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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Sintering and Fracture Behavior of Plasma-sprayed Thermal Barrier Coatings

Thermal barrier coatings will be more aggressively designed to protect gas turbine engine hot-section components in order to meet future engine higher fuel efficiency and lower emission goals. There is a need to characterize the fundamental sintering and fracture behavior of the current ZrO2-(7 to 8)wt%Y2O3 coating, in order to fully take advantage of the coating capability. In addition, a thorough evaluation of the coating behavior and temperature limits will be useful for more accurately assessing the benefit gained from future advanced coating systems. In this study, the sintering behavior of plasma-sprayed ZrO2-8wt%Y2O3 coatings was systematically investigated as a function of temperature and time using a dilatometer in the temperature range of 1200-1500 C. The coating sintering kinetics obtained by dilatometry were compared with the coating thermal conductivity increase kinetics, determined by a steady-state laser heat-flux testing approach, under high temperature and thermal gradient sintering conditions. The mode I, mode II, and mixed mode I-mode II fracture behavior of as-processed and sintering-annealed coatings was determined in asymmetric flexure loading at ambient and elevated temperatures in order to evaluate the coating sintering effects on the fracture envelope of K(sub I) versus K(sub II). The coating thermal conductivity cyclic response associated with the interface delamination of the coating systems under simulated engine heat-flux conditions will be discussed in conjunction with the sintering and fracture testing results.

Zhu, Dongming↗
DOE OSTI2015

Material for solid state sintered material

A solid state sintered material is described that includes a mixed oxide of lanthanum, strontium, cobalt, iron and oxygen, and CaCO3 inclusions. The solid state sintered material can also include calcium oxide, which can form from thermal composition of calcium carbonate. The solid state sintered material can also include a pore-forming particulate material such as carbon black and/or a doped ceramic metal oxide ionic conductor such as Sm-doped ceria uniformly dispersed in the solid state sintered material. The solid state sintered material can be formed from a two-step process in which a portion of the CaCO3 is mixed with the mixed oxide materials and heated to form porous agglomerates, and the remaining CaCO3 is added during the formation of a sintering paste. The solid state sintered material described herein can be used as a cathode material for solid oxide fuel cell.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Rapid Laser Reactive Sintering of Garnet Li 6.1 La 3 Zr 2 Al 0.3 O 12 Solid-State Electrolyte

All solid-state lithium-ion batteries (ASSLIBs) have gained significant interest in recent years due to their wide range of applications, including mobile devices, electric vehicles, and grid storage. Garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) solid-state electrolyte (SSE) continues to be a significant player in the fabrication of ASSLIBs with excellent ionic conductivity on the order of 10 -3 S•cm -1 with the integration of dopants and sintering aids to assist conductivity and structural evolution during the sintering procedure. Traditional sintering techniques, such as solid-state sintering (SSS), have been proven to yield desirable crystal structures. However, the low ionic conductivity results from inferior microstructure, and lithium loss is a significant challenge. Recently, a relatively novel sintering process called rapid laser reactive sintering (RLRS) has shown great potential for achieving fully dense solid oxide electrolytes with less surface element loss, resulted in high ionic conductivity. Here, we applied the same RLRS method to fabricate LLZO dense electrolyte with different amounts of aluminum dopants. We hope the rapid high-temperature sintering can densify the electrolyte and avoid the lithium loss for achieving high lithium-ion conductivity. In this work, we optimized multiple combinations of laser parameters (speed, power, and defocus distance), initial precursor composition, and controlled atmospheres to discover the optimal conditions for reaching the efficacious crystal structure, microstructure, and ionic conductivity.

