Apparent Porosity Research Articles

Synthesis, characterization and corrosive resistance of ZnO and ZrO2 coated TiO2 substrate prepared via polymeric method and microwave combustion

The TiO2 substrate coatings containing varied ZnO or ZrO2 nanoparticles were made using the polymeric and microwave combustion methods and then thermally treated at various temperatures. Furthermore, before coating on the substrate, the produced nanoparticles undergo characterization and calcination to optimize the conditions for developing ZnO and ZrO2 phases and track their composition. The X-ray diffraction method (XRD), transmission electron microscopy (TEM), and infrared analysis (IR) are used to characterize the calcined produced nanoparticles. After heat treatment at 1000 °C, the TiO2 substrate is prepared. The produced coated substrate is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared (IR), apparent porosity, bulk density, chemical corrosive properties and electrochemical measurement in 3.5 % NaCl and 1 M HCl solutions. The corrosion resistance of ZnO or ZrO2-covered TiO2 substrate is ascertained by anticorrosive behaviors, which include weight loss, apparent porosity, corrosion rate, and SEM. The findings showed that 800 °C is the ideal temperature for preparing ZrO2-coated substrate, whereas 1000 °C is the perfect temperature for preparing ZnO-coated substrate. The microstructure reveals surface micro-cracks on the ZrO2-coated TiO2 substrate. Good dispersion, homogeneity, and compaction were noted for the ZnO-coated substrate. Between 14 and 17 % of the ZnO-coated substrate and 20–21 % of the ZrO2-coated substrate, made via polymeric and microwave combustion techniques, had visible porosity when ZnO-coated samples exhibited greater corrosion resistance against NaCl media. In contrast, ZrO2-coated samples had much stronger anticorrosive qualities in HCl media than uncoated and Zn-coated samples. According to the electrochemical results, the ZnO-coated TiO2 synthesized by polymeric technique at 1000 °C showed 99.86 % inhibitory efficiency against NaCl. An inhibitory efficiency of 94.4 % was observed in a ZrO2-coated TiO2 substrate that was produced at 800 °C using a polymeric technique.

Effect of ferrotitanium slag particle size on properties of Al2O3–SiC–C castables

Ferrotitanium slag can be used to replace bauxite to fabricate refractories owing to its high refractoriness (>1790 °C) and Al2O3 content (≥70 wt%). However, impurities in the ferrotitanium slag is harmful to the materials. In this paper, the mechanical properties and molten slag resistance of Al2O3–SiC–C castables were improved by replacing part of bauxite with large size ferrotitanium slag (8-5 mm). The large size ferrotitanium slag contained a small amount of impurities, which reacted with SiO2 at high temperature to form CaO–Al2O3–SiO2–TiO2 liquid layer on the surface of particles. Under the action of the liquid phase, the ferrotitanium slag particles and the matrix were combined more closely. With the decrease of the particle size of ferrotitanium slag, the slag resistance of the castables began to decrease. This was because the specific surface area of the particles with smaller particle size was relatively larger, large contact area with molten slag resulted in worse slag resistance. Meanwhile, decreasing ferrotitanium slag particle size brought the increase of apparent porosity of Al2O3–SiC–C castables, resulting in weak mechanical properties.

Sustainable valorization of mining waste: Phosphate sludge repurposing for advanced ceramic production

