Polyurethane Template Research Articles

A novel negative thermal expansion ceramic network interlayer for releasing high residual stress of Cf/SiC heterogeneous brazed joint

Negative thermal expansion (NTE) ceramics have been widely concerned in adjusting the coefficient of thermal expansion (CTE) to release the high residual stress of heterogeneous joint. However, one major problem that needs to be solved is the agglomeration problem caused by excessive ceramic particles addition. In this work, a novel NTE ceramic Sc2W3O12 network interlayer is prepared by the polyurethane template method. The Sc2W3O12 network interlayer with a single NTE phase presents a three-dimensional network structure. The NTE Sc2W3O12 ceramic is uniformly distributed in brazing seam without agglomeration with the help of unique network structure. The active Ti elements play an important role in the interface bonding, reacted with Sc2W3O12 network interlayer and Cf/SiC composites to form Cu3Ti3O and TiC/Ti5Si3 reaction layer, respectively. After introducing Sc2W3O12 network interlayer, the CTE of the composite filler is reduced from 16.6 × 10−6 K−1 to 11.9 × 10−6 K−1, a decrease of 29 %. The highest shear strength of the Cf/SiC heterogeneous joint is reached 130 MPa, which is 5.4 times than that without Sc2W3O12 network interlayer.

High porosity and low thermal conductivity lanthanum zirconate porous ceramics via replica method

ABSTRACT Low thermal conductivity and excellent high-temperature stability make lanthanum zirconate (La2Zr2O7, LZO) a very promising material for high-temperature insulation applications. In this study, LZO porous ceramics with ultra-high porosity and an open-pore structure were prepared by the replica method using a polyurethane template. The flowability and coating quality of the ceramic slurry were optimized. When the dispersant content of the slurry was 0.6 wt% and the alcohol to water ratio was 1:1, the slurry had low surface tension and low viscosity, leading to good coating quality of the ceramic slurry on the sponge template. The pore size between hollow skeletons was 100–500 μm with the hollow structure of the skeletons forming secondary pores. LZO porous ceramics showed high porosity of 87.6%-96.0%, low thermal conductivity of 0.048–0.126 W/(m·K), and compressive strength of 0.13–0.74 MPa by adjusting the ceramic content. A high temperature insulation performance test showed that the temperature difference between the cold side and the hot side of the sample was over 1000°C, indicating the excellent thermal insulation properties of LZO porous ceramics. LZO porous ceramics had good high-temperature stability without sintering shrinkage at heat treatment temperatures below 1500°C.

Improving strength and microstructure of SiC reticulated porous ceramic through in-situ generation of SiC whiskers within hollow voids

SiC reticulated porous ceramic with excellent strength and high-density ceramic struts was successfully prepared using the polymer replica method, followed by pressureless sintering under a buried charcoal atmosphere. First, a polyurethane (PU) template was coated with a Si slurry and then a SiC-containing slurry, and subsequently heated under the buried charcoal atmosphere. To ensure excellent coating ability of the slurries, the viscosity, thixotropy, and yield stresses of the Si slurry were optimized by adjusting the content of the thickening agent. During heating, Si in the coating layer reacted with the residual C and CO gas from the PU template and buried charcoal, forming SiC whiskers that filled hollow voids within the SiC struts. Additionally, catalyst ferric nitrate was added to the Si slurry to promote the generation and growth of SiC whiskers. As a result, when compared to the untreated SiC reticulated porous ceramic, the SiC reticulated porous ceramic pre-coated with Si layers exhibited significant improvements in mechanical strength and thermal shock resistance, despite minor differences in porosity. Furthermore, an industrial test conducted in the copper smelting industry showed that the structure of SiC reticulated porous ceramic, prepared in this study and used as filters, remained intact even after 7 days of continuous use. Meanwhile, a significant number of inclusions was adhered to the surfaces of the filters. Therefore, the processes combined with in-situ generation of SiC whiskers is an ideal and low-cost method for fabricating SiC filters with excellent properties.

SiC Foams for the Photocatalytic Degradation of Methylene Blue under Visible Light Irradiation.

