Lamellar Pores Research Articles

Manufacturing of Open-Cell Aluminium Foams: Comparing the Sponge Replication Technique and Its Combination with the Freezing Method.

The manufacturing of aluminium foams with a total porosity of 87% using the sponge replication method and a combination of the sponge replication and freezing technique is presented. Foams with different cell counts were prepared from polyurethane (PU) templates with a pore count per inch (ppi) of 10, 20 and 30; consolidation of the foams was performed in an argon atmosphere at 650 °C. The additional freezing steps resulted in lamellar pores in the foam struts. The formation of lamellar pores increased the specific surface area by a factor of 1.9 compared to foams prepared by the sponge replication method without freezing steps. The formation of additional lamellar pores improved the mechanical properties but reduced the thermal conductivity of the foams. Varying the pore cell sizes of the PU template showed that—compared to foams with dense struts—the highest increase (~7 times) in the specific surface area was observed in foams made from 10 ppi PU templates. The effect of the cell size on the mechanical and thermal properties of aluminium foams was also investigated.

Green and simple production of graphite intercalation compound used sodium bicarbonate as intercalation agent

In view of the technical difficulties in the preparation of graphite intercalation compound (GIC) such as complex processes, the need to use strong acid reagents, and the product containing corrosive elements. A novel, efficient and simple method used sodium bicarbonate as intercalation agent was developed, which combined with mechanical force and chemical method for the green production of GIC. The production parameters were optimized by the single factor experiments, the optimal conditions were the ball mill speed 500 r/min for 4 h (6 mm diameter of the stainless-steel beads as ball milling media), the decomposition temperature 200 ℃ for 4 h, and 1:1 mass ratio of flake graphite to sodium bicarbonate. SEM results revealed that the prepared product appears the lamellar separation, pores, and semi-open morphology characteristic of GIC. FT-IR results indicated that the preparation method does not change the carbon-based structure, and the sodium bicarbonate intercalant has entered the interlayer of graphite flakes to form GIC. XRD results further showed that the GIC products still maintained the structure of carbon atoms or molecules, and the sodium bicarbonate intercalation agent has entered the interlayer of the graphite, and increased the interlayer distance of the layered graphite. The expandability of GIC products was studied, and the results show that it was expandable, and the expandable volume of GIC products prepared under optimal conditions has reached 142 mL/g. The theoretical basis for large-scale production was provided by studied the mechanism of the preparation method and designed the flow chart. The method has the advantages of simple process, products free of impurities, no use of aggressive reagents, process stable, and does not pollute the environment, being favorable to mass production, and provided new preparation method and idea for two-dimensional nanomaterials with preparation technical difficulties.

Evaluation of the pore morphologies for piezoelectric energy harvesting application

Piezoelectric energy harvesting has attracted significant attention in recent years due to their high-power density and potential applications for self-powered sensor networks. In comparison to dense piezoelectric ceramics, porous piezoelectric ceramics exhibit superiority due to an enhancement of piezoelectric energy harvesting figure of merit. This paper provides a detailed examination of the effect of pore morphology on the piezoelectric energy harvesting performance of porous barium calcium zirconate titanate 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 (BCZT) ceramics. Three different pore morphologies of spherical, elliptical, and aligned lamellar pores were created via the burnt-out polymer spheres method and freeze casting. The relative permittivity decreased with increasing porosity volume fraction for all porous BCZT ceramics. Both experimental and simulation results demonstrate that porous BCZT ceramics with aligned lamellar pores exhibit a higher remanent polarization. The longitudinal d 33 piezoelectric charge coefficient decreased with increasing porosity volume fraction for the porous ceramics with three different pore morphologies; however, the rate of decrease in d 33 with porosity is slower for aligned lamellar pores, leading to the highest piezoelectric energy harvesting figure of merit. Moreover, the peak power density of porous BCZT ceramics with aligned lamellar pores is shown to reach up to 38 μW cm -2 when used as an energy harvester, which is significantly higher than that of porous BCZT ceramics with spherical or elliptical pores. This work is beneficial for the design and manufacture of porous ferroelectric materials in devices for piezoelectric energy harvesting applications.