Managing the vast quantities of waste constantly generated by mining activities is one of the major environmental and economic problems facing mankind today. Fluorapatite is separated from the associated gangue minerals by a series of crushing and screening, washing, and flotation processes. These processes produce a significant amount of phosphate sludge, which is stored on the mine site in drift rock and large surface ponds. One possible environmental option is to reuse it as an alternative raw material in ceramics and building materials. Consequently, two phosphate sludges from two different Moroccan towns, Youssoufia and Khouribga, were studied. Due to the complexity of these raw materials resulting from long geological processes, in-depth physical, chemical, mineralogical, and thermal characterization is required. Dry compressed powder pellets were sintered at 900 °C, 1000 °C, and 1100 °C for 2 h. The study focuses on the effect of sintering temperature on mineralogical transformations and ceramic properties such as apparent porosity, water absorption, and mechanical strength. At 1100 °C, a slight increase in density was observed for both phosphate sludges. Water absorption was reduced by 2.51 % in both sludges for pellets sintered at 1100 °C compared to those sintered at 900 °C. Mechanical strength improved significantly, with an increase of about 60 % for samples sintered at 1100 °C, recording 227 N for Youssoufia sludge and 247 N for Khouribga sludge. This work has provided new data on the physical, chemical, mineralogical, and thermal changes in ceramics as the sintering temperature increases. These data will be useful for the manufacture of high-value ceramics.

Engineering and microstructural properties of environmentally friendly alkali-activated composites containing clinker aggregate: heat-curing regime and elevated-temperature effect

The common wisdom in the literature about clinker aggregate (CA) is that it improves the performance properties of mortar or concrete to some extent. The current study, in this context, investigated the physical characteristics and mechanical performances of alkali-activated composites (AACs) made entirely with CA. The CA was used in three particle sizes of 0–2 mm (named No.10), 2–4 mm (named No.5), and 4–8 mm (named medium). To examine the impact of the fine CA-size fraction on the characteristics of AAC, No.10 CA was partially replaced by No.5 CA up to 50%, while the content of the medium CA was kept constant in all AAC mixtures. Moreover, to evaluate the influence of the 8-h curing temperature on the performance of the AACs, different temperature-based curing strategies (ambient, 45, and 75 °C) were applied to the AACs. In the production of AACs, granulated blast furnace slag was employed as an aluminosilicate-rich raw material, and a sodium silicate and sodium hydroxide combination was used as an alkaline activator. Physical properties (flowability, water absorption, capillary water absorption, and dry unit weight), and 8-h strength performances (flexural and compressive) were determined. Furthermore, to monitor the influence of high temperatures on the characteristics of the AAC, the mixtures were exposed to elevated temperatures (200, 500, and 800 °C). In SEM image analysis, it was determined that spherical CSH gels were formed in the heat-cured AACs. It has been observed that the geopolymerization products decompose in AACs exposed to 800 °C. To evaluate statistically the experimental results, a multi-factor analysis of variance (ANOVA) was also applied. The results revealed that increasing the coarser fine aggregate fraction led to higher water absorption and apparent porosity capacities and lower unit weight. Besides, strength performance was improved by applying a heat-curing strategy to the AAC, whereas a decrease was observed by increasing the No.5 CA fraction. There was a remarkable reduction in compressive strength and considerable loss of mass when the AAC mixes were exposed to high temperatures.

Superior comprehensive performance CaO‐based core achieved by optimizing particle gradation via orthogonal experiments

AbstractThe effect of CaCO3 particle size on the viscosity of slurry, phase formation, microstructural evolution, and performances of the water‐soluble CaO‐based ceramic core sintered at different temperatures was systematically investigated and discussed, and the particle gradation orthogonal experiments were used to adjust flexural strength, water‐soluble rate, shrinkage rate, apparent porosity, and hygroscopicity rate. The results showed that the finer particle size increased the effective contact area between CaO and SiO2, which promoted the generation of CaO–SiO2 system phase and the dense microstructure in the sintered CaO‐based cores. The higher sintering resulted in dense microstructure. The optimal gradation scheme included 28 wt.%, 56 wt.%, and 16 wt.% CaCO3 powder with D50 = 11.0 µm, 6.17 µm, and 4.62 µm, respectively, and the resulting flexural strength was 9.57 MPa, water‐soluble rate was 65.37 g/h in 60°C water, shrinkage rate was 8.62%, porosity rate was 38.85%, presenting a well‐balanced comprehensive performance, which is significant for the complex internal castings.

