Thermochemical Calculations Research Articles

Three-Dimensional Predominance Volume Diagrams: The Ni-As-S-O System

The 3D predominance volume diagram (PVD) for the Ni-As-S-O system at 700 K (427 °C) was constructed using independent gases O2, SO2, and As4O6. The system has 15 four-condensed-phase invariant points. Invariant points, fixed by any combination of boundaries and condensed phases totaling four, were determined by a Gibb’s minimization routine that searched from a corner of the PVD along each undetermined line emanating from this and subsequently-identified invariants. The search direction was determined from the cross product of the two independent planes’ normal direction vectors. The 0.25 atm and 1.00 atm isobaric surfaces intersect the Ni3As2O8, NiO, NiSO4, Ni1−xS, NiS2, and Ni11As8 phases. The 1.00 atm surface also intersects the NiAs phase. The PVD results agree with published ternary and quaternary phase diagram Alkemade lines. If the roasting of gersdorffite (NiAsS) parallels the roasting of enargite (Cu3AsS4), gersdorffite is expected to initially react irreversibly with O2 in the roasting gas to form NiS and NiSO4 topochemical layers with arsenic being expelled as As4O6 gas and perhaps As4 gas once a diffusion-controlled topochemical reaction sequence is established. Thermochemical calculations showed that the formation of NiO from NiSO4 and Ni3As2O8, if present, becomes more favorable as the temperature is increased with complete conversion to NiO above 1086 K and 1160 K (813 °C and 887 °C), respectively, at 1.00 atm.

Chemical degradation of magnesia-chromite refractory used in the conversion step of the pyrometallurgical copper-making process: A thermochemical approach

Refractory wear in furnaces is a key cost driver in pyrometallurgical processes, leading to periodical relining that involves maintenance and increased operational costs. One of the main factors in refractory wear is the chemical attack by the molten phases from the bath. This chemical interaction generates new phases in the refractory, producing different properties and causing spallation due to the aggregate effect of the thermal and mechanical shocks during operation.This paper uses thermodynamic databases (Fact Sage® software) to study the interaction between the molten phases and the magnesia-chromite refractory in the conversion step of the copper-making process. Input data were taken from an industrial furnace at Atlantic Copper S.L.U. (Huelva, Spain) and the calculations were conducted at different temperatures and oxygen partial pressures (pO2). These thermochemical calculations allow the chemical degradation of the refractory to be evaluated.The results show the characterization of the new phases (mainly spinel and olivine) formed after the chemical interaction between the molten phases and the refractory. Since the composition and mass distribution of the new phases change, the degree of refractory wear is calculated for each scenario designed.

Thermochemical calculations of the oxidation behavior of Nb2AlC MAX phase in ZrO2–matrix composites

The oxidation behavior of Y-TZP/Nb2AlC composite was explored by thermo-chemical phase equilibrium calculations and experimental oxidation studies at 1200 °C. Growth of a compact surface reaction layer requires migration of oxygen from the surface to the reaction front and a gradient of oxygen content is likely to develop. The results of phase equilibria calculations show that at low oxygen concentration preferential oxidation of Al favors thermal degradation of Nb2AlC which yields Al2O3 and Nb-carbides. With increasing oxygen content various Nb-oxides are formed and finally a mixture of NbAlO4 and Nb2O5 is present after full oxidation of a Nb2AlC particle. Experimental measurements confirmed the formation of a compact oxidation reaction layer at 1200 °C composed mainly of NbAlO4 and a co-doped (Nb,Y)-TZP matrix.

