Low Melting Point Materials Research Articles

Particle discrimination in a NaI crystal using the COSINUS remote TES design

The COSINUS direct dark matter experiment situated at Laboratori Nazionali del Gran Sasso in Italy is set to investigate the nature of the annually modulating signal detected by the DAMA/LIBRA experiment. COSINUS has already demonstrated that sodium iodide crystals can be operated at mK temperature as cryogenic scintillating calorimeters using transition edge sensors, despite the complication of handling a hygroscopic and low melting point material. With results from a new COSINUS prototype, we show that particle discrimination on an event-by-event basis in NaI is feasible using the dual-channel readout of both phonons and scintillation light. The detector was mounted in the novel remoTES design and operated in an above-ground facility for 9.06 g·d of exposure. With a 3.7 g NaI crystal, e−/γ events could be clearly distinguished from nuclear recoils down to the nuclear recoil energy threshold of 20 keV. Published by the American Physical Society 2024

Enzymatic hydrolysis lignin and kraft lignin from birch wood: a source of functional bio-based materials

In the pursuit of sustainable biomass utilization, this study investigates the hydrothermal treatment of birchwood and its subsequent impact on enzymatic hydrolysis lignin (EHL). Additionally, birchwood undergoes processing with NaOH (4% w/w) within a Parr reactor to precipitate lignin from the black liquor, resulting in lignin-rich substrates (LRSs) which are then subject to thorough characterization. Notably, EHL produced after hydrothermal pretreatment at 190 °C exhibits the highest lignin content at 67%, while kraft lignin (KL) obtained at 140 °C (pH 1.5) produces 65% lignin content. Among these LRSs, the KL sample produced at 190 °C (pH 4) stands out, displaying a robust aromatic skeletal structure and an abundance of methoxyl groups, primarily owing to its high purity. Furthermore, for these LRSs' it is shown that chemical configuration influences their thermal behaviour, allowing the lignin to be tailored for diverse applications, from low melting point materials to carbonaceous materials capable of withstanding temperatures exceeding 700 °C. This comprehensive understanding of the chemical, thermal, and physical attributes of LRSs not only enriches our knowledge of lignin-rich substrates but also paves the way for the development of sustainable bio-based materials, marking a step towards sustainable materials development.

Development of Multi-Analysis By Operando Spectroscopy / Elemental Measurement in Oxide-Type All-Solid-State Na Batteries