Impact of mineralization in Hevea brasiliensis fibers on the production of extruded fiber-cements with cellulosic micro/nanofibrils (MFC/NFC) and quartzite residues

New processes and applications for waste generated in forestry and mineral activities favor the circular economy and reduce pressure on conventional raw materials, thus promoting the sustainability of activities. This research aimed to apply quartzite powder to replace limestone and fibers and cellulosic micro/nanofibrils (MFC/NFC) from Hevea brasiliensis as reinforcement in extruded fiber-cement. To improve fiber/matrix compatibility, some fiber treatments with NaOH and Aℓ2(SO4)3 + C6H8O7 were also evaluated. The fiber cements were produced by an extrusion process using a formulation of 66.5 % of CPV-ARI Portland cement, 28.5 % of quartzite powder and 5 % of fiber reinforcement. The physical (apparent density, water absorption, and porosity), mechanical properties (modulus of rupture, modulus of elasticity, limit of proportionality, and toughness), thermal conductivity, and microstructural properties of the fiber-cements were evaluated after 28 days of curing. Treatments with 5 % fibers exhibited better mechanical performances. It was possible to improve the microstructure and physical-mechanical performance of the composites using small amounts of MFC/NFC (0.5 %). Quartzite positively affected the properties and provided thermal comfort (∼0.11 W/mK). Therefore, the materials showed promise for producing extruded fiber-cement composites.

Oxygen transport mechanism and the effect of microstructure on the oxygen response behavior of an oxygen-sensitive composite Ce0.9Gd0.1O2-ẟ – La0.6Sr0.4FeO3-ẟ at high temperature

Compositions like gadolinium doped cerium oxide Ce0.9Gd0.1O2-ẟ and strontium doped lanthanum ferrite La0.6Sr0.4FeO3-ẟ, or their composites are well known in the field of fuel cell electrolyte, oxygen transporting membrane and catalytic reactor applications. This work offers insight into composite material's oxygen response characteristics, taking Ce0.9Gd0.1O2-ẟ and La0.6Sr0.4FeO3-ẟ in 70: 30 wt percent. One pot sol-gel method was employed for the powder synthesis. The powder was characterized by TG-DSC, XRD, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). FESEM-EDX and EDX-line profiling techniques were used to check the compositional homogeneity of sintered bodies. Oxygen response tests were conducted from ambient (20 % O2) to 100 % O2 concentration, using bulk samples sintered at three different temperatures, i.e., 1000, 1150, and 1250 °C at a fixed soaking time of 4 hours. The sintered specimens' apparent porosity, bulk density, surface morphology, and electrical conductivity were also examined. The sintering temperature significantly impacts response behavior as the porosity and grain size of the sintered body plays a vital role in sensing performance. The mechanism of response towards oxygen is also discussed. Sample 73–100 displayed the best performance among others. We achieved the lowest response and recovery time of 15 – 48 sec and 45 – 80 sec from a 0.60 mm thick bulk material at 950 °C. Harsh environments were intentionally created to check the reliability and reproducibility of the response data. This material could be a good candidate as an oxygen gas sensor at high temperatures owing to its good sensitivity, reliability, reversibility, and stability.

Raw material design, sintering temperature optimization and development mechanism investigation of self-foaming porous bricks with high solid waste addition

