Peritectic Melting Research Articles

Textures of Peritectic Crystals as Guides to Reactive Minerals in Magmatic Systems: New Insights from Melting Experiments

Peritectic crystals in igneous rocks may be derived from either the source or country rocks, or may have formed by reactive assimilation of source-inherited solids, primary magmatic minerals during self- or magma mixing, or country-rock xenoliths or xenocrysts. Identifying such peritectic crystals is important for constraining the components and textures of igneous rocks and the underlying processes of magmatic evolution. In this study we demonstrate that peritectic olivine formed in melting experiments crystallizes as clusters of euhedral to subhedral crystals. Olivine replacing orthopyroxene, amphibole, and phlogopite forms crystal clusters with distinct crystal to melt ratios, 2D surface area, grain boundary segmentation, and inclusion relations. In our experiments the textures of peritectic crystals are primarily controlled by the stability temperature and decomposition rate of reactive minerals. High-temperature minerals such as orthopyroxene slowly decompose to form high-density clusters of large crystals with long grain boundary segments. The SiO2-rich peritectic melt produced favours formation of melt inclusions. Low-temperature minerals such as amphibole and phlogopite rapidly decompose to form low-density clusters of small crystals with short grain boundary segments. The relatively SiO2-poor peritectic melt produced results in the formation of fewer melt inclusions. Host melt composition has a minor effect on the textures of peritectic olivine formed in the melting experiments of this study and previous contamination experiments, but affects the assemblages of the peritectic crystal clusters. Cluster density and 2D surface area of peritectic olivine tend to decrease, whereas grain boundary segment length increases with increasing experimental temperature and H2O content. Using textural criteria that distinguish olivine formed after different minerals in our melting experiments, we hypothesize that two olivine populations from a basaltic^andesitic lava flow of the Tatara^San Pedro volcanic complex, Chile, may be peritectic crystals formed after amphibole and orthopyroxene. Both amphibole and orthopyroxene are common in xenoliths preserved in some Tatara^San Pedro lava flows. One notable difference between the experimental and natural olivine crystals is that the natural olivine crystals have 2D surface areas and 2D grain boundary segments up to � 1000 and � 100 times larger, respectively, than those produced in our experiments. We propose that this size difference is primarily controlled by comparatively slow heating and decomposition of reactive crystals and textural coarsening of peritectic crystals during prolonged magma residence in the natural system.

Al-V (Aluminum-Vanadium)

The Al-V phase diagram was reviewed by [2001Oka]. Further investigation was needed because the phase diagram assessed by [1989Mur] disagreed significantly with the experimental result reported later by [2000Ric]. For example, the peritectic melting point of Al8V5 estimated at 1670 C by [1989Mur] must be 1408 C [2000Ric]. Figure 1 shows the Al-V phase diagram assessed by [2004Gon] by taking into account the result of [2000Ric]. The Al-V phase diagram was calculated earlier by [1987Kau] based on old data. [2006Kos] also calculated the phase diagram, but the data of [2000Ric] were overlooked. The AlV3 phase has not been discussed in all thermodynamic models described above. In order to attract attention, boundaries of the AlV3 phase has been copied from [1989Mur] in Fig. 1. References

Substrate Effect on Thermal Stability of Superconductor Thin Films in the Peritectic Melting

Systematic experiments were performed by in situ observation of the YBa(2)Cu(3)O(z) (Y123 or YBCO) melting. Remarkably, the superheating phenomenon was identified to exist in all commonly used YBCO thin films, that is, films deposited on MgO, LaAlO(3) (LAO), and SrTiO(3) (STO) substrates, suggesting a universal superheating mode of the YBCO film. Distinctively, YBCO/LAO films were found to possess the highest level of superheating, over 100 K, mainly attributed to the lattice match effect of LAO substrate, that is, its superior lattice fit with Y123 delaying the Y123 dissolving and inferior lattice matching with Y(2)BaCuO(5) (Y211) delaying the Y211 nucleation. Moreover, strong dependence of the thermal stability on the substrate material for Y123 films was also found to be associated with the substrate wettability by the liquid and the potential element doping from the substrate. Most importantly, the understanding of the superheating behavior is widely valid for more film/substrate constructions that have the same nature as the YBCO film/substrate.

