Heat Of Dissolution Research Articles

A novel thermal buffer utilizing dissolution heat to cooling electronic devices in isolated environment

A thermal buffer with high cooling capacity can rapidly absorb heat, preventing electronic devices in isolated conditions from overheating and extending their working time. This paper introduced the design of a thermal buffer featuring a meltable partition to utilize dissolution heat and conducted experimental investigations into the endothermic characteristics of CO(NH2)2 dissolving in water under different solute proportions, dissolving temperatures, and heat fluxes. The results demonstrated that natural convection was suppressed by the high viscosity of the CO(NH2)2 solution, preventing the cooling capacity of the thermal buffer from achieving the expected performance. Fortunately, the utilization efficiency of sensible heat was improved by movement and higher dissolving temperatures, significantly enhancing the cooling capacity. It should be noted that the cooling capacity of a thermal buffer filled with NH4NO3/H2O can surpass that of paraffin by >12 times at q = 1 W·cm−2 and tp = 70 °C, attributed to the advantages of the endothermic reaction, including a replaceable dissolving temperature, short dissolving time, and considerable dissolution heat. Moreover, these advantages are significantly amplified with increased heat flux and decreased operating temperatures of electronic devices. These insights deepen our understanding of the endothermic characteristics of solute dissolution in water, providing valuable guidance for designing thermal buffers with superior cooling capacity.

Preparation and pipeline transport of CO2 as a hydrate slurry – Modelling and techno-economic analysis

CO2 transportation as a hydrate slurry is modelled in Aspen Plus, including the slurry preparation and the pipeline transport. Due to the lack of built-in models for the hydrate formation, mass and energy balances were developed and implemented using a User-block function. NRTL-RK global property method was used, given the accuracy in predicting the CO2 solubility in water under incipient hydrate formation conditions and the dissolution heat of CO2 in water. The conventional process of transporting CO2 in a supercritical state was also modelled to benchmark the hydrate-based technology. The hydrate-based process is safer than the conventional process as it requires lower operating pressures, but the estimated costs are higher due to the need for refrigeration and larger pipeline diameters for transportation. The addition of thermodynamic promoters, that moderate the hydrate formation conditions, the integration of cold streams with other processes, and valuing the water transported with CO2, will enhance the economic attractiveness of the hydrate-based process.

Effects of Laves phase precipitation embrittlement and its dissolution kinetics in super-ferritic stainless steels on the ductile-brittle transition

This study simulated the Laves phase precipitation embrittlement of super-ferritic stainless steels (SFSSs). The dissolution kinetics of the Laves phase, grain coarsening, and their effects on the mechanical properties and ductile-brittle transition during dissolution heat treatment were subsequently studied. The Laves phase dissolution adhered to the Johnson-Mehl-Avram-Kolmogorov variation expression, exhibiting an activation energy of approximately 368 kJ mol−1. High-temperature reheating (1100 °C) resulted in severe grain coarsening, leading to brittle fracture. A dissolution treatment of only 0.5 h at 1050 °C resulted in a high yield strength of 407.8 MPa, large elongation of 29.6%, and impact toughness of 237.2 J/cm2 because the entirety of the Laves phase was dissolved and no obvious grain growth was observed. This indicates that dissolution heat treatment is a simple and feasible method for recovering the ductility and toughness of Laves phase precipitation-embrittled SFSSs.

Influence of liquid-to-solid ratios on properties and microstructure of coal gasification slag-based one-part geopolymer

Limited studies have been conducted on the synthesis of one-part geopolymer involving coal gasification slag by alkali fusion and component additive method (AFCAM). The ratio of liquid-to-solid (L/S) is the key aspect that has a major impact on the one-part geopolymer's compressive strength (UCS). Our research aims to determine how different L/S ratios affect the microstructure and characteristics of one-part geopolymers. MIP analysis and hydration heat test were conducted to analyze the influence caused by different L/S ratios. The results showed that as the L/S ratio increased, the UCS of geopolymers decreased, and the setting time of fresh slurry increased steadily. Additionally, geopolymer with 0.25 as an L/S ratio (G-L/S-0.25) achieved a higher UCS at 48.31 MPa, whereas the total setting time was more than 23 h. The low L/S ratio produced more gel pores and less total porosity in the geopolymer matrix, which improved the UCS. Moreover, lower porosity suggested that the geopolymer sample had higher compactness and a better internal structure. It is found that the dissolution of the fusion product released heat in the first hour, and no coal gasification slag dissolution heat was detected after one hour. This suggested coal gasification slag showed low reactivity as the additive and was embedded in the geopolymer matrix after 28-day curing. The tested results showed that G-L/S-0.25 had a greater reaction degree. This study illustrated the effects of the L/S ratio on one-part geopolymer and provided a new thought to enhance the UCS of coal gasification slag-based geopolymer.

Rheological and early hydration of cementitious material containing recycled concrete powders collected from recycled aggregates

Recycled aggregate (RA) is the primary approach to treatment and utilization of construction and demolition waste in China. During RA preparation, many finer powders with sizes smaller than 0.15 mm are produced compared with those of the natural aggregate preparation, which further reduces the RA quality. Direct separation and individual use are expected to improve the performance of RAs and develop their potential applications in fine powders. Recycled concrete powders with sizes smaller than 0.15 mm (recycled coarse powder, RCP), 0.075 mm (recycled medium powder, RMP) and 0.045 mm (recycled fine powder, RFP) were collected. The rheological and early hydration of cementitious materials containing different volumes of RCP, RMP, and RFP were investigated. The incorporation of RCP decreased the yield stress and plastic viscosity of the cement paste and improved the workability of the slurry, whereas the incorporation of RMP and RFP increased the yield stress and reduced the fluidity of the cement paste compared to that of the pure cement sample. The time-dependent properties of the rheological parameters indicated that the cement paste containing RCP exhibited shear-thinning properties, whereas those incorporating RMP and RFP displayed shear-thickening characteristics. The addition of RMP and RFP increased the initial heat of dissolution of the cement paste and caused the cumulative heat release in 24 h to exceed that of pure cement paste. The effect of RFP on the hydration products and microstructure of the cement paste resulted in mechanical properties comparable to those of mortar without recycled concrete powder.

Effect of Storage Time on Wax–Wax–Hydrolyzate Canola Oil Oleogels

AbstractIn this study, two natural waxes, beeswax (BW) and sunflower wax (SFW), are combined with their hydrolyzed variants to deliberately alter the waxes’ composition. The properties of the produced oleogels with different wax inclusion levels (4%, 8%, 12%, and 16% w/w) are investigated after defined intervals (2 days, 7 days, 3 weeks, and 3 months). To do so, the gels are monitored via penetrometry, microscopy, and calorimetry. Although the gels do not show any significant difference during storage in the micrographs, the calorimetric and firmness data reveal meaningful results. The heat of dissolution increases in every system investigated, indicating post‐crystallization processes. Due to different solubilities of wax components, the critical gelling concentration is determined and the solid wax content is retrieved to further address the structure efficiency (S.E.). It is demonstrated that although the quantity of solids over time increases, the scaffolding effectiveness decreases in most cases. Only SFW, most likely due to sintering, shows an increase in S.E. over the storage time. Identified synergistic effects in BW and hydrolyzate mixtures decrease with increasing storage time. This work aims to contribute to a better understanding of the behavior of wax‐based oleogels upon storage.Practical Applications: Although much is known about the gel properties of wax‐based oleogels at short‐term, the behavior over the storage period remains largely unresolved. However, this behavior is immensely important for a real application in fast and slow moving consumer goods. After all, products should always have the same consumer‐relevant properties when stored at variable time frames. This applies to both food and pharmaceutical products. Knowledge of the behavior of wax‐based oleogels in terms of a time‐dependent change can help to choose a targeted product design and ensure product quality and consumer satisfaction.

Superimposed hydration exothermic model of cement slurry considering different reaction rates of various active substances

Cement components usually contain two or more hydration active substances with different hydration reaction rates, and the existing hydration exothermic model of cement-based materials do not consider the difference of reaction rates of active substances. This paper proposes a new exothermic hydration model of cement-based materials, which takes into consideration the different reaction rates of multi-component active substances. Firstly, the hydration heat and the representative temperatures of cement slurry with the water-cement ratio of 0.3, are tested through adiabatic and dissolution heat methods. Secondly, the total hydration reaction process is assumed as the composition of the reaction processes of multi-component active substances. Then, a hydration exothermic model witch is superimposed by several exponential functions is fit according to the exothermic hydration experimental data and the Arrhenius chemical expression. The comparison results show that the proposed model is more accurate than the monomial exponential function model, especiallyat the early age before the initial setting time. In conclusion, the proposed model can better explain the influence of the reaction rate difference of different active substances of cement on the exothermic process, and the accuracy of hydration analysis is more accurate by using it than others.

Peculiar points of aqueous solutions of mono-hydrogen alcohols

The work is devoted to the detailed study of the peculiar points in aqueous solutions of mono-hydrogen alcohols. The main attention is focused on water-methanol and water–ethanol solutions for which there are numerous experimental data. It is taken into account that H-bond interaction between alcohol and water molecules stimulates the formation of hydration complexes or elementary clusters, stable for temperatures: T<42°C. A solution at the peculiar point has a cell-like structure, where every cell consists of one alcohol molecule surrounded by water molecules forming mono-molecular layer. The volume and dissolution heat per cluster are determined. It is shown that the peculiar point arises at the concentration leading to the full filling of a solution by elementary clusters. The instability of elementary clusters near the peculiar point is considered. The possible existence of peculiar point of another type is discussed.

Classroom experiments with artificial sweeteners: growing single crystals and simple calorimetry.

An easily accessible experimental set-up to grow large single crystals of two sweeteners readily available in supermarkets, erythritol and xylitol, is described. The crystallization of these compounds illustrates the principles of crystallization by evaporation. As these artificial sweeteners are also known to induce a cool sensation in the mouth, the crystal-growing experiment is complemented with a simple calorimetric set-up to demonstrate the endothermic nature of the dissolution of the selected sweeteners in a more qu-anti-tative approach by measuring the heat of dissolution (ΔH diss). The choice of these two sweeteners also allows use of the freely available WebCSD and Mercury tools to visualize their three-dimensional structure, crystal packing and powder diffractograms, and to deepen stereochemical concepts such as stereoisomers and meso compounds.

The dissolution behavior of σ-phase and the plasticity recovery of precipitation-embrittlement super-ferritic stainless steel

In this study, a dissolution heat treatment was applied planning to recover the plasticity of an embrittled super-ferritic stainless steel caused by the precipitation of σ-phase, χ-phase and Laves phase. The dissolution behaviors of the brittle precipitation phase, and the concerned grain coarsening phenomena, as well as their effects on the mechanical properties were investigated. It was observed that the χ-phase dissolved first then did the σ-phase and therefore the Laves phase. The σ-phase dissolution kinetics showed a strong dependence on the reheating temperature. A weak grain growth phenomenon was found during the reheating process at 1100 °C. The Laves phase re-formation was observed during reheating at 1000 °C–1050 °C, which was generated by the Nb and Mo atoms diffusion. The plasticity of the tested steels was recovered after dissolution treatment at the temperature range of 1050 °C–1100 °C, during which the fracture mode was remodeled from brittle fracture to toughness fracture. The dissolution treatment at the temperature of >1050 °C was effective to recover the plasticity of precipitation- embrittlement SFSSs.

Safety Criteria for Solid-Liquid Heterogeneous Systems in Semibatch Reactors.

An exothermic reaction in a semibatch reactor can potentially cause thermal runaway due to evolved energy accumulation or a secondary reaction. This research aims to propose safety criteria for solid–liquid reactions in semibatch reactors. Simulation modeling was carried out to build thermal runaway criteria for solid–liquid reactions in semibatch reactors. A new model for the energy and mass balance of solid–liquid reactions was successfully established. Criteria for the safety boundary diagram and the temperature diagram were ameliorated for solid–liquid reactions. The results showed that the dissolution heat has a great influence on the thermal behavior of the reaction. Experiments to neutralize citric acid and sodium hydroxide were carried out to determine the critical parameters for the neutralization reaction using the temperature diagram criterion. The proposed criteria would be reasonably expected to provide some guidance for chemical process optimization and safety design for engineering.

Influence of organic and inorganic precipitators on the efficiency of surfactants extraction from wastewater by flotation

The chemical structure of surfactants causes their accumulation on the surface of water sources and leads to the formation of stable foam, which prevents the access of oxygen to the water and leads to the death of hydrobionts and deterioration in water quality. Therefore, the extraction of surfactants from wastewater is an urgent task. Increase the efficiency of flotation extraction of cationic surfactants, namely hexadecyl pyridinium chloride [C 16 H 33 NC 5 H 5]Cl (CHDP) and surfactants based on it - cetazol, by introducing organic – (sodium alkyl sulfate (SAS), CnH 2n+1 OSO 3 Na, n=10-16), and inorganic - potassium hexacyanoferrate (II, III) precipitators. The solubility of the products of interaction of cationic surfactants with SAS (sublates) was determined, which are extracted from solutions at different temperatures and impurities of electrolytes. The Gibbs free energy (), enthalpy (), and entropy (), which take place in the process of dissolution, are calculated. The low value of the heat of dissolution (2.1-16.6 kJ/mol) indicates a small effect of temperature on the solubility of sublates. The thermodynamic analysis of the process of formation of sublates allows determining the optimal length of the hydrocarbon radical of the precipitator. It is established that the extraction of the studied cationic surfactants should be extracted from water solutions and wastewater by the method of precipitation flotation using organic and inorganic precipitators. The presence of electrolytes and an increase in temperature leads to an increase in the degree of extraction hexadecyl pyridinium alkyl sulphonates sublates.

СПРАВОЧНОЕ ОБЕСПЕЧЕНИЕ РАСЧЁТА ТЕПЛОВЫХ ЭФФЕКТОВ РЕАКЦИЙ

By calculation under standard conditions, the sign of the enthalpy of formation of a dimethylammonium ion in an aqueous solution at infinite dilution was specified, the heats of formation of methylammonium nitrate in water, the heats of dissolution of alkyl-substituted ammonium nitrates with the formation of an extremely dilute aqueous solution were calculated

Acetic Acid Modified Steel Slag via Dry Chemical Modification Method for Enhancing the Hydraulic Reactivity

To activate the early-age hydraulic reactivity of steel slag powder (SS), a method of using acetic acid (AA)-anhydrous alcohol solution to modify the SS via dry chemical modification technology was proposed. The compressive strength and hydraulic reactivity of SS pastes and SS blended cement pastes were investigated, then the mineral composition, surface morphology and specific surface area of unmodified SS and AA modified SS were characterized. The results show that calcite, portlandite and dicalcium ferrite in SS react with AA to produce calcium acetate and pores in the modified process, thus leading to AA modified SS with the greater specific surface area and rougher surface. Water is easier to absorb onto the surface of modified SS and enters the inner of SS particles along the pores, resulting in higher dissolution heat and reaction heat of active minerals in SS. The result show that, the higher 72 h cumulative hydration heat, the 3 d, 7 d and 90 d compressive strengths of AA modified SS pastes and AA modified SS blended cement pastes are obtained, compared to the unmodified pastes.

STANDARD ENTHALPY OF FORMATION OF LORNOXICAM AND ITS ANION L- IN AQUEOUS SOLUTION

Lornoxicam was chosen as the object of our research. It is a derivative of thienothiazine monocarboxylic acid amide. It plays the role of a nonsteroidal anti-inflammatory drug, a non-narcotic analgesic and an antipyretic. Lornoxicam is practically insoluble in water. The heat of dissolution of crystalline lornoxicam in solutions of potassium hydroxide at 298.15 K was measured by direct calorimetric method. Measurements were carried out on a calorimeter with an isothermal shell and automatic recording of the temperature-time curve, in a reaction vessel with a volume of 60 cm3 and at T = 298.15 ± 0.01 K and P = 100.5 ± 0.7 kPa. The relative measurement error for the heat of dissolution of the standard substance was 0.1-0.3%. The operation of the calorimetric unit was tested according to the generally accepted calorimetric standard – the heat of dissolution of crystalline potassium chloride in water. The calculation of the equilibrium composition of the system, taking into account the processes of stepwise dissociation of lornoxicam and dissociation of water, was carried out according to the KEV program. The value of the standard enthalpy of lornoxicam formation was calculated using an additive group method based on group systematics with a classification of fragments of the Benson classification type, which takes into account the influence of the initial environment for atoms. The standard enthalpy of lornoxicam anion formation in an aqueous solution was determined using data on the heat of dissolution of lornoxicam in alkali solutions with a ratio of equivalents of at least 1:2. The standard enthalpy of lornoxicam formation and its dissociation products in an aqueous solution are calculated. The values of the standard enthalpy of lornoxicam formation and its dissociation products in an aqueous solution were obtained for the first time. They are key quantities in the thermochemistry of this compound, open up the possibility of conducting rigorous thermodynamic calculations in systems with lornoxicam.

Thermodynamic and economic assessment of cyano functionalized anion based ionic liquid for CO2 removal from natural gas integrated with, single mixed refrigerant liquefaction process for clean energy

The study proposes a novel integrated process in which ionic liquid is utilized to control carbon dioxide (CO2) emissions from the natural gas combined with a single mixed refrigerant-based liquefaction process to assist safe transportation over long distances providing a sustainable and cleaner energy. Commercially amines are utilized for CO2 sequestration, but amines entail energy-intensive regeneration with elevated process costs. The present study offers a solvent screening mechanism based on important parameters such as heat of dissolution, viscosity, selectivity, working capacity, vapor pressure, corrosivity, and toxicity. The selected solvents’ performance is computed by sensitivity analysis suggesting imidazolium-based cation 1-hexyl-3-methylimidazolium[Hmim] functionalized with tricyanomethanide(tcm) as anion a potential natural gas sweetening solvent in comparison with commercially used solvent monoethanoloamine(MEA), conventional ILs 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][Pf6] and 1-butyl-3-methylimidazolium methyl sulfate [Bmim][MeSO4]. The obtained sweet gas is liquefied using a single mixed refrigerant-based process providing 0.99 mol fraction of liquefied CH4 with less overall specific compression power requirement of 0.41 kW/kg of natural gas. Moreover, an exergy analysis demonstrates that the [Hmim][tcm] based process has lower total exergy destruction of 7.49 × 103 kW and is found to utilize less overall specific energy consumption 0.49 kWh/kg of NG in contrast to other studied solvents. Furthermore, a detailed economic analysis establishes [Hmim][tcm]-based CO2 integrated with liquefaction technology offers 50.7%, 74.4%, and 85.8% of total annualized cost (TAC) savings compared with the MEA-,[Bmim][Pf6]-, and [Bmim][MeSO4], respectively. Hence, [Hmim][tcm] for CO2 removal and integration with liquefaction process will incur unit cost based on the total annualized cost to be $2.2 × 104/kmol of purified NG.

Solubility and stability of ozone in acetonitrile

The solubility and stability of ozone in acetonitrile (CH3CN) in the temperature range 233–295 K was studied, and optimum conditions were found in order to use this liquid as an ozonation medium. The molar absorption coefficients of ozone in CH3CN are ε259 = 2900 ± 150 mol L–1 cm−1 (Hartley region) and ε588 = 5.1 ± 0.1 mol L–1 cm−1 (Chappuis region). The rate constant of the O3 decomposition at 295 K is 3.3 × 10–5 s−1. The O3 decomposition rate increases with the increasing amount of water in CH3CN. The O3 solubility coefficients and its limiting solubility at 233–295 K were calculated. The heat of O3 dissolution in acetonitrile is 10.2 ± 0.2 kJ mol−1.

Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding.

Silicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp2 hybridized carbon, tetrahedrally coordinated SiO4, and tetrahedrally coordinated silicon with carbon substitution for oxygen, called “mixed bonds.” Here we synthesize two preceramic polymers possessing both phenyl substituents as unique organic groups. In one precursor, the phenyl group is directly bonded to silicon, resulting in a SiOC polymer-derived ceramic (PDC) with mixed bonding. In the other precursor, the phenyl group is bonded to the silicon through Si-O-C bridges, which results in a SiOC PDC without mixed bonding. Radial breathing-like mode bands in the Raman spectra reveal that SiOC PDCs contain carbon nanoscrolls with spiral-like rolled-up geometry and open edges at the ends of their structure. Calorimetric measurements of the heat of dissolution in a molten salt solvent show that the SiOC PDCs with mixed bonding have negative enthalpies of formation with respect to crystalline components (silicon carbide, cristobalite, and graphite) and are more thermodynamically stable than those without. The heats of formation from crystalline SiO2, SiC, and C of SiOC PDCs without mixed bonding are close to zero and depend on the pyrolysis temperature. Solid state MAS NMR confirms the presence or absence of mixed bonding and further shows that, without mixed bonding, terminal hydroxyls are bound to some of the Si-O tetrahedra. This study indicates that mixed bonding, along with additional factors, such as the presence of terminal hydroxyl groups, contributes to the thermodynamic stability of SiOC PDCs.

Solubility data for Nitrous Oxide (N2O) and Carbon dioxide (CO2) in Piperazine (PZ) and a new eNRTL model

A new set of VLE data for low and medium pressures and data for N2O solubility in aqueous piperazine (PZ) solutions are provided as function of temperature and CO2 loading. Together with VLE data from literature, these data were used for parameter fitting in an eNRTL model for the CO2/water/PZ system in a sequential procedure from pure PZ via the binary water/PZ and to the ternary CO2/water/PZ system. New Antoine parameters and new binary interaction parameters are proposed. The NRTL model predicts well the VLE data, the SLE data, the calorimetric data and the activity coefficient of PZ. The two dissociation constants for PZ and PZH+ were refitted from literature data and used in the ternary parameter fitting. The eNRTL model predicts well the ternary data, for PCO2 (AARD = 22.8%), for PT (AARD = 20.9%) and N2O solubility (AARD 4.7 %), The volatility of PZ as function of concentration, temperature and loading is also well predicted at high concentrations of PZ but under-prediction was seen at low concentrations.Good predictions were also obtained for the heat of reaction of the PZ/H2O/CO2 system with the most significant contributions from piperazine protonation up to a loading of 0.4, PZCO2− formation up to loading about 0.6 and zwitterion formation up to loading 1. Dicarbamate and bicarbonate are formed but play minor roles. Above loading 1 mole CO2/ mole PZ, only the heat of CO2 dissolution plays an important role in the total heat of reaction.

Standard Enthalpies of Formation of Picolinic Acid and the Products of Its Dissociation in an Aqueous Solution

The heats of dissolution of crystalline picolinic acid in water and in potassium hydroxide solutions at 298.15 K are measured via direct calorimetry. The standard enthalpies of formation of the acid and its dissociation products in an aqueous solution are calculated.