B2O3 Melt Research Articles

Cathodic Processes in the KF–AlF3–Al2O3–B2O3 Melt

Cathodic Processes in the KF–AlF3–Al2O3–B2O3 Melt

Structural characteristics and ablative behavior of C/C–ZrC–SiC composites reinforced with “Z-pins like” Zr–Si–B–C multiphase ceramic rods

In order to improve the ablation and oxidation resistance of C/C–ZrC–SiC composites in wide temperature domain, “Z-pins like” Zr–Si–B–C multiphase ceramic rods are prepared in the matrix. The influence of different sintering temperatures on the microstructure of ceramic rods and the ablative behavior of heterogeneous composites are studied. The results showed that the ZrB2 and SiC phases are formed in the sintered matrix, and the increase of sintering temperature is beneficial to improve the density of the ceramic rods. The ablation properties of samples have been greatly improved. The mass and linear ablation rate are 0.8 mg/s and 3.85 μm/s, respectively, at an ablation temperature of 3000 °C and an ablation time of 60 s. After ablation, the matrix surface is covered with SiO2 and ZrO2 mixed oxide films. This is due to the preferential oxidation of “Z-pins like” Zr–Si–B–C multiphase ceramic rods in the ablation process, and B2O3 melt, SiO2 melt, borosilicate glass, ZrSiO4 melt and ZrO2 oxide film can be generated successively from the low-temperature segment to the ultra-high temperature segment. These oxidation products can be used as compensation oxide melts for the healing of cracks and holes on the matrix surface in different temperature ranges and effectively prevent the external heat from spreading into the matrix. Therefore, C/C–ZrC–SiC composites with “Z-pins like” Zr–Si–B–C multiphase ceramic rods achieve ablation resistance in wide temperature domain.

Вязкость расплавов систем B2O3-CaO-NiO (FeO)

Structure of the B2O3 melt was analyzed as well as CaO modifier additives (25, 34, and 45 mass %) effect to it. As was proved, non-ring groups of associated rings proper to pure B2O3 are transformed into BO2O – metaborate triangles. The released oxide ions increase the coordination number of modifying ions, which occupy cationic vacancies place in the most disordered part of the melt greed. The B2O3–CaO–NiO and B2O3–CaO–FeO melts viscosity were measured by the method of vibration viscometry. Ratio of Boron to Calcium oxide mass fractions was taken as 3/1 and content of Nickel and Iron oxides in the range up to 5 and 20 % mass respectively. The experiments had been carried out using vibration viscometer operating in the mode of forced oscillations. The melt temperature was measured by Platinum –Platinum – Rhodium thermocouple. The measurements were carried out in cooling mode of the melt from 1800 K at 7-10 K/min speed. The viscosity temperature dependencies as well as its dependence on Nickel and Iron oxides were determined. Data processing was performed using the Table curve application software. Viscosity experimental data of the B2O3-CaO-NiO system melts for 1373, 1423, 1473, 1523, 1573 K temperatures have been described by the equation: η = a + b·exp(-cx), and for B2O3 – CaO – FeO melts by equation: η = a + b·x2 + c·exp (x) + d·exp(-x). Experimental data and calculations results show good convergence. The results are supposed to be used for describing the kinetics of metal reduction in bubbling processes, accompanied by the concentrations change of the oxides under reduction. The obtained information is useful for correction the slag melts properties in non-ferrous metal production.

Preparation and microwave dielectric properties of B2O3 bulk

AbstractThe transparent B2O3 bulks were prepared by quenching B2O3 melt or cooling it down to room temperature with the rate of 0.1‐1°C/min. The quenched sample exhibited the dense microstructure, while the pores were observed for low cooling rates, and this is consistent with the slight decrease in density and permittivity (εr) with decreasing the cooling rate. Both the amorphous and cubic phases of B2O3 were indicated by XRD, and the content of the cubic phase increased with the decrease in cooling rate, which was responsible for the decreasing Qf value with the lower cooling rate. The temperature coefficient of resonant frequency (τf) was insensitive to the cooling rate, and the microwave dielectric properties with εr = 3.86‐3.97, Qf = 3,200‐5,300 GHz and τf = −48.9 to −42.8 ppm/°C were obtained in the B2O3 bulks. The reported microwave dielectric properties of B2O3 bulk are helpful to estimate the effects of the residual B2O3 on the properties of the microwave dielectric ceramics with B2O3 and H3BO3 as the sintering aid.

Understanding the tribological impacts of alkali element on lubrication of binary borate melt.

