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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Structural changes during milling of aluminum oxide powders

The mechanical activation of four fused corundum powders and a calcined Al2O3 powder was studied. The milled powders were characterized by their structural properties, crystallite size, and lattice distortions. Structural changes during milling, detected by X-ray line broadening analysis, gave information about the enhanced activity of the powders caused by the lattice distortions and by the decreasing crystallite size during milling. The structural changes during milling, under the same milling conditions, can be quite different for the same ceramic material, but with different characteristics in the as received state.

Ziepler, G.↗
NASA NTRS1985

Parametric evaluation of ball milling of SiC in water

A statistically designed experiment was conducted to determine optimum conditions for ball milling alpha-SiC in water. The influence of pH adjustment, volume percent solids loading, and mill rotational speed on grinding effectiveness was examined. An equation defining the effect of those milling variables on specific surface area was obtained. The volume percent solids loading of the slurry had the greatest influence on the grinding effectiveness in terms of increase in specific surface area. As grinding effectiveness improved, mill and media wear also increased. Contamination was minimized by use of sintered alpha-SiC milling hardware.

Kiser, J. D.↗
NASA NTRS1984

Demonstration of a silicon nitride attrition mill for production of fine pure Si and Si3N4 powders

To avoid metallic impurities normally introduced by milling ceramic powders in conventional steel hardware, an attrition mill (high-energy stirred ball mill) was constructed with the wearing parts (mill body, stirring arms, and media) made from silicon nitride. Commercial silicon and Si3N4 powders were milled to fine uniform particles with only minimal contamination - primarily from wear of the sintered Si3N4 media.

Herbell, T. P.↗
NASA NTRS1986

Particle size reduction of Si3N4 with Si3N4 milling hardware

The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.

Herbell, T. P.↗
NASA NTRS1985

Parametric evaluation of ball milling of SiC in water

A statistically designed experiment was conducted to determine optimum conditions for ball milling alpha-SiC in water. The influence of pH adjustment, volume percent solids loading, and mill rotational speed on grinding effectiveness was examined. An equation defining the effect of those milling variables on specific surface area was obtained. The volume percent solids loading of the slurry had the greatest influence on the grinding effectiveness in terms of increase in specific surface area. As grinding effectiveness improved, mill and media wear also increased. Contamination was minimized by use of sintered alpha-SiC milling hardware.

Kiser, J. D.↗
NASA NTRS1986

Particle-size reduction of Si3N4 powder with Si3N4 milling hardware

The grinding of Si3N4 powder using reaction bonded Si3N4 attrition, vibratory, and ball mills with Si3N4 media was examined. The rate of particle size reduction and the change in the chemical composition of the powder were determined in order to compare the grinding efficiency and the increase in impurity content resulting from mill and media wear for each technique. Attrition and vibratory milling exhibited rates of specific surface area increase that were approximately eight times that observed in ball milling. Vibratory milling introduced the greatest impurity pickup.

Herbell, T. P.↗
NASA NTRS1987

Effects of milling brominated P-100 graphite fibers

Preliminary procedures have been developed for the ball milling of pristine and brominated P-100 graphite fibers. Because of the lubricative properties of graphite, large ball loads (50 percent by volume) are required. Use of 2-propanol as a milling medium enhances the efficiency of the process. The fibers, when allowed to settle from the milling medium, tend to be preferentially aligned with rather few fibers standing up. Milled, brominated P-100 fibers have resistivities that are indistinguishable from their pristine counterparts, apparently because of loss of bromine. This suggests that bromine would not be the intercalate of choice in applications where milled fibers of this type are required. It was found that brominated graphite fibers are stable in a wide variety of organic solvents.

Gaier, James R.↗
NASA NTRS1998

Elevated Temperature Compressive Strength Properties of Oxide Dispersion Strengthened NiAl After Cryo-milling and Roasting in Nitrogen

In an effort to superimpose two different elevated temperature strengthening mechanisms in NiAl, several lots of oxide dispersion strengthened (ODS) NiAl powder have been cryo-milled in liquid nitrogen to introduce AlN particles at the grain boundaries. As an alternative to cryo-milling, one lot of ODS NiAl was roasted in nitrogen to produce AlN. Both techniques resulted in hot extruded AlN-strengthened, ODS NiAl alloys which were stronger than the base ODS NiAl between 1200 and 1400 K. However, neither the cryo-milled nor the N2-roasted ODS NiAl alloys were as strong as cryo-milled binary NiAl containing like amounts of AlN. The reason(s) for the relative weakness of cryo-milled ODS NiAl is not certain; however the lack of superior strength in N2-roasted ODS NiAl is probably due to its relatively large AlN particles.

