Computer-aided Thermal Analysis Research Articles

The influence of Gd content on the solidification and microstructure of AlSi7Mg0.3 casting alloy

The effects of Gd content on the solidification path and microstructure of an AlSi7Mg0.3 alloy have been studied. Two different Gd levels, 0.1 and 0.5 mass%, respectively, have been investigated while the material has been solidified at low (0.2 °C s−1) and high (1.3 °C s−1) cooling rates. Computer-aided thermal analysis and metallographic techniques have been used to study the solidification and microstructural evolution of the alloy at different Gd contents and cooling rates. The results show how Gd has no effect on the grain refinement at both cooling rates. The eutectic structure is unaffected at Gd level of 0.1 mass%. A concentration of 0.5 mass% Gd promotes the precipitation of the gadolinium phosphide (GdP) phase instead of aluminium phosphide (AlP) compounds, thus suppressing the eutectic plateau during the solidification and serving as nucleant for the GdAl2Si2 phase. The eutectic Si crystals solidified at low cooling rate are refined at 0.5 mass% Gd content, while the morphology of Si crystals is only partially modified at high cooling rate.

Computer Aided Thermal Analysis of the FSW Tool Geometry

The thermal analysis will be realised in a Computer Aided Parametric Design program for three tools with different pin geometries to determine the transfer and distribution of the thermal energy produced during the process and to observe the influence of the pin geometry has on the distribution. Due to the fact that the joining process can be done at a lower temperature than the melting point of the material certain steps must be followed prior and correct selection of the machine’s parameters. Information on the parameters for specific materials and the preparation of the base material are readily available but considering the method of producing the thermal energy necessary for the process the quality of the weld is highly influenced by preheat time (of the material and tool), room temperature, cooling of the tool or work piece if the machine is equipped with such a configuration. We will observe in this study the effect of tool pin geometry over dwell time for reaching a uniform temperature of the tool in the shortest amount of time. The parameters used for the acquiring the data needed for the thermal analysis regarding tool material are tungsten carbide and the material of the plates will be aluminium 1200. The paper’s subject will be the realisation of a thermal analysis of the FSW (Friction Stir Welding) tools.

Surface-segregation mediated Mg2Si and Mg(Zn,Cu,Al)2 formation on primary α-Al phase during solidification of the hot-tear sensitive AA 7xxx aluminum alloys

Computer-aided thermal analysis and phase diagram calculation using the ThermoCalc® software were used to study the solidification path of Al7.8Zn2.6Mg2Cu alloy containing average values of 0.1 wt% Si and 0.1 wt% Fe as impurity elements. The Al6(Fe,Cu), Mg2Si, and Mg(Zn,Cu,Al)2 phases were detected as the main secondary phases precipitated during the solidification of the alloy. A four-step surface segregation-mediated description was proposed to explain the formation mechanism of the Mg-bearing, Mg2Si and Mg(Zn,Cu,Al)2, phases: i) surface segregation of Mg atoms form the bulk toward the surface of the primary α-Al phase, ii) adsorption of liquid Si atoms on the Mg-rich surface, iii) nucleation of Mg2Si, and iv) lateral growth of Mg2Si nuclei on the surface. Interfering with the kinetics of any or all of the first three steps may postpone or preclude the Mg2Si formation, alleviating the hot-tearing susceptibility of the alloy. Mg2Si can decrease the non-equilibrium solidus point of the alloy by depleting the source of Mg atoms on the surface of the primary α-Al phase, thereby postponing the formation of the Mg(Zn,Cu,Al)2 phase to lower temperatures. The freezing range is thus enlarged, increasing the hot-tearing susceptibility of the alloy. Therefore, the surface segregation of the primary α-Al phase appears to be a key feature for understanding the hot tearing phenomena of an alloy. A more accurate calculation of the solidification path to be used with Kou’s index of hot-tearing requires taking into account the possibility of surface segregation.