Enhanced mechanical properties of porous titanium implants via in-situ synthesized titanium carbide in lamellar pore walls

Directional lamellar porous titanium scaffolds are widely used as bone implant bearing materials because of their anisotropic pore structure. Their mechanical properties can be effectively improved by enhancing the strength of pore walls through the introduction of ceramics. In this work, porous titanium implants were prepared by freeze casting combined with TiH2 decomposition. The graphene was introduced into the pore walls of porous titanium, which could transform into titanium carbide (TiC) in situ upon sintering. TiC was evenly distributed in the lamellar pore walls, and the interface was well bonded. The compression strength of the fabricated implants was up to 389.94 MPa when the graphene content was 3 wt%, which was 377.8% times as high as the porous titanium. The crack propagation was resisted by TiC because of the “pinning” effect on the pore wall. Some of TiC were pulled out from the matrix, and others were fractured. The strength of the fabricated implants was improved significantly by the large consumption of fracture energy. Also, fabricated porous titanium implants with TiC are suitable for bone implantation.

Effect of Heat Treatment on Microstructure and Thermal Conductivity of Thermal Barrier Coating.

Thermal barrier coatings (TBCs) are essential for increasing the inlet temperature of gas turbines to improve their thermal efficiency. Continuous exposure to flames is known to affect the thermal properties of TBCs, degrading the performance of gas turbines as a consequence. In this study, we quantified the changes in the thermal conductivity of yttria-stabilized zirconia coatings with respect to various heat treatment temperatures and times. The coating exhibited an increase in thermal conductivity after heat treatment, with higher heat treatment temperatures resulting in greater thermal conductivity. The coatings were analyzed by X-ray diffraction and scanning electron microscopy before and after heat treatment. Results showed that there was little change in thermal conductivity due to phase changes and grain size. We conclude that pore structures, i.e., circular and lamellar pores, affected the change in thermal conductivity. Specifically, we confirmed that the change in thermal conductivity depends on the size of the lamellar pores.

Comparison of morphology and compressive deformation behavior of copper foams manufactured via freeze-casting and space-holder methods

Copper (Cu) foams with high porosity of about 63–78% were processed by the freeze-casting (FC) and space-holder (SH) methods. The FC and SH techniques yielded lamellar and polygonal pore structures, respectively, with similar porosities. The deformation behaviors of the two different types of Cu foams were compared using uniaxial compression and a simultaneous acoustic emission (AE) and video recording analysis. It was found that the compressive yield strength values for the FC-Cu and SH-Cu foams were significantly different, which were 19–29 MPa and 1.2–2.3 MPa, respectively. Furthermore, the energy absorbed during compression up to the strain of 50% was obtained as ∼12.3 MJ m−3 and ∼2.7 MJ m−3 for the FC-Cu and SH-Cu foams, respectively, resulting in approximately 4.6 times higher energy absorption capability for the FC-Cu foam. The deformation processes occurring during compression in the two Cu foams were studied by the AE and image analysis. The video and the evaluated AE parameters (e.g., the AE voltage, the cumulative number of events, and the cumulative energy) revealed that, in the case of the FC foam, the localized fracture of the struts within a well-defined single deformation band took place, which gave rise to pronounced AE signals (mostly in the plateau stage of compression). By contrast, the deformation was highly homogeneous in the case of the SH-Cu foam, and the main deformation mechanisms were gradual bending and buckling of the foam struts during compression.

Preparation of high strength lamellar porous calcium silicate ceramics by directional freeze casting

In this study, porous calcium silicate (CS) ceramics with oriented arrangement of lamellar macropore structure were prepared by directional freeze casting method. The lamellar macropores were connected by the micropores on the pore wall, which had good pore interconnectivity. The effects of solid loading of the slurry, freezing temperature, sintering additive content, and sintering temperature on the microstructures and compressive strength of the synthesized porous materials were investigated systematically. The results showed that with the increase of solid loading (≤20 vol%) and sintering additive content, the sizes of lamellar pores and pore walls increased gradually, the open porosity decreased and the compressive strength increased. The sintering temperature had little effect on the pore size of the ceramics, but increasing the sintering temperature (≤1050 °C) promoted the densification of the pore wall, reduced the porosity, and improved the strength. The decrease of freezing temperature had little effect on porosity, but it reduced the size of lamellar pore and pore wall, so as to improve the strength. Finally, porous CS ceramics with lamellar macropores of about 300–600 μm and 2–10 μm micropores on the pore wall were obtained. The porous CS ceramics had high pore interconnectivity, an open porosity of 66.25% and a compressive strength of 5.47 MPa, which was expected to be used in bone tissue engineering.

