Early Stages Of Melting Research Articles

Heat management in sonochemical reactor using fins-PCM integrated system: Unveiling the influence of the sonicated volume

With the purpose of enhancing the heat management in the ultrasonic reactor, the present innovative research aims at the exploration of the thermal behavior of sonochemical reactor integrated with fins and phase change material (PCM), focusing on the influence of different liquid heights (LH). The performance of this combination (i.e., sonicated water, fins, and PCM) is investigated for the first time with consideration of the water volume variation. The interplay between fins, liquid height and heat transfer efficiency is explored through detailed numerical analysis of temperature profiles, PCM melt fractions, and enthalpy distributions. The numerical investigation has been conducted using a validated CFD model implemented in ANSYS Fluent® software. The results highlight the significant role of fins in accelerating the PCM melting process and improving heat transfer within the reactor. Notably, fins facilitates efficient conductive heat transfer during the early stages of melting. At t = 1000 s, PCM melt percentages of 22.2 %, 32.6 % and 30 % were attained with fins, compared to 15 %, 18 % and 22 % (without fins), for LH = 5.1, 10.2 and 15.3 cm, respectively. Therefore, LH = 10.2 cm showcased a 43.5 % improvement at this specific time point (1000 s). Moving forward to t = 2000 s, the most favorable melting performance is achieved with LH = 15.3 cm, resulting in a melting percentage increase to 66 % (with fins) compared to 44 % (without fins). Besides, the inclusion of fins results in significant increases of 32.56 % (5.1 cm), 57.6 % (10.2 cm) and 14.4 % (15.3 cm) in PCM enthalpy, while water temperature declined by approximately 4 K for LH = 5.1, 10.2 and 15.3 cm. These outcomes indicate clearly the importance of fins in improving the heat transfer from the irradiated water to the surrounding PCM in the annular space of the reactor.

Treatment of compressed leachate from refuse transfer stations by freeze-melt method

A small amount of leachate with complex composition will be produced during the compressing of municipal solid waste in refuse transfer stations. In this study, the freeze-melt method, a green and efficient wastewater treatment technology, was used to treat the compressed leachate. The effects of freezing temperature, freezing duration, and ice melting method on the removal rates of contaminants were investigated. The results showed that the freeze-melt method was not selective for the removal of chemical oxygen demand (COD), total organic carbon (TOC), ammonia-nitrogen (NH3-N) and total phosphorus (TP). The removal rate of contaminants was positively correlated with freezing temperature and negatively correlated with freezing duration, and the slower the growth rate of ice, the higher the purity of ice. When the compressed leachate was frozen at −15 °C for 42 h, the removal rates of COD, TOC, NH3-N and TP were 60.00%, 58.40%, 56.89% and 55.34%, respectively. Contaminants trapped in ice were removed during the melting process, especially in the early stages of melting. The divided melting method was more beneficial than the natural melting method in removing contaminants during the initial stage of melting, which contributes to the reduction of produced water losses. This study provides a new idea for the treatment of small amounts of highly concentrated leachate generated by compression facilities distributed in various corners of the city.

On the Melting Thresholds of Semiconductors under Nanosecond Pulse Laser Irradiation

In this work, a unified numerical model is used to determine the melting thresholds and to investigate the early stages of melting of several crystalline semiconductors (Si, Ge, GaAs, CdTe and InP) irradiated by nanosecond laser pulses. A molten fraction approach is used for continuous transition over the melting point. The results are compared with previously published theoretical and experimental data. A survey on the thermophysical and optical properties of the selected materials has been carried out to gather the most relevant data on temperature dependent properties for the solid and liquid states of these semiconductors where such data are available. A generalization of the obtained results is established that enables evaluation of the melting thresholds for different semiconductors based on their properties and irradiation conditions (laser wavelength, pulse duration).

