Pressureless Consolidation Research Articles

Dependence of the Raman vibration modes on structural properties of Tm:(ScxY1-x)2O3 laser ceramics with 0 ≤ x < 1.

We report on micro-Raman spectra of several mixed laser ceramics, i.e., 5at.%Tm:(ScxY1-xO2)3 with x = 0.121, 0.252, 0.489 and 5at.%Tm:Y2O3 ceramic. The samples were fabricated by solid-state pressureless consolidation of nanopowders produced by laser ablation of solid target in air flow. In particular, we studied the influence of Sc3+ content on the active vibration modes in terms of peak positions and shifts, linewidths and shapes: these parameters are relevant for the emission bandwidth of the laser medium. A shift towards higher frequencies is measured with the increase of the Sc3+ content in all samples in particular in (Tm0.048Y0.463Sc0.489O2)3 where the main Raman peaks are placed at 395, 494, 635 cm-1 while their shifts with Tm:Y2O3 are 22.6, 25.1, 40.1 cm-1, respectively. The assignment of the vibrational spectrum was obtained by density functional theory (DFT) with the Perdew-Burke-Enzerhof (PBE) exchange-correlation functional within the harmonic approximation framework.

Pressureless consolidation of boron nitride fiber ceramics via a chemical bonding approach

Pressureless consolidation of boron nitride fiber ceramics via a chemical bonding approach

Micromechanical properties and microstructures of AC and DC flash-sintered alumina

Alumina (α-Al2O3), one of the most widely used structural ceramics for industrial applications, requires high temperature and long sintering time to achieve a fully dense structure through conventional pressureless consolidation and sintering methods. Recently, several attempts have been made to reduce sintering time and temperature of Al2O3 through the application of electric field with limited success. In this study, alternating current (AC) and direct current (DC) flash sintering techniques were employed to obtain high-density Al2O3 within 10 min. The density of flash-sintered (FS) specimens was greater than the specimens prepared by the pressureless sintering technique (hereinafter designated as conventional sintering) at the same temperature for 10 h. Furthermore, AC technique can reduce the electric field necessary for flash sintering substantially comparing to the DC flash sintering. The microindentation measurements reveal that the AC-FS Al2O3 provides the highest fracture toughness and a high hardness among all sintered specimens. The improved mechanical properties of AC-FS Al2O3 are attributed to defects, such as dislocations as well as stacking faults observed in the FS specimens. This study provides a fresh perspective on the low-energy manufacturing of structural ceramics with improved properties.

Ultra-fast High-temperature Sintering (UHS) of translucent alumina

Pressure-less consolidation of transparent alumina requires several hours dwelling at high temperature (1600 °C) under a strongly reducing atmosphere (hydrogen). Here, we report on the ultrafast consolidation of translucent alumina ceramics at 1360 °C. Transparency was promoted by synergistic effects of high initial green density (62.7%) and rapid sintering using Ultra-fast High-temperature Sintering (UHS) technique. The proposed approach, using a heating rate of 430 °C/min and dwelling time of 15 min, resulted in ultra-fine-grained translucent alumina ceramics with a grain size of 0.39 μm, and an in-line transmittance of 28.7% at a wavelength of 700 nm. For comparison, conventionally fired counterparts were opaque due to their incomplete densification and pore coalescence.

Effect of graphene nanoplatelets on the physical and mechanical properties of Al6061 in fabricated and T6 thermal conditions

Lightweight aluminium matrix composites find wide applications in automobile and aerospace sector. Aluminium alloy composites with graphene nanoplatelets (GNPs) were prepared by powder metallurgy route containing four different loadings, i.e. 0.1 wt%, 0.5 wt%, 1 wt% and 3 wt%. Two methods for exfoliation of GNPs were employed to achieve uniform dispersion in Al6061 matrix. Pressureless consolidation followed by sintering was carried out to obtain near-theoretical densities. Comparison of the fabricated thermal condition and artificially aged T6 samples was carried out to investigate the contribution of GNPs in the strengthening of Al6061 matrix. Microstructure evolution was confirmed by X-ray diffraction, optical and scanning electron microscopy. Electrical conductivity increased with increasing content of GNPs up to 1 wt% due to conductive network around the matrix grains. Mechanical properties were found to increase 93%, 61% and 92% in hardness, compression strength and flexural strength up till 1 wt% GNPs in matrix alloy. Agglomeration at 3 wt% GNPs resulted in deterioration of properties. The fractured surfaces were examined to determine the change in fracture morphology, associated strengthening mechanism and behaviour of GNPs.