Introduction Oxide-type all-solid-state Na batteries (ASSBs) are attracted attention owing to their high safety, resource abundant and intrinsic chemical stability, toward electric storage system for renewable energies, such as photovoltaics and wind generations, using electrochemical devices in urban locations. Although the ASSBs shows low output performances and high internal resistances due to their low sinter density in general, the improvement of these properties have been strenuously studied by using the spark-plasma-sintering (SPS) and sintering additives of low melting point material such as B2O3. However, charge-discharge process is complex reactions extremely, which includes redox reactions of electrode, ionic transport of solid electrolyte at macro / micro-scales every component material. Therefore, to perspective understanding of charge-discharge reactions in the ASSBs, the construction of analysis technique is strongly desired by combination of evaluation methods with suitable selection for each scale. Herein, the multi-scale analysis was demonstrated by using Operando scanning electron microscopy / energy dispersive X-ray spectroscopy (SEM / EDS) (µm-scale) and Raman spectroscopy (atomic-order) for observing changes of Na concentration, bonding states during charge-discharge processes, respectively, in addition evaluation of elemental distributions through the time-of-fright secondary ion mass spectrometry (TOF-SIMS) (nm-scale). Experimental The ASSBs were fabricated by multi-step-sintering method using SPS1 from Na3V2(PO4)3 (NVP) as positive (PE) and negative electrode (NE) active materials, Na3Zr2Si2PO12 (NZSP) as solid electrolyte (SE), B2O3 as adhesive between PE/SE and SE/NE layers. The electrode composition were NVP : NZSP : carbon = 25 : 60 : 15 by weight ratio. The sintered ASSB was physically split for arbitrary size, and then obtained piece loaded into a sample holder of Ar-ion milling system in Ar atmosphere to prepare smooth surface of cross-sectional direction. After the Ar-ion milled sample was transferred to holder enabled to apply voltage, Operando SEM-EDS was performed by cyclic voltammetry (CV) with 0.2 mV s-1 of scan rate, 0.5 - 2.5 V of voltage range at room temperature, and acquired elemental mapping images every 0.5 V for 3 min of recording time. As evaluation at 2, 3 cycle, Operando Raman spectroscopy using the same sample was performed by CV with same conditions at room temperature (at 2 cycle) and 60oC (at 3 cycle), using electrochemical measurement cell having observation window of quartz glass. After 3 cycles, the TOF-SIMS mappings were acquired from all area of the cross-sectional ASSB by using plus mode. Results & Discussion From the Operando SEM / EDS, the distributions of Na element clear changed in PE and NE layers under charge-discharge processes, the 2D-dimensional profile on Na counts normalized by P, which is estimated to be not contribute electrochemical reactions, is shown Figure 1 (a). The Na concentration were confirmed decrease / increase trends at charge process, even though there were decreased / increased at discharge process in the PE and NE layers, respectively. These behaviors of concentration change mean to Na transport between the PE and NE layers with deintercalation and intercalation reactions of NVP during charge-discharge processes. On other hand, Figure 1 (b), (c) shows the Raman spectra changes for PE and NE layers at 2 cycle. Although the D- (1380 cm-1) and G- (1520 cm-1) bands related to carbon material did not change, the integrated intensities at about 780 cm-1 clear increased / decreased at PE layer in charge-discharge processes, respectively. These peaks were assigned to PO4 bonding of NVP, and suggested to reversible structural change owing to intercalation and deintercalation reactions of Na. In addition, the calculation result of Na pathway in the NVP was reported by migration between PO4 tetrahedral along the x direction with low activation energy, and should affect bonding states owing to change of backbone structure during charge-discharge processes.2 Therefore, the peak of PO4 bonding is considered as estimation index on the state-of-charge with electrode redox reactions in ASSBs. In other words, intercalation / deintercalation of Na affects not only structural change of NVP, but also concentration change in all areas of PE and NE layers and these reactions could be directly observed by combination of Operando SEM / EDS and Ram.an spectroscopy. In this presentation, we will also report the results of elemental distributions after 3 cycles by acquired from the TOF-SIMS analysis and correlationship between each evaluation technique for ASSB. D. Kutsuzawa, et al., ACS Appl. Energy Mater., 5, 4025–4028 (2022)W. Song et al., J. Mater. Chem. A, 2, 5358 (2014). Figure 1

Study on lap joining and characterization of tin (Sn) powder on stainless steel SS304 using microwave heating

AbstractMetal bonding via joints of low melting point materials such as zinc and tin has been technically challenging. This paper presents a unique technique for bonding small dimensions and the low melting point of materials through the microwave hybrid heating (MHH) process. Joint of stainless steel SS304 was applied to the joint with the tin (Sn) powder with the application of microwave radiation by using domestic microwave oven at 2.45 GHz of constant frequency, 200–360 W of microwave power, 120–180 s of exposure time, and 10–20 % of the epoxy rate. A developed heat chamber was used as a susceptor and insulator in the microwave hybrid heating (MHH) process. The tin powder and parent metals were strongly bonded as lap position by the microwave hybrid heating (MHH) process at 360 W of microwave power, 180 s of constant exposure time, and 20 % of the constant epoxy rate. Characterization of the joint was evaluated through microhardness and x‐ray diffraction (XRD) analysis techniques. It was found that the intermetallic compounds (phase) of nickel tin (NiSn), iron tin (Fe1.84Sn), sulfur tin (SSn), chromium tin (Cr2Sn3), chromium tin (CrSn2), and tin phosphorus (SnP) at the joint surface with highest microhardness obtained at 498.4 HV 0.05 at 360 W of microwave power.