Melt lubricants have been regarded as an effective class to deliver lubrication on moving mechanical contacts at extreme temperatures. Among the elementary constituents, alkali elements play a critical role in governing the physical–chemical characteristics of the lubricant despite the obscurity regarding their intrinsic roles on the rubbing interfaces. The present study attempts to unfold the effects of sodium on the tribological responses of mating steel pair under borate melt lubrication. It has been found that the involvement of Na inspires a total reversal in lubricating potentials of the lone B2O3 melt manifested by remarkable friction reduction, wear inhibition and prolonged load-bearing capacity. These exceptional performances are attributed to the accretion of nanothin Na layers on the contact interfaces. The interfacial occurrences are interpreted from a physico-chemistry perspective while the influences of surface microstructure are also discussed in detail. Multiple characterizations are employed to thoroughly examine the sliding interfaces in multi-dimensions including Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM) and Atomic Force Microscopy (AFM). In addition, chemical fingerprints of relevant elements are determined by Energy Dispersive Spectroscopy (EDS) and Electron Loss Energy Spectroscopy (EELS).

Study of the optical absorption and photoluminescence in (Pb,Gd)3(Al,Ga)5O12: Ce epitaxial films grown from Pb-containing melt solutions

The optical absorption and photoluminescence properties of cerium-activated (Pb,Gd)3(Al,Ga)5O12 epitaxial films are studied. The films are grown on single-crystal (111)-oriented Gd3Ga5O12 substrates by liquid-phase epitaxy from supercooled PbO – B2O3 melt solutions at different concentrations of gadolinium, cerium, and aluminium oxides in the charge. The photoluminescence band of Ce3+ ions is shown to peak at 532 nm. The highest cathodoluminescence yield of about 51500 photons MeV−1 at a decay time of the slow component of 61.0 ns (light yield fraction 68%) is found for the Pb0.01Ce0.03Gd2.96Al3.14Ga1.86O12 film, grown from melt solution with gadolinium oxide, cerium oxide, and aluminium oxide concentrations of 0.4, 0.2, and 4.5 mol % in the charge, respectively. Epitaxial films with these spectroscopic characteristics are promising for application in scintillation screens.

Trisodium scandium bis(orthoborate)

Single crystals of tris­odium scandium bis­(orthoborate), Na3Sc(BO3)2, have been obtained by spontaneous crystallization from an Na2O–Sc2O3–B2O3 melt. The crystal structure features a three-dimensional framework composed of planar [BO3]3− groups and distorted ScO6 octa­hedra with Na atoms in the cavities. The Sc atom occupies a special position (Wyckoff position 2b, site symmetry -1) and of the two Na atoms, one occupies a special position (Wyckoff position 2c, site symmetry -1).

Noncontact Measurement of Viscosity of B2O3 Melt Using Electric-field Tweezers

We propose a novel noncontact method for measuring the viscosity of high-temperature glass melt using a small amount of sample. This method combines the electric-field tweezers system developed for measuring the local and dynamic surface properties of soft condensed materials and the hot-thermocouple technique for in situ observation and measurement of high-temperature liquids. The viscosity of B2O3 melt was measured in the temperature range of 873 to 1473 K. The temperature dependence of the viscosity presented in this work is in reasonable agreement with that reported in the references.

In Situ Observation of Phase Separation of a Barium Borate Melt in a Stable Immiscibility Region under Microgravity

The precipitation of droplets was directly observed on a BaO–B2O3 melt in a drop shaft experiment. This is the first time that precipitation of droplets has been observed in a 4.5 s drop test. The melt film of 4BaOz96B2O3 (mol%) held on a platinum wire loop was heated above the critical tem-perature to produce uniformity and was cooled down to the phase separation temperature range. Phase separation of the melt was observed directly with a video camera. The IR image of the melt was simultaneously detected with a CCD array and was converted into a two-dimensional thermograph.

Density of Bi2O3–B2O3 Binary Melts

The densities of xBi2O3·(100−x)B2O3 binary melts (x= 0–100 mol%) have been measured systematically in the temperature range of 973 to 1373 K using the Archimedean double‐bob method. In addition, the molar volume and coefficient of volume expansion have been determined from these density measurements. The density of melts in the Bi2O3–B2O3 binary system decreased with increasing temperature for all compositions, and increased with increasing Bi2O3 content. The molar volume calculated at 1273 K showed a minimum at around 20–30 mol% Bi2O3. The deviation of molar volume from ideality and the partial molar volumes of B2O3 and Bi2O3 single‐component melts were calculated, and the relationships between these properties and Bi2O3 content were investigated. The Δ(MV) (deviation of molar volume from ideality) was negative in the Bi2O3–B2O3 binary melts and showed a minimum of −7.5 cm3 (−17.3%) at 40 mol% Bi2O3 and 1273 K. The PMV (partial molar volume) of the B2O3 melt decreased with increasing Bi2O3 content, up to 70 mol% Bi2O3, and was constant above 70 mol% Bi2O3. The PMV of the Bi2O3 melt was constant up to 30 mol% B2O3 (considered from the viewpoint of Bi2O3), and then decreased sharply with further addition of B2O3. The coefficient of volume expansion increased sharply up to 20 mol% Bi2O3 and decreased with further addition of Bi2O3 at 1273 K. From this result, it can be inferred that the temperature‐induced structural changes taking place in the melts are greatest at 20 mol% Bi2O3.