Parameter Surveys on Glass-Bonded Sodalite Synthesis Conditions from Spent Salt Generated in Pyroprocess

A parameter-based survey of the synthesis conditions by a so-called pressureless consolidation method to fabricate glass-bonded sodalite waste form for stabilizing fission products generated in pyrometallurgical reprocessing of spent metal fuel was performed. The maximum temperature, the heating duration at the maximum temperature, the glass fraction in the initial material, and the weight load used for pressing the material were chosen as the variable parameters. Accordingly, modified conditions to reduce the maximum temperature and increase the weight load were selected for reducing the volatilized-salt ratio during the heating and the free-salt ratio in the product. By fabricating a simulated waste under the modified conditions, the effect of changing the conditions was confirmed. Leaching tests in pure water using the consolidated products fabricated under both reference and modified conditions showed that the stability of the products was not significantly deteriorated by modifying the heating conditions.

Scale Up of Ceramic Waste Forms for Electrorefiner Salts Produced during Spent Fuel Treatment

A full-scale process has been developed to immobilize fission products that accumulate within the Mark IV electrorefiner (ER) electrolyte at Idaho National Laboratory. ER salt was blended with treatment additives, followed by pressureless consolidation (PC) in a furnace to produce a durable ceramic waste form (CWF). The goal is the development of a process to consolidate actual radioactive ER salt into a form suitable for transportation and disposal. Four batches (300 to 400 kg per batch) of full-scale pre-qualification material preparation runs have been prepared. From these four batches of nonradioactive salt-loaded surrogate material, three full-scale PC trials have been conducted. The first PC test run, established equipment parameters with a basic CWF container design. The second trial included a modified CWF container design, real-time measurement of CWF consolidation, and an audio recording to identify cracking during the CWF cool-down. During the third trial, salt was doped (from the fourth material preparation batch) to create a nonradioactive salt material and to more closely represent actual ER salt. The second and third trials were also used to validate a model developed for the CWF. The CWF model is beneficial for understanding and predicting the physical processes that occur during the heat cycle. This would be particularly useful when the CWF is located in a hot cell, which makes accessing and examining a CWF difficult.

Conditioning of Chloride Salt Wastes from Pyroprocesses Through the Pressureless Consolidation Process

Sodalite has been taken into account as a matrix for conditioning chloride salt wastes coming from pyroprocesses. The present paper illustrates the research activities finalized to demonstrate the feasibility of sodalite synthesis through the Pressureless Consolidation (PC) process, proposed by Idaho National Laboratories (INL) in USA. A homogeneous powder of nepheline, chloride salts and glass frit was put into an alumina crucible and slightly pressed with another alumina crucible of a smaller diameter, inside which a stainless steel bar had been inserted. The entire assembly was introduced in a furnace inside an Argon-atmosphere glove-box and heated at 925°C for 7hours. The product obtained has then been characterized by means of density measurements, thermal analysis, stereomicroscopy observations, as well as FTIR and XRD. The latter correspond to the ones of sodalite reported in the spectral library. Leach tests under static conditions according to ASTM C1285-02 (reapproved 2008) have been carried out and successfully compared with those obtained by INL.