The effect of disintegrated iron-ore pellet dust on deposit formation in a pilot-scale pulverized coal combustion furnace. Part II: Thermochemical equilibrium calculations and viscosity estimations

Fly ash particles from the combustion of solid-fuels together with disintegrated particles arising from iron-ore pellets result in accumulation of deposits on the refractory linings of the grate-kiln induration machine during the iron-ore pelletizing process. The deposits amass in the high-temperature regions of the induration furnace thus disturbing the flow of gas and pellets. Therefore, to tackle the above-mentioned issues, an understanding of deposit formation mechanism is of crucial importance. This study was conducted with the objective of addressing the effect of disintegrated iron-ore pellet dust on deposit formation and the mechanisms behind deposition (slagging) in the grate-kiln process. A comprehensive set of experiments was conducted in a 0.4 MW pilot-scale pulverized-coal- fired furnace where three different scenarios were considered as follows; Case 1 (reference case): Coal was combusted without the presence of pellet dust. Case 2: Natural gas was combusted together with simultaneous addition of pellet dust to the gas stream. Case 3: Coal was combusted together with the addition of pellet dust simulating the situation in the large-scale setup. Fly ash particles and short-term deposits were characterized and deposition was addressed in Part I of this study. In light of the experimental observations (Part I) and the thermochemical equilibrium calculations (Part II), a scheme of ash transformation during the iron-ore pelletizing process was proposed. The dissolution of hematite particles into the Ca-rich-aluminosilicate melt (from the coal-ash constituents) decreased the viscosity and resulted in the formation of stronger (heavily sintered) deposits. Overall, this pilot-scale work forms part of a wider study which aims at deepening the understanding of ash transformation phenomena during the large-scale pelletizing process.

VUV Dissociative Photoionization of Quinoline in the 7–26 eV Photon Energy Range

Abstract The dissociative photoionization of quinoline was studied by photoionization mass spectrometry and ion yield measurements over a synchrotron photon excitation energy range 7–26 eV. The ionic and neutral products were identified with the aid of thermochemical calculations that, in some cases, led to deeper understanding of photodissociation pathways and the determination of upper limits of heats of formation of ionic and neutral dissociation products. A detailed comparison between the 20 eV photon excitation and 70 eV electron impact mass spectra, coupled with estimation of thermochemical appearance energies, leads to assignment of the dissociative ionization cation and neutral products for each detected ion. Reaction schemes for formation of these products are proposed in a number of cases. Ion intensities in the photon and electron impact mass spectra were used to consider extending a rule of charge retention in simple bond cleavage to more complex cases of dissociative ionization.

Benchmark properties of diphenyl oxide as a potential liquid organic hydrogen carrier: Evaluation of thermochemical data with complementary experimental and computational methods

The standard molar enthalpy of vaporisation of diphenyl oxide was derived from the vapour pressure temperature dependences measured by the transpiration method. Thermodynamic data on vaporisation processes available in the literature were collected. They were evaluated and combined with our own experimental results. Additional combustion experiment on the highly pure diphenyl oxide helped to resolve ambiguity in the enthalpy of formation for this compound. We have evaluated and recommended the set of vaporisation and formation enthalpies for the diphenyl oxide at 298.15 K (in kJ·mol−1): ΔlgHmo = (66.7 ± 0.2), ΔfHmo (liq) = −(15.8 ± 1.4), and ΔfHmo (g) = (50.9 ± 1.4), as the reliable benchmark properties for further thermochemical calculations. Gas phase molar enthalpy of formation of diphenyl oxide calculated by the high-level quantum-chemical method G4 was in an excellent agreement with the recommended experimental data. The standard molar Gibbs function of formation and the standard molar entropy of formation of diphenyl oxide were estimated. The hydrogenation/dehydrogenation reaction enthalpy of diphenyl oxide was calculated and compared with the data for other potential liquid organic hydrogen carriers.

Post-mortem study of magnesia-chromite refractory used in Peirce-Smith Converter for copper-making process, supported by thermochemical calculations

A cost driver in copper production is the periodical relining of the furnaces because of wear. This paper presents a post-mortem study carried out in a Peirce-Smith Converter (PSC). Samples taken from different locations after a 250-batch campaign at Atlantic Copper (Spain) were analyzed.New phases are generated as a result of the chemical interaction between the molten phases of the bath and the refractory, creating a reaction layer on the hot face of the refractory. This layer has properties that differ from the refractory, so spallation occurs due to mechanical and thermal shocks during operation.Thermochemical calculations were carried out to support the post-mortem study. An evaluation was made of the chemical interaction between the molten phases and the refractory under different conditions (slag-refractory volume ratio and Fe/SiO2 ratio in slag). The solidus and liquidus of the new phases, the amount and composition of the spinel and olivine formed, and the density increase of the refractory in the reaction layer were also determined.

