Search

Bismuth (III) sulfide has been widely researched in recent years due to its application, but little emphasis has been placed on research regarding its behavior at elevated temperatures. This is of great importance, considering that bismuth, in the form of Bi2S3, is found in copper sulfide concentrates and is considered one of the most harmful components, along with lead, arsenic and antimony. The removal of these substances is one of the basic tasks in the processes of pyrometallurgical extraction of copper, in order to obtain a high purity metal. In order to better understand the behavior of bismuth (III) sulfide during oxidation at elevated temperatures, this paper characterized the synthesized sample of Bi2S3 at room temperature and the oxidation products at 500 °C by X-Ray diffraction (XRD), as well as thermodynamic, thermal and kinetic analysis of the oxidation process of Bi2S3 at elevated temperatures. In order to understand the behavior of Bi2S3 during oxidation and the distribution of oxidation products, phase stability diagrams in the Bi-S-O system were constructed at different temperatures and the values of the Gibbs free energy change at 400 °C and 1000 °C were calculated. Kinetic analysis of Bi2S3 oxidation process was performed by Kissingers method in non-isothermal conditions.

The removal of copper ions from aqueous solutions using bean shells as an adsorbent is presented in this paper. The influence of the solution solution pH on the biosorption capacity was investigated. The biosorption capacity increased with the increase in the solution pH. The pseudo-second order kinetic model showed the best agreement with the analyzed experimental data, indicating that chemisorption could be a possible way of binding the copper ions to the surface of the bean shells. The Langmuir isotherm model best fitted the analyzed isotherm data. The SEM-EDS analysis was performed before and after the biosorption process. The change in the morphology of the sample after the biosorption process was evident, whereby K, Mg, Si, and Ca were possibly exchanged with copper ions. Response Surface Methodology (RSM) based on the Box-Behnken design (BBD) was used to optimize the biosorption process, with the selected factors: the solution pH, initial copper ions concentration, and contact time. The optimum biosorption conditions were determined to be: pH = 3-4, initial copper ions concentration 100 mg dm-3, and contact time 10-30 minutes.

The roasting of sulfide ores and concentrates is one of the most important steps in pyrometallurgical metal production from primary raw materials, due to the necessity of excess sulfur removal, present in the virgin material. Pentlandite is one of the main sources for nickel pyrometallurgical production. The knowledge of its reaction mechanism, products distribution during oxidation and reaction kinetics is important for optimizing the production process. Raw pentlandite-bearing ore from the Levack mine (Ontario, Canada) was subjected to oxidative roasting in the air atmosphere. A chemical analysis of the initial sample was conducted according to EDXRF (Energy-Dispersive X-ray Fluorescence) and AAS (Atomic Adsorption Spectrometry) results. The characterization of the initial sample and oxidation products was conducted by an XRD (X-ray Diffraction) and SEM/EDS (Scanning Electron Microscopy with Energy Dispersive Spectrometry) analysis. Thermodynamic calculations, a phase analysis and construction of Kellogg diagrams for Ni-S-O and Fe-S-O systems at 298 K, 773 K, 923 K and 1073 K were used for proposing the theoretical reaction mechanism. A thermal analysis (TG/DTA—Thermogravimetric and Differential Thermal Analyses) was conducted in temperature range 298–1273 K, under a heating rate of 15° min−1. A kinetic analysis was conducted according to the non-isothermal method of Daniels and Borchardt, under a heating rate of 15° min−1. Calculated activation energies of 113 kJ mol−1, 146 kJ mol−1 and 356 kJ mol−1 for three oxidation stages imply that in every examined stage of the oxidation process, temperature is a dominant factor determining the reaction rate.

Copper has long been known as a metal with outstanding antimicrobial properties. Although ancient healers were not familiar with the mechanisms of its influence on microorganisms, they had empirically established its effectiveness in sterilizing drinking water, disinfecting wounds, treating skin diseases, various infections and other maladies. Recently, there has been renewed interest in investigating copper and its alloys as possible materials that can limit the spread of bacteria and viruses, given that humanity is often facing various local epidemics, and rarely pandemics, as ongoing Corona virus, SARS CoV-2, first detected in March 2020. This paper reviews the recent literature in the research field of antimicrobial properties of metallic copper, its alloys and other copper - based materials, with the aim to promote their future implementation on contact surfaces, primarily in hospitals and institutions with a high frequency of people where the probability of spreading infection is increased.

