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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

A Two-Way Shape Memory Study on Ni-Rich NiTi Shape Memory Alloy by Combination of the All-Round Treatment and the R-Phase Transformation

Ni{sub 4}Ti{sub 3} precipitates are formed in Ni-rich NiTi shape memory alloys (SMAs) after a certain heat treatment. Such a treatment then results in the changed phase transformation behavior of the alloy switching from the one-step reversible phase change B2 ↔ B19′ to the two-step, B2 ↔ R ↔ B19′, phase change. The present study reports a two-way shape memory (TWSM) due to an all-round treatment followed by an R-phase constraint aging at room temperature. The enhanced TWSM behavior was observed upon temperature cycling between 273 K (R-phase) and 77 K (B19′ phase). The effect of various constraint strains in R-phase aging by employing different diameters of the constraint ring was studied. However, the TWSM effect due to constraining the R-phase will be eliminated after a temperature rise of specimen to the fully parent phase (373 K).

36 MATERIALS SCIENCE↗
DOE OSTI2025

The Ce-Fe-Ti System: Phase Equilibria in the Fe-rich Corner at 1000 °C

The rare earth–iron–transition metal systems are of increasing interest in the search for novel permanent magnet phases. This work reports on the solidification behavior, phase equilibria and stability range of solid phases in the ternary Ce-Fe-Ti system, focusing on the iron-rich region (> 65 at.% Fe) of the isothermal section at 1000 °C. Further, two ternary phases Ce 1.03 Fe 12-x Ti x (x = 0.87–1.02) with ThMn 12 structure type and Ce 3.06 Fe 27.6 Ti 1.4 with Nd 3 Fe 29 structure type were observed. Magnetic measurements of Ce 1.03 Fe 12-x Ti x and Ce 3.06 Fe 27.6 Ti 1.4 revealed ferromagnetic ordering with Curie temperatures of 550 K and 327 K, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Phase equilibria and microstructure evolution in the Ni-rich region of binary Ni-Ce and ternary Ni-Ce-X (X=Al, Nb, Cr, Ti) systems at 900 °C

The equilibrium compositions of all phases in the Ni-rich region of binary Ni-Ce and ternary Ni-Ce-X (X=Al, Nb, Cr, Ti) systems at 900 °C were determined experimentally through isothermal annealing for up to 500 h and compared with currently available computational thermodynamic descriptions. Additionally, the study examined how adding a third element to the binary system affects the microstructure by analyzing changes in the volume fraction of the intermetallic phase in the eutectic region. It was observed that Nb and Ti addition lowered the intermetallic fraction in the eutectic region while Al and Cr addition did the opposite. The fraction of intermetallic phase in the eutectic region is very important because it contributes to extreme brittleness of these alloys. Also, Al, Nb and Ti addition promoted different precipitates upon annealing when added in sufficient amounts. The collected data on composition and phase equilibria provides crucial information for improving the thermodynamic assessments of the binary and ternary alloy systems.

energy dispersive spectrometry↗
DOE OSTI2018

Neutronic experiments with fluorine rich compounds at LR-0 reactor

Here, research on molten salt reactor (MSR) neutronics continues in Research Centre Rez (Czech Republic) with experimental work being conducted using fluoride salt that was originally used in the Molten Salt Reactor Experiment (MSRE). Previous results identified significant variations in the neutron spectrum measured in LiF-NaF salt. These variations could originate from the fluorine description in current nuclear data sets. Subsequent experiments were performed to try to confirm this phenomenon. Therefore, another fluorine-rich compound, Teflon, was used for testing. Critical experiments showed slight discrepancies in C/E-1 for both compounds, Teflon and FLIBE, and systematic overestimation of criticality was observed in calculations. Different nuclear data libraries were used for data set testing. For Teflon, the overestimation is higher when using JENDL-3.3, JENDL-4, and RUSFOND-2010 libraries, all three of which share the same inelastic-to-elastic scattering cross section ratio. Calculations using other libraries (ENDF/B-VII.1, ENDF/B-VII.0, JEFF-3.2, JEFF-3.1, and CENDL-3.1) tend to be closer to the experimental value. Neutron spectrum measurement in both substances revealed structure similar to that seen in previous measurements using LiF-NaF salt, which indicates that the neutron spectrum seems to be strongly shaped by fluorine. Discrepancies between experimental and calculational results seem to be larger in the neutron energy range of 100–1300 keV than in higher energies. In the case of neutron spectrum calculation, none of the tested libraries gives overall better results than the others.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