25 ENERGY STORAGE↗
DOE OSTI2018

Reflow-oven-processing of pressureless sintered-silver interconnects

Here, a method was developed to pressurelessly fabricate strong and consistent sinterable-silver joints or interconnects using reflow oven heating. Circular sinterable-silver interconnects, having nominal diameter of 5 mm and 0.1 mm thickness were stencil printed, contact-dried, and then pressurelessly sinter-bonded to Au-plated direct copper bonded ceramic substrates at 250 °C in ambient air. That sintering was done in either a reflow oven or a convective oven (latter being a conventional heating source for processing sinterable-silver). Consistently strong (>40 MPa) interconnects were produced with reflow oven heating and were as strong as those produced with convective oven heating. This is significant because reflow oven technology affords better potential for continuous mass production and it was shown that strong sintered-silver bonds can indeed be achieved with its use.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Enhancing low-temperature sintering in the MgO-LiF system: Mechanistic insights

In the present article, we provide compelling evidence that minor (1 wt%) additions of micron and nanometre-sized LiF particles in MgO decompose leading to free Li diffusing into MgO surfaces enhancing vacancy production during direct current sintering. The addition of nanometre-sized LiF particles leads to a > 500 °C reduction in the sintering temperature and over 99 % theoretical density of final consolidated compacts. Correlating differential scanning calorimetry with in-situ x-ray diffraction, together with Schottky calculations, post sintering electron microscopy and laser induced breakdown spectroscopy, we uncover critical insights into this impressive reduction in sintering temperature. Our quantitative analysis reveals that MgO and LiF interact at low temperatures with the diffusion of Li into the surface of MgO particles due to the intrinsic structural disorder of the LiF and MgO crystallites. Nanometre-sized LiF particles were found to react the most at low temperatures due to their increased structural disorder. Our multimodal characterization points to a Li-promoted densification and sintering mechanism. This impressive reduction in sintering temperature can be harnessed to promote low-temperature fabrication of MgO-based composites for technological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Exploring the relationship between solvent-assisted ball milling, particle size, and sintering temperature in garnet-type solid electrolytes

Garnet-type solid electrolytes, such as Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO), are promising materials for solid-state batteries, but processing remains a challenge, in part due to the high sintering temperature required for densification. Additionally, this temperature can be lowered by decreasing the initial particle size via solvent-assisted ball milling, but the relationship between solvent choice, particle properties, sintering behavior, and ionic conductivity is not well understood. In this work, we systematically explore these parameters, showing that milling in commonly used protic solvents, such as alcohols, effectively decreases the particle size but results in lithium loss (through Li + /H + exchange) that leads to poor sintering. By contrast, milling in aprotic solvents with surfactant reduces the particle size to ~220 nm without lithium loss, enabling the fabrication of dense samples (5.1 g/cm 3 ) with good ionic conductivity (0.43 mS/cm at 25 °C) at a lower sintering temperature (1000 °C). We compare ionic conductivities and activation energies for samples prepared with different particle sizes and sintering temperatures and use multiphase-field simulations to identify the mass transport and microstructural mechanisms responsible for the observed sintering dependence on particle size. These results further clarify the relationship between processing parameters and performance and represent important progress toward overcoming fabrication challenges for these materials.

25 ENERGY STORAGE↗
DOE OSTI2014

Crystallite-growth, phase transition, magnetic properties, and sintering behaviour of nano-CuFe{sub 2}O{sub 4} powders prepared by a combustion-like process

