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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Fabrication, Analysis of Microstructure and Oxidation Resistance of Cemented C/C Composites by Laser

Cylindrical carbon–carbon composites have been cemented using a CO{sub 2} laser actuated by a raster scanning mirror system in a four-step sequence. Complete and homogenous surface cementation as well as thermal stability of the composites was sought after and achieved. The line of heat created from the laser beam impinged parallel to the axis of the pre-coated cylinder, while suspended from one end and slowly rotated. Four slurry compositions, all containing chloride salts from refractory elements, some combined with silicon, were pre-deposited by air spraying it over each specimen and then laser treated sequentially. Confined heat sublimed the chlorine ions resulting in silicide compounds that reacted with the carbon substrate to form a bonding layer. Microstructure characterization was performed using scanning electron microscopy, energy-dispersive spectroscopy and x-ray diffraction, immediately after the cementation was consolidated and after heat treated under argon. Preliminary oxidation weight loss tests were performed up to 1423 K under argon and air, revealing a 9.8 and 30.6% weight reduction, respectively, after 9 h of exposure. Cemented specimens were then coated with a glass overcoat layer that allowed them to perform moderately better against oxidation achieving up to a 28% weight loss after 20 h at 1273 K in air.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Tailoring the Properties of Calcium Aluminate Macro-Defect-Free Cements: From Brittle to Ductile Behavior

Cementitious macro-defect-free (MDF) materials can be obtained processing a mixture of a water-soluble polymer, namely polyvinyl alcohol (PVA) and the calcium aluminate cement. Based on process techniques typical of plastics, the MDF products can be obtained in complex forms and, thanks to the reduced water to cement ratio, w/c, their strength is very high compared to standard cements. However, these materials show both the sensitivity typical of water-soluble polymers, presenting a low glass transition temperature (T{sub g}), and the brittle behavior typical of ceramic materials and therefore low toughness. The aim of this work is to modify the mechanical properties of MDF cements by tuning their unacceptable brittle behavior. Water solution of carboxylate styrene butadiene rubber is used as reactive additives, and different mixture formulations are tested changing the rubber-like content both with respect to the fixed water content and PVA amounts. It is shown that the modifications of the organic phase imply small or negligible effects on paste formation of different recipes as detected by the torque–time responses. From flexural and fracture toughness tests, a wide range of responses was observed, and depending on the particular recipe, the mechanical behavior can be tuned from a brittle to a ductile behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Wellbore cement alteration and roles of CO 2 and shale during underground hydrogen storage

To mitigate climate change and adopt renewable energy, energy storage is crucial and can be done in the form of hydrogen gas (H 2 ). Subsurface geologic reservoirs are positioned to store H 2 on the largest scales for the longest terms of all potential options. However, H 2 injection may boost reactions that consume hydrogen, generate undesired gases, and alter pore structures of geomedia. To explore the extent of H 2 -associated biotic reactions at a near wellbore location, four experiments were conducted under underground storage conditions with wellbore cement cores and, in most instances, shale samples submerged in synthetic formation brine. Post-reaction gas, aqueous, and solid phase samples were analyzed using olfactory screening and, later, gas chromatography (GC-MS), inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), and synchrotron micro-scale x-ray fluorescence (μ-XRF). Within a period of 16 weeks, hydrogen sulfide (H 2 S) was generated in systems containing both H 2 and shale. XRF mapping identified a zone enriched in iron(II) and reduced sulfur along the rim of cement cross sections that was largely associated with CO 2 -induced cement carbonation. Shale did not show noticeable alteration, but there is evidence it contributed to the initial inoculation of the system and provided nutrients for microbes via water-rock interactions. Here, this study considers both rock formations and wellbore cement not previously evaluated concurrently. Findings support understanding and modeling of H 2 -associated biogeochemical reactions during underground hydrogen storage.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Cement and concrete as carbon sinks: Transforming a climate challenge into a carbon storage opportunity

Cement and concrete, while traditionally recognized as the main contributors to anthropogenic CO 2 emissions, also have untapped capacity to serve as substantial and scalable carbon sinks. This perspective examines how engineered mineral carbonation can transform cement-based materials into functional carbon storage systems, generating both environmental and economic value. We review the fundamental mechanisms of CO 2 uptake in cementitious systems, highlighting current limitations in reaction kinetics, phase control, and durability under varying environmental conditions. Emphasis is placed on the utilization of alkaline industrial residues and emerging magnesium-based cements, which offer synergistic pathways for carbon sequestration and circular resource use. We further assess the performance trade-offs associated with CO 2 uptake and the feasibility of deploying these technologies on industrial scales. A strategic roadmap is proposed that integrates scientific innovation, regulatory alignment, and carbon accounting in the life cycle to accelerate the adoption of carbon-storing concrete. This perspective provides a comprehensive framework to advance cement and concrete as engineered carbon sinks and supports the transition to a climate-positive construction industry.