Microstructural study on the effect of thermo-physical properties for plasma sprayed Ni and Ni[sbnd]20Cr splats formed on Cu substrates

Ni and Ni20Cr powder particles were air plasma sprayed onto polished copper substrates to gain insight into the flattening behaviour of both Ni and Ni20Cr particles (splats) formed on a relatively low melting point material (i.e. copper) substrate. The extent of any interfacial bonding, along with any splat-substrate intermixing derived from the different thermo-physical properties of the sprayed particles were characterised. The plan-view features of the splats were captured using scanning electron microscopy (SEM), while splat-substrate interfacial properties were examined using focused ion beam microscopy (FIB) and transmission electron microscopy (TEM). The chemical characteristics of the splat and substrate were analyzed using energy-dispersive X-ray spectroscopy (EDS). The addition of ∼20 wt% chromium to Ni (i.e the Ni20Cr particles) was observed to significantly influence the spreading behaviour of the particles on impact with the substrate, both the extent of any splat splashing and the splat flattening ratio, as well as the microstructure of the splat-substrate interface, including the degree of substrate melting and the likelihood of material from the substrate jetting into the body of the splat. The evidence of intermixing between the splat and the copper substrate for both feedstocks is an intriguing feature of this study. The presence of a thermodynamically formed copper oxide layer during substrate preheating also influenced both the splat formation behaviour and substrate melting as observed by both microstructural examination and investigation through numerical models.

Mineral detection of neutrinos and dark matter. A whitepaper

Minerals are solid state nuclear track detectors - nuclear recoils in a mineral leave latent damage to the crystal structure. Depending on the mineral and its temperature, the damage features are retained in the material from minutes (in low-melting point materials such as salts at a few hundred degrees C) to timescales much larger than the 4.5 Gyr-age of the Solar System (in refractory materials at room temperature). The damage features from the $O(50)$ MeV fission fragments left by spontaneous fission of $^{238}$U and other heavy unstable isotopes have long been used for fission track dating of geological samples. Laboratory studies have demonstrated the readout of defects caused by nuclear recoils with energies as small as $O(1)$ keV. This whitepaper discusses a wide range of possible applications of minerals as detectors for $E_R \gtrsim O(1)$ keV nuclear recoils: Using natural minerals, one could use the damage features accumulated over $O(10)$ Myr$-O(1)$ Gyr to measure astrophysical neutrino fluxes (from the Sun, supernovae, or cosmic rays interacting with the atmosphere) as well as search for Dark Matter. Using signals accumulated over months to few-years timescales in laboratory-manufactured minerals, one could measure reactor neutrinos or use them as Dark Matter detectors, potentially with directional sensitivity. Research groups in Europe, Asia, and America have started developing microscopy techniques to read out the $O(1) - O(100)$ nm damage features in crystals left by $O(0.1) - O(100)$ keV nuclear recoils. We report on the status and plans of these programs. The research program towards the realization of such detectors is highly interdisciplinary, combining geoscience, material science, applied and fundamental physics with techniques from quantum information and Artificial Intelligence.

Probing finite element modelling of defects in friction stir welding by tailoring mass scaling factor

