Calorimetric study and thermal analysis of Al–Sn system

The results of calorimetric study and thermal analysis of binary Al–Sn system are presented in this paper. The Oelsen calorimetry was used in thermodynamic analysis. Following thermodynamic properties were determined at 727 °C: activities, activity coefficients, partial/integral molar Gibbs excess, and mixing energies. The energetics of mixing in liquid Al–Sn alloys has been analyzed through the study of concentration fluctuation in the long-wavelength limit. Thermal analysis of selected alloys in Al–Sn system was done using differential thermal analysis. Defined characteristic phase transition temperatures were used for comparison with calculated phase diagram of investigated system. Good agreement with available literature data was obtained. Structural analysis of selected alloys was done using optic microscopy.     

Effect of morphology and precipitation of Si phase on thermal properties of Al–Si–Mg–Cu foundry alloy

Journal of Thermal Analysis and Calorimetry - In this study, CuAl13?xTax (% mass x?=?1; 1.5; 2; 2.5) shape-memory alloys were produced through arc-melting method. Phase...     

Cooling curve thermal analysis of Al–Mg2Si–Cu–xSr composite

Journal of Thermal Analysis and Calorimetry - In situ composites are today being considered for industrial use, owing to the fewer production steps involved, lower production cost, and better...     

Monomer-Dimer Equilibrium of Rhodamine B Encapsulated in Si–Al and Si–Ti Binary-Oxide Thin Films

Si—Al and Si—Ti binary-oxide thin films including Rhodamine B (RB) have been prepared. They were dip-coated as a function of time after mixing of each sol-gel reaction system. The absorption and fluorescence spectra of the individual films have been observed. These spectra were analyzed in order to clarify the behavior of RB along with the change in the environment around the RB molecules, caused by the progress of the sol-gel reaction, in the fluid sol and the prepared thin films. Some amount of the RB dimers (H- and J-types) were formed in the Si—Al and Si—Ti binary-oxide films (Si : M = 75 : 25) prepared at the initial stage of the sol-gel reaction and aged under relative humidity of 60%. In the case of Si—Al binary-oxide films, the amount of the J-dimer decreased along with the reaction time at which the films were prepared, indicating that growing polymer networks of metal alkoxides around the RB molecules prevent the formation of the J-dimer. On the other hand, larger amounts of the H- and J-dimers were formed in the Si—Ti binary-oxide films prepared at longer reaction time of the solution. RB interacts more strongly with —TiOH compared with —AlOH. In the case of the Si—Ti binary-oxide films, with the progress of the sol-gel reaction, RB molecules in the prepared films easily cohere around the —TiOH and form the dimers because of increase in the amount of the —TiOH and contraction in the volume of the spaces where RB molecules exist.     

The usage of computer-aided cooling curve thermal analysis to optimise eutectic refiner and modifier in Al–Si alloys

Bismuth, antimony and strontium concentrations were optimised to alter the eutectic Al?CSi phase in a commercial Al?CSi?CCu?CMg alloy by way of computer-aided cooling curve thermal analysis. The results show that the eutectic growth temperature shifted to lower temperatures for all three inoculants. However, addition of Sr resulted in more depression of growth temperature compared with Bi and Sb. No further significant changes were observed with increasing the concentrations to more than 1, 0.5 and 0.04?wt% of Bi, Sb and Sr, respectively. The recalescence of these concentrations, meanwhile, showed a significant increase of magnitude. A good correlation was found between the results of thermal and microstructural analysis. For Bi and Sb, the eutectic depression temperature can be used as an individual criterion to gauge optimal levels of content in the refinement of Si, whereas for Sr, both depression temperature and recalescence magnitude must be considered. Based on the observed depression in eutectic growth temperature and recalescence, it can be concluded that the optimal concentrations to refine the eutectic Al?CSi phase with Bi and Sb and to modify it with Sr at the given solidification conditions were 1, 0.5 and 0.04?wt%, respectively.     

Computer-aided cooling curve thermal analysis of near eutectic Al–Si–Cu–Fe alloy

The effects of bismuth (Bi), antimony (Sb) and strontium (Sr) additions on the characteristic parameters of the evolution of aluminium dendrites in a near eutectic Al–11.3Si–2Cu–0.4Fe alloy during solidification at different cooling rates (0.6–2 °C) were investigated by computer-aided cooling curve thermal analysis (CA-CCTA). Nucleation temperature ( $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ ) is defined with a new approach based on second derivative cooling curve. The results showed that $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ increased with increasing cooling rate but both the growth temperature ( $ T_{\text{G}}^{{\alpha {\text{ - Al}}}} $ ) and the coherency temperature (T _DCP) decreased. Increase in the temperature difference for dendrite coherency ( $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} - T_{\text{DCP}} $ ) with increasing cooling rate indicate a wider range of temperature before the dendrite can impinge on each other and higher fraction solid ( $ f_{\text{S}}^{\text{DCP}} $ ). Additions of Bi, Sb and Sr to the base alloy produced only a minor effect on $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} $ . Additions of Bi and Sb resulted in an increase in fraction solid and an increase of 30 % in the value of $ T_{\text{N}}^{{\alpha {\text{ - Al}}}} \, - \,T_{\text{G}}^{{\alpha {\text{ - Al}}}} $ to almost 13 °C.     