Kinetics and Products of the Reactions of F2 with Br‐Atom and Br2

ABSTRACTReactions of F2 molecules exhibit unusual features, manifesting in high reactivity of F2 with respect to some closed‐shell molecules and low reactivity toward chemically active species, such as halogen and oxygen atoms. The existing data base on the reactions of F2 being rather sparse, kinetic and mechanistic studies (preferably over a wide temperature range) are needed to better understand the nature of the specific reactivity of fluorine molecule. In the present work, reactions of F2 with Br atoms and Br2 have been studied for the first time in an extended temperature range using a discharge flow reactor combined with an electron impact ionization mass spectrometer. The rate constant of the reaction F2 + Br → F +BrF (1) was determined either from kinetics of the reaction product, BrF, formation or from the kinetics of Br consumption in excess of F2: k1 = (4.66 ± 0.93) × 10−11 exp(−(4584 ± 86)/T) cm3 molecule−1 s−1 at T = 300–940 K. The rate constant of the reaction F2 + Br2 → products (2), k2 = (9.23 ± 2.68) × 10−11 exp(−(8373 ± 194)/T) cm3 molecule−1 s−1, was determined in the temperature range 500–958 K by monitoring both reaction product (FBr) formation and F2 consumption kinetics in excess of Br2. The results of the experimental measurements of the yield of FBr (1.02 ± 0.07 at T = 960 K) combined with thermochemical calculations indicate that F+Br2F forming channel of reaction (2) is probably the dominant one, at least, at highest temperature of the study.

Modeling solid-state detonation based on thermochemical equilibrium calculations

ABSTRACTThe present work describes the application of a recently developed Calculation of Phase Diagrams (CALPHAD) method to perform condensed-phase thermochemical equilibrium calculations of Chapman–Jouguet (CJ) detonation properties for a number of new mixtures speculated to support gasless detonation. Mixtures in question are titanium–silicon (Ti–Si), the common thermite mixture of aluminum–iron oxide (Al–Fe2O3), and zinc–sulfur (Zn–S). The high-pressure products of these reactive mixtures were found to be stable, and thus suitable for gasless CJ detonation calculations. The CJ calculation method was found to be successful for these mixtures, and the results showed CJ detonation properties with high temperatures, but only marginal volume increase. While this is expected for condensed-phase products, the calculations nevertheless show that gasless detonation may be possible under a very narrow range of conditions.

Ash and slag properties for co-gasification of sewage sludge and coal: An experimentally validated modeling approach

Regulatory changes in the EU and Germany, and environmental aspects direct the attention of the agricultural and energy sector towards sewage sludge as a new resource. The present study evaluates the co-gasification of sewage sludge with brown coal in a slagging gasifier. Currently, a lack of experimental data on phosphorous containing ashes and slags under reducing atmospheres limits our understanding of gasification of this fuel. To address this gap, in this study the ash and slag properties of one brown coal and its mixtures with sewage sludge were experimentally investigated under a reducing atmosphere and predicted with FactSage™. An ASPENplus™ simulation of the co-gasification is conducted to evaluate the impact of the changing feedstock characteristics on major process parameters when different mixtures of sewage sludge and brown coal are fed into a Siemens gasifier.The flow temperature of the coal ash can noticeably be reduced if the sewage sludge ash content is increased up to 50 wt%. Thermochemical calculations using FactSage™ are in good agreement with the experimental ash fusion behavior. This paper describes a method to improve the calculation to better fit the experimental values. The elemental liberation of the main ash components are modeled using FactSage™ and experimentally validated. Except for potassium, no significant release into the gas phase was detected in the experiment. This is in contrast to the predicted evaporation of phosphorous. The addition of sewage sludge results in a lower viscosity of the slags of the mixtures in this study. As a result, the studied entrained-flow gasifier can be operated at lower temperatures while staying at an optimal viscosity for slag tapping. On the other hand, it decreases the temperature working range inside a slagging gasifier, where the slag viscosity lies between 2 and 25 Pa s. The resulting implications on the process parameters of entrained flow gasification have been modeled with ASPENplus™. Even low sewage sludge additions to the brown coal allow for lower gasifier temperatures, decreasing the specific oxygen consumption. Moreover, the cold gas efficiency and the H2/CO ratio are increased.