Friction stir welding (FSW), a solid-state welding process primarily used to join the low melting point materials, often encounters surface and subsurface defects. Modelling surface texture and internal volumetric defects in the FSW process using any numerical method is computationally expensive. The analysis of thermo-mechanical behavior of the FSW process using coupled Eulerian-Lagrangian (CEL) method is sensitive to mass scaling factor (MSF). Tailoring this factor for a computationally efficient model is a promising approach to predict defect in FSW process. The influence of MSF on the computational framework of the CEL finite element method (FEM) in the context of defect formation for two different types of materials (difference in densities) is addressed in the present work. The progress of different energies associated with the CEL approach is indicative of the solution availability by the application of MSF. The variation of these energies is significantly high in FSW process when encountering a defect and dictates the optimum conditions of MSF. An optimum range of MSF is deliberated on account of an efficiently model of FSW process. The simulated surface and subsurface defects, and the discrete temperature data are compared with experimental observation. The maximum difference between the predicted and experimentally measured tunnel defect is ∼ 0.75 mm, whereas the predicted temperature is within 5% of experimental result. It establishes the reliability of the developed numerical model and directs to trigger the model parameters for minimizing the computational time by tailoring the MSF. The optimum range of MSF between 106 and 107 strikes a balance between the result accuracy and computational feasibility for welding of AZ31B. Here, the distribution of strain and strain rate is representative of predicting the defect formation, such as, void, no material zone, crack, surface texture etc. The strain rate is almost double on the retreating side (RS) compared to advancing side (AS) due to the presence of the tunnel defect on AS.

Deposition of YSZ Layer by PS-PVD on Different Materials

Plasma Spray Physical Vapour Deposition (PS-PVD) method was designed for production of ceramic layer on nickel superalloys. In typical process before deposition the base material is heated by plasma up to 900 °C. In present article the yttria stabilized zirconia (YSZ) was deposited on low melting point materials: 2017A-type aluminium alloy and Cu-ETP copper. The influence of power current, process time and powder feed rate on structure and thickness of obtained coatings was analysed. During first deposition process the overheating of Al-sample was observed and as result the power current was decreased to 1600 A. In the next experimental the approx. 5 mm thick dense coating was formed. During experimental processes of YSZ deposition on copper the thickness of coating increased from approx. 5 to 22 mm. The copper-oxide layer was formed under ceramic layer. The microscopic assessment showed the difficulties in formation of columnar ceramic layer on use base materials. The obtained coating was characterized by dense structure as a result of lower plasma energy during process. The increasing of power current is not possible in the case of overheating of base material.

Microstructure characterisation and mechanical behaviour of AA 6063 T-6 welded joint by friction stir welding

ABSTRACT Solid-state welding for low-melting point materials is suitable to produce defect-free weld joints. Therefore, in the present work AA 6063 alloy was welded using friction stir welding (FSW) to know the fracture strength of the welded joint along with the microstructural characterisation. The join was made using a tool of cylindrical shape having varied tool shoulder diameter. The qualities of weld joint are evaluated with the existence of weld defects and microstructure, whereas mechanical properties are obtained as tensile strength, bend test and micro-hardness. The hardness of welded samples at the nugget zone is more or less similar for all process parameters and tool shape. Whereas, the bending strength and tensile strength were found to be varied with rotational speed but decrease as a function of transverse speed. The fractured image revealed that the ductility is higher at the lower band angle. Microstructural examination revealed that the grain growth exhibited in the thermo-mechanical affected zone (TMAZ) and heat-affected zone (HAZ).

Characterization of femtosecond laser ablation processes on as-deposited SnAg solder alloy using laser ablation ionization mass spectrometry

Laser ablation ionization mass spectrometry studies on polished surface structures of hard, high melting point multicomponent interconnect structures using our femtosecond-laser time-of-flight mass spectrometer have previously been proven capable of providing spatially resolved chemical depth profile data at the micro- and nanometer level. Transfer of experimental protocols tailored to suit such type of samples to low melting point materials with high surface roughness, however, is highly challenging, as thermal effects caused by interactions of the laser light with the targeted surface play a severe role in the latter case and may significantly deteriorate the analysis outcome. In this contribution we present a dedicated and detailed comparison of the distinct effects of near infrared and ultraviolet irradiation on the ablation process in femtosecond laser ablation ionization mass spectrometry studies on low melting point materials. As model substrate we use high surface roughness, as-deposited SnAg solder alloy, a material of major industrial relevance in microchip fabrication. We will demonstrate herein that polydimethylsiloxane replica casting is possible also from granularly structured, high surface roughness samples. Characterization of the laser ablation craters as well as of their polydimethylsiloxane replicas is carried out by mass spectrometric analysis, Scanning Electron Microscopy imaging, and furthermore, as a novel approach for this purpose, by white light interferometry. Integration of all obtained results significantly adds to the detailed understanding of laser ablation processes on low melting point, high surface roughness materials and allows identifying optimal depth profiling conditions for these demanding samples.