Carbon storage↗
DOE OSTI2014

The existence of amorphous phase in Portland cements: Physical factors affecting Rietveld quantitative phase analysis

Rietveld quantitative phase analysis has become a widespread tool for the characterization of Portland cement, both for research and production control purposes. One of the major remaining points of debate is whether Portland cements contain amorphous content or not. This paper presents detailed analyses of the amorphous phase contents in a set of commercial Portland cements, clinker, synthetic alite and limestone by Rietveld refinement of X-ray powder diffraction measurements using both external and internal standard methods. A systematic study showed that the sample preparation and comminution procedure is closely linked to the calculated amorphous contents. Particle size reduction by wet-grinding lowered the calculated amorphous contents to insignificant quantities for all materials studied. No amorphous content was identified in the final analysis of the Portland cements under investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Use of X-ray diffraction to quantify amorphous supplementary cementitious materials in anhydrous and hydrated blended cements

The content of individual amorphous supplementary cementitious materials (SCMs) in anhydrous and hydrated blended cements was quantified by the PONKCS [1] X-ray diffraction (XRD) method. The analytical precision and accuracy of the method were assessed through comparison to a series of mixes of known phase composition and of increasing complexity. A 2σ precision smaller than 2–3 wt.% and an accuracy better than 2 wt.% were achieved for SCMs in mixes with quartz, anhydrous Portland cement, and hydrated Portland cement. The extent of reaction of SCMs in hydrating binders measured by XRD was 1) internally consistent as confirmed through the standard addition method and 2) showed a linear correlation to the cumulative heat release as measured independently by isothermal conduction calorimetry. The advantages, limitations and applicability of the method are discussed with reference to existing methods that measure the degree of reaction of SCMs in blended cements.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Influence of sodium borate on the early age hydration of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements are potential candidates for the conditioning of radioactive wastes with high sodium borate concentrations. This work thus investigates early age hydration of two CSA cements with different gypsum contents (0 to 20%) as a function of the mixing solution composition (borate and NaOH concentrations). Gypsum plays a key role in controlling the reactivity of cement. When the mixing solution is pure water, increasing the gypsum concentration accelerates cement hydration. However, the reverse is observed when the mixing solution contains sodium borate. Until gypsum exhaustion, the pore solution pH remains constant at ~ 10.8, and a poorly crystallized borate compound (ulexite) precipitates. A correlation is established between this transient precipitation and the hydration delay. Decreasing the gypsum content in the binder, or increasing the sodium content in the mixing solution, are two ways of reducing the stability of ulexite, thus decreasing the hydration delay.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Binding and leaching of trace elements in Portland cement pastes

Portland cement contains trace elements originating from the raw materials and the fuels used for cement production. The trace elements are bound to some extent during cement hydration. A small fraction remains dissolved in the pore solution. The dissolved fractions of antimony, barium, chromium, lead, molybdenum and vanadium were quantified in the course of hydration of four different Portland cements. The development of heavy metal concentrations signifies the relevant hydration products for the binding of heavy metals. For chromate and molybdate a substitution for sulfate in ettringite was found. Vanadium and antimony are most likely not bound in ettringite. Barium precipitates as barium sulfate. For lead no clear trends could be observed. Leaching experiments were carried out and the concentrations of the leachates were compared to pore solution concentrations to check if the solubility of the heavy metals is relevant or if the leaching process is controlled by diffusion.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Compatibility of hydrogarnet, Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub x}(OH){sub 4(3−x)}, with sulfate and carbonate-bearing cement phases: 5–85 °C