In recent years, the contradiction between the huge production of municipal sludge and industrial residue and the shortage of landfill space has driven the exploration of novel effective methods to valorize these solid wastes. In this research, blast furnace slag (BFS), municipal sewage sludge (MSS) and kaolin are combined innovatively as precursor materials to manufacture self-foaming porous bricks, and the sintering behavior of bricks under different BFS doses and sintering temperatures is deeply studied to reveal the development mechanism. The results indicate that the formation of Fe2O3-hematite during sintering leads to a reddish-brown appearance of the bricks, while the generation of CaAl2Si2O8-anorthite with lower melting points helps to enhance the vitrification process. Besides, the increase in BFS dose or sintering temperature has significant impacts on the evolution of the brick physicochemical properties. This occurs because changing the dose of BFS or sintering temperature can obviously regulate the internal morphological characteristics of bricks, such as particle consolidation, pore size and structural compactness. Among them, large-sized pores are considered as the weak areas of mechanical strength, which is also the responsibility for the worst compressive strength of bricks sintered at 1300 °C. Finally, under the optimal sintering conditions of 15 % BFS dose and 1250 °C sintering temperature, the compressive strength, water absorption, apparent porosity, bulk density and linear shrinkage of the resulting brick are 65 MPa, 0.45 %, 2.50 %, 2.34 g/cm3 and 19.56 %, respectively. Overall results demonstrate that using recycled sludge and waste slag in brick manufacturing can produce products with desired performance, providing preferable solutions for solid waste valorization and sustainable brick production.

Study of Physical Properties and Alterability of Natural Stones and Artificial Agglomerated

Objective: This work aims to evaluate the physical and alterability properties such as resistance to staining and chemical attack of two natural stones (Siena White and White Marble) and two artificial agglomerated stones (Aldan White and Galaxy White), using Brazilian technical standards as methodology. ABNT NBR 15845 (2015), NBR 16596 (2017) and NBR 10545 (2017). Theoretical Framework: Ornamental stones, such as granite, marble and quartzite, are valued in construction and decoration for their durability and natural beauty. Artificial agglomerated stones are industrially produced to imitate the appearance of natural stones, offering additional advantages such as greater uniformity and resistance. Both options have their various aesthetic and functional applications. Method: Ten specimens measuring 60 x 60 x 20 mm were used for each material. Apparent density, apparent porosity and water absorption tests were carried out. To determine resistance to chemical attack, ABNT NBR 16596 (2017) was used, where the stones were exposed to a variety of chemical agents. The determination of stain resistance was carried out according to the ABNT NBR 10545-14 (2017) standard in an adapted form. The samples were exposed for 24 hours to penetrating agents and household products. Subsequently, the material was classified according to the ease of removing stains, after the cleaning steps described in the standard. Results and Discussion: The results showed that natural stones and artificial agglomerates were satisfactory in meeting the requirements of the ABNT NBR 15844 (2015) standard, as the lower porosity and reduced water absorption generally make these materials more durable and easier to maintain, especially in environments where the Exposure to moisture and liquids is an important factor, such as in kitchens and bathrooms. Research Implications: Evaluate the physical indices, staining and chemical attack of natural stones and artificial agglomerated stones produced by the industry. Originality/Value: Carry out tests on natural stones and artificial agglomerates in materials sold in industry and certify their technological characteristics through tests established by Brazilian standards.

Microstructure and properties of in situ TiC-reinforced Ti750 composite prepared by SPS