Sulfide copper concentrate from domestic ore deposit (Bor, Serbia) was subjected to oxidation in the air atmosphere due to a better understanding of reaction mechanism and oxidation of various sulfides present in the copper concentrate at elevated temperatures. Results of the initial sample characterization showed that concentrate is chalcopyrite–enargite-tennantite type, with an increased arsenic content. Characterization of the oxidation products showed the presence of sulfates, oxysulfates, and oxides. Based on predominance area diagrams for Me-S-O systems (Me = Cu, Fe, As) combined with thermal analysis results, the reaction mechanism of the oxidation process was proposed. The reactions which occur in the temperature range 25 – 1000 °C indicate that sulfides are unstable in the oxidative conditions. Sulfides from the initial sample decomposed into binary copper and iron sulfides and volatile arsenic oxides at lower temperatures. Further heating led to oxidation of sulfides into iron oxides and copper sulfates and oxysulfates. At higher temperatures sulfates and oxysulfates decomposed into oxides. Kinetic analysis of the oxidation process was done using Ozawa’s method in the non-isothermal conditions. The values for activation energies showed that the reactions are chemically controlled and the temperature is the most influential parameter on the reaction rates.

Selective arsenic extraction from enargite based complex concentrate from Copper Mine in Bor (Serbia), using sodium hypochlorite as a leaching agent, was investigated in this paper. The aim was to assess the optimal conditions for the most efficient arsenic removal from the investigated concentrate, based on factorial design applied to experimentally obtained data. Five important factors with three factor levels were used as the input variables and experimentally obtained arsenic extraction yield was taken as the output variable. The first and the second final order model equations were obtained. It was found that the leaching temperature had the strongest effect on the arsenic extraction. The strongest positive interaction was between the sodium hypochlorite molar concentration and the stirring speed during extraction. [Projekat Ministarstva nauke Republike Srbije, br. TR 34023]

The paper presents the characterization results of various types of steel component at the end of product life with the unknown chemical composition, mechanical properties and previously implemented thermo–mechanical treatment. This study was done aiming to examine the possibilities for reuse of some end–of–life agricultural and industrial steel products in order to obtain blades for knives in non–industrial conditions with appropriate and acceptable properties. Demanded shapes of the blades were obtained by applying various types of thermo–mechanical treatment. Chemical analysis of the investigated steel components was done using the energy–dispersive spectrometer. The microstructure was analyzed using optical and scanning electron microscopy. Hardness of analyzed steel scrap and obtained blades was measured using Rockwell C scale. The hardness values of the obtained blades (with optional quenching or not) indicate to a good selection of the steel end–of–life products for this purpose.

Electrochemical behavior of an alloy AgCu50, pure copper, and pure silver, respectively, was investigated by measuring the open circuit potentials using anodic potentiodynamic polarization and potentiostatic method in 0.1 moldm-3 NaOH + 0.02 moldm-3 NaCl solution, without and with adding 2-mercaptobenzothiazole in various concentrations (0.00001 - 0.001 moldm-3). Anodic polarization curves for AgCu50 alloy, showed four current peaks. Potentiostatic curves showed that values of the stationary current densities drop down with the increase of 2-mercaptobenzothiazole concentration in the electrolyte. The electrode surface was analyzed by optical microscopy after the potentiostatic oxidation. Micrographs confirmed that 2-mercaptobenzothiazole has got the inhibitory effect by forming the film of CuMBT and AgMBT which protect the electrode surface from corrosion. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. ON.172060]

The 6000 series alloys belong to the group of aluminium alloys that contain magnesium and silicon as their two main alloying elements. In addition to these two alloying elements, the alloys contain manganese and other elements, in accordance to the type of alloy. Alloys from this series belong to the group of aluminium alloys which are susceptible to thermo-mechanical treatment. These alloys exhibit the best mechanical and physical properties when they are artificially aged, with the occurrence of the strengthening β'' phase. The process of ageing includes solution heat treatment, quenching and ageing at predefined temperatures for a specified amount of time. All the aforementioned processes have a direct impact on the physical and mechanical properties of the alloy following the performed thermal treatment. In this paper the influence of the temperature of solution heat treatment on the properties of two aluminium alloys belonging to the 6000 series was examined, EN AW-6060 and EN AW-6082. The samples were examined at five different temperatures varying from 510-590°C. In order to examine the influence of the temperature of solution heat treatment, measurements of the hardness and electrical conductivity of the samples were performed, following adequate thermal treatment. After the testing, analysis of the results showed that with the increase of the temperature of soluble annealing, there occurred an increase in hardness, and a decrease in electrical conductivity in the aged samples, due to a better homogenization which caused a better distribution of metastable phases.

