Thermal evaluation of the use of porous ceramic plates on ventilated façades – Part I: Effect of composition and firing temperature on porosity and bending strength

The effect of composition and firing temperature on porosity and bending strength of porous ceramic plates for using in ventilated façades were investigated. Two byproducts, basalt and lime mud, were used to obtain porous ceramic plates in accordance with the circular economy concept. Basalt, which is a fine powder-based byproduct generated from the processing of basaltic rock, was used to replace feldspar as the flux mineral in a ceramic composition. Lime mud, a byproduct of the pulp and paper mill process and containing a high content of calcium carbonate (CaCO₃), was incorporated in the ceramic composition to generate pores. The specimens were prepared using three different amounts of lime mud (20, 30, and 40 wt%) and three firing temperatures (900°C, 1000°C, and 1100°C), and their porosity and bending strength were determined. The highest performing specimen (5.1 ± 1.3 MPa bending strength and 42.6 ± 0.5% porosity) was obtained by using 40 wt% of lime mud and a firing temperature of 1100°C with potential for further thermal tests in a ventilated façade in comparison with a commercial porcelain ceramic tile as reference material.     

Research on color harmony of building façades

In this study, the 28 primary colors and 11 complementary colors suggested by Chang et al in their investigation on building colors in Wanhua District of Taipei City were taken as color samples. The two-color combination mode was adopted to obtain 308 simulation photos, and two-color harmony was discussed from the perspective of visual evaluation using psychophysical tests. This study explored building façade color harmony in the CIELAB color space, and the relationship between the color attributes (hue, lightness, and chroma) and the color harmony, and between the differences of the color attributes and color harmony. It found that a high lightness of a building's primary color is associated with a high level of building color harmony, while the color harmony is reduced when the color falls in the green or blue sector in the CIELAB color space; a greater lightness difference between building façade colors is associated with a higher level of building color harmony, while the colors are disharmonized when they tend to the blue sector in the CIELAB color space. The contribution of this study is to summarize the principles for the application of building color harmony in urban renewal, and proposed suggestions on building color harmony in the urban renewal process.     

Thermal cyclic behavior of glass–ceramic bonded thermal barrier coating on nimonic alloy substrate

Thermal barrier coating system comprised of 8 wt.% yttria stabilized zirconia (YSZ) top coat, glass–ceramic bond coat and nimonic alloy (AE 435) substrate was subjected to thermal shock test from 1000 °C to room temperature for 100 cycles. Two types of thermal shock testing were performed. In one test, specimens held at 1000 °C for 5 min were forced air quenched while in the other test specimens were water quenched from the same conditions. Microstructural changes were investigated by scanning electron microscopy (SEM) and phase analysis was conducted by XRD and energy dispersive X-ray (EDX) analysis. In the case of forced air quenched specimens, no deterioration was observed in the top coats after 100 cycles while the top coats were damaged in the water quenched ones. In both forced air quenched and water quenched specimens, interfacial crack was not observed at the top coat–bond coat and bond coat–substrate interfaces after thermal cycling experiments and the top coat maintained its phase stability.     

Combustion synthesis of porous ceramic β- Si3N4 -based composites with the use of ferroalloys

A method for manufacturing silicon nitride-based composites with a desired porosity using a self-propagating high-temperature synthesis has been developed. The effects of the composition of starting specimens, pressure and diameter on the combustion parameters of pre-structured specimens based on ferro-silicoaluminum with addition of aqueous-alkali solution were studied. The phase composition of composites was determined. The obtained composites showed porosities of 25.11%–55.08% with a predominance of open pores of average size in the range of 21–305 μm.     