High porous ceramics with isometric pores by a novel saponification/gelation/freeze-casting combined route

A new route based on the combination of saponification/gelation/freeze-casting processes, in which the water was used as the solvent, was proposed to produce highly porous ceramics with isometric pores. The saponification reaction using gelatin promoted an inter-connected and equiaxial pore structure with the absence of lamellar pores, even using water as a solvent. The final porosity was up to ∼95 %, and the average pore size ranged from ≈200 up to 500 μm. The amount of saponifying agent had a significant influence on the pore size, while the contents of solids had a more substantial effect on the open porosity. The results indicate that the in situ production of surfactant combined with freeze casting technique allows obtaining ceramics with high porosity and isometric pores even using water as a solvent.

Pore modification mechanisms in a deeply buried non-marine sandstone: The Early Cretaceous Upper Sarir Sandstone Formation, Sirte Basin, Libya

Critical understanding of the reservoir pore-system is crucial for effective fluid-flow. Core-sedimentological description (40 core plugs), petrography (thin section and scanning electron microscopy with energy dispersive spectrometry), x-ray diffractometry, and high-resolution imaging were integrated to characterize pore-modification processes in a deeply buried (ca. 12470–12558 Ft.) non-marine sandstone. The reservoir is dominantly subrounded to subangular, well-sorted to moderately well-sorted, and medium-to fine-grained quartz arenite and lithearenite. Framework ranges from matrix-supported to matrix-devoided types. With a mean point-counted composition of Q95F0L5, quartz is the dominant mineral in all samples. Core-derived porosity and permeability range from 0.88 to 16.89% (Average 9.99%) and ~0.00–431.06 mD (Average 66.42 mD), respectively. Intergranular (ɸI), micro (ɸμ), fracture (CF), and dissolution (Diss) porosities constitute an estimated 60%, 35%, 3%, and 2% of the total porosity. The pore-spaces are randomly distributed and largely disconnected from one another. Connected pores are linked by necking, tubular, and lamellar pore throats. Pore-destructive diagenetic processes occurred mainly in the early-intermediate diagenetic phase, and to lesser extent in the late diagenetic phase. Pore-enhancement processes were of sparse occurrences. Mechanical compaction, quartz overgrowth development, kaolinitization, sideritization, and calcite cementation are the main pore-occluding processes identified. Quartz overgrowth increased with depth and it shows an inverse relationship with poro-perm. The formation of quartz overgrowth haloes in the Upper Sarir Sandstone Formation were most likely formed from non-insitu silica mobilized into the pore system during post-rift cooling. This study confirms the need for careful heterogeneity modelling even in non-marine deposited reservoir sandstone, notwithstanding their known clean nature in contrast to mud-rich marine reservoirs.

Terahertz Birefringent Biomimetic Aerogels Based on Cellulose Nanofibers and Conductive Nanomaterials.

Biomimetic, lamellar, and highly porous transition-metal carbide (MXene) embedded cellulose nanofiber (CNF) aerogels are assembled by a facile bidirectional freeze-drying approach. The biopolymer aerogels have large-scale, parallel-oriented micrometer-sized pores and show excellent mechanical strength and flexibility, tunable electrical properties, and low densities (2.7-20 mg/cm3). The CNF, MXene, and lamellar pores are efficiently utilized to endow the aerogels with exceptionally high birefringence in the terahertz (THz) regime. Birefringence values as high as 0.09-0.27 at 0.4 THz are achieved, which is comparable to most commercial THz birefringent materials such as liquid crystals, which suffer from fast disintegration, high cost, and complicated preparation processes. Empirical modeling for different MXene contents and an experimental comparison with silver nanowire or carbon nanotube embedded CNF aerogels suggest that the intrinsic conductivity and content of embedded nanomaterials, the aerogel porosity, and the lamellar cell walls can affect the optical properties such as the THz birefringence and absorption. The determination of optical anisotropy in the biopolymer aerogels lays a foundation for further exploration of ultralight, freestanding, and low-cost biomimetic porous architecture-based THz devices.

