA and DSC analysis.
Table 1. Fragmentation events observed for KCuSOH powder in TG-DTA and DSC analysis.
TGTpeak
DTA [°C]		Tpeak
DSC [°C]		Molecular
Fragment		Chemical
Reactions
Temp. Range
[°C]		Weight
Loss
[%]		Weight
Loss
[mg]		Molar Mass
[g∙mol−1]
58–10016.510.592“72.06”
*72.98*		71634∙H2OK2Cu(SO4)2(H2O)6 →
K2Cu(SO4)2(H2O)2 + 4∙H2O↑
110–1758.090.290“36.02”
*35.75*		1401212∙H2OK2Cu(SO4)2(H2O)2 →
K2Cu(SO4)2 + 2∙H2O↑
175–600---528--K2Cu(SO4)2 → β-K2SO4 + Cu(SO4) →
α-K2SO4 + Cu(SO4)
600–9008.400.301“441.96”
*437.12*		--inorganic
compounds		sulfates decomposition
Values “experimental” and *calculated*.
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MDPI and ACS Style

de Oliveira Neto, J.G.; Santos, R.S.; Abreu, K.R.; da Silva, L.M.; Lang, R.; dos Santos, A.O. Temperature-Induced Phase Transformations in Tutton Salt K2Cu(SO4)2(H2O)6: Thermoanalytical Studies Combined with Powder X-Ray Diffraction. Physchem 2024, 4, 458-469. https://doi.org/10.3390/physchem4040032

AMA Style

de Oliveira Neto JG, Santos RS, Abreu KR, da Silva LM, Lang R, dos Santos AO. Temperature-Induced Phase Transformations in Tutton Salt K2Cu(SO4)2(H2O)6: Thermoanalytical Studies Combined with Powder X-Ray Diffraction. Physchem. 2024; 4(4):458-469. https://doi.org/10.3390/physchem4040032

Chicago/Turabian Style

de Oliveira Neto, João G., Ronilson S. Santos, Kamila R. Abreu, Luzeli M. da Silva, Rossano Lang, and Adenilson O. dos Santos. 2024. "Temperature-Induced Phase Transformations in Tutton Salt K2Cu(SO4)2(H2O)6: Thermoanalytical Studies Combined with Powder X-Ray Diffraction" Physchem 4, no. 4: 458-469. https://doi.org/10.3390/physchem4040032

APA Style

de Oliveira Neto, J. G., Santos, R. S., Abreu, K. R., da Silva, L. M., Lang, R., & dos Santos, A. O. (2024). Temperature-Induced Phase Transformations in Tutton Salt K2Cu(SO4)2(H2O)6: Thermoanalytical Studies Combined with Powder X-Ray Diffraction. Physchem, 4(4), 458-469. https://doi.org/10.3390/physchem4040032

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