Synergistic Effect of Nitrogen and Refractory Material on TiN Formation and Equiaxed Grain Structure of Ferritic Stainless Steel

The effect of nitrogen content on the formation of an equiaxed solidification structure of Fe-16Cr steel was investigated. Moreover, two different kinds of refractory materials, i.e., alumina and magnesia, were employed to control the type of oxide inclusion. The characteristics of TiN(-oxide) inclusions were quantitatively analyzed in both molten steel and solidified samples. When the melting was carried out in the alumina refractory, the grain size continuously decreased with increasing nitrogen content. However, a minimum grain size was observed at a specific nitrogen content (approx. 150 ppm) when the steel was melted in the magnesia refractory. Most of the single TiN particles had a cuboidal shape and fine irregularly shaped particles were located along the grain boundary due to the microsegregation of Ti at the grain boundary during solidification. The type of TiN-oxide hybrid inclusion was strongly affected by the refractory material where Al2O3-TiN and MgAl2O4-TiN hybrid-type inclusions were obtained in the alumina and magnesia refractory experiments, respectively. The formation of oxide inclusions was well predicted by thermochemical computations and it was commonly found that oxide particles were initially formed, followed by the nucleation and growth of TiN. When the nitrogen content increased, the number density of TiN linearly increased in the alumina refractory experiments. However, the number of TiN exhibits a maximum at about [N] = 150 ppm, at which a minimum grain size was obtained in the magnesia refractory experiments. Therefore, the larger the number density of TiN, the smaller the primary grain size after solidification. The number density of TiN in the steel melted in the magnesia refractory was greater than that in the steel melted in the alumina refractory at given Ti and N contents, which was due to the lower planar lattice disregistry of MgAl2O4-TiN interface rather than that of Al2O3-TiN interface. When ∆TTiN (= difference between the TiN precipitation temperature and the liquidus of the steel) was 20 K to 40 K, the number density of effective TiN was maximized and thus, the grain size was minimized after solidification. Finally, although most of the TiN particles were smaller than 1 μm in the molten steel samples irrespective of the nitrogen content, TiN particles larger than 10 μm were observed in the solidified samples when the nitrogen content was greater than 150 ppm. The growth of TiN particles during melting and solidification was well predicted by the combinatorial simulation of the ‘Ostwald ripening model’ based on the Lifshitz–Slyozov–Wagner theory in conjunction with the ‘Diffusion controlled model’ using Ohnaka’s microsegregation equation.

THERMOCHEMICAL CALCULATIONS USING SERVICEORIENTED ARCHITECTURE IN THE WEB SERVICE FORM

The subject of this article is the service-oriented architecture utilization in the design and implementation of a web service that is intended to perform selected thermochemical calculations for chemical reactions. Computing functions allow the chemical reaction calculations, such as molar heat capacity, enthalpy, entropy and Gibbs free energy. In the next part, there is a description of each function, the method of service calling in the client application and the structure specification of outputs and error states of the service. In addition to computing functions, the web service also has a group of three information functions that characterize the purpose of the web service and its parameters, provide in tabular form a list of all web service functions and a list of all error states of the web service. The final section describes the presentation web service application with a demonstration of the specific calculations, the possibilities of using the service, and a further solution treatment.