Hierarchical‐Porous Copper Foams by a Combination of Sponge Replication and Freezing Techniques

Open‐porous copper foams with additional strut porosity are manufactured by two different manufacturing routes. The first is based on the Schwarzwalder sponge replication technique. The second method is a combination of Schwartzwalder sponge replication and freezing technique in which an additional strut porosity is generated inside the struts of the sponge‐replicated foams by freezing at −20 °C for 24 h and subsequent sublimation. Thermal processing of both types of foams is conducted at 500 and 900 °C for 6 h in a hydrogen‐containing atmosphere to reduce copper oxides and to facilitate the sintering process of the copper powder particles. Despite significant shrinkage of both foam series after thermal processing, hollow struts and lamellar pores keep their shape and do not collapse. The influences of the additional lamellar pores and thermal processing temperature on the cellular structure, porosity, specific surface area, yield strength, absorbed energy, and thermal conductivity are studied. The additional strut porosity generated by the freezing step significantly increases the specific surface area of the copper foams by a factor of 2 in comparison to the sponge replicated foams.

Open-Cellular Alumina Foams with Hierarchical Strut Porosity by Ice Templating: A Thickening Agent Study.

Alumina replica foams were manufactured by the Schwartzwalder sponge replication technique and were provided with an additional strut porosity by a freeze-drying/ice-templating step prior to thermal processing. A variety of thickeners in combination with different alumina solid loads in the dispersion used for polyurethane foam template coating were studied. An additional strut porosity as generated by freeze-drying was found to be in the order of ~20%, and the spacings between the strut pores generated by ice-templating were in the range between 20 µm and 32 µm. In spite of the lamellar strut pore structure and a total porosity exceeding 90%, the compressive strength was found to be up to 1.3 MPa. Combining the replica process with freeze-drying proves to be a suitable method to enhance foams with respect to their surface area accessible for active coatings while preserving the advantageous flow properties of the cellular structure. A two-to-threefold object surface-to-object volume ratio of 55 to 77 mm−1 was achieved for samples with 30 vol% solid load compared to 26 mm−1 for non-freeze-dried samples. The freeze-drying technique allows the control of the proportion and properties of the introduced pores in an uncomplicated and predictable way by adjusting the process parameters. Nevertheless, the present article demonstrates that a suitable thickener in the dispersion used for the Schwartzwalder process is inevitable to obtain ceramic foams with sufficient mechanical strength due to the necessarily increased water content of the ceramic dispersion used for foam manufacturing.

Fretting wear mechanism of plasma-sprayed CuNiIn coating on Ti-6Al-4V substrate under plane/plane contact

The fretting wear mechanism of plasma-sprayed CuNiIn coating on Ti-6Al-4V substrate under plane/plane contact conditions was investigated systematically using a bench level test. The obtained experimental results showed that the fretting wear mechanism of the CuNiIn coating can be divided into three stages: (I) In the initial stage, the asperities on the rough surface were flattened to form debris and fill the nearby pits. The contact surface gradually flattened, which was accompanied by slight abrasive wear. (II) With increasing number of fretting cycles, the fretting wear process of the CuNiIn coating entered the delamination wear stage. Under the action of alternating shear loads, the lamellar structure and pores in the CuNiIn coating rapidly cracked and propagated to the surface. In addition, some fatigue cracks propagated into the matrix along the direction of maximum shear stress. (III) Eventually, the CuNiIn coating entered a stable wear state under the lubrication of a third body, which was accompanied by local delamination. The lamellar structure greatly enhanced the fretting wear resistance of the CuNiIn coating. In the process of fretting wear, the lamellar structure of the CuNiIn coating effectively hindered fatigue crack growth, guided crack deflection along the lamellar interface, and induced crack bifurcation. In addition, the pores can blunt the crack tip. • A new self-balancing device was developed to improve geometrical adaptation of friction pairs with plane/plane contact. • The fretting wear resistance of CuNiIn coating was better than that of Ti-6Al-4V. • The wear rate of the CuNiIn coating was non-monotonic with increasing number of cycles. • The lamellar structure of CuNiIn coating was conducive to delamination wear. • The lamellar structure of CuNiIn coating could induce crack deflection, stop crack propagation, and guide crack bifurcation.

Programmable Local Orientation of Micropores by Mold-Assisted Ice Templating.

