Oxide Melt Research Articles

The deuteron NMR Hahn echo decay in polyethylene oxide melts

The deuteron transverse relaxation properties of polyethylene oxide melts of four different molecular weights, covering the range from the onset of entanglements to the regime of fully entangled chains, are investigated using Hahn echo decays over an extensive time interval up to ten times the effective transverse spin relaxation time. The results are compared to predictions based on the Rouse and reptation formalisms, taking into account the dynamical heterogeneity of linear polymer chains produced by the end segments. The experimental results can be described qualitatively by a combination of both models, with the contribution of reptation dynamics increasing with growing chain length. The transition is continuous, rather than being characterized by sharp regime boundaries. Up to a molecular weight of 300.000 g/mol, the predicted limit of pure reptation dynamics is not yet reached. Quantitative deviations from the predicted decays as computed by numerical procedures become observable toward the long-time limit of the Hahn echo decays and are being discussed in terms of shortcomings of the available reptation theories.

Heat capacity and thermodynamic properties of PbS: Optimization based on calorimetric and electrochemical data

Heat capacity of PbS (galena) has been measured in the temperature range from 12 to 338 K using adiabatic calorimetry. Results of the measurements are consistent with previous adiabatic calorimetric data measurements but differ notably from those obtained by relaxation calorimetry. Using experimental data on adiabatic heat capacity measurements in the range of 12–338 K (including our data), results of EMF measurements, and literature data on H0(T) – H0(298.15 K) as inputs, we have optimized the thermodynamic properties of lead sulfide (PbS, galena) based on the quasi-harmonic model vibrational spectrum proposed by Kieffer and advanced to consider intrinsic anharmonicity. In this approach, the volume and temperature dependence of vibrational frequencies are considered, and the enthalpy of formation of PbS, ΔfH0(298.15 K), is treated as an optimized model parameter. The thermodynamic properties of PbS are described with a single set of model parameters over the entire range of its stability (0–1374 K) at a pressure of 1 bar. The model can be optimized based on either the reduced (Cp0 and ΔfG0(T)) or full (Cp0, H0(T) – H0(298.15 K), ΔfG0(T)) datasets. The both variants of the optimization predict the similar thermodynamic properties of PbS, in particular, values of the enthalpies of formation differ less than 0.1 kJ mol−1 and are consistent with ΔfH0(298.15 K) obtained experimentally by oxide melt solution calorimetry. The low-temperature adiabatic calorimetry data and high-temperature results of EMF experiments (or other reliable experimental data on ΔfG0(T)) represent a minimal sufficient set of input data providing optimization of thermodynamic properties at ambient pressure by the technique established in present study.

First‐principles calculation of mechanical properties and electronic structures of W 4 Co 4− n X n B 4 (X = V, Mn, Fe, Ni; n = 0,1)

The first-principles calculation is performed to explore the mechanical properties and electronic structures of transition elements X (X = V, Mn, Fe, Ni) doped WCoB (tungsten cobalt boron), which has shown high oxidation resistance and melting point under high pressure. The energy analysis indicates that the high pressure leads to the lower lattice constants and less stable structures. The deviation of cohesive energy and formation enthalpy between doped and undoped structures indicates that W4Co3FeB4 and W4Co3NiB4 have similar stability. The high pressure contributes to the increasing of elastic, shear, and bulk moduli, which indicates the increase of covalence. The increase of Poisson's ratio, B/G ratio, and anisotropy index AU indicates the higher ductility and higher anisotropy under high pressure. Based on bulk modulus and shear modulus, the hardness of W4Co4B4, W4Co3FeB4, and W4Co3NiB4 increases under high pressure, which consists of the variation of electronic structures. The density of states (DOS) and partial DOS analysis indicate that the high pressure leads to lower density around Fermi level and higher hybridization. W4Co4B4, W4Co3FeB4, and W4Co3NiB4 show similar variation of mechanical properties, which is determined by the similar atom properties of Co, Fe, and Ni. Similarly, W4Co3VB4 and W4Co3MnB4 also imply similar variation of mechanical properties and electronic structures.

