Onset Of Crystallization Research Articles

Soft magnetic cobalt based amorphous alloys with low saturation induction

The influence of the concentration of alloying components on thermal stability, magnetic and electrical properties of amorphous alloys of Co73-66Fe4,6-3Cr0-9(B,Si)22-29 system was studied by methods of differential scanning calorimetry, XRD, resistometry and magnetometry. The crystallization of several alloys with advanced magnetic characteristics was studied. At continuous heating of the ribbons, either primary or eutectic crystallization was observed depending on the chemical composition of these alloys. Certain tendencies in the anomalous behavior of temperature dependence of electrical resistance of ribbons were revealed. By increasing chromium and metalloids concentrations, we obtained the alloys with relatively low saturation induction and large difference between the Curie temperature and the temperature of crystallization onset. The heat treatment regimes to obtain the best magnetic properties of these alloys were found. Prospective applications of Co73-66Fe4,6-3Cr0-9(B,Si)22-29 amorphous ribbons for fabrication of high sensitive sensors of magnetic field were discussed.

Physical, Optical, Structural and Thermal Studies of xWO3 + (30 − x)As2O3 + 70TeO2 (where x = 10, 20, 30 mol%) glasses by UV–vis, Raman, IR and DSC Studies

Optical, Structural and Thermal properties of xWO3 + (30 − x)As2O3 + 70TeO2 glass system (where x = 10, 20, & 30 mol%) have been investigated by Optical absorption, Raman & FT-IR, and DSC studies respectively. Physical properties such as, density (ρ), molar volume (Vm), oxygen packing density (OPD), and oxygen molar volume (Vo) are determined for all the glass samples. Density and oxygen packing density (OPD) of glasses have been increasing monotonically with increase in WO3 content in the range 6.52–6.99 g m/cc, and 85.951–88.690 mol/l respectively. These values are correlated with molar volume and oxygen molar volume that are decreasing linearly with increase in WO3 content (10–30 mol%) falling in the range 26.745–25.932 cm3/mol and 11.628–11.274 cm3/mol respectively. The optical transitions and electronic band structure has also been investigated through optical absorption spectra. The fundamental absorption edge is measured in the short wavelength of the visible region, that shows, glasses exhibits the redshift (449 → 483 nm), at photon energy in the range 2.89–2.70 eV for direct allowed transitions. Raman and IR spectral studies reveals that the glass network consists of TeO4 (tbp), TeO3/TeO3+1 (tp), WO6 (octahedral), WO4 (tetrahedra) and AsO3 groups as basic structural units. Thermal behavior of the glasses was studied in terms of glass transition temperature (Tg), onset crystallization (To), peak crystallization (Tp) temperatures, and the thermal stability (ΔT) from DSC thermogrms. In the present glass system, it is found that the glass transition temperature (Tg = 331 → 341 → 353 °C) and thermal stability (ΔT = 56 → 93 → 120 °C) both increases linearly with increase in concentration of WO3 (10, 20, & 30 mol%).

Analytical characterization of polyamide 11 used in the context of selective laser sintering: Physico-chemical correlations

Polyamide 11 is an attractive material for additive manufacturing, however, in the selective laser sintering process it is subject to significant thermally induced stress. Suitable analytical methods are necessary to indicate any changes in the material properties. In this work, thermally stressed powder samples and printed tensile bars were analyzed by size exclusion chromatography-multi angle laser light scattering and differential scanning calorimetry. Based on the molecular weight distribution, crystallization and melting temperatures, ageing states of the investigated powders can be defined and transferred to the particles of the printed components. As a result, thermal stress led to an increase in molar mass and polydispersity. Moreover, calorimetric measurements indicated a delayed nucleation process as well as a decrease in polymorphism. Additionally, polymeric material with lower polydispersity values across the tensile bars could lead to decreasing elongation at break (εB) values. For the crystallization onset temperature the opposite effect on εB was observed.