Whittenberger, J. Daniel↗
DOE OSTI2017

Long-Term Stewardship at a Former Uranium Mill Tailings Site in Riverton, Wyoming WM2017-17090

The US Department of Energy Office of Legacy Management (LM) is responsible for maintaining protective public health and environmental conditions at former uranium mill tailings sites nationwide via long-term stewardship. One of these sites, a former uranium mill near Riverton, Wyoming, is within the boundary of the Wind River Indian Reservation and operated from 1958 to 1963. Tailings and contaminated material associated with mill operations were removed and transported to an offsite disposal cell in 1989. The remedial action was completed under Title I of the Uranium Mill Tailings Radiation Control Act of 1978. Milling operations, which included an unlined tailings impoundment and an unlined evaporation pond, contaminated the shallow groundwater, resulting in a downgradient groundwater plume that discharges to the Little Wind River. A natural flushing compliance strategy was implemented in 1998. This strategy allows contaminants of concern to naturally flush from the groundwater, provided that contaminants flush below US Environmental Protection Agency maximum concentration limits within 100 years. As part of the compliance strategy, LM has implemented a groundwater monitoring program along with institutional controls that include the installation of an alternate water supply, continued sampling of private wells, and restrictions on well drilling and gravel pit construction. LM works closely with local stakeholders and community members to ensure that these institutional controls are in place and maintained. The Riverton site provides an interesting case study where contaminant remobilization due to river flooding prompted a reevaluation of the conceptual site model to verify if the current compliance strategy would remain protective of human health and the environment. Concentrations of groundwater contaminants, which include sulfate, molybdenum, and uranium, were transiently elevated following flooding of the Little Wind River in 2010 and 2016. These flood events provided the impetus to investigate other aspects of the hydrologic system, including the unsaturated zone, naturally reduced (sulfidic) zones, and evaporite deposits. New site conceptual models, field and laboratory studies, and numerical models are being developed to explain how biogeochemical sediment–water interactions contribute to plume persistence and flood-related increases in groundwater concentrations. Updated human health and ecological risk assessments are progressing to evaluate the risk to human health and the environment based on current site conditions. Groundwater concentrations may remain above US Environmental Protection Agency maximum concentration limits beyond the 100-year natural flushing regulatory time frame. LM in its capacity as a long-term steward continues to monitor the site to ensure protectiveness is maintained and to determine the feasibility of alternative compliance and remediation strategies.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Integrated Methodology for the Impact Assessment of an Uranium Mill Contaminated Site - 19031

This work describes the development of mathematical models for radionuclides distribution and transport in the environment. The applicability of the models involves an integrated approach to assess the quantitative dispersion of the radionuclides in different environmental compartments when released from uranium tailings or from other low-activity mining wastes storages. For every compartment the important pathways of contamination and the radionuclides of major concern are identified and selected, based on their chemical, physical, radiological and toxic properties. Each compartment represents an environmental media: air, soil, water, vegetation and biota. Depending on the characteristics of the sources different types of possible releases are evaluated using phenomenological models. Models of environmental release, dispersion, transport and fate within each environmental compartment, as well as models of transfer between them, are applied to a specific site. The model outputs are the radionuclides activities for each one of the environmental compartments, where relevant exposure end-points are previously identified. The methodology was applied to a specific Uranium Mill Site, referred here as the 'Mill'. The site comprises approximately 3.2 km and includes two inactive mills, former ore stockpiles areas, a partially reclaimed tailings pond disposal area and a current tailings pond disposal area. The Mill site began operations in the late 1950's extracting uranium ore by alkaline leaching. Later on, a new facility using acid leaching for extracting uranium begun to operate in 1980. The mill operated first continuously and after intermittently until its closure, in March 2006. The data required for the model input was acquired from different sources: direct measurements from this particular site and available from multiple site investigation reports (in particular, environmental data for groundwater, soil, surface water, sediments and biota); other, were selected from published data. For the unknown data, assumptions were made. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Excess Conductivity Investigation of Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18±δ} Superconductors Prepared by Various Parameters of Planetary Ball Milling Technique

Superconducting samples of type Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18±δ} were elaborated by using a planetary high-energy ball milling (HEBM) technique with various parameters. Phases, microstructure, and superconductivity have been examined using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electrical resistivity measurements. SEM investigation shows the occurrence of nanoentities embedded into the superconducting matrix for samples prepared by a ball milling technique. The main objective of this study is to investigate the influence of ball milling parameters on the fluctuation-induced conductivity (FIC). The electrical resistivity versus temperature, ρ(T), above T{sub c} was analyzed using Lawrence–Doniach (LD) and Aslamazov–Larkin (AL) models. Different fluctuation regimes indicated by short-wave fluctuation (SWF) and three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and critical region (CR) fluctuations were identified. The coherence length at zero temperature, the effective layer thickness, the critical magnetic fields, and the critical current densities are determined. The superconducting parameters strongly depend on the planetary ball milling technique, and the results are explained in relevancy to the microstructure. It was found that the achievement of a microstructure with well-dispersed nanoentities is an effective way for introducing pinning centers for enhancing critical current density and flux pinning capability of bulk Y-358.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Static and dynamic modeling of steam integration for a NuScale small modular reactor and pulp and paper mill coupling for carbon-neutral manufacturing