Purpose Titanium alloys and composites have proven to contain desirable properties for use at elevated temperatures. One such material is the Ti750 composite, which can be used at temperatures up to 750°C for a brief period. This paper aims the microstructure, phase compositions, apparent porosity and hardness of both sintered and heat-treated TiC reinforced Ti750 composites for consideration in aircraft engine design. Design/methodology/approach The fabrication of TiC-reinforced Ti750 composites was achieved through spark plasma sintering (SPS). To analyze the microstructure and X-ray diffraction, a scanning electron microscope (SEM) with model number S-3400N and a D8 advance model machine were used, respectively. The microhardness of the samples was measured using a Vickers hardness tester with model HV-1000. The research incorporated three solid solution treatments: 975°C/3 h/AC, 1,010°C/3 h/AC and 1,025°C/3 h/AC, along with a solid-solution aging treatment at 1,010°C/3 h/AC + 750°C/8 h/AC. Additionally, oxidation analysis was conducted on the samples. Findings The microstructures contained enhanced TiC and Ti5Si3 phases in the near a-Ti matrix. The microhardness of the sintered composite was over twice that of the matrix alloy, and its porosity was reduced by about 0.35%. The sample treated at 1,010°C/3 h/AC had the highest enhanced peaks and microhardness of 1,277.1 HV. After oxidation at 800°C for 100 h, the accumulated weight of the solid solution composite at 1,010 °C/3 h/AC was the lowest (3.0 mg.cm-2). The surface microstructure contained oxides of TiO2 and a spalling white area containing a small amount of Al2O3 and SiO2. Originality/value There is limited research on Ti-Al-Sn-Zr-Mo-Si-based TMCs using a combination of the SPS method. This study used SiCp as a reinforcement for the Ti750 matrix alloy. The consolidation of SiCp and Ti750 powders using the SPS method, heat treatment of the resulting TiC reinforced Ti750 composites and study of the microstructure and properties of the composites are not found in literature or under consideration for publication in any media.

Comparative analysis of the technological properties of natural and agglomerated stones in epoxy matrix

Brazil occupies a prominent position among the countries that produce the most ornamental stones in the world, with emphasis on the state of Espírito Santo. However, despite this success in production, the sector faces a considerable challenge in relation to waste generation. The objective of this study was to produce and evaluate the technological properties of an agglomerated stone using 87 wt% waste from the processing of Branco Fortaleza stone in a matrix with 13 wt% epoxy resin, using the vacuum vibro-thermo-compression process. The waste was characterized by X-ray fluorescence (XRF) and X-ray diffraction (XRD). The stones were subjected to evaluation of density, apparent porosity, water absorption, abrasion resistance test, staining, chemical attack, 3-point flexural strength and microstructural analysis (SEM). The results showed a density of 2.26 ± 0.02 g/cm3, water absorption of 0.24 ± 0.01%, apparent porosity of 0.55 ± 0.03%, abrasion resistance test of 1.38 mm and flexural strength of 30.13 ± 1.74 MPa. The results compared with the literature reveal a material with technical feasibility to be used as a coating in the construction sector, presenting high mechanical resistance, good interfacial adhesion, application on high traffic floors, as well as environments subject to liquid penetration such as sinks, floors and countertops. Using this waste to manufacturing new materials, such as agglomerated stones, can not only help reduce dependence on raw materials, but also play an important role in minimizing the environmental impact associated with the extraction and processing of natural stones.

Effects of Alumina Bubble Addition on the Properties of Corundum-Spinel Castables Containing Cr2O3.

Purging plugs made of corundum-spinel castables containing Cr2O3 have been widely utilized in secondary refining process. However, their poor thermal shock resistance has greatly limited the improvement of their service life. Aiming to enhance their properties, we introduced alumina bubbles (ABs) to corundum-spinel castables, and the effects of the AB addition on the properties of the castables are studied in this manuscript. The results indicate that the apparent porosity, permanent linear change, cold strength, and hot strength all increased with an increasing AB amount. The thermal shock resistance of the samples with the AB addition was improved; the residual strength and residual strength ratio of the sample with 4 wt% ABs was the best. The effects of ABs on the tabular alumina aggregate distribution and relationship between the cold strength of the samples and the AB content was evaluated via the box dimension method. With the increments of AB content, the box dimension value of the tabular alumina within the samples significantly decreased, indicating that the tabular alumina aggregate distribution was related to the amount of ABs. In addition, the relationship between the box dimension and the strength was also established.