DSC analysis of phase transformations during precipitation hardening in Al–Zn–Mg alloy (7020)

The hardening of the Al–Zn–Mg alloys during ageing process is based on very complex phase transformations. In order to contribute to the comprehension of these phenomena, we proceed to study the phase transformations of 7020 alloy using differential scanning calorimetry and X-ray diffraction analysis. The results confirm the formation of hardening phase GP zones, intermediate hardening metastable phase η′ and the equilibrium phase η. The calorimetric and X-ray diffraction results are in good agreement and confirm the successive precipitation/dissolution sequence. The dissolution of the precipitates is accompanied by the increase in the crystallographic lattice parameter due to the increase in solid solution concentration and by the softening of the material. On the contrary, the precipitation produces a lower concentration of the Zn/Mg solutes in the Al matrix, which generates a decrease in the lattice parameter value. These precipitates produce the hardening of the alloy. The sequence of phase formation and dissolution explains the evolution of the 7020 hardness as a function of the ageing temperature.

     

Direct and indirect photoinduced gas–liquid phase transitions

The condensation of supersaturated vapors of various substances in air under UV irradiation in a cloud chamber has been studied. The irradiation and subsequent photodissociation greatly facilitate the condensation of vapors in comparison with unirradiated mixtures, wherein both a vapor that directly absorbs radiation (direct photoinduced phase transition) and, for example, water vapor in the presence of photodissociating impurities (indirect photoinduced transition) can be condensed.     

Experimental investigation of the Nd–Al–Si system

The isothermal section of the Nd–Al–Si ternary system at 500 °C has been investigated using differential thermal analysis, X-ray diffraction analysis, scanning electron microscopy and electron micro-probe analysis. Four ternary intermetallic compounds were confirmed: NdAl₂Si₂ (τ₁), hP5-CaLa₂O₂ structure type, Nd₂Al₃Si (τ₂), hP3-AlB₂ structure type, NdAl_1−x Si_1+x , 0.25 ≤ x ≤ 0.3 (τ₃), tI12-αThSi₂ structure type and Nd₂Al_1−x Si_1+x , 0 ≤ x ≤ 0.2, (τ₅), oS8-CrB structure type. A new ternary intermetallic phase (τ₄) was found: Nd₄Al₃Si₃, orthorhombic oS20, isotypic with Pr₄Al₃Ge₃.     

Phase equilibria in the Sm–Al–Si system at 500 °C

The isothermal section at 500 °C of the Sm–Al–Si system has been experimentally investigated by using scanning electron microscopy, electron microprobe analysis and X-ray powder diffraction. Four intermetallic compounds have been confirmed: τ₁-SmAl₂Si₂ (hP5-CaAl₂Si₂ type), τ₂-SmAl_xSi_1?x (tI12-Th₂Si type), τ₄-SmAl_0.5Si_0.5 (oS8-CrB type) and τ₅-Sm₆Al₃Si (tI80-Tb₆Al₃Si type). A new ternary intermediate has been found: τ₃-Sm₄Al₃Si₃ that crystallizes orthorhombic isostructural with Pr₄Al₃Ge₃.     

Thermodynamic analysis of precipitation processes in Nb–Ti-microalloyed Si–Al TRIP steel

The work deals with the thermodynamic calculations of precipitation processes in austenite of the Nb–Ti-microalloyed steel with increased Si and Al content dedicated for the automotive industry. The analysis is based on the equilibrium precipitation of individual MX-type interstitial phases, as well as the effect of various Mn and Si additions is included. The solubility products and corresponding limits of the mutual solubility of microalloy and metalloid additions in austenite were calculated. The temperature sequence of the precipitation under equilibrium conditions was determined. The Dutta–Sellars model has been applied for determination of recrystallization stop temperature of austenite and time needed for Nb(C,N) precipitation. The calculations were verified by microstructure investigations including revealing prior austenite grain size as a function of austenitizing temperature and the identification of complex carbonitrides using transmission electron microscopy. The model calculations are in good agreement with experimental results.     

Manufacturing of ceramic nanomaterials in Ti–Si–C–N system by sol–gel method

Problems concerning sol–gel synthesis of ceramic nanomaterials, methods of investigation of these materials and of processes proceeding with their participation have been presented. One-component nc-TiC, nc-TiN and multi-component TiC + SiC + C and Ti(C,N) + Si(C,N) + Si₃N₄, powders have been investigated. The sol–gel synthesis is carried out in two stages: low-temperature, in which the raw nc-TiC_x product is obtained, and high-temperature one. In the high-temperature stage carbonization of carbides and elimination of excessive organic compounds, being the source of carbon in carbonization process, take place. It has been demonstrated that the oxygen, present at trace level in argon, can react with components of the system in certain range of temperature, influencing the quality of obtained product. High-temperature oxidation resistance of investigated materials in dry air was also determined, applying kinetic methods. TG-DSC measurement data were used as the basis of kinetic analysis. The method of investigation has been presented at the example of TiC + SiC + C powder oxidation. Is has been demonstrated, that in case of multi-component materials, components were oxidized in temperature ranges characteristic for pure phases.     