Eutectic Nucleation in 7xxx Series Aluminum Alloys from a Non-classical Viewpoint

The early stages of eutectic solidification in a copper-containing 7xxx series aluminum alloy (AA 7068 or AMS 4331) were studied using the two-thermocouple computer-aided thermal analysis (CATA) technique. A feature was detected on the cooling rate curve at the equilibrium solidus temperature of the alloy which persists until the peak of the subsequent final eutectic solidification. Detailed analysis of the temperature difference between the wall and the center of the thermal analysis sample, together with examination of the eutectic solidified on the walls of porosities and a study of the eutectic nucleation on the basis of the non-classical theory of adsorption heterogeneous nucleation, indicated how the feature can be related to the faceting of the atomic structure of the solid/liquid (S/L) interface. The solidification of the remnant liquid after the faceting transition at the equilibrium solidus point depends on the interfacial undercooling and proceeds via either primary phase re-nucleation or secondary phase nucleation by adsorption. The eutectic solidification is affected by the presence of the primary phase which acts like an adsorbent.

Synthesis of W-AG Nanoalloys and Computer Aided Thermal Analysis of W-AG Nanoalloys Based Heat Sink

W-Ag finds applications in many frontier areas such as heat sinks and microwave absorbers for microelectronics devices, arcing tips, resistance welding electrodes, electrical contacts and heavy duty electronic contacts. These nanoalloys prepared by mechanical milling process result in highly dense product. Chemical approaches have significant advantages in terms of better stoichiometric control, purity and controllable particle size. The variation in chemical composition of these composites allows the match of thermal expansion coefficient with ceramic substrates used in semiconductor devices. In the present study, Ag nanoalloys with average sizes below 200 nm were prepared using tungsten powder and silver nitrate as precursors. Compositional characterization of W-Ag nanoalloys was carried out using portable XRF.The developed material i.e. W-Ag is used as heat sink application in which the heat sink is modeled and thermally analyzed for evaluation of heat flux. The heat flux obtained was compared with aluminum heat sink. It was perceived that W-Ag heat sink exhibited superiority in withstanding higher temperature. Whereas, heat sink designed from aluminum was limited with their parameter which is thermal conductivity.

Synthesis of Mo-Cu Nanoalloys and Computer Aided Thermal Analysis of Mo-Cu Nanoalloys Based Heat Sink

Mo-Cu alloys are used as heat sinks, microwave absorbers in microelectronic devices and as electric contacts in circuit breakers. Mo-Cu nanoalloys with average sizes below 200 nm were prepared using molybdenum powder and copper nitrate. Compositional characterization of Mo-Cu alloys was carried out using portable XRF. The developed material i.e. Mo-Cu is used as heat sink application in which the heat sink is modeled and thermally analyzed for evaluation of heat flux. The heat flux obtained was compared with heat sink made of aluminum. It was observed that the Mo-Cu heat sink exhibited superiority in withstanding higher temperature whereas, heat sink designed from aluminum was limited with their parameter which is thermal conductivity.

Impact of large sized inertinite particles on thermo-swelling and volatile release of coking coals

A reflux classifier system was employed to concentrate large sized inertinite-rich particles (1.6–2.0 mm) from two different ranked coking coals A and B. The impact of these concentrates on swelling, permeability and volatile evolution rates of another two coking coals C and D was investigated using the Computer Aided Thermal Analysis (CATA) and Dynamic Elemental Thermal Analysis (DETA) techniques. The results indicated that the concentrated inertinite-rich particles contained inertinite up to 75% for both coals A and B. When 25% inertinite particles were blended with 75% coal C or D by mass, the low rank inertinite concentrates A caused higher extents of effect on swelling and permeability than the high rank inertinite concentrates B, leading to higher softening temperatures with smaller plastic ranges. During swelling, inertinite concentrates B can compress volatile evolution rates of both coals C and D, however, inertinite concentrates A promoted volatile evolution rate of coal C. Concentrates from both coals A and B can compress the utilization of volatiles for driving swelling, the blend containing concentrate A used nearly half of volatiles that coals C and D themselves used for driving swelling. This study suggested that the additive internite concentrates not only provided a pathway for gas diffusion, but also interacted with the blended coals, which affected thermoplasticity of the whole blends.