Asymmetric ceramic membranes from Langmuir–Blodgett deposition precursors: deposition of fatty acid salts on porous ceramic substrates

Nanoporous 7930 Vycor silica tubes and mesoporous and macroporous Anopore anodic alumina discs are examined as substrates for the multilayer Langmuir–Blodgett (LB) deposition of Cd, Mg, Zn and Ca salts of the arachidic and stearic fatty acids. Conditions for successful deposition are reported. Under appropriate conditions both mesoporous and macroporous Anopore aluminas allow for a full substrate coverage (maximum degree of deposition, D_d,max→1), while a Vycor substrate imposes a D_d,max⩽0.7 and a mechanism explaining the observed D_d,max values is presented. The produced ceramic oxide–LB film composites are prototype precursors for gas-separating all-ceramic asymmetric membranes, following the application of an oxidative plasma treatment.     

DLP 3D printing porous β-tricalcium phosphate scaffold by the use of acrylate/ceramic composite slurry

Digital light processing (DLP) 3D printing has been utilized to fabricate controlled porous β-tricalcium phosphate (β-TCP) scaffolds, which promote cell adhesion and angiogenesis during bone regeneration. However, the current limitation of DLP 3D printing for the fabrication of β-TCP scaffold is how to prepare a low viscosity ceramic slurry and remove the toxicity of residual non-polymerized slurry. The present study has developed a low viscosity ceramic slurry system by mixing β-TCP with photosensitive acrylate resin, and the viscosity of slurry is about 3 Pa s and the solid content of β-TCP can be as high as 60 wt%. After optimizing the ratio of slurry, printing, degreasing and sintering processes, the maximum compressive strength of the DLP printed scaffolds reaches up to 9.89 MPa, while the porosity keeps ca. 40%. According to the proliferation of cells, it confirms the preserved biocompatibility of DLP-fabricated β-TCP scaffolds. These porous scaffolds made by DLP 3D printing technology is of great significance for bone regeneration, and will also help to expand the application of DLP technology in biomedical field.     

A filtration model for the flow of dilute,stable emulsions in porous media—II. Parameter evaluation and estimation

Part I of this work outlined a new theory, based on deep-bed filtration concepts, to describe the flow of dilute, stable emulsions in underground porous media. Here, in Part II, we quantitatively test the proposed theory against experimental data and we indicate how the filtration model parameters can be estimated from first principles.Comparison is made between the theory and data on transient permeability and effluent concentration for dilute, oil-in-water emulsions of mean drop-size diameters ranging from 1 to 10 μm and volume concentrations of 0.5–2.5% flowing in quartz sandpacks of 0.57–2.0 μm² permeability. The pH of the continuous aqueous phase is kept constant at 10. Filtration theory successfully represents the data, permitting unambiguous evaluation of the theoretical parameters.Procedures are described for a priori calculation of the filtration parameters from knowledge of the drop size and the pore-size and grain-size distributions of the porous medium. Good agreement is achieved between the experimentally determined parameters and their estimated values. Thus, the proposed filtration model provides a reliable tool for predicting emulsion flow behaviour in porous media.     

Thermogelling polysaccharides for aqueous gelcasting—part II: influence of gelling additives on rheological properties and gelcasting of alumina

In the present work the influence of the addition of aqueous solutions of agar, agarose and carrageenan on the rheological properties of alumina slurries is studied. Precursor binder solutions were prepared to concentrations between 1.5 and 4 wt.% in water by heating at 92 °C. Alumina suspensions were prepared at a solid loading of 50 vol.% and heated to 60 °C. At this temperature different amounts of the starting precursor solutions of each gelling binder were added so that the final concentrations of binder were 0.25, 0.5 and 0.75 wt.% referred to dry solids. For concentrations of the precursor solution ⩽2 wt.%, the viscosity of the slurry tends to decrease when the total amount of gel increases, while for concentrations of the precursor solution ⩾3 wt.% viscosity increases with the amount of gel. This defines a yield concentration of precursor solution where the suspension properties change. Gelcasting performance is a function of slurry viscosity, gelling behaviour and time, and body deformation during drying. In general, carrageenan leads to higher shape distortion in the body. Better shape retention is achieved with precursor solutions with ⩾3 wt.% additive and total content of gel of ⩾0.5 wt.%.     