SiC foams were synthesized by impregnating preceramic polymer into polyurethane foam templates, resulting in a photo-catalytically active material for the degradation of methylene blue. The crystalline structure, electronic properties, and photocatalytic performance of the SiC foams were characterized using a series of experimental techniques, including X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, N2 physisorption measurements, UV-visible spectroscopy, and methylene blue photodegradation tests. The original polyurethane template's microporous structure was maintained during the formation of the SiC foam, while additional mesopores were introduced by the porogen moieties added to the preceramic polymers. The prepared SiC-based photocatalyst showed attractive photocatalytic activity under visible light irradiation. This structured and reactive material offers good potential for application as a catalytic contactor or membrane reactor for the semi-continuous treatment of contaminated waste waters in ambient conditions.

Влияние количества стадий импрегнации на макроструктурные и прочностные характеристики стеклоуглеродных пен

The template synthesis of glassy carbon foams was used in the work and the influence of the initial template cell size, the concentration of the solution, and the number of impregnation stages on the macrostructural and strength characteristics of the obtained materials was studied. As a carbon precursor was used the solution of Novolac resin grade SFP-012A2, the coke residue of which is more than 57 wt. %. It was shown that increasing the number of impregnation stages makes it possible to improve strength characteristics while maintaining open porosity at the level of 90 %, while glassy carbon foam based on a polyurethane template with a porosity of 60 pores per inch and 4 stages of impregnation with a solution with a concentration of 30 wt. % has the best set of properties due to the uniform wall thickening in the material volume. The value of compressive strength was 1.12 MPa, which is 2 times higher than the value of foreign analogues, while the open porosity was 91 %. It has been established that a decrease in the size of the cells of the initial template can lead to embrittlement of the material due to the formation of a cluster of overlapped cells. Increasing the mechanical strength of glassy carbon foams while maintaining an open-cell structure expands the field of application of this class of materials.

A Stretchable Conductor Based on Spray-Coated Micro/Nano Scale Ag Flakes with Ultralow Resistance for Wearable Antennas

With the rapid development of wireless communication, there are demands on the flexible antennas. In this work, a wearable dipole antenna has been fabricated by spray-coating nano/microscale Ag flakes onto the polyurethane (TPU) template. It demonstrates an ultrahigh electrical conductivity even under large deformation such as bending, twisting, folding and stretching to 170%. Thus, the resultant antenna maintains good properties under the aforementioned deformation. And even under a stretching of 50%, in contact with the body, it can still provide good antenna characteristics. We hope that our results can be adopted for adaptive skin contactable flexible antenna under different conditions, which is crucial for the next generation of wireless communication.

Highly porous bio-glass scaffolds fabricated by polyurethane template method with hydrothermal treatment for tissue engineering uses.

Bioglass scaffolds, which contain a significant percentage of porosity for tissue engineering purposes, have low strength. For increasing the strength and efficiency of such structures for use in tissue engineering, fabrication of hierarchical meso/macro-porous bioglass scaffolds, developing their mechanical strength by hydrothermal treatment and adjusting pH method, and achieving the appropriate mesopore size for loading large biomolecules, were considered in this study. Mesoporous bioglass (MBG) powders were synthesized using cetyltrimethylammonium bromide as a surfactant, with different amounts of calcium sources to obtain the appropriate size of the mesoporous scaffolds. Then MBG scaffolds were fabricated by a polyurethane foam templating method, and for increasing scaffold strength hydrothermal treatment (90 °C, for 5 days) and adjustment pH (pH=9) method was used to obtain hierarchical meso/macro-porous structures. The sample characterization was done by Simultaneous thermal analysis, Fourier transform infrared spectroscopy, Field Emission Scanning electron microscopy, small and wide-angle X-ray powder diffractions, transmission electron microscopy, and analysis of nitrogen adsorption-desorption isotherm. The mechanical strength of scaffolds was also determined. The MBG scaffolds based on 80.28 (wt.) % SiO2- 17.89 (wt.) % CaO- 1.81 (wt.) % P2O5 presented interconnected large pores and pores in the range of 100-150 μm and 6-18 nm, respectively and 0.4 MPa compressive strength. The total pore volume and specific surface area were obtained from the Brunauer-Emmett-Teller theory, 0.709 cm3 g-1 and 213.83 m2 g-1, respectively. These findings could be considered in bone-cartilage tissue engineering.