Impact of Coal Pyrolysis Products as a Rheological Additive on Thermoplasticity of a Coking Coal

Thermoplasticity is a determining factor for the development of the coke structure and coke strength. Mobile phase, whether vaporizable or not, may significantly affect thermoplasticity during coal coking. This work studies the effect of the mobile phase, including the volatile tar and extractable metaplast generated from one bituminous coking coal, on the thermo-swelling of the raw coal. The volatile tar was collected when the raw coal was heated from room temperature to 450 °C at a heating rate of 5 °C/min, while the metaplast was extracted from the heated char. Molecular properties of the tar and metaplast were characterized using a laser desorption/ionization–time of flight–mass spectrometry technique (LDI–TOF–MS). Thermo-swelling of the raw coal and its blends with the volatile tar and extractable metaplast was investigated using a computer-aided thermal analysis (CATA). The volatile (C and H) evolution rate of the heating coal samples was tracked using a dynamic elemental thermal analysis (DETA), an...

Investigation of thermal properties of blast furnace slag to improve process energy efficiency

Blast furnace slag (BFS) is the main by-product of iron making and is produced in large amounts worldwide. To improve energy use, it is necessary to understand the thermal behaviour of slags under differing compositions at varying temperatures. This study determines the thermal properties and behaviour of selected slag samples using several experimental techniques, including high temperature Hot Stage Scanning Electron Microscopy (HS-SEM), and Computer Aided Thermal Analysis (CATA). Further methods, such as Energy Dispersive Spectroscopy (EDS) and Fourier Transfer Infrared Spectroscopy (FTIR) were applied to determine the chemical content and nature of the studied BFS samples. Comparing the chemical composition of the slags and their thermal behaviour, the effect of magnesium oxide and aluminium oxide was evident on the crystallisation and fluidity of the molten slag. Additionally, the content of silicon dioxide had an effect on the crystallisation temperature and network strength.

Thermo-swelling Behavior of Australian Coking Coals from Different Basins: Relating to Rank and Maceral Compositions

Eight Australian coking coal samples (RvMax from 0.8 to 1.6) from six different basins were employed to investigate the effect of coal maceral compositions and rank on thermo-swelling behavior. Coal pyrolysis experiments were conducted at a heating rate of 5 °C/min from room temperature (25 °C) to 1000 °C with a top coal particle size of 212 μm. Thermoplasticity of coal was evaluated on the basis of the change of permeability of coal pellets, plastic range, swelling factor (defined by maximum swelling %/vitrinite %), and heat of exothermic reactions during the primary devolatilization. The endothermic and exothermic processes were identified by the estimate of the apparent specific heat using the computer-aided thermal analysis (CATA) technique, while swelling and permeability of gas flowing through coal pellets were simultaneously investigated with extended volumetric measurement downstream and pressure sensor upstream, respectively. Volatile evolution profiles of heating coal samples with temperature we...

Effect of the Heating Rate on the Thermochemical Behavior and Biofuel Properties of Sewage Sludge Pyrolysis

Treatment of sewage sludge is a major environmental concern for society. One treatment option that converts wastes into valuable biofuels is pyrolysis. The aim of this study was to investigate the effect of heating rates (10, 40, 70, and 100 °C/min) on the thermal behavior and biofuel properties of sewage sludge pyrolysis from room temperature to 1000 °C. Thermogravimetric analysis indicated three main reaction zones in respective temperature ranges of 600 °C for the sewage sludge pyrolysis. The most intense mass loss rate took place at 210–600 °C, with a maximum value of 0.2 wt %/°C at around 330 °C. Increasing the heating rate resulted in shifting of the mass loss peaks to higher temperatures. Computer-aided thermal analysis was applied to identify the specific heat and reaction heats of sludge during heating. The endothermic reaction peaks at 150–300 °C and exothermic peaks at 500–600 °C shifted to higher temperatures when increasing the heating rate. Gas chromatography results show...

Thermo-swelling Properties of Particle Size Cuts of Coal Maceral Concentrates

A suite of coal maceral concentrates were prepared from a single coal using a water-based method for two discrete particle size fractions. Coal macerals were produced with the vitrinite content varying from 91.2% to 26.1% for the 106–212 μm particle size fraction and 96.0% to 38.2% for the 212–500 μm particle size fraction. Thermo-swelling of coal maceral concentrates were evaluated by the Computer Aided Thermal Analysis (CATA) technique with extended volumetric measurements. This novel CATA technique allows the apparent specific heat, thermal conductivity, and transient volumetric swelling of the coal sample to be measured simultaneously, as a function of temperature. The experimental results indicated that the maximum swelling (∼510 °C) and high-temperature contraction (600–1000 °C), as well as exothermic heat during primary devolatilization and thermal conductivity at maximum swelling all increased with vitrinite content, with the data inferring a linear relationship, and was independent of particle si...