3D polymer hydrogel for high-performance atomic iron-rich catalysts for oxygen reduction in acidic media

Current platinum group metal (PGM)-free carbon nanocomposite catalysts for the oxygen reduction reaction (ORR) in acidic electrolyte often suffer from rapid degradation associated with carbon corrosion due to the use of large amount of amorphoous carbon black supports. Here, we developed a new concept of using freestanding 3D hydrogel to design support-free Fe-N-C catalysts. A 3D polyaniline (PANI)-based hydrogel was used for preparing a new type of single atomic iron site-rich catalyst, which has exhibited exceptionally enhanced activity and stability compared to conventional Fe-N-C catalysts supported on amorphous carbon blacks. The achieved performance metric on the hydrogel PANI-Fe catalysts is one of the best ever reported PGM-free catalysts, reaching a half-wave potential up to 0.83 V vs. RHE and only leaving 30 mV gap with Pt/C catalysts (60 μgPt/cm2) in challenging acidic media. Remarkable ORR stability was accomplished as well on the same catalyst evidenced by using harsh potential cycling tests. The well dispersion of atomic iron into partially graphitized carbon, featured with dominance of micropores and porous network structures, is capable of accommodating increased number of active sites, strengthening local bonding among iron, nitrogen and carbon, and facilitating mass transfer. The 3D polymer hydrogel approach would be a new pathway to advance PGM-free catalysts.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2023

Single-step conversion of ethanol into n-butene-rich olefins over metal catalysts supported on ZrO 2 -SiO 2 mixed oxides

With airlines committed to drastically reduce their carbon footprint by 2050, producing jet fuel from renewable ethanol is of particular interest. Here we reported on an Ag/ZrO 2 /SBA-16 catalyst that is very effective for directly converting ethanol into to n-butene-rich olefins jet fuel precursors (i.e., 88% at full conversion). Here, we report on a Cu/ZrO 2 /SBA-16 catalyst that presents remarkable olefins selectivity (i.e., 89% at 96% conversion) and enhanced stability as compared to Ag/ZrO2/SBA-16 catalyst. Under severe operating conditions a conversion loss < 10% was observed with the Cu/ZrO 2 /SBA-16 catalyst as compared to a 50% loss of conversion with the Ag/ZrO 2 /SBA-16 catalyst. Combined experimental and computational tools revealed that replacing Ag with Cu shifts the reaction pathway of crotonaldehyde hydrogenation from 1,3-butadiene (i.e., coke precursor) production to butyraldehyde formation. Experiments conducted with 4%Cu/4%ZrO 2 supported on SBA-16, dealuminated zeolite Beta, and aluminum silicate revealed the performance and stability advantage of the SBA-16-supported catalyst.

09 BIOMASS FUELS↗
DOE OSTI2012

Acidic leucine-rich nuclear phosphoprotein 32 family member B (ANP32B) contributes to retinoic acid-induced differentiation of leukemic cells

Highlights: Black-Right-Pointing-Pointer ANP32B was down-regulated during ATRA-induced leukemic cell differentiation. Black-Right-Pointing-Pointer Knockdown of ANP32B enhanced ATRA-induced leukemic cell differentiation. Black-Right-Pointing-Pointer Ectopic expression of ANP32B inhibited ATRA-induced leukemic cell differentiation. Black-Right-Pointing-Pointer ANP32B inhibited ATRA activated transcriptional activity of RAR{alpha}. -- Abstract: The acidic leucine-rich nuclear phosphoprotein 32B (ANP32B) is a member of a conserved superfamily of nuclear proteins whose functions are largely unknown. In our previous work, ANP32B was identified as a novel direct substrate for caspase-3 and acted as a negative regulator for leukemic cell apoptosis. In this work, we provided the first demonstration that ANP32B expression was down-regulated during differentiation induction of leukemic cells by all-trans retinoic acid (ATRA). Knockdown of ANP32B expression by specific shRNA enhanced ATRA-induced leukemic cell differentiation, while ectopic expression of ANP32B attenuated it, indicating an inhibitory role of ANP32B against leukemic cell differentiation. Furthermore, luciferase reporter assay revealed that ANP32B might exert this role through inhibiting the ATRA dependent transcriptional activity of retinoic acid receptor (RAR{alpha}). These data will shed new insights into understanding the biological functions of ANP32B protein.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Inhibition of the proliferation and acceleration of migration of vascular endothelial cells by increased cysteine-rich motor neuron 1