Effect of carbon nanofibers fabricated from electrospun PAN precursors on the characteristics and densification of MgO–CaO ceramic systems

MgO–CaO composites are basic materials with high melting points, high chemical resistance to alkaline environments, clean steel production, environmental friendliness, and abundant sources. In the current work, carbon nanofibers (CNFs) with diameters between 150 and 270 nm were prepared at different temperatures (up to 1200 °C) by carbonization of electrospun polyacrylonitrile (PAN) precursors. Then, the MgO–CaO composites were prepared in two steps. First, 3 wt% CNFs carbonized at different temperatures were added to the composite to determine the optimal carbonization temperature. Subsequently, the physical properties (apparent porosity and bulk density) and mechanical properties (flexural strength (FS) and cold crushing strength (CCS)) of the MgO–CaO-CNF composites were investigated. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDS), and thermogravimetric analysis (TGA) were used to analyze the composition, morphology, and structure of the CNFs powders and composite samples. Based on the results obtained, such as the percentage graphitization, length, average diameter, and morphology of the CNFs, 1000 °C was determined as the appropriate carbonization temperature for the next steps of this study. In a second step, the CNFs synthesized at 1000 °C were added to the MgO–CaO with different wt% (0, 0.5, 1, 1.5, 2, 2.5, and 3 wt%). It was found that by adding CNFs (up to 1.5 wt%) into the MgO-CaO composites, the physical properties increased due to the improvement of densification, and mechanical properties improved due to the activation of reinforcing mechanisms, the reduction of surface defects and the creation of a dense body. However, these properties decreased from 1.5 to 3 wt% due to the agglomeration and poor dispersion of the CNFs. Finally, the results illustrated that adding CNFs, even in small amounts, significantly improved the features of MgO-CaO compounds; the ideal content was 1.5 wt% CNFs.

Density and porosity analyses of porous hybrid microparticles containing gas in closed pores using centrifugal liquid sedimentation-dynamic light scattering combined analytical method.

Porous hybrid microparticles are characterized by their densities and porosities. Consequently, the evaluation for density and porosity of porous hybrid microparticles in liquids is crucial for predicting the transport of particles in the atmosphere, human body, and industrial processes. However, direct measurement of the density and porosity of porous hybrid microparticles in liquids remains a challenge. In this study, we investigated the centrifugal sedimentation of polystyrene-silica hybrid microparticles with and without gas-containing closed pores. A centrifugal liquid sedimentation-dynamic light scattering combined analytical method was employed to determine the apparent densities of hybrid microparticles with and without gas-containing closed pores. The porosity of the hybrid microparticles with gas-containing closed pores was elucidated based on the inner buoyancy, which is a centrifugal force generated by the presence of low-density gas inside numerous closed pores. Further, the inner gas buoyancy was analyzed to estimate the particle porosity in liquids. The results obtained in this study confirmed the feasibility of utilizing the proposed method to determine the apparent density and porosity of porous hybrid microparticles in liquids.

Clay influence on lightweight brick’s properties: Investigating the impact of waste’s nature and amount as secondary variables

The present study aims to examine whether incorporating a specific proportion of a particular waste material consistently yields bricks with favorable properties, regardless of the raw clay type utilized. In this context, different mixtures were produced with a clay named AMD2 and 0 wt%, 5 wt% and 10 wt% addition of two wastes named argan nut shell and wheat straw. A first investigation of the used raw clay material revealed the presence of Quartz as a dominant mineral, along with Orthoclase, Illite, and Hematite. Furthermore, the elaborated bricks have been subjected to a physical, mechanical, and structural characterization including loss on ignition (LOI), linear shrinkage (LS), water absorption (WA), apparent porosity (AP), bulk density (BD), and compressive strength (CS). A comparison between the current study and a previous one using the same waste materials and identical proportions of addition but employing a different clay type revealed notable differences in outcomes. In the previous study, bricks fabricated with AMD1 clay and 5 wt% of argan nut shell displayed excellent characteristics. However, in the current investigation using AMD2 clay, bricks with the same waste addition ratio exhibited less favorable properties. Specifically, bricks made with AMD2 clay and 5 wt% argan nut shell showed a loss on ignition of 7.30 %, a linear shrinkage of 3.7 %, a water absorption of 23.3 %, an apparent porosity of 38.20 %, a bulk density of 1.64 g/cm3, and a compressive strength of 9.90 MPa. These outcomes indicated a water absorption above the specified limit and significantly higher apparent porosity compared to bricks produced with AMD1 and 5 wt% argan nut shell, which met standard specifications. This variation highlights how the mineral composition of clay significantly impacts brick properties, even when using the same waste materials and proportions, confirming the importance of considering the raw clay material's nature in bricks’ production, and thus emphasizing the need for a preliminary study before combining clay and wastes in order to achieve excellent results.