Pore geometry plays a crucial role in determining the properties and functions of porous materials. Various methods have been developed to prepare porous materials that have randomly distributed or well-aligned pores. However, a technique capable of fine regulation of local pore orientation is still highly desired but difficult to attain. A technique, termed mold-assisted ice templating (MIT), is reported to control and program the local orientation of micropores. MIT employs a copper mold of a particular shape (for instance a circle, square, hexagon, or star) and a cold finger to regulate the 3D orientation of a local temperature gradient, which directs the growth of ice crystals; this approach results in the formation of finely regulated patterns of lamellar pore structures. Moreover, the lamellar thickness and spacing can be tuned by controlling the solution concentration.

Freeze‐assisted Tape Casting of Vertically Aligned MXene Films for High Rate Performance Supercapacitors

Conventional electrode preparation techniques of supercapacitors such as tape casting or vacuum filtration often lead to the restacking or agglomeration of two‐dimensional (2D) materials. As a result, tortuous paths are created for the electrolyte ions and their adsorption onto the surfaces of the active materials can be prevented. Consequently, maintaining high rate performance while increasing the thickness of electrodes has been a challenge. Herein, a facile freeze‐assisted tape‐casting (FaTC) method is reported for the scalable fabrication of flexible MXene (Ti3C2Tx) supercapacitor electrode films of up to 700 μm thickness, exhibiting homogeneous ice‐template microstructure composed of vertically aligned MXene walls within lamellar pores. The efficient ion transport created by the internal morphology allows for fast electrochemical charge–discharge cycles and near thickness‐independent performance at up to 3000 mV s−1 for films of up to 300 μm in thickness. By increasing the scan rate from 20 to 10,000 mV s−1, Ti3C2Tx films of 150 μm in thickness sustain 50% of its specific capacitance (222.9 F g−1). When the film thickness is doubled to 300 μm, its capacitance is still retained by 60 % (at 213.3 F g−1) when the scan rate is increased from 20 to 3000 mV s−1, with a capacitance retention above 97.7% for over 14,000 cycles at 10 A g−1. They also showed a remarkably high gravimetric and areal power density of 150 kW kg−1 at 1000 A g−1 and 667 mW cm−2 at 4444 mA cm−2, respectively. FaTC has the potential to provide industry with a viable way to fabricate electrodes formed from 2D materials on a large scale, while providing promising performance for use in a wide range of applications, such as flexible electronics and wearable energy storage devices.

Effects of lamellar microstructure of retinoic acid loaded-matrixes on physicochemical properties, migration, and neural differentiation of P19 embryonic carcinoma cells

Abstract In this study, retinoic acid loaded-PLGA-gelatin matrixes were prepared with both freeze-casting and freeze-drying techniques. Herein, the effect of unidirectional microstructure with tunable pores on release profile, cellular adhesion, migration, and differentiation was compared. Morphological observation determined that highly interconnected porous structure can be formed, but lamellar pore channels were observed in freeze-casting prepared constructs. The absorption ratio was increased, and the biodegradation rate was decreased as a function of the orientation of microstructure. The in-vitro release study illustrated non-Fickian release mechanism in both methods, so that erosion has predominated over diffusion. Accordingly, PLGA-gelatin scaffolds prepared with freeze-drying technique showed no adequate erosion due to the rigid structure, while freeze-casting one presented more favorable erosion. Microscopic observations of adhered P19 embryonic cells on the scaffolds showed that the freeze-casting matrixes with unidirectional pores provide a more compatible microenvironment for cell attachments and spreading. Besides, it facilitated cell migration and penetration inside the structure and may act as guidance for neuron growth. Improvement in the expression of neural genes in unidirectionally oriented pores proved the decisive role of contact guidance for nerve healing. It seems that the freeze-cast PLGA-gelatin-retinoic acid scaffolds have initial features for nerve tissue regeneration studies.

