Thermodynamic properties,detonation characterisation and free radical of N-acetyl-3,3-dinitroazetidine

N-acetyl-3,3-dinitroazetidine (ADNAZ) is an important precursor for synthesizing new multinitroazetidine energetic compounds. Its thermal behaviour was studied under a non-isothermal condition by DSC and TG/DTG methods, the results show that there are one melting process and one endothermic decomposition process. The specific molar heat capacity (C_p,m) of ADNAZ was determined by a continuous C_p mode of micro-calorimeter and theoretical calculation, and the C_p,m of ADNAZ was 240.37 J · K⁻¹ · mol⁻¹ at T = 298.15 K. The detonation velocity (D) and detonation pressure (P) of ADNAZ were estimated using the nitrogen equivalent equation according to the experimental density, the value of D and P are (6685.83 ± 3.12) m · s⁻¹ and (18.36 ± 0.02) GPa, respectively. The free radical signals of ADNAZ were detected by electron spin resonance (ESR) technique, which is used to estimate its sensitivity.     

Molar heat capacity and thermodynamic properties of 1-cyclohexene-1,2-dicarboxylic anhydride [C8H8O3]

The molar heat capacity C_p,m of 1-cyclohexene-1,2-dicarboxylic anhydride was measured in the temperature range from T=(80 to 360) K with a small sample automated adiabatic calorimeter. The melting point T_m, the molar enthalpy Δ_fusH_m and the entropy Δ_fusS_m of fusion for the compound were determined to be (343.46 ± 0.24) K, (11.88 ± 0.02) kJ · mol⁻¹ and (34.60 ± 0.06) J · K⁻¹ · mol⁻¹, respectively. The thermodynamic functions [H_(T)−H_(298.15)] and [S_(T)−S_(298.15)] were derived in the temperature range from T=(80 to 360) K with temperature interval of 5 K. The mass fraction purity of the sample used in the adiabatic calorimetric study was determined to be 0.9928 by using the fractional melting technique. The thermal stability of the compound was investigated by differential scanning calorimeter (DSC) and thermogravimetric (TG) technique, and the process of the mass-loss of the sample was due to the evaporation, instead of its thermal decomposition.     

Non-isothermal decomposition kinetics,thermal behavior and computational detonation properties on 4-amino-1,2,4-triazol-5-one (ATO)

The thermal behavior of 4-amino-1,2,4-triazol-5-one (ATO) was studied under non-isothermal condition by DSC method in a sealed cell of stainless steel. The melting enthalpy and melting entropy of ATO are 21.34 ± 0.49 kJ mol⁻¹ and 46.54 ± 0.30 J mol⁻¹ K⁻¹, respectively. The kinetic parameters were obtained from the analysis of DSC curves by Kissinger method, Ozawa method, the differential method and the integral method. The main exothermic decomposition reaction mechanism of ATO is classified as nucleation and growth, and the kinetic parameters of the reaction are E_a = 119.50 kJ mol⁻¹ and A = 10^9.03 s⁻¹. The gas products and condensed phase products of the thermal decomposition of ATO were studied on two simultaneous devices of the fast thermolysis reaction cell (gas reaction cell) in situ in conjunction with rapid scan transform infrared spectroscopy (RSFT-IR) and the solid reaction cell in situ. The heat of formation (HOF) for ATO was evaluated by G3 theory. The detonation velocity (D) and detonation pressure (P) were estimated by using the well-known Kamlet–Jacobs equation, based on the theoretical HOF and the determined crystal density.     