Kyanite petrogenesis in migmatites: resolving melting and metamorphic signatures

Aluminosilicates (kyanite, sillimanite and andalusite) are useful pressure–temperature (P–T) indicators that can form in a range of rock types through different mineral reactions, including those that involve partial melting. However, the presence of xenocrystic or inherited grains may lead to spurious P–T interpretations. The morphologies, microtextural positions, cathodoluminescence responses and trace element compositions of migmatite-hosted kyanite from Eastern Bhutan were investigated to determine whether sub-solidus kyanite could be distinguished from kyanite that crystallised directly from partial melt, or from kyanite that grew peritectically during muscovite dehydration reactions. Morphology and cathodoluminescence response were found to be the most reliable petrogenetic indicators. Trace element abundances generally support petrographic evidence, but protolith bulk composition exerts a strong control over absolute element abundance in kyanite. Sample-normalised concentrations show distinctive differences between petrogenetic types, particularly for Mg, Ti, V, Cr, Mn, Fe and Ge. LA-ICP-MS element maps, particularly combined to show Cr/V, provide additional information about changing geochemical environments during kyanite growth. Most kyanite in the studied migmatitic leucosomes is of sub-solidus origin, with less widespread evidence for peritectic crystallisation. Where present, grain rims commonly crystallised directly from the melt; however, entire grains crystallised exclusively from melt are rare. The presence of kyanite in leucosomes does not, therefore, necessarily constrain the P–T conditions of melting, and the mechanism of growth should be determined before using kyanite as a P–T indicator. This finding has significant implications for the interpretation of kyanite-bearing migmatites as representing early stages of melting during Himalayan evolution.

Photobleaching reduces the contribution of dissolved organic carbon to glacier melting in the Himalayas and the Tibetan Plateau

Dissolved organic carbon (DOC) makes an important contribution to glacier melting in the Himalayas and the Tibetan Plateau (HTP). Photobleaching can effectively reduce the light absorption ability of DOC, further changing its impact on glacier melting, which is not yet well researched in the HTP. Therefore, snowpit samples from the Bayi, Ganglongjiama (GLJM), Jiemayangzong (JMYZ) and Demula (DML) glaciers were collected to study the influence of photobleaching on the light absorption ability of DOC and its impact on glacier melting. The results showed that the DOC concentration of snowpit samples, which was affected by the melting state and photobleaching, decreased from the northern HTP to the southern HTP. At an early stage of melting, the mass absorption cross-section value at 365 nm (MAC365) values showed a negative correlation with DOC concentrations in the snowpit at the JMYZ and DML glaciers, indicating that colored DOC tended to be concentrated in the snowpit during the melting process. With the aggravation of ablation, some snowpit samples in the GLJM and Bayi glaciers had both low concentrations and MAC365 values of DOC due to the reduced influence of photobleaching on the light absorption ability of DOC. Similarly, two fluorescence components (one protein-like component and one humic-like component) were identified in the extracted DOC at the JMYZ and DML glaciers, while those components were not detected in the GLJM glacier. Based on the sources of fluorescent DOC and five-day backward air mass trajectories, long-distance transport of pollutants from South Asia was an important source of snowpit DOC in the southern HTP. In this study, photobleaching can effectively remove colored and fluorescent DOC from snowpit samples in the HTP, further reducing the radiation forcing and glacier melting caused by DOC.

A 4,565-My-old andesite from an extinct chondritic protoplanet

The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun's photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.

Modelling the partial melting of metasediments in a low-pressure regional contact aureole: the effect of water and whole-rock composition

AbstractLow-pressure regional aureoles with steep metamorphic field gradients are critical to understanding progressive metamorphism in high-temperature metasedimentary rocks. Delicately layered pelitic and psammitic metasedimentary rocks at Mt Stafford, central Australia, record a greenschist- to granulite-facies Palaeoproterozoic regional aureole, associated with S-type granite plutons, reflecting metamorphism in the range 500–800 °C and at ∼3 kbar. The rocks experienced minimal deformation during metamorphism and partial melting. Partial melting textures evolve progressively along the steep metamorphic field gradient from the incipient stages of melting marked by cuspate grains with low dihedral angles, to melt proportions sufficient to form diatexite with schollen. Phase equilibria modelling in the NCKFMASHTO system for pelitic, semi-pelitic and high- and low-ferromagnesian psammitic samples quantitatively illustrates the dependence of partial melting on rock composition and water volume. Pelitic compositions are more fertile than psammitic compositions when the water content in the rocks is low, especially during the early stages of melting. The whole-rock ferromagnesian component additionally influences melt fertility, with ferromagnesian-rich psammite being more fertile than psammite with a lower ferromagnesian component. Subtle variations in free water content can result in obvious changes in melt volume but limited variation in melt composition. Distinct melting histories of pelitic and psammitic rocks inferred from field relationships may be partially attributed to potential differences in water volume retained to super-solidus conditions. Melt composition is more dependent on the rock composition than the variation in water content.