Phase Range of the Type-I Clathrate Sr8AlxSi46–x and Crystal Structure of Sr8Al10Si36

Samples of the type-I clathrate Sr(8)Al(x)Si(46-x) have been prepared by direct reaction of the elements. The type-I clathrate structure (cubic space group Pm3n) which has an Al-Si framework with Sr(2+) guest atoms forms with a narrow composition range of 9.54(6) ≤ x ≤ 10.30(8). Single crystals with composition A(8)Al(10)Si(36) (A = Sr, Ba) have been synthesized. Differential scanning calorimetry (DSC) measurements provide evidence for a peritectic reaction and melting point at ∼1268 and ∼1421 K for Sr(8)Al(10)Si(36) and Ba(8)Al(10)Si(36), respectively. Comparison of the structures reveals a strong correlation between the 24k-24k framework sites distances and the size of the guest cation. Electronic structure calculation and bonding analysis were carried out for the ordered models with the compositions A(8)Al(6)Si(40) (6c site occupied completely by Al) and A(8)Al(16)Si(30) (16i site occupied completely with Al). Analysis of the distribution of the electron localizability indicator (ELI) confirms that the Si-Si bonds are covalent, the Al-Si bonds are polar covalent, and the guest and the framework bonds are ionic in nature. The Sr(8)Al(6)Si(40) phase has a very small band gap that is closed upon additional Al, as observed in Sr(8)Al(16)Si(30). An explanation for the absence of a semiconducting "Sr(8)Al(16)Si(30)" phase is suggested in light of these findings.

Development and investigation of WC–C fixed-point cells

Three cells of the WC–C peritectic fixed point with a temperature of about 3021 K were built and investigated. Two different sources of tungsten with nominal purities of 5N and 3N were used, and two different filling techniques were applied. There was no difference in plateau shapes between the cells. The 3N purity cell showed a small difference (0.22 K) in the melting temperature from the 5N cell, which indicates significant purification of initially contaminated tungsten. The typical melting range and repeatability of the observed peritectic melting plateaux were 100 mK and 15 mK, respectively. The melting point was stable and reproducible within 25 mK per two weeks. T90 temperature of the WC–C melting point was found to be (2747.6 ± 1.1) °C (k = 2). The observed freezing plateaux were flat and repeatable within 50 mK and 15 mK, respectively. The WC1−x–WC eutectic transition showed a melting temperature about 29 K lower than the peritectic one with a repeatability of about 0.2 K. The problem of deep supercooling is discussed and a method for its solution is shown and tested.

Hydrate formation in the system n-propanol–water

The phase diagram of the binary system n-propanol alcohol–water was investigated with use of differential thermal analysis and powder X-ray diffraction. The phase diagram has three groups of thermal effects, which can be considered as peritectic melting of three different hydrates (−60.0, −53.5, and −41.5 °C). At the same time, powder X-ray diffraction data indicate the existence of only one compound in this system (cubic unit cell, a = 12.09 ± 0.01 A and 12.15 ± 0.01 A at −109 to −66 °C, respectively). The most probable explanation of this contradiction seems to be the existence of several hydrates belonging to the same structural type but different in composition.

Segregation of Mg in Zn1−xMgxO single crystals grown from the melt

Solid solutions between zinc oxide and magnesium oxide containing up to 4at.% Mg were grown from the melt using a modified Bridgman technique. Chemical analysis (ICP-OES) and photoluminescence (PL) measurements revealed that the Mg concentration in the melt is larger compared with the starting material. This observation contradicts the commonly accepted assumption, that the ZnO–MgO phase diagram is of eutectic type. Peritectic melting of Zn-rich Zn1−xMgxO can explain the new experimental results, and a new ZnO–MgO phase diagram is proposed. Furthermore a distribution coefficient for Mg of keff=1.32…1.4 has been determined.

Oxygen partial pressure effect on the thermal stability of Nd-123 superconductor thin films

The effect of oxygen partial pressure on the thermal stability of Nd-123 superconductor thin films was investigated by means of high temperature in situ microscopy. It was found that the thermal stability of Nd-123 films decreases as the oxygen partial pressure increases. We attribute the thermal stability suppression to the increased growth rate of Nd-422 and a high concentration difference ratio. Under the assumption of quasi-equilibrium, a simplified model for peritectic melting of RE-123 was suggested.

Y211 particle refinement in YBCO bulk superconductors by CeO<SUB align=right>2 addition

The influence of preparation parameters as nominal composition (Y 2 O 3 and CeO 2 additions), particle size of starting Y123 powder, milling and mixing conditions and sintering temperature on the refinement of Y 2 BaCuO 5 (Y211) particles in the single-grain YBa 2 Cu 3 O 7 /Y 2 BaCuO 5 (Y123/Y211) bulk superconductors prepared by top-seeded melt-growth process has been studied. The microstructure was analysed after sintering and melt processing by polarised light microscopy and electron microscopy. It is shown that cerium is active in the Y211 particle refinement when it is solved in the peritectic melt, L p . When cerium is present as barium cerate, it has no refining effect. The addition of CeO 2 and barium cerate formation even leads to a faster growth of Y211 particles at the sintering stage due to intensive melt production. Refinement of Y211 particles in the samples with large Y123 particles is related to the formation of very dense Y211 skeleton which is resistant to melt formation at the sintering stage. Critical current density of these single-grain bulk superconductors is significantly influenced by final microstructure.

Phase equilibria in the SrS-Ga2S3 system

In the SrS-Ga2S3 system, there exist two individual compounds: SrGa2S4 (a = 2.084 nm, b = 2.050 nm, c = 1.220 nm; congruent melting at 1530 K) and Sr2Ga2S5 (a = 1.253 nm, b = 1.203 nm, c = 1.117 nm; peritectic melting at 1330 K); both are orthorhombic. We discovered a compound of composition Sr4Ga2S7; this compound crystallizes in cubic system with the unit cell parameter a = 0.6008 nm, space group Pa3, and decomposes by a solid-phase reaction at 870 K. Eutectic compositions are 42 and 73 mol % Ga2S3; eutectic melting temperatures are 1210 and 1170 K, respectively. The SrS solubility in γ-Ga2S3 at 1070 K reaches 4 mol %.

Thermoanalytical study of the polymorphism and melting behavior of Cu2V2O7

We have developed a procedure for the synthesis of phase-pure α- and β-Cu2V2O7. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability range 25–610°C), while α-Cu2V2O7 (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase γ-Cu2V2O7, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu2V2O7, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu2V2O7, CuVO3, and other compounds.

The melting behavior of lutetium aluminum perovskite [formula omitted

DTA measurements with mixtures of aluminum oxide and lutetium oxide around the 1 : 1 perovskite composition were performed up to 1970 ∘ C . A peak with onset 1901 ∘ C was due to the melting of the eutectic Lu 4 Al 2 O 9 (monoclinic phase) and LuAlO 3 (perovskite). Neither peritectic melting of the perovskite nor its decomposition in the solid phase could be resolved experimentally. The maximum of the eutectic peak size is near x = 0.44 , on the Lu-rich side of the perovskite, which is consistent with the conclusion that LuAlO 3 melts peritectically at ca. 1907 ∘ C as proposed by Wu, Pelton, J. Alloys Compd. 179 (1992) 259. Thermodynamic equilibrium calculation reveals that under strongly reducing conditions (oxygen partial pressure < 10 − 13 bar ) aluminum(III) oxide can be reduced to suboxides or even Al metal. It is shown that under such conditions a new phase field with liquid Al can appear.

Hexametavanadates M 4 + M2+(VO3)6: Thermal stability and luminescent characteristics

Rhombohedral hexametavanadates K4Sr(VO3)6, K4Ba(VO3)6, Rb4 Ba(VO3)6, and Cs4Ba(VO3)6 melt incongruently in the temperature range of 491 to 600°C. Cooling of peritectic melts yields mixtures of compounds typical of M2+O-M2+O-V2O5 systems, far from equilibrium and depending on the cooling kinetics. The vanadate Cs4Ba(VO3)6 undergoes reversible polymorphic transformation at 360°C. All compounds show broad-band luminescence with a maximum of the luminescence spectrum at 490–590 nm with three types of excitation. The vanadates K4Sr(VO3)6 and Rb4Ba(VO3)6 show the highest luminescence intensity at room temperature. The latter is also most efficient at liquid nitrogen temperatures. The luminescence spectra depend on the excitation of vanadates. Three hypotheses were put forward to interpret this finding. The nature of luminescence is attributed to the relaxation of electronic excitation in [VO4]3− structural tetrahedra present in the vanadates. The performance characteristics of luminophores were determined. These luminophores may be promising as X-ray luminescent screens, radioluminescence indicators, and light-emitting diode devices.

The CaF2-CaCl2-CaSO4 system

The liquidus surface of the CaF2-CaCl2-CaSO4 system has been investigated by differential thermal analysis. Two invariant equilibria (one eutectic and one peritectic) are realized in the system. The eutectic and peritectic melt at 597 and 703°C, and the enthalpies of phase transitions are 206 and 378.1 kJ/kg, respectively. Investigation of the ternary system formed by the natural minerals fluorite (CaF2), anhydrite (CaSO4), and calcium chloride (a relatively low-melting inorganic solvent) is undertaken with the goal of developing power-intensive heat-accumulating phase-transition materials and electrolytes of diversified application.

Melting in the Fe–C system to 70 GPa

We determined high-pressure melting curves for Fe 3C, Fe 7C 3 and the Fe–Fe 3C eutectic using laser-heated diamond anvil cell techniques. The principal criterion for melting is the observation of plateaus in the temperature vs. laser power function, which is an expected behavior at isobaric invariant points (e.g. congruent, eutectic, or peritectic melting) as increased power provides the latent heat of melting. We verified this technique by reproducing the melting curves of well-studied congruently melting compounds at high pressure (Fe, Pt, FeS, Pb), and by comparison with melting determinations made using thermocouple-based large-volume press techniques. The incongruent melting curve of Fe 3C measured to 70 GPa has an apparent change in slope at ~ 8 GPa, which we attribute to stabilization of Fe 7C 3 at the solidus and the creation of a P– T invariant point. We observe that Fe 7C 3 melts at higher temperatures than Fe 3C between 14 and 52 GPa and has a steep P– T slope, and on this basis predicts an expanding field of Fe 7C 3 + liquid with pressure. The Fe–Fe 3C eutectic melting curve measured to 70 GPa agrees closely with multi-anvil data and thermodynamic calculations. We also measured the eutectic composition as a function of pressure using an in situ X-radiographic imaging technique, and find a rapid drop in carbon in the eutectic composition above about 20 GPa, generally consistent with previous thermodynamic calculations, and predict that the eutectic lies close to pure iron by ~ 50 GPa. We use these observations to extrapolate phase relations to core-relevant pressures. Convergence of the Fe 3C and Fe–Fe 3C eutectic melting curves indicate that Fe 3C is replaced at the solidus by Fe 7C 3 at ~ 120 GPa, forming another P– T invariant point and a new eutectic between Fe and Fe 7C 3. Thus, Fe 3C is unlikely to be an important crystallizing phase at core conditions, whereas Fe 7C 3 could become an important crystallizing phase.

Thermal stability and cathodoluminescence of potassium strontium vanadates

We have studied the thermal stability of five potassium strontium vanadates: KSr(VO3)3, K2Sr(VO3)4, K4Sr(VO3)6, K6Sr(VO3)8, and KSrVO4. The double orthovanadate undergoes a reversible polymorphic transformation at 1117°C and is stable up to 1500°C. The double metavanadates melt peritectically in the range 490–517°C to give Sr2V2O7 crystals and peritectic melt. Pulsed cathodoluminescence studies have shown that the potassium: strontium ratio in the vanadates and their crystal structure have little effect on their optical emission properties. The performance parameters of new vanadate-based phosphors have been determined.

Heat and mass transfer characteristics during rapid solidification of Fe-Cu peritectic alloys

The viscose flow and microstructure formation of Fe-Cu peritectic alloy melts are investigated by analyzing the velocity and temperature fields during rapid solidification, which is verified by rapid quenching experiments. It is found that a large temperature gradient exists along the vertical direction of melt puddle, whereas there is no obvious temperature variation in the tangent direction of roller surface. After being sprayed from a nozzle, the alloy melt changes the magnitude and direction of its flow and velocity rapidly at a height of about 180 μm. The horizontal flow velocity increases rapidly, but the vertical flow velocity decreases sharply. A thermal boundary layer with 160–300 μm in height and a momentum boundary layer with 160–240 μm in thickness are formed at the bottom of melt puddle, and the Reynolds number Re is in the range of 870 to 1070 in the boundary layer. With the increase of Re number, the cooling rate increases linearly and the thickness of thermal boundary layer increases monotonically. The thickness of momentum boundary layer decreases slowly at first, then rises slightly and decreases sharply. If Re < 1024, the liquid flow has remarkable effects on the microstructure formation due to dominant momentum transfer. The separated liquid phase is likely to form a fiber-like microstructure. If Re>1024, the heat transfer becomes dominating and the liquid phase flow is suppressed, which results in the formation of fine and uniform equiaxed microstructures.

Microstructure of YBCO bulk superconductors with CeO 2 addition

The refinement of Y 2BaCuO 5 (Y211) particles by CeO 2 in the single-grain YBa 2Cu 3O 7/Y 2BaCuO 5 (Y123/Y211) bulk superconductors of nominal composition Y 1.5Ba 2Cu 3O x prepared by top-seeded melt-growth process with Y 2O 3 addition has been studied by polarised light microscopy. It is shown that cerium is active in the Y211 particle refinement when it is solved in the peritectic melt, L p. Observed growth of Y211 particles during sintering stage is ascribed to higher amount of melt induced by CeO 2 reaction with Y123 phase producing barium cerate and CuO.

Experimental Establishment of the CaAl2O4–MgO and CaAl4O7–MgO Isoplethal Sections within the Al2O3–MgO–CaO Ternary System

The isoplethal sections CaAl2O4–MgO and CaAl4O7–MgO of the Al2O3–MgO–CaO ternary system have been experimentally established at 1 bar total pressure and air of normal humidity. The sections obtained provide new data and information that are in disagreement with thermodynamic evaluations and optimizations of the Al2O3–MgO–CaO ternary system published to date. These differences arise mainly from the inclusion, or exclusion, of the binary compound Ca12Al14O33, mayenite, as a stable phase in the reported studies of the system. The presence or absence of this compound within the system has an important impact on the solid state and melting relationships of the whole ternary system. The present study confirms the solid‐state compatibility CaAl2O4–MgO and CaAl2O4–MgO–MgAl2O4up to 1372°± 2°C, the peritectic melting point of the later mentioned subsystem.

Phase Equilibria and Crystal Growth for LiREF4 Scheelite Laser Crystals

AbstractThe scheelite type laser crystals LiREF4 melt congruently only for RE being one of the elements Er, Tm, Yb, Lu, or possibly Y, respectively. For RE = Eu, Gd, Tb, Dy, or Ho the corresponding scheelites undergo a peritectic melting under the formation of the corresponding rare earth fluoride. The melting behavior of LiREF4 mixed crystals with two or more RE is not yet known well. If RE is a mixture of Gd and Lu, Gd rich solid solutions melt peritectically under formation of (Gd,Lu)F3 and Lu rich solid solutions melt directly without formation of other solid phases.