Influence of materials and processes on the robustness of apparent porosity control methods for fair-faced concrete

Fair-faced concrete is a new type of concrete that directly uses the surface of concrete as the facing, with good surface integrity, no chiseling and repairing after forming, and no need for decoration. In recent years, it has developed rapidly after being introduced into China, but there are some problems, the stability of pore control is difficult and the formation mechanism is insufficient. It also exists chromatic aberration. Aiming at the formation mechanism of apparent pores in fair-faced concrete, by changing raw materials and mix ratio of fair-faced concrete, adjusting raw materials, construction process and formwork parameters, this paper put forward the control interval of high robustness parameters of fair-faced concrete with few apparent pores and excellent aesthetic grade. It makes it possible to prepare fair-faced concrete repeatedly and stably with a good economy. It also has good guiding significance for practical projects. The material parameters included initial gas content, maximum particle size of coarse aggregate, plastic viscosity coefficient, initial dynamic yield stress and bleeding rate. Construction process parameters included vibration frequency, vibration time and vibration amplitude. Formwork parameters included release agents with different contact angles. The results show that the initial gas content of the fair-faced concrete slurry was 2%–3%, the particle size of the coarse aggregate was 5 mm–25 mm, the plastic viscosity coefficient of the fair-faced concrete slurry was 5 Pa·s-10 Pa s, the yield stress was 100 Pa–200 Pa, the water secretion rate was 8%–10 %, and the vibration frequency was 10,000 times/min-12,000 times/min. When the vibration time was 20 s–25 s, the vibration amplitude was 1.0 mm–1.2 mm, and the contact angle was 102°–112°, the apparent porosity of the fair-faced concrete could be controlled well.

Hierarchical porous ceramics constructed by interlocked alumina platelets with hollow glass spheres as pore formers

Hierarchical porous alumina ceramics were prepared through hydratable alumina gel-casting method. The matrices were constructed by interlocked alumina platelets. Hollow glass spheres as pore formers participated in the fluorine-catalyzed structure formation process. The samples with 20 wt% hollow spheres added (1000–1300 °C) had volume densities, apparent porosities, linear shrinkages and compression strengths of 0.59–0.90 g/cm3, 81.68 %∼74.20 %, 1.40 %∼14.07 % and 12.64–23.36 MPa, respectively. Changing the fraction of hollow spheres (10–30 wt%, 1100 °C) had effects on tailoring the compression strengths (3.13–13.40 MPa), without apparently affecting the densities (0.58–0.60 g/cm3)/porosities (79.70 %∼82.28 %)/shrinkages (1.47 %∼1.93 %). The pore size distributions demonstrated the interlocking pores built by alumina platelets, the pores that inherited from the gel network, and the large pores provided by hollow spheres. The reheated (1300 °C) samples presented good structure stability with shrinkages of 6.60 %∼18.57 %. The synthesized ceramics with both high porosities and satisfactory strengths could meet the requirements of high temperature gas/liquid filtration or catalyst supporting, etc.