Development of cordierite-based glass-ceramics by slip casting through selecting the appropriate sintering conditions

The present work aims to prepare a dense cordierite-based glass-ceramic through slip casting and consequent heat treatment procedures. In this regard, sintering conditions were considered as the key variables to improve the properties of the glass-ceramic. For this purpose, glass frit powder was prepared through melting oxide powders (in the system of SiO2-Al2O3-TiO2-K2O-CaO-MgO). The mixed powders were then heat treated at 1450 °C for 1 hour and quenched in water. The glass frit powder was slip cast using the appropriate dispersant. Sintering was carried out by one-step, two-step, and three-step procedures. Specimens were characterized in terms of various analysis techniques including dilatometry, X-ray diffractometry, scanning electron microscopy, and mechanical strength measurement. Among the examined specimens, the sample sintered by a three-step approach was considered the optimized one which attained zero porosity. According to the obtained results, cordierite crystals were observable in this glass-ceramic matrix. A low coefficient of thermal expansion and a low dielectric constant were observed for the optimized glass-ceramic sample. The obtained results confirmed that the homogenous distributions of crystalline phases are responsible for the appropriate and desirable properties of the prepared glass-ceramic.

Solid-liquid equilibria in the Bi-Ca-Co-O system

Thermodynamic properties of the quaternary phases in the Bi-Ca-Co-O system, namely those of oxide melt and the misfit bismuth calcium cobaltite, Bi1.85Ca2Co1.7O7.4−δ, were assessed based on the knowledge of phase diagrams of the respective ternary sub-systems and the heat capacity, variable oxygen content and melting behavior of the misfit phase. The isothermal and isoactivity sections of the phase diagram, projections of the liquidus surface at fixed activity of oxygen and pO2 vs. T diagram for a fixed ratio of metal elements were constructed using FactSage program. The variable oxygen stoichiometry of the misfit phase derived from thermogravimetry was described in terms of simple point defect model obtaining a fair agreement with experiment and extrapolating the oxygen content to different values of pO2 and T even above the peritectic melting.

Viscosity of niobium oxide systems for production of complex ferroalloys

The relevance of the development of modern technological solutions for the processing of niobium ore materials used for the production of complex ferroalloys of domestic deposits is shown. The need to develop new technological processes of processing is caused by the fact that when switching to new types of niobium concentrates, the chemical and phase compositions of the starting materials change, and, consequently, this leads to a change in the composition and properties of the melting products (both metallic and oxide). Using an electrovibration viscometer, the temperature dependences of viscosity were studied and the crystallization temperatures of oxide melts of the Nb2O5 – SiO2 – CaO – TiO2 – Al2O3 system were calculated. The compositions of the studied samples correspond to phosphorless niobium slags, which can be obtained by carbothermic method from rough concentrates. The samples were obtained by fusing oxide materials in a high-temperature laboratory electric furnace. On the basis of the obtained data, graphical dependences of viscosity – temperature are constructed. It was experimentally established that oxide melts containing 15 – 26 % Nb2O5 are more “long” (having a wide crystallization range) and unfavorable according to the characteristic viscosity – temperature dependence. An increase in the concentration of niobium pentoxide to 40 % translates slags into the category of “short” (with a high crystallization rate). It is shown that an increase in the concentration of niobium oxide Nb2O5 from 15 to 40 % leads to a decrease in the crystallization temperature of melts by 200 °C and a decrease in the viscosity of melts from 1.32 to 0.24 Pa·s at 1350 °C. The improvement of the physico-chemical characteristics of oxide melts with an increase in the concentration of niobium pentoxide can favorably affect the technical and economic indicators of ferroalloy production.

THERMODYNAMIC MODELING OF PHASE EQUILIBRIA AT STEEL ALLOYED WITH MANGANESE AND CHROME

In order to analyze the phase equilibria that are realized in the Fe–Mn–Cr–C–O system at the liquid metal existence temperatures, an extensive material on the thermodynamics of the interaction reactions of components dissolved in liquid iron has been generalized and systematized, and a database of mutually consistent data has been created. For the first time, the thermodynamic modeling of liquidus line coordinates has been performed and state diagrams for MnO–Cr2O3 and FeO–MnO–Cr2O3 systems have been plotted. The temperature for MnCr2O4 incongruent melting ( = 1812°С) and the enthalpy and entropy for formation of this compound from the components of the oxide melt of the MnO–Cr2O3 system were calculated ( = 190.77 kJ/mol and ( = 75.62 J/(mol•K), respectively). It is shown that for the FeO–MnO–Cr2O3 system phase diagram, there are extensive areas of equilibrium for the oxide melt with solid oxides solutions FeO, MnO and solid solutions of chromites FeCr2O4, MnCr2O4 with variable composition. The energy parameters of the theory of subregular ionic solutions were determined and used for calculation of the activities of oxide melt components (FeO, Cr2O3, MnO). The data obtained made it possible to refine the boundaries of the liquid metal composition in areas, which is in equilibrium with specific oxide phases. It is shown that at steelmaking temperature (1600°C) and contents of manganese and chromium in liquid iron about 1 wt. %, the formation of spinels’ solid solution inclusions is possible. Increasing the temperature to 1800°C (for example, when metal is blown with oxy-gen) can shift the equilibrium towards the formation of liquid oxide inclusions. The obtained results can be used in modeling of steel alloying with manganese and chromium. The effect of carbon on the nature of the phase equilibria that are realized in the system is taken into account. It is shown that already at a carbon content in the liquid metal at the level of 0.1–0.2 wt. %, there is a wide range of metal compositions that are in equilibrium with the gas phase {CO, CO2}. The obtained results can be used in modeling of the processes of steel alloying with manganese and chromium