Cysteine-rich motor neuron 1 (CRIM1) is upregulated only in extracellular matrix gels by angiogenic factors such as vascular endothelial growth factor (VEGF). It then plays a critical role in the tube formation of endothelial cells. In the present study, we investigated the effects of increased CRIM1 on other endothelial functions such as proliferation and migration. Knock down of CRIM1 had no effect on VEGF-induced proliferation or migration of human umbilical vein endothelial cells (HUVECs), indicating that basal CRIM1 is not involved in the proliferation or migration of endothelial cells. Stable CRIM1-overexpressing endothelial F-2 cells, termed CR1 and CR2, were constructed, because it was difficult to prepare monolayer HUVECs that expressed high levels of CRIM1. Proliferation was reduced and migration was accelerated in both CR1 and CR2 cells, compared with normal F-2 cells. Furthermore, the transient overexpression of CRIM1 resulted in decreased proliferation and increased migration of bovine aortic endothelial cells. In contrast, neither proliferation nor migration of COS-7 cells were changed by the overexpression of CRIM1. These results demonstrate that increased CRIM1 reduces the proliferation and accelerates the migration of endothelial cells. These CRIM1 effects might contribute to tube formation of endothelial cells. CRIM1 induced by angiogenic factors may serve as a regulator in endothelial cells to switch from proliferating cells to morphological differentiation. - Highlights: • CRIM1 was upregulated only in tubular endothelial cells, but not in monolayers. • Increased CRIM1 reduced the proliferation of endothelial cells. • Increased CRIM1 accelerated the migration of endothelial cells. • Increased CRIM1 had no effect on the proliferation or migration of COS-7 cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

PRELP (proline/arginine-rich end leucine-rich repeat protein) promotes osteoblastic differentiation of preosteoblastic MC3T3-E1 cells by regulating the β-catenin pathway

Proline/arginine-rich end leucine-rich repeat protein (PRELP) is a collagen-binding proteoglycan highly expressed in the developing bones. Recent studies indicated that PRELP could inhibit osteoclastogenesis as a NF-κB inhibitor. However, its role during osteoblast differentiation is still unclear. In this study, we confirmed that the expression of PRELP increased with the osteogenesis induction of preosteoblastic MC3T3-E1 cells. Down-regulation of PRELP expression by shRNA reduced ALP activity, mineralization and expression of osteogenic marker gene Runx2. Our microarray analysis data suggested that β-catenin may act as a hub gene in the PRELP-mediated gene network. We validated furtherly that PRELP knockdown could inhibit the level of connexin43, a key regulator of osteoblast differentiation by affecting β-catenin protein expression, and its nuclear translocation in MC3T3-E1 preosteoblasts. Therefore, this study established a new role of PRELP in modulating β-catenin/connexin43 pathway and osteoblast differentiation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Thermodynamic contribution of backbone conformational entropy in the binding between SH3 domain and proline-rich motif

Biological functions of intrinsically disordered proteins (IDPs), and proteins containing intrinsically disordered regions (IDRs) are often mediated by short linear motifs, like proline-rich motifs (PRMs). Upon binding to their target proteins, IDPs undergo a disorder-to-order transition which is accompanied by a large conformational entropy penalty. Hence, the molecular mechanisms underlying control of conformational entropy are critical for understanding the binding affinity and selectivity of IDPs-mediated protein-protein interactions (PPIs). Here, we investigated the backbone conformational entropy change accompanied by binding of the N-terminal SH3 domain (nSH3) of CrkII and PRM derived from guanine nucleotide exchange factor 1 (C3G). In particular, we focused on the estimation of conformational entropy change of disordered PRM upon binding to the nSH3 domain. Quantitative characterization of conformational dynamics of disordered peptides like PRMs is limited. Hence, we combined various methods, including NMR model-free analysis, δ2D, DynaMine, and structure-based calculation of entropy loss. This study demonstrates that the contribution of backbone conformational entropy change is significant in the PPIs mediated by IDPs/IDRs. - Highlights: • Conformational entropy plays critical roles in the regulation of protein-protein interactions. • Conformational entropy change upon binding of disordered ligands to a protein is not well understood. • We estimated backbone conformational entropy change upon complexation of SH3 domain and PRM. • Energetic contribution of backbone conformational entropy is significant in SH3-PRM interaction.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