Effect of cooling rate on the microstructure and solidification characteristics of Al2024 alloy using computer-aided thermal analysis technique

The aim of this work was to investigate the effect of different cooling rates on the microstructure and solidification parameters of 2024 aluminum alloy. Solidification characteristics are recognized from the cooling curve and its first and second derivative curves which have been plotted using thermal analysis technique. In this study, a mold having high cooling rate was designed and used to simulate the direct-chill casting process. The results of thermal analysis show that the characteristic parameters of Al2024 alloy are influenced by cooling rate. The cooling rates used in the present study range from 0.4 to 17.5 °C s−1. Increasing the cooling rate affects the undercooling parameters both in liquidus and eutectic solidification regions. Investigations showed that solidification parameters such as nucleation temperature, recalescence undercooling temperature, and range of solidification temperature are influenced by variation of cooling rates. Microstructural evaluation was carried out to present the correlation between the cooling rate and dendrite arm spacing.

Effect of cooling rate on solidification parameters and microstructure of Al-7Si-0.3Mg-0.15Fe alloy

The effects of cooling rate on the solidification parameters and microstructure of Al-7Si-0.3Mg-0.15Fe alloy during solidification process were studied. To obtain different cooling rates, the step casting with five different thicknesses was used and the cooling rates and solidification parameters were determined by computer-aided thermal analysis method. The results show that at higher cooling rates, the primary α(Al) dendrite nucleation temperature, eutectic reaction temperature and solidus temperature shift to lower temperatures. Besides, with increasing cooling rate from 0.19 °C/s up to 6.25 °C/s, the secondary dendritic arm spacing decreases from 68 μm to 20 μm, and the primary dendritic volume fraction declines by approximately 5%. In addition, it reduces the length of Fe-bearing phase from 28 μm to 18 μm with a better uniform distribution. It is also found that high cooling rates make for modifying eutectic silicon into fibrous branched morphology, and decreasing block or lamella shape eutectic silicon.

In situ melting and solidification assessment of AZ91D granules by computer-aided thermal analysis during investment casting process

Computer-aided thermal analysis was carried out to precisely measure the thermal characteristics of AZ91D magnesium alloy granules during in situ melting and solidification in investment casting process. Ceramic shell moulds of two different thicknesses equipped with highly sensitive thermocouples at three different locations were prepared to provide a range of heating and cooling rates during in situ melting and solidification. The results revealed that dissimilar thermal regimes were experienced by the granules at different locations of the mould during heating, which led to asynchronous melting of the granules. It was found that both melting commencement and completion were increased with increasing heating rate; in contrast inverse behaviour was observed during cooling. The onset and the end of solidification temperatures and duration decreased with increasing cooling and solidification rates. The information from this approach is very crucial for suppressing mould-metal reaction especially during cooling in casting of magnesium alloys by investment casting process.

Study on the effect of cooling rate on the solidification parameters, microstructure, and mechanical properties of LM13 alloy using cooling curve thermal analysis technique

In this study, the effect of cooling rate on the microstructure, solidification parameters, and mechanical property of LM13 alloy has been investigated. To obtain different cooling rates, an air-cooled graphite mold, 3 sand molds with different moisture content, a water-cooled graphite mold, and a water-cooled steel mold were used. The cooling rates and the solidification parameters were determined by using computer-aided thermal analysis method. Results show that with increasing cooling rate from 1.1 to 50°C/s, secondary dendrite arm spacing decreases 65%. At higher cooling rates, the nucleation temperature of reactions shifts to higher temperature, except the final reaction, but the eutectic recalescence undercooling is eliminated. It modifies eutectic microstructure and decreases parallel eutectic layers distance from 23.24 to 4μm. In addition, it reduced primary silicon particle appearance (PSPA) from 1.17 to 0.3. The equivalent porosity diameter also reduces from 72.5μm to 27.8μm. Shear punch test (SPT) shows improvement of ultimate shear stress, yield shear stress, and normalized displacement at higher cooling rates. Hardness has also been improved about 30 Vickers as a result of increasing cooling rate.