A Novel Method for Assessment of the Velocity of Detonation for Primary Explosives

AbstractPrimary explosives are hazardous energetic materials with considerable sensitivities to external stimuli such as impact, friction, flame, heat, electric spark, and shock. A novel correlation has been introduced for prediction of detonation velocities of different hazardous primary explosives. The needed data for the new model are the loading density, the heat of detonation, the sum of the moles of gaseous products per gram of explosive and the average molecular weight of gaseous products. Decomposition products were specified based on the oxygen balance of primary explosives. Cross‐validation of the model and the statistical parameters were used for evaluating the goodness‐of‐fit, goodness‐of‐prediction, accuracy, and precision of the new model. The statistical parameters of the new model, as compared to the outputs of one of the best available thermochemical computer codes, confirm the higher reliability of the new correlation.

Effect of Titanium and Zirconium Hydrides on the Detonation Heat of RDX‐based Explosives – A Comparison to Aluminium

AbstractDetonation heats of RDX‐based non‐ideal explosives containing 15, 30 and 45 % of Al, (Al/ZrH2), TiH2 and ZrH2 were measured with a water calorimeter set. To get more information on the behaviour of the additives in the detonations performed in an argon atmosphere, the solid post‐detonation products extracted from the calorimetric bomb were analysed to determine their elemental and phase compositions. The calorimetric heats were compared with the detonation energies obtained from thermochemical calculations. All the tested explosives produce more energy during detonation in the bomb than RDX itself, but only aluminium positively influences the total energy release. The results of thermal and XRD analyses indicate that post‐detonation products contain mainly carbonaceous materials, metal oxides, unreacted hydrides and/or the metals. Unexpectedly TiH2 is the least reactive additive. At TiH2 content of 45 %, the heat effect is close to that of calculated with an assumption of complete inertness of the additive. Moreover TiH2 and metallic titanium are present in the bomb residues in a significant amount.

Emission of Gas and $$\hbox {Al}_{2}\hbox {O}_{3}$$ Al 2 O 3 Smoke in Gas–Al Particle Deflagration: Experiments and Emission Modeling for Explosive Fireballs

Emission of gas and $$\hbox {Al}_{2}\hbox {O}_{3}$$ smoke within the deflagration of $$\hbox {H}_{2}{-}\hbox {O}_{2}$$ –{ $$\hbox {N}_{2}{-}\hbox {CO}_{2}$$ }–Al particles has been studied in a closed combustion chamber at pressures of up to 18 bar and at gas temperatures of up to 3700 K. Measurements of radiance intensity were taken using a five wavelength pyrometer (0.660 $$\upmu \hbox {m}$$ , 0.850 $$\upmu \hbox {m}$$ , 1.083 $$\upmu \hbox {m}$$ , 1.260 $$\upmu \hbox {m}$$ , 1.481 $$\upmu \hbox {m}$$ ) and a grating spectrometer in the range (4.10 $$\upmu \hbox {m}$$ to 4.30 $$\upmu \hbox {m}$$ ). In order to characterize the aluminum oxide smoke size and temperature, an inversion method has been developed based on the radiation transfer equation and using pyrometer measurements and thermochemical calculations of $$\hbox {Al}_{2}\hbox {O}_{3}$$ smoke volume fractions. Temperatures in combustion gas have been determined using a method based on the assumed blackbody head of the 4.26 $$\upmu \hbox {m}$$ $$\hbox {CO}_{2}$$ emission line and on its spectral shift with pressure and temperature. For validation purpose, this method has been applied to measurements obtained when calibrated alumina particles are injected in a combustion chamber prior to gaseous deflagrations. This mathematical inversion method was developed to investigate explosive fireballs.