Use of the Weibull model on sizing thickeners—Part II: Methods of thickener sizing

Among several methods employed for sizing thickeners available in the literature, the Kynch, Biscaia Jr., Talmadge and Fitch, Roberts, Coe and Clevenger, and Oltmann methods use experimental data from sedimentation curves and graphical approaches. By using the Weibull distribution, it is possible to represent sedimentation curves with algebraic equations, which does not require the use of graphical approaches and provides more accuracy and speed for sizing calculations. In the present work, the main objective is the development of a set of equations for sizing continuous thickeners, for six conventional methods found in the literature, using the Weibull model. A comparative analysis of calculated and literature diameters for each graphical method presented variations between 0.73% and 8.93%. The use of the Weibull model presented the best accuracy for the Biscaia Jr. method, with a 0.73% average absolute error.     

Studies on Mechanical and Thermal Properties of Ternary Blends of Polyethylenes Having Fixed Percentage of High-Density Polyethylene—II

Six film samples of varying compositions of low-density polyethylene (LDPE); (20–45 wt%) and linear low-density polyethylene (LLDPE); (25–45 wt%) having a fixed percentage of high-density polyethylene (HDPE) at 30 wt% have been extruded by melt blending in a single screw extruder (L/D ratio = 20:1) of uniform thickness of 2 mil. The tensile strength and elongation at break have been found to increase up to 40 wt% with LLDPE addition, starting from 25 wt% LLDPE, in the blends and then decreased. The blend sample containing 30 wt% LDPE, 40 wt% LLDPE, and 30 wt% HDPE (sample C-300) was found to be more thermally stable blend amongst all the prepared blends. In most of the blends, two exothermic peaks appeared that showed the formation of immiscible blend systems; this was further confirmed by scanning electron microscopic (SEM) analysis.     

Effect of ZrO2 Additives on the Thermal Shock Resistance of MgO—MA Refractory

The additirn of three kins ZrO2-bearing additives into MgO-MA refractory could all increase the latter‘s C.C.S.and the thermal shock resistance,XRD,polarizing microscope and electron probe analysis were used to analyze the mechanism to improve the thermal shock resistance of the material.The mechanism is that ZrO added into the material improves the microstructure,introduces asppropriate micro cracks into matrix ,enhances the matrix,and therefore increases the thermal shock resistance of ther refractory.     

Studies on the promotion of nickel—alumina coprecipitated catalysts: II. Lanthanum oxide

Two series of lanthanum promoted nickel—alumina catalysts have been prepared by coprecipitation of the metal nitrates, using potassium carbonate. The molar ratio between nickel and the sum of aluminium and lanthanum was kept constant at 2.5 or 9.0 within each series. The calcination and reduction of these samples were studied by thermogravimetry and their structures before and after calcination and reduction were examined by X-ray diffraction. The methanation activities of the final catalysts were determined by differential scanning calorimetry. The results showed clearly that the methanation of carbon monoxide over nickel—alumina catalysts is enhanced by the presence of La₂O₃. With low percentages of lanthanum, the promoter is built into the precursor structure during the coprecipitation process. This is a meta-stable situation; phase separation occurs during hydrothermal treatment. In both series there was an optimum amount of lanthanum at which the activity per gram of nickel reached a maximum. The optimum specific activity of a lanthanum promoted nickel—alumina catalyst was twice as large as that of the unpromoted material. Above these optimum values, the activity per gram of nickel decreased because of two effects: an increase in the nickel particle sizes and an increase in the amounts of potassium remaining from the precipitation step. Alumina is needed to stabilize the nickel crystallites against sintering. The promoting action of La₂O₃ is slightly higher after reduction at 400°C than after reduction at 600°C. Lanthanum increased the amount of carbon monoxide which was adsorbed slowly; the amount of carbon monoxide which was rapidly adsorbed, however, was not altered. The increase in activity was accompanied by an increase in the apparent activation energy.     

