High-pressure Densification Research Articles

High-pressure low-temperature densification of NASICON-based LATP electrolytes for solid-state lithium batteries

Ceramic oxides are promising solid electrolytes for Lithium metal solid-state batteries (SSBs) because of their high ionic conductivity and stability under ambient conditions. Nonetheless, the need for high-temperature densification approaches challenges their processability towards upscaling and their implementation into practical SSB devices. Here, we investigate a High-Pressure Low-Temperature (HPLT) processing technique for the densification of NASICON-based Li1+xAlxTi2-x(PO4)3 (LATP) solid electrolyte, providing an understanding of several key parameters such as temperature, pressure and time. Our results show that nanometric LATP can be densified using the HPLT technique at 200°C within 2 min delivering an ionic conductivity of 6.15×10−5 Scm−1, which is the highest reported value at this temperature without the addition of solvents. On the other hand, by combining HPLT with a short post-heat treatment at 700 or 800 °C for 1 hour, highly dense pellets with an ionic conductivity of 10−4 Scm−1 can be obtained. This represents a reduction of the densification temperature of 400°C compared to conventional high-temperature sintering and shows the potential of HPLT to overcome current densification constraints derived from the use of very high temperatures.

Investigating densification processes of amorphous silica phases through activation energy distribution

We investigated thermal stability of silica glass that underwent high-temperature (HT), high-pressure (HP) densification followed with electron irradiations. We performed isothermal annealing and in situ Raman spectroscopy to observe changes in the silica structure. By determining the activation energy distributions at the root of the densification process, we aimed to gain insights into the relaxation pathway of densified silica and its relationship with the structural properties. Of particular interest we observed a non monotonous behavior of D2 band in Raman spectra in HP-HT samples exposed at low dose ≤107 Gy, which we attribute to presence of a specific phase of silica glass known as the high-density amorphous phase. Our study highlights the impact of irradiation on the ratio between high-density amorphous and low-density amorphous phases, and on relative activation energy distributions. These findings have important implications for development of high-performance optical devices based on silica densification for a wide range of applications.

Determination of the material model parameters for high pressure densification induced glass inferred through analytical comparison and its ballistic performance as used in composite laminates

The Drucker Prager material model, Ductile Damage and Mie-Gruneisen equation of state parameters for high-pressure densification induced glass were derived analytically in the current study by comparing them to the Johnson Holmquist-II (JH-2) model. These parameters were then utilized to simulate the ballistic impact behaviour of bullet-resistant glass in ABAQUS/Explicit and the results were compared to the simulation results using JH-2 model in ANSYS/Autodyn and the results were found in good agreement. Following that, their experimental equivalents were tested for validation prospective. The findings were then compared to conventional bullet-resistant glass. It was found that the new bullet-resistant glass fabricated from layers of high-pressure densification induced glass was superior in strength as compared to the conventional bullet-resistant glass.

Densification of a polymer glass under high-pressure shear flow

The properties of glasses can change significantly as they evolve toward equilibrium. Mechanical deformation appears to influence this physical aging process in conflicting ways, with experiments and simulations showing both effects associated with rejuvenation away from and overaging toward the equilibrium state. Here we report a significant densification effect in a polymer undergoing shear flow under high pressure. We used the high-aspect ratio geometry of the layer compression test to measure the uniform and homogeneous accumulation of plastic strain during isothermal confined compression of a deeply quenched film of polystyrene glass. Combined scanning transmission x-ray microscopy (STXM) and atomic force microscopy confirmed defect-free deformation leaving up to 1.2% residual densification under conditions of confined uniaxial strain. At higher peak strain, plastic shear flow extruded glass from below the compressing punch under conditions of a high background pressure. A further density increase of 2% was observed by STXM for a highly thinned residual thickness of polymer that nevertheless showed no signs of crystallization or internal strain localization. While the confined uniaxial densification can be accounted for by a simple elastic--plastic constitutive model, the high-pressure extrusion densification cannot.