In Situ Atomic Force Microscopy Tracking of Nanoparticle Migration in Semicrystalline Polymers.

We present in situ tracking of silica nanoparticle (NP) migration from a poly(ethylene oxide) (PEO) melt into interlamellar region using in situ atomic force microscopy (AFM). Our results confirm the previous hypothesis that NPs migrate into the interlamellar regions at crystallization growth rates smaller than a critical value under isothermal conditions. Under these slow crystallization conditions, bare silica NPs are rejected as defects by the growing crystal of PEO, and the in situ imaging on the large (50 nm) NPs helps track the migration into the amorphous zones. We extend this AFM technique to estimate lamellar growth rates that correlate with spherulite growth rates determined by polarized light optical microscopy (PLOM) but at smaller undercoolings than are typical for PLOM.

A New Methodological Approach on the Characterization of Optimal Charging Rates at the Hydrogen Plasma Smelting Reduction Process Part 2: Results.

To meet the target for anthropogenic greenhouse gas (GHG) reduction, the European steel industry is obliged to reduce its emissions. A possible pathway to reach this requirement is through developments of new technologies for a GHG-free steel production. One of these processes is the hydrogen plasma smelting reduction (HPSR) developed since 1992 at the Chair of Ferrous Metallurgy at the Montanuniversitaet Leoben in Austria. Based on the already available publication of the methodology in this work, potential process parameters were investigated that influence the reduction kinetics during continuous charging to improve the process further. Preliminary tests with different charging rates and plasma gas compositions were carried out to investigate the impacts on the individual steps of the reduction process. In the main experiments, the obtained parameters were used to determine the effect of the pre-reduction degree on the kinetics and the hydrogen conversion. Finally, the preliminary and main trials were statistically evaluated using the program MODDE® 13 Pro to identify the significant influences on reduction time, oxygen removal rate, and hydrogen conversion. High hydrogen utilization degrees could be achieved with high iron ore feeding rates and low hydrogen concentrations in the plasma gas composition. The subsequent low reduction degree and thus a high proportion of oxide melt leads to a high oxygen removal rate in the post-reduction phase and, consequently, short process times. Calculations of the reduction constant showed an average value of 1.13 × 10−5 kg oxygen/m2 s Pa, which is seven times higher than the value given in literature.

Composition-dependent signinversion of the Soret coefficient of SiO2 in binary borosilicate melts.

Using a laser-induced local-heating experiment combined with temperature analysis, we observed the composition-dependent signinversion of the Soret coefficient of SiO2 in binary silicate melts, which was successfully explained by a modified Kempers model used for describing the Soret effect in oxide melts. In particular, the diffusion of SiO2 to the cold side under a temperature gradient, which is an anomaly in silicate melts, was observed in the SiO2-poor compositions. The theoretical model indicates that the thermodynamic mixing properties of oxides, partial molar enthalpy of mixing, and partial molar volume are the dominant factors for determining the migration direction of the SiO2 component under a temperature gradient.

New Insights into the Traditional Charge Compensation Theory: Amphoteric Behavior of TiO2 under the Guidance of Supply-Demand Relationship.

Polymerization degree theory and traditional charge compensation theory are the most fundamental principles to understand the structure and properties of oxide melts. It can well explain the behavior characteristics of acidic oxides and basic oxides in a melt. However, the amphoteric behavior of oxides cannot be explained well by these two theories. Herein, the octahedral connection mode and the behavior of the amphoteric transition of TiO2 are analyzed by molecular dynamics simulation, and then, a calculation model which can quantitatively calculate the amphoteric transition of the oxide is established by analyzing a large number of data. On the basis of the model, a novel theory of supply and demand is put forward, which can explain the amphoteric transition behavior of oxides very well. To a great extent, the supply and demand theory makes up for the deficiency of the atomic structure theory of oxide melts and provides mechanism explanation and model prediction for the oxide amphoteric transformation behavior.

