Melting Procedure Research Articles

Unusual crystallization pathways revealed in six barium disilicate (BaSi2O5) glasses

Due to the unusual crystallization of (nominally) stoichiometric BaSi2O5 (BS2) glass, which shows unexpected and diverse crystal phases, a series of six glasses with different chemicals and melting procedures were prepared in three laboratories and characterized before and after crystallization by differential scanning calorimetry, density measurements, X-ray diffraction, FTIR, and Raman spectroscopy. The aim of this study was to assess whether there is systematic behavior in the crystallization pathways in relation to precursor chemicals, impurities, and hydroxyl content of this glass. Small glass monoliths were treated at the first DSC crystallization peak and quenched to determine which phases formed in the early-stages of crystallization. The glass transition temperatures (Tg) divide these six glasses between those with a Tg near 690 °C versus those near 700 °C. The DSC peak crystallization temperatures varied even more; from 855 to 917 °C. In these six glasses, our results are best explained by a combination of metastable high-BaSi2O5 and Ba6Si10O26. Monotonic trends in crystallization show that the DSC signal from the Ba-rich phases increases as the Tg and the crystallization temperatures increase. The BS2 glasses with both the lowest Tg and lowest DSC crystallization temperatures show the most barium disilicate crystal. This leads to the conclusion that the metastable monoclinic high-BaSi2O5 is favored in these conditions. The small differences in glass synthesis conditions and chemicals used strongly influence the relative proportions of phases which crystallize and their kinetics. In-situ and ex-situ diffraction measurements confirm the conclusions above. The structural distinctions between the barium silicate crystals and the BS2 supercooled liquid, and the implications for the role of structural polymerization are discussed. We conclude that high-BaSi2O5 or Ba6Si10O26 are the predominant phases in the earliest stages of crystallization. This study highlights the extreme sensitivity of BS2 glass crystallization kinetics and pathways to minor differences in composition and synthesis conditions and explains the different conclusions reached by distinct authors that worked on the crystallization of BS2 glasses.

Heat storage system for air conditioning purpose considering melting in existence of nanoparticles

Mixture of MWCNT nanoparticles and paraffin with melting point of 24.5 °C has been utilized for saving the energy inside the ventilating system. The utilized duct for transportation of air has various tubes containing the paraffin and four styles for such obstacles have been presented. Finite volume method for modeling the melting procedure was utilized and validation test based on previous numerical article indicated good accommodation. Temperature of system at t = 0 is 6.5 °C less than 24.5 °C and hot laminar air flow with temperature of 14 K greater than initial temperature makes the paraffin to melt. With adding MWCNT nanoparticles the required time of charging reduce from 7.015 h to 6.74 h when DR = 0.16 which is associated with promising influence of such particles in augmentation of heat absorption. Moreover, as diameter of tube changes from 9.7 cm to 5 cm, the melting time declines from 6.74 h to 4.12 h. The needed time of process declines around 58.7 % with utilizing smaller tubes in existence of nanoparticles.

Thermal behavior and explosive properties of TNT/RGO

2,4,6-trinitrotoluene (TNT), is the most widely accessible explosive. Thanks to the melt cast characteristics (melting temperature of TNT is 80-82 °C,), lead to contribute in many applications as mortars, grenades, artillery rounds, warheads, and antipersonnel mines. TNT has high chemical stability, and moderate sensitivity. In this paper, a novel addition of nano particles of reduced graphene oxide (RGO) was added to enhance the TNT characteristics. A composite TNT/RGO 98:2 wt. % was prepared. The morphology of the composite mixture was captured using scanning electron microscopy (SEM). Impact sensitivity and friction sensitivity were evaluated, thermal behavior was investigated using diffeential scanning calorimetry (DSC), the characterization of the prepared composite and pure TNT was examined using an X-Ray diffractometer. Explosive characteristics were determined by detonation velocity and brisance by Kast . The results showed improvement in the sensitivity with reserving the high explosive characteristics of TNT. Interestingly, a decrease in the melting point of TNT due to the presence of RGO in the composite was observed. This addition might be an effective parameter in the melting procedure of TNT.