The synthesis of nano-crystalline CuFe{sub 2}O{sub 4} powders by a combustion-like process is described herein. Phase formation and evolution of the crystallite size during the decomposition process of a (CuFe{sub 2})—precursor gel were monitored up to 1000 °C. Phase-pure nano-sized CuFe{sub 2}O{sub 4} powders were obtained after reaction at 750 °C for 2 h resulting in a crystallite size of 36 nm, which increases to 96 nm after calcining at 1000 °C. The activation energy of the crystallite growth process was calculated as 389 kJ mol{sup −1}. The tetragonal⇄cubic phase transition occurs between 402 and 419 °C and the enthalpy change (ΔH) was found to range between 1020 and 1229 J mol{sup −1} depending on the calcination temperature. The optical band gap depends on the calcination temperature and was found between 2.03 and 1.89 eV. The shrinkage and sintering behaviour of compacted powders were examined. Dense ceramic bodies can be obtained either after conventional sintering at 950 °C or after a two-step sintering process at 800 °C. Magnetic measurements of both powders and corresponding ceramic bodies show that the saturation magnetization rises with increasing calcination-/sintering temperature up to 49.1 emu g{sup −1} (2.1 µ{sub B} fu{sup −1}), whereas the coercivity and remanence values decrease. - Graphical abstract: A cheap one-pot synthesis was developed to obtain CuFe{sub 2}O{sub 4} nano-powders with different crystallite sizes (36–96 nm). The optical band gaps, phase transition temperatures and enthalpies were determined depending on the particle size. The sintering behaviour of nano CuFe{sub 2}O{sub 4} was studied in different sintering procedures. The magnetic behaviour of the nano-powders as well as the corresponding ceramic bodies were investigated. - Highlights: • Eco-friendly and simple synthesis for nano CuFe{sub 2}O{sub 4} powder using starch as polymerization agent. • Monitoring the phase evolution and crystallite growth kinetics during the synthesis. • Determination of the optical band gap, phase transition temperature, and enthalpy change. • Sintering behaviour of nano-sizes CuFe{sub 2}O{sub 4}. • Magnetic behaviour of CuFe{sub 2}O{sub 4} powders and ceramics depending on their particle size.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Fractographical characterization of hot pressed and pressureless sintered AlN-doped ZrB{sub 2}–SiC composites

In this paper, ZrB{sub 2}–SiC composites doped with 0–5 wt.% AlN were prepared by a low pressure hot pressing as well as a pressureless sintering methods at 1900 °C for 2 h. The influence of aluminum nitride addition on the sinterability and microstructure development of such ceramic composites was studied by a fractographical approach. The results revealed that only 1 wt.% AlN can aid the densification process of the hot pressed ceramic composite via the liquid phase sintering mechanism due to the formation of nano-scale metakaolinite spinel layers. In the pressureless sintering method, adding more AlN can increase the formation of gaseous products which raised the amount of porosities in the final microstructure. The formation of nano-graphite phase in the hot pressing process, the formation of Al{sub 2}OC in the pressureless sintering process, and the formation of BN in the both processes were disclosed by X-ray diffraction, SEM and TEM analyses. - Highlights: • The effect of AlN addition on densification of ZrB{sub 2}–SiC composites was studied. • AlN promotes the densification in hot pressed samples by liquid phase formation. • A fully dense composite was obtained by adding 1 wt.% AlN in hot pressing process. • In pressureless sintering, more AlN content intensifies the formation of porosities.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Characterization of the porous structures of the green body and sintered biomedical titanium scaffolds with micro-computed tomography

The present research was aimed at gaining an understanding of the porous structure changes from the green body through water leaching and sintering to titanium scaffolds. Micro-computed tomography (micro-CT) was performed to generate 3D models of titanium scaffold preforms containing carbamide space-holding particles and sintered scaffolds containing macro- and micro-pores. The porosity values and structural parameters were determined by means of image analysis. The result showed that the porosity values, macro-pore sizes, connectivity densities and specific surface areas of the titanium scaffolds sintered at 1200 °C for 3 h did not significantly deviate from those of the green structures with various volume fractions of the space holder. Titanium scaffolds with a maximum specific surface area could be produced with an addition of 60–65 vol% carbamide particles to the matrix powder. The connectivity of pores inside the scaffold increased with rising volume fraction of the space holder. The shrinkage of the scaffolds prepared with > 50 vol% carbamide space holder, occurring during sintering, was caused by the reductions of macro-pore sizes and micro-pore sizes as well as the thickness of struts. In conclusion, the final porous structural characteristics of titanium scaffolds could be estimated from those of the green body. - Highlights: •Porous structures of green body and sintered titanium scaffolds was studied. •Porous structures of both samples were quantitatively characterized with micro-CT. •Porous structures of scaffolds could be controlled from the green body. •Shrinkage mechanisms of titanium scaffolds during sintering was established.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structural evolution, sintering behavior and microwave dielectric properties of (1−x)Li{sub 2}TiO{sub 3} + xLiF ceramics