Density and isothermal compressibility for two trialkylimidazolium-based ionic liquids at temperatures from (278 to 398) K and up to 120 MPa

In this paper, a densimeter based on vibrating tube principle is used to determine experimentally the density of 1-butyl-2,3-dimethylimidazolium tris(pentafluoroethyl)trifluorophosphate and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide at temperatures between (278.15 and 398.15) K and at pressures up to 120 MPa. The apparatus was calibrated by using water, vacuum and bromobenzene. The Tammann–Tait equation of state was used to correlate (p, T, ρ) results with standard deviations around 2 · 10⁻⁴ g · cm⁻³. Other volumetric properties, such as isothermal compressibility and isobaric thermal expansivity, were obtained from this equation. For each ionic liquid, the α_p isotherms present a crossing point within the experimental pressure range. Besides, the effect that the C2-methylation in the imidazolium cation provokes on density values is analyzed. The prediction ability of the group contribution methods of Gardas and Coutinho and Jacquemin et al. were tested with the experimental densities.     

Ab initio calculations and mechanism of two proton migration reactions of ethoxy radical

We present a direct ab initio and density functional theory dynamics study of the thermal rate constants of the two H-migration reactions of C₂H₅O radical. MPW1K/6-31+G(d,p) methods were employed to optimize the geometries of all stationary points and to calculate the minimum energy path (MEP). The energies of all the stationary points were refined at the QCISD(T)/aug-cc-pVTZ level of theory. The thermal gas phase rate constants were evaluated based on the energetics from the QCISD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) level of theory using both microcanonical variational transition state theory (μVT) and canonical variational transition state theory (CVT) with the Eckart tunneling correction in the temperature range of 200–2500 K. The extended Arrhenius expression fitted from the μVT/Eckart rate constants of 1,2 H-shift and 1,3 H-shift reactions of C₂H₅O radical in the temperature range of 200–2500 K are k = 3.90 × 10⁻³¹T^12.4e^{(−2.13 × 103/T)} and k = 2.83 × 10⁻²⁹T^11.9e^{(−2.24 × 103/T)} s⁻¹, respectively. The two isomerization rate constants exhibited positive temperature dependence in the calculated temperature region. The variational effects for the two isomerizations of ethoxy radical are small and the tunneling effects are important in the low temperature range. The titled reactions are minor and not essential compared to the decomposition pathways of ethoxy radical.     

The estimation of the heat capacity of NpO2

The heat capacity C_{p, m}of NpO₂was estimated for temperatures between 300 K and 1400 K. The C_{p, m}was evaluated as a sum of three terms, phonon vibration C_{ph, m}, dilation C_{d, m}, and Schottky specific heat C_{s, m}. The C_{ph, m}and C_d,mwere calculated using the Debye temperature, Grüneisen constant and thermal expansion data obtained by high-temperature X-ray diffractometry. The coefficient of the linear thermal expansion (l.t.e.) for NpO₂was given as a polynomial function up to T =  1573 K. The estimated C_p,mwas compared with that of previous studies. The present result at T =  300 K was 66.87 J · K ^− 1· mol ^− 1, which agreed well with previous results, 66.22 J · K ^− 1· mol ^− 1, measured by using calorimetry. The thermodynamic functions were given as a function of temperature.     

Apparent molar volumes and apparent molar heat capacities of aqueous solutions ofα- andβ-cyclodextrins at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar heat capacities C_{p, φ}and apparent molar volumesV_φ were determined for aqueous solutions of α - and β -cyclodextrins at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa. The molalities investigated ranged from 0.008 mol · kg ^− 1to 0.12 mol · kg ^− 1forα -cyclodextrin and from 0.004 mol · kg ^− 1to 0.014 mol · kg ^− 1for β -cyclodextrin. We used a vibrating-tube densimeter (DMA 512P, Anton PAAR, Austria) to determine the densities and volumetric properties. Heat capacities were obtained using a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, USA). Equations were fit by regression to our experimental (V_φ, T, m) and (C_{p, φ},T , m) results. Infinite dilution partial molar volumes V₂^oand heat capacities C_p,2^owere obtained over the range of temperatures by extrapolation of these surfaces to m =  0.     