ENHANCEMENT OF SOLUBILITY OF POORLY SOLUBLE DRUG LANSOPRAZOLE

Objective: To improve the solubility of lansoprazole with solid dispersion (SD) method by using hydrophilic polymer PEG 6000, PEG 15000 and amphiphilic polymer solupus. Methods: Solid dispersions of lansoprazole were prepared with polymers PEG 6000, PEG 15000 and amphiphilic polymer soluplus, using three methods of preparation–1) solvent melting 2) solvent evaporation and 3) microwave heating method along with different drug: carrier ratios. Performance of the prepared formulations were evaluated for solubility, fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC) parameters. Results: All SDs showed enhancement in solubility of lansoprazole. Solubility and also carrier concentration showed a positive effect on solubility. The lansoprazole-soluplus solid dispersion 1:3 in concentration showed enhanced aqueous solubility when formulated with a solvent melting procedure. Conclusion: The studies indicated that PEG 6000, PEG 15000 and Soluplus inhibite crystallization of lansoprazole, subsequently form amorphous state in solid dispersion, which is, confirmed via FTIR and DSC results of lansoprazole solid dispersion.

Melting and solidification of phase change materials in metal foam filled thermal energy storage tank: Evaluation on gradient in pore structure

• Melting-solidification of phase change material in graded metal foam is studied; • Gradient in porosity rather than pore density affects greatly phase change; • Complete melting time under positive graded porosity is shortened by 17.9%; • Optimal design reduces melting-solidification cycle time by 10.9%; Solar energy as a renewable energy has sufficient development potential in energy supply applications, with the help of heat storage equipment that deals with its intermittence problem. To further improve melting/solidification efficiency, a novel energy storage tank filled by phase change materials with graded metal foams is proposed. Three gradient structures (positive gradient, non-gradient, and negative gradient) in porosity or pore density are designed. Three pieces of metal foam with the fixed porosity of 0.94 but varying pore densities of 15, 45, and 75 pore per inch is packed to form gradient in pore density design. For gradient in porosity, three selected porosities of 0.90, 0.94, and 0.98 are employed. A test bench for the phase interface visualization is set up and experiment on melting/solidification evolution and temperature are carried out. Achieving satisfactory agreement with experiments, numerical models are employed to explore the thermal features for phase change materials embedded in various kinds of graded metal foams during melting and solidification procedures. Results demonstrate that gradient design in pore density does not affect the melting and solidification procedures, while graded porosity helps notably the melting and solidification processes. Design on graded porosity reduces the complete melting time by 21.1% compared with the non-gradient structure. The global phase change process can be strengthened only if the melting is strengthened. The optimal gradient in porosity reduces the overall cycle of melting and solidification time by 10.9%, compared to the uniform filling pattern.

UV/Vis dose response of a reusable PMMA-NaCl polymer composite

Purpose:Two-dimensional dosimeters are convenient tools for quickly checking the radiation profile in radiotherapy. The currently used solution is costly, especially in busy institutions with extensive quality control procedures. This study fabricates a reusable 2-mm-thick PMMA-NaCl polymer composite sheet and assesses its dosimetric properties. Methods:The PMMA-NaCl composite sheets were prepared using hot melting procedures. For dosimetric evaluations, the samples were irradiated using 6 MV X-ray photons from a medical linac. The absorbed doses were measured as changes in the optical absorption spectrum using a UV–Vis spectrometer. Results:The lowest dose detected by the samples was 5 Gy, with a linear dose response of at least 20 Gy. The repeatability of the measurements was good, with a standard deviation of 5.03%. The signal was bleachable by using a 100 W filament-type lamp for dosimetric reuse. Conclusion:The 2-mm-thick PMMA-NaCl polymer-composite sheet could measure absorbed radiation doses from 6 MV X-ray photons down to 5 Gy. Because the sample is reusable, it can be used in a cost-effective two-dimensional radiation dosimeter to ensure the quality of medical linacs.

Manufacturing and analysis of VNbMoTaW refractory high-entropy alloy fabricated by selective laser melting