Structural Properties of Porous Silicon Carbide Bonded with Bentonite, Prepared by a Gas-Emitting Chemical Reaction Method

Direct foaming and bonding techniques were used to fabricate porous silicon carbide ceramics. Silicon carbide is characterized by a high melting temperature; it is always referred to as being bonded with low melting point materials such as bentonite. The technique of generating gases from the reaction of hydrochloric acid HCl with aluminum was used in silicon carbide-bentonite suspension, and by means of which high porosity bodies were prepared by adding different bentonite (10,15,20 and 25 wt.%). After molding them, it is dried and fired at 1100°C. The results of the X-ray diffraction analysis was founded that the main phases appearing after the firing process are α and β–SiC with quartz and mullite, where a part of (β–SiC) is transformed to (α-SiC) and transformation a part of Quartz to Tridymite, which means an increase in the stability of the crystalline phases. The porosity of specimens was decreased with bentonite increases after the firing process, and the values ranged between 62.3% and 72.3%. The compressive strength was increased with bentonite additions increases in the range from 4.35 MPa to 5.08 MPa. From the above results, it is clear that this type of porous (SiC-bentonite) composites can be used in fluid filtration with high efficiency, especially at high temperatures.

Variable Rigidity Module with a Flexible Thermoelectric Device for Bidirectional Temperature Control.

Dynamic stiffness tuning is a promising approach for shape reconfigurable systems that must adapt their flexibility in response to changing operational requirements. Among stiffness tuning technologies, phase change materials are particularly promising because they are size scalable and can be powered using portable electronics. However, the long transition time required for phase change is a great limitation for most applications. In this study, we address this by introducing a rapidly responsive variable rigidity module with a low melting point material and flexible thermoelectric device (f-TED). The f-TED can conduct bidirectional temperature control; thereby, both heating and cooling were accomplished in a single device. By performing local cooling, the phase transition time from liquid to solid is reduced by 77%. The module in its rigid state shows 14.7 × higher bending stiffness than in the soft state. The results can contribute to greatly widening the application of phase transition materials for variable rigidity.

Optimizing the Crystalline State of Cu Slag by Na2CO3 to Improve Cu Recovery by Flotation

Cu is the most important component in Cu slag, which is usually recovered by flotation. However, the crystalline state of Cu slag is not conducive to flotation, which limits the recovery of Cu. This study investigated the effect of Na2CO3 on the crystalline state of Cu slag and the recovery of Cu by flotation. The mechanism was investigated by thermodynamic, viscosity, X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM). The results of thermodynamic, viscosity and XRD analysis demonstrate that Na2CO3 is beneficial for the transformation of fayalite to low-melting point materials, such as Na2SiO3, Na4SiO4 and NaFeSi3O6, thereby reducing the viscosity of Cu slag. Moreover, SEM results indicate that the addition of Na2CO3 during the melting modification process can promote the aggregation of Cu-bearing minerals and simplify its intercalation relationship with gangue minerals. The flotation results verify the above conclusions that at 10% Na2CO3, the Cu flotation recovery index is the best. Compared with that without Na2CO3, the use of Na2CO3 has resulted in increased Cu grade and recovery by 3.544% and 28.94%, respectively.