Thermodynamics of proton dissociations from aqueous l-methionine at temperatures from (278.15 to 393.15) K,molalities from (0.0125 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of l-methionine,methioninium chloride,and sodium methioninate

We have measured the densities of aqueous solutions of l-methionine, l-methionine plus equimolal HCl, and l-methionine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.0125 ⩽ m/mol · kg⁻¹ ⩽ 1.0 as solubilities allowed, and at p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from protonated aqueous cationic l-methionine. We integrated these results in an iterative algorithm using Young’s Rule to account for the effects of speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for methioninium chloride {H₂Met⁺Cl⁻(aq)} and for sodium methioninate {Na⁺Met⁻(aq)} which successfully modeled our observed results. Values are given for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous l-methionine as functions of T and m.     

Microstructure,stability and biocompatibility of hydroxyapatite – titania nanocomposites formed by two step sintering process

In the present work, we report the characterization of TiO₂-hydroxyapatite (HA) nanocomposites obtained by a two-step sintering (TSS) process of a mixture of HA and titanium hydride (TiH₂) powders. The reactions underwent by TiH₂ in the presence of HA and hydrogen release, and subsequently, titanium oxidation was examined by thermal analysis. A longer holding time in the second sintering stage enabled obtaining a homogenous TiO₂-HA (36% rutile) composite with a thermal expansion coefficient of 11.46 · 10⁻⁶ C⁻¹ in the 40–1000 °C range. Unconventional TSS process hinders HA decomposition to detrimental tricalcium phosphate (TCP). Wear rate of ceramics was determined by tribological measurements and the material biocompatibility was evaluated using MTT assay. Overall, cell viability results correlated with morphological observations indicated a good biocompatibility of HA-based composites at all tested concentrations. Incorporation of the TiO₂ phase in HA by TSS process was found to be an efficient way to prepare bioceramics with improved performances.     

Apparent molar volumes and apparent molar heat capacities of aqueous magnesium nitrate,strontium nitrate,and manganese nitrate at temperatures from 278.15 K to 393.15 K and at the pressure 0.35 MPa

Apparent molar volumes V_ϕ and apparent molar heat capacities C_p,ϕ were determined at the pressure 0.35 MPa for aqueous solutions of magnesium nitrate Mg(NO₃)₂ at molalities m = (0.02 to 1.0) mol · kg⁻¹, strontium nitrate Sr(NO₃)₂ at m = (0.05 to 3.0) mol · kg⁻¹, and manganese nitrate Mn(NO₃)₂ at m = (0.01 to 0.5) mol · kg⁻¹. Our V_ϕ values were calculated from solution densities obtained at T = (278.15 to 368.15) K using a vibrating-tube densimeter, and our C_p,ϕ values were calculated from solution heat capacities obtained at T = (278.15 to 393.15) K using a twin fixed-cell, differential, temperature-scanning calorimeter. Empirical functions of m and T were fitted to our results, and standard state partial molar volumes and heat capacities were obtained over the ranges of T investigated.     

Volumetric properties of aqueous solutions of glutaric acid

Densities of aqueous solutions with molalities up to 6 mol · kg⁻¹ were determined at 5 K temperature intervals, from T = 288.15 K to T = 333.15 K. Densities served to evaluate the apparent molar volumes, V_2,ϕ(m, T), the cubic expansion coefficients, α(m, T), and the changes of isobaric heat capacities with respect to pressure, (∂C_P/∂P)_T,m. They were qualitatively correlated with the changes in the structure of water when glutaric acid is dissolved in it.     

