Space Holder Method Research Articles

Synthesis and Characterization of Ti-13Ta-6Sn Foams Produced Using Mechanical Alloying, the Space Holder Method and Plasma-Assisted Sintering

Highly porous titanium foams are great candidates for replacing bone structures with a low elastic modulus owing to their ability to avoid the stress shielding effect. However, the production of highly porous foams (>70 vol.%) with well-distributed, stable, and predictable porous architectures using powder compaction and space holders is challenging. In this study, pure titanium powder and mechanically alloyed Ti-13Ta-6Sn were mixed with 50, 70, and 80 vol.% KCl powders as a space holder, cold-compacted, and sintered in a plasma-assisted sintering reactor to produce highly porous foams. The space holder was completely removed using heat and plasma species collisions prior to sintering. A Ti-13Ta-6Sn alloy powder with α, β, and metastable FCC-γ phases was synthesized. The characteristics of the alloyed powder, mixing step, and the resulting sintered samples were compared to those of CP-Ti. After sintering, the alloy exhibited α and β phases and a reduced elastic modulus. Foams with an elastic modulus in the range of the cortical and trabecular bones were obtained. The results showed the effects of the space holder volume fractions on the volume fraction, size, distribution, interconnectivity, and shape of the pores. The Ti-13Ta-6Sn foams exhibited a uniform open-celled porous architecture, lower elastic modulus, higher yield strength, and higher passivation resistance than CP-Ti. Ti-13Ta-6Sn exhibited a nontoxic effect for the mouse fibroblast cell line.

Self-exothermic reaction behavior and pore structures of Ni-Al intermetallics with more than 70% porosity

Abstract In this study, high-porosity Ni-Al alloys with complete shape and controllable pore structures were prepared by combining the self-exothermic reaction with the space holder method. The observations show that porous Ni-Al sintered discs appeared to melt and deform after a violent reaction without adding space holder particles. The link between the volume content of urea particles and macroscopic morphology, combustion behavior, phase composition and pore structures of porous Ni-Al compounds were studied. The space holder pores acts as a heat absorber, greatly increasing the open porosity to 76.0% when adding 50 vol% urea particles. This leachable space holder method can be an effective strategy to regulate the sample shape and pore characteristics of porous Al-containing intermetallics.

Enhancing Capillary Pressure of Porous Aluminum Wicks by Controlling Bi-Porous Structure Using Different-Sized NaCl Space Holders.

Capillary pressure and permeability of porous media are important for heat transfer devices, including loop heat pipes. In general, smaller pore sizes enhance capillary pressure but decrease permeability. Introducing a bi-porous structure is promising for solving this trade-off relation. In this study, the bi-porous aluminum was fabricated by the space holder method using two different-sized NaCl particles (approximately 400 and 40 μm). The capillary pressure and permeability of the bi-porous Al were evaluated and compared with those of mono-porous Al fabricated by the space holder method. Increasing the porosity of the mono-porous Al improved the permeability but reduced the capillary pressure because of better-connected pores and increased effective pore size. The fraction of large and small pores in the bi-porous Al was successfully controlled under a constant porosity of 70%. The capillary pressure of the bi-porous Al with 40% large and 30% small pores was higher than the mono-porous Al with 70% porosity without sacrificing the permeability. However, the bi-porous Al with other fractions of large and small pores did not exhibit properties superior to the mono-porous Al. Thus, accurately controlling the fractions of large and small pores is required to enhance the capillary performance by introducing the bi-porous structure.

Effects of the Space Holder Shape on the Pore Structure and Mechanical Properties of Porous Cu with a Wide Porosity Range.