Engineering lithium-ion battery cathodes for high-voltage applications using electromagnetic excitation

Microwave radiation (MWR), a type of electromagnetic excitation source, reduces the synthesis temperature and processing time for chemical reactions compared to traditional synthesis methods. Recently, we demonstrated that MWR can engineer ceramics with different crystal phases compared to traditional methods [Journal of Materials Chemistry A5, 35 (2017)]. In this study, we further apply the MWR-assisted technique to improve the electrochemical performance of LiCoO2 cathodes by engineering TiO2 and ZrO2 ceramic coatings. Electrochemical tests suggest that the TiO2 coating improves the rate capability of the LiCoO2 electrode. Both TiO2 and ZrO2 coatings improve the high-voltage (4.5 V) cycling stability of LiCoO2. The capacity remaining is improved from 52.8 to 84.4% and 81.9% by the TiO2 coating and the ZrO2 coating, respectively, after 40 cycles. We compare these results with existing studies that apply traditional methods to engineer TiO2/ZrO2 on LiCoO2, and find that the MWR-assisted method shows better performance improvement. X-ray photoelectron spectroscopy measurements suggest that the improved cycling stability arises from the formation of metal fluorides that protect the electrode from side reactions with electrolytes. This mechanism is further supported by the reduced Co dissolution from TiO2/ZrO2-coated LiCoO2 electrode after cycling. This study provides a new toolbox facilitating the integration of many delicate, low melting point materials like polymers into battery electrodes.

Modified CZ technique for the growth of organic crystals having low melting point and high vapour pressure

Abstract Most of the industrially important semiconductor, oxide and optical crystals are grown by Czochralski (CZ) technique. However, CZ technique is seldom used for the growth of low melting point organic/semi organic crystals for which solution grown method is popularly used. Further, due to requirement of sophisticated infrastructure and high cost, CZ set up is normally out of reach of universities in developing country. This article is about designing a low-cost crystal growth system, based on the concepts of CZ technique, which can be used to grow single crystals of low melting point (about 100 °C) and high vapour pressure organic materials. The main changes are in the design of heating system and growth chamber. The difficulties in the crystal growth of low melting and high vapour pressure organic materials by conventional CZ set up and various modifications in the set up for the growth of these crystals are discussed. In the present article, single crystal growth of organic 2-hydroxy biphenyl (2-HBP) single crystal (with diameter ~1 cm and 7 cm length) by low cost modified CZ setup is reported. The crystal structure and composition of 2-HBP crystal were studied by powder X-ray diffraction and CHNS analysis. The orthorhombic system with non-centrosymmetric space group Fdd2 were confirmed by powder XRD study. The thermal stability and melting point of grown crystal was obtained with the help of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) technique. The observed optical properties viz. lower cut-off wavelength at 312 nm and optical bandgap of 3.91 eV in UV spectroscopy along with intense photoluminescence (PL) emission in UV region at 332 nm make 2-HBP crystal a suitable material for photo-electronic applications and tuneable laser system.

The casting of materials using microwave energy: A review

Knowing the advantages of microwave processing on different materials, it has established a good base for the sintering process. Although it has similar advantages for other processes, still other fields are not much established for industrial use. Microwave casting is one of the emerging fields which are yet to be studied in detail. In this paper, a literature review is carried out for the microwave casting of different materials such as metals, metal matrix composites (MCC), etc. Microwave casting is processed under an apparatus that involves microwave hybrid heating (MHH) where heat is transferred to charge using susceptor material. Further depending upon the designed apparatus, microwave casting is divided as in-situ and ex-situ casting processes. If molten material is allowed to solidify inside the microwave cavity is termed as “in-situ” casting while if molten material is allowed to solidify outside the microwave cavity it is termed as “ex-situ” casting. From the review, it can be concluded that the microwave casted materials produce better properties as compared to conventional casting processes in terms of homogeneity and mechanical properties. But most of the research is reported for low melting point materials like Aluminum and their alloys. With the implementation of a new design setup, microwave casting can be used for the materials that are having a melting point above 1000 °C.