Thermodynamics of proton dissociations from aqueous alanine at temperatures from (278.15 to 393.15) K,molalities from (0.0075 to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of alanine,alaninium chloride,and sodium alaninate

We have measured the densities of aqueous solutions of alanine, alanine plus equimolal HCl, and alanine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, at molalities 0.0075 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure p = 0.35 MPa using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a twin fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T, m) for ionization of water to calculate parameters for Δ_rC_p,m(T, m) for the two proton dissociations from protonated aqueous cationic alanine. We integrated these results in an iterative algorithm using Young’s Rule to account for the effects of speciation and chemical relaxation on V_ϕ(T, m) and C_p,ϕ(T, m). This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for alaninium chloride {H₂Ala⁺Cl⁻(aq)} and for sodium alaninate {Na⁺Ala⁻(aq)} which successfully modeled our observed results. Values are given for Δ_rC_p,m, Δ_rH_m, pQ_a, Δ_rS_m, and Δ_rV_m for the first and second proton dissociations from protonated aqueous alanine as functions of T and m.     

P, ρ, and T measurements of the (limonene + β-pinene) mixtures

The density, ρ, and two derived properties, isothermal compressibility, κ_T, and the coefficient of cubic expansion, α_P, were obtained for the mixtures of 1-methyl-4-(1-methylethenyl)-cyclohexene, known as limonene, and (1S,5S)-6,6-dimethyl-2-methylenebibyclo[3.1.1]heptane, known as β-pinene, for nine different compositions and the pure components at five pressures from 20 MPa to 40 MPa and six temperatures from 283.15 K to 358.15 K. The experimental uncertainty for ρ, κ_T, and α_P were respectively ±0.5 kg · m⁻³, ±14 TPa⁻¹, and ±0.005k K⁻¹, with k = 2 for all of them. Density behaviour with temperature and pressure was as expected. The values of α_P and κ_T increase with temperature and decrease with increasing pressure. Two different equations of state, conventional SAFT and PC-SAFT, were applied to predict the densities of the mixture. The best predictions were achieved with PC-SAFT.     

Thermodynamics of proton dissociations from aqueous serine at temperatures from (278.15 to 393.15) K,molalities from (0.01 up to 1.0) mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of serine,serinium chloride,and sodium serinate

We have measured the densities of aqueous solutions of serine, serine plus equimolal HCl, and serine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at the pressure p = 0.35 MPa, using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a fixed-cell differential temperature-scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values from the literature for V_ϕ(T,m) and C_p,ϕ(T,m) for HCl(aq), NaOH(aq), and NaCl(aq) and the molar heat capacity change Δ_rC_p,m(T,m) for ionization of water to calculate Δ_rC_p,m(T,m) for proton dissociations from protonated aqueous cationic serine and from the zwitterionic form. We integrated these results in an iterative algorithm using Young’s rule to account for the effects of speciation and chemical relaxation on the observed V_ϕ(T,m) and C_p,ϕ(T,m) of the solutions. This procedure yielded parameters for V_ϕ(T,m) and C_p,ϕ(T,m) for serinium chloride {H₂Ser⁺Cl⁻(aq)} and for sodium serinate {Na⁺Gly⁻(aq)} which successfully modeled our observed results. We have then calculated Δ_rC_p,m, Δ_rH_m, Δ_rV_m and pQ_a for the first and second proton dissociations from protonated aqueous serine as functions of T and m.     

Thermodynamics of proton dissociations from aqueous glycine at temperatures from 278.15 to 393.15 K,molalities from 0 to 1.0 mol · kg−1, and at the pressure 0.35 MPa: Apparent molar heat capacities and apparent molar volumes of glycine,glycinium chloride,and sodium glycinate