High pressure effect in the near-infrared emission of Nd3+-doped alkali silicate glasses

ABSTRACT The effect of high pressure (7.7 GPa) densification on the absorption and near-infrared emission of Nd-doped lithium, sodium and potassium disilicate glasses was investigated. Judd-Ofelt parameters Ωλ (λ = 2, 4 and 6) were calculated from the absorption spectra, before and after densification of glasses, indicating that the irreversible structural changes induced by pressure increased the symmetry of the Nd-O bonding. Density and refractive index of the glasses also increased, probably related to the close packing of SiO4 tetrahedra during densification. The magnitude of the splitting due to the Stark effect was larger for potassium silicate, before and after densification. The radiative transition probabilities of the hypersensitive transition for sodium and potassium silicate increased after densification while the radiative lifetime decreased. For lithium silicate, the opposite behavior was observed. The experimental results corroborate the influence of alkali ion and densification on the luminescence properties of Nd-doped alkali silicate glasses.

High pressure densification behavior of alumina particles

Pressure is an important thermodynamic parameter in addition to temperature and chemical composition during material sintering process. However, few experimental images intuitively describing the densification process of grains during compression, especially for the high melting point ceramics. Here we observed deformation evolution and mechanical response of spherical alumina particles after high pressure treatment. By analyzing the plastic deformation and grain boundary characters of spherical alumina particles, and the boundary stress and yield stress variation of grains under various pressures and temperatures, a clear picture of the high-pressure powder densification and sintering process is depicted.

High Pressure Densification Behavior of Alumina Particles

Pressure is an important thermodynamic parameter in addition to temperature and chemical composition during material sintering process. However, few experimental images intuitively describing the densification process of grains during compression, especially for the high melting point ceramics. Here we observed deformation evolution and mechanical response of spherical alumina particles after high pressure treatment. By analyzing the plastic deformation and grain boundary characters of spherical alumina particles, and the boundary stress and yield stress variation of grains under various pressure temperature, a clear picture of the high-pressure powder densification and sintering process is depicted.

High-pressure densification and hydrophobic coating for enhancing the mechanical properties and dimensional stability of soft poplar wood boards

Effects of high-pressure (HP) treatment on densification of poplar sapwood boards and subsequent coatings were evaluated. Tung oil (TO) and epoxy resin (ER)-coated treatments were used to improve the dimensional stability of HP-densified wood. The density of the wood after HP densification increased from 450 ± 50 kg/m3 for the control to 960 ± 20 kg/m3 at 125 MPa. This process also resulted in the average thickness of HP-densified boards to reduce significantly from 29.7 ± 0.11 mm for the control to 18.8 ± 0.53 mm after HP densification at 25 MPa and 14.3 ± 0.10 mm after 125 MPa treatment for 30 s. The mechanical strength measured as the hardness of densified wood significantly increased from 35% at 25 MPa to 96% at 125 MPa treatment, compared to untreated wood. As expected both TO and ER-coated treatments significantly reduced set-recovery of densified wood when stored at four relative humidity environments. ER showed better anti-swelling performance than TO, and would be a better choice.

Interplay between cold densification and malic acid addition (C4H6O5) for the fabrication of near-isotropic MgB2 conductors for magnet application

Abstract The effect of cold high pressure densification (CHPD) on anisotropy of the critical current density (Jc) in « in situ » single core binary and alloyed MgB2 tapes has been determined as a function of temperatures at 4.2 K, 20 K and 25 K as well as at applied magnetic fields up to 19 T. The study includes binary and C4H6O5 (malic acid) doped MgB2 tapes before and after CHPD. It is remarkable that the CHPD process not only improved the Jc values, in particular at the higher magnetic fields, but also decreased the anisotropy ratio, Γ = Jc///Jc┴. In binary MgB2 tapes, the anisotropy factor Γ increases with higher aspect ratios, even after applying CHPD. In malic acid (C4H6O5) doped tapes, however, the application of CHPD leads only to small enhancements of Γ, even for higher aspect ratios. This is attributed to the higher carbon content in the MgB2 filaments, which in turn is a consequence of the reduced chemical reaction path in the densified filaments. At all applied field values, it was found that CHPD processed C4H6O5 doped tapes exhibit an almost isotropic behavior. This constitutes an advantage in view of industrial magnet applications using wires with square or slightly rectangular configuration.

