Fraction Of Pores Research Articles

Morphological and mechanical properties of foamed thick-walled Wood-Plastic-Composite structures

Microcellular wood fiber reinforced polymers offer the possibility to reduce the use of fossil raw materials. In particular, thick-walled structures with thicknesses greater than 6 mm offer a high potential for weight savings. This study investigates the cell structures and mechanical properties of injection-molded test specimens. The influence of different thicknesses (6–10 mm) along with different chemical blowing agents (endothermic, exothermic) with varying dosages (0–2 wt%) is analyzed. The investigations reveal that exothermic chemical blowing agents form finer cells consistently to thin-walled structures than endothermic ones. Higher foaming agent content leads to higher pore fractions, with many small cells coalescing into a large open-pore cell network. The mechanical properties depend mainly on the pore content of the sample. The specific tensile properties deteriorate with the use of chemical blowing agents (CFA), whereas the sandwich structure produced with compact edge layers has a positive influence on the specific flexural properties.

Effect of gravel content on soil water retention characteristics and thermal capacity of sandy and silty soils

Abstract The presence of gravel in soils modifies the porosity, pore connectivity and pore size distribution in the soil matrix as well as the soil matrix-gravel interfaces. The aim of the present study is to investigate the effect of relative volume of gravel in samples with gravel mass fractions of 5,10, 20 wt% and varying bulk densities (1.3, 1.45, 1.55, 1.60, 1.65 g cm–3) on (i) total porosity, field capacity, plant available water holding capacity, (ii) pore size distribution and (iii) thermal capacity of repacked sandy and silty soils. The focus of the study was to determine if laboratory measured soil water retention curves considering (i), (ii), and (iii) can be predicted by a gravel-based weighting factor, Rv, considering comprehensive significance tests. The sand-gravel mixtures show a decrease in the volume fractions of macropores and wide cores pores with an increase in the gravel contents, while the silt-gravel mixtures show an opposite trend. The root mean square errors (RMSE) between measured and fitted volumetric water contents, θ, between 0.006 and 0.0352 and between 0.002 and 0.004 for Rv-weighted volumetric water contents indicate that the van Genuchten-based Peters-Durner-Iden (PDI) model is appropriate for fitting. The soil water retention curves with mass gravel contents of up to 10 wt% for silt and 20 wt% for sand can be well predicted by weighting factors (relative volume of rock fragments) in the range between 0.045 and 0.058 for silt, and between 0.112 and 0.119 for sand. The results also indicate a decrease in the Rv-weighted saturated, cvsat, and dry, cvdry, thermal capacity with an increase in the gravel contents for both soils. Further investigations are needed to examine if and whether measured sand- and silt-gravel mixtures with mass gravel contents below 10 % or rather 20 % can be predicted with a weighting factor.

Parameters Optimization and Repeatability Study on Low-Weldable Nickel-Based Superalloy René 80 Processed via Laser Powder–Bed Fusion (L-PBF)

This work aims to investigate the processability of René 80 via laser powder–bed fusion (L-PBF). René 80 is a poorly weldable Ni-superalloy, currently processed via investment casting to fabricate turbine blades working at an operating temperature of about 850 °C. The L-PBF parameters optimization aims to increase part integrity and enhance processing repeatability. This part was tackled by creating a complete design of experiments (DOE) in which laser power, scan speed and hatching distance were varied accordingly. Optimizing the abovementioned parameters minimized the crack density and pore area fraction. Hence, five parameter sets leading to a crack density lower than 100 µm/mm2 and a pore fraction between 0.045% and 0.085% were selected. Furthermore, the intra-print repeatability was studied by producing three specimens’ repetitions for each optimal set of parameters in the same build. The porosity value obtained was constant among repetitions, and the crack density (around 75 µm/mm2) had a slight standard deviation. The third step of the research assessed the inter-prints repeatability by producing a replica of the five selected parameter sets in a different build and by comparing the results with those studied previously. According to this latter study, the porosity fraction (ca. 0.06%) was constant in intra- and inter-print conditions. Conversely, crack density was lower than 100 µm/mm2 only in three sets of parameters, regardless of the intra- or inter-build cross-check. Finally, the best parameter set was chosen, emphasizing the average flaw fraction (least possible value) and repeatability. Once the optimal densification of the samples was achieved, the alloy’s microstructural features were also investigated.