The stable existence of hydrogarnet in Portland cement compositions cured at temperatures below 55 °C has long been predicted from application of equilibrium thermodynamics. However hydrogarnet is not often reported in hydrated commercial Portland cements. The substitutions (SO{sub 4}–CO{sub 3}–OH) in AFm have previously been shown to stabilise AFm to higher temperatures and raise the temperature at which AFm converts to Si-free hydrogarnet, C{sub 3}AH{sub 6}. But unanswered question remains about the compatibility of AFm and AFm solid solutions with Si-substituted hydrogarnet, Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub x}(OH){sub 4(3} {sub −} {sub x)}. Phase relations of C{sub 3}AH{sub 6} and Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub x}(OH){sub 4(3} {sub −} {sub x)} at sulfate and carbonate activities conditioned respectively by (gypsum and SO{sub 4}-AFt) and (calcite and CO{sub 3}-AFt) have been determined experimentally in the range 5–85 °C. The results confirm the instability of Si-free hydrogarnet with carbonate and sulfate-bearing cement phases, but do indicate that a range of silica-substituted hydrogarnet solid solutions are stable under conditions likely to be encountered in blended cement systems.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Influence of spraying on the early hydration of accelerated cement pastes

In practice, most of the studies about the interaction between cement and accelerators is performed with hand-mixed pastes. However, in many applications mixing occurs through spraying, which may affect accelerators reactivity and the microstructure of the hardened paste. The objective of this study is to analyze how the mixing process influences the early hydration of accelerated cement pastes. Isothermal calorimetry, X-ray diffraction, thermogravimetry and SEM imaging were performed on cement pastes produced by hand-mixing and by spraying, using equivalent doses of an alkali-free and an alkaline accelerator and two types of cement. Results showed a great influence of the spraying process on the reactivity of accelerators and on the morphology of the precipitated hydrates. Variations in hydration kinetics caused by the mixing method are explained and the results obtained might have a significant repercussion on how future research on the behavior of accelerated mixes will be performed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Parameters controlling early age hydration of cement pastes containing accelerators for sprayed concrete

The objective of this work is to parametrize the early age hydration behavior of accelerated cement pastes based on the chemical properties of cement and accelerators. Eight cements, three alkali-free and one alkaline accelerators were evaluated. Isothermal calorimetry, in situ XRD and SEM imaging were performed to characterize kinetics and mechanisms of hydration and the microstructure development. The reactivity of all accelerators is directly proportional to their aluminum and sulfate concentrations and to the amount and solubility of the setting regulator contained in cement. Alite hydration is enhanced if a proper C{sub 3}A/SO{sub 3} ratio (between 0.67 and 0.90) remains after accelerator addition and if limestone filler is employed, because undersulfated C{sub 3}A reactions are avoided. Combinations of compatible materials are recommended to enhance the performance of the matrix and to prevent an undesirable hydration behavior and its consequences in mechanical strength development.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Role of calcium on chloride binding in hydrated Portland cement–metakaolin–limestone blends

Chloride binding is investigated for Portland cement–metakaolin–limestone pastes exposed to CaCl{sub 2} and NaCl solutions. The phase assemblages and the amount of Friedel's salt are evaluated using TGA, XRD and thermodynamic modeling. A larger amount of Friedel's salt is observed in the metakaolin blends compared to the pure Portland cement. A higher total chloride binding is observed for the pastes exposed to the CaCl{sub 2} solution relative to those in the NaCl solution. This is reflected by the fact that calcium increases the quantity of Friedel's salt in the metakaolin blends by promoting the transformation of strätlingite and/or monocarbonate to Friedel's salt. Calcium increases also the amount of chloride in the diffuse layer of the C-S-H for the pure cement. A linear correlation between the total bound chloride and the uptake of calcium from the CaCl{sub 2} solution is obtained and found to be independent on the type of cement blend.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Physico-chemical mechanisms involved in the acceleration of the hydration of calcium sulfoaluminate cement by lithium ions

This work investigates the influence of lithium ions on the hydration at 25 °C of two calcium sulfoaluminate (CSA) cements comprising 0 or 10% gypsum. Small concentrations of lithium salts (LiOH, LiNO{sub 3}) accelerate the early hydration of both CSA cements either in paste or in diluted and stirred suspension. The effect of the lithium cation is much stronger than its counter-ion. Hydration is accelerated by an increase in the lithium concentration up to 30 μmol Li/g of the used CSA cement (with a high ye'elimite content), and then levels off. The postulated mechanism relies on a fast precipitation of amorphous Li-containing Al(OH){sub 3}, which acts as seeds for accelerating the precipitation of amorphous Al(OH){sub 3} that speeds up the whole hydration process. This process seems to be closely related to the one involved in the acceleration of the hydration of calcium aluminate cement by lithium ions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of set retarding admixtures on calcium sulfoaluminate cement hydration and property development