Graphical abstract: - Highlights: • Structure, sinterability and dielectric properties of LiF-doped Li{sub 2}TiO{sub 3} were studied. • Li{sub 2}TiO{sub 3} can be densitied (TD 98%) at lower sintering temperature by LiF additions. • Excellent microwave dielectric properties could be obtained. - Abstract: Structural evolution, sintering behavior, and microwave dielectric properties of (1−x)Li{sub 2}TiO{sub 3} + xLiF (0.05 ≤ x ≤ 0.70) ceramics have been studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectra, thermal dilatometry and microwave resonant measurement at the frequency of about 7–11 GHz. The results show that Li{sub 2}TiO{sub 3} can form limited solid solution with LiF (x ≤ 0.4) and LiF second phase appeared when x{sup 3}0.5. The structure of the solid solution transformed from ordered monoclinic phase (β-Li{sub 2}TiO{sub 3} (ss)) to disordered cubic rock salt (α-Li{sub 2}TiO{sub 3} (ss)) when x{sup 3}0.15. The presence of short range ordering was confirmed for the cubic phase. The sinterability was considerably improved by doping with LiF. Densified ceramics with about 95–98% theoretical density could be obtained for the doped compositions after sintering at 900–1150 °C/2 h. An optimized microwave dielectric properties with ε{sub r} of ∼23.6, Q × f of ∼108,000 GHz and τ{sub f} of ∼4.2 ppm/°C could be obtained for the x = 0.1 composition after sintering at 1100 °C/2 h.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Reactive sintering of tungsten-doped high strength ZrB{sub 2}–SiC porous ceramics using metastable precursors

Graphical abstract: - Highlights: • Tungsten-doped porous ZrB{sub 2}–SiC specimens were fabricated by reactive sintering. • Both sintering and mechanical properties were improved by doping with tungsten. • Optimum concentration to obtain high mechanical properties was W/Zr (mol) = 0.05. • Sintering might be promoted by self-accelerated diffusion. • Mechanical properties might be improved by solid solution strengthening. - Abstract: Tungsten-doped porous ZrB{sub 2}-20 vol.% SiC specimens with a high strength skeleton were fabricated by reactive sintering using metastable reactants, i.e., as-synthesized amorphous hydrous ZrO{sub 2}–WO{sub 3}/ZrO{sub 2}, amorphous boron, nanocarbon, and β-SiC. Doping with tungsten clearly promoted sintering and improved mechanical properties; the optimum tungsten concentration to obtain high mechanical properties was investigated. A single-phase solid solution (Zr,W)B{sub 2} was formed in the specimens with tungsten. We suggest that sintering was promoted by self-accelerated diffusion owing to the formation of point defects caused by doping with tungsten. The improvement of mechanical properties could be attributed to solid solution strengthening.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Spark Plasma Sintering of high-density fine-grained Y2.5Nd0.5Al5O12+SiC composite ceramics

Highlights: • YAG + (10, 20) wt.% α-SiC high-density ceramics obtained by SPS. • YAG + α-SiC ceramics have a more fine-grained structure than pure garnet. • The optimal sintering temperature of YAG + SiC ceramics is lower than that of garnet. • Introduction of α-SiC particles creates internal stress fields in garnet. • Introduction of α-SiC particles results in lower sintering activation energy of garnet. - Abstract: Spark Plasma Sintering (SPS) has been used to produce samples of fine-grained composites Y{sub 2.5}Nd{sub 0.5}Al{sub 5}O{sub 12} + x wt.% α-SiC (x = 1020) with ∼98–99% density. The microstructure of the composites has been studied, as well as the impact of α-SiC particles on the mechanical properties and kinetics of composite sintering. The introduction of the α-SiC part has been demonstrated to form a more fine-grained structure and under the given SPS conditions change the sintering mechanism in ceramics. The study has also demonstrated that introduction of α-SiC particles into garnet results in formation of internal stress fields, which, in turn, leads to a decrease in the activation energy of sintering of fine-grained composites at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The physical chemistry and materials science behind sinter-resistant catalysts