Refractory high entropy alloys (RHEAs) have provided a new research direction for the development of structural materials with high-temperature characteristics due to their excellent heat tolerance and mechanical properties. Along these lines, in this work, bulk VNbMoTaW RHEA on a tungsten substrate was fabricated by enforcing the selective laser melting (SLM) technique. The impact of the laser scanning speed on the surface morphology, internal defect, microstructure and mechanical properties of the VNbMoTaW RHEA specimen were thoroughly investigated. The extracted results showed that the pores and cracks were the main sources of defects within SLMed VNbMoTaW RHEA. Interestingly, the pores disappeared when a lower scanning speed was applied. However, the manifestation of cracks was inevitable regardless of the employed scanning speed. The microstructure of the VNbMoTaW RHEA was observed in cross-section, indicating the existence of a columnar dendritic structure, which revealed the existence of a strong epitaxial growth along the building direction. In addition, the typical microstructure feature of the VNbMoTaW RHEA on the top surface was cellular structure. The average microhardness of the VNbMoTaW RHEA fabricated by the SLM method was about 664 HV, which was 1.3 times higher than that processed by arc-melting (525 HV). Moreover, the surface of the VNbMoTaW RHEA specimen was subjected to tensile residual stress, which gradually decreased as the laser scanning speed was increased. The VNbMoTaW RHEA specimens prepared by SLM exhibit higher compressive strength than the corresponding specimens, which were prepared by enforcing the vacuum arc melting procedure.

Numerical approach for melting of paraffin inside a duct containing multi sinusoidal PCM containers

New design of system for providing cold air within the building was recommended in this study. Mixture of TiO2 (with fraction of 0.04) and RT25 was applied as NEPCM and three-lobed ducts were filled with them. Air become warmer outside the building owing to sun radiation and with moving along the channel, its temperature reduces because of melting procedure. Homogeneous model for NEPCM has been incorporated in equations of paraffin zone which contain laminar flow. Also, the range of inlet velocity contains the turbulent flow at air flow with Re = 6e3 to 1e4. The temperature of inlet air (Tin) was assumed as another active parameter. Irreversibility of system has been analyzed, too. Testing the exactness of procedure of modeling was applied according to previous published work and good accommodation has been reported. To decline the computing price, size of grid and time step were analyzed to find the optimized values. With adding TiO2 particles, the temperature of paraffin enhances and speeds of charging increases. At t = 5hr, dispersing nano-powders makes temperature and LF to grow around 0.19% and 0.79%, respectively. The required time declines around 31.26% and 40.78% with rise of Re and Tin.

Upconversion Luminescence Enhancement In Lanthanide Ions Doped Bismuth Tellurite Glasses

Lanthanide ions doped glasses are studied by researchers for upconversion luminescence. Rare earth doped bismuth tellurite glasses codoped with and without silver nanoparticle were synthesized by melt and quench procedure for the study of enhanced upconversion luminescence. Physical parameters as molar mass, molar volume, and density were evaluated. Amorphous nature of samples was verified by x-ray diffraction. DSC is carried for information of thermal properties. UV-Visible absorption and fluorescence spectra is obtained to get detail information of upconversion luminescence. Upconversion mechanism of rare earth erbium and ytterbium ions discussed. Three prominent upconversion luminescence is observed two in green region and one is in red.

Formulation and Evaluation of Obeticholic Acid Solid Dispersion Tablet

Obeticholic acid is a farnoside X receptor agonist that was recently licenced by the US Food and Drug Administration. In a solvent, solubility is lower, therefore it is necessary to improve solubility. Solid dispersion is one of the most effective methods for increasing Obeticholic acid's solubility. Solid dispersion can be prepared in a variety of ways. Fusion (Hot Melting) is one of the most straightforward and cost-effective methods for producing solid dispersion. Poloxamer is one of the finest polymers for solid dispersion production. Poloxamer 188 and Poloxamer 407 are widely accessible. Above solid dispersion is made using the fusion or hot melting procedure. The solubility of the prepared solid dispersion has increased to 0.347 mg/ml. In comparison to the polymer combination, which has a drug release rate of 99.63 percent, the percent drug release is also superior. Precompression settings were found to be within a reasonable range. Post compression parameters such as Hardness, Friability, Uniformity of weight, content uniformity are in standard range. F7 formulation shows 99.63 ± 0.19 in 60 minutes of time. Phosphate buffer 7.4 is used for dissolution test apparatus. All result parameter shows that prepared solid dispersion of Obeticholic acid by using poloxamer gives improved solubility and increased drug release.

Construction of a Removable Partial Denture (RPD): Comparison between the Analog Procedure and the Selective Laser Melting Procedure

A partial removable denture is a device that allows the patient to recover from a partial edentulism. This case report describes the realization of a chrome–cobalt partial removable denture by using two different realization methods: (1) analogic framework and (2) hybrid framework. This allowed us to compare the stability, retention as well as clasp quality of both the products and to highlight their respective advantages, disadvantages, and limitations.