Plastic and Elastic Strains in Poplar Wood under High-Pressure Densification

HighlightsHigh-pressure densification (HPD) resulted in more than 100% increase in the density of poplar wood.Density of wood during HPD treatment was up to 300% and 100% higher than observed before and after HPD.A method was developed to measure elastic recovery in the radial and tangential directions under HPD.Abstract. Plastic and elastic strains of poplar wood in the radial and tangential directions were investigated after high-pressure densification (HPD) using a special method that detected the elastic strain. There was a large difference in plastic and elastic strains obtained in compressed wood between the radial and tangential directions. The maximum total strain in the radial and tangential directions reached 26.9% and 66.9%, respectively, when compressed at 150 MPa for 300 s. Longer holding time (300 s) increased the plastic strain, by reducing the elastic strain, when the applied pressure was lower than 60 MPa. In addition, a large difference in compressed wood density prevailed when still under pressure as compared with the density measured after the pressure treatment, and both were nearly 1 to 3 times higher than the density of fresh wood. Further, the maximum density observed under pressure was related to the maximum reported density of dry crystalline cellulose plus the entrapped moisture. The mechanical properties of densified wood were also investigated and found to depend on the pressure treatment conditions. Keywords: Elastic strain, High-pressure densification, Mechanical properties, Plastic strain, Wood density.

Novel 1D carbon nanotubes uniformly wrapped nanoscale MgH2 for efficient hydrogen storage cycling performances with extreme high gravimetric and volumetric capacities

Magnesium hydride (MgH2) offers large capacity for hydrogen storage, but poor thermodynamics and kinetics for releasing hydrogen. In this work, the novel 1D bamboo-shaped carbon nanotubes (BCNTs) are firstly used as carriers for the self-assembly of MgH2 (denoted as MgH2@BCNTs). The high specific surface area (262.3 m2g-1) and large diameter (over 80 nm) of BCNTs contribute to extremely high loading capacity (76.8 mass fraction), small particle size (15–20 nm) and uniform distribution of MgH2 nanoparticles (NPs). The well-defined MgH2@BCNTs shows remarkably improved thermodynamics and kinetics for H2 adsorption and desorption. In particular, it starts to release hydrogen at about 220 °C, near 170 °C lower than that of the commercial MgH2, as well it tends to be hydrogenated even at a relatively low temperature of 100 °C by absorbing 3.56 wt% H2. Moreover, a reversible capacity up to 5.79 wt%, including the “dead weight” of BCNTs, and is well maintained after 10 cycles. The dehydrogenation Ea and ΔH of MgH2@BCNTs can be reduced to 97.97 kJ/mol and 68.92 kJ/mol, which are 111.24 kJ/mol and 6.07 kJ/mol lower than those of the commercial MgH2, respectively. By high pressure densification treatment, the MgH2@BCNTs system achieves an exceptional volumetric capacity up to 65.90 g/L without obvious performance degeneration, resulting from the special structure of BCNTs with inner intervals which works as supports under ultra-high pressure of 750 MPa. Our innovative design of 1D BCNTs supporting MgH2 NPs with high loading weight offers new strategy to synchronously improve the gravimetric and volumetric capacity, as well as the hydrogen storage kinetics and thermodynamics of the nanoconfinement system in the future.