This paper presents the experimental investigation results of the polymetallic copper concentrate oxidation process with the oxygen from the air. Concentrate characterization included chemical analysis, X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), and light microscopy. Chemical analysis and EDXRF results showed that the investigated copper concentrate consisted mainly of copper, iron and sulphur, with small amounts of zinc, lead, arsenic and other minor elements. XRD analysis showed that metals were bonded to sulphur in sulphide minerals: chalcopyrite, pyrite, luzonite, sphalerite and enargite. Those minerals were mutually bonded into aggregates, confirmed by light microscopy. The results of DTA/TG analysis were used for determining the mechanism of the oxidation process. Comparison between experimental data obtained by XRD, DTA/TG and data obtained from the phase stability diagrams, implied that the oxidation process of the investigated concentrate can be divided in two stages: the first stage consisted of sulphide oxidation reactions with the characteristic exothermal effects below 973 K while forming sulphates and oxysulphates, and the second stage, which consisted of sulphates and oxysulphates decomposition reactions and forming copper and iron oxides, with endothermal effects above 973 K. Kinetic studies were carried out in isothermal conditions in the temperature range (573–873) K. Calculations were done according to Sharp’s method of reduced half-time reaction. Calculated values for the activation energies were 82 kJ mol−1 for the initial stage of the oxidation process (up to 723 K), and 42 kJ mol−1 for the stage of the process where desulphurization degree reached 68–86 % for the oxidation temperatures 748 K and higher. Calculated activation energy values indicated that the reaction of oxidation is a chemically controlled reaction.

Nanotechnologies are being spoken of as the driving force behind a new industrial revolution. Nanoscience has matured significantly during the last decade as it has transitioned from bench top science to applied technology. Presently, nanomaterials are used in a wide variety of commercial products such as electronic components, sports equipment, sun creams and biomedical applications. The size of nanoparticles allows them to interact strongly with biological structures, so they present potential human and environmental health risk. Nanometer size presents also a problem for separation, recovery, and reuse of the particulate matter. Therefore, industrial-scale manufacturing and use of nanomaterials could have strong impact on human health and the environment or the problematic of nanomaterials recycling. The catch-all term ''nanotechnology' is not sufficiently precise for risk governance and risk management purposes. The estimation of possible risks depends on a consideration of the life cycle of the material being produced, which involves understanding the processes and materials used in manufacture, the likely interactions between the product and individuals or the environment during its manufacture and useful life, and the methods used in its eventual disposal. From a risk-control point of view it will be necessary to systematically identify those critical issues, which should be looked at in more detail. Brief review of actual trends in nanomaterials environmental risks and recycling is given in this paper.

The results of some lead-free bronzes characterization are presented in this paper. Investigated samples, produced in the Company for production, processing and trade of non-ferrous, rare and noble metals “11. mart” AD Srebrenica (BiH), were examined using optic microscopy, hardness, microhardness and electric conductivity measurements in order to determine their structural, mechanical and electric characteristics.

The results of calorimetric study of the Al–Ga system using Oelsen method are presented in this paper. Following thermodynamic parameters were obtained: activities, activity coefficients, partial and integral molar quantities at temperature of 727 °C, and compared with available literature data. Also, the energetic of mixing in liquid alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit.

The knowledge of the phase diagram of the Al–Ge–Zn ternary system is of importance in the development of high temperature soldering materials. In this study, the phase diagram of the Al–Ge–Zn ternary system was calculated by the calculation of phase diagrams method using binary thermodynamic parameters included in the COST MP0602 thermodynamic database. Chosen alloys with compositions along two vertical sections with molar ratio Al/Ge = 3/1 and 1/3 were measured using DTA (differential thermal analysis). The experimentally determined phase transition temperatures from this work and phase equilibria data from literature were compared with calculation results and good mutual agreement was noticed.