Ablation behaviour of (Hf-Ta-Zr-Nb)C high entropy carbide ceramic at temperatures above 2100 °C

The ablation behaviour of (Hf-Ta-Zr-Nb)C high entropy carbide (HEC4) was studied at temperatures above 2100 °C using a plasma flame gun in air. The microstructures, phase and chemical compositions of the HEC4 samples were investigated after ablation. The mass ablation rate of the HEC4 samples increased with increasing ablation time from 0.21 mg cm−2 s−1 for 60 s to 0.45 mg cm−2 s−1 for 120 s. Compared to the mono- and binary carbides with commonly decreased mass and thickness after ablation, the HEC4 samples with the increased mass and thickness after ablation showed good resistance to mechanical scouring at such high temperatures and an oxidation controlled ablation mechanism. The ablation processes mainly include the oxidation of the carbide, the phase separation of the oxides, the melting of oxides, and the diffusion of oxygen. A composition gradient in the oxide layer was detected due to the different melting temperatures of the different oxides; Nb-Ta rich oxides formed at the front surface melted and became enriched at the edge of the samples, and the Zr-Hf rich oxides were enriched in the centre of the samples. The oxide layer with complex compositions and phase distributions acted as an effective ablation barrier.

ZnO under Pressure: From Nanoparticles to Single Crystals

In the present review, new approaches for the stabilization of metastable phases of zinc oxide and the growth of ZnO single crystals under high pressures and high temperatures are considered. The problems of the stabilization of the cubic modification of ZnO as well as solid solutions on its basis are discussed. A thermodynamic approach to the description of zinc oxide melting at high pressures is described which opens up new possibilities for the growth of both undoped and doped (for example, with elements of group V) single crystals of zinc oxide. The possibilities of using high pressure to vary phase and elemental composition in order to create ZnO-based materials are demonstrated.

Phase and microstructure optimization of grain boundary oxides and its effect on the thermal conductivity of Y2O3-doped AlN ceramics

AlN green bodies with variable O and C contents were employed to fabricate Y2O3-doped AlN ceramics of different grain-boundary phase compositions and microstructures via debinding in air and N2, respectively. The microstructural evolution and grain-boundary oxide migration and their effects on the properties of the ceramics were explained. Finally, modified models were built to predict the thermal conductivity of these AlN ceramics with complex microstructures. During sintering, the oxide melt migrates to the ceramic surface driven by the differences between the surface energy and solid/liquid interface energy of the melt. The phase compositions and distributions of the grain-boundary oxides vary with sintering temperature. In addition, the amorphous layers were detected experimentally. All of these factors have great effects on ceramics properties. AlN ceramics were shown to have a thermal conductivity as high as 221.64 W/(m·K), which agrees with the value predicted via modified models.

Experimental study, thermodynamic calculations and industrial implications of slag/matte/metal equilibria in the Cu–Pb–Fe–O–S–Si system

Present work is a part of the series of the integrated experimental and modelling studies aimed at better prediction of the conditions of matte formation in the pyrometallurgical processing of lead (Pb) during the oxidative smelting and slag reduction conditions. Experiments involved high-temperature equilibration of samples within the Cu–Pb–Fe–O–S–Si system, targeting the formation of slag, matte, metal and tridymite phases. Compositions of phases in quenched samples were determined using electron probe X-ray microanalysis (EPMA). New experimental results were used together with earlier data from literature to develop the combined thermodynamic database. Main phases were described using two separate solutions: slag solution was developed within the framework of Modified Quasichemical Model in Quadruplet Approximation, while matte/metal solution used the Modified Quasichemical Model in Pair Approximation. An example of the processing of primary and secondary complex lead-copper-containing materials in electric furnace at Aurubis, was used to demonstrate the application of the thermodynamic database. Calculations were performed within the Cu–Pb–Fe–O–S–Si–(Al, Ca, Mg, Zn, As) chemical system using FactSage software. The database also works within the environment of ChemApp, ChemSheet and SimuSage software packages.

Electrical conductivity, microstructures, chemical compositions, and systematic multivariable models to evaluate the effect of waste slag smelting (pyrometallurgical) on the compressive strength of concrete.