Molecular dynamics simulation of structural transformation in SiO2 glass under densification

Molecular dynamics simulation of silica glass has been carried out to investigate the structural transformation in high-pressure densification. The fractions of SiOx (x = 4, 5, and 6) structural units change with the change of density. We found that only corner-sharing bond (one common oxygen atom) appears in the SiO4-SiO4 connectivity, whereas both of corner- and edge-sharing (two common oxygen atom) bonds appear in the SiO5-SiO5 connectivity and three types (corner-, edge- and face- (three common oxygen atom)) of sharing bonds appear in the SiO6-SiO6 connectivity. The first peak splitting of the pair radial distribution function (RDF) GSi-Si(r) is caused by Si atoms linked together via edge- and face-sharing bonds. The new second peak of the pair RDF GO-O(r) at the high density originates from oxygen atoms of the edge-sharing bonds. Void analysis indicated that a significant number of O-voids, in which void contacted with four oxygen atoms, exist in the samples. The biggest voids belong to these O-voids. The volume of O-voids changes slightly whereas one of total voids decreases quickly with increasing density. We also found that the density of each SiOx unit type change under high-pressure densification and the density of silica glass can be expressed via the fraction and partial density of SiOx units. Oxygen atoms in the form of hexagonal close packed (hcp) structure are found in the sample of 3.96 g.cm−3. Both of oxygen hcp and faced centered cubic (fcc) clusters are found in the sample with the density above 3.96 g.cm−3.

Effect of High Pressure in the Luminescence of Pr3+-Doped Ge2O–PbO Glass Containing Au Nanoparticles

In this paper, the combined effect of gold nanoparticles and high-pressure densification on the luminescence of Pr3+-doped heavy metal GeO2–PbO photonic glass was investigated. Localized states related to ion-trapped exciton defects, S1 and S2, were observed at 342 and 412 nm before densification. After densification under 7.7 GPa, the structure of the glass host changed irreversibly, as indicated by the infrared spectrum, refractive index, and density measurements. Transmission electron microscopy analyses indicated that the high-pressure densification induced the formation of clusters of gold nanoparticles. The modifications observed in the absorption and luminescence spectra of Pr3+ ions in the VIS–NIR range were associated to the changes in the local field surrounding the Pr3+ ions in the host glass induced by high pressure. For excitation at 445 nm (luminescence from 3P2) and 593 nm (luminescence from 1D2), the combined effect of densification and gold nanoparticles induced an increase in the emissio...

Effect of High-pressure Densification on Moisture Sorption Properties of Paulownia Wood

The effect of high-pressure (HP) densification (30, 90, and 150 MPa for 3, 30, and 300 s) on the moisture sorption properties of Paulownia wood was investigated. After the densification, samples were conditioned at three temperatures (20, 30, and 40 °C) and five equilibrium moisture contents (from 11.20 to 95.62%) during the study, after which the equilibrium moisture contents of the control and treated samples were measured. The HP-treated groups had higher equilibrium moisture contents than the controls at higher relative humidity levels. The hysteresis phenomenon and the scanning electron microscopy observations were explained by the transformation of the structural elements by the HP treatment. Finally, two moisture sorption isotherm (MSI) models (a linear polynomial model for adsorption and a quadratic polynomial model for desorption) were established with good performance to describe the relationship between HP treatment parameters, environmental conditions, and equilibrium moisture contents.

High-Pressure Treatment Effects on Density Profile, Surface Roughness, Hardness, and Abrasion Resistance of Paulownia Wood Boards

Abstract. The goal of this study was to investigate the effects of high-pressure (HP) treatment on the mechanical performance properties of Paulownia ( spp.) wood boards. The boards were HP treated at selected pressures (20, 40, 60, 80, and 100 MPa) for 30 s. A special vacuum-packing technique that sandwiched the test boards between two steel plates was used for the HP treatment to prevent board distortion. Thickness, density, vertical density profile (VDP), cell wall percentage (VC), porosity percentage (VH), surface roughness, hardness, and abrasion resistance were evaluated to assess the performance properties of the treated and untreated boards. HP treatment resulted in 45.7% to 60.0% reduction in thickness of the boards, while it increased the density by 88% to 170%. The VDP of densified boards was distributed uniformly, and core densities were only slightly higher than surface densities. HP treatment made the Paulownia board surfaces much smoother, and three roughness parameters were reduced with increasing treatment pressure level. Hardness values of the boards were improved by 84% to 173%. The mass loss values of HP treated wood samples in abrasion tests were significantly reduced by 40.7% to 75.0%. The results of this study demonstrate that HP treatment is a useful method to improve the end-use properties of low-density wood like Paulownia. Keywords: Abrasion resistance, Hardness, High-pressure densification, Paulownia wood boards, Vertical density profile, Surface roughness.