Porous copper (Cu), with varying porosities, has been made using carbamide as a space holder through the powder metallurgy route. Two shapes of carbamide particles were used, (i) needlelike and (ii) spherical, in order to investigate the effect of the space holder shape on the pore structure and mechanical properties of porous Cu. The compressive deformation behavior of porous Cu was studied under a compression test. The pores' structural characteristics and mechanical properties of the porous Cu varied significantly with the shape of the space holder. Although the effect of the space holder shape on the porosity was not regular, the effect on the mechanical properties was regular. The stress increased monotonically with the increase in the strain, and strain hardening occurred at the plastic yield stage. The elastic modulus and yield strength followed the power law, with the relative density irrespective of the space holder shape. The empirical constants associated with different empirically developed power law relations were different, according to the shape of space holder. A quantitative relationship between the elastic modulus and yield strength and the spacer content was obtained to control the mechanical properties of the present porous Cu or other porous metals and metal foams using the well-known space holder method.

Exploring the Potential of MIM-Manufactured Porous NiTi as a Vascular Drug Delivery Material.

Porous nickel-titanium (NiTi) manufactured using metal injection molding (MIM) has emerged as an innovative generation of drug-loaded stent materials. However, an increase in NiTi porosity may compromise its mechanical properties and cytocompatibility. This study aims to explore the potential of porous NiTi as a vascular drug delivery material and evaluate the impact of porosity on its drug loading and release, mechanical properties, and cytocompatibility. MIM, combined with the powder space-holder method, was used to fabricate porous NiTi alloys with three porosity levels. The mechanical properties of porous NiTi were assessed, as well as the surface cell growth capability. Furthermore, by loading rapamycin nanoparticles onto the surface and within the pores of porous NiTi, we evaluated the in vitro drug release behavior, inhibitory effect on cell proliferation, and inhibition of neointimal hyperplasia in vivo. The results demonstrated that an increase in porosity led to a decrease in the mechanical properties of porous NiTi, including hardness, tensile strength, and elastic modulus, and a decrease in the surface cell growth capability, affecting both cell proliferation and morphology. Concurrently, the loading capacity and release duration of rapamycin were extended with increasing porosity, resulting in enhanced inhibitory effects on cell proliferation in vitro and inhibition of neointimal hyperplasia in vivo. In conclusion, porous NiTi holds promise as a desirable vascular drug delivery material, but a balanced consideration of the influence of porosity on both mechanical properties and cytocompatibility is necessary to achieve an optimal balance among drug-loading and release performance, mechanical properties, and cytocompatibility.

Numerical Study on Fluid Flow Behavior and Heat Transfer Performance of Porous Media Manufactured by a Space Holder Method.

The velocity field and temperature field are crucial for metal foams to be used as a heat exchanger, but they are difficult to obtain through physical experiments. In this work, the fluid flow behavior and heat transfer performance in open-cell metal foam were numerically studied. Porous 3D models with different porosities (55-75%) and pore sizes (250 μm, 550 μm, and 1000 μm) were created based on the porous structure manufactured by the Lost Carbonate Sintering method. A wide flow velocity range from 0.0001 m/s to 0.3 m/s, covering both laminar and turbulent flow regimes, is fully studied for the first time. Pressure drop, heat transfer coefficient, permeability, form drag coefficient, temperature and velocity distributions were calculated. The calculated results agree well with our previous experimental results, indicating that the model works well. The results showed that pressure drop increased with decreasing porosity and increasing pore size. Permeability increased and the form drag coefficient decreased with increasing porosity, and both increased with increasing pore size. The heat transfer coefficient increased with increasing velocity and porosity, whereas it slightly decreased with increasing pore size. The results also showed that at high velocity, only the metal foam close to the heat source contributes to heat dissipation.