Monitoring the Crystallization Behavior of Hydrogenated Coconut Oil Using Ultrasonic Phase Velocity

AbstractFat crystals are known to affect the stability and applicability of fat‐containing foods, and changes in quality during low‐temperature preservation. Therefore, understanding fat crystallization behavior is important for product development and quality control. Ultrasonic measurement is a nondestructive, noncontact, and highly versatile on‐line measurement method. Herein, we aim to verify the applicability of the ultrasonic characteristics to monitor fat crystallization behavior of hydrogenated coconut oil (HCO) using ultrasonic phase velocity (UPV) at 1.98 MHz under different cooling rates and with different emulsifier additives. The UPV was found to increase with decreasing HCO temperature, and the UPV‐temperature relation had an inflection point at approximately 20–25 °C. The inflection point coincided with the crystallization onset temperature determined by differential scanning calorimetry. The density of HCO was found to increase with decreasing temperature, while the compressibility of HCO decreased with the temperature. From the Laplace equation established between the UPV (c) and the density (ρ), c = (ρβ)−0.5, the increase in the compressibility (β) of UPV indicates a decrease in ρβ. Consequently, since the density increases with cooling, the dominant factor that causes an increase in UPV is a reduction in compressibility. The UPV of the solid phase was highly correlated with the crystallization enthalpy (R2 = 0.99).

Effect of CeO2 and Eu2O3 on the calorimetric behavior of Si–Al–Zn–K–Ti oxide glass

Glasses and glass-ceramics based on SiO2 have attracted a large attention. In this work, the thermal properties and crystallization kinetics of Si–Al–Zn–K–Ti glasses are investigated. Based on the thermal parameters derived from the differential scanning calorimetry technique ran upon various heating rates, the characteristic glass transition temperature, onset crystallization temperature and crystallization temperature were extracted. The crystallization peaks are carefully investigated by Kissinger, Ozawa and modified-Kissinger methods. Avrami index and the dimensionality of the crystal growth vary from 2 to 4 at the same time that crystallization activation energy decrease from 177.80 kJ/mol to 145.40 kJ/mol in Ozawa method and the thermal stability reaches to 177.20 ΔC° by doping with 0.5 wt% of CeO2 and 0.5 wt% of Eu2O3, both in excess. Our results confirm the role of rare earth ions in the crystallization kinetics, as well as improvement in the glass thermal stability.

Effects of Nb Addition and Heat Treatment on the Crystallization Behavior, Thermal Stability and Soft Magnetic Properties of FeSiBPCuC Alloys

In this paper, the effect of the replacement of Fe by Nb on the glass forming ability (GFA), the thermal stability and the crystallization behavior of Fe84.5−xSi0.5B10.5P3.5C0.7C0.3Nbx (x = 0, 1, 2) alloys were investigated. The results show that the addition of Nb increases the GFA. Increasing Nb content can enhance the first onset crystallization temperature (Tx1), the second onset crystallization temperature (Tx2) and ΔTx (ΔTx = Tx2 − Tx1), which broadens the range of annealing temperatures. The coercivity (Hc) of ribbons decreases with increasing Nb content after annealing at a low heating rate and reach as a minimum of 24.5 A/m when the Nb content is 2 at.%. The process of annealing at a high heating rate distinctly decreases Hc, and all samples present excellent soft magnetic properties. The nanocrystalline alloy exhibits the lowest Hc of 6.4 A/m after annealing at 460 °C for 5 min.

Isothermal crystallization kinetics of (Cu60Zr25Ti15)99.3Nb0.7 bulk metallic glass

This paper reports the crystallization kinetics of (Cu60Zr25Ti15)99.3Nb0.7 bulk metallic glass under isothermal conditions. Differential scanning calorimetry (DSC) has been employed for isothermal annealing at ten different temperatures prior to the onset of crystallization (To) temperature. X-ray diffraction and transmission electron microscopy have been used to confirm the amorphous structure of the as cast sample. Crystallized volume fractions (x) are calculated from the exothermic peaks of DSC scans. Crystallized volume fractions (x) against time show sigmoidal type of curves as well as the curves become steeper at higher annealing temperatures. Continuous heating transformation diagram has been simulated to understand the stability of the bulk metallic glass. Crystallization kinetics parameters are calculated using Arrhenius and Johnson–Mehl–Avrami equations. Activation energy (Ea) and Avrami exponential factor (n) have exhibited strong correlation with crystallized volume fraction (x). The average activation energy for isothermal crystallization is found to be 330 ± 30 kJ/mol by Arrhenius equation. Nucleation activation energy (Enucleation) is found to be higher than that of growth activation energy (Egrowth). The Avrami exponential factor (n) indicates about the diffusion controlled mechanism of the nucleation and three-dimensional growth.

Effect of bismuth incorporation on thermal properties of quaternary chalcogenide glass Se80Te15-xCd5Bix (x=0,5,10) alloys

Differential scanning calorimetry has been employed to investigate the thermal properties of Se80Te15-xCd5Bix (x = 0, 5, 10) glass system. The Variation of characteristic temperatures such as glass transition temperature (Tg), onset crystallization temperature (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) are studied as a function of composition and heating rate. A stepwise increase in values of characteristic temperatures has been observed with the increase in heating rate. Further, obtained values of characteristic temperatures display decreasing trend with increase in bismuth concentration. The compositional and heating rate dependence of Thermal parameters such as glass forming ability (ΔT), thermal stability (Hg), enthalpy (ΔH) and entropy (ΔS) has been investigated. It has been observed that ΔT and Hg have lowest and highest values for Se80Te5Cd5Bi10 and Se80Te15Cd5 compositions respectively. Avrami index (n) and activation energy for crystallization (Ec) have been calculated for all the samples. Values of n obtained for Se80Te15Cd5, Se80Te15Cd5 Bi5 and Se80Te5Cd5Bi10 compositions are found to be 1.44, 2.16 and 2.16 respectively. Based on the obtained values of n, the nucleation process in alloys is discussed. It is noteworthy to mention that least value of Ec is observed for the alloy Se80Te5Cd5Bi10 containing the highest amount of bismuth. Furthermore, calculated thermal parameters are used to anticipate the electrical switching behavior of the alloys.

Disequilibrium Rheology and Crystallization Kinetics of Basalts and Implications for the Phlegrean Volcanic District

Large volcanic eruptions are frequently triggered by the intrusion of hot primitive magma into a more evolved magma-chamber or -mush zone. During intrusion into the cooler mush zone, the basaltic magma undergoes crystallization, which in turn releases heat and volatiles to the mush. This should cause a drop in bulk mush-viscosity, potentially leading to its mobilization and even eruption. The non-linear changes in the transport properties of both magmas during this interaction modulate how the magmas accommodate deformation during both interaction and ascent. As such, this interaction represents a complex disequilibrium phenomenon, during which the material properties guiding the processes (dominantly viscosity) are in constant evolution. Such a scenario highlights the importance of non-isothermal sub-liquidus processes for the understanding of natural magmatic and volcanic systems and underlines the need for a rheological database to inform on, and to model, this interaction process. Here we present new experimental data on the disequilibrium rheology of the least evolved end-member known to be involved in magma mixing and eruption triggering as well as lava flow processes in the Phlegrean volcanic district (PVD). We measure the melt´s subliquidus rheological evolution as a function of oxygen fugacity and cooling rate and map systematic shifts in its rheological “cut off temperature; Tcutoff” (i.e. the point where flow ceases). The data show that 1) the rheological evolution and solidification behavior both depend on the imposed cooling-rate, 2) decreasing oxygen fugacity decreases the temperature at which the crystallization onset occurs and modifies the kinetics of melt crystallization and 3) the crystallization kinetics produced under dynamic cooling are significantly different than those observed at or near equilibrium conditions. Based on the experimental data we derive empirical relationships between the environmental parameters and Tcutoff. These empirical descriptions of solidification and flow may be employed in numerical models aiming to model lava flow emplacement or to reconstruct the thermomechanical interaction between basalts and magma mush systems. We further use the experimental data in concert with models of particle suspension rheology to derive the disequilibrium crystallization kinetics of the melt and its transition from crystallization to glass formation.

Crystallization, microstructure and polymorphic properties of soybean oil organogels in a hybrid structuring system

Organogels are semi-solid systems where the liquid phase is immobilized for three-dimensional network self-sustained formed by structuring agents capable to hold a larger quantity of liquid oil. The use of these structuring agents or crystallization modifiers, as specific triacylglycerols, emulsifiers and high molecular weight - high melting point lipids, have been recognized as the main alternative for obtaining low saturated fats for food formulation. The aim of this work was to evaluate the crystallization, microstructure and polymorphism properties of hybrid soybean oil (SO) organogels, formulated with 6% (w:w) of structuring agents through a centroid simplex system added singly, in binary or ternary association of candelilla wax (CW), sorbitan monostearate (SMS) and fully hydrogenated palm oil (FHPO). The thermal behavior, crystallization kinetics, physical stability by temperature cyclization, microstructure and polymorphism were evaluated. FHPO and CW increased the stability and ability to form crystalline networks in organogels, while SMS accelerated the crystallization process. The structuring agents increased the initial and final crystallization temperatures, even as the melting temperatures and the enthalpy values of organogels. Time-temperature cyclization (cyclization 1: 5 °C/48 h + 35 °C/24 h + 5 °C/24 h; cyclization 2: 35 °C/48 h + 5 °C/72 h) showed that all the systems resulted in firm and stable organogels, except when SMS or FHPO were used singly. CW promoted formation of denser crystalline networks with higher solids content, quick crystallization onset and higher melting points that indicates adequate thermal resistance; while FHPO increased the solid content although it was effective to obtain organogels only at the cooling temperature (5 °C). The binary interaction of FHPO + CW increased the thermal resistance of organogels; and the interactions among SMS + CW and SMS + CW + FHPO although it was effective to obtain organogels. Regardless of the presence and proportions of structuring agents, organogels were characterized by beta polymorphism.

Critical analysis of the different glass stability criteria in chalcogenide glasses

In this endeavor, various glass stability criteria have been discussed by using two ternary alloys of SeTePb glassy system. These criteria can be obtained based on the interrelationship between the characteristic temperatures. Differential Thermal Analysis measurements under the non-isothermal conditions can be used for this purpose. Two groups of these criteria according to the onset and peak crystallization temperaturas have been studied as a function of composition. The heating rate and composition dependences of all criteria concluded that the C ZW and C LX criteria are not suitable to discuss the glass stability (GS) for the studied compositions. The extracted data from various GS criteria and their relative change parameters reveal that the criterion C YL of Yuan et al is best and it exhibits the best ability for apprising the GS.

Annealing induced structural evolution in feldspar dental glass-ceramics investigated by solid-state NMR spectroscopy

Glass-ceramics are an attractive oxide-based material routinely used for biomineral repair such as porcelain veneers in dental crown applications. The short- and long-range structure of a commercial glass-ceramic feldspar material, VITA VM9, has been investigated as a function of annealing temperature. The relative amounts of amorphous and crystalline components were monitored using a combination of powder X-ray diffraction and solid-state 23Na, 27Al, and 29Si nuclear magnetic resonance spectroscopy. The insight gained from this study was then applied to analyze a series of synthetic lab-grade ceramics Na0.5K0.5Al1–xMxSi3O8 (x ​= ​0.1; M ​= ​B, Al, Ga), whose onset of crystallization was found to resemble that of the commercial ceramic material.

Impact of phospholipid digests and bile acid pool variations on the crystallization of atazanavir from supersaturated solutions

Oral delivery of poorly water-soluble drugs (PWSDs), which predominate the development pipeline, poses significant challenges. Weakly basic compounds, such as atazanavir, represent a critical class of PWSDs as even the administration of the crystalline solid may invoke supersaturation during gastric-intestinal transfer. The absorption advantage afforded by this supersaturated state can be offset by inherent metastability and a tendency to revert to the lower energy crystalline state. Therefore, it is important to understand the physiological factors that can affect crystallization to improve in vitro-in vivo predictiveness and to regulate inter-individual responses. The first aim of this study was to elucidate the influence of lyso-phosphatidylcholine (lyso-PC) and sodium oleate on crystallization, as the products of phosphatidylcholine (PC) hydrolysis and the major lipid components of human intestinal fluid (HIF) and updated fasted state simulated intestinal fluid version 3 (FaSSIF-V3). Secondly, as an individual’s bile acid pool is unique, dynamic and related to gut microbiome community structure, it was of interest to investigate the impact of bile acid pool variations on crystallization from supersaturated solutions.To study the effect of PC hydrolysis, media with 2.8 mM sodium glycocholate (GCA) and sodium taurocholate (TCA) (1:1) but varying concentrations of PC, lyso-PC or sodium oleate were prepared. To investigate the influence of inter-individual variations in intestinal bile acid pool size and composition, media simulating the profiles of six healthy Western volunteers were prepared based on previously published data. The crystalline and amorphous solubility of atazanavir, a weakly basic antiretroviral drug, was firstly determined in these media. Nucleation-induction time experiments were then performed at an equivalent extent of supersaturation in each medium (corresponding to the amorphous solubility).At a constant level of GCA/TCA, increasing concentrations of both PC and lyso-PC accelerated crystallization onset; however, this was at least 2-fold more pronounced with lyso-PC at a given molar concentration. The addition of sodium oleate was also observed to induce crystallization. Interestingly, substituting GCA/TCA with the bile salt fraction of other biorelevant media partially circumvented the crystallization-inducing effect of phospholipids and their digests. The presence of dihydroxy bile salts was found to be particularly significant in decelerating the crystallization process. Nucleation-induction times in simulated volunteer pools were found to be dependent upon bile salt concentration, with higher bile salt levels generally prolonging supersaturation. Differences of up to 6-fold were observed.This study demonstrates that the choice of biorelevant medium used to evaluate supersaturating formulations can influence the observed crystallization kinetics. While the presence of lyso-PC and sodium oleate in FaSSIF-V3 medium is more physiologically relevant, further attention should be paid to the bile salt fraction when designing a biorelevant medium for supersaturating formulations. In vivo, inter-individual differences in the amount and types of bile acids and phospholipids present may influence the behaviour of supersaturating formulations.

Direct observation of amorphous to crystalline phase transitions in Ge–Sb–Te thin films by grazing incidence X-ray diffraction method

Ge–Sb–Te (GST)-based PCM alloys are currently used in optical data storage. The crystallization of GST materials is the rate-limiting step for these devices, hence a deeper knowledge of the crystallization mechanism is crucial for insightful development of faster devices. In the present work, the diffraction patterns for GST-225 thin films are studied using the in situ Grazing Incidence X-ray Diffraction method upon heating. It is shown that initial amorphous film in the temperature range from 120 to 140 °C is crystallized into two phases-cubic GST-225 (Fm$${\bar{3}}$$m), and trigonal GST-147 (P$${\bar{3}}$$m1). The crystallized film is stressed and highly textured, and should be characterized by the value of the lattice parameters averaged over all crystallographic planes. The structural transition of GST-225 from cubic to trigonal phase begins at T > 180 °C. The appearance of large-scale inhomogeneities in GST-225 film at T ≥ 100 °C indicates that the process of rearrangement of atoms Ge, Sb, and Te in the as-deposited amorphous film begins long before the onset of crystallization.

Evolution of the magnetic anisotropy and magnetostriction in Co-based amorphous alloys microwires due to current annealing and stress-sensory applications

Abstract In this paper, the transformation in easy-axis anisotropy and magnetostriction in Co-rich amorphous microwires by dc current annealing has been studied with the aim to realize stress-sensitive magnetization process and magnetoimpedance (MI). With increasing the annealing current intensity I a n , the anisotropy and magnetostriction undergo non-monotonic changes owing to different processes occurring during annealing: structural relaxation, atomic pair ordering, atomic rearrangements, internal stress relief and phase transformation at the crystallization onset. At moderate values of I a n the induced anisotropy sets a near-circumferential easy direction whilst the magnetostriction parameter increases from a very low negative value in the as-cast state to positive values. At optimal combination of the induced anisotropy and positive magnetostriction a highly stress-sensitive MI behavior is observed which is important for stress-sensory applications. At these conditions, the impedance vs. magnetic field plots may change shape in the presence of tensile stress which at zero field is accompanied by a huge impedance change in the range of 70–162% per 100 MPa.

Compositional dependence of crystallization temperatures and phase evolution in hafnia-zirconia (HfxZr1−x)O2 thin films

Polymorphic (HfxZr1−x)O2 (HZO) thin films exhibit ferroelectric, dielectric, and antiferroelectric properties across a wide compositional range due to the existence of orthorhombic, monoclinic, and tetragonal phases. To better understand the phase stability across the HfO2–ZrO2 compositional range, we investigate the structural evolution of HZO thin films in situ via high-temperature x-ray diffraction (HTXRD) for five different compositions [ZrO2, (Hf0.23Zr0.77)O2, (Hf0.43Zr0.57)O2, (Hf0.67Zr0.33)O2, and HfO2]. The real-time monitoring of HZO crystallization reveals a competing driving force between the tetragonal and monoclinic phase stabilities for HfO2-rich vs ZrO2-rich compositions. Additionally, we confirm an XRD peak shift toward lower 2θ with increasing temperature in ZrO2, (Hf0.23Zr0.77)O2, and (Hf0.43Zr0.57)O2 films, which we ascribe to the appearance of a metastable orthorhombic phase during heating. A monotonic trend for the onset crystallization temperature is reported for five compositions of HZO and reveals an increase in onset crystallization temperature for HfO2-rich compositions. Relative intensity fraction calculations suggest a higher fraction of monoclinic phase with increasing annealing temperature for (Hf0.67Zr0.33)O2. This study of phase stability and onset crystallization temperatures offers insight for managing the thermal budget for HZO thin films, especially for temperature-constrained processing.

Microwave-assisted Synthesis of 1-(perfluorohexyl)-3-methylimidazolium iodide

ABSTRACTA perfluorinated ionic liquid, 1-(perfluorohexyl)-3-methylimidazolium iodide, was synthesized via microwave reaction and compared to a non-fluorinated analog. Typically, the synthesis of fluorinated ionic liquids involves long reaction times and multiple steps. We have demonstrated a shortened synthesis and a more straightforward procedure, by using a microwave reactor for the microwave-assisted synthesis of 1-(perfluorohexyl)-3-methylimidazolium iodide. The addition of fluorinated alkyl chains on imidazolium ionic liquid cations increases the molecular free volume of the ionic liquid which is beneficial for increasing CO2 physisorption. Computational and experimental data shows an increased CO2 solubility and capacity for fluorinated ionic liquids. The perfluoroalkyl functionalized ionic liquid is characterized using 1H and 19F NMR spectroscopy, FTIR spectroscopy, and DSC. By DSC, a crystallization onset is near -31 °C and while the onset of the melting point between -30 and -17 °C.

Upconversion luminescence of germanate nanophosphors activated by Er3+ and Yb3+ ions

The crystallophores of the composition Sr2La8(1x-y)ErxYbyGe6O26 (x = 0.01, 0.05, 0.075, 0.1, 0.15) were synthesized. Nanophosphores in the amorphous state were obtained for the first time by the method of pulsed electron beam evaporation using a phosphor of the composition Sr2La7.85Er0.075Yb0.075Ge6O26 with the structure of oxyapatites as a target. DSC-TGA analysis was performed to determine the temperature stability and the onset of crystallization of the nanosample. A change in the Raman spectra of the samples with a decrease in the particle dimension from the bulk to nanoscale state was found. The spectral characteristics of the upconversion photoluminescence of samples in polycrystalline and nano-amorphous states are studied. It has been shown that luminescence is influenced by nonradiative processes between different transitions of Er3+ ions. There is a threshold population of the Er3+ and Yb3+ levels (level 2F5/2) in the region of relatively low pumping powers of nanosamples by laser radiation with a wavelength of λex = 980 nm. Above this threshold a sharp increase in the intensity of upconversion photoluminescence occurs.

Short-Range Ordering Structure of the Cu2In Intermetallic Compound in the Precrystallization Temperature Range

The structure of Cu2In melts is investigated by the X-ray diffraction method within a temperature range close to the temperature of onset of crystallization. We analyze the structural factors and functions of the radial distribution of atoms computed by the method of Fourier transforms. The results of structural investigations are compared with the literature data on the enthalpy of mixing and thermodynamic activity. It is shown that the short-range ordering structure is microinhomogeneous and has a heterocoordinated distribution of atoms.

Early sulfide saturation in arc volcanic rocks of southeast China: Implications for the formation of co-magmatic porphyry–epithermal Cu–Au deposits

It is widely considered that arc magmas are highly oxidized, and can thus dissolve a large amount of sulfur, thereby preventing significant sulfide saturation prior to fluid saturation. Therefore, chalcophile metals (e.g., Cu and Au) are retained in the magma and finally extracted by exsolved hydrothermal fluids. To test this hypothesis, we analyzed the abundances of platinum-group elements (PGEs) in a suite of arc volcanic rocks, which are the extrusive counterparts of magmas associated with the world-class Zijinshan porphyry–epithermal Cu–Au ore district in SE China. All of these volcanic rocks are depleted in PGEs (e.g., Pd = 0.02–0.40 ppb) in comparison with fertile arc magmas, and the PGE contents decrease with decreasing MgO from basalt to dacite. The results show that the parental magmas for these rocks reached sulfide saturation before they evolved to 7 wt.% MgO, which is earlier than the onset of magnetite crystallization. Sulfide liquid and monosulfide solid solution (MSS) were removed from the magma before it evolved into a dacitic composition. This process extracted most of the Au and Cu from the magma. Modeling results indicate that Au concentrations would not exceed 7–10 times the Pd concentrations in the residual silicate magma, irrespective of the partition coefficients between the sulfide and silicate melt. Given the low Pd contents in dacitic arc magmas worldwide, depletion of Au and Cu might be a common feature of highly evolved arc magmas. Thus, the hydrothermal ore fluids separated from such evolved arc magmas would not contain enough metals to form the giant Zijinshan porphyry–epithermal Cu–Au ore district. We propose a model in which the magmas parental to the arc volcanic rocks achieved S saturation, and thus large amounts of sulfides accumulated in the underlying magma chamber before the magmas were extruded from depth to the surface. During solidification of the magma chamber, these deposits formed from exsolved magmatic hydrothermal fluids that dissolved abundant pre-existing magmatic Cu–Au-rich sulfide assemblages. Release of large amounts of Au, Cu and S to the ore-forming aqueous fluids by dissolution of sulfides can account for the metal and S budgets of giant porphyry–epithermal Cu–Au deposits.