Study of neck formation and densification in porous hydroxyapatite ceramics using thermal conductivity measurements

Neck formation and densification during sintering have strong effects on the thermal conductivity of a porous ceramic body. This has been described by an analytical model using grain conductivity, grain size, pore fraction and particle – particle contact area as input parameters. It has been tested on hydroxyapatite ceramics sintered with conventional, microwave and spark plasma techniques. The green bodies containing at least 40% porosity yield conductivity values in the range 0.24–0.29 Wm−1K−1. Neck formation in the initial stage of sintering increases the values to above 0.5 Wm−1K−1. Further increase is achieved by densification, well described by Landauer's relation as part of the model with close agreement to experiment for hydroxyapatite ceramics containing 40 to 5% porosity. An evaluation of thermal conductivity for 100% dense hydroxyapatite gives a value of 1.5 Wm−1K−1 which is almost constant between room temperature and 900 °C.

Novel Method for the Production of Titanium Foams to Reduce Stress Shielding in Implants.

Titanium foams have potential applications in orthopedic and dental implants because of their low elastic modulus and good bone in-growth properties. In the present study, a novel method for the preparation of three-dimensional interconnected microporous titanium foams has been developed. This method is based on the insertion of a filler metal into the titanium metal by arc melting, followed by its removal by an electrochemical dealloying process for the development of foams. Complete removal of the filler metal by the electrochemical dealloying process was confirmed by an X-ray diffractometry (XRD) analysis, whereas scanning electron microscopy (SEM) analysis of the developed foams showed the development of interconnected porosity. Ti foams with different levels of porosities were successfully developed by varying the amount of the filler metal. Mechanical and thermal characterizations of the developed foams were carried out using compression testing and laser flash apparatus, respectively. The yield strength and elastic modulus of the developed foams were found to decrease by increasing the volume fraction of pores. The elastic modulus of the developed titanium foams (15.5-36 GPa) was found to be closer to that of human bones, whereas their yield strength (147-170 MPa) remained higher than that of human bones. It is therefore believed that the developed Ti foams can help in reducing the problem of stress shielding observed in orthopedic implants. The thermal diffusivity of the developed foams (4.3-0.69 mm2/s) was found to be very close to that of human dentine.

Оценка локальных механических свойств керамических огнеупоров на основе SiO2 с помощью микромасштабного моделирования

The development of multiscale mechanical models of promising refractory materials is an urgent problem in the mechanics of solids. One of the reasons is the applicability of these models when creating digital twins of advanced refractories. The authors of this paper recently developed and validated a mesoscopic model of the SiO2-based refractory material that is widely used in metallurgy. This model takes into account the characteristic structural features of SiO2 refractory in the scale range of 10-5 - 10-2 m and the mechanical behavior features in a wide range of strain rates. However, the full use of the model requires knowledge of local mechanical properties of mesoscopic structural elements, in particular, the highly porous regions, which are formed by fine grains less than 102 pm in size. An experimental study of effective mechanical characteristics of such regions is an extremely difficult task. Therefore, the purpose of this work is to obtain the theoretical estimate using the microscale numerical simulation of highly porous regions of SiO2 refractory material and to determine their integral mechanical characteristics. To study this problem, the two-dimensional model samples are developed that simulate fine-grained regions of the refractory and are characterized by different porosity and pore structure types (channel-like or closed type). The intervals of the variation of Young’s modulus and strength characteristics of the samples are obtained depending on the porosity and morphology of the pore space. The contribution of the closed-type porosity to the integral mechanical characteristics of the refractory is determined; though, the volume fraction of such pores is low as compared to that of the channel-like pores. The obtained data will be used as input parameters of mesoscale refractory models for solving the urgent problems related to the study of the effect of microstructure parameters on the macroscopic mechanical and thermomechanical properties of SiO2-based refractories.

Reconstruction of LWD-NMR T2 water spectrum and fluid recognition based on microscopic pore structure constraints