We have measured the densities of aqueous solutions of glycine, glycine plus equimolal HCl, and glycine plus equimolal NaOH at temperatures 278.15 ⩽ T/K ⩽ 368.15, molalities 0.01 ⩽ m/mol · kg⁻¹ ⩽ 1.0, and at p = 0.35 MPa, using a vibrating tube densimeter. We have also measured the heat capacities of these solutions at 278.15 ⩽ T/K ⩽ 393.15 and at the same m and p using a fixed-cell differential scanning calorimeter. We used the densities to calculate apparent molar volumes V_ϕ and the heat capacities to calculate apparent molar heat capacities C_p,ϕ for these solutions. We used our results and values of V_ϕ(T, m) and C_p,ϕ(T, m) for HCl(aq), NaOH(aq), NaCl(aq) from the literature to calculate parameters for Δ_rC_p,m(T, m) for the first and second proton dissociations from protonated aqueous cationic glycine. We then integrated this value of Δ_rC_p,m(T, m) in an iterative algorithm, using Young’s Rule to account for the effects of speciation and chemical relaxation on the observed V_ϕ and C_p,ϕ of the solutions. This procedure yielded parameters for V_ϕ(T, m) and C_p,ϕ(T, m) for glycinium chloride {H₂Gly⁺Cl⁻(aq)} and sodium glycinate {Na⁺Gly⁻(aq)} which successfully modeled our observed results. We have then calculated values of Δ_rC_p,m, Δ_rH_m, Δ_rV_m, and pQ_a for the first and second proton dissociations from protonated aqueous glycine as functions of T and m.     

Prediction of thermophysical properties of novel ionic liquids based on serine [Cnmim][Ser] (n = 3, 4) using semiempirical methods

Two novel ionic liquids based on serine [C_nmim][Ser] (n = 3, 4) were prepared by the neutralization method and their structures were confirmed by ¹H NMR spectroscopy and differential scanning calorimetry (DSC). The density, surface tension, and refractive index of the two ILs were measured from T = (298.15 to 338.15) K. Since these ILs [C_nmim][Ser] (n = 3, 4) could form strong hydrogen bonds with water, small amount of water in the ILs is difficult to removed by common methods. In order to eliminate the effect of trace of water, the standard addition method (SAM) was applied to these measurements. On the basis of the experimental data, the speed of sound (μ), thermal expansion coefficient (α), molecular volume (V_m), standard entropy (S⁰298), entropy of surface (S_a), energy of surface (E_a), parachor (P), molar polarization (R_m), and polarization coefficient (α_p) were calculated, and the relationship between each of these properties of [C_nmim][Ser] (n = 3, 4) and temperatures was discussed. According to the additivity, the average value of anionic parachor, P_−(ave), was 180.81 for [Ser]⁻. At the same time, the surface tension of these serine ionic liquids could be estimated from their parachor and refractive index. The estimated values of the surface tension and the corresponding experimental data were almost identical.     

Heat capacity and enthalpy of fusion of pyrimethanil laurate (C24H37N3O2)

Low-temperature heat capacities of pyrimethanil laurate (C₂₄H₃₇N₃O₂) were precisely measured with an automated adiabatic calorimeter over the temperature range between T = 78 K and T = 340 K. The sample was observed to melt at (321.52 ± 0.04) K. The molar enthalpy and entropy of fusion as well as the chemical purity of the compound were determined to be (67244 ± 11) J · mol⁻¹, (209.28 ± 0.02) J · mol⁻¹ · K⁻¹, (0.9943 ± 0.0004) mass fraction, respectively. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was (322.264 ± 0.006) K.     

The thermodynamic properties of DyBr3(s) and DyI3(s) from T=5 K to their melting temperatures

Low-temperature calorimetric measurements have been performed on DyBr₃(s) in the temperature range (5.5 to 420 K ) and on DyI₃(s) from T=4 K to T=420 K. The data reveal enhanced heat capacities below T=10 K, consisting of a magnetic and an electronic contribution. From the experimental data on DyBr₃(s) a C⁰_p,m (298.15 K) of (102.2±0.2) J·K⁻¹·mol⁻¹ and a value for {S⁰_m (298.15 K) − S⁰_m (5.5 K)} of (205.5±0.5) J·K⁻¹·mol⁻¹, have been obtained. For DyI₃(s), {S⁰_m (298.15 K) − S⁰_m (4 K)} and C⁰_p,m (298.15 K) have been determined as (226.9±0.5) J·K⁻¹·mol⁻¹ and (103.4±0.2) J·K⁻¹·mol⁻¹, respectively. The values for {S⁰_m (5.5 K) − S⁰_m (0)} for DyBr₃(s) and {S⁰_m (4 K) − S⁰_m (0)} for DyI₃(s) have been calculated, giving S⁰_m (298.15 K)=(212.3±0.9) J·K⁻¹·mol⁻¹ in case of DyBr₃(s) and S⁰_m (298.15 K) =(233.1±0.7) J·K⁻¹·mol⁻¹ for DyI₃(s). The high-temperature enthalpy increment has been measured for DyBr₃(s) in the temperature range (525 to 799 K) and for DyI₃(s) in the temperature range (525 to 627 K). From the results obtained and enthalpies of formation from the literature, thermodynamic functions for DyBr₃(s) and DyI₃(s) have been calculated from T→0 to their melting temperatures at 1151.0 K and 1251.5 K, respectively.     