Catalyst sintering, a main cause of the loss of catalytic activity and/or selectivity at high reaction temperatures, is a major concern and grand challenge in the general area of heterogeneous catalysis. Although all heterogeneous catalysts are inevitably subjected to sintering during their operation, the immediate and drastic consequences can be mitigated by carefully engineering the catalytic particles and their interactions with the supports. In this tutorial review, we highlight recent progress in understanding the physical chemistry and materials science involved in sintering, including the discussion of advanced techniques, such as in situ microscopy and spectroscopy, for investigating the sintering process and its rate. We also discuss strategies for the design and rational fabrication of sinter-resistant catalysts. To conclude, we showcase recent success in improving the thermal stability and thus sinter resistance of supported catalytic systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Sintering Effects on Morphology, Thermal Stability and Surface Area of Sol-Gel Derived Nano-Hydroxyapatite Powder

Hydroxyapatite (HAP) ceramics have been recognized as substitute materials for bone and teeth in orthopedic and dentistry field due to their chemical and biological similarity to human hard tissue. The nanosized and nanocrystalline forms of HAP have great potential to revolutionize the hard tissue-engineering field, starting from bone repair and augmentation to controlled drug delivery systems. This paper reports the synthesis of biomimetic nano-hydroxyapatite (HAP) by sol-gel method using calcium nitrate tetrahydrate (CNT) and potassium dihydrogen phosphate (KDP) as calcium and phosphorus precursors, respectively to obtain a desired Ca/P ratio of 1.67. Deionized water was used as a diluting media for HAP sol preparation and ammonia was used to adjust the pH to 11. After aging, the HAP gel was dried at 55 deg. C and sintered to different temperatures (200 deg. C, 400 deg. C, 600 deg. C, 800 deg. C, 1000 deg. C and 1200 deg. C). The dried and sintered powders were characterized for phase composition using Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The particle size and morphology was studied using transmission electron microscopy (TEM). The thermal behavior of the dried HAP nanopowder was studied in the temperature range of 55 deg. C to 1000 deg. C using thermal gravimetric analyser (TGA). The BET surface area of absorbance was determined by Nitrogen adsorption using Brunauer-Emmett-Teller (BET) method. The presence of characteristic peaks of the phosphate and OH groups in FTIR spectrums confirmed the formation of pure HAP in dried as well as sintered powders. XRD results also confirmed the formation of stoichiometric nano-HAP. Sintering revealed that with increase in temperature, both the crystallinity and crystallite size of nano-HAP particles increased. The synthesized nano-HAP powder was found to be stable upto 1000 deg. C without any additional phase other than HAP, whereas peak of {beta}-TCP (tricalcium phosphate) was observed at 1200 deg. C. Photomicrograph of TEM showed that the nanopowder sintered at 600 deg. C is composed of hydroxyapatite nanoparticles (26.0-45.6 nm), which is well in agreement with the crystallite size calculated using XRD data. TGA study showed the thermal stability of the synthesized nano-HAP powder. The BET surface area decreased with increase in sintering temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Microwave sintering of Ag-nanoparticle thin films on a polyimide substrate