The existing fluid property identification methods are not applicable to low resistivity reservoirs. In order to accurately identify low-resistivity oil reservoirs, the effects of fluid properties on the NMR T2 spectrum under different pore structures were analyzed. The results show that the T2 spectrum of the low-resistivity oil section shows a broad and gentle hilly shape, and the T2 spectrum of the water section shows a steep and mountainous shape. Based on the difference characteristics of T2 spectrum of reservoirs with different fluid properties, a new NMR water spectrum reconstruction and fluid property identification method based on microscopic pore structure constraint is innovatively proposed. Based on the drilling NMR logging data, three parameters characterizing the microscopic pore structure are firstly extracted from the NMR T2 spectrum of standard water reservoirs, which reflect the overall shape of the T2 spectrum in terms of transverse relaxation time, longitudinal pore fraction and These three parameters reflect the pore structure, water and oil and gas information of the reservoir in terms of the transverse relaxation time, the longitudinal pore fraction and the overall morphology of the T2 spectrum. Secondly, the microscopic pore structure parameters are used as the coordinate axes to construct a 3D water spectrum sample library, and the standard water formation T2 spectrum samples of the target block are stored in the 3D water spectrum library through the constraints of the three parameters. Finally, the NMR T2 spectrum parameters are extracted from the whole well section and the samples in the water spectrum library are called to realize the water spectrum reconstruction. The parameters that can distinguish oil and water formations are extracted from the measured T2 spectrum and the reconstructed water spectrum and fluid identification is performed. The results show that the reconstructed water spectrum is highly similar to the actual measured T2 spectrum in the production-proven standard water layer, which verifies the accuracy of the water spectrum reconstruction technique; in Caofeidian A oilfield, the fluid identification was performed on 20 production-proven test sections, of which 18 reservoirs were correctly identified, and the identification compliance rate reached 90%. The method circumvents the influence of pore structure in NMR T2 spectrum and highlights the information of its fluid properties, which improves the fluid property identification capability of logging with drilling (LWD) NMR logging.

Sintering of Industrial Uranium Dioxide Pellets Using Microwave Radiation for Nuclear Fuel Fabrication

In this study, the possibility of sintering industrial pressed uranium dioxide pellets using microwave radiation for the production of nuclear fuel is shown. As a result, the conditions for sintering pellets in an experimental microwave oven (power 2.9 kW, frequency 2.45 GHz) were chosen to ensure that the characteristics of the resulting fuel pellets meet the regulatory requirements for ceramic nuclear fuel, including the following: a density of about 10.44 g/cm3; a volume fraction of open pores of tablets of about 0.1%; an oxygen coefficient of no more than 2.002; hydrogen content of about 0.30 ppm; and the change in density after re-sintering on average no more than 1.16%.

Pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing

Partial replacement of cement with high-volume slag reduces the amount of cement in concrete and thereby lessens the environmental pressure caused by cement production. This paper investigates the pore structure evolution and sulfate attack of high-volume slag blended mortars under standard curing and steam curing, discusses the effects of slag content and pore structure on sulfate attack, and evaluates the methods for determining the sulfate resistance performance. The pore structure results show that the hydration of cement and/or slag reduces the porosity and most probable pore diameter (MPPD) and refines the pore structure of mortars. Steam curing primarily affects the pore size distribution but not the porosity for the mortars within 3 d. Increasing slag replacement increases the porosity for standard-cured and steam-cured mortars at the age of 28 d; however, it significantly reduces the air voids that are detrimental to sulfate resistance. Sulfate attack results show that the combination of the flexural strength test with the sulfate-ion content can evaluate the sulfate resistance well. The sulfate resistance improves with increasing slag content, and 70% of slag improves the sulfate resistance significantly for both standard-cured and steam-cured mortars. In addition, the MPPD, gel pores, and mesopores do not seem to determine the sulfate resistance. Reducing the volume fractions of large capillary pores, especially air voids, can improve sulfate resistance.

Solidification behavior and porosity in electron-beam powder bed fusion of Co–Cr–Mo alloys: Effect of carbon concentrations

An increased carbon content strengthens Co–Cr–Mo alloys for use in a broad range of industrial applications. In this study, we investigated the influence of the carbon content (0.04–2.5 mass%) on the porosity and microstructure of Co–27Cr–6Mo (mass%) alloys during atomization and electron-beam powder bed fusion (EB-PBF). Quantitative X-ray computed tomography clarified that the volume fraction of pores in the raw powders monotonically increased with the carbon content, as a potential effect of the significant reduction in the liquidus temperature. In contrast, the porosity evolution in the investigated alloys during EB-PBF under identical building conditions suggested an influence of carbon concentration that was distinct from that in the powder. These alloys exhibited negligible porosity fraction for 0.04 and 0.22 mass% and a maximum volume fraction (∼0.3 vol.%) at 2.0 mass%, followed by a remarkable reduction caused by further carbon addition. The porosity of the as-built alloys could be correlated to the solidification behavior varying with carbon concentration. The smoother and more flat solidification front during the cellular (0.04 and 0.22 mass%) and eutectic (2.5 mass%) solidification could effectively eliminate the gas bubbles from the melt pool, whereas the complicated morphology at the solid–liquid interfaces during the dendritic growth (1.5 and 2.0 mass%) hindered the pore elimination in the melt pool. Adding carbon significantly increased the Rockwell hardness of the as-built specimens, reaching a significantly high value of HRC59 at 2.5 mass% of carbon, primarily due to the formation of hard carbide precipitates. The obtained findings could be beneficial to reduce entrapped gas pores thereby contributing to the development of highly durable metal components.