Heat capacities,third-law entropies and thermodynamic functions of the negative thermal expansion material Zn2GeO4 from T=(0 to 400) K

The molar heat capacity of Zn₂GeO₄, a material which exhibits negative thermal expansion below ambient temperatures, has been measured in the temperature range 0.5⩽(T/K)⩽400. At T=298.15 K, the standard molar heat capacity is (131.86 ± 0.26) J · K⁻¹ · mol⁻¹. Thermodynamic functions have been generated from smoothed fits of the experimental results. The standard molar entropy at T=298.15 K is (145.12 ± 0.29) J · K⁻¹ · mol⁻¹. The existence of low-energy modes is supported by the excess heat capacity in Zn₂GeO₄ compared to the sums of the constituent binary oxides.     

(Solid + solute) phase equilibria in aqueous solution. XIII. Thermodynamic properties of hydrozincite and predominance diagrams for (Zn2 + + H2O + CO2)

The thermodynamic properties ofZn₅(OH)₆(CO₃)₂ , hydrozincite, have been determined by performing solubility and d.s.c. measurements. The solubility constant in aqueous NaClO₄media has been measured at temperatures ranging from 288.15 K to 338.15 K at constant ionic strength (I =  1.00 mol · kg ^− 1). Additionally, the dependence of the solubility constant on the ionic strength has been investigated up to I =  3.00 mol · kg ^− 1NaClO₄at T =  298.15 K. The standard molar heat capacity C_{p, m}^ofunction fromT =  318.15 K to T =  418.15 K, as well as the heat of decomposition of hydrozincite, have been obtained from d.s.c. measurements. All experimental results have been simultaneously evaluated by means of the optimization routine of ChemSage yielding an internally consistent set of thermodynamic data (T =  298.15 K): solubility constant log ^* K_{ps 0}⁰ =  (9.0  ±  0.1), standard molar Gibbs energy of formationΔ_fG_m^o {Zn₅(OH)₆(CO₃)₂ }  =  ( − 3164.6  ±  3.0)kJ · mol ^− 1, standard molar enthalpy of formation Δ_fH_m^o{Zn₅(OH)₆(CO₃)₂ }  =  ( − 3584  ±  15)kJ · mol ^− 1, standard molar entropy S_m^o{Zn₅(OH)₆(CO₃)₂ }  =  (436  ±  50)J · mol ^− 1· K ^− 1and C_p,m^o / (J · mol ^− 1· K ^− 1)  =  (119  ±  11)  +  (0.834  ±  0.033)T / K. A three-dimensional predominance diagram is introduced which allows a comprehensive thermodynamic interpretation of phase relations in(Zn^2 +  +  H₂O  +  CO₂) . The axes of this phase diagram correspond to the potential quantities: temperature, partial pressure of carbon dioxide and pH of the aqueous solution. Moreover, it is shown how the stoichiometric composition{n(CO₃) / n(Zn)} of the solid compoundsZnCO₃ and Zn₅(OH)₆(CO₃)₂can be checked by thermodynamically analysing the measured solubility data.