Chemisorption of halogen on carbon—II Thermal reversibility of Cl2, HCl and H2 chemisorption

There are surface double bonds on carbons which differ from the graphitic surface π-bonds in their chemical reactivity. They may be created by degassing prechlorinated or prehydrogenated carbon samples, besides their natural occurrence in nontreated carbons.Cl₂, H₂ and HCl may be added to these double bonds and partially degassed by thermal cycling in presence of the gases. This indicates that at least part of these olefinic bonds are thermally labile and are, therefore, important for catalysis and surface chemical modifications of carbons. The surface concentration of the labile bonds is low, amounting to a few hundredths of meq/100m² of carbon surface area. Discrimination between physisorption and chemisorption of H₂ on carbon can be made by analysis of the dependence of adsorption on temperature. With Cl₂, considerable overlap between the two processes takes place.     

Sintered glass-ceramics from Municipal Solid Waste-incinerator fly ashes—part I: the influence of the heating rate on the sinter-crystallisation

A glass composition, made by mixing 70% of MSW ashes and 30% of waste from feldspar production, was studied. The batch was melted at 1350 °C and the melt was quenched in water. The chemical stability of the glass was investigated by TCLP leaching test. DTA experiment, at 10 °C/min heating rate in the 20–1200 °C range, showed that the glass has a high crystallisation trend with a gehlenite (2CaO.Al₂O₃.SiO₂) formation at 935 °C. The percentage of crystal phase formed as a function of the heat treatment was measured by density variation and XRD. In order to obtain sintered glass ceramics, the frit was heat treated in Al₂O₃ moulds at 950, 1000 and 1050 °C by 2 and 20 °C/min heating rates. At high heating rate predominantly surface crystallisation occurred with fibre-like crystals growing perpendicularly from the surface; at low heating rate bulk crystallisation took place. At low rate, the sintering was inhibited by the crystallisation process. Non porous sintered samples were obtained by a 30 °C/min heating rate and a 40 min isothermal step at 1120 °C, near the liquidus temperature.     

Thermal behavior of longitudinal convective–radiative porous fins with different section shapes and ceramic materials (SiC and Si3N4)

In this study, heat transfer and temperature distribution equations for longitudinal convective–radiative porous fins are presented. It is assumed that the thickness of fins varies with length, so four different shapes (rectangular, convex, triangular and exponential) are considered. Temperature-dependent heat generation, convection and radiation are considered and heat transfer through porous media is simulated using passage velocity from Darcy's model. After deriving equation for all geometries, the Least Square Method (LSM) and fourth order Runge–Kutta method (NUM) are applied for predicting the temperature distribution in the porous fins. The selected ceramic porous materials are Al, SiC, and Si₃N₄. Effects of porosity, Darcy number, Rayleigh number, etc. on transferred heat are examined. As a main outcome, exponential section fin with Si₃N₄ material has the most amount of transferred heat among other shapes and materials.     

Forty years after the promise of «ceramic steel?»: Zirconia-based composites with a metal-like mechanical behavior

Forty years ago, Garvie and his Australian co-workers reported that the stress-induced transformation of metastable tetragonal zirconia grains to the monoclinic symmetry could give rise to a powerful toughening mechanism. Their results even led them to consider zirconia systems as analogues of certain steels. This seminal paper generated extraordinary excitement in the ceramic community and it is still the subject of extensive research. Transformation toughening is widely used in zirconia materials and results in an increase in strength and toughness when compared to nontransformable ceramics, but the implementation into strong, tough, and sufficiently stable materials has not been fully reached. Zirconia ceramics generally fail at low strains with a much larger scatter in the strength values than metals and require statistical approaches to failure. Here we describe in detail the mechanical behavior laws of ceria-doped zirconia composites exhibiting a high degree of stress-induced transformation. They present, to some extent, mechanical behavior analogous to a metal, displaying, (a) significant amount of transformation-induced plasticity without damage, (b) very high flaw tolerance and (c) almost no dispersion in strength data. They potentially open new application avenues in situations where the advantages of ceramics were dampened by their brittle failure behavior. In particular, the consequences of such behavior for dental implants and additive-manufactured structures are highlighted.     