Investigation on the melting process of phase change material in a square cavity with a single fin attached at the center of the heated wall

In this study, melting of a phase change material (PCM) in a square cavity with a single fin attached at the center of the heated wall is studied numerically employing the enthalpy-porosity method. The opposite wall to the heated wall in the square cavity is cold. The other two adjacent walls are thermally insulated. Paraffin wax is chosen as a PCM due to its demonstrable favorable properties. The thermophysical properties of the paraffin wax are assumed to be a dual function of temperature and phase. The influence of the fin length on the melting process of the paraffin wax is examined. Moreover, the orientation of the square cavity on the melting process is scrutinized. The numerical results elucidate that the melting rates increase significantly by embedding the fin into the paraffin wax. As the fin length is incremented, the melting rate intensifies considerably during the early stages of melting. However, the effect of the fin length on the melting rate diminishes after a long period of heating has happened. It is also observed that the melting rate can be augmented significantly by changing the orientation of the heated wall in the square cavity.

Experimental investigation of transient melting and heat transfer behavior of nanoparticle-enriched PCM in a rectangular enclosure

Abstract An experimental study was conducted to investigate the transient melting and heat transfer behavior of nanoparticle-PCM mixtures in a rectangular enclosure. Four types of nanoparticles, silver, copper oxide, aluminum oxide and multi-walled carbon nanotubes were considered, and paraffin wax was used as the PCM. The results show that all four nanoparticle-enriched PCM mixtures provided better thermal performance as compared to the case with the plain PCM. It has been argued that the addition of surfactant to improve the suspension-ability of nanoparticles in the PCM counteracted the viscosity enhancement due to nanoparticles in the PCM. Among the four tested nanoparticles, silver nanoparticles were found to be the most effective in the heat transfer enhancement, followed by copper oxide nanoparticles. The performances of aluminum oxide and MWCNT were hampered due to their higher settlement rates. The transient heat transfer coefficients for all cases were computed and found to have increased rapidly in the early stages of melting up to the melted fraction of about 0.2, after that they remained almost constant for the rest of the melting process. The heat transfer coefficients for CuO and silver were found to be about 18% and 14% higher than the plain PCM case, while aluminum oxide and MWCNT were lower and closer to the plain PCM case due to higher sinking rates. The thermal behavior of CuO-enriched PCM was further investigated for 1, 3, 6, 8 and 10% mass fractions of CuO. It was found that under given conditions, 6% CuO fraction provides the best thermal performance and highest melting rate. For this case, the melting rate and heat flux were about 25% higher than that for the plain PCM case.

Effect of Technetium-99 sources on its retention in low activity waste glass

Small-scale crucible melting tests on simulated waste glass were performed with technetium-99 (Tc-99) introduced as different species in a representative low activity waste simulant. The glass saw an increase in Tc-99 retention when TcO2∙2H2O and various Tc-minerals containing reduced tetravalent Tc were used compared to tests in which pertechnetate with heptavalent Tc was used. We postulate that the increase of Tc retention is likely caused by different reaction paths for Tc incorporation into glass during early stages of melting, rather than the low volatility of reduced tetravalent Tc compounds, which has been a generally accepted idea. Additional studies are needed to clarify the exact mechanisms relevant to the effect of reduced Tc compounds on Tc incorporation into or volatilization from the glass melt.

The initial stages of melting of graphene between 4000 K and 6000 K.

