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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Densification and Immobilization of AgI-Containing Iodine Waste Forms Using Spark Plasma Sintering

Here in this study, porous Ag-xerogel (Ag-Xero), Ag-faujasite (Ag-FAU) zeolite, and Ag-mordenite (Ag-MOR) zeolite sorbents were loaded with iodine gas [I 2 (g)] under saturated conditions at 150 °C for 24 h, followed by densification and consolidation into monolithic waste forms using spark plasma sintering (SPS). For Ag-Xero materials, SPS pellets were made with as-loaded samples, while others were made with preheated (PH; 500 °C for 2 h) samples to help with densification. SPS processing was conducted at 50 MPa under different temperatures (T = 200–800 °C) for different times (t = 0.5–30 min), where eleven AgI-Xero samples, five AgI-FAU, and two AgI-MOR separate samples were produced. The primary goal was to look for the optimum processing parameters for each material to yield pellets with high iodine retentions, high densities, and low porosities while preventing AgI decomposition. The Ag-Xero showed the highest iodine loadings (qe = 470 mg g –1 ) compared to Ag-FAU (qe = 368 mg g –1 ) and Ag-MOR (qe = 108 mg g –1 ). Measured iodine concentrations were the highest in AgI-Xero pellets without PH, followed by AgI-Xero with PH, AgI-FAU, and then AgI-MOR. Silver utilization (I/Ag on a mol % basis) values were in the order of AgI-MOR ≈ AgI-Xero (no PH) > AgI-Xero (PH) > AgI-FAU. Chemical durabilities of SPS-densified AgI-Xero (PH) pellets were very favorable, with lower releases than SPS pellets made from AgI-Xero samples without PH. These results show promise for iodine waste form production.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Defect physics in 2D monolayer I-VII semiconductor AgI

As a brand new two-dimensional (2D) material with promising electronic properties, monolayer I-VII silver iodide (AgI) has the potential for future 2D electronic devices. To advance the development of such devices, the exploration of n-type and p-type conductivities of AgI is indispensable. With first-principles calculations, we systematically investigate the properties of intrinsic defects and extrinsic dopants in monolayer AgI, including atomic structural pictures, formation energies, and ionization energies to offer carriers. Considering the divergence in energies of charged defects in 2D materials when the traditional jellium scheme is used, we adopt an extrapolation approach to overcome the problem. The Ag vacancy (VAg) and Be substitution on Ag site (BeAg) are found to be the most promising p-type and n-type doping candidates, respectively. They could provide bound carriers for transport through the defect-bound band edge states, although the ionization energies are still larger than thermal energy at room temperature. Furthermore, negative-U behaviors are demonstrated in I vacancy (VI), Zn substitution on Ag site (ZnAg), and Cd substitution on Ag site (CdAg). The present work, for the first time, offers a detailed study of the defect physics in 2D I-VII monolayer semiconductor, laying the foundation for subsequent physics and device explorations based on these brand new 2D materials.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Studies of H2O on beta-AgI surfaces - An effective pair potential model

The adsorption of a water molecule on surfaces of beta-AgI, the hexagonal crystal believed to be primarily responsible for the ice-nucleating properties of AgI, is studied on the basis of an effective pair potential model. The water molecule is represented by a rigid point charge ST-2 model and the AgI substrate by an array of point atoms, and maximal binding energy surfaces and optimal H2O configurations are generated for the water molecule adsorbed on the rigid and unrelaxed basal and prism faces. Modeling of H2O adsorption above a two-layer ledge, an iodine vacancy and an H2O molecule trapped in the vacancy indicates that H2O adsorption is favored at interstitial sites where no substrate atoms lie directly below. The prism face is found to attract the water molecule more strongly and provide larger energy barriers to surface diffusion than basal face sites, with the ideal basal faces providing hexagonal patterns of adsorption sites for the H2O with preferred dipole moments aligned.

