Temperature Time Research Articles

The effects of heat-treatment parameters on the mechanical properties and microstructures of a low-carbon dual-phase steel

The austenite decomposition phase transformation in a low-carbon dual-phase (DP) steel is studied as a function of inter-critical annealing parameters: annealing time, annealing temperature, and cooling rate. The austenization kinetics are obtained by dilatometric analyses, water-quenched metallography, and thermodynamic calculations, and the austenite formed at different inter-critical annealing temperatures influences the subsequent formation of secondary phases during continuous cooling. Results indicate that the austenite volume fraction increases with both annealing temperature and time; although their effect on the final microstructure and mechanical properties lessens when the cooling rate decreases to the slow cooling regime below air cooling. Interestingly, the yield strength (YS) values of samples cooled at ∼1 °C/s with sand cooling, are 75∼100 MPa greater than the corresponding values at a rate of ∼6 °C/s with air-cooling. The results indicate that the yield strength is positively correlated with yield-point elongation but negatively correlated with the ultimate tensile strength. The effects of the cooling rate on the mechanical properties can be explained by the formation of Cottrell atmospheres of carbon together with the increase of the pearlite volume fraction. Based on the secondary phase components and strength evolutions, there are four possible outcomes for the different cooling rates: (I) martensite (M); (II) ferrite-martensite (FM); (III) coexistence of martensite and pearlite (MP); and (IV) ferrite-pearlite (FP). Our results reveal that the microstructure-property correlation can be illustrated schematically as a function of cooling rates and can thereby direct the heat-treatment parameters required to obtain desirable mechanical properties.

Direct Visualization of CO Interaction on Oxygen Poisoned Co(0001).

The poisoning of catalysts has always been a vital issue in catalytic reactions. In this study, direct observation of the interaction of CO and oxygen-poisoned Co(0001) has been achieved with scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), and density functional theory calculation. A two-stage adsorption process of CO on a well-prepared p(2×2)-O layer covered Co(0001) was directly visualized. With increasing annealing time at a certain temperature after the CO dosage, the ordered (2 × 2) pattern formed in the first stage can be recovered, suggesting the weak interaction of CO with the O-covered Co(0001) surface in the latter stage. Compared to the clean Co(0001) surface, on an oxygen-poisoned surface, no further reaction was observed, illustrating the poisoning of the catalyst. Moreover, TPD results are in good agreement with the STM observation; a desorption energy of 0.35 eV is evaluated with a simple but accurate scheme.

Effect of Annealing Time on Texture Evolution of Fe–3.4 wt% Si Nonoriented Electrical Steel

Herein, the effect of annealing time on the texture evolution in Fe–3.4 wt% Si non‐oriented electrical steel is investigated. Strip samples are cast using a vacuum sampling method, which simulate the solidification conditions of an industrial twin roll thin strip casting (TRSC) process. As‐cast samples with different carbon and sulfur (C&S) levels are hot rolled (HR) with varying levels of hot deformation, cold rolled (CR) to 0.35 mm thickness, and then annealed at 1050 °C for different holding times (1, 6, 24 h). To Fe–3.4 wt% Si nonoriented electrical steel, the observed texture evolution can be divided into different stages as annealing time is increased from 1 to 24 h. With increasing annealing time, the fraction of Goss texture decreases initially and then increases again through the consumption of grains with other textures. With additional time, a decrease of pinning force due to precipitate coarsening results in normal grain growth, resulting in an increase of grain size. In this step, Cube grains can form from rotated Goss grains. A model for core loss is presented and used to explain the core loss results.

Effect of Germinated Sorghum Extract on the Physical and Thermal Properties of Pre-Gelatinized Cereals, Sweet Potato and Beans Starches.