Near-spherical micron-porous NiTi alloys with high performances fabricated via metal injection molding

In this study, NiTi alloys with different porosity were prepared using metal injection molding combined with the powder space-holder method (MIM-PSH). The microstructures, transformation temperatures, compression and its recovery properties were investigated. The porous structure consisted of near-spherical pores (40.8 and 44.9 μm). The pore size was tied to the size of space-holder but not porosity, which was beneficial to controllability of pore diameter. The matrix was dominated by B2 austenite, with small amounts of B19′ martensite and Ti2Ni inclusions. Ni4Ti3 precipitates were also observed, not only in micrometer scale, but also as nanodomains. Highly broadened R peaks were observed in the differential scanning calorimetry thermograms, which were attributed to extensive, non-uniform, multi-scale precipitation. Overall, pores at this scale shown no influence on the transformation behaviors. Due to the low final oxygen content (0.19 % and 0.23 %) and homogeneous near-spherical pores, high compressive properties had been exhibited. The compressive recovery was almost complete at 3 %, 6 % and 8 % pre-strains. Irreversible strain increased with increasing pre-strain. The average volume variation of the pores under different deformations was analyzed in detail. In the future, MIM-PSH should be used to further enhance the customized fabrication of porous NiTi alloys.

Систематический обзор технологий производства металлической пены

Introduction. The paper presents a comprehensive overview of the manufacturing methods, materials, properties, and challenges associated with cellular metallic foams, primarily focusing on aluminum and titanium-based foams. Cellular metallic foams are gaining interest due to its unique combination of low density, high stiffness, and enhanced energy absorption capabilities. Cellular metallic foam is renowned for its special combinations of physical and mechanical characteristics, containing their increased stiffness, specific strength at high temperatures, light weight, and good energy absorption at relatively low plateau stress. It has extensive uses in the automotive, shipbuilding and space industries. It has high porosity, low relative density and high strength, which increases performance of the product. The aerospace and automotive industries require a material with a high strength-to-weight ratio. Methods. To meet this need, many metal foam production methods have been developed, such as melt route method, deposition method and powder metallurgy method. Melt route method is widely used to manufacture metallic foam as compared to other methods. Results and Discussion. In the production of aluminum foams, the melt route method is usually used. Titanium hydride (TiH2) has been a popular foaming agent, but its high decomposition rate and cost limitations have led to the development of alternative foaming agents, such as CaCO3 (calcium carbonate). Titanium foam is often manufactured using the space holder method. This method involves mixing titanium powder with a space holder material, forming a preform, and then sintering to remove the space holder and produce a porous structure as the space holder method allows for precise control over the properties of the foam, including pore size, porosity, and relative density. Results also indicate that porosity in cellular metallic foams can range from 50 % to 95 %, as reported in various journals. Pore structures can include mixed types, open cells, and closed cells, each offering different mechanical and thermal properties. It is also observed from various literature sources that relative density, which is the ratio of the foam's density to the bulk material's density, varies from 0.02 to 0.44 based on the production method used.

Mechanical and corrosion properties of highly porous Ta-Nb-Sn alloy for intervertebral disc in spinal applications

Abstract In this study, low Young’s modulus, highly porous Ta-Nb-Sn alloy foam was manufactured by using the space holder method. The aim of this study is development of an alloy with high wear resistance, with Young’s modulus, with good imaging (MRI, CT) properties, and with high bioactivity. Ta alloy foam can be used in spinal applications (intervertebral disc) or dental applications. The space holder method enables the manufacturing of open-cell foam with a low elastic modulus. Powder mixtures were prepared through mechanical alloying. Carbamide was used to form pores. Ta has suitable strength, ductility, corrosion resistance, and biocompatibility. Ta has high price, however, and a high melting temperature, high activity, and high density. Nb addition lowered the melting temperature, elastic modulus, and cost of using Ta. The sinterability of Ta was enhanced by Sn addition. The corrosion behaviour of Ta alloy was examined. Young’s modulus was determined by compression and ultrasonic tests. Tomography and radiography tests were also used.