A New Insight into the Role of Silicate-Type Binders on the Crushing Strength of Alumina Foams

Semi-closed cell macroporous alumina foams with relative densities ranging from 0.26 to 0.35 have been produced by the well-established replication method based on the coating of a polyurethane (PU) template foam by a ceramic slurry, followed by burnout of the PU template, and sintering of the ceramic skeleton. Collapse of the three-dimensional structure upon the volatilisation of the PU sponge can only be prevented using appropriate binders. Scarce data are available on the slurry formulations of commercial alumina foams. The aim of this study was to investigate the influence of silicate-type binders, namely kaolin and bentonite additives, on the crushing strength of alumina foams. The highest crushing strength of around 10 MPa was observed at a porosity of 66 ± 2%. The open-cell model is inadequate to fit the crushing strength data of such semi-closed cell type structures. Both microscopic and macroscopic flaws resulting from the foam processing method contribute to the wide scatter of the strength, thereby explaining the Weibull modulus ranging from 4 to 7. Both flaw populations require further improvement to maximise the crushing strength of these foams with high potential for the design of structured catalyst carriers and molten aluminium filters.

Effect of the Cell Count on Geometrical, Mechanical, and Thermal Properties of Hierarchical‐Porous Reticulated Copper Foams from a Combination of Sponge Replication and Freeze‐Drying Techniques

Effect of the Cell Count on Geometrical, Mechanical, and Thermal Properties of Hierarchical‐Porous Reticulated Copper Foams from a Combination of Sponge Replication and Freeze‐Drying Techniques

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.

Structural, Electrical, and Mechanical Properties Investigation of Open-Cell Aluminum Foams Obtained by Spark Plasma Sintering and Replication on Polyurethane Template.

The present paper illustrates a comparison of open-cell aluminum foams. The foams were fabricated by two different methods: spark plasma sintering and replication on a polyurethane template. The influence of pressure, temperature, and diameter of space holding material on foam obtained by the spark plasma sintering method was investigated. Additionally, the aluminum powder content in slurry and atmosphere during thermal processing of foam prepared by the replication technique were studied. The morphology and structure of obtained samples were analyzed by scanning electron microscopy and X-ray diffraction analysis. Supplementarily, mechanical properties and electrical conductivity were studied. The porosity of obtained samples was 83% for the SPS sample and 85% for the replication sample. The results of the studies carried out gave us an understanding that the SPS method is more promising for using the obtained foams as cathode current collectors in lithium-ion batteries due to excessive aluminum oxidation during sintering in the furnace.

High Strain‐Rate Compression Experiments on Ni/Polyurethane Hybrid Metal Foams Using the Split‐Hopkinson Pressure Bar Technique

Open‐cell metal foams are a versatile class of porous lightweight materials, which are predominantly used as kinetic energy absorbers in a wide scope of applications. Based on their bio‐inspired inhomogeneous 3D porous structure, they are capable to significantly reduce the mass of structural designs. Starting with a polyurethane (PU) template foam, the specimens in the present contribution are manufactured by an electrochemical nickel (Ni) deposition. This manufacturing process is beneficial regarding both the specimen design and the adjustment of mechanical properties correlated with the Ni‐coating thickness. Herein, the strain‐rate sensitivity of open‐cell Ni/PU hybrid metal foams is investigated by quasistatic compression tests and high‐velocity impact tests conducted with a conventional split‐Hopkinson pressure bar device.

Synthesis of 3D-porous scaffold from cockle shells waste-based hydroxyapatite with addition silica from tin tailings

This study aims to synthesize a porous scaffold based on hydroxyapatite and silica using the polymer sponge replication method. In bone tissue engineering technology, the development of porous scaffolds is a topic that is intensively studied because it is expected to be a solution to various problems of conventional bone therapy. In addition to proposing a porous scaffold synthesis method, we also utilize natural waste-based materials such as cockle shells and tin tailings as raw materials in this research. Investigation through x-ray diffraction (XRD) pattern with the goodness of fit coefficient, X 2 = 0.09 shows that the coprecipitation method is effective for the synthesis of hydroxyapatite. Analysis of XRD pattern of tin tailings sand with a value of X 2 = 0.008 showed that the diffraction pattern was related to silica with space group P 41 21 2. The polymer sponge replication method with polyurethane template succeeded in obtaining scaffolds with macropores above 300 μm. Based on the diffraction pattern of the three porous scaffolds prepared with different percentages of HA, it is known that all porous scaffolds have peaks related to HA and silica. It indicates that the decomposition temperature of polymer does not provide sufficient energy for the HA and silica to transform or react chemically.

