Influence Of Melt Composition Research Articles

Influence of Melt Composition on the Formation of Powder Particles When Spraying High-Alloy Steels with High-Pressure Water

Influence of Melt Composition on the Formation of Powder Particles When Spraying High-Alloy Steels with High-Pressure Water

Mineral–melt partition coefficients and the problem of multiple substitution mechanisms: insights from the rare earths in forsterite and protoenstatite

A trace element may substitute into a mineral by more than one substitution mechanism, complicating the thermodynamic description of its partition coefficients. In order to understand this phenomenon better, the mineral/melt partition coefficients for all 14 rare earth elements (REE) plus Y and Sc were measured experimentally for coexisting forsterite and protoenstatite in the system CaO–MgO–SiO2 ± Al2O3 ± TiO2 at 1406 °C and atmospheric pressure. For both phases, the results show these large trivalent cations (REE3+) replace Mg2+ on octahedral sites, but with charge-balance achieved by two different mechanisms: (1) cation vacancies (2 REE3+ + vacancy = 3 Mg2+); and (2) substitution of Al for Si (REE3+ + Al3+ = Mg2+ + Si4+). The overall REE partition coefficient is the sum of the partition coefficients for each substitution mechanism. Because the stoichiometric control is different for each mechanism, the relative importance of the mechanism varies with melt composition, including the activities of both silica and alumina in the melt ($${{a}}_{{{\text{SiO}}_{ 2} }}^{\text{melt}}$$ and $${{a}}_{{{\text{AlO}}_{ 1. 5} }}^{\text{melt}}$$). The coexistence of forsterite and protoenstatite fixes the silica activity, allowing the effect of $${{a}}_{{{\text{AlO}}_{ 1. 5} }}^{\text{melt}}$$ to be separated from that of $${{a}}_{{{\text{SiO}}_{ 2} }}^{\text{melt}}$$. The relative importance of the two mechanisms depends strongly on the identity of the REE for forsterite, but not for protoenstatite. The results are used to test the lattice strain model: the two substitution mechanisms in forsterite imply different values for the Young’s modulus in the Brice equation, despite the fact that the REE3+ cations likely occupy the same crystallographic site in both mechanisms, casting doubt on the physical basis of the lattice strain theory. Comparison with literature data confirms earlier observations that the activity coefficients of REE2O3 in silicate melts decrease with increasing SiO2 content of the melt, but the effect decreases with increasing atomic number, from La to Lu, and is almost negligible for Sc. The influence of melt composition should apply to the mineral/melt REE partition coefficients of all other minerals. Recognizing that observed mineral/melt partition coefficients are often the sums of contributions from multiple substitution mechanisms, each with its own dependence on both crystal composition and the stoichiometric control from the melt composition, will improve parameterizations of the mineral/melt partition coefficients of other rock-forming minerals. Partition coefficients for Na, Al, Ca, Ti, and Zr are also reported.

Broadband Near-IR photoluminescence of bismuth-doped pollucite-related phase CsGaGe2O6

Polycrystalline samples of bismuth-doped CsGaGe2O6 with pollucite-related structure were prepared by crystallization from the melt. Intense broadband near-IR photoluminescence was observed in this phase. The photoluminescence emission and excitation spectra are characteristic for Bi+ monocation. Structural disorder in the framework of pollucite-related phase leads to the inhomogeneous broadening of photoluminescence emission spectrum. The influence of melt composition on the stabilization of subvalent Bi+ monocation was discussed in the terms of oxoacidity concept.