The Ceramic Waste Form Process at Idaho National Laboratory

The treatment of spent nuclear fuel for disposition using an electrometallurgical technique results in two high-level waste forms: a ceramic waste form (CWF) and a metal waste form. Reactive metal fuel constituents, including all of the transuranic metals and the majority of the fission products, remain in the salt as chlorides and are processed into the CWF. The solidified salt is containerized and transferred to the CWF process, where it is ground in an argon atmosphere. Zeolite 4A is dried in a mechanically fluidized dryer to ~0.1 wt% moisture and ground to a particle-size range of 45 to 250 μm. The salt and zeolite are mixed in a V-mixer and heated to 500°C for ~18 h to occlude the salt into the structure of the zeolite. The salt-loaded zeolite is cooled, mixed with borosilicate glass frit, and transferred to a crucible, which is placed in a furnace and heated to 925°C. During this process, known as pressureless consolidation, the zeolite is converted to the final sodalite form and the glass thoroughly encapsulates the sodalite, producing a dense, leach-resistant final waste form. During the last several years, changes have occurred to the process, including particle size of input materials and conversion from hot isostatic pressing to pressureless consolidation. This paper is intended to provide the current status of the CWF process, focusing on the adaptation to pressureless consolidation. Discussions include impacts of particle size on final waste form and the pressureless consolidation cycle. A model is presented that shows the heating and cooling cycles and the effect of radioactive decay heat on the amount of fission products that can be incorporated into the CWF.

The Ceramic Waste Form Process at Idaho National Laboratory

The treatment of spent nuclear fuel for disposition using an electrometallurgical technique results in two high-level waste forms: a ceramic waste form (CWF) and a metal waste form (MWF). The CWF is a composite of sodalite and glass, which stabilizes the active fission products (alkali, alkaline earths, and rare earths) and transuranic (TRU) elements. Reactive metal fuel constituents, including all the TRU metals and the majority of the fission products remain in the salt as chlorides and are processed into the CWF. The solidified salt is containerized and transferred to the CWF process where it is ground in an argon atmosphere. Zeolite 4A is dried in a mechanically-fluidized dryer to about 0.1 wt% moisture and ground to a particle-size range of 45µ to 250µ. The salt and zeolite are mixed in a V-mixer and heated to 500°C for about 18 hours. During this process, the salt occludes into the structure of the zeolite. The salt-loaded zeolite (SLZ) is cooled and then mixed with borosilicate glass frit with a comparable particle-size range. The SLZ/glass mixture is transferred to a crucible, which is placed in a furnace and heated to 925°C. During this process, known as pressureless consolidation, the zeolite is converted to the final sodalite form and the glass thoroughly encapsulates the sodalite, producing a dense, leach-resistant final waste form. During the last several years, changes have occurred to the process, including: particle size of input materials and conversion from hot isostatic pressing to pressureless consolidation, This paper is intended to provide the current status of the CWF process focusing on the adaptation to pressureless consolidation. Discussions will include impacts of particle size on final waste form and the pressureless consolidation cycle. A model will be presented that shows the heating and cooling cycles and the effect of radioactive decay heat on the amount of fission products that can be incorporated into the CWF.

The Ceramic Waste Form Process at Idaho National Laboratory

The treatment of spent nuclear fuel for disposition using an electrometallurgical technique results in two high-level waste forms: a ceramic waste form (CWF) and a metal waste form. Reactive metal fuel constituents, including all the transuranic metals and the majority of the fission products remain in the salt as chlorides and are processed into the CWF. The solidified salt is containerized and transferred to the CWF process where it is ground in an argon atmosphere. Zeolite 4A is ground and then dried in a mechanically-fluidized dryer. The salt and zeolite are mixed in a V-mixer and heated to 500°C to occlude the salt into the structure of the zeolite. The salt-loaded zeolite is cooled, mixed with borosilicate glass frit, and transferred to a crucible, which is placed in a furnace and heated to 925°C. During this process, known as pressureless consolidation, the zeolite is converted to the final sodalite form and the glass thoroughly encapsulates the sodalite, producing a dense, leach-resistant final waste form.

Thermal properties and crystallization kinetics of a sodium aluminophosphate based glass

A ternary sodium aluminophosphate glass, NaAlP, has been used as an encapsulating phase for a calcium phosphate ceramic employed as a host for halide-containing radioactive waste, the final wasteform being prepared by a pressureless consolidation route or alternatively by cold pressing and sintering of ceramic/glass mixtures. During processing, the glass partially crystallizes to yield a mixture of crystalline products. In an attempt to improve the thermal stability and resistance of this glass to devitrification small additions of various additives were made to the glass, including Fe2O3, B2O3 and ZnO in amounts of less than 10 mol%. The thermal properties and crystallization kinetics of the resultant glasses were measured using non-isothermal differential scanning calorimetry, DSC, and differential thermal analysis, DTA. The glass transition and crystallization temperatures, and the activation energy for crystallization, increased with increasing Fe2O3 content, whilst the reduced glass temperature decreased. The other additives, and in particular the mixed Fe2O3/B2O3 addition, also led to minor improvements in some of these parameters, but overall it was concluded that the additives offered no great advantages over use of the unmodified NaAlP ternary glass as an encapsulating phase”.