Ag-nanoparticle thin films on a polyimide substrate were subjected to microwave sintering by use of a single-mode waveguide applicator. A two-step sintering process was employed. First, at low conductivities of the film, the film sample was placed at the site of the maximum electric field and subjected to microwave irradiation. Second, when the conductivity of the film increased, the film sample was placed at the site of the maximum magnetic field and again subjected to microwave irradiation. The microwave sintering process was completed within 1.5 min, which is significantly lower than the time required for the oven heating process. The resulting conductivity of the film, albeit only 30% of that of the bulk material, was seven times that of a film annealed at the same temperature in a furnace. Scanning electron microscopy images revealed that the nanoparticles underwent both grain necking and grain growth during microwave sintering. In addition, this sintering process was equivalent to the oven heating process performed at a 50 °C higher annealing temperature. An electromagnetic wave simulation and a heat transfer simulation of the microwave sintering process were performed to gain a thorough understanding of the process.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of sintering temperature on structural and dielectric properties of Bi and Li co-substituted SrTiO{sub 3}

Sintering is an important factor that affects the microstructure development in ceramics. In this work, Bi and Li co-substituted Strontium Titanate (ST) ceramics samples sintered at different temperatures are prepared and analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD was used to detect phase structure of the sintered samples and SEM was used for microstructure analysis. Dielectric properties of Bi and Li co-substituted SrTiO{sub 3} samples were measured using Agilent 4294A Impedance analyzer in the frequency range 40 Hz to 5 MHz at room temperature. The result reveals that the dielectric constant of Bi and Li co-substituted SrTiO{sub 3} ceramics increases with increasing sintering temperature up to 1250°C and then decreases beyond that. The highest value of dielectric constant obtained is 860 at 1KHz frequency and lowest dielectric loss observed is 0.04 at the same frequency for samples sintered at 1250°C. Also the grain size increases with increase of sintering temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Improvement of the electrochromic response of a low-temperature sintered dye-modified porous electrode using low-resistivity indium tin oxide nanoparticles

An indium tin oxide (ITO) nanoparticle-based porous electrode sintered at low temperatures was investigated as a transparent electrode for electrochromic displays (ECDs). The electrochromic (EC) response of the dye-modified ITO porous electrode sintered at 150 °C, which exhibited a generally low resistivity, was markedly superior to that of a conventional dye-modified TiO{sub 2} porous electrode sintered at the same temperature. Moreover, the EC characteristics of the dye-modified ITO porous electrode sintered at 150 °C were better than those of the high-temperature (450 °C) sintered conventional dye-modified TiO{sub 2} porous electrode. These improvements in the EC characteristics of the dye-modified ITO porous electrode are attributed to its lower resistivity than that of the TiO{sub 2} porous electrodes. In addition to its sufficiently low resistivity attained under the sintering conditions required for flexible ECD applications, the ITO porous film had superior visible-light transparency and dye adsorption capabilities. We conclude that the process temperature, resistivity, optical transmittance, and dye adsorption capability of the ITO porous electrode make it a promising transparent porous electrode for flexible ECD applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Reliability and Lifetime Prediction Model of Sintered Silver Under High-Temperature Cycling

Although excellent reliability has been reported for sintered silver as a die-attach material under both thermal and power cycling loads in power electronics applications, the promise of this material as a large-area attachment at temperatures beyond 200 degrees C needs to be investigated. This paper presents insights into the thermomechanical behavior and reliability of sintered silver under extreme thermal cycling conditions. In this study, we bonded sintered silver samples and subjected it to a thermal cycling profile of -40 °C to 200 °C with high ramp rates. We periodically monitored samples under thermal cycling to detect the presence of any failure mechanisms using a scanning acoustic microscope. We also included 95Pb5Sn solder in the study to obtain reference data. Results show the occurrence of cracks in sintered silver followed by a rapid rate of crack growth that exceeded the failure criterion in just 50 cycles. The predominant failure mechanism we observed was adhesive failure. As a large-area attachment, solder exhibited a higher reliability than sintered silver but failed within 100 cycles. Finally, we performed thermomechanical modeling to compute strain energy density values and correlated these with the experimentally observed crack growth rates to formulate a lifetime prediction model for sintered silver.

30 DIRECT ENERGY CONVERSION↗