Small modular reactors (SMRs) are reactor designs producing less than 300 MWe and are generally planned for deployment as multimodule nuclear power plants. The possibility of factory-manufactured, flexibly sized plants expands the opportunities for nuclear power to different communities and industries, including manufacturing plants that currently utilize fossil fuels to produce both steam and electricity. This paper examines the feasibility of coupling a NuScale SMR with a midsize pulp and paper mill in the Southeastern United States. A steady-state mill model was developed in Aspen HYSYS, based on real data from the operation of the mill, and modified it to include the SMR while maintaining steam quality requirements and making as few changes as possible to existing equipment. Dynamic plant models were also developed Dymola to demonstrate possible plant conditions, using three configurations. Preliminary results suggest that, while SMR coupling is physically feasible, its economic feasibility is limited by the differences in steam and electricity demands. Because of limitations in the amount of steam the mill can take from the SMR, sizing the SMR for the plant’s steam demand may result in an electricity deficit, or vice versa. Furthermore, dynamic analyses show that the addition of a thermal storage system could reduce such deficits, but this entails its own challenges. Each plant must determine the best configuration and control scheme for itself, based on its electricity and heat needs, including the peak duration and intensity for both. Ultimately, an implementation of SMRs with manufacturing processes would benefit from partnering with a local utility to purchase excess electricity generated by the SMR. This will help manufacturing facilities meet their environmental and cost-savings goals, in addition to meeting the need for cost-effective baseload power across the United States.

03 NATURAL GAS↗
DOE OSTI2022

Receptance coupling substructure analysis and chatter frequency-informed machine learning for milling stability

This paper describes a milling stability identification approach that simultaneously considers: physics-based models for the tool tip frequency response functions and stability predictions; the binary result from a milling test (automatically labeled as stable or unstable based on frequency content); chatter frequency when an unstable result is obtained; and user risk tolerance. The algorithm applies probabilistic Bayesian machine learning with adaptive, parallelized Markov Chain Monte Carlo sampling to update the probability of stability with each milling test. Furthermore, the result is a robust solution for rapid convergence to optimized milling parameters for maximum metal removal rate using all available information.

42 ENGINEERING↗
DOE OSTI2013

Solid-state synthesis of Mg{sub 2}Si via short-duration ball-milling and low-temperature annealing

In this work, a short duration ball-milling of elemental Mg and Si followed by a thermal treatment is suggested in order to synthesize magnesium silicide via solid-state reaction. The formation of magnesium silicide was studied in terms of its structure and thermal characteristics by powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and differential scanning calorimetry. Pure Mg{sub 2}Si was formed after short milling and heating at temperatures as low as 280 Degree-Sign C. Differential scanning calorimetry analysis was performed to study the kinetics of the reaction. The activation energy of the reaction was calculated using the Ozawa-Flynn-Wall and Friedman methods. The thermoelectric properties suggested semiconducting behavior whereas thermal conductivity values of highly dense hot-pressed pellets are consistent with the literature. - Graphical abstract: Thermographs of ball-milled Mg and Si powders (1 and 2) show exothermic areas suggesting Mg{sub 2}Si formation at low temperatures. Unmilled Mg and Si mixture (3) forms Mg{sub 2}Si at higher temperatures. Highlights: Black-Right-Pointing-Pointer Ball-milling process is crucial for the formation of pure Mg{sub 2}Si at low temperatures. Black-Right-Pointing-Pointer Synthesis profiles based on different temperature settings and duration are suggested. Black-Right-Pointing-Pointer Thermal analysis confirms the shift of the Mg{sub 2}Si formation at low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis and characterization of nano-structured TiB{sub 2} processed by milling assisted SHS route