Coal macerals separation by reflux classification and thermo-swelling analysis based on the Computer Aided Thermal Analysis

The reflux classifier is a water based device designed for classifying and separating particles using inclined plates. Particles of sufficiently high settling rate are refluxed back to the slurry, while slow settling particles (low density vitrinites) are removed in the overflow. In this study, the reflux classifier was used to separate coal macerals less than 212μm in size. The thermo-swelling characteristics of separated macerals were evaluated on the basis of the Computer Aided Thermal Analysis (CATA) technique with extended volumetric measurements. A suite of maceral concentrates with various densities, ash contents, particle sizes and vitrinite percentages was obtained, which indicated that the reflux classifier can offer an alternative method of macerals separation/concentration without the use of dense media. The pyrolysis experiments of maceral concentrates indicated that the vitrinite-rich macerals showed a higher extent of volumetric swelling, exothermic reactions and thermal conductivity between 400 and 600°C than inertinite-rich macerals. Addition of inertinite to vitrinite concentrates showed that inertinite can suppress volumetric swelling and shift the swelling to a higher temperature during the primary devolatilization, but does not have a significant influence on high temperature contraction. Further observations about the interaction among different maceral groups were also discussed in this study.

Investigation of the Effects of Ni, Fe, and Mn on the Formation of Complex Intermetallic Compounds in Al-Si-Cu-Mg-Ni Alloys

The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples, and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases was measured using the image analysis technique. The results show that Ni mainly participates as Al3Ni, Al9FeNi, and Al3CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al9FeNi the only Ni-rich phase, and Al12(Fe,Mn)3Si2 appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents.

Thermal Decomposition of Wheat Straw and Mallee Residue Under Pyrolysis Conditions†

The pyrolysis behavior of wheat straw and mallee residue and resulting gases, liquids, and chars were examined. The specific heat and thermal conductivity of both species were measured using computer-aided thermal analysis at heating rates of 10 and 100 °C/min to a temperature of 1000 °C. The sample decomposition was also measured by thermogravimetry. Gas chromatography detected evolved gases, and the bio-oils were characterized using GC-MS. Chars were examined using FTIR, proximate, and ultimate analysis. Both species initially displayed endothermic behavior, followed by rapid decomposition and fluctuating specific heat and thermal conductivity between 250 and 500 °C. Oxides of carbon were the primary gases evolved, with small amounts of hydrocarbons and hydrogen. The bio-oils predominantly contained oxygenated aromatics and organic acids, and the chars had high fixed carbon and low sulfur. In all instances approximately half of the product output was liquid. Straw produced 14% gas and 32% solid at 500 °...

Thermal characterisation of microalgae under slow pyrolysis conditions

Aquatic microalgae have high potential for production of bio-chemicals, liquid transport fuels and charcoal. Their main advantage over existing energy crops is that they have faster growth rates and do not compete with food production. In this study six species of microalgae ( Tetraselmis chui, Chlorella like, Chlorella vulgaris, Chaetocerous muelleri, Dunaliella tertiolecta and Synechococcus) were selected, presenting a broad cross-section of physical characteristics and known behaviour under cultivation. The objective of this work was to ascertain differences in thermal conversion behaviour between the microalgae species under slow pyrolysis conditions. The samples were first analysed with a Computer Aided Thermal Analysis (CATA) technique at a standard heating rate of 10 °C/min. For all species, the energy required to achieve thermal conversion was found to be approximately 1 MJ/kg. Gas chromatography was then applied to measure the evolution of biogas compounds with temperature. The heat of combustion of the biogas compounds was estimated to vary significantly between species, ranging from 1.2 to 4.8 MJ/kg. Pyrolysis oil product yields were also estimated at 500 °C. The oils produced at this temperature were collected and their molecular weight distribution assessed by Matrix Assisted Laser Desorption/Ionisation (MALDI). The species were found to produce up to 43% by volume of bio-oils. In all samples the char fraction remained above one third of total sample weight.