A new processing route for net-shaped nanoparticulate materials

Abstract This paper reviews our recent investigations on the synthesis and processing of nanocrystalline (NC) alloy/composite powder and suggests a new processing route for fabricating bulk NC materials. Development of nanoparticulate materials technology is essential to processing of highly functional nanoparticulate materials and components with small and complex shape. For this purpose, two core technologies of producing nanoalloy and nanocomposite powders and net shaping the powders into small device and component parts are very important. Relating to consolidation of nanopowder, the pressure-assisted sintering process for consolidation is usually known to be suitable for both reaching full density and suppressing grain growth. However, the pressureless consolidation is inevitable for bulk processing of nano powders into small-sized and complex-shaped nanomaterial parts. In this overview, a new processing concept for net-shaped nanoparticulate materials such as the two processing routes of the intrinsic and extrinsic type is introduced; the intrinsic type process is for processing bulk nanostructured alloy and composites that have the same composition as the nanopowder (Fe–Ni), and the extrinsic one is for the nanoparticle dispersed ceramic composite materials (Al 2O 3–Ni).

Dissolution of a Multiphase Waste Form

ABSTRACTThe dissolution behavior of the ceramic waste form (CWF) is being investigated to support its qualification for disposal in the proposed repository at Yucca Mountain. The CWF consists of sodalite and glass phases and has been consolidated either by hot isostatic pressuring (HIP) or by pressureless consolidation (PC). In this paper we compare the dissolution behavior of the two materials using in MCC-1 type tests at 90°C in a simulated silicate groundwater. The test solutions were periodically exchanged limit feedback effects. The solid surface area to volume ratio was 10 m-1. Five types of samples were tested: (1) HIP CWF, (2) binder glass vitrified by HIP, (3) PC CWF, (4) binder glass vitrified by PC, and HIP sodalite. Boron releases were used to monitor glass dissolution; these were similar in tests with HIP CWF, HIP glass, and PC CWF, but about 3X higher in tests with PC glass. At the end of the tests, the surfaces of the reacted materials were examined with scanning electron microscopy for signs of preferential dissolution. Differences in the dissolution behaviors of the materials are described and the implications of the test results regarding the performance of the CWF in the disposal system are discussed.

Corrosion of Glass-Bonded Sodalite and its Components as a Function of ph and Temperature

ABSTRACTA glass-bonded sodalite ceramic waste form (CWF) has been developed to immobilize electrorefiner salt wastes from electrometallurgical treatment of spent sodium-bonded reactor fuel for disposal. A degradation model is being developed to support qualification of the CWF for disposal in the federal high-level waste disposal system. The parameter values in the waste form degradation model were previously determined from the dissolution rates measured in MCC-1 tests conducted at 40, 70, and 90°C. The results of several series of tests that were conducted to confirm the applicability of the dissolution rate model and model parameters are presented in this paper: (1) Series of MCC-1 tests were conducted in five dilute buffer solutions in the pH range of 4.8 – 9.8 at 20°C with hot isostatic pressing (HIP) sodalite, HIP glass, and HIP CWF. The results show that the model adequately predicts the dissolution rate of these materials at 20°C. (2) Tests at 20 and 70°C with CWF made by pressureless-consolidation (PC) indicate that the model parameters extracted from the results of tests with HIP CWF can be applied to PC CWF. (3) The dissolution rates of a glass made with a composition corresponding to 80 wt. % glass and 20 wt. % sodalite were measured at 70°C to evaluate the sensitivity of the rate to the composition of binder glass in the CWF. The dissolution rates of the modified binder glass were indistinguishable from the rates of the binder glass.