One-step precipitated all-inorganic perovskite QDs from amorphous media for backlighting display and reproducible laser-driven white lighting

Embedded within an inorganic amorphous media, all-inorganic perovskite CsPbX3 (X = Br, I) quantum dots (QDs) overcome the limitation of poor stability for practical application, which has attracted widespread attention. However, the employed thermal treatment strategies for the melting procedure to obtain the amorphous matrix are time- and energy-consuming. Here, we propose an efficient and cost-saving approach for mass production of CsPbBr3 QDs@glass one-step, which maintains the high photoluminescence quantum yield (PLQY 47 %) and narrow full width at half maximum (FWHM 24 nm) of CsPbBr3 QDs. Furthermore, a red shift from 523 to 645 nm of the as-prepared perovskite is achieved by adjusting the halogen composition of the amorphous host from Br to Br/I. Herein, the well-addressed photo- and moisture-stability of the green CsPbBr3 and red CsPbBr1.2I1.8 QDs@glass perovskites endow a 118 % National Television Standards Committee (NTSC) and 88 % Rec. 2020 standards color gamut, combined with a commercial blue GaN chip, for state-of-the-art backlighting display. Moreover, it is found that the performance degradation of the laser-driven white lighting device, causing by the damages of high-power laser irradiation, can be fully recovered after a facile thermal treatment process. We believe that the synthesis strategy opens up a new avenue for the large scale synthesis of high quality perovskite QDs with low cost.

Evolution Mechanism of Transient Strain and Residual Stress Distribution in Al 6061 Laser Welding

Considering the harm that residual stress causes to the mechanical properties of a weld joint, the evolution mechanisms of transient strain and residual stress distribution are investigated in laser welding of Al 6061, considering that these originate from non-uniform temperature distribution and are intensified further by the unbalanced procedure of melting and solidification. Thermal-elastic-plastic finite element method is developed and analyzed, while the actual weld profile is novel fitted by a B-spline curve. Transient strain is extracted by strain gauges. Longitudinal strain starts from a fluctuating compressive state and progresses to an ultimate residual tension state at the starting and ending welding positions, respectively. The maximum fitting deviation of the weld profile is 0.13 mm. Experimental and simulation results of residual strain are 842.0 μ and 826.8 μ, with a relative error of 1.805% at the starting position and −17.986% at the ending position. Near the weld center, mechanical behavior is complexly influenced by thermal expansion and contraction in the weld zone and the reaction binding force of the solid metal. Within a distance between −10 mm and 10 mm, and longitudinal stress is in a tension state, transverse stress fluctuates with a high gradient (~100 MPa).

Evaporation for element Al in K417 Ni-based superalloy during electron beam remelting

To date, few researches describe the evaporation for Al well in superalloy during electron beam (EB) melting, for the reason that Al has a very high saturated vapor pressure but has a relatively low evaporation. In order to study the evaporation for Al, EB technology has been used to remelt a multi-component Ni-based superalloy K417 in our work. The difference between melting and smelting procedure has been emphasized particularly. The weighted average mixing heat was used to describe activity coefficient, and the effective temperature during 9, 12 and 15 kW EB smelting is 2290, 2320 and 2430 K, respectively. In addition, Al evaporation was described well after compensation and the corresponding compensation constant ω is suggested to be applicable for Ni-based superalloy preparation. This work shows its significance in theoretical guidance for the preparation of Ni-based superalloys.

Considering the tap-changing modifications in protection of EAF transformers

This paper deals with the modeling of EAF feeding system taking into account the tap transition for assessment of a suggested scheme of differential protection. There are several challenges in the implementation of the differential protection in the EAF transformer which reveal the importance of the system modeling. Large current in the secondary side of the transformer, similarity of normal and fault conditions, and frequent tap variation in the transformer during the melting procedure are the most serious concerns. Considering the mechanism of the tap changers, the new tap setting is readjusted in the algorithm to prevent mal-operation of the protection. These challenges can be rectified by suitable modeling of EAF feeding system and an efficient differential protection scheme. To this end, the EAF as an electrical load, the EAFs' transformer, and the mechanism of the tap changing are properly modeled in this work. The proposed model of the EAF is based on real recorded data from EAFs used in a steel company, to fully simulate the nonlinear and time-variant characteristics of this electrical load. The proposed models of the EAFs' transformer and tap changer enable us to simulate different tap variations and internal faults in the system. The performance of the suggested differential protection algorithm is evaluated using plenty of simulations in different conditions of the system.