Heat of formation of petalite, LiAlSi 4 O 10

The enthalpy of formation of petalite, LiAlSi4O10, has been measured using high-temperature solution calorimetry. The measurements were carried out in a Calvet-type twin micro calorimeter at 728 degreesC. A 2PbO . B2O3 melt was used as a solvent. Tabulated heats of formation of the components and tabulated heat capacities of the reactants and the product (Robie and Hemingway 1995) were used to calculate the standard heat of formation of petalite from the measured heats of solution. The calculations yielded a mean value of Delta H-f(298.15)pet = -4872 +/- 5.4 kJ mol(-1). This value may be compared to the heat of formation of Delta H-f(298.15)pet = -4886.5 +/- 6.3 kJ mol(-1) determined by the HF solution calorimetry by Bennington et al. (1980). Fa ss hauer et al. (1998) combined thermodynamic data with phase-equilibrium results to obtain best-fit thermodynamic results using the Bayes method, in order to derive an internally consistent dataset for phases in the NaAlSiO4-LiAlSiO4-Al2O3-SiO2-H2O system. They determined -4865.6 +/- 0.8 kJ mol(-1) as the enthalpy of formation of petalite, a value that is appreciably closer to the enthalpy found in this work.

Thermodynamic properties and dissociation of SrLaAlO4

The enthalpy of solution of SrLaA1O4 in the 2PbO · B2O3 melt at 973 K was measured using a hightemperature Cal vet microcalorimeter. The enthalpies of formation of SrLaA1O4 from the constituent oxides and constituent elements at 298.15 K were determined to be -97.7 ±5.5 and -2422.9 ±5.6 kJ/mol, respectively. The partial pressures of the vapor species over molten SrLaA1O4 at Tm = 1923 K were evaluated. The equilibrium oxygen pressure at 1923 K was found to be 5.05 × 10-3 Pa.

Growth and luminescence of epitaxial Yb0.3ErxGd2.7-xGa5O12 films

A series of (Gd,Yb,Er)3Ga5O12 films with a variable Er content was grown on Gd3Ga5O12 substrates with the (111) orientation by liquid-phase epitaxy from a supercooled PbO — B2O3 melt. Variation of the film growth from sample to sample, grown under the same conditions, was explained by degradation of the molten solution. The violet colour of the first film of the series was attributed to enhanced capture, from the molten solution, of lead and platinum impurity ions and also to characteristics of charge compensation of these ions at high growth rates. Blue — green luminescence was observed for films with erbium content in excess of 0.01 at.%.

Solidification of Undercooled Ge73.7Ni26.3 Alloy Subjected to Sputtering-Deposition of Ni Clusters

Undercooled melt of Ge73.7Ni26.3 alloy sample floated on B2O3 melt was subjected to sputtering-deposition of Ni clusters on cooling to induce solidification. The initial temperature of solidification was 975 K. Its undercooling ΔT was 134 K with respect to the melting temperature of the primary phase Ge. On the cooling curve existed dual recalescences representing the transformation of the primary phase (Ge) and the eutectics (Ge+GeNi) respectively. But for the sample unsputtered, only a single exothermic peak presented on the cooling curve with the initial solidification temperature of 904 K and undercooling of 205 K. Careful observation of the microstructure proved that the Ge phase primarily formed in the sputtering experiment was now formed together with the formation of the eutectics in the experiment without sputtering.

In situ electrochemical and spectrophotometric investigation of the oxygen pressure dependence of the [Cr(VI)]/[Cr(III)] ratio in a borosilicate melt

AbstractThe ratio R = [Cr(VI)]/[Cr(III)] has been measured in a Na2O·1.2SiO2·1.2B2O3 melt at 1000°C by spectrophotometry and by electrochemistry as a function of the partial pressure of oxygen in the gaseous atmosphere above the melt. Spectrochemical and electrochemical determinations are in quite good agreement and fit the linear relationship between log R and logP(O2) which is predicted by a thermodynamic development. This double agreement gives a good degree of confidence to in situ high temperature electrochemical measurements in oxide melts.