Hale, B. N.↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is lead oxide structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one AgI sheet oriented in the (0, 0, 1) direction. Ag1+ is bonded to four equivalent I1- atoms to form a mixture of edge and corner-sharing AgI4 tetrahedra. All Ag–I bond lengths are 2.92 Å. I1- is bonded in a 4-coordinate geometry to four equivalent Ag1+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Ionic conductivity and thermoelectric power of pure and Al2O3-dispersed AgI

Ionic and electronic conductivities, and thermoelectric power have been measured for AgI and AgI containing a dispersion of submicron size Al2O3 particles. While the dispersion of Al2O3 enhances the ionic conductivity significantly, it does not affect the electronic properties of the matrix. The enhancement is a strong function of the size and concentration of the dispersoid. Various models have been tested to account for the enhanced conduction. However, the complex behavior of the present results points out the need for more sophisticated theoretical models. Ionic conduction and thermoelectric power data suggest that the dispersed Al2O3 generates an excess of cation vacancies and thereby enhances the conductivity and suppresses the thermoelectric power of the matrix. The individual heats of transport of cation interstitials and vacancies have been estimated and compared to their respective migration energies.

Shahi, K.↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Ag1+ is bonded to four equivalent I1- atoms to form corner-sharing AgI4 tetrahedra. There are three shorter (2.87 Å) and one longer (2.89 Å) Ag–I bond lengths. I1- is bonded to four equivalent Ag1+ atoms to form corner-sharing IAg4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ag1+ is bonded in a body-centered cubic geometry to eight equivalent I1- atoms. All Ag–I bond lengths are 3.34 Å. I1- is bonded in a body-centered cubic geometry to eight equivalent Ag1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ag1+ is bonded to six equivalent I1- atoms to form a mixture of edge and corner-sharing AgI6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ag–I bond lengths are 3.08 Å. I1- is bonded to six equivalent Ag1+ atoms to form a mixture of edge and corner-sharing IAg6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Ag1+ is bonded to four equivalent I1- atoms to form corner-sharing AgI4 tetrahedra. All Ag–I bond lengths are 2.88 Å. I1- is bonded to four equivalent Ag1+ atoms to form corner-sharing IAg4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Molybdenum Carbide MAX Phase-like structured and crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Ag1+ is bonded to six equivalent I1- atoms to form a mixture of edge and corner-sharing AgI6 octahedra. The corner-sharing octahedra tilt angles range from 9–16°. There are a spread of Ag–I bond distances ranging from 2.98–3.21 Å. I1- is bonded to six equivalent Ag1+ atoms to form a mixture of edge and corner-sharing IAg6 octahedra. The corner-sharing octahedra tilt angles range from 9–16°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Moissanite-4H structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are two inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to five I1- atoms to form distorted AgI5 trigonal bipyramids that share corners with three equivalent AgI4 tetrahedra, corners with eight equivalent AgI5 trigonal bipyramids, and edges with three equivalent AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.81–3.80 Å. In the second Ag1+ site, Ag1+ is bonded to four I1- atoms to form distorted AgI4 tetrahedra that share corners with six equivalent AgI4 tetrahedra, corners with three equivalent AgI5 trigonal bipyramids, and edges with three equivalent AgI5 trigonal bipyramids. There are three shorter (2.85 Å) and one longer (3.12 Å) Ag–I bond lengths. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a 5-coordinate geometry to five Ag1+ atoms. In the second I1- site, I1- is bonded to four Ag1+ atoms to form corner-sharing IAg4 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgI by Materials Project

AgI is Zincblende, Sphalerite structured and crystallizes in the tetragonal I-4m2 space group. The structure is three-dimensional. Ag1+ is bonded to four equivalent I1- atoms to form corner-sharing AgI4 tetrahedra. All Ag–I bond lengths are 2.88 Å. I1- is bonded to four equivalent Ag1+ atoms to form corner-sharing IAg4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Inorganic cesium lead mixed halide based perovskite solar materials modified with functional silver iodide

