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Highly porous SiOC ceramic foams with gradient or uniform macrostructures were obtained through polymer derived ceramic routes. Precuring of preceramic polymers and introduction of SiO2 powders were used to tailor precursor viscosity and hence SiOC foam macrostructure. Effects of polymer viscosity on porosity, pore size, pore distribution were investigated by light microscopy and micro-computed tomography techniques. SiOC ceramic foams. Foams from one unmodified precursor, showed pore size gradient with small pores located at bottom and large pores at the top. To address this non-uniformity, the viscosity of the precursor was increased by pre-curing the preceramic polymer, which resulted in decrease of the average pore size and improvement in pore size uniformity. For a different system with a self-foaming preceramic polymer, because of the simultaneous release of foaming gases and rapid increase in viscosity during crosslinking, the foam had non-uniform macrostructure with large pores and thick struts at the bottom. By addition of SiO2 fillers, the crosslinking reaction rate was reduced leading to homogeneous pore nucleation and uniform small pore size foams.

Silica aerogels are low-density, low-thermal conductivity, and highly porous solids used in a wide range of applications. In the present work, the glass fibers-reinforced silica aerogels nanocomposite models were investigated for thermal conductivity using molecular dynamics (MD) simulations. Here, the glass fibers weight percentage (% wt) was varied from 2.14 to 21.20%, i. e., the density of the silica aerogel nanocomposite ranged from 252 to 307 kg m−3. The thermal conductivity increases with the % wt of glass fibers for the considered range. However, the increase was insignificant, i. e., from 0.0357 to 0.048 W m−1 K−1. Moreover, the thermal conductivity varies with the density of nanocomposite according to a power-law with an exponent of 1.90 ± 0.18. Furthermore, the obtained thermal conductivity values of silica aerogels and their nanocomposites are in good agreement with experimental and computational studies. The outcome shows that the glass fibers-reinforced silica aerogels nanocomposites can be used for low-thermal conductivity applications.

Geopolymers, composed of an amorphous three-dimensional inorganic network and synthesized by the activation of a solid alumino-silicate precursor with an alkaline activating solution, have attracted increasing attention because of their environmental benefits and favorable characteristics. This review deals with the development of organic/inorganic composite materials made by adding organic liquids into inorganic geopolymer matrices. Firstly, the incorporation processing approaches are presented and are divided into three categories: (i) Direct incorporation, (ii) Pre-emulsification (iii) Solid impregnation. Their main advantages and drawbacks are discussed in relation to the aimed properties. Secondly, this review highlights that geopolymers are low-cost candidates allowing technologically significant applications, through the incorporation of various organic liquids. Aside from the well-studied immobilization of industrial waste streams commonly known as stabilization/solidification (S/S), the development of highly porous geopolymer foams and the design of reinforced organic/inorganic composite matrices are being notably investigated. This review aims at summarizing the main published results, and fostering further investigations into innovative uses of organic liquids incorporated into geopolymers for a wide range of applications.

The highly porous silica ceramics were fabricated by direct foaming with mixed surfactants and the influence of silicon nitride addition and solid content on the microstructures and properties were investigated. The results showed that silicon nitride can impede the formation of cristobalite and facilitates the sintering of silica ceramics. When the addition of silicon nitride powders reached 15 wt%, the highest compressive strength of silica ceramic foams could be obtained. The porosity of silica ceramic foams was tailored in the range of 84.61%–91.35% by adjusting the solid content, and the compressive strength of the obtained ceramic foams ranged from 5.89 MPa to 0.94 MPa. Sound absorption characteristics of silica ceramics foams were investigated. With the porosity of ceramic foams increased from 84.61% to 91.35%, the sound absorption coefficients in the entire sound wave frequency were enhanced due to the reduction of flow resistances, besides, the sound absorption peak varied from 4200 Hz to 2300 Hz, and became more intense and sharper.

Cellular ceramics with 3D network architecture are attracting ever-increasing attention because of their great application potential in multiple fields. Unfortunately, a daunting challenge still remains for fabricating such materials. A novel methodology is provided in the current work to construct cellular ZrO2 ceramics with such architecture by combining polyurethane foaming and chemical modification technology. Stearic acid grafted ZrO2 powder with improved dispersibility allows the successful assembly into the polyurethane porous framework. The obtained cellular materials possess a three-dimensional network architecture with windows on the cell wall. The resulting ZrO2 cellular ceramic with such unique structure exhibits a relatively high porosity (83.5%) and robust compressive strength (13.5 MPa), which outperforms most of the existing ZrO2-based counterparts. With above advantages, we envision that as-prepared products are promising for filter applications.