Fabrication of poly (1, 8-octanediol-co-Pluronic F127 citrate)/chitin nanofibril/bioactive glass (POFC/ChiNF/BG) porous scaffold via directional-freeze-casting

Abstract The citrate-based thermoset elastomer is a promising candidate for bone scaffold material, but the harsh curing condition made it difficult to fabricate porous structure. Recently, poly (1, 8-octanediol-co-Pluronic F127 citrate) (POFC) porous scaffold was creatively fabricated by chitin nanofibrils (ChiNFs) supported emulsion-freeze-casting. Thanks to the supporting role of ChiNFs, the lamellar pore structure formed by directional freeze-drying was maintained during the subsequent thermocuring. Herein, bioactive glass (BG) was introduced into the POFC porous scaffolds to improve bioactivity. It was found the complete replacement of ChiNF particles with BG particles could not form a stable porous structure; however, existing at least 15 wt% ChiNF could ensure the formation of lamellar pore, and the interlamellar distance increased with BG ratios. Thus, the BG granules did not contribute to the formation of pore structure like ChiNFs, however, they surely endowed the scaffolds with enhanced mechanical properties, improved osteogenesis bioactivity, better cytocompatibility as well as quick degradation rate. Reasonably adjusting BG ratios could balance the requirements of porous structure and bioactivity.

Preceramic polymer-derived ceramic foams with lamellar strut porosity

Open porous replica foams with additional lamellar strut pores were prepared by preceramic polymer processing combined with a freeze-drying process. Polymer foam templates were coated with an aqueous polymethylsilesquioxane system followed by freezing at - 20 °C to generate hierarchical porosity within the foam struts. The cellular structure was preserved during freeze drying, cross-linking, template removal and pyrolysis, and additional strut porosity was formed. The size of the lamellar strut pores was found to depend on the solid load of the preceramic slurry and its pretreatment procedure. The cellular materials obtained in this work possess additional lamellar strut pore channels with a thickness of approximately 40 µm and a total foam porosity of > 90 %.

Mussel-inspired polydopamine induced the osteoinductivity to ice-templating PLGA-gelatin matrix for bone tissue engineering application.

In this study, poly(lactic-co-glycolic acid) (PLGA)-gelatin scaffolds were fabricated using the freeze-casting technique. Polydopamine (PDA) coating was applied on the surface of scaffolds to enhance the hydrophilicity, bioactivity, and cellular behavior of the composite constructs. Further, the synergistic effect of PDA coating and lamellar microstructure of scaffolds was evaluated on the promotion of properties. Based on morphological observations, freeze-casting constructs showed lamellar pore channels while the uniformity and pore size were slightly affected by deposition of PDA. The hydrophilicity and swelling capacity of the scaffolds were assessed using contact angle measurement and phosphate buffered saline absorption ratio. The results indicated a significant increment in water-matrix interactions following surface modification. The evaluation of the biodegradation ratio revealed the higher degree of degradation in PDA-coated samples owing to the presence of hydrophilic functional groups in the chemical structure of PDA. On the other hand, the bioactivity potential of PDA in the simulated body fluid solution confirmed the possibility of using coated constructs as a bone reconstructive substitute. The improvement of cellular attachment and filopodia formation in PDA-contained matrixes was the other benefit of the coating process. Furthermore, cellular proliferation and ALP activity were enhanced after PDA coating. The suggested PDA-coated PLGA-gelatin scaffolds can be applied in bone tissue regeneration.

Manufacture of Highly Porous Tubular Alumina Substrates with Anisotropic Pore Structure by Freeze‐Casting

This work investigates the production of freeze‐cast tubular alumina substrates with anisotropic pores. The freeze‐casting method allows accurate control of the radial pore structure by adjusting the solid loading and sintering temperature. High porosities of 91% are attained, which decrease inversely proportional to the solid loading. Water is used as the pore forming agent by the freeze‐cast process, producing lamellar pores with highly connected aligned structure. Substrates with solid loadings within 15–20% show maximum pore alignment and anisotropy, as higher solid loading creates more isotropic pores. The average pore size distribution decreases from 11 to 2 μm as a function of the solid loading. By increasing the sintering temperature from 1300 to 1500 °C, the crushing strength significantly increases for samples prepared with high solid loading, reaching values as high as 25.4 MPa. A plot of the mechanical stability versus porosity reveals that the substrates obtained in this study show a similar trend when compared with previously reported flat substrates. Water permeation reaches 510 L m−2 min−1, showing a strong influence of the pore size. Therefore, processing of freeze‐cast tubular substrates from aqueous suspensions proves to be a versatile technique for manufacturing advanced engineering materials with anisotropic pore structure.