Concrete is a composite material widely used in construction. Waste slagsmelting(pyrometallurgical) (steel slag (SS)) is a molten liquid melt of silicates and oxides created as a by-product of steel production. It is a complex solution of silicates and oxides. Steel slag recovery conserves natural resources and frees up landfill space. Steel slag has been used in concrete to replace fine and coarse particles (gravel). Three hundred thirty-eight data points were collected, analyzed, and modeled. It was determined which factors influenced the compressive strength of concrete with steel slag replacement in the modeling phase. Water/cement ratio was 0.3-0.872, steel slag content 0-1196kg/m3, fine aggregate content 175.5-1285kg/m3, and coarse aggregate content (natural aggregate) 0-1253.75kg/m3. In addition, 134 data were collected regarding the electrical conductivity of concrete to analyze and model the effect of SS on electrical conductivity. The correlation between compressive strength and electrical conductivity was also observed. This research used a linear regression (LR) model, a nonlinear regression (NLR) model, an artificial neural network (ANN), a full quadratic model (FQ), and an M5P tree model to anticipate the compressive strength of normal strength concrete with steel slag aggregate substitution. For predicting the electrical conductivity, the ANN model was performed. The compressive strength of the steel slag was raised based on data from the literature. Statistical techniques like the dispersion index and Taylor diagram showed that the ANN model with the lowest RMSE predicted compressive strength better than the other models.

Energetics and structure of the B‐type solid solution in the Nd2O3–Y2O3 system

AbstractThe system Nd2O3–Y2O3 contains solid‐solution phases with several different structures. Single‐phase B‐type (Nd1−xYx)2O3 solid solutions in the range of were formed at 1873 K and retained on cooling to ambient temperature. They showed a linear composition dependence of lattice parameters, enabling extrapolation to x = 0 and 1 for comparison with the structures of the stable endmembers. A positive enthalpy of formation from A‐type Nd2O3 and C‐type Y2O3 determined using oxide melt solution calorimetry indicated entropic stabilization of the B‐type phase. A positive interaction parameter for mixing in the B‐type solid solution, Ω 47.46 ± 4.04 kJ/mol, was obtained by fitting the data using a regular solution model. This value is significantly more positive than that obtained by previous phase diagram analysis using the CalPhaD approach. Exsolution into two B‐type phases is predicted to occur below 1427 K, making it unimportant for the equilibrium phase relations that will be dominated by other structures at low temperature.

Molecular Simulations of Oxide and Silicate Melts and Glasses

Research Article| May 01, 2022 Molecular Simulations of Oxide and Silicate Melts and Glasses Sandro Jahn Sandro Jahn Institute of Geology and Mineralogy, University of Cologne, Zülpicher Straße 49b, 50674 Köln, Germany. s.jahn@uni-koeln.de Search for other works by this author on: GSW Google Scholar Author and Article Information Sandro Jahn Institute of Geology and Mineralogy, University of Cologne, Zülpicher Straße 49b, 50674 Köln, Germany. s.jahn@uni-koeln.de Publisher: Mineralogical Society of America First Online: 01 May 2022 Copyright © 2022 by the Mineralogical Society of AmericaMineralogical Society of America Reviews in Mineralogy and Geochemistry (2022) 87 (1): 193–227. https://doi.org/10.2138/rmg.2022.87.05 Article history First Online: 01 May 2022 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Sandro Jahn; Molecular Simulations of Oxide and Silicate Melts and Glasses. Reviews in Mineralogy and Geochemistry 2022;; 87 (1): 193–227. doi: https://doi.org/10.2138/rmg.2022.87.05 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search The last twenty-five years have seen a tremendous increase in computing power. It is therefore not surprising that computer simulations of melts and glasses have become an indispensable tool to study the structure and properties of geological materials in general and of melts and glasses in particular. Although many of the molecular-scale simulation methods had already been developed at the time of volume 32, Structure, Dynamics and Properties of Silicate Melts, of Reviews in Mineralogy (Stebbins et al. 1995), their applications were still quite limited. This is especially true for ab initio or first-principles simulations that are... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Partial molar volumes of metal oxides in silicate melts: Effects of Coulombic interactions