Study on Drying Organic Sludges by Thermal Jet Dryer—Part 1: Drying Performance of Thermal Jet Dryer

The authors are developing a thermal jet dryer (TJD), with a vertical disc-shaped drying tank, for the purpose of weight and volume reduction of solid wastes with high water content, such as organic sludges. In order to obtain the drying performance of TJD, drying experiments using three kinds of solid wastes were carried out. The following results were obtained: (1) Drying performance depended most on the disintegration characteristics of sample. (2) There was little influence of the samples' properties on the gas–solid multiphase flow in the tank. (3) There was a critical feed rate at which the drying performance changed drastically.     

Reconstruction of Grenfell Tower fire. Part 2: A numerical investigation of the fire propagation and behaviour from the initial apartment to the façade

The dramatic event of the Grenfell Tower in 2017 reminds the importance of addressing fire issues as a whole and clearly highlighted one of the major roles played by the façade as fire propagation vector. To understand and analyse this disaster, numerical simulation allows particular phenomena to be evaluated more easily. The numerical model addressed for the fire behaviour of the façade system was developed using a multiscale approach and validated at different scales. In this paper, the fire behaviour of the façade and of its window frames is addressed. A computational fluid dynamics (CFD) model is used to investigate the fire spread from the initial apartment to the overall façade with different scenarios for the fire source and ventilation. Fire propagation through windows to the façade and to upper apartments is addressed. General curves representing the re-entry of flames into upper apartment are extracted from simulations. The numerical results are validated by comparison with observations from videos and pictures of the real fire. Numerical results show that whatever the initial fire location and ventilation conditions, even if the fire source is of hundreds kilowatts, it is enough to ignite the adjacent element early and to the appearance of external flames shortly after.     

Influence of slag chemistry on the hydration of alkali-activated blast-furnace slag — Part II: Effect of Al2O3

The hydration and microstructural evolution of three alkali activated slags (AAS) with Al₂O₃ contents between 7 and 17% wt.% have been investigated. The slags were hydrated in the presence of two different alkaline activators, NaOH and Na₂SiO₃·5H₂O. The formation of C(A)–S–H and hydrotalcite was observed in all samples by X-ray diffraction, thermal analysis and scanning electron microscopy. Higher Al₂O₃ content of the slag decreased the Mg/Al ratio of hydrotalcite, increased the Al incorporation in the C(A)-S-H and led to the formation of strätlingite. Increasing Al₂O₃ content of the slag slowed down the early hydration and a lower compressive strength during the first days was observed. At 28 days and longer, no significant effects of slag Al₂O₃ content on the degree of hydration, the volume of the hydrates, the coarse porosity or on the compressive strengths were observed.     

Effects of porous C/C density on the densification behavior and ablation property of C/C–ZrC–SiC composites

C/C–ZrC–SiC composites were prepared by precursor infiltration and pyrolysis process using a mixture solution of organic zirconium-containing polymer and polycarbosilane as precursors. Porous carbon/carbon (C/C) composites with density of 0.92, 1.21 and 1.40 g/cm³ were used as preforms, and the effects of porous C/C density on the densification behavior and ablation resistance of C/C–ZrC–SiC composites were investigated. The results show that the C/C preforms with a lower density have a faster weight gain, and the obtained C/C–ZrC–SiC composites own higher bulk density and open porosity. The composites fabricated from the C/C preforms with a density of 1.21 g/cm³ exhibit better ablation resistance with a surface temperature of over 2400 °C during ablation. After ablation for 120 s, the linear and mass ablation rates of the composites are as low as 1.02 × 10⁻³ mm/s and −4.01 × 10⁻⁴ g/s, respectively, and the formation of a dense and continuous coating of molten ZrO₂ solid solution is the reason for their great ablation resistance.