Fabrication of Cordierite Ceramic Foam Filter by Replication Method

Ceramic foam filter (CFF) is widely used to improve the quality of molten metal prior to casting. Cordierite is one of the most commonly used materials for making CFF. In this research, the fabrication of cordierite-based CFF by a replication method using a polyurethane template has been studied. Waterglass and polymethacrylic acid (PMAA) were used as defloculants to synthesize ceramic suspensions. CFF was made from kaolin, talc, alumina with a defloculant concentration of 0.3% which is sintered at a temperature of 1300 - 1350 oC. The experimental results showed that the porosity obtained for all CFF samples were above 70%. The best shape of CFF was obtained by using PMAA as defloculant. However, CFF did not reach the maximum strength yet so it is necessary to carry out further research on the CFF body composition.

Macroporous Ceramic Filter through Polyurethane Template Replication Method: Characterization and Detergent Wastewater Filtration Trials

Macroporous ceramic filters were made through the template replication method with raw materials, i.e. clay, silica sand and iron oxide powder with a ratio of 70: 27.5: 2.5. The mixture of these ingredients was wet milled in a potmill for 5 hours. Polyurethane as a template was dipped in the mixture slurry with a variation dipping time of 6 and 24 hours. The greenbody filter was calcined at temperature of 900 o C with a slowly heating rate. The resulting filter was macroporous with very porous morphology and has interconnections or channels between pores. The pore diameter of the filter which was not added with iron oxide was 1.87 mm and the pore wall was 0.31 mm. The filter added with iron oxide had the highest density and porosity, that is 1.9004 g/cm 3 and 38.49%. Filters made of iron oxide powder added material show better filtration performance for pH, TSS and COD parameters for 1% detergent water and detergent wastewater. The best results for the filtration of detergent water samples were pH to 9, TSS reduced by 34.45% and COD decreased by 24.99%.

Study on the thermal treatment conditions for fabricating open-cell structure Cu–Sn alloy foams

Cu–Sn alloy foams, with an open-cell structure, were fabricated by Cu/Sn coelectrodeposition onto a polyurethane (PU) template in an alkaline electrolyte with a citrate complexing agent before undergoing a subsequent thermal treatment for PU removal in a N2 gas environment. These foams were predominantly comprised of a Cu matrix along with Cu6Sn5 and Cu3Sn intermetallic compounds, which are known as active materials in Cu–Sn alloy electrodes used in rechargeable batteries. The chemical phase change of Cu–Sn alloy foams and its influence on the electrical resistance were studied according to the heating temperature and N2 gas flow rate. Assuming the thermal degradation of PU as a first-order reaction, the dependence of the PU removal process on the heating temperature was also theoretically investigated. In addition, a postannealing process of the Cu–Sn alloy foams was employed to reduce their electrical resistance by promoting grain growth.

Three dimension phenolic resin derived carbon-CNTs hybrid foam for fire retardant and effective electromagnetic interference shielding

Three dimension fire retardant carbon-CNTs hybrid foams for electromagnetic interference (EMI) shielding effectiveness (SE) were fabricated using a polyurethane (PU) template. Phenolic resin with different contents (0.2–2 wt.%) of mutltiwalled carbon nanotubes (MWCNTs) was mixed using a magnetic stirrer for making a homogenous slurry and then PU foam was impregnated in this slurry followed by carbonization at 1000 °C. The foams were characterized for their morphological, structural, mechanical, EMI shielding, and fire-retardant properties. The total EMI shielding effectiveness (SE) of -57.2 dB was achieved for the carbon foam containing 1 wt.% MWCNTs in the frequency range of 8.2–12.4 GHz. Moreover, the addition of MWCNTs into phenolic resin also enhanced the compressive strength (6.5 MPa), thermal stability and fire retardant performance of carbon-CNTs hybrid foams. The multifunctional carbon-CNTs hybrid foams demonstrate that they are outstanding materials with potential applications in EMI shielding and thermal management for defense and aerospace sectors.