The results of comparative thermodynamic study of GaSb-Sn system are presented in this paper. Calorimetric measurements according to Oelsen's method and EMF measurements with zirconia as solid electrolyte were used for experimental investigation, while Chou's general solution model, Toop, Kohler and Muggianu methods were used for predicting thermodynamic characteristics in this system. Also, phase diagram of this quasibinary system, determined by DTA and optical microscopy, is presented.

The results of calorimetric investigations and thermodynamic calculation of Zn–Al–Ga system are presented in this article. The research was carried out experimentally, using Oelsen calorimetry in temperature interval 800–1,000 K, and by thermodynamic calculation, applying general solution model in temperature interval 800–1,600 K. The enthalpy space diagram, the enthalpy isotherm diagram, as well as the values for zinc activities, partial and integral molar Gibbs excess energies have been determined. Comparison of experimentally obtained results and the results calculated by general solution model was done at the temperatures 800, 900, and 1000 K, which indicated a good mutual agreement.

The results of calorimetric investigations of liquid In–Sn alloys using Oelsen calorimetry are presented in this article. Based on obtained enthalpy space diagram and enthalpy isotherm diagram, thermodynamic parameters for the liquid In–Sn alloys, including mixing and excess integral and partial molar quantities at temperature of 600 K, have been determined and compared with available literature data.

The knowledge about phase diagram of the Bi–Cu–Pb ternary system is of importance in development of copper–lead based bearing materials, soldering and in refining of copper and lead. In this work, the phase diagram of the Bi–Cu–Pb ternary system was calculated by the CALPHAD method using binary thermodynamic parameters included in the COST 531 database. The results include liquidus projection, invariant equilibria and three vertical sections with molar ratio Cu:Pb = 1, Cu:Pb = 1:3 and Bi:Cu = 1. Alloys, with compositions along three predicted vertical sections, were measured using differential scanning calorimetry (DSC). The experimentally determined phase transition temperatures were compared with calculated results and good mutual agreement was noticed.

The results of thermodynamic analysis and characterization of some alloys in Bi-Cu-Sb lead-free solder system are presented in this paper. Thermodynamic analysis was done using general solution model, while optic microscopy, SEM-EDX analysis, hardness and electroconductivity measurements were used in order to determine structural, mechanic and electric characteristics of selected samples in section from bismuth corner with molar ratio Cu:Sb=3:7.

Physico-chemical processes that take place during the refining process in the extractive metallurgy of lead are associated with the ternary Pb-Zn-Ag system, hence it is necessary to study it from both theoretical and practical aspects. Such an investigation is important from the production point of view, because of the phenomena that occur during desilvering of lead which is one of the important stages in the lead refining process. The connection between the process of lead desilvering and the ternary Pb-Zn-Ag system was the reason for numerous investigations, both from a thermodynamic point of view and in terms of testing and determining the phase diagram, bearing in mind the theoretical and practical importance of knowledge about the processes that take place in the investigated system. The paper presents the results of thermodynamic analysis and investigation of phase equilibria of the Pb-Zn-Ag ternary system using the method of thermodynamic predictions and phase diagrams calculations, respectively, and the experimental results of metalography obtained by optical microscopy. The phase diagram of the vertical section Pb-Zn80Ag20 is presented, obtained by CALPHAD calculation methodology, and using PANDAT thermodynamic software, compared to experimental results obtained by DTA analysis. The results show a pronounced break in solubility, which is characteristic for the entire ternary Pb-Zn-Ag system. Also, it can be noticed that the thermodynamic properties follow the behavior of this system, which is expressed through positive deviation of Raoult's law, pointing to the lack of lead affinity compared to the other two components in the system. The optical microscopy results of the investigated system show the following: 1) sample L1 (98 mass% Pb): the structure of the observed section shows a double eutectic point (Pbsol+Zn-Agsol) which lies in the base of the primary crystals of lead (Pbsol); 2) samples L2-L5: the structure consists of a dual eutectic (Pbsol+Zn-Agsol) and primary crystals Zn-Agsol. Also, certain structural in homogeneity can be noticed as a consequence of stratification that occurs in the ternary Pb-Zn-Ag system. However, the metallographic investigation confirm the results obtained by defining the phase diagram and mutually agree relatively well in accordance to existing literature data.