Evolution of nano-pores during annealing of technically pure molybdenum sheet produced from different sintered formats

Molybdenum is a refractory metal with no phase transformation in the solid state and a high melting point. It is therefore an excellent structural material for various high temperature applications. Especially in this field of operation, significant creep resistance is essential. To achieve this, a microstructure with grains in the range of millimeters is desired. However, as demonstrated in the present study, the onset temperature for secondary recrystallization, which would lead to a beneficial grain size, is among other things dependent on the initial dimensions of the sintered part. One possible reason for the different microstructural evolutions is the influence of residual pores in sub-micrometer size. Sheets were thus fabricated via three different production routes employing the same initial Mo powder to exclude chemical variation as an influencing factor. The samples were investigated by in-situ small-angle X-ray scattering at a synchrotron radiation source with two different heating rates. Additionally, selected annealed samples were studied ex-situ with high energy X-rays. The apparent volume fraction of pores is compared to a volatilization model for the vaporization of typical accompanying elements and the induced thermal expansion.

Investigation on Microstructure, Tensile Properties and Fatigue Characterization of Porous Date Palm Fiber

ABSTRACT Date palm fibers have been studied as potential reinforcement in composite materials. Their density is equal to 1.22 g.cm−3; making them suitable for use in lightweight applications. In order to efficiently use these fibers and understand their mechanical properties, quasi-static tensile tests and cyclic fiber fatigue tests were performed to determine the mechanical properties. Their internal structure, elementary fibers and porosity were analyzed by scanning electron microscopy. The results show that the mechanical properties are clearly improved by taking into account the porosity by calculating the real section of the fibers by using the imageJ software a cross-sectional pore fraction of the fibers has been determined and the ultimate properties of the pore-free bulky fibers has been calculated with stress and Young’s modulus increased by approx. 54% as compared to the highly porous natural fibers.

Study on Mechanical Properties and Microstructure of Basalt Fiber Reactive Powder Concrete

In order to promote the wide application of reactive powder concrete (RPC) in practical engineering. In this paper, RPC was prepared using conventional and economical natural river sand instead of quartz sand and economical and environmentally friendly basalt fiber (BF) instead of steel fiber, and the macroscopic properties of basalt fiber reactive powder concrete (BFRPC) with different fiber content, such as flowability, failure mode, compressive strength and splitting tensile strength were studied, and the strength calculation formula of BFRPC was established based on the mechanical property results. The microscopic morphology and structure of BFRPC were characterized by scanning electron microscope (SEM) and Image Pro Plus (IPP) image processing software. The results show that BF has a small effect on the compressive strength of RPC, while it has a significant increase on the splitting tensile strength. When BF content is at 2 kg/m3, the 28-day compressive strength reaches 95.2 MPa and splitting tensile strength reaches 7.78 MPa. Compared with the RPC with BF of 0 kg/m3, the BFRPC shows an improvement in its 28-day compressive strength by 25.70% and an increase in its splitting tensile strength by 83.92%. According to the microscopic analysis, reasonable fiber content can optimize the internal microstructure of BFRPC, but excessive BF content will produce agglomeration and overlap, resulting in strength loss. Based on the gray correlation analysis method, it was concluded that the particle area ratio and pore fraction dimension were the most correlated with the mechanical properties of BFRPC. In addition, the feasibility and applicability of the BFRPC strength calculation formula were summarized. This research results of this paper provides a valuable reference for the further research and promotion of BFRPC.

Bulk morphology of porous materials at submicrometer scale studied by dark-field x-ray imaging with Hartmann masks

We present the quantitative investigation of the submicron structure in the bulk of porous graphite by using the dark-field x-ray imaging with Hartmann masks. By scanning the correlation length and measuring the mask visibility reduction, we obtain the average pore size, relative pore fraction, fractal dimension, and Hurst exponent of the structure in a simple and flexible setup with relaxed requirements on beam coherence. Profiting from the dimensionality of the mask, we obtain scattering signals in two orthogonal directions, which reveals the anisotropy of pore sizes.