Self-standing zeolite foam monoliths with hierarchical micro-meso-macroporous structures.

The zeolite monoliths were synthesized by a facile polymer scaffold template assisted hydrothermal method. The selected foam-shaped template of a polyurethane (PU) foam monolith, was used to prepare the self-standing zeolite foam (ZF) monolithic materials. The obtained ZF products can preserve the same size, shape and macroporous network structure of the original PU foam scaffold template, although the zeolite nano-crystallites had been fully substituted for the PU template to form the new skeleton struts and walls. The as-synthesized ZF products demonstrated abundant hierarchical porosity (involving triple micro-, meso- and macropores). Meanwhile, compared with the conventional zeolite powders, the self-standing ZF monolithic materials exhibited greater total pore volume and nearly three times higher mesopore volume, suggesting wider applications as catalysts, catalyst supports and adsorbents in industry.

Preparation of biphasic hydroxyapatite/ β-tricalcium phosphate foam using the replication technique

Biphasic hydroxyapatite/β-tricalcium phosphate foams were prepared using the replication technique starting from a precipitated hydroxyapatite (Ca10(PO4)6(OH)2: HAP) powder, and sodium glycerophosphate (GP). The effect of the grinding time, solid loading, dispersant amount, and etching, replication, and sintering processes were investigated. The SEM, OEM and FTIR analyses proved that the surface of the polyurethane template must be treated with NaOH solution to make it more hydrophilic prior to the coating process. With a solid loading of 40 wt-%, the slurries prepared from the precipitated hydroxyapatite presented a shear thinning behavior, which was useful for the coating process. The SEM analysis of the foams showed that the optimum number of coating layers to obtain foam with an identical structure with the template was limited to three. The use of GP and the optimized preparation parameters helped to decrease the consolidation temperature of the ceramic foams to 1000 °C. The XRD and FTIR analyses of the prepared foams showed that the thermal treatment of the GP and the HAP mixture led to a partial decomposition of the HAP to tricalcium phosphate. The fitting of the XRD patterns and the obtained lattice parameters proved that the decomposition was accompanied by the insertion of sodium from GP toward the lattice of tricalcium phosphate and the formation of Na-β-tricalcium. The results of the SEM analysis, the pore size distribution and the mechanical strength showed that the presence of the Na-β-tricalcium reduced the pore size distribution from 500-2700 to 100–1700 μm, decreased slightly the total porosity from 80 vol-% to 70 vol-%; and improved the mechanical strength of the obtained foam from 1.56 MPa to 2.60 MPa.

Processing and thermal characterization of polymer derived SiCN(O) and SiOC reticulated foams

Highly porous polymer-derived SiCN(O) and SiOC ceramics with low thermal conductivity were developed by replicating polyurethane (PU) foams. The PU templates were impregnated with polysilazane or polysiloxane precursor, followed by pyrolysis at different temperatures (1200 °C - 1500 °C) yielding SiCN(O) or SiOC ceramic foams, respectively. The swelling and cross-linking behavior of the used precursors had a significant impact on the morphology of the prepared foams. The samples had bulk densities ranging from 0.03 g.cm-3 to 0.56 g.cm-3 and a total porosity in the range from 75 to 98 vol%. Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) were employed to follow the structural evolution together with morphological characterization by scanning electron microscopy (SEM). The obtained ceramics were thermally stable up to 1400 °C, and the linear thermal expansion coefficient values of the porous SiCN(O) and SiOC components in the temperature range from 30 to 850 °C were found to be ~1.72 x 10-6.K-1 and ~1.93 x 10-6.K-1, respectively. Thermal conductivity (λ) as low as 0.03 W.m-1 K-1 was measured for the SiCN(O) and SiOC foams at room temperature (RT). The λ of the ceramic struts were also assessed by using the Gibson-Ashby model and estimated to be 2.1 W.m-1 K-1 for SiCN(O), and 1.8 W.m-1 K-1 for SiOC.