Mechanical Evaluation of Open Pore Titanium Foam Obtained via Space Holder Method

Mechanical Evaluation of Open Pore Titanium Foam Obtained via Space Holder Method

Production and Characterization of Ta-Sn Alloy Foam for Biomedical Applications

In this study, Ta-Sn alloy foam was manufactured by using space holder method for biomedical applications. The aim of the study is development of an alloy with suitable mechanical properties, with good medical imaging (digital radiography, computed tomography) properties (radiopacity), with high bioactivity. Powder metallurgy-based space holder method enables manufacturing of open-cell foam with low elastic modulus. Powder mixtures were prepared by mechanical alloying. Carbamide was used as a pore former. Ta has suitable radiopacity, strength, ductility, corrosion resistance and biocompatibility. But Ta has high price, high melting temperature, high activity, and high density. Sn addition was lowered the melting temperature, and cost of Ta. Sinterability of Ta, which is a refractory metal, was enhanced by Sn addition. Corrosion behaviour of Ta alloy was examined. Young’s modulus was determined by compression and ultrasonic tests. Increasing Sn content of the alloy increased the Young’s modulus. Increasing porosity decreased the Young’s modulus. Ta alloy has no cytotoxic potential according to neutral red test. Sn addition was lowered the polarization resistance and slightly increased the corrosion rate of Ta-Sn alloy samples.

Preparation and investigation of porous chitosan/carbon nanotube biocomposite coating by space holder method

For implants that can be used instead of bone, a porous chitosan/carbon nanotube biocomposite coating on the titanium surface was produced by the spacer holder method. Different chemical contents and varying amounts of space-holding material were studied. Carbon nanotube fibers and pore distributions are homogeneously dispersed in the biopolymer chitosan matrix. NaCl was used as a space holder, and the rate of space holder was increased by 90 % to obtain a trabecular bone-like structure successfully. By increasing the amount of spacer in the coating content from 0.45 g to 0.90 g, the pore size has reached from approximately 1–3 μm to 12 μm. XRD, FTIR, and Raman analysis interpreted the characterization of the coatings. With the addition of carbon nanotubes to the chitosan matrix coating, the stiffness and elastic modulus increased by 55 % and 80 %, respectively. The elastic modulus (12 GPa) of the chitosan/carbon nanotube composite coating is compatible with that of cortical bone. The surface roughness of the chitosan/carbon nanotube coating reached from 1 to 6 μm to 6–16 μm, forming a porous structure. The surface properties of the porous biocomposite coating are promising for orthopedic implant applications.

Processing and surface modification of titanium open cell porous structures for PEM fuel cell bipolar plates

Bipolar plate (BP) and porous transport layer (PTL) materials and designs are critical for the performance of a proton exchange membrane fuel cell (PEMFC) and electrolyser (PEMEC) due to their role as fluid distributor and electron transporter between cells. Designs based on open cell porous structures require a good control on the porosity features. The aim of this work is to use powder metallurgy to manufacture titanium porous structures and the use of suitable surface modification techniques that can improve the performance of the PEM systems, focusing on fuel cells. Using the space holder method, porous structures of up to 63% porosity and controlled pore size can be processed to tailor the characteristics for an optimal design and, through a simple gas nitriding treatment, the performance of the material in terms of interfacial contact resistance (below 10 mΩcm2 after corrosion) and corrosion resistance (below 1 μAcm−2) are improved for both dense and porous structures.

Synthesis and characterization of gentamicin loaded ZSM-5 scaffold: Cytocompatibility and antibacterial activity.

Porous structure, biocompatibility and biodegradability, large surface area, and drug-loading ability are some remarkable properties of zeolite structure, making it a great possible option for bone tissue engineering. Herein, we evaluated the potential application of the ZSM-5 scaffold encapsulated GEN with high porosity structure and significant antibacterial properties. The space holder process has been employed as a new fabrication method with interconnected pores and suitable mechanical properties. In this study, for the first time, ZSM-5 scaffolds with GEN drug-loading were fabricated with the space holder method. The results showed excellent open porosity in the range of 70-78% for different GEN concentrations and appropriate mechanical properties. Apatite formation on the scaffold surface was determined with Simulation body fluid (SBF), and a new bone-like apatite layer shaping on all samples confirmed the in vitro bioactivity of ZSM-5-GEN scaffolds. Also, antibacterial properties were investigated against both gram-positive and gram-negative bacteria. The incorporation of various amounts of GEN increased the inhibition zone from 24 to 28 (for E. coli) and 26 to 37 (for S. aureus). In the culture with MG63 cells, great cell viability and high cell proliferation after 7 days of culture were determined.