Mechanical performance of basalt and PVA fiber reinforced hybrid-fiber engineered cementitious composite with superimposed basalt fiber content

• PVA/basalt HF-ECC with multiple cracking behavior was achieved by superimposition of basalt fiber. • Increasing basalt fiber superimposing content improved overall strength of PVA/basalt HF-ECC. • The advised optimal superimposing volume fraction of basalt fiber is 0.8%. • The effect of basalt fiber on tensile strain capacity was analyzed by micro-mechanical analysis. The large-scale application and popularity of engineered cementitious composites (ECC) is hindered by the relatively high price and increased CO 2 footprint of PVA fiber. PVA and basalt fiber reinforced hybrid-fiber ECC (PVA/basalt HF-ECC) is a promising way to deal with such drawbacks. Hence, this study focused on the influence of basalt fiber superimposing content on the properties of PVA/basalt HF-ECC. Compressive tests indicated basalt fiber could elevate compressive strength and its corresponding strain, the obtained maximum values were 46.37 MPa and 0.47 % as basalt fiber content increased up to 1.2 %. Tensile tests showed that first cracking strength and ultimate tensile strength increased up to 6.62 MPa and 7.85 MPa as basalt fiber content increased up to 1.2 %. Although tensile strain capacity continuously decreased to 0.62 %, all specimens showed multiple cracking behavior due to the superimposed performances derived from PVA and Basalt fibers. Mercury intrusion porosimetry test showed volume fraction of large capillary pore that influences strength decreased up to 31.65 % when basalt fiber content increased to 1.2 %. Based on test results, predicting equations of mechanical properties were proposed by curve fitting and showed good agreement with test results. Micro-mechanical analysis was conducted based on modified crack bridging model, and its results further interpreted change mechanism of tensile strain capacity. This study explores the feasibility of developing PVA/basalt HF-ECC by basalt fiber superimposition and facilitates the popularity of ECC.

New insight into anodization of aluminium with focused ion beam pre-patterning

The self-ordered anodic aluminium oxide (AAO) structure consists of micron-scale domains—defect-free areas with a hexagonal arrangement of pores. A substantial increase in domain size is possible solely by pre-patterning the aluminium surface in the form of a defect-free hexagonal array of concaves, which guide the pore growth during subsequent anodization. Among the numerous pre-patterning techniques, direct etching by focused gallium ion beam (Ga FIB) allows the preparation of AAO with a custom-made geometry through precise control of the irradiation positions, beam energy, and ion dosage. The main drawback of the FIB approach includes gallium contamination of the aluminium surface. Here, we propose a multi-step anodizing procedure to prevent gallium incorporation into the aluminium substrate. The suggested approach successfully covers a wide range of AAO interpore distances from 100 to 500 nm. In particular, anodization of FIB pre-patterned aluminium in 0.1 M phosphoric acid at 195 V to prepare AAO with the interpore distance of about 500 nm was demonstrated for the first time. The quantification of the degree of pore ordering reveals the fraction of pores in hexagonal coordination above 96% and the in-plane mosaicity below 3° over an area of about 1000 μm2. Large-scale defect-free AAO structures are promising for creating photonic crystals and hyperbolic metamaterials with distinct functional properties.

Development and implementation of a micromechanically motivated cohesive zone model for ductile fracture

Gaining popularity after its coupling with the finite element method, cohesive zone modeling has been used extensively to model fracture, especially in delamination problems. Its constitutive relations, i.e. traction-separation laws, are mostly derived phenomenologically without considering the underlying physical mechanisms of crack initiation and propagation. The approach could potentially be used for ductile fracture as well where the micromechanics of the phenomenon is explained by nucleation, growth and coalescence of pores. In this context, the objective of this work is to develop and implement a physically motivated cohesive zone modeling framework for ductile fracture in metallic materials. In order to accomplish this, a micromechanically motivated traction-separation relation which considers the growth of a physical pore is developed. Tractions are directly represented as a function of pore fraction, and its evolution is driven by separations. The model is implemented as an intrinsic cohesive zone element in a two-dimensional setting. Implementation steps and methodology including the finite element framework are presented in detail for mode-I, mode-II and mixed-mode fracture cases. The derivation of the mixed-mode case leads to a novel yield function representation of tractions and separations, instead of an explicit expression. Hence, an incremental implicit elasto-plastic numerical integration scheme is utilized to solve mixed-mode system of equations required for crack initiation and propagation. The framework is implemented as a user element subroutine in Abaqus (UEL) and the numerical simulations are conducted with compact tension (CT) and single edge notch (SEN) specimens to test the implementation and influence of the micromechanical parameters such as pore size, shape and spacing on the ductile crack initiation and propagation. The work is concluded by presenting an outlook for the capability of the model to predict crack path.