A tomato proline-, lysine-, and glutamic-rich type gene SpPKE1 positively regulates drought stress tolerance

Highlights: • Overexpression of SpPKE1 confers tomato and tobacco tolerance to drought stress. • SpPKE1 modulate the expressions of stress-responsive genes. • SpPKE1 interacts with an F-box protein in yeast. Plant abiotic resistance in cultivated species features limited variability. Using genes of wild species serves as a valid approach for improving abiotic resistance of cultivated plants. In this study, we uncovered a previously uncharacterized proline-, lysine-, and glutamic-rich protein gene (SpPKE1), which was isolated from drought-resistant wild tomato species Solanum pennellii (LA0716). When M82, which is a drought-sensitive tomato cultivar, was engineered to overexpress SpPKE1, its tolerance under drought stress was significantly improved by the accumulation of more chlorophyll, proline, and limited malondialdehyde compared with that in RNA interference (RNAi)-suppression lines, which were more sensitive than the wild-type plants. Several ion transporter genes, abiotic-related transcriptional factors, and reactive oxygen species-scavenging genes were upregulated in PKE1 overexpression (OE) lines but downregulated in RNAi plants. OE of SpPKE1 enhanced drought tolerance in tobacco. Screening results of yeast two-hybrid protein–protein interaction revealed that SpPKE1 can bind to an F-box protein that plays an important role in plant drought resistance. We posited that PKE1 enhanced drought tolerance by modulating the expressions of stress-responsive genes and interacting with the F-box protein.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

MiR-141-3p is upregulated in esophageal squamous cell carcinoma and targets pleckstrin homology domain leucine-rich repeat protein phosphatase-2, a negative regulator of the PI3K/AKT pathway

Highlights: • The PI3K/AKT pathway plays essential roles in their development and progression. • PHLPP2 is a negative regulator of the PI3K/AKT pathway. • MiRNAs are involved in cancer progression and metastasis. • MiR-141-3p expression is upregulated in esophageal squamous cell carcinoma cells. • MiR-141-3p targets PHLPP2 at its 3′-untranslated region. The phosphatidylinositol-3-kinase (PI3K)/AKT pathway is frequently activated in various human cancers and plays essential roles in their development and progression. Accumulating evidence suggests that dysregulated expression of microRNAs (miRNAs) is closely associated with cancer progression and metastasis. Here, we focused on miRNAs that could regulate genes related to the PI3K/AKT pathway in esophageal squamous cell carcinoma (ESCC). To identify upregulated miRNAs and their possible target genes in ESCC, we performed microarray-based integrative analyses of miRNA and mRNA expression levels in three human ESCC cell lines and a normal esophageal epithelial cell line. The miRNA microarray analysis revealed that miR-31-5p, miR-141-3p, miR-200b-3p, miR-200c-3p, and miR-205-5p were expressed at higher levels in the ESCC cell lines than the normal esophageal epithelial cell line. Bioinformatical analyses of mRNA microarray data identified several AKT/PI3K pathway-related genes as candidate targets of these miRNAs, which include tumor suppressors such as DNA-damage-inducible transcript 4 and pleckstrin homology domain leucine-rich repeat protein phosphatase-2 (PHLPP2). To validate the targets of relevant miRNAs experimentally, synthetic mimics of the miRNAs were transfected into the esophageal epithelial cell line. Here, we report that miR-141-3p suppress the expression of PHLPP2, a negative regulators of the AKT/PI3K pathway, as a target in ESCC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Spin label EPR suggests the presence of cholesterol rich domains in cultured insect cell membranes

Highlights: • Membranes of cultured insect cells were studied with spin label EPR. • Two kinds of spin labels (SL) with different chemical affinity were used. • EPR of SL chemically akin to cholesterol indicates its uneven distribution in intact cells. • Evidence of cholesterol enriched nanodomains in intact cell membranes. • Cholesterol depletion erases the EPR evidence of cell membrane domains. Different spin labels were incorporated to the membranes of cultured insect UFL-AG-286 cells in order to characterize their physical properties by Electron Paramagnetic Resonance spectroscopy (EPR). The spectrum of the spin label 12-SASL incorporated to cell membranes was similar as those obtained in membrane model systems composed of eggPC/cholesterol. However, the spectrum of the spin label CSL, chemically related to cholesterol, was drastically different in the two systems. Interestingly, when cell cholesterol content was reduced using methyl beta cyclodextrin, an EPR spectrum similar to those of model membranes was obtained. The analysis of these experiments suggests the existence of cholesterol rich regions in UFL-AG-286 cell membranes.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