Pressure-induced property improvement of magnesium diboride wire

The 4.2 K non-barrier transport Jc values of the powder-in-tube (PIT) in-situ MgB2 wires have been enhanced by cold high pressure densification (CHPD). With respect to the control wire, the 1.5 GPa pressure induced the Jc improvement of the wire at 4.2 K and 10 T by 25 %. The Jc enhancement induced by the CHPD may result from two aspects. First, the CHPD resulted in the reduction of the transverse MgB2 core area. Second, the grain connectivity of the PIT in-situ MgB2 wire was improved by the CHPD, which is reflected by the reduced porosity.

The dielectric signature of glass density

At present, we are witnessing a renewed interest in the properties of densified glasses prepared by isobaric cooling of a liquid at elevated pressure. As high-pressure densification emerges as a promising approach in the development of glasses with customized features, understanding and controlling their unique properties represent a contemporary scientific and technological goal. The results presented herein indicate that the applied high-pressure preparation route leads to a glassy state with higher density (∼1%) and a reduced free volume of about 7%. We show that these subtle structural changes remarkably influence the dielectric response and spectral features of β-relaxation in etoricoxib glass. Our study, combining dynamical and structural techniques, reveal that β-relaxation in etoricoxib is extremely sensitive to the variations in molecular packing and can be used to probe the changes in glass density. Such connection is technologically relevant and may advance further progress in the field.

High-Pressure Densification of Composite Lunar Cement

AbstractIn order to minimize the binder content in composite lunar “cement,” this paper uses JSC-1A lunar soil simulant and unsaturated polyester resin (UPR) to produce low-binder-content composite...

Memory versus irreversibility in the thermal densification of amorphous glasses

We report on dynamic effects associated with thermally-annealing amorphous indium-oxide films. In this process the resistance of a given sample may decrease by several orders of magnitude at room-temperatures, while its amorphous structure is preserved. The main effect of the process is densification - increased system density. The study includes the evolution of the system resistivity during and after the thermal-treatment, the changes in the conductance-noise, and accompanying changes in the optical properties. The sample resistance is used to monitor the system dynamics during the annealing period as well as the relaxation that ensues after its termination. These reveal slow processes that fit well a stretched-exponential law, a behavior that is commonly observed in structural glasses. There is an intriguing similarity between these effects and those obtained in high-pressure densification experiments. Both protocols exhibit the "slow spring-back" effect, a familiar response of memory-foams. A heuristic picture based on a modified Lennard-Jones potential for the effective interparticle interaction is argued to qualitatively account for these densification-rarefaction phenomena in amorphous materials whether affected by thermal-treatment or by application of high-pressure.

Viewpoint on fast creation of dense MgB2 phase in wires made by internal Mg diffusion process

Md Shahriar Al Hossain, University of Wollongong, shares his views on a letter by P KovaAcA○ and colleagues on fast creation of dense MgB phase in wires made by internal Mg diffusion process. According to him, In situ and ex situ powder metallurgical processes are currently used for the industrial fabrication of mono- and multi-filamentary MgB wires. The mass density in the MgB filaments of the wires after the final heat treatment is quite low with respect to the theoretical density. The typical effective superconductor area in the wire is only about 10%. Cold high pressure densification (CHPD) has been suggested as an alternative to enhance filament mass density. The authors showed that 8 min sintering time is sufficient for the formation of a uniform MgB2 phase 90 μm in thickness and without cracks, which is nearly identical to samples produced under the same sintering temperature conditions but longer sintering time of 3?5 h that were previously reported by the NIMS group. This finding is important for economical industrial production, but a question still remains as to how the round wires with a hollow filament will perform in magnet design and application, where enhancement of the filling factor, reduction of filament size, and mechanical and electrical stability and reliability are key factors.