Remains of metallurgical activities have been discovered recently at the locality Felix Romuliana near Zajecar (Eastern Serbia), with a lot of slag occurrences and metal findings. Samples, taken from this locality, have been investigated using different characterization methods - chemical analysis, XRD and SEM-EDX, in order to clarify the Early Byzantine metallurgical activities at Felix Romuliana.

Life-cycle assessment (LCA) presents a relatively new approach, which allows comprehensive environmental consequences analysis of a product system over its entire life. This analysis is increasingly being used in the industry, as a tool for investigation of the influence of the product system on the environment, and serves as a protection and prevention tool in ecological management. This method is used to predict possible influences of a certain material to the environment through different development stages of the material. In LCA, the product systems are evaluated on a functionally equivalent basis, which, in this case, was 1000 cubic centimeters of an alloy. Two of the LCA phases, life-cycle inventory (LCA) and life-cycle impact assessment (LCIA), are needed to calculate the environmental impacts. Methodology of LCIA applied in this analysis aligns every input and output influence into 16 different categories, divided in two subcategories. The life-cycle assessment reaserch review of the leadfree solders Sn-Cu, SAC (Sn-Ag-Cu), BSA (Bi-Sb-Ag) and SABC (Sn-Ag-Bi-Cu) respectively, is given in this paper, from the environmental protection aspect starting from production, through application process and finally, reclamation at the end-of-life, i.e. recycling. There are several opportunities for reducing the overall environmental and human health impacts of solder used in electronics manufacturing based on the results of the LCA, such as: using secondary metals reclaimed through post-industrial recycling; power consumption reducing by replacing older, less efficient reflow assembly equipment, or by optimizing the current equipment to perform at the elevated temperatures required for lead-free soldering, etc. The LCA analysis was done comparatively in relation to widely used Sn-Pb solder material. Additionally, the impact factors of material consumption, energy use, water and air reserves, human health and ecotoxicity have been ALSO considered including the potentials for dissolution and recycling processes.

The separation process of atmospheric air into its components by means of cryogenic low-pressure procedure, which takes place in the Oxygen plant in the Copper Mining and Smelting Complex, yields various products of different quantities and purities. Proper assessment of the energy consumption, hence assignments production cost of individual products may present considerable problem. For that goal, the least invested technical operation was adopted as criteria, and was restrained for all costs of production and distribution of specific energy. Case study was carried out in the Oxygen factory by monitoring producing parameters for the process in the 2007 year. Based on the monitoring of production parameters and their costs for 20 months in the period 2004-2005, correlation equations for power consumption in the total monthly amount and per mass of produced gaseous oxygen were created. The energy and exergy efficiency of the air separation process into the components are expressed as the ratio of input and useful energy and exergy of the process. On the basis of the adopted criteria, the assignments of energy consumption and production costs for cryogenic air separation process into the components are as follows: 82.59% for gaseous oxygen, 14.04% for liquid oxygen, 1.39% for gaseous nitrogen and 1.98% for liquefied nitrogen. The air separation efficiency is achieved in the amount of energy 0.0872-0.1179 and exergy 0.0537-0.1247. Power consumption per mass of the products in 2007 year is 1325.059 kWh/t of liquid oxygen, 828.765 kWh/t of liquid nitrogen, 429.812 kWh/t of gaseous oxygen and 309.424 kWh/t of nitrogen gas. Production costs of the technical gases at the dawn of the factory are: 6730.69 RSD/t of liquid oxygen, 4209.74 RSD/t of liquid nitrogen, 2183.25 RSD/t of gaseous oxygen and 1571.73 RSD/t of gaseous nitrogen.

The results of thermodynamics and characterization of alloys in ternary Ag-In-Sn system is presented in this paper. Thermodynamic properties, in three investigated sections with molar ratio In:Sn=1:1, 1:2 and 1:4, have been calculated at the temperature of 1423 K using different predicting methods (general solution model, Toop, Hillert, Muggianu, Kohler, Redlich-Kister), compared mutually and with literature experimental data. The alloys in investigated sections have been characterized using DTA, XRD, SEM and optic microscopy.