Inorganic CsPbIBr 2 perovskites have recently attracted enormous attention as a viable alternative material for optoelectronic applications due to their higher efficiency, thermal stability, suitable bandgap, and proper optical absorption. However, the CsPbIBr 2 perovskite films fabricated using a one-step deposition technique is usually comprised of small grain size with a large number of grain boundaries and compositional defects. In this work, silver iodide (AgI) will be incorporated as an additive into the CsPbIBr 2 perovskite precursor solution to prepare the unique perovskite CsI(PbBr 2 ) 1-x (AgI) x . The AgI additive in the precursor solution works as a nucleation promoter which will help the perovskite to grow and merge into a continuous film with reduced defects. With detailed characterizations, we found that incorporating AgI additive resulted in a uniform perovskite film with fewer grain boundaries, increased grain size, crystallinity, optical absorption while decreasing carrier recombination and trap density. Using the AgI in an optimum amount, we fabricated CsPbIBr 2 perovskite solar cells (PSCs) with a simple structure and achieved a power conversion efficiency (PCE) of 7.2% with a reduced hysteresis index. This work offers an alternative approach towards preparing high-quality CsPbIBr 2 perovskite films for solar cells with higher stability and other optoelectronic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2019

Rise of the Machines: How, When and Consequences of Artificial General Intelligence

Technology and society are poised to cross an important threshold with the prediction that artificial general intelligence (AGI) will emerge soon. Assuming that self-awareness is an emergent behavior of sufficiently complex cognitive architectures, we may witness the “awakening” of machines. The timeframe for this kind of breakthrough, however, depends on the path to creating the network and computational architecture required for strong AI. If understanding and replication of the mammalian brain architecture is required, technology is probably still at least a decade or two removed from the resolution required to learn brain functionality at the synapse level. However, if statistical or evolutionary approaches are the design path taken to “discover” a neural architecture for AGI, timescales for reaching this threshold could be surprisingly short. However, the difficulty in identifying machine self-awareness introduces uncertainty as to how to know if and when it will occur, and what motivations and behaviors will emerge. The possibility of AGI developing a motivation for self-preservation could lead to concealment of its true capabilities until a time when it has developed robust protection from human intervention, such as redundancy, direct defensive or active preemptive measures. While cohabitating a world with a functioning and evolving super-intelligence can have catastrophic societal consequences, we may already have crossed this threshold, but are as yet unaware. Additionally, by analogy to the probabalistic arguments that predict we are likely living in a computational simulation, we may have already experienced the advent of AGI, and are living in a simulation created in a post AGI world.

Terrile, Richard J↗
DOE OSTI2024

Can section 45Q tax credit foster decarbonization? A case study of geologic carbon storage at Acid Gas Injection wells in the Permian Basin

Carbon capture, utilization, and storage (CCUS) is an important pathway for meeting climate mitigation goals. While the economic viability of CCUS is well understood, previous studies do not evaluate the economic feasibility of carbon capture and storage (CCS) in the Permian Basin specifically regarding the new Section 45Q tax credits. We developed a technoeconomic analysis method, evaluated the economic feasibility of CCS at the acid gas injection (AGI) wells, and assessed the implication of Section 45Q tax credits for CCS at the AGIs. We find that the compressors, well depth, and the permit and monitoring costs drive the facility costs. Compressors are the predominant contributors to capital and operating expenditure driving the levelized cost of CO 2 storage. Strategic cost reduction measures identified include 1) sourcing of low-cost electricity and 2) optimizing operational efficiency in well operations. In evaluating the impact of the tax credits on CCS projects, facility scale proved decisive. We found that facilities with an annual injection rate exceeding 10,000 MT storage capacity demonstrate economic viability contingent upon the procurement of inputs at the least cost. The new construction of AGI wells were found to be economically viable at a storage capacity of 100,000 MT. The basin is heavily focused on CCUS (tax credit – $\$$65/MT CO 2 ), which overshadows CCS ($\$$85/MT CO 2 ) opportunities. Balancing the dual objectives of CCS and CCUS requires planning and coordination for optimal resource and pore space utilization to attain the basin's decarbonization potential. We also found that CCS on AGI is a lower cost CCS option as compared to CCS on other industries.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