A histidine-rich elastin-like polypeptide functions as a quickly detectable and easily purifiable protein fusion tag

Highlights: • A HRELP fusion tag is designed and highly expressed in E. coli. • HRELP fusion tag can be specifically and quickly stained with Pauly's reagent. • HRELP fusion protein can be detected in both cell lysate and SDS-PAGE. • HRELP fusion protein can be purified by pH-triggered ITC. Although many protein fusion tags have been developed for recombinant protein production to improve protein yields or facilitate purification, determining the expression and purification of the fusion protein still remain to be a time-consuming and laborious procedure. In this work, we designed a histidine-rich elastin-like polypeptide (HRELP) fusion tag and found that it could be efficiently expressed in E. coli cells and specifically stained with Pauly's reagent in a couple of minutes post SDS-PAGE analysis. Moreover, in Pauly's reagent-stained polyacrylamide gels, only the bands of HRELP fusion proteins were yellow and could be clearly visualized with little background. Furthermore, both HRELPs and HRELP20-BMP2 fusion protein could be purified by a method of pH shift-mediated inverse transition cycling (ITC). In our opinion, the HRELP established in this study may be considered as a multifunctional protein tag which could make its fusion proteins being quickly detected by Pauly staining and simply purified by pH-triggered ITC in addition to having the potential to sustained release its fusion proteins.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Growing grasses in unprofitable areas of US Midwest croplands could increase species richness

The US has large potential to grow perennial energy crops, but because these crops are rarely grown in current agricultural landscapes, it is unclear how biodiversity may be affected. Over time, as agriculture has increased, many grassland species have declined. In addition, not all agricultural land is profitable for growing annual crops. Unprofitable areas were responsible for a loss of approximately $110 million USD per year from 2013 to 2016. Based on this, we want to know how converting less-profitable portions of agricultural fields to switchgrass, a native prairie grass, would influence species occurrence. To address this question, we developed an alternative landscape in which clustered corn/soy acres with a low return on investment (ROI) were replaced with grassland. We also developed and validated species distribution models to predict changes in species occurrence for 28 avian species in Iowa in response to landscape management. Furthermore, we compared results for three different models: Random forest (RF), Stochastic gradient boosting (GBM), and Neural network (Nnet) and found that all models performed well and predicted similar species distribution. Predicted species richness increased by 3.66% (RF), 2.79% (GBM), and 7.51% (Nnet) when we simulated a change in management for ~3% of Iowa's low ROI corn/soybean areas to grassland. If harvested, these areas could generate approximately 7.6 million dry tons/year of switchgrass for bioenergy, thereby increasing farmers earnings. Unprofitable areas tended to occur along streams, which suggest that incorporating partially harvested riparian buffers can benefit avian biodiversity, while improving water quality and reducing unnecessary costs for farmers.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

Advancing Ethanol-to-Jet cost Effectiveness via direct conversion to n -Butene-Rich olefins and Co-Product Valorization

Ethanol is a promising feedstock for sustainable aviation fuel production; however, conventional routes face significant energy and cost challenges, particularly due to the ethanol dehydration step to ethylene. Here, this study leverages breakthrough experimental data to perform comprehensive techno-economic and life-cycle assessments of an innovative ethanol-to-jet process. The process employs a single-step catalytic conversion, enabled by multifunctional Cu-ZrO 2 /SBA-16 catalyst, to directly upgrade ethanol into a mixed olefin stream rich in n-butene. The single-step conversion eliminates the costly ethanol dehydration step in the conventional process. High selectivity toward n-butene offers key advantages: it simplifies downstream oligomerization into jet-range hydrocarbons and enables the co-production of renewable n-butene alongside sustainable aviation fuel. The analysis estimates a minimum fuel selling price as low as $\$$2.50 per gallon, whether using corn ethanol or cellulosic ethanol from corn stover. Life cycle CO 2 equivalent emissions are projected to be as low as 10.6 g CO 2 eq/MJ sustainable aviation fuel, representing over 70% reduction compared to conventional petroleum-based jet fuel. This one-step ethanol upgrading approach not only facilitates SAF and n-butene co-production but also provides operational flexibility. The ability to tailor product outputs allows the ethanol-to-jet process to adapt to varying feedstocks, incentive programs, and market dynamics, ultimately enhancing the economic viability of sustainable aviation fuel production.