The mechanical strength of highly porous ceramic foams shows significant attenuation with the increase of porosity, especially for ceramic foams with very high porosity level above 95%. Ultra-light bulk composite ceramic foams were fabricated via introducing 20 wt% zirconia in alumina-based cell wall, aiming at improving mechanical strength of alumina based ceramic foams. The preparation and stability of alumina and zirconia particles synergistically stabilized foams were investigated. The obtained bulk ceramic foams manifested an exciting combination of both high porosity above 96% and excellent specific compressive strength, due to their closed pore structure, defect-free cell wall with uniform thickness, and uniformly distributed zirconia grains in alumina matrix. The alumina/zirconia composite ceramic foams with porosity of 96.7% exhibited compressive strength of 1.11 ± 0.07 MPa, which was much higher than that of alumina ceramic foams in the case of same porosity.

Three dimensional bioceramic scaffolds can be produced by several fabrication methods. Selecting the appropriate fabrication method requires a detailed investigation to produce scaffold with required properties. The present study aims to compare five different fabrication methods which are replication methods, combination of sacrificial template and direct foaming, freeze casting, gelate-freeze casting and salt leaching. Here, the discussion centers on comparison of these five fabrication methods, their respective advantages and disadvantages and parameters involve in the fabrication methods. Morphology and mechanical properties of the β-tricalcium phosphate (β-TCP) scaffold produced from these methods were compared and discussed. Highly porous β-TCP scaffolds with porosity of more than 50% and pore size of at least 100 µm have been fabricated using these methods. The compressive strength of the fabricated scaffolds is in the range of 0.05–2.0 MPa. It is observed that the properties of β-TCP scaffolds are influenced by the raw materials required by each of the processing, solid concentration and processing parameter. In conclusion, the gelate-freeze casting fabrication method with cellular structure shows the higher compressive strength and comparable pore size and porosity compared to other fabrication methods.

The novelty of this work is the production of nano- and submicrometric silica and spinel-ferrite fibers using the solution blow spinning (SBS) method. A pseudo-core-shell method for the production of large surface area silica fibers is also reported. Silica fibers present mean diameters and specific surface areas ranging from 280 nm to 640 nm and from 140 m2/g to 630 m2/g, respectively, while spinel-ferrite fibers of nickel ferrite and nickel-zinc ferrite show mean diameters of 180 nm. Spun materials display a cotton-like morphology and are produced at higher output rates than those achieved by current spinning technologies.

Compressive strength is one of the most important mechanical properties for ceramic foams but the dependence of compressive strength of highly porous ceramic foams on porosity remains unclear up to now, especially for the ceramic foams with porosity above 94%. In this paper, the relationship between compressive strength and porosity of ceramic foams with high porosity in the range of 79–98% was studied for the first time. The alumina ceramic foams and zirconia foams were prepared by particle-stabilized foaming method using sodium dodecyl sulfonate (SDS) as foaming agent. It was found that the function relation between compressive strength and porosity depended on porosity level. Specifically, compressive strength of ceramic foams fitted well with Rice Model when the porosity ranged from 79% to 94%. When the porosity increased above 95%, compressive strength of ceramic foams showed linear relation to porosity, which was probably due to the characteristic of highly porous ceramic foams with thin and lamellate cell wall.

The present work demonstrates a very simple and unique strategy for efficient photocatalysis using ZnO ceramic nano- and microtetrapods synthesized by a flame transport synthesis approach. Due to their three-dimensional (3D) morphology, highly porous interconnected networks as flexible ceramics with sufficient mechanical strength can be easily fabricated and efficiently utilized in applications like e.g., photocatalysis, liquid filtering, and membranes. The photocatalytic response can be further enhanced by hybridization of the ZnO tetrapods with different metal oxides which has been explored in detail here. The Cu- and Bi- hybridized ZnO tetrapodal ceramic networks showed the least and highest photocatalytic activities against methylene blue, respectively, whereas, the others exhibited intermediate responses. The observed photocatalytic behaviors of pure and hybrid ZnO tetrapods based flexible ceramic 3D networks are briefly presented and discussed.

In this article, V 2 O 5 with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V 2 O 5 with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V 2 O 5 electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g −1 (at a current density of 100 mA g −1 ) could be delivered and a stable discharge capacity of 240 mAh g −1 after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.

This study demonstrates a novel, simple way of synthesizing bone morphogenetic protein (BMP)-loaded hydroxyapatite (HA) microspheres for enhanced bone regeneration. To accomplish this, calcium phosphate cement (CPC) microspheres, consisting of α-TCP and TTCP powders, were prepared using water-in-oil (W/O) emulsion, followed by treatment at 37 °C for 3 days to convert the CPC to HA. The BMP-loaded HA microspheres with a well-defined spherical shape had a highly porous structure, which was created by the entanglement of precipitated HA crystals with a needle-like morphology. The unique porous structure with the bone mineral-like HA phase resulted in a considerable improvement in in vitro biocompatibility. In addition, the bone regeneration ability of the HA microspheres was significantly enhanced by BMP loading, which was examined by in vivo animal testing using a rabbit vertical guided bone regeneration model.