Starches from different botanical sources are affected in the presence of enzymes. This study investigated the impact of α-amylase on several properties of pre-gelatinized starches derived from chickpea (Cicer arietinum L.), wheat (Triticum aestivum L.), corn (Zea mays L.), white beans (Phaseolus vulgaris), and sweet potatoes (Ipomoea batatas L.). Specifically, the water holding capacity, freezable water content, sugar content, and water sorption isotherm (adsorption and desorption) properties were examined. The source of α-amylase utilized in this study was a germinated sorghum (Sorghum bicolor L. Moench) extract (GSE). The starch samples were subjected to annealing at temperatures of 40, 50, and 60 °C for durations of either 30 or 60 min prior to the process of gelatinization. A significant increase in the annealing temperature and GSE resulted in a notable enhancement in both the water-holding capacity and the sugar content of the starch. The ordering of starches in terms of their freezable water content is as follows: Chickpea starch (C.P.S) > white beans starch (W.B.S) > wheat starch (W.S) > chickpea starch (C.S) > sweet potato starch (S.P.S). The Guggenheim-Anderson-de Boer (GAB) model was only employed for fitting the data, as the Brunauer-Emmett-Teller (BET) model had a low root mean square error (RMSE). The application of annealing and GSE treatment resulted in a shift of the adsorption and desorption isotherms towards greater levels of moisture content. A strong hysteresis was found in the adsorption and desorption curves, notably within the water activity range of 0.6 to 0.8. The GSE treatment and longer annealing time had an impact on the monolayer water content (mo), as well as the C and K parameters of the GAB model, irrespective of the annealing temperature. These results can be used to evaluate the applicability of starch in the pharmaceutical and food sectors.

Annealing Effect on Mechanical and Tribological Behaviors of Nanoscale Mechanics of Zr60Cu25Al5Ag5Ni5 Thin-Layer Metallic Glasses for Engineering Materials Applications.

A new and unique alloy formulation design strategy has been developed in order to fabricate thin-layered metallic glasses (TLMGs) with superior fracture resistance and low coefficient of friction (COF) during the nanoscratching test. Due to the outstanding properties, TFMG could be applied for different uses, such as for surface coating, biomedical, bioimprinting, electronic devices, spacecraft, and railway, all of which need surface fracture resistance. The fabricated Zr-based metallic glass was prepared from Zr, Al, Cu, Ni, and Ag above 99.9 Wt % in purity by arch melting techniques. TFMGs were coated on silicon wafer by sputtering the vapor deposition method from bulk metallic glass then annealed below glass transition temperature Tg ∼ 450 °C for 10, 30, and 60 min. Nanoindentation and nanoscratch tests were used to investigate nanomechanical and nanotribological properties, and atomic force microscopy (AFM) was used to examine the surface morphology and microstructures of TLMG. The nanoindentation data indicated that the average hardness of metallic glasses increased from 9.75 (as-cast MG) to 13.4 GPa (annealed for 60 min). Coefficients of friction for the cast sample, annealed for unannealed, 10, 30, and 60 min, were 0.062, 0.049, 0.039, and 0.03, respectively, as well as the wear depths were 201.56, 148.43, 37.32, and 25.27 nm, respectively. These studies show that the coefficient of friction and wear rate decreases when the annealing time increases as a result of atomic reordering and structural relaxation that occurred at longer annealing times. Furthermore, continuous wear process, wear depth, wear track volume, and contact area decrease with increasing annealing time. This study can be used to design protocols to prepare novel TLMGs, which have outstanding mechanical and tribological properties for engineering materials applications.

The effect of physical aging on the viscoelastoplastic response of glycol modified poly(ethylene terephthalate)

For most amorphous polymers, their long term viscoelastic behaviour is greatly affected by physical aging, referring to the transition of their non-equilibrium structure towards equilibrium. This, in turn, affects their thermomechanical properties. In this study, we successfully applied a constitutive model, originally developed for semi-crystalline polyesters to assess the impact of physical aging on stress relaxation and creep in two glycol modified poly(ethylene terephthalate) grades, (poly(ethylene-co-1,4-cyclohexylenedimethylene terephthalate) (PECT) and poly(ethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol terephthalate) (PETT). Both copolyesters are subject to annealing at Tg-20 °C for up to 504 h and subsequent uniaxial stress relaxation tests and, for PECT, creep tests. The results show that the annealing time has a significant influence on the viscoelastic behaviour increasing the resistance to creep and stress relaxation. The effect of physical aging on model parameters is described and analysed while it is found that the concentration of active polymer junctions decreases exponentially with annealing time. Generally, PETT and PECT showed almost identical viscoelastic behaviours at 30 °C, suggesting that the chemical structure of the glycol unit (2,2,4,4-tetramethyl-1,3-cyclobutanediol and 1,4-cyclohexylenedimethanol) does not have significant effect on their viscoelasticity. However, when stress relaxation is tested at increased temperatures, the structural effects are more apparent, demonstrating higher activation energies for PECT than those for PETT, describing the rate of the rearrangement of interchain interactions. Physical aging is also found to decrease these activation energies from 326.6 to 128.1 kJ mol−1 for PECT and from 262.7 to 78.5 kJ mol−1 for PETT.