The paper presents DTA/TG results of polymetallic sulphide copper concentrate from the mine 'Veliki Krivelj' (Serbia) at 25-1000 °C. The reaction mechanism at elevated temperatures was proposed. As confirmation to the proposed mechanism, the results of EDXRF and, XRD analysis of the initial sample and the oxidation products at 550 and 950 °C, and the results of SEM/EDS analysis of the initial sample and the oxidation products at 675 ° C were presented. It can be concluded that the oxidation process goes through sulfide oxidation with characteristic exothermic effects, followed by sulfates and oxy- sulfates formation and their. Kinetic analysis of the oxidation process concentrates the test was performed according to the methods of Kissinger and Ozawa in non-isothermal conditions. The results of kinetic studies have shown that the oxidation process in the whole investigated temperature range is located in the kinetic field.

The materials based on gallium-antimonide are widely used in electronic industry in the production of various electronic devices. The results of characterization of selected alloys in the Ga-InSb system obtained by experimental investigation of some thermal, structural, mechanical and electrical properties are presented in this paper. Applied experimental techniques included: differential thermal analysis, light optical microscopy, scanning electron microscopy with EDX, hardness, micro hardness and electrical conductivity measurements.

U radu su prikazani rezultati istraživanja sprovedenog u Osnovnoj skoli "Stanoje Miljkovi�" Brestovac, opstina Bor, u cilju upoznavanja sa navikama dece skolskog uzrasta vezanim za koris�enje Interneta. Iako visestruko koristan u obrazovnom i saznajnom smislu, Internet nosi i opasnosti koris�enja u pogresne svrhe, naroito kod dece skolskog uzrasta. Stoga je cilj istraživanja bio da se prosvetni radnici i drustvena zajednica najpre upoznaju sa na- vikama dece u koris�enju Interneta, kao i pretnjama i zamkama sa kojima se deca mogu suoiti koris�enjem globalne drustvene mreže. Rezultati istraživanja pokazali su da veina uenika koristi Internet, ali ga u najveoj meri koriste za zabavu i aktivnosti na popular- nim drustvenim mrežama. Mali broj uenika izjasnio se da Internet koristi u edukativne svrhe. Rezultati istraživanja ukazuju na neophodnost definisanja strategije za usmeravanje uenika kroz tekui obrazovno-vaspitni proces da vreme provedeno na Internetu vise ko- riste u obrazovno-saznajne svrhe, kao dopunu tekuim nastavnim aktivnostima. Takoe neophodno je sprovesti edukaciju i uenika i roditelja o potencijalnim opasnostima pri koris�enju Interneta, prvenstveno o zloupotrebi dece na drustvenim mrežama. Svako dete, nezavisno od uzrasta, treba da ima bar neka prethodna saznanja o Internet pretnjama i nainima njihovog izbegavanja. Upravo je zadatak prosvetnih radnika da informacije, do kojih se doslo na osnovu sprovedenog istraživanja, transformisu u saznanja kojae preneti uenicima i njihovim roditeljima u cilju zastite dece tokom njihovog boravka na Internetu.

Pyrometallurgical copper production is a big consumer of energy resources of all kinds. A large part of invested energy is used in the metallurgical process. The process products are holders of large energy amount that is lost uncontrolled in the environment, thereby affecting adversely the economic and environmental effects.

The results of comparative thermodynamic analysis and phase diagram prediction of the Ga – Sn – Zn system are presented in this work. The thermodynamic study was done experimentally – using Oelsen calorimetry, for the section Ga – SnZneut, and analytically – according to the general solution model, for the whole system. Main thermodynamic quantities – integral and partial molar Gibbs excess energies, activities and activity coefficients were calculated over a wide temperature range. Additionally, the phase diagram of the section Ga – SnZneut was investigated using differential thermal analysis and predicted using the CALPHAD method. Comparison with available literature data showed reasonable agreement. The liquidus projection of the ternary Ga – Sn – Zn was also calculated.

The results of kinetic investigation of silver sulfide (Ag2S) phase transformations–monoclinic (α) to body-centered-cubic (β) and body-centered-cubic to face-centered-cubic (γ) crystal form – are presented in this paper. Measured data obtained by thermal analysis under non-isothermal conditions were used for kinetic analysis. The activation energy for investigated phase transformation process was determined according to the methods by Kissinger and Ozawa.