Xu, Yiling [Pacific Northwest National Laboratory ↗
DOE OSTI2013

Photovoltaic's silica-rich waste sludge as supplementary cementitious material (SCM)

Waste sludge, a solid recovered from wastewater of photovoltaic-industries, composes of agglomerates of nano-particles like SiO{sub 2} and CaCO{sub 3}. This sludge deflocculates in aqueous solutions into nano-particles smaller than 1 μm. Thus, this sludge constitutes a potentially hazardous waste when it is improperly disposed. Due to its high content of amorphous SiO{sub 2}, this sludge has a potential use as supplementary cementitious material (SCM) in concrete. In this study the main properties of three different samples of photovoltaic's silica-rich waste sludge (nSS) were physically and chemically characterized. The characterization techniques included: scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nitrogen physical adsorption isotherm (BET method), density by Helium pycnometry, particle size distribution determined by laser light scattering (LLS) and zeta-potential measurements by dynamic light scattering (DLS). In addition, a dispersability study was performed to design stable slurries to be used as liquid additives for the concrete production on site. The effects on the hydration kinetics of cement pastes by the incorporation of nSS in the designed slurries were determined using an isothermal calorimeter. A compressive strength test of standard mortars with 7% of cement replacement was performed to determine the pozzolanic activity of the waste nano-silica sludge. Finally, the hardened system was fully characterized to determine the phase composition. The results demonstrate that the nSS can be utilized as SCM to replace portion of cement in mortars, thereby decreasing the CO{sub 2} footprint and the environmental impact of concrete. -- Highlights: •Three different samples of PV nano-silica sludge (nSS) were fully characterized. •nSS is composed of agglomerates of nano-particles like SiO{sub 2} and CaCO{sub 3}. •Dispersability studies demonstrated that nSS agglomerates are broken to nano-size. •nSS can be classified as a pozzolanic material with activity index higher than 100. •nSS can be use as a potential SCM to partly replace cement in concrete.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Mechanical and physical properties of inorganic polymer cement made of iron-rich laterite and lateritic clay: A comparative study

In this work, two different laterites (iron contents of 13.07 and 49.34 wt%, respectively, for lateritic clay, LAC, and iron-rich laterite, LAI) were selected and calcined at 600 °C. The obtained calcined laterites, namely LAI600 and LAC600, were separately mixed with an alkaline solution (silicate modulus of 1.35) or an acidic solution (phosphoric acid solution at pH ≤ 2) for the synthesis of inorganic polymer products. The fabricated products were cured at 20 °C (ambient) and 40 °C (oven). The obtained results showed that the compressive strength of each series of alkaline-based inorganic polymer binder increased with ageing time (7 and 28 days) for room temperature curing, while the reverse trend was noted for oven-cured specimens. The best mechanical performance was obtained when using a phosphoric acid solution, 38 and 52 ± 1 MPa; 62 and 65 ± 1 MPa at 28 days for LAC and LAI respectively. It appeared that a higher iron content within the laterite contributed to an increase in the compressive strength under acidic conditions (LAI (59 MPa) > LAC (48 MPa)) compared to the behavior obtained under alkaline conditions (LAI (6 MPa) < LAC (29 MPa)). Accordingly, the acidic products exhibited a dense structure (with lower porosity) and contained amorphous iron/aluminium phosphate phases such as berlinite (FePO{sub 4}), iron hydrogen phosphate hydrate (Fe{sub 3}H{sub 15}(PO{sub 4}){sub 8·}4H{sub 2}O), ferrowyllieite (AlFe{sub 2}Na{sub 2}(PO{sub 4}){sub 3}) and sodium iron phosphate (Na{sub 3}Fe{sub 2}(PO{sub 4}){sub 3}) arising from the alteration of iron minerals in an acidic medium, confirmed by Mössbauer spectroscopy and electron paramagnetic resonance spectroscopy.

36 MATERIALS SCIENCE↗