Graphene and its analogues have some of the highest predicted melting points of any materials. Previous work estimated the melting temperature for freestanding graphene to be a remarkable 4510 K. However, this work relied on theoretical methods that do not accurately account for the role of bond breaking or complex bonding configurations in the melting process. Furthermore, experiments to verify these high melting points have been challenging. Practical applications of graphene and carbon nanotubes at high temperatures will require a detailed understanding of the behavior of these materials under these conditions. Therefore, we have used reliable ab initio molecular dynamics calculations to study the initial stages of melting of freestanding graphene monolayers between 4000 and 6000 K. To accommodate large defects, and for improved accuracy, we used a large 10 × 10 periodic unit cell. We find that the system can be heated up to 4500 K for 18 ps without melting, and 3-rings and short lived broken bonds (10-rings) are observed. At 4500 K, the system appears to be in a quasi-2D liquid state. At 5000 K, the system is starting to melt. During the 20 ps simulation, diffusion events are observed, leading to the creation of a 5775 defect. We calculate accurate excitation energies for these configurations, and the pair correlation function is presented. The modified Lindemann criterion was calculated. Graphene and nanotubes together with other proposed high melting point materials would be interesting candidates for experimental tests of melting in the weightless environment of space.

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Volatile loss of radioactive technetium-99 (99Tc) to off-gas is a major challenge when vitrifying low-activity waste (LAW) at the U.S. Department of Energy's Hanford Site in Washington State. We investigated the partitioning and incorporation of rhenium (Re) (a nonradioactive surrogate for 99Tc) into the glass melt during crucible melting of two simulated LAW feeds that have exhibited a large difference in 99mTc/Re retention in glass from small-scale melter tests. Each feed was prepared from a simulated liquid LAW and additives (boric acid, silica sand, etc.). The as-mixed slurry feeds were dried at 105°C and heated to 600–1100°C at 5K/min. The dried feeds and heat-treated samples were leached with deionized water for 10min at room temperature followed by 24-h leaching at 80°C. Chemical compositions of the resulting solutions and insoluble solids were analyzed. Volume expansion measurements and X-ray diffraction (XRD) analyses were performed on dried feeds and heat-treated samples to characterize the progress of feed-to-glass conversion reactions. We found that incorporation of Re into the glass melt was virtually completed during the major feed-to-glass conversion reactions that occurred at ≤700°C. The results of our study suggest that the different compositions of the salt phases formed during early stages of melting at ≤700°C are responsible for the large difference in Re incorporation into the glass melt in these two feeds.

Modeling radar backscattering from melting snowflakes using spheroids with nonuniform distribution of water

In a number of studies it is reported that at the early stages, melting of aggregate snowflakes is enhanced at lower parts. In this paper, the manifestation of the resulting nonuniform distribution of water is studied for radar backscattering cross sections at C, Ku, Ka and W bands. The melting particles are described as spheroids with a mixture of water and air at the bottom part of the particle and a mixture of ice and air at the upper part. The radar backscattering is modeled using the discrete-dipole approximation in a horizontally pointing geometry. The results are compared to the T-matrix method, Mie theory, and the Rayleigh approximation using the Maxwell Garnett mixing formula. We find that the differential reflectivity and the linear depolarization ratio show systematic differences between the discrete-dipole approximation and the T-matrix method, but that the differences are relatively small. The horizontal cross sections show only small differences between the methods with the aspect ratio and the presence of resonance peaks having a larger effect on it than the nonuniform distribution of water. Overall, the effect of anisotropic distribution of water, reported for early stages of melting, is not significant for radar observations at the studied frequencies.

Experimental and numerical study of constrained melting of n-octadecane with CuO nanoparticle dispersions in a horizontal cylindrical capsule subjected to a constant heat flux

Constrained melting of n-octadecane as phase change material (PCM) dispersed with CuO nanoparticles as thermal conductivity enhancer (TCE) that was contained and heated in a horizontal cylindrical vessel under a constant heat flux is investigated experimentally and numerically. The experiments entailed recording of temperatures at different radial and angular coordinates inside the test cell, thus allowing for monitoring the progress of the melting front under various rates of heat flux and multiple nanoparticle weight concentrations. The simultaneous governing conservation equations are solved computationally by utilizing the finite element approach. The computational model is validated and the results showed a good agreement with previous related work. The agreement between the experimental and simulated results is reasonable. The effects of the nanoparticle weight concentration and the amount of applied heat flux (Rayleigh number) on the melting characteristics are examined. The melting process is characterized by progress of the shape of the solid–liquid interface, melting rate, melt fraction and charging time. The experimental and numerical results reveal that there is an enhancement in melting characteristics with the increase of both nanoparticle loading (intensifying the effective thermal conductivity) and the Rayleigh number (augmenting the role of natural convection). This enhancement in the melting process can be indicated by increasing the melting rate which leads to acceleration of the melting time. In early stages of melting, conduction is dominant leading to concentric isotherms and high melting rate. As time progresses, natural convection will develop and increase the melting rate in the top region of the cylindrical container. On the other hand, melting at the bottom region is governed by conduction and secondary recirculation flow due to thermal instabilities which are recorded by waviness of the interface there. The melt fraction, melting rate and rate of enhancement in charging time are improved with the increasing of the Rayleigh number. Additionally, the rate of acceleration of melting is comparably high for low nanoparticle concentration and it will degrade as the amount of nano-additives increases as the augmentation effect of viscosity, agglomeration and precipitation may be negating the enhancement in thermal conductivity.