Little published data is available to guide specification calcium sulfoaluminate cement (CSA) mixtures with citric acid retarder dosage rates capable of achieving adequate field working times, nor to understand the effect of retarder dosage on hydration and property development, representing a significant barrier to widespread CSA concrete use. Thus, this study investigated the use of citric acid with two commercially-available CSA cements, tracking the effects of dosage on phase development, hydration, setting, and compressive strengths. Key findings were that: citric acid successfully retarded initial set past 120 min for both cements despite significantly different chemistries; increasing cement anhydrite content reduced retarder effectiveness and altered hardened binder microstructure, reducing compressive strengths; greater retarder dosages did not negatively affect cumulative hydration, nor strengths; and the time at which the maximum rate of heat evolution occurred correlated with final setting, a relationship useful for predicting field mixture behavior based on laboratory testing.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Development of silica-enriched cement-based materials with improved aging resistance for application in high-temperature environments

Understanding the effects of high temperature (HT) and high pressure (HP) conditions on the microstructure of cement-based materials is critical to the construction and safe operation of deep oil and gas wells. Under such conditions, the persistence of calcium-silicate-hydrate (C-S-H) gel is compromised by ongoing crystallization that, if not controlled, may adversely affect the durability of the cement sheath. This work investigates the effect of silica content >35% by-weight-of-cement (BWOC), silica particle size, and solid volume fraction (SVF) on the microstructure and phase composition of cement-silica blends cured hydrothermally at 200 °C and 20.7 MPa. The results of X-ray diffraction and electron microprobe analysis revealed significant impact of these three mix design parameters on the final phase assembly, and on the conversion rate of semi-crystalline C-S-H to gyrolite and 11 Åtobermorite. Incorporation of more fine siliceous material suppressed dissolution of coarse silica particles, resulting in a matrix with improved homogeneity and dominated by fine gel pores. Mixes with lower SVF showed greater formation of 11 Å tobermorite, a higher degree of crystallinity and/or greater crystallite size. Prolonged HTHP curing of all systems (up to three months in this study), irrespective of the initial SVF, increased the fraction of capillary pores, indicating void coalesce caused by crystal growth. However, we find that this coarsening is less pronounced in systems with less pore space available for crystallization.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Reaction mechanism of magnesium potassium phosphate cement with high magnesium-to-phosphate ratio

Understanding reaction mechanisms of magnesium potassium phosphate (MKP) cement is of significant importance, as it is closely related to the optimum design of MKP cement-based materials. In this study, reaction mechanisms of MKP cements with a high magnesium-to-phosphate (Mg/PO{sub 4}) molar ratio of 8 were investigated at two different water-to-solid (w/s) ratios of 0.5 and 5. The experimental findings show that the use of this high Mg/PO{sub 4} molar ratio suppresses the formation of potassium-free magnesium phosphate hydrates. K-struvite is mainly formed with probably more phosphate than the theoretical value. Moreover, the w/s ratio plays a crucial role on governing the reaction path of MKP cements. The lower w/s ratio (w/s = 0.5) leads to higher potassium concentration and pH value, thus suppressing the formation of intermediate product, Mg{sub 2}KH(PO{sub 4}){sub 2}·15H{sub 2}O, which is formed at the higher w/s = 5. However, it causes the formation of minor amount of brucite at 28 d, which coexists with K-struvite in the paste.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Inhibition mechanisms of steel slag on the early-age hydration of cement

Steel slag inhibits the early-age hydration of cement. However, its mechanism is still unclear. In this paper, the early-age hydration kinetics and the evolution of the solid phases, aqueous species and microstructures in a cement-steel slag composite binder are investigated to explore how steel slag inhibits the early-age hydration of cement. Two novel phenomena are found: (1) steel slag slows the depletion of gypsum and reduces the formation of ettringite, and (2) steel slag significantly inhibits the precipitation of CH and CSH. The results show that the addition of steel slag increases the Ca concentration in the pore solution, reduces the supersaturation of the pore solution with respect to CH and inhibits the nucleation and growth of CSH. Based on the above results, the retardation mechanisms of steel slag on the initial setting of cement paste are explained.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Long-term cement hydration studies with isothermal calorimetry

The purpose of this study was to investigate for how long the thermal power of hydration can be measured with isothermal calorimetry, which is a general measurement technique with stable properties that, in many cases, can detect low rates of processes. Measurements were conducted for 365 days on cement paste with Portland cement, fly ash blended Portland cement and different water-to-binder ratios. The results showed that all the tested systems still produced a measureable signal after one year. The samples with Portland cement were also analyzed by XRD after 365 days, and phase composition calculations were made with GEMS. Together with the calorimetric results, these results were used to determine the degree of hydration by five methods, the results of which showed good agreement.

36 MATERIALS SCIENCE↗