Preparation and properties of mullite ceramic-based porous aggregates with high closed porosity utilizing low-voltage electroceramics waste

Mullite ceramic-based porous aggregates, known for their high strength and closed porosity, are widely utilized in engineering. This study successfully prepared mullite-ceramic-based porous aggregates from low-voltage electroceramics waste, investigating the impact of pore-forming agents, bauxite chamotte, and sintering temperature on the physical properties and cold compressive strength. Finally, a mechanism of closed and open pores formation was proposed. The results show that when 10 wt% activated carbon was added, enhanced particle dispersion and stability in apparent porosity, bulk density, and diameter shrinkage ratio were observed, with an optimal range of activated carbon addition identified at around 10.0 wt%. Furthermore, increasing bauxite chamotte addition from 5.0 wt% to 15.0 wt% at 1000°C promoted mullite nucleation, facilitating mullite crystal formation and reducing the relative content and viscosity of the liquid phase. This led to increased apparent porosity, reduced closed porosity, and a decrease in average pore size. However, stress concentration around surface pores resulted in reduced cold compressive properties. The sintering temperature was then increased from 900°C to 1200°C using 10.0 wt% activated carbon and 15 wt% bauxite chamotte, leading to changes in crystallinity and porosity. At 1100°C, isolated islands of the liquid phase between grain boundaries resulted in the highest cold compressive strength and bulk density, while further heating to 1200°C led to a reduction in these properties due to excess liquid phase filling grain boundaries. The formation of closed and open pores is primarily influenced by changes in sintering temperature, which affect the quantity, viscosity, and flowability of the aluminum-silicon liquid phase.

Preparation of novel reticulated porous ceramics with textured structures enabled by in situ generated interlocking Al2O3 platelets

Al2O3 reticulated porous ceramics (ARPCs) are extensively employed in high-temperature catalytic support, molten metal filtration, and porous media combustion because of their high specific surface area and heat resistance. The high specific surface area is usually maintained by high apparent porosity, but unfortunately, the accompanying poor mechanical properties severely compromise the durability of ARPCs. To synergistically improve the mechanical properties and apparent porosity, a new strategy was proposed to prepare ARPCs with textured structures of in situ interlocking Al2O3 platelet integration using vacuum impregnation Na3AlF6–SiC–Al2O3 slurry technique. The obtained textural structure had a significant strengthening effect on ARPCs, attributed to the increased contact area among non-equiaxed grains, and the compact growth of Al2O3 platelets with high aspect ratios provided the high apparent porosity and specific surface area of ARPCs, resulting in compressive strength as high as 3.93 MPa at an apparent porosity of 85.31 %, as well as the degradation of Congo red up to 75.35 % due to the Al2O3 platelets facilitating the loading of TiO2.

Quartz and feldspar-blended clay composites for thermal and structural applications

In this study, some selected clay samples were beneficiated and blended with quartz and feldspar in various proportions to develop composites with good thermal and structural performance for sustainable development. X-ray fluorescence (XRF) analysis affirms the aluminosilicate nature of the clay samples and other trace oxides. The pore volume of the fired bulk composites disappears at 1200 °C leading to a decline in apparent density, apparent porosity, and water absorption. Furthermore, this study revealed that at the same temperature, the bulk density (1.69, g/cm3, 1.78, g/cm3, 1.78 g/cm3), modulus of rupture (33.2 kg/cm3, 39.34 kg/cm3, 38.88 kg/cm3), and total shrinkage (23.6 %, 22.3 %, 20.6 %) were maximum. Additionally, the results showed that the relative plasticity of the clay samples improved with the addition of feldspar and quartz from 1.27 to 1.33 and 1.35 for the fired composites (BO1: 50 % clay, 30 % feldspar, 20 % quartz, and CO1: 50 % clay, 25 % feldspar, 25 % quartz), respectively. Results obtained from thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis confirmed the clay samples to be thermally stable. The X-ray diffraction (XRD) patterns of all the fired composites showed major peaks, with quartz content being the highest at 27.5° (2θ) angle, albite presenting the lowest non-clay mineral content. Based on the analyses conducted in this study, it could be inferred that the clay sample is suitable for thermal insulation and structural applications.