Three-dimensional (3D) macroporous hydroxyapatite (HAp) ceramics were fabricated via a facile emulsion templating technique for bone tissue engineering applications. The prepared scaffolds have an open, uniform, and 3D fully interconnected pore structure with high porosities, mechanical strength, and a large surface/volume ratio. The porous structure, which is composed of an array of quasi-spherical large cells interconnected through windows, has a pore diameter in the range of 5–30 μm. The samples sintered at the optimal temperature (1200 °C) have an open porosity of ~76.5% and a high compressive strength of 4.26 MPa. The technique discussed here is a significant advancement over other previously used methods to produce HAp ceramics and is expected to enable much improvement in the topology of the porous structure of scaffolds.

Porous alumina ceramics with ultra-high porosity were prepared through combining the gel-casting process with the pore-forming agent technique. Porosity and pore size distribution of the sintered bulks were evaluated with and without adding starch, respectively. In particular, the influences of starch addition on the properties, including thermal conductivity and compressive strength were studied. It was found that the incorporation of starch increased the nominal solid loading in the suspension and subsequently promoted the particle packing efficiency. The porosity is raised with increasing starch content from 0 to 30 vol%, which brings the decrease in thermal conductivity, whereas the compressive strength isn't seriously degraded. The further higher starch addition (40 vol%), however, would deteriorate the performance of the alumina porous ceramics. It is believed that the appropriate starch amount (lower than 30 vol%), working as a pore-forming agent, suppresses the driving force of densification without affecting the connections of neighboring grains while excessive starch amount would lead to the collapse of the porous structure.

Porous silicon nitride ceramics having properties similar to the human trabecular bone have been sintered and characterized in order to develop a material applicable as bone substitute. At first, human trabecular bone was characterized especially in terms of pore structure which is, besides the non-toxicity, the most critical for acceptation of the substitute. The pore network of highly porous trabecular bone is formed by interconnected large pores of approximately 300–1000 μm. Similar pore structure of silicon nitride-based ceramics was attained by the replica method with polyurethane sponge as pore forming agent. Porous ceramics were prepared in two ways, namely as air-sintered silicon nitride and sintered reaction-bonded silicon nitride. The materials were characterized using the same methods as for the human bone samples. Both types of ceramic materials fulfilled the microstructural requirements for bioapplications. Moreover, their non-cytotoxicity was proved by measuring the yellow tetrazolium MTT proliferation assay using human fibroblast cell line.

Hydroxyapatite (HAp)-based highly porous integrated orbital implants with a property of mimicking the movements of fellow eye have been developed recently. Before designing this kind of scaffolds, vascularization and angiogenesis in the constructs need to be considered. Moreover, eye cells expressed with time on these highly porous implants may exert some compressive load whose effect both mechanically and physiologically may indicate its long-term life in vivo. In the present investigation the effect of expression of eye cell lines [rabbit corneal epithelial cell line (SIRC)] on highly porous HAp scaffolds were compared with the normal fibroblastic cells on HAp in general, in terms of in vitro dissolution studies, cell culture cytotoxicity and cell adhesion properties. Elastic properties of macro-porous HAp with a wide range of porosities have also been estimated by ultrasonic non-destructive test methods and the results were compared with its compressive properties for potential application as integrated ocular implants. Cell viability of HAp in contact with SIRC is far better than the L-929 during the initial periods (48 h) but cell adhesion behavior however showed better results in L-929 than the SIRC during the same initial time period. SIRC cells however eventually formed better adhesion properties on the surface of HAp as the days goes by than L-929. High concentration of both Ca and P in culture media might be another factor in cell growth modification. Both the ions had a counter effect on the L-929 and SIRC cells.

Novel graded porous Si 3 N 4 ceramics with different solid content have been fabricated by a new water-based freeze-casting method. A 25 μm-thick surface dense layer on the porous layer was successfully formed without any noticeable defects. A great number of fibrous grains protruding from the internal walls of the macroscopic aligned channels were observed in the porous Si 3 N 4 samples with 20–25 vol.% solid content, but little fibrous grains were formed in the sample with 15 vol.% solid content at the similar processing route. As the solid content increasing from 15 to 25 vol.%, the porosity decreased from 76.8% to 66.4%, while the flexural strength and dielectric constants at 10 GHz increased from 14.3 MPa to 33.5 MPa and 1.78 to 2.64, respectively. The dense/porous Si 3 N 4 ceramic is feasible in broadband radomes application at high temperature due to ultra-low dielectric constants and moderate strength.