Study of the Cu–Li–Mg–H system by thermal analysis

Finite fossil-fuel supplies, nuclear waste and global warming linked to CO₂ emissions have made the development of alternative/‘green’ methods of energy production, conversion and storage popular topics in today’s energy-conscious society. These crucial environmental issues, together with the rapid advance and eagerness from the electric automotive industry have combined to make the development of radically improved energy storage systems a worldwide imperative. CuMg₂ has an orthorhombic crystal structure and does not form a hydride: it reacts reversibly with hydrogen to produce Cu₂Mg and MgH₂. However, CuLi _x Mg_2−x (x = 0.08) has a hexagonal crystal structure, just like NiMg₂, a compound known for its hydrogen storage properties. NiMg₂ absorbs up to 3.6 wt% of H. Our studies showed that not only CuLi _x Mg_2−x absorbs a considerable amount of hydrogen, but also starts releasing it at a temperature in the range of 40–130 °C. In order to determine the properties of the hydrogenated CuLi _x Mg_2−x , absorption–desorption, Differential scanning calorimeter and thermo-gravimetric experiments were performed. Neutron spectra were collected to elucidate the behavior of hydrogen in the Li-doped CuMg₂ intermetallic. Using DFT calculations we were able to determine the best value for x in CuLi _x Mg_2−x and compare different possible structures for the CuLi _x Mg_2−x hydride.     

The section of the Fe–Ni–S phase diagram constructed by directional crystallization and thermal analysis

A nontrivial polythermal cross-section through the Fe–Ni–S phase diagram was plotted using a combination of directional crystallization and DTA methods. The crystallized sample was grown from the liquid (L) of the following composition Fe = 18, Ni = 35, and S = 47 at.%. It consisted of two single-phase sites formed from mss (Fe _z Ni_1?z )S_1±δ and hzss (Ni _z Fe_1?z )_3±δS₂. The phase reaction L + mss = hzss proceeded on the boundary between these sites. The trajectories of melt and solid composition on the Gibbs triangle were calculated from the distribution of components along the sample. The tie-line transformation was determined from these data. Liquidus temperatures along the trajectory were measured by the DTA method and calculated with the help of a mathematical model. The nontrivial cross-section of the diagram constructed from these data shows the phase equilibrium conditions. The cross-section consists of two tie-line linear surfaces L–mss and L–hzss.     

Pitting of Al and Al–Si alloys in KSCN solutions and the effect of light

The pitting corrosion susceptibility of pure Al and three Al-Si alloys, namely (Al-6%Si), (Al-12%Si) and (Al-18%Si) has been studied in 0.04 M KSCN solution. Measurements were carried out under the effect of various experimental conditions using cyclic polarization, potentiostatic and galvanostatic techniques. In all cases, the potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of a thin film of Al₂O₃ on the anode surface. The passive region is followed by pitting corrosion, at a certain critical potential, pitting potential (E_pit), as a result of breakdown of the passive film by SCN^? anions. Cyclic polarization measurements allowed the determination of the pitting corrosion parameters, namely the pitting potential and the repassivation potential (E_rp). Alloyed Si decreased the passive current (j_pass) and shifted both E_pit and E_rp towards more positive values. Thus alloyed Si suppressed pitting attack. The effect of illumination on passivity and the initiation of pitting corrosion on Al in KSCN solutions was also studied. It is observed that illumination of Al leads to an increase in its pitting corrosion resistance-apparent from j_pass, E_pit, and E_rp measurements in aggressive KSCN solutions.     

Phase transition temperatures of Sn–Zn–Al system and their comparison with calculated phase diagrams

The Sn?CZn?CAl system was studied in connection with the possible substitution of lead-based solders for temperatures up to 350?°C. Ternary alloys with up to 3?wt% of aluminium were prepared. The investigated alloys lie close to the monovariant line (eutectic valley) of the Sn?CZn?CAl system. The temperatures of phase transitions of six binary Sn?CZn reference alloys and fourteen ternary Sn?CZn?CAl alloys using DTA method were investigated in this paper. DTA experiments were performed at the heating/cooling rate of?4?°C?min^?1 using Setaram SETSYS 18_TM experimental equipment. The temperatures of phase transitions in the ternary Sn?CZn?CAl system were obtained, namely, the temperature of ternary eutectic reaction T _E1 (197.7?±?0.7?°C), temperature of ternary transition reaction T _U1 (278.6?±?0.7?°C), temperatures of liquidus and other transition temperatures for studied alloys. Temperatures obtained during DTA heating runs were used as authoritative. DTA curves obtained during cooling enabled realising better differentiation of the obtained overlapped heat effects (peaks) during heating. Theoretical isopleths of the Sn?CZn?CAl phase diagram were calculated using the Thermocalc software and MP0602 thermodynamic database. Experimental data were compared with the calculated temperatures, and a good agreement was obtained.