Microcapsules composed of stearic acid core and polyethylene glycol‐based shell as a microcapsule phase change material

The shell materials of the existing microcapsule phase change materials (PCMs) are always not PCMs, so the enthalpy change (ΔH) in the phase transition processes of these microcapsule PCMs is much smaller compared with the pure encapsulated PCMs (the core materials), reducing the storage ability for thermal energy of the microcapsules. Herein, we prepared microcapsules composed of stearic acid (SA) core and polyethylene glycol (PEG)-based shell as a microcapsule PCM. The PEG-based shell is a solid-solid PCM with cross-linked network, which is in solid state even at 80°C, avoiding the leakage and lose of the whole microcapsule PCM. Additionally, the microcapsule PCM has high ΔH of 113.4 and 115.3 J g−1 during their solidification and melting procedures respectively, displaying outstanding storage capacity for thermal energy. The microcapsule PCM shows dual temperature range in the melting/solidification process resulting in a wide effective temperature range, and has better thermal stability than pure SA. Moreover, the thermal property of the microcapsules changes a little after 100 times of thermal cycling, indicating high thermal reliability of the material.

Development of low‐loss lead‐germanate glass for mid‐infrared fiber optics: II. preform extrusion and fiber fabrication

AbstractFor lead‐germanate glass fibers, reducing the content of hydroxyl (OH) groups and the formation of metallic Pb species is essential to pave the way for their applications as low‐loss mid‐IR fiber optics since OH and metallic Pb species cause intense absorption and scattering loss, respectively, in the mid‐IR spectral range. The first part of this study reported the optimization of the glass melting procedure to obtain low amount of OH while preventing formation of metallic Pb species in lead‐germanate glass. Here, the second part of this study reports the investigation of the process conditions to fabricate low‐loss lead‐germanate glass fiber through further understanding of the co‐effects of glass melting and heat treatment atmospheres on the formation of nano‐ and micron‐scale metallic Pb species in both the as‐produced and heat treated lead‐germanate glasses. Finally, using this advance in knowledge, we successfully fabricated low‐loss lead‐germanate glass fibers with no presence of reduced metallic Pb particles by optimizing dehydration agent, glass melting, preform extrusion and fiber drawing conditions. The optimized fabrication conditions reduced the unstructured fiber loss by almost one order to <0.3 dB/m at 1.55 μm.

A parametric local remelting approach to improve mechanical properties of selective laser melted 24CrNiMo steel

An approach of parametric local remelting (PLR) during selective laser melting (SLM) procedure was carried out based on 24CrNiMo steel. The specimens fabricated with this method exhibited an excellent combination of strength and ductility (tensile strength ~ 1303.3 MPa, yield strength ~ 1175.2 MPa and elongation ~ 16.2%) compared with the common near-fully dense counterpart (tensile strength ~ 1252.6 MPa, yield strength ~ 1108.6 MPa and elongation ~ 14.0%). The performance presents a periodic mechanical distribution, leading to a more uniform deformation along the loading direction. This developed approach would be beneficial to the mechanical design and manufacture for SLM process almost without additional cost.

Recyclable and Reprocessable Crosslinked Rubber Enabled by Constructing Ionic Crosslinked Networks

The recycling of covalently crosslinked rubber faces paramount challenges as it is difficult to be recycled by melting or solution procedures because of its irreversible crosslinked structure forme...

The Influence of a Microalloying System on the Structure of a Coiled Strip Produced under Conditions of Endless Strip Production

This study investigates the influence of various microalloying systems (Nb–V–Ti, V–Nb–Ti, V‒N, V–Ti–N, V–Ti) of low-carbon pipe steels on the formation of the microstructure, fine structure, and deposition of dispersive particles in rolled items produced under conditions of endless strip production (ESP) at Vyksa Steel Works in accordance with a combined procedure of melting, casting into thin slab (with the thickness of 90 mm), direct rolling with subsequent accelerated cooling, and coiling into a roll. It has been demonstrated that addition of titanium into steel leads to the formation of particles in austenite region. These particles are coarser in steels with titanium and niobium. In steels with higher nitrogen content fine interphase particles are formed, which are not observed in systems with Nb, V, and Ti. In steels of the Nb–V–Ti, and V‒Nb–Ti microalloying systems no particles with vanadium are observed.