Unusually Long trans/gauche Conformational Equilibration Time during the Melting Process of BmimCl, a Prototype Ionic Liquid

Abstract The melting process of 1-butyl-3-methylimidazolium chloride (bmimCl), a prototype room-temperature ionic liquid, has been studied with fast low frequency Raman spectroscopy. Simultaneous tracing of the lattice vibrations and trans/gauche conformational marker bands reveals that the conformational change in the butyl group occurs a few seconds after the loss of lattice vibrations. This finding indicates that the alkyl chain interaction in bmimCl is so strong that the butyl conformation hardly changes in the very early stage of melting.

Molecular and crystal structure of 4-alkoxybenzoic acids: Design of the mesogenic phase

The crystal and molecular structures of 4-alkoxybenzoic acids CnH2n + 1-O-C6H4-COOH, n = 4–12, which are nematic (n = 4–6) or smectic-nematic (n = 7–12) mesogenes, are studied. No direct relationship between the molecular geometry and mesogenic properties is found. All the crystal structures contain dimers formed by pairs of O…H-O hydrogen bonds between carboxyl groups. Crystals belonging to the group of smectic-nematic liquid crystals (SNLC) are built of separate regions, namely, loosely packed aliphatic regions and closely packed aromatic regions with significant π-stacking interactions. Loose aliphatic regions occur in crystals belonging to the group of nematic liquid crystals (NLC); however, they are surrounded by dense aromatic regions and do not run throughout the crystal. In NLC, π-stacking interactions are far weaker than in SNLC. At the early stage of melting of SNLC crystals, structurized associates due to both π-stacking interactions and hydrogen bonds are retained in the melt (smectic phase), whereas, upon further heating, only hydrogen-bonded associates are left (nematic phase). In the course of melting of NLC, only hydrogen-bonded dimers are retained in the melt (nematic phase).

Organic Contaminant Release from Melting Snow. 1. Influence of Chemical Partitioning

A melting snowpack can deliver organic contaminants to terrestrial and aquatic ecosystems in the form of short and concentrated pulses. The mechanisms and kinetics of the underlying processes need to be understood to successfully integrate them into contaminant and water quality models. Controlled laboratory-based snowmelt experiments using artificially produced snow spiked with organic target contaminants reveal how chemical behavior during melting is dependent on the partitioning between the different phases within the bulk snow. Behaving similar to inorganic ions, water soluble organic chemicals, such as atrazine, are preferentially released at an early stage of melting, because such chemicals, accumulated at the snow grain surface, dissolve in the downward percolating meltwaterfront. Hydrophobic substances attached to particles, such as the larger polycyclic aromatic hydrocarbons, are often released at the very end of the melt period, because particle coagulation and snow densification render the melting snowpack an efficient filter trapping the particles. A notable fraction of volatile chemicals, such as naphthalene, will transfer from the melting snowpack to the lower atmosphere due to evaporation. Organic pollutants with intermediate partition properties, such as lindane, can easily switch between the bulk snow phases and their elution behavior is therefore more sensitive to varying snow and melt characteristics.