Preparation and Heat Dissipation Properties Comparison of Al and Cu Foam

The space holder method, a kind of powder metallurgy method which can avoid the process of melting metal to prepare metal foams, has particular significance in solving the difficulty of preparing metal foams with high melting points. In this paper, Na2S2O3·5H2O, a novel space holder, was used to prepare aluminium foam and copper foam, which were then used to test the heat dissipation performance of the metal foams. We first prepared two kinds of cell structures for (spherical cell and composite cells) aluminium and copper foam, then, we compared the performances of their heat dissipation, and it was found that both the spherical cell metal foam and composite cell metal foam promoted heat dissipation in the environment of natural convection, and the difference between them was not apparent. In the environment of forced convection, the composite porous metal showed a better heat dissipation performance.

Manufacturing hydroxyapatite scaffold from snapper scales with green phenolic granules as the space holder material

Hydroxyapatite (HA) scaffold was made using the powder metallurgy with an use of a space holder method with a pore-forming agent from green phenolic (GP) granules. The novelty of this study was the use of GP granules as an agent that does not melt at high temperatures to avoid damaging the tangential contact between the HA powder during the sintering process. HA from snapper scales was added and mixed with polyvinyl alcohol (PVA) and ethanol to form a slurry. The ethanol content was then removed by drying at room temperature. The HA, which contained PVA, was added with GP granules as a pore-forming agent in various amounts to get the desired porosity. The green body was made using a stainless steel mold with the uniaxial pressing process under a pressure of 100 MPa. To make a scaffold sintered body, a sintering process ran at 1200 °C with a holding time of 2 h while maintaining the heating and cooling rates at 5 °C/min. The physical properties of the scaffold sintered body were characterized through linear shrinkage test, pore measurement, porosity test, phase observation by X-ray diffraction (XRD), and microstructure observation by scanning electron microscopy (SEM) and digital microscopy (DM). So were the mechanical ones through a compressive strength test. The results showed that the sintered body had a compressive strength value of 1.6 MPa at a porosity of 60.7% with a pore size of 129–394 μm. The scaffold contained interconnections between pores at a HA:GP ratio of 55:45 wt%, which matched the condition required for cell tissue growth. The conclusion is that GP granules are good enough to be used as a pore-making agent on scaffolds using the space holder method because they do not damage the tangential contact between the HA powder during the sintering process. However, efforts are needed to remove the remaining GP ash on the scaffold.

Sintering Analysis of Porous Ti/xTa Alloys Fabricated from Elemental Powders.

The present work is focused on developing Ti-xTa porous alloys processed by the space holder method and solid-state sintering. The volume fraction of Ta ranged between 20 and 30 wt.%. The sintering kinetics was evaluated by dilatometry tests. Sintered materials were characterized by SEM, XRD and computed tomography. Porosity features and permeability were determined from 3D images, and their mechanical properties were evaluated from microhardness and compression tests. The sintering behavior and the final microstructure are driven by the Ta diffusion into the Ti, slowing down the densification and modifying the transition temperature of α-to-β. Due to β-stabilization, martensite α′ was obtained after sintering. Mechanical properties are reduced because of the β-stabilization and pore addition, being predominantly the pore effect. Permeability depended on the pore characteristics, finding values close to the human bones. It was concluded that powder metallurgy generates highly TixTa alloys with a combination of α, β and α′ Ti phases as well as remaining Ta particles that are beneficial to improve the biocompatibility and osseointegration of such materials. Being the Ti25Ta40salt alloy the most suitable for orthopedic implants because of its characteristics and properties.