Control of Ag acceptor concentration and pn-junction depth in single crystalline Mg2Si photodiodes

We have investigated the relationship between the Ag concentration and the pn-junction depth in the Mg2Si pn-junction photodiodes fabricated by thermal diffusion of the Ag acceptor. The Ag concentration profiles and pn-junction depths in the samples annealed between 400 and 550 °C were studied by secondary ion mass spectroscopy and electron beam-induced current (EBIC) images. We observed two kinds of lattice diffusions of substitutional and interstitial Ag atoms with two different diffusion coefficients, of which activation energies were ∼0.97 and 0.75 eV, respectively. The depth of pn-junction observed by EBIC images increased with annealing temperature and annealing time. On the other hand, the average Ag concentration did not depend on the annealing time but depended on the annealing temperature. These results indicate that the average Ag concentration and pn-junction depth in Mg2Si photodiodes can be controlled by annealing temperature and annealing time, respectively. This study would contribute to the development of Mg2Si pn-junction photodiodes.

Effect of prolonged annealing on the morphology and optical properties of ZnO films produced by magnetron sputtering

The effect of annealing time on the structural and optical properties of ZnO films, which are formed from Zn films obtained by magnetron sputtering followed by oxidation in air, is described. Thermal oxidation in air was carried out for 7 and 24 hours, respectively, in a programmable muffle furnace at T = 750°C. A change in the structure of the film surface depending on the annealing time of the Zn film and the substrate material was found, which manifests itself in the optical properties of the films.

Structure evolution of the interfacial layer of BaTiO3 thin films during annealing process and related good resistive switching behaviors

BaTiO3 thin films with different annealing times were grown on LSMO/STO (001) substrates by pulsed laser deposition. An interesting phenomenon of loss-and-reappearance of the interfacial layer in BaTiO3 was detected in the x-ray diffraction results, and the ordered–unordered–ordered lattice transformation caused by oxygen vacancies’ filling was thought to be the reason. The ferroelectric domain was also confirmed to form during such an annealing process according to the piezoresponse force microscopy, transmission electron microscopy, and phase-field simulation. A Ti-displacement-rotation region considered an intermediate structure during the domain formation was observed at the interfacial layer of the 5.5-min-annealing film. Because of the oxygen deficiency and the effect of ferroelectric domain modulation of the built-in barrier height, a good memristive behavior with a resistive switching ratio of 1916 was obtained in the 10-min-annealing BaTiO3 (BTO) film, offering an avenue toward the application of oxygen-deficient BTO in neural network applications.

Evolution of the Structure and Phase Composition of a High-Entropic CoCrFeNiCu Alloy during Prolong Annealing

Abstract—The thermal stability of a high-entropy alloy (HEA) CoCrFeNiCu was studied during long-term annealing for 204 days in the temperature range 873–1273 K. The alloy obtained by mechanochemical alloying of metal powders in a planetary mill during 120 min in an Ar environment is a substitutional solid solution based on a high-entropy phase with a face-centered cubic structure (FCC). Upon annealing, the initial FCC phase decomposes within 1–3 days into a copper-enriched FCC1 phase and a copper-depleted FCC2 phase with similar crystal lattice parameters of 3.60 and 3.57 Å, respectively. During the entire annealing time, the intensities of the diffraction lines of theFCC1 and FCC2 phases are redistributed, the dynamics and nature of which depends on the temperature and duration of the process. After the first three days and until the end of the annealing, the HEA retains the FCC structure of the substitutional solid solution, and the unit cell parameters of the formed FCC phases remain constant with an error of 0.1% up to 204 days. The five-component matrix formed after annealing has the chemical composition Co0.23Cr0.23Fe0.23Ni0.23Cu0.08 and is stable. Also, during the entire period of annealing, an increase in the grain size is observed: at first, when an active rearrangement of the structure occurs, the size increases rapidly, then, in the period from 1 to 30 days, grain growth is limited by the diffusion of components, and at very long time intervals, grain growth is even more inhibited.