TiB{sub 2} was synthesized via milling assisted self-propagating high-temperature synthesis (SHS) route using TiO{sub 2}, H{sub 3}BO{sub 3} and Mg powders as starting materials. The milling products were compacted and subjected to a hot filament on their top to initiate SHS. Effects of the milling time and addition of NaCl as a process diluent on the phase composition and morphology of the products were investigated. X-ray diffraction analysis indicated the formation of nano-crystalline TiB{sub 2} with mean crystallite size of 31 nm after acid leaching process at room temperature. Addition of 2 mol of NaCl in the same sample decreases the mean crystallite size to 27 nm. SEM and TEM micrographs showed that the mean particle size of TiB{sub 2} decreased from 200 nm in the un-milled sample to about 50 nm in the 5-hour mechanically activated (MA) sample. - Graphical abstract: High purity nano particles of TiB{sub 2} were achieved after complete elimination of undesirable phases by acid leaching of MA-SHS product at ambient temperature. Highlights: Black-Right-Pointing-Pointer Nano-structured pure TiB{sub 2} was synthesized by MA-SHS route. Black-Right-Pointing-Pointer The mean particle size of TiB{sub 2} phase was 50 nm. Black-Right-Pointing-Pointer Impurities were eliminated by leaching of the products at ambient temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

GaN decomposition after high-energy ball milling and its transformation to BN hollow spheres in annealing samples doped with B

Highlights: • B- and Si-doped GaN semiconductor are processed by high-energy ball milling. • TEM observations indicate GaN structural decomposition. • DSC-TGA analysis confirms the GaN temperatures decomposition. • GaN decomposition is more influenced by B element. • BN hollow particles is formed after annealing treatment of the B-doped GaN. - Abstract: In this work, GaN powders doped with B and Si were treated by high-energy ball milling, and subsequently, annealing at different temperatures. Transmission electron microscopy (TEM) observations showed the in-situ GaN decomposition in the undoped GaN specimen milled for 5 h. TEM also revealed that the chemical decomposition of GaN was more affected in samples doped with B. Thermo-gravimetric analysis indicates that an undoped GaN specimen decomposes at 1120 °C, Si-doped GaN samples disintegrate at 1150 °C, and finally, B-doped GaN samples decompose at the lower temperature of 940 °C. TEM and SEM results show that the annealing treatment of the as-milled B-doped GaN samples at 1150 °C for 15 min leads to the GaN decomposition and BN hollow nanostructures formation under an N{sub 2} atmosphere. The synthesized product consists of mesoporous powders with variable particle sizes from 500 nm to 1 μm having variable cavities in the range from 60 nm to 800 nm.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Brownian-like kinematics of ball milling for particulate structural modeling

Ball milling motion has been previously studied through computationally expensive, off-line experimental video processing and numerical simulations by the discrete element method. Here, this research establishes a more efficient formulation of the ball energetics and kinetics similar to the Brownian kinetic theory of statistical mechanics. Based on assumptions of thermomechanical equilibrium, negligible gravitational, aerodynamic and surface condition effects, and decoupled impact interaction among balls and with milled particulates, this model proposes mono-parametric spectral energy and velocity probability density functions akin to Maxwell-Boltzmann statistics, along with uniformly distributed impact directionality. The model predictions are calibrated and validated by comparison with published experimental measurements and computationally derived spectra. This descriptive Brownian-like motion model enables effective simulation of contact and impact, material deformation and micro-joining of ball milled bimetallic powders. A comprehensive simulation of the evolving internal fractal microstructure of the processed particulates is implemented at real-time computation speed, and its predictions are compared with experimental micrographs of ball milled Ni—Al particulates.

42 ENGINEERING↗
DOE OSTI2014

Sample preparation and biomass determination of SRF model mixture using cryogenic milling and the adapted balance method

Highlights: • An alternative sample comminution procedure for SRF is tested. • Proof of principle is shown on a SRF model mixture. • The biogenic content of the SRF is analyzed with the adapted balance method. • The novel method combines combustion analysis and a data reconciliation algorithm. • Factors for the variance of the analysis results are statistically quantified. - Abstract: The biogenic fraction of a simple solid recovered fuel (SRF) mixture (80 wt% printer paper/20 wt% high density polyethylene) is analyzed with the in-house developed adapted balance method (aBM). This fairly new approach is a combination of combustion elemental analysis (CHNS) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. This method shows a great potential as an alternative way to determine the biomass content in SRF. However, the employed analytical technique (CHNS elemental analysis) restricts the probed sample mass to low amounts in the range of a few hundred milligrams. This requires sample comminution to small grain sizes (<200 μm) to generate representative SRF specimen. This is not easily accomplished for certain material mixtures (e.g. SRF with rubber content) by conventional means of sample size reduction. This paper presents a proof of principle investigation of the sample preparation and analysis of an SRF model mixture with the use of cryogenic impact milling (final sample comminution) and the adapted balance method (determination of biomass content). The so derived sample preparation methodology (cutting mills and cryogenic impact milling) shows a better performance in accuracy and precision for the determination of the biomass content than one solely based on cutting mills. The results for the determination of the biogenic fraction are within 1–5% of the data obtained by the reference methods, selective dissolution method (SDM) and {sup 14}C-method ({sup 14}C-M)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