Fabrication and Characterization of Porous Copper with Ultrahigh Porosity

The fabrication of porous copper with ultrahigh porosity by adding 90% spacer content was an unsolved technical problem in the field. In this study, the green compacts placed on a layer wire mesh during the decomposition process of needlelike carbamide as space holder with volume content up to 90% was successfully conducted to fabricate nondestructive porous copper. Compared with the green compacts directly placed on an alumina plate, the use of this support was crucial for manufacturing highly-porous copper. Characterization of macro- and microscopic morphologies as well as quasi-static compressive test for the obtained porous copper samples was carried out. The results show that the porosity of porous copper samples with 87.3% was slightly smaller than the spacer content. The SEM observation indicates that the internal pores of porous copper formed an open-cell structure and its skeleton was very dense. The compressive tests show that the stress–strain curve of a porous copper sample exhibits the typical characteristics of elastic-plastic metal foam. The energy absorption properties of porous copper samples were also comparable. This study provides a possibility for the preparation of porous copper and other metals with ultrahigh porosity by the well-known space holder method.

Antibacterial Activity and Cell Responses of Vancomycin-Loaded Alginate Coating on ZSM-5 Scaffold for Bone Tissue Engineering Applications.

Despite the significant advancement in bone tissue engineering, it is still challenging to find a desired scaffold with suitable mechanical and biological properties, efficient bone formation in the defect area, and antibacterial resistivity. In this study, the zeolite (ZSM-5) scaffold was developed using the space holder method, and a novel vancomycin-loaded alginate coating was developed on it to promote their characteristics. Our results demonstrated the importance of alginate coating on the microstructure, mechanical, and cellular properties of the ZSM-5 scaffold. For instance, a three-fold increase in the compressive strength of coated scaffolds was observed compared to the uncoated ZSM-5. After the incorporation of vancomycin into the alginate coating, the scaffold revealed significant antibacterial activity against Staphylococcus aureus (S. aureus). The inhibition zone increased to 35 mm. Resets also demonstrated 74 ± 2.5% porosity, 4.3 ± 0.07 MPa strength in compressive conditions, acceptable cellular properties (72.3 ± 0.2 (%control) cell viability) after 7 days, good cell attachment, and calcium deposition. Overall, the results revealed that this scaffold could be a great candidate for bone tissue engineering.

Hydroxyapatite Scaffold Manufacturing under the Space Holder Method: Analysis of Physical Properties and Biocompatibility

The space holder method was applied to the manufacture of hydroxyapatite (HA) scaffolds by a pressureless sintering process. The aim is to develop the stages of making scaffold using the space holder method and to prove the readiness of the scaffold, especially from its physical properties and biocompatibility. The novelty of this work is the stages of processing scaffold materials in the form of slurries to produce green body scaffolds. Micron- and nano-sized HA powders were mixed in the form of slurry with polyvinyl alcohol (PVA) and ethanol. The PVA-containing HA was added with polymethyl methacrylate (PMMA) to have ratios ranging from 90:10 wt% to 65:35 wt%. The green bodies were prepared by uniaxial pressing at 200 MPa. The sintering was carried out by preheating at temperature of 700°C with a holding time of 1 h. The temperature was then increased to 1200°C with holding time of 3 h (heating rates were maintained at 5°C/min). The HA scaffolds were characterized by observing the phase, microstructures, and macrostructures; measuring the pores, testing their porosity and compressive strength. The biocompatibility properties were analyzed by testing for direct toxicity. The results indicated that the HA scaffolds made in this study met the standards since the compressive strength value was 2.23 MPa with 65.64% porosity and 126 μm to 385 μm pores size. SEM image showed the interconnection between the pores, the HA scaffolds made were non-toxic. The resulting scaffold has a great potential for further testing in living organisms.