Thermal evolution and physics of melt extraction on the ureilite parent body

We develop a physical model of the thermal history of the ureilite parent body (UPB) that numerically tracks the history of its heating, hydration, dehydration, partial melting and smelting as a function of its formation time and the initial values of its composition, formation temperature and water ice content. Petrologic and chemical data from the main group (non-polymict) ureilite meteorites, which sample the interior of the UPB between depths corresponding to pressures in the range 3–10 MPa, are used to constrain the model. We find that to achieve the ∼30% melting inferred for ureilites from all sampled depths, the UPB must have had a radius between ∼80 and ∼130 km and must have accreted about 0.55 Ma after CAI formation. Melting began in the body at ∼1 Ma after CAI, and the time at which 30% melting was reached varied with depth in the asteroid but was always between ∼4.5 and ∼5.8 Ma after CAI. The total rate at which melt was produced in the UPB varied from more than 100 m 3 s −1 in the very early stages of melting at ∼1 Ma after CAI to ∼5 m 3 s −1 between 2 and 3 Ma after CAI, decreasing to extremely small values as the end of melting was approached beyond ∼5 Ma. Although the initial period of high melt production occupied only a short time around 1 Ma after CAI, it corresponded to ∼half (16%) of total silicate melting, and all strictly basaltic (i.e. plagioclase-saturated) melts must have been produced during this period. A very efficient melt transport network, consisting of a hierarchy of veins and larger pathways (dikes), developed quickly at the start of melting, ensuring rapid (timescales of months) transport of any single parcel of melt to shallow levels, thus ensuring that chemical interaction between melts and the rocks through which they subsequently passed was negligible. Volatile (mainly carbon monoxide) production due to smelting began at the start of silicate melting in the shallowest parts of the UPB and at later times at greater depths. Except at the very start and very end of melting, the volatile content of the melts produced was always high – generally between 15 and 35 mass % – and most of the melt produced was erupted at the surface of the UPB with speeds well in excess of the escape velocity and was lost into space. However, we show that 30% melting at the 3 MPa pressure level was only possible if ∼15% of the total melt produced in the asteroid was retained as a small number (∼5) of very extensive, sill-like intrusions centered at a depth of ∼7 km below the surface, near the base of the ∼8 km thick outer crust of the asteroid that was maintained at temperatures below the basalt solidus by conductive heat loss to the surface. The horizontal extents of these sills occupied about 75% of the surface area of the UPB, and the sills acted as buffers between the steady supply of melt from depth and the intermittent explosive eruption of the melt into space. We infer that samples from these intrusions are preserved as the rare feldspathic (loosely basaltic) clasts in polymict ureilites, and show that the cooling histories of the sills are consistent with these clasts reaching isotopic closure at ∼5 Ma after CAI, as given by 26Al– 26Mg, 53Mn– 53Cr and Pb–Pb age dates.

Interfacial tension measurement of Ni-S liquid using high-pressure X-ray micro-tomography

High-pressure, high-temperature X-ray tomography experiments have been carried out using a large volume toroidal cell, which is optimized for interfacial tension measurements. A wide anvil gap, which corresponds to a field of view in the radiography imaging, was successively maintained to high pressures and temperatures using a composite plastic gasket. Obtained interfacial tensions of Ni-S liquid against Na, K-disilicate melt, were 414 and 336 mN/m at 1253 and 1293 K, respectively. Three-dimensional tomo-graphy images revealed that the sample had an irregular shape at the early stage of melting, suggesting either non-equilibrium in sample texture and force balance or partial melting of surrounding silicate. This information cannot always be obtained from two-dimensional radiographic imaging techniques. Therefore, a three-dimensional tomography measurement is appropriate for the precise interfacial measurements.

Interactions of Simulated High Level Waste (HLW) Calcine with Alkali Borosilicate Glass

ABSTRACTThis study looks at the interactions between simulated calcined high level waste from fuel reprocessing and mixed alkali borosilicate glass frit in the early stages of melting, and the possibility of the formation of yellow phase during these stages. Simulant “calcine” from a full scale inactive trial (Magnox: oxide “blend” 25:75) was pre-mixed with alkali borosilicate glass, to achieve a 25wt% waste loading, and melted at 1050°C at various times. It is shown that dissolution occurs in two separate stages; the first involves formation of a low density CsLiMoO4 fluid, which separates and forms a yellow/green layer on the surface of the melt, accompanied by some dissolution of rare- earth elements (Nd, Ce, Gd) and Zr from the waste into the glass matrix. The second stage entails more extensive migration of these rare-earth elements into the glass, and the disappearance of the surface layer on the melt. The glass appears more homogenized at the later stages of melting, but still contains undissolved particles of calcine after 16 minutes.