B4C‐Reinforced Al–Zn Foams Having Superior Energy Absorption Efficiency

The low density of the aluminium foam and high energy absorption make them favourable for automobile, aerospace, and defence industries. However, the melt route for foam fabrication has challenges in achieving homogeneous distribution of pores. Hence, we have adopted the space holder technique using the powder metallurgy methodology to overcome such a challenge. In the current study, we fabricated Al–Zn alloy foams reinforced with varying volume fractions of B4C particles using NaCl as a space holder implemented by hot pressure‐assisted sintering and dissolution. X‐ray computed tomography revealed a homogeneous distribution of pores. The quasistatic compression studies showed that the samples containing a higher volume fraction of pores exhibited higher energy absorption efficiency in the fabricated foam. The maximum energy absorption efficiency (η) achieved was ≈93% for the pristine Al alloy foam with ≈50% porosity, which is ≈11% higher than the η value of 9 vol% B4C samples with similar porosity. Additionally, B4C particles delay the sudden collapse of cell walls and stabilize the compression behaviour. Adding B4C improves the η and strength at higher relative density. This fabrication methodology would help us develop foams with a homogenous pore distribution and regular geometry, achieving highly desirable mechanical properties.

3D concrete printing with cement-coated recycled crumb rubber: Compressive and microstructural properties

• Recycled crumb rubber is coated with cement paste via a ball milling machine. • Three weight ratios of cement to rubber are designed for different coating quality. • X-ray micro-computed tomography is used to analyse pores and crack propagation. • Degree of increase in compressive strength relies on the coating quality of rubber. • Anisotropic compressive property is primarily related to pore shape and orientation. The modification of a rubber surface, such as cement coating, is an effective method for enhancing the mechanical performance of concrete containing recycled rubber particles. Although this method has been widely investigated for cast concrete, there is limited research on 3D-printed cementitious materials. This study explored the correlation between the compressive strength and microstructural property of 3D-printed rubberised mortar with cement-coated crumb rubber (15 wt% replacement of river sand). Multiple ratios of cement-to-rubber (C/R) were designed to achieve different coating qualities, including C/Rs of 0.25 (CR-0.25), 0.4 (CR-0.4) and 0.55 (CR-0.55). Scanning electron microscopy (SEM) images showed the existence of hardened cementitious shells outside the rubber particles, which effectively improved the interfacial bonding between the rubber surface and the cement matrix. The compressive strengths of the printed specimens did not always improve as the ratio of cement to rubber for coating increased. Moreover, the anisotropy in compressive strength was more obvious in the CR-0.4 and CR-0.55, where the strength in the Y (printing) direction was about 7 % higher than that observed in the Z (layer deposition) direction. X-ray micro-computed tomography (μCT) analysis revealed that the mechanical anisotropy in CR-0.4 and CR-0.55 could be primarily attributed to two factors – pore morphology and pore orientation relative to the external loading direction. For CR-0.25, the rubber-to-matrix interface bonding appeared more critical for the compressive strength. Finally, the printed specimens showed the higher compressive strengths than the cast ones due to the lower fraction of large pores (diameters ≥ 1 mm).

Compositional effect on humidity self-regulation functionality in gibbsite-based ceramic tiles

This paper analyses the effect of the starting composition on the humidity regulating capacity of a gibbsite-based composition successfully tested for the manufacture of ceramic tiles. For this purpose, the proportion of gibbsite and quartz has been varied and the effect of these two ingredients of the composition on the moisture regulating capacity and on the kinetics of adsorption-desorption of sintered tiles has been studied. To explain the effect, the microstructure of the sintered bodies has been also characterised. It has been found that increasing the proportion of gibbsite in the starting composition produces a significant increase in the moisture regulating capacity as a consequence of the higher proportion of transition alumina in the sintered bodies that provide a larger mesopore reservoir. In contrast, the addition of quartz does not affect the moisture regulating capacity but does affect the rate at which moisture adsorption and desorption phenomena take place by increasing the fraction of larger pores in the structure. In both cases, the kinetic model tested corroborates the observed relationship between microstructure and moisture regulating capacity.