Lattice geometry controlled synthesis of Cu – Doped nickel oxide nanoparticles

NiO3+δ and Ni1−xCuxO3+δ (x = 5, 10, 20) were synthesized by solid state precipitation method, using precursors, nickel chloride and copper chloride with potassium hydroxide as an alkalizing agent. The present work reports the synthesis of copper doped nickel oxides. The phase formation, crystallinity index, crystal structure and microstructure with composition analysis were investigated with the help of various characterization techniques. The FTIR spectrum reveals that characteristic metal oxygen bands of the Ni–O stretching at 447cm−1 with crystallinity index 0.39. Phase pure, hexagonal NiO3+δ formation was identified from the XRD data. Nanosized particles with size as small as ~ 6 to 15nm for pure sample and ~ 11 to 50nm for the copper doped sample are observed from field emission scanning electron micrographs. Thermo chemical calculations such as enthalpy of reaction 77.44kJmole−1, Gibbs free energy − 639.23kJmole−1and entropy of the reaction 0.0024kJK−1mole−1 have been calculated. Specific surface area of NiO3+δ and Ni1−xCuxO3+δ (x = 5, 10, 20) is obtained by Sauter formula, i.e. ~ 292m2/g, ~ 656m2/g, ~ 557m2/g, and ~ 517m2/g respectively.

Calculation and Experimental Validation of Pressure and Temperature Effects on COG-Air Fuel Mixtures

COG have been widely used together with blast furnace gas and blast furnace oxygen gas in the steel industry in Moravian-Silesian region of Czech Republic. COG is a flammable and explosive substance. Most explosion characteristics published so far are valid for pure compounds and limited experimental conditions, mostly ambient. There have been no explosion characteristic exists for COG-air mixtures which cover industrial conditions up to 423 K. Experimental tests have been carried out in a 20-L closed explosion chamber adopted for the explosion tests. The element potential approach in the thermochemical equilibrium calculations applied in the Chemkin subroutine has been used for explosion pressure calculations. Different explosion characteristics have been reported in a range from 298 K up to 423 K and from 0.5 bar(a) up to 1.0 bar(a).

High-pressure C-H-O diagrams: Fuel composition, carbon deposition, and open circuit voltage of pressurized SOFCs

Solid oxide fuel cells (SOFCs) can operate by using various fuel species. Pressurized SOFCs with gas/steam turbine(s) may achieve higher power generation efficiency as hybrid or triple-combined power generation systems. In this study, fuel gas composition is systematically investigated by thermochemical equilibrium calculations on the anode side of SOFCs, pressurized up to 30 bar over a wide temperature range, up to 1000 °C. Since conventional hydrogen-containing fuel gas consists mainly of carbon, hydrogen, and oxygen, high-pressure C-H-O equilibrium diagrams are numerically obtained. It is revealed that the carbon deposition region contracts in the hydrogen-rich area and expands in the oxygen-rich area with increasing total pressure. The molar fraction of each gas component, described in such C-H-O diagrams, also depends on the total pressure. The theoretical open circuit voltage (OCV) increases by pressurization. The effect of nitrogen in high-pressure SOFC fuels is also considered, which is important especially for air-blown coal gas. The minimum amount of H2O, O2, and CO2 required to prevent carbon deposition in steam reforming, partial oxidation, and CO2 (dry) reforming, respectively, is also derived up to 30 bar. The high-pressure C-H-O diagrams are also applicable to various high-temperature/high-pressure energy systems such as solid oxide electrolyzer cells (SOECs) and reversible fuel cells.

A comparison of methods for detonation pressure measurement

Detonation pressure is an important parameter describing the process of detonation. The paper compares three methods for determination of detonation pressure on the same explosive charge design. Pressed RDX/wax pellets with a density of $$1.66 \hbox { g cm}^{-3}$$ were used as test samples. The following methods were used: flyer plate method, impedance window method, and detonation electric effect. Photonic Doppler velocimetry was used for particle velocity measurements in the first two cases. The outputs of the three methods are compared to the literature values and to thermochemical calculation predictions.

Importance of the ligand basis set in ab initio thermochemical calculations of transition metal species

The impact of basis set choice has been considered for a series of transition metal (TM) species. The need for higher level correlation consistent basis sets on both the metal and ligand has been investigated, and permutations in the pairings of basis set used for TM’s and basis set used for ligands can lead to effective routes to complete basis set (CBS) limit extrapolations of thermochemical energetics with little change in thermochemical predictions as compared to those resulting from the use of traditional basis set pairings, while enabling computational cost savings. Basis set superposition errors (BSSE) that can arise have also been considered.