Improving near-infrared luminescence in Er3+ doped CsPbBr3 quantum dots glasses through a certain energy transfer process

Er3+ has received extensive attention due to its excellent optical properties, especially its emission at 1535 nm in atmospheric propagation window. Enhancement and regulation of 1535 nm emission of Er3+ is of great significance to optical communication. In this work, growing of CsPbBr3 QDs has been controlled through adjusting annealing time which would precisely regulate conduction band of CsPbBr3 QDs to match energy levels of Er3+ enabling energy transfer between Er3+ and CsPbBr3 QDs. By steady-state and transient PL emission and excitation spectroscopy, we reveal multiple energy transfer processes between Er3+ and CsPbBr3 QDs under different excitation wavelengths in Er3+ doped CsPbBr3 QDs glass: under higher energy excitation (∼378 nm), energy transfer from Er3+ to CsPbBr3 QDs and this extra energy within CsPbBr3 QDs decay via a non-radiative pathway; under lower energy excitation (∼524 nm), energy transfer from conduction band of CsPbBr3 QDs to 4S3/2 energy level of Er3+ which significantly enhances PL emission of Er3+ in near infrared region (∼1535 nm, 4I13/2 → 4I15/2). These results provide a facile approach to enhance and regulate PL emission of Er3+ in near infrared region.

Partially recrystallized triplex-phase medium Mn steel strengthened by B2 precipitates

We report the annealing time-dependent microstructure–mechanical properties relationship of cold-rolled and annealed Fe–6Mn-0.05C–3Ni-1.5Al (wt.%) steel, containing Ni and Al to form NiAl B2 precipitates. The microstructures of the investigated materials after cold-rolling and intercritical annealing show a mixture of lath and equiaxed zones consisting of a triplex matrix phase (ferrite, austenite, and tempered martensite) with B2 precipitates. Recovery of the deformed martensite in the cold-rolled microstructure during annealing resulted in the formation of sub-boundaries and a continuous transition from partially-recrystallized tempered martensite to recrystallized ferrite. The investigated materials showed a decrease in strength and an increase in ductility and strain-hardening rate with increasing annealing time. A decrease in the fraction of tempered martensite, an increase in the fraction of recrystallized ferrite/austenite grains, and enhanced transformation-induced plasticity (TRIP) kinetics with increasing annealing time led to enhanced ductility and strain hardening of the materials. The mixed presence of less stable equiaxed austenite and more stable lath austenite resulted in sustained TRIP effect during tensile deformation and superior strain hardening capacity of the specimen annealed for 24 h. This study provides a novel microstructure design solution for medium Mn steels, and further optimization of the composition and processing will lead to the development of medium Mn steels with superior mechanical performance.

Rapid annealing of an ultralow carbon steel: in-depth exploration of the microstructure-mechanical properties evolution

The elaborate comparisons of microstructure, mechanical properties and texture evolution between rapid annealing and conventional industrial annealing in an ultralow carbon plate cold commercial steel were performed. And in-depth exploration of the microstructure-mechanical properties evolution by different rapid annealing parameters was investigated. Results manifested that optimal balance between tensile strength (494.07 MPa) and elongation (24.7%) accompanied with a product of strength and elongation of 12.20 GPa·% was achieved in steel rapid annealed at 650 °C for 15 s. The increased yield strength (171.03 MPa) was attributed to the refined ferrite grains (7.96 μm) providing the better grain refinement effect by the rapid annealing. While the decreased ductility (24.70%) in rapid annealed steel was ascribed to the deteriorated work hardening and {111} texture. The deteriorated work hardening was synergistically ascribed to the refined ferrite grains accompanied by suppressed cementite particles, and the stored geometry necessary dislocations. Furthermore, the intensity of {111} texture increased with the annealing time accompanied by the decreased α texture, thus generating a weak γ texture by rapid annealing although α and γ texture both formed. In addition, the ferrite grains were refined and uniformized by rapid annealing, manifesting the strong grain refinement effect by the recrystallization nucleation density and nucleation driving force provided by rapid annealing although with a high annealing temperature. More importantly, the greatly increased tensile strength and enough elongation by rapid annealing process highlighted one novel method to further improve the strength in ultra-low carbon steel with reasonable elongation. What's more, the whole annealing process was radically shortened from tens of hours (16–17 h) into seconds (2–15 s) by rapid annealing.

An Amorphous Native Oxide Shell for High Bias-Stress Stability Nanowire Synaptic Transistor.

The inhomogeneous native oxide shells on the surfaces of III-V group semiconductors typically yield inferior and unstable electrical properties metrics, challenging the development of next-generation integrated circuits. Herein, the native GaOx shells are profitably utilized by a simple in-situ thermal annealing process to achieve high-performance GaSb nanowires (NWs) field-effect-transistors (FETs) with excellent bias-stress stability and synaptic behaviors. By an optimal annealing time of 5min, the as-constructed GaSb NW FET demonstrates excellent stability with a minimal shift of transfer curve (ΔVth ≈ 0.54V) under a 60min gate bias, which is far more stable than that of pristine GaSb NW FET (ΔVth ≈ 8.2V). When the high bias-stress stability NW FET is used as the chargeable-dielectric free synaptic transistor, the typical synaptic behaviors, such as short-term plasticity, long-term plasticity, spike-time-dependent plasticity, and reliable learning stability are demonstrated successfully through the voltage tests. The mobile oxygen ion in the native GaOx shell strongly offsets the trapping states and leads to enhanced bias-stress stability and charge retention capability for synaptic behaviors. This work provides a new way of utilizing the native oxide shell to realize stable FET for chargeable-dielectric free neuromorphic computing systems.

Effects of Continuous and Cycled Annealing on the Physicochemical Properties and Digestibility of Water Caltrop Starch.

The effects of treatment time of continuous annealing (ANN) and cycle numbers of cycled ANN on the structural, physicochemical, and digestive properties of water caltrop starch were studied under 70% moisture at 65 °C. It was found that continuous and cycled ANN have no significant effects on the morphology of starch granules. However, the relative crystallinity and content of resistant starch increased pronouncedly, possibly due to crystalline perfection, which also led to the rise in gelatinization temperature and the narrowed gelatinization temperature range of starch. The treatment time in continuous ANN generally showed a pronounced effect on the rheological properties of water caltrop starch. During pasting, the breakdown viscosity and setback viscosity of all treatment decreased, implying that ANN modified starch was less susceptible to the condition in heating and continuous shearing, and less likely to cause short-term retrogradation. In contrast, peak viscosity decreased with increasing treatment time of continuous ANN, indicating crystalline perfection restricted the swelling of starch granules and viscosity development during pasting process, which was consistent with the results of steady and dynamic rheological evaluation. All ANN-modified samples showed pseudoplastic behavior with weak gel viscoelastic characteristic. Under a total annealing time of 96 h, the pasting and rheological properties of water caltrop starch were essentially less affected by annealing cycle numbers. However, multistage ANN showed stronger resistance to enzyme hydrolysis.

The Study of Hardness Evolution during the Tempering Process of 38MnB5Nb Ultra-High-Strength Hot Stamping Steel: Experimental Analysis and Constitutive Models

To elucidate the hardness evolution behaviors for 38MnB5Nb ultra-high-strength hot stamping steel, a series of tempering processes with varying tempering temperatures and times were carried out with a dilatometer. Meanwhile, the hardness of each sample was measured after dilatometer experiments. The results indicated that the tempering process parameters (including the tempering temperature and time) play an important role in the hardness of the studied steel. The hardness of 38MnB5Nb ultra-high-strength hot stamping steel at the quenched state is about 580 Hv, while it is 240 Hv for the quasi-annealed state. As the tempering time extends, the hardness is decreased sharply at the initial stage; then, the hardness is decreased in a quasi-linear trend with a slight slope; finally, the hardness almost keeps a constant value, which depends on the tempering temperature. In addition, the tempering process has a big effect on the mechanical properties of 38MnB5Nb ultra-high-strength hot stamping steel by increasing the product of the strength and elongation by about 40%.

Unexpected non-monotonic changing in the heterogeneity of glasses during annealing

The heterogeneity of glasses has critical influences on the properties. How heterogeneity evolves during annealing is an intriguing cutting-edge question. In this work, the heterogeneity of the annealed metallic and polymer glasses has been studied systematically by using stress relaxation and nanoindentation tests. The stress relaxation processes are analyzed using Kohlrausch-Williams-Watts (KWW) equation. We surprisingly find that the heterogeneous factor βKWW in KWW equation does not change monotonously but increases first and then decreases along with the annealing time. The two-stage process implies that glasses do not evolve as expected toward the more homogeneous glassy state but become homogeneous first and then more heterogeneous. This is further verified by the evolution of critical shear stress for local plasticity. It is revealed that the two-stage process is correlated with different relaxation modes, which is further interpreted using a phenomenological model. These findings not only give insights into understanding the nature of glasses, but also are useful for designing glasses with superior properties.

Effect of annealing time on the structure and conductivity of amorphous polycarbosilane-derived silicon carbide ceramics

The isothermal evolution of free carbon structure and conductivity of polycarbosilane-derived SiC(O) ceramics pyrolyzed at 1100 °C, 1200 °C, and 1300 °C for 3–55 h was systematically investigated using different characterization methods, which include X-ray photoelectron spectrophotometer (XPS), Raman spectroscopy, Electron Paramagnetic Resonance (EPR), and Transmission electron microscope (TEM). At 1100 °C, increasing annealing time led to structural rearrangement of free carbon, anti-growth behavior, higher degree of order, and increasing and then decreasing number of defects. At 1200 °C, a complex structural evolution of free carbon was observed, which followed the sp3-to-sp2 transition and increased the ordering degree. At 1300 °C, increasing annealing time resulted in both lateral growth and increasing ordering of free carbon, which enhanced the carbon cluster size and decreased the number of defects. Enhanced sample conductivity with prolonged annealing time was observed and is discussed based on structural evolution of SiC(O) ceramics at different temperatures.

Molecular dynamics study influence of factors on the structure, phase transition, and crystallization of the Ag1-xAux, x = 0.25, 0.5, 0.75 alloy

In this research, Molecular Dynamics (MD) method simulations were used to study the influence factors such as concentration of Au doping in Ag1-xAux alloy, atomic number, temperature, annealing time on the structure, transition process phase, and crystallization of Ag1-xAux alloy by choosing Sutton-Chen (SC) interaction potential field and periodic boundary conditions. The results show that, when the concentration of Au doping in Ag1-xAux alloy increases, the number of crystallization processes decreases at temperature, while the number of atoms and the annealing time at the glass temperature Tg = 900 K increase, the process results for crystallization increase. The crystallization process is expressed through the number of structural units Hexagonal Close Packed (HCP), Body-Centered Cubic (BCC) and Amorphous (Amor), and the total energy of the system (Etot). The results show that there is a significant influence of doping concentration, atomic number, temperature, and annealing time. Then the length of the links Ag-Ag, and Au-Au varies greatly. The link Ag-Au remains constant because with the r = 2.82 Å value, the total energy of the system and the size of the material change very little. During the phase transition, the length of the links (r), the total energy of the system, size (Etot), and the number of FCC, HCP, BCC, and Amor structural units change significantly. The results obtained on Ag1-xAux alloy can serve as a basis for future experimental studies.

Tracing titanomagnetite alteration with magnetic measurements at cryogenic temperatures

SUMMARY Titanomagnetite containing up to 0.6–0.7 Ti atoms per formula unit is a primary magnetic mineral phase in submarine basalts and in some terrestrial volcanic rocks. On a geological timescale, it often undergoes alteration, forming new magnetic phases that may acquire (thermo)chemical remanent magnetization. The initial stage of this natural process can be modelled by prolonged laboratory annealing at moderately elevated temperatures. In this study, our goal is to characterize the alteration products resulting from annealing a submarine basalt containing homogeneous titanomagnetite Fe3−xTixO4 (x ≈ 0.46) at temperatures of 355, 500 and 550 °C for up to 375 hr, by examining their magnetic properties over a wide range of temperatures. The effect of extended annealing is most apparent in the low-temperature magnetic properties. In the fresh sample, a magnetic transition is observed at 58 K. Below the transition temperature, the field-cooled (FC) and zero-field-cooled (ZFC) saturation isothermal remanent magnetization (SIRM) curves are separated by a tell-tale triangular-shaped area, characteristic for titanomagnetites of intermediate composition. The room-temperature SIRM (RT-SIRM) cycle to 1.8 K in zero field has a characteristic concave-up shape and is nearly reversible. For the annealed samples, the magnetic transition temperature shifts to lower temperatures, and the shape of the curves above the transition changes from concave-up to concave-down. The shape of the RT-SIRM cycles also progressively changes with increasing annealing time. The SIRM loss after the cycle increases up to ∼30 per cent for the samples annealed for 375 hr at 355 °C, and for 110 hr at 500 and 550 °C. The Curie temperatures of the newly formed magnetic phases exceed the Curie temperature of the fresh sample (205 °C) by up to 350 °C. While this effect is most commonly attributed to extensive single-phase oxidation (maghemitization), the behaviour observed at cryogenic temperatures appears incompatible with the known properties of highly oxidized titanomaghemites. Therefore, we propose that, at least in the initial stage of the ‘dry’, that is, not involving hydrothermalism, alteration of titanomagnetite, temperature- and time-controlled cation reordering is the primary mechanism driving changes in both low- and high-temperature magnetic properties.