Influence of tool geometry on morphology and mechanical properties of friction stir welded dissimilar joints: A review

In this paper, the effect of tool geometry and its parameter on properties of dissimilar materials weld joint has been studied. Joining of dissimilar alloys (such as Al and Mg-alloy) are abundantly used in aeronautical, automobile, and marine industries because of its outstanding characteristics such as low weight, high strength, good corrosive resistance, and cheap cost. The fusion welding techniques were not suitable for the joining of low melting point materials, due to the defects formed such as porosity, voids, and cracks. To reduce these problems, researchers paid attention towards the solid-state technique for welding such as Friction stir welding apart from the fusion welding. Tool geometry and its parameters play a crucial role in the fabrication of good weld joints with better morphological and mechanical properties. Hence the design of FSW tool is very essential. During FSW process, the plastic deformation of materials depends on the tool size; heat generation depends on the shoulder size; the grain size and morphology depends on the heat generated at the weld joint. The objective of this review is to discuss the different types of tool geometry and their effect on morphological and mechanical properties to achieve a sound weld joint.

Effect of oxygen on pressureless silver sintering in a nitrogen atmosphere

To withstand the high working temperatures of next-generation power devices, bonding technologies have evolved from soldering with low melting point materials to sintering with high melting point materials. To date, silver has been widely used as a sintering material due to its high melting point, high thermal conductivity, and low electrical resistance. Since sintering methods require low temperature and pressure to minimize internal damage to the power device, we herein achieved pressureless sintering by controlling the initial vacuum pressure in a nitrogen atmosphere. The residual oxygen present during sintering decreased with lower initial vacuum pressures, which affected the sintered Ag microstructure. Thermogravimetric analysis showed that the weight loss of the Ag sintering paste was slightly faster in air than in nitrogen atmosphere. In air atmosphere, the Ag particles aggregated to a greater degree than under vacuum. In addition, sound bonding with high die-shear strength > 40 MPa was achieved in nitrogen atmosphere when an initial vacuum pressure of > 6.7 kPa was employed, due to the higher residual oxygen content present during sintering. We therefore expect that the proposed method could be promising for the production of alternative interconnects for next-generation power devices.

Rapid immobilization of complex simulated radionuclides by as-prepared Gd2Zr2O7 ceramics without structural design

It is rather necessary to find a simple and rapid way to immobilize complex nuclear waste into stable ceramic matrix. In this work, complicated lattice occupation design was avoided through introducing complex waste into as-prepared host matrix. Two types of simulated TRPO (trialkyl phosphine oxides) wastes were introduced into as-prepared Gd2Zr2O7 matrix by spark plasma sintering (SPS) in 3 min. It is assumed that the waste composition, especially the contents of oxides with relatively low melting point (MoO3, RuO2 and PdO) and raw material for Gd2Zr2O7 (ZrO2), determines the final solubility. Moreover, the obtained compounds exhibit highly densified microtopography. Mo, Ru and Pd show more obvious enrichment with increased dopant while other doped elements show unobservable enrichment to the highest dopant. These results express a rapid and efficient way to immobilize oxides of high melting point into as-prepared host matrix without lattice occupation consideration.

Experimental and numerical analysis of the effect of preheating in friction stir welding

Friction stir welding has been frequently used for fabrication of low melting point materials. Nevertheless, it is capable to join thin sheet of high melting point materials such as stainless steel, titanium etc. but tool wear rate is high. A Heat-assisted backing plate (HABP) was developed to preheating the welded specimen. In this paper, a modified 3D FE model was established to simulate the heat-assisted backing plate of friction stir welding by using ANSYS APDL to study of the temperature distribution of workpiece. Numerical simulation was defined by six different load steps for preheating, plunge, dwell, traverse, pull out of tool and cooling stage. Observations of preheated friction stir welding were compared with traditional friction stir welding results. It was found that the preheated friction stir welding increased 7.39 % and 7.55 % of peak temperature as compared to traditional friction stir welding in FEA and experimental respectively. In addition, preheating improve the uniform temperature distribution along the thickness of welded joint.