The influence of melt composition on the partitioning of trace elements between anorthite and silicate melt

The effect of melt composition on the partitioning of trace elements between anorthite and silicate melts has been studied experimentally in five compositions in the system CaO–Al2O3–SiO2 (CAS) at ~ 1400 °C and four compositions in the system CaO–MgO–Al2O3–SiO2 (CMAS) at 1332 °C. Melt composition has a significant impact on the substitution of trace elements into anorthite, particularly if the trace-element substitution is aliovalent and requires a charge balance for substitution. Melt composition strongly influences the partitioning of the trivalent rare earth element (REE) cations into the large-cation site (M) of anorthite. Due to charge balance requirements, the activity of alumina in the melt is the most important compositional variable for the REE partitioning in anorthite. Scandium, another trivalent cation, is much more compatible than is predicted for trivalent cations partitioning on the M-site. Therefore, scandium is likely partitioning onto the tetrahedral site in place of aluminium, which requires no charge balance and therefore is not affected strongly by melt composition. Similarly, the partitioning of the small divalent cations (Be and Mg) show a stronger relationship with changing melt composition than the large divalent cations (Ca, Sr, and Ba) and therefore are likely to partition on the tetrahedral site (T) of plagioclase rather than the large-cation site (M). Detailed thermodynamic modelling of the effects of melt composition is required for an adequate parameterization of trace-element mineral/melt partition coefficients, in addition to models of the effects of mineral composition.

Structure and Composition Effects on the Oxygen Isotope Fractionation in Silicate Melts

The influence of melt composition and structure on the oxygen isotope fractionation was studied for the multicomponent (SiO2 ± TiO2 + Al2O3 ± Fe2O3 + MgO ± CaO) system at 1500°C and 1 atm. The experiments show that significant oxygen isotope effects can be observed in silicate melts even at such high temperature. It is shown that the ability of silicate melt to concentrate 18O isotope is mainly determined by its structure. In particular, an increase of the NBO/T ratio in the experimental glasses from 0.11 to 1.34 is accompanied by a systematic change of oxygen isotope difference between melt and internal standard by values from–0.85 to +1.29‰. The obtained data are described by the model based on mass-balance equations and the inferred existence of O0, O–, and O2– (bridging, non-bridging, and free oxygen) ions in the melts. An application of the model requires the intra-structure isotope fractionation between bridging and non-bridging oxygens. Calculations show that the intra-structure isotope fractionation in our experiments is equal to 4.2 ± 1.0‰. To describe the obtained oxygen isotope effects at the melts relatively to temperature and fraction of non-bridging oxygen a general equation was proposed.

Ra-partitioning between phlogopite and silicate melt and 226Ra/Ba– 230Th/Ba isochrons

In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~ 0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~ 1 ppb). D Ra phlogopite/melt was determined to 2.28 ± 0.44 and 2.84 ± 0.47 in two experiments, the ratio D Ra/ D Ba is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of D Ra and D Ra/ D Ba for magmatic minerals containing appreciable Ra, yields D Ra mineral/melt ranging from ~ 2.6 for phlogopite down to 2–3 • 10 − 5 for pyroxenes, and D Ra/ D Ba mineral/melt from ~ 4 for leucite to 2 • 10 − 2 for orthopyroxene. The influence of melt composition on D Ra/ D Ba is less than 10%. All investigated minerals have different D Ra/ D Ba, strongly fractionating Ra from Ba. Thus, for magmatic systems, ( 226Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the ( 226Ra)/Ba–( 230Th)/Ba system at the time of crystallization and thus, there is no ( 226Ra)/Ba–( 230Th)/Ba isochron at t 0. 226Ra– 230Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known D Ra.

The influence of melt composition on the partitioning of REEs, Y, Sc, Zr and Al between forsterite and melt in the system CMAS

Partition coefficients for a range of Rare Earth Elements (REEs), Y, Sc, Al and Zr were determined between forsteritic olivine (nearly end-member Mg 2SiO 4) and ten melt compositions in the system CaO–MgO–Al 2O 3–SiO 2 (CMAS) at 1 bar and 1400 °C, with concentrations of the trace elements in the olivine and the melt measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The REEs and Sc were added at levels sufficient to ensure that concentrations in the olivine were well above the detection limits. The REE partition coefficients ( D REE ol / melt ) decrease with increasing silica in the melt, indicating strong bonding between REEO 1.5 and SiO 2 in the melt. The variation of D REE ol / melt as a function of ionic radius is well described by the Brice equation for each composition, although a small proportion of this variation is due to the increase in the strength of the REEO 1.5–SiO 2 interactions in the melt with ionic radius. Scandium behaves very similarly to the REEs, but a global fit of the data from all ten melt compositions suggests that D Sc ol / melt deviates somewhat from the parabolas established by the REE and Y, implying that Sc may substitute into olivine differently to that of the REEs. In contrast to the behaviour of the large trivalent cations, the concentration of Al in olivine is proportional to the square root of its concentration in the melt, indicating a coupled substitution in olivine with a high degree of short-range order. The lack of any correlation of REE partition coefficients with Al in olivine or melt suggests that the REE substitution in olivine is charge-balanced by cation vacancies. The partition coefficient of the tetravalent trace element Zr, which is highly incompatible in olivine, depends on the CaO content of the melt.

Water solubility in phonolite melts: Influence of melt composition and temperature

The water solubility in various phonolite melts was determined experimentally at pressures between 50 and 395 MPa and at temperatures between 850 and 1200 °C. The aim of this study was to elucidate to which extent chemical and physical parameters such as relative amounts of alkali and alkaline earth elements or temperature affect the water solubility. For this purpose a total of 10 different phonolite glasses were prepared. For a series of four glasses, the Na/(Na + K) ratio was varied from 0.2 to 0.8, for another series of four glasses, the (Na + K)/(Ca + Mg) ratio was varied from 2.8 to 10.1, while keeping Na/(Na + K) constant at 0.4. For these two series water solubility experiments were performed at 1200 °C and pressures between 50 and 395 MPa in an internally heated pressure vessel. The data show that both chemical variables have rather small effects on the water solubility. For instance, at 2 kbar and 1200 °C an increase in Na/(Na + K) ratio from 0.2 to 0.8 leads to an increase in water solubility of about 0.4 wt.% (5.58 to 5.94 wt.%), while increasing the (Na + K)/(Ca + Mg) ratio from 2.8 to 10.1 leads to an increase of about 0.2 wt.% water. The effect of temperature was investigated for two phonolite compositions, representative of Montaña Blanca, Tenerife, Spain and the Laacher See volcanic complex, East Eifel, Germany at pressures of 50, 100, 150, 200, 250 and 300 MPa, and temperatures between 850 and 1200 °C. At these conditions both melts exhibit negative temperature dependence ranging from about − 0.1 to − 0.24 wt.% water per 100 °C. The strongest temperature dependence (most negative values) occurs at 150 to 200 MPa and seems to approach zero slightly above 300 MPa.

Crack-free K 3Li 2− xNb 5+2 xO 15+2 x crystals grown by the resistance-heated Czochralski technique

We report that crack-free K 3Li 2− x Nb 5+2 x O 15+2 x crystals (KLN) have been grown by the resistance-heated Czochralski technique. The influence of melt composition and growth parameters on crystal growth and crystal cracks are described. Blue light (445–476 nm) has been obtained by frequency doubling of the light wave (890–952 nm) generated from a Ti : sapphire laser.

Partial‐melt electrical conductivity: Influence of melt composition

The electrical conductivity of a partial melt is influenced by many factors, including melt conductivity, crystalline conductivity, and melt fraction, each of which is influenced by temperature. We have performed measurements of bulk conductivity as a function of temperature of an Fo80‐basalt partial melt between 684° and 1244°C at controlled oxygen fugacity. Melt fraction and composition variations with temperature calculated using MELTS [Ghiorso and Sack, 1995] indicate that the effect on melt conductivity of changing melt composition is balanced by changes in temperature (T). Thus bulk conductivity as a function of T or melt fraction in this system can be calculated assuming a constant melt conductivity. The bulk conductivity is well modeled by simple parallel calculations, by the Hashin‐Shtrikman upper bound, or by Archie's law (σpartial melt/σmelt = C1Xmn). We estimate apparent values of the Archie's law parameters between 1150° and 1244°C as C1 = 0.73 ± 0.02 and n = 0.98 ±0.01. Estimates of the permeability of the system are obtained by using an electrical conductivity‐critical scale length relationship and range from ∼10−14 to 10−18 m2, comparing favorably with previously published values.

Growth by LPE of Nd: YAG single crystal layers for waveguide laser applications

Nd:YAG layers, for waveguide laser applications, have been grown by liquid phase epitaxy on [111] YAG substrates from a saturated PbO/B 2 0 3 flux using the horizontal dipping technique. The influence of melt composition on growth conditions is discussed. Some substitutions (gallium, lutetium) were studied with the purpose of optimizing the waveguide properties.

Influence of melt composition on electron mobility in Si-doped LEC GaAs

A number of GaAs single crystals has been grown by means of the LEC technique starting from silicon doped melts which were Ga-rich, As-rich and stoichiometric, respectively. The electrical properties were assessed in order to establish a correlation between silicon incorporation, electron mobility and melt composition. It was found that the electron mobility is higher in crystals grown from As-rich melts. The chemical incorporation of silicon is independent of the melt composition though the distribution of the dopant atoms in acceptors, donors and, possibly, complexes changes drastically with stoichiometry.

Influence of melt composition on the longitudinal distribution of midgap native donor concentration in semi-insulating liquid-encapsulated Czochralski GaAs crystal

The longitudinal distribution of midgap native donor concentration was investigated in detail using semi-insulating liquid-encapsulated Czochralski GaAs crystals grown from various melt compositions. The midgap native donor concentration was found to decrease with fractional solidification under Ga-rich conditions, to increase under As-rich conditions, and not to change under stoichiometric conditions. Moreover, it varied with the magnetic field intensity and the crystal-pulling speed depending on the melt composition. These phenomena were consistently explained by assuming that the midgap native donor acts like a dopant with a certain segregation coefficient k, where k<1 under As-rich conditions, k=1 under stoichiometric conditions, and k>1 under Ga-rich conditions. This is in good agreement with the expected segregation of As atoms determined from a phase diagram with a narrow solid-solution region.

Control of the growth-induced magnetic anisotropy in ferrimagnetic garnet films grown by liquid-phase epitaxy

The influence of melt composition and growth temperature T g on the growth-induced magnetic anisotropy constant K g u in Bi substituted LPE ferrimagnetic garnet films has been investigated. In films grown from Bi 2O 3 based and from PbO B 2 O 3 based melts the value of K g u increased upon decreasing T g, associated with an increasing incorporation of B1. However, at given Bi content the films grown from Bi 2O 3 based fluxes generally exhibited smaller values of K g u than those from PbO B 2 O 3 based melts. The addition of small amounts of Ca 2+ to the Bi 2O 3 based melts resulted in (Y,Bi)-garnet films changing from n- to p-type electrical conductivity at a minimum value of K g u. Additions of Si 4+ to a PbO B 2 O 3 based melt reduced the uniaxial magnetic anisotropy of La-YIG-Ga films accompanied by a change from p- to n-type conductivity. Similarly, (Gd,Bi)-garnet films from PbO B 2 O 3 based melts changed from n- to p-type conductivity upon decreasing T g where K g u changes sign from negative to positive. From the temperature dependence of the electrical conductivity the electron and hole concentrations in some of these films were estimated suggesting that the sign change of K g u in the investigated (Gd,Bi)-garnet films and the minimum of K g u in the investigated (Y,Bi)-garnet films and (La,Y)-garnet films occur at donor-acceptor compensation. This experimental evidence led us to conclude that the growth induced magnetic anisotropy may be correlated with the presence of donor and acceptor centers in the garnet structure.