Dynamics of a glass-forming system: 11B NMR of B2O3

The dynamics of the relaxation processes in a glass-forming system, B2O3, was investigated by means of 11B nuclear magnetic resonance (NMR). Using a homemade high temperature NMR probe, we collected NMR data over a wide temperature range from room temperature to 1200 °C. The NMR data were interpreted in terms of a Fourier transform of the Kohlrausch decay function, f(t)=exp[−(t/τc)−b], where the parameter b varied from 0 to 1. The temperature dependence of τc and b in the decay function was estimated by using both the data from a 11B NMR longitudinal relaxation and a line shape measurement at each temperature. Above 800 °C, the NMR data were well simulated by a single exponential decay of the function (i.e., b=1). Below 800 °C, stretched exponential was introduced to the simulation with the b parameters of 0.6 and 0.8. An Arrhenius plot of τc showed a bend at around 600 °C, which indicates the existence of two distinct reorientational processes crossing each other at that temperature. Below 600 °C, an almost linear dependence of the logarithm of τc vs the inverse of temperature with the activation energy of 40 kJ/mol was observed. This process persists below the glass transition temperature. Above 600 °C, the temperature dependence of τc became non-Arrhenius-like and was identical with that of the previous relaxation measurements. The isotropic chemical shift for the B2O3 melt suggests that the network structure constructed from the BO3 triangle is preserved in the whole temperature range.

The effect of B2O3 on the crystallization of zirconium titanate

Crystallization of coprecipitated zirconium-titanium hydroxide in the presence of the B2O3 melt as far as its action on ZrTiO4 powder and ceramics was studied by XRD and SEM investigations. It was found that ZrTiO4 formation from the X-ray amorphous ZT precursor is inhibited by the presence of liquid B2O3 leading to ZT decomposition, yielding Zr(Ti)O2 and Ti(Zr)O2 substitutional solid solutions. The concentration of substituents continuously decreased up to 4 mol% with increasing temperature. The decomposition process was followed by the change of oxide particle morphology due to recrystallization via incongruent dissolution of oxide phases in the B2O3 melt. Crystalline ZrTiO4 (powders and ceramics) were also found to be decomposed by the B2O3 melt treatment.

A molecular dynamics and neutron diffraction study of the structure of Na2OB2O3 melts

The structures of sodium borate melts with 10 and 30 mol%Na2O at 1073 K have been studied by the use of molecular dynamics simulation and pulsed neutron total scattering measurements. With an increase in Na2O content, the first peak of the experimental radial distribution function corresponding to nearest-neighboring BO correlation spread asymmetrically to the higher-r side, and the coordination number of O atoms around a reference B atom, nBO, increased from 3.0 to 3.5 reflecting a structural change from BO3 triangle units to BO4 tetrahedral units. The observed nBO agreed well with those obtained from the molecular dynamics calculations, which showed clear evidence of the appearance of BO4 units, in that the distribution of ∢OBO bond angles spread from 120° to the smaller-angle side for 30 mol%Na2OB2O3. It can be conluded from these results that some BO3 units present are converted to BO4 units on the addition of up to 30 mol%Na2O to the B2O3 melt in the same way as in Na2OB2O3 glasses.

Structural Analysis of Na2O-B2O3 Melts by Pulsed Neutron Total Scattering Method and Molecular Dynamics Simulation.

In order to obtain direct information on the structure of sodium borate melts which are of use in metallurgical processes, pulsed neutron total scattering measurements have been carried out on 10mol%Na2O- and 30mol%Na2O-B2O3 melts at 1073 K, in addition to the previous measurement on pure B2O3 melt. Molecular dynamics (MD) calculations have also been made on pure B2O3 and 30mol%Na2O-B2O3 melts at 1073 K.With increase in Na2O content, the first peak of RDF(r), representing B-O correlation, spread asymmetrically to larger r side, and the coordination number of O atoms around a reference B atom nB-O increased from 3.0 to 3.5, showing variation of B-O correlation. This increase in nB-O could be explained by the simple assumption that two BO3 triangle structure units are converted to two BO4 tetrahedron structure units with the addition of one Na2O molecule in the same way as in Na2O-B2O3 glasses. These nB-O values also agreed well with those obtained by MD calculations, which showed the clear evidence of the appearance of BO4 units that the distribution of O-B-O bond angle spread from 120° to smaller angle side for 30mol%Na2O-B2O3.From these results, it is safely concluded that a part of BO3 triangle structure units converted to BO4 tetrahedron structure units with the addition of Na2O up to 30 mol% to B2O3 melt in the same way as in Na2O-B2O3 glasses.

FORMATION OF BULK METALLIC GLASS OF Pd-Ni-P AND TRANSFORMATION KINETICS

This paper reports the result of undercooling experiment of Pd-Ni-P alloy. Bulk metallic glass of Pd41)Ni40P19 has been formed by thermal treatment with B2O3 as fluxing. The effect of cooling rate on the undercooling behavior was studied. The surface heterogeneous nuclea-tion was reduced by embeding the sample into B2O3 melt. Thus the cooling rate used to form the glass was as low as 1 K/s at the glass transition temperature of 590 K. The temperature-time-transformation curves were calculated by using the classical homogeneous and heterogeneous nucleation theory. The critical cooling rates for the glass formation were calculated. The resuits are discussed in some detail.