Alkaline, alkaline earth, many 3d and most 4f modifier oxides dissolved in siliceous melts mix <i>non-ideally</i> with SiO₂ to produce <i>linear</i>, density-compositional mixing trends from which partial molar volumes of modifier oxides (<i>V</i>*) are determined. An analysis of these experimental data reveals that the partial molar volumes of alkali, alkaline earths, most 4f and many 3d modifier oxides partial molar volumes are accurately reproduced by: where F_C = (z⁺•z⁻)/d² (Coulomb9s Law) and z indicates charge. The bond length ‘d’ is the sum of the radii of the cation (M⁺, M²⁺, M³⁺ or M⁴⁺) and oxide ion (O²⁻) observed in ionic crystals. The coefficients ‘m’ and ‘b’ are 0.325 and 1.38 Å/atom respectively. Partial molar volumes of network-forming oxides also conform to the above equation where ‘m’ = ∼3.25 and ‘b’ is 1.68 Å/atom. Coulomb9s force of attraction (F_C) is the product of the cationic field strength (z⁺/d²) and the charge on an anion, where ‘d’ is the distance separating the centers of the two charges. In silicate melts containing modifier cations, apical O atoms of Si tetrahedra are negatively charged and are displaced toward the cations due to Coulombic attraction. The resulting collapse around the cations is referred to as ‘electrostriction’. Partial molar volumes (<i>V</i>*) of modifier oxides are thus composed of two terms, the volume of the polyhedron of the modifier cation (V_Poly) and a volume associated with collapse of tetrahedra around the cation (V_Col): V_Col is negative for all modifier oxides and becomes increasingly negative with increased charge on the cation and with increased coordination number (CN). V_Poly is itself composed of two terms, an intrinsic volume (V_Int) and an excluded volume (V_Ex). The intrinsic volume can be calculated using cationic and O²⁻ radii evaluated from ionic crystals. V_Ex reflects the state of packing around cationic polyhedra. It is equal to 6.83 ų/atom for all modifier oxides so that the expression for V_Poly is: A linear relationship exists between V_Poly and V_Col which results in the observed linear density-composition trends from which partial molar volumes are determined. In spite of their linearity, these trends are the result of non-ideal mixing of modifier oxide and SiO₂ components in siliceous melts. Our finding that tetrahedra collapse around modifier cations differs from the traditional perspective where modifier cations were considered to occupy voids within the silicate network but otherwise had limited effect on melt structure. These results demonstrate that modifier cations affect the network substantially by causing surrounding tetrahedra to rotate, twist, tilt and flex during their collapse toward modifier cations.

Thermodynamic characterization of synthetic lead-arsenate apatites with different halogen substitutions

AbstractThermodynamic parameters have been measured for synthetic analogs of the mimetite-group minerals Pb5(AsO4)3X (X = OH, Cl, Br, I) belonging to the apatite supergroup. Phases precipitated from aqueous solutions under ambient conditions with well characterized structures and compositions were studied. For each phase, dissolution enthalpy was experimentally determined by oxide melt drop solution calorimetry in a molten solvent of sodium molybdate (3Na2O·4MoO3) at 976 K. The enthalpy of formation from the elements ΔHf,elo was calculated using thermochemical cycles and was −3030.6 ± 11.5, −3026.6 ± 15.8, −2967.6 ± 25.0, and −2993.1 ± 12.2 kJ/mol for Pb5.00(AsO4)3.00OH0.86(CO3)0.07, Pb5.00(AsO4)3.00Cl0.80(CO3)0.10, Pb5.00(AsO4)3.00Br0.80(CO3)0.10, and Pb5.00(AsO4)3.00I0.45OH0.35(CO3)0.10, respectively. These ΔHf,elo values exhibit typical trends for apatites: they increased (were less negative) with the increasing molar mass and ionic radius of X and decreased with the electronegativity and ionization energy of X. The compilation and comparison of data for Ca-, Pb-, P-, and As-apatites revealed correlations indicating that thermodynamic enthalpic stability is largely influenced by chemical factors (e.g., differences in electronegativities of the elements, ionization energy, or ionic characteristics of the bonds) and to a lesser extent by physical and geometric parameters in the crystal structure related to the mass and size of the X anion. Using the correlations, it was possible to estimate the value of hitherto unknown ΔHf,elo for Pb5(AsO4)3F, −3144.3 ± 66.5 kJ/mol. The observed relationships apply to the entire apatite supergroup and can be used to predict the values of ΔHf,elo for phases that have not been studied experimentally. The new data on environmentally significant phases will contribute to the modeling of mineral-water interactions, particularly for potential use in the remediation of soils and wastes contaminated with Pb and As and in the immobilization of radioactive waste containing I-129.