A new adsorption–desorption model for water adsorption in porous carbons

A new model is proposed to describe the adsorption and desorption branches of water adsorption in carefully synthesized mesoporous carbon materials. This model is an extension of a previous adsorption–desorption model proposed by Do et al. We prepared mesoporous resorcinol–formaldehyde carbon cryogels (RFCCs) by sol–gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution, followed by drying with freeze-drying and then carbonizing the RF cryogels at a high temperature under a nitrogen atmosphere. The resulting carbon materials have different surface and pore properties, which are valuable in the study of their effects on water vapor adsorption and desorption on RFCCs. The experimental data were used to test the model, and we have found that the model describes reasonably well all the data. We have also observed some interesting, but not unexpected, results in the analysis: the water cluster size in mesopore is larger than that in micropore, and the hysteresis loop of adsorption–desorption in mesopores is greater than that in micropores.     

A new molecular model for water adsorption on graphitized carbon black

Adsorption of water on graphitized carbon black at various temperatures has been studied with a new molecular model of graphitized carbon black using Monte Carlo simulation. The model is a collection of graphene layers, modelled by the Steele potential, and a number of phenol groups forming clusters of various sizes which are placed randomly at the graphene edge sites to give an O/C ratio of 0.006. The results are compared with experimental data reported by Kiselev et al. [1] in 1968 for a range of temperatures, and for the first time a reconciliation between the experimental data and simulation has been successfully achieved. The simulation results show that water adsorbs preferentially around the functional groups to form clusters, which then grow and merge at the edges of the graphene layers, rather than adsorbing onto the basal planes of the graphene because the electrostatic interactions (hydrogen bonding) between water molecules are stronger than the basal plane–water dispersion interactions.     

A new procedure to measure water adsorption isotherms of porous fibrous materials

A typical relation between accumulated liquid, temperature, and vapour pressure characterizes any surface, in particular any porous structure. This relationship is usually described by means of “adsorption isotherms”, which are functions that correlate the amount of liquid in the porous material to the partial pressure of its vapour, for a given constant temperature. Speaking about fibrous insulation materials or building materials, the fluid of interest is simply water. The knowledge of water adsorption isotherms is of great importance in the formulation of heat and mass transfer models inside moist bodies. Typical experimental techniques for adsorption isotherm evaluation (salt solution methods, climatic chamber methods, etc.) require the conteporary control of both temperature and relative humidity of the environment surrounding the specimen. This often results in the need of dedicated and expensive experimental set-ups. In this work the possibility to use a simpler apparatus to obtain the sorption-desorption characteristics of a body is investigated from the theoretical point of view by means of simulated experiments. The proposed measurement procedure uses a closed, non permeable system in which only temperature is to be controlled, while the total water content, liquid plus vapor, remains constant. The new procedure offers an additional benefit, since both the constant water and the constant dry air mass constraints are used as further a␣priori information to improve the precision of the estimated results.     

A new mass transfer model for cyclic adsorption and desorption

This article presents a new mass transfer model which describes mass transfer rates in a spherical particle where cyclic adsorption and desorption occur. The parameters in the model equation were determined by matching the exact numerical solution to the prediction of this rate law over a range of cycle times. The maximum error was found to be 4.3%. Since the parameters are independent of cycle time, this model equation can be generally used for cyclic adsorption and desorption process regardless of the cycle time and cycle configuration.     

A multi-scale model for predicting the thermal shock resistance of porous ceramics with temperature-dependent material properties

This paper develops a novel multi-scale thermal/mechanical analysis model which not only can efficiently measure the thermal shock response but also highly reflects the effects of diversiform micro-structures of porous ceramics. Knowledge of the temperature distribution and time-varied thermal stress intensity factors (SIF) is derived by finite element/finite difference method and the weight function method in the macro continuum model. The finite element analysis employs a micro-mechanical model in conjunction with the macro model for the purpose of relating the SIF to the thermal stress in the struts of the porous ceramics. The micro model around the crack tip was established by using Voronoi lattices to accurately explore the micro-architectural features of porous ceramics. Hot shock induced center crack and cold shock induced edge crack are both considered. Effects of relative density and pore size on the thermal shock resistance are investigated and the results are well coincident with the experimental tests. The influence of cell regularity and cross section shape of the cell struts is discussed and the corresponding explanations are provided. The importance of incorporating temperature-dependent material properties on the thermal shock resistance prediction is quantitatively represented. These multi-faceted models and results provide a significant guide to the design and selection of porous ceramics against the thermal shock fracture failure for the future thermal protection system of space shuttle.     

A novel route to produce porous ceramics

The possibility to consolidate alumina powder stabilized Pickering emulsions of paraffin oil in ethanol by means of electrophoretic deposition (EPD) into freestanding porous objects is reported. The pore forming paraffin is extracted from the consolidated powder compact by means of evaporation prior to sintering. The sintered ceramics contain spherical pores with a diameter that can be tuned from 200 μm to 20 μm. Both open and closed porosities can be obtained by altering the emulsion composition. Since no pore forming fugitive solid organic binder is used, the delicate and time-consuming debinding step during processing is eliminated.     

Combustion synthesis assisted water atomization-solid solution precipitation: A new guidance for nano-ZTA ceramics

It is difficult to synthesize ceramics with ultra-fine nanostructures because of inevitable grain growth during the sