Browsing by Author "Sibarani, David"

Now showing 1 - 9 of 9

Critical Evaluation and Calorimetric Study of the Thermodynamic Properties of Na2CrO4, K2CrO4, Na2MoO4, K2MoO4, Na2WO4, and K2WO4
(2023-12-06) Benalia, Sara; Tesfaye, Fiseha; Lindberg, Daniel; Sibarani, David; Hupa, Leena; Chartrand, Patrice; Robelin, Christian
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This paper evaluates crystallographic data and thermodynamic properties for sodium chromate, potassium chromate, sodium molybdate, potassium molybdate (K2MoO4), sodium tungstate, and potassium tungstate collected from the literature. A thorough literature review was carried out to obtain a good understanding of the available data, and a critical evaluation has been performed from room temperature to above the melting temperatures. Also, the solid-solid transition and melting properties of the six pure salts were measured by differential scanning calorimetry, and high-temperature x-ray powder diffraction measurements were performed to determine the crystal structures and space groups associated with the phases of K2MoO4. This work is the first step towards the development of a thermodynamic model for the Na+, K+//Cl−, SO42−, CO32−, CrO42−, Cr2O72−, MoO42−, Mo2O72−, WO42−, W2O72−, O2− system that is relevant for high temperature corrosion in atmospheres containing O-H-S-C-Cl and alkali salts.
Critical evaluation of CuSO4-H2O system up to solubility limit, from eutectic point to 373.15 K
(2022-08-10) Sibarani, David; Sippola, Hannu; Taskinen, Pekka; Lindberg, Daniel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The solubility of copper(II) sulfate in water as a function of temperature and ionic strength is successfully modelled using Pitzer formalism. Four types of experimental data from the literature were implemented for the assessment, namely activity and osmotic coefficients, freezing point depression and solubility of CuSO4 in water. This work proved that four Pitzer parameters with eight terms are sufficient to create a consistent thermodynamic model of the CuSO4-H2O system up to 5 mol/kg-H2O of CuSO4, from the eutectic point to 373.15 K. The whole optimization study included a critical deviation analysis to sort out less reliable experimental data. To verify the results of this work, comparisons were carried out with experimental data which were not included in the assessment, i.e. the vapour pressure of the saturated solution, thermodynamic values of the cell reaction as well as electrochemical cell potential (EMF).
Experimental determination of freezing point depressions in the CuSO4-H2SO4-H2O system
(2024-04-05) Sibarani, David; Vielma, Tuomas; Sippola, Hannu; Lindberg, Daniel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Limited experimental data of the aqueous ternary CuSO4-H2SO4-H2O system hinders the modelling of its thermodynamic properties. Although different mixing rules for predicting the behavior of mixed electrolyte solutions have been proposed in the literature, significant deviations from them can be expected for systems where e.g., changes in speciation occur. In this work, freezing points of the ternary aqueous solutions were measured using a purpose-built apparatus. The measured samples spanned the concentration range 0.0140 to 0.5534 mol·(kg-H2O)–1 at four different CuSO4–to–H2SO4 ratios. The experimental results were compared with Zdanovskii's rule predictions.
Impact of recently discovered sodium calcium silicate solutions on the phase diagrams of relevance for glass-ceramics in the Na2O-CaO-SiO2 system
(2022-05) Santoso, Imam; Riihimäki, Markus; Sibarani, David; Taskinen, Pekka; Hupa, Leena; Paek, Min Kyu; Lindberg, Daniel
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Although phase relations in the Na2O-CaO-SiO2 system are vital to melting and thermal treatments in glass and glass-ceramics industries, the available data for thermodynamic modeling are mostly based on reports published in 1920s and 1950s. The present investigation verifies the formation of solid solutions of Na2CaSiO4 and Na2Ca2Si2O7 which have previously assumed to be stoichiometric compounds. The impact of these solid solutions on the features of the phase diagram were investigated using the equilibration-quenching-EDS/EPMA technique. The data were reported as liquidus projections and in isothermal sections within the temperature range of 1000 and 1400 °C. Ten primary phase fields were identified, namely SiO2, Na2Ca3Si6O16, combeite, Na4CaSi3O9ss, CaSiO3, Na2CaSiO4ss, Na2Ca2Si2O7ss, Na2Ca6Si4O15, Ca3Si2O7 and Ca2SiO4. In addition, some novel liquidus data and invariants points were examined in more detail. The fundamental data obtained can be employed for the thermodynamic reassessment of the Na2O-CaO-SiO2 system. The present study also discusses the findings and their impact on melting and annealing processes during the manufacture of glass and glass-ceramics.
Oxidation Behavior of AlxHfNbTiVY0.05 Refractory High-Entropy Alloys at 700–900 °C
(2024-08) Muhammad, Fadhli; Sukhomlinov, Dmitry; Klemettinen, Lassi; Sibarani, David; Basuki, Eddy Agus; Lindberg, Daniel; Taskinen, Pekka; Korda, Akhmad Ardian; Zulhan, Zulfiadi; Prajitno, Djoko Hadi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Refractory high-entropy alloys (RHEA) are considered as potential candidates for new-generation energy-related high-temperature applications. However, the poor high-temperature oxidation resistance of RHEAs, resulting in phenomena such as significant weight gain, scale spallation, pesting, and even complete oxidation, limits their applications. In this study, the oxidation behavior of AlxHfNbTiVY0.05 (x = 0.75; 1; 1.25) high-entropy alloys was investigated at 700–900 °C. The isothermal oxidation tests showed that the oxidation resistance of AlxHfNbTiVY0.05 RHEA is strongly influenced by temperature and time. In addition, accelerated oxidation, known as pesting, was observed to occur at 700 °C for all alloys; while, partial spallation was observed at 800 °C for the Al1 and Al1.25 alloys. Detailed analyses of oxidation kinetics have been carried out for the oxidation test series at 900 °C. The mechanism behind disintegration was investigated and attributed to accelerated internal oxidation followed by the formation of voluminous Nb2O5, TiNb2O7, and fast-growing AlNbO4, and is also thought to be related to the partial evaporation of V2O5.
Phase equilibria of the Na2O-TiO2-SiO2 system between 900 and 1600°C in air
(2024-09) Santoso, Imam; Sibarani, David; Hidayat, Taufiq; Zulhan, Zulfiadi; Sukhomlinov, Dmitry; Chen, Min; Klemettinen, Lassi; Taskinen, Pekka; Lindberg, Daniel; Jokilaakso, Ari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The Na2O-SiO2-TiO2 system is important for the glass, ceramic, and metallurgical industries. Its features provide information on the composition and melting temperature to be utilized during the production of glass and ceramic and during the processing of TiO2-bearing material in the metallurgical industry. The liquidus temperatures between 900 and 1600°C in the ternary system at saturation of solid SiO2, TiO2, Na2Ti6O13, Na2SiTiO5, and Na2Ti3O7 were measured using the equilibration-quenching energy-dispersive X-ray spectroscopy/Electron Probe Microanalyzer technique. A wide range of liquidus compositions were obtained with Na2O between 0 and 41.7 mol% in the SiO2- and TiO2-rich regions. The present study provides liquidus data at 1500 and 1600°C for the first time. Liquidus temperatures at various double saturations were also obtained in the present investigation to determine univariant lines in the phase diagram. The present experimental data were compared with previous investigations and computed phase diagrams. The data obtained in the present investigation can be employed to optimize the thermodynamic properties and phase diagrams of the Na2O-SiO2-TiO2 system.
Solubility of nickel sulfate in water and sulfuric acid solutions
(2022-05-24) Oinonen, Jesse
Kemiantekniikan korkeakoulu | Bachelor's thesis
Thermal conductivity of copper smelting mattes and slags
(2019-07-31) Sibarani, David
Kemian tekniikan korkeakoulu | Master's thesis
Current cooling system in copper flash smelting furnace has been developed to have a capability of predicting condition of refractory inside an operating furnace. This system requires thermal conductivity of copper matte and fayalite slag, which have never been analyzed in any research. Since flash smelting furnaces process raw material from solid to liquid, the aim of thesis is to measure thermal conductivity of copper mattes and fayalite slag at low to high temperature. The analysis must be able to explain causes of the measured values, their behavior at elevated temperatures, and their connections to characteristics of the samples. Characterization of samples, e.g. using SEM-EDS and XRD, was done prior to thermal conductivity measurement. The method of thermal conductivity measurement, laser flash analysis, was predetermined from the start of thesis. Five matte samples and three slag samples were prepared. Among the five matte samples, two were doped with arsenic to observe its effect to thermal conductivity of copper matte. The measurement temperature points were 300 °C, 600 °C, and 900 °C, which resemble raw material’s temperature inside flash smelting furnace. To observe thermal conductivity of molten slag, one slag sample was measured as well at 1000 to 1200 °C. Thermal conductivity analysis is executed by NETZSCH company, using NETZSCH 467 HT HyperFlash®. The thermal conductivity measurement results for copper matte were 1.2 to 1.5 W m-1 K-1 at 300 °C and around 2.1 W m-1 K-1 at 900 °C. Meanwhile, arsenic containing matte samples had lowered thermal conductivity, between 0.5 and 1.3 W m-1 K-1 at 300 to 900 °C. The observation of experimental data concluded that thermal conductivity of copper mattes increases linearly with temperature. Its dependence on temperature was weak since the margin was barely 1 W m-1 K-1. Low values of thermal conductivity were within expectation as copper sulfide has low thermal conductivity based on prior research. Positive relation between thermal conductivity and temperature, however, was outside expectation because it indicated non-conductor material. Thermal conductivity of observed slags are between 1.6 and 1.9 W m-1 K-1. These values were close to prior research in silicate slag. The three slag samples had more than 30 wt-% SiO2 content and they behaved as glassy slag. Glassy structure of slag samples probably because the basic oxides were only Al2O3 and a minor amount of FeO, meanwhile the iron content in all slag samples were not enough for complete fayalite formation. Experimental data of the three slag samples were not conclusive as well because one slag sample had thermal conductivity which was lower than expected. In addition, experimental data of molten slag did not match the references. Its thermal conductivity increased with temperature, although it was supposed to decrease.
Thermal Conductivity of Solidified Industrial Copper Matte and Fayalite Slag
(2020-05) Sibarani, David; Hamuyuni, Joseph; Luomala, Matti; Lindgren, Mari; Jokilaakso, Ari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The thermal conductivity of various copper matte and fayalite slag was measured using laser flash analysis, a non-steady state measurement method. Industrial matte and slag samples were taken in such a way that their composition represented typical process conditions. Thermal conductivities for solid copper matte (average 64% Cu) were found to be from 1.2 W m−1 K−1 at 300°C to 2.1 W m−1 K−1 at 900°C. Because arsenic is one of the most important impurities in copper matte, its effect on thermal conductivity was investigated with As-doped matte samples up to 0.59% As. The results showed substantially lower thermal conductivity, between 0.5 W m−1 K−1 and 1.3 W m−1 K−1 at 300–900°C with low As matte, behavior that is analogous to that of a semiconductor. The data obtained showed that the thermal conductivity of copper matte increased linearly with temperature, but the gradient was small. The thermal conductivity of slags was found to be between 1.6 W m−1 K−1 and 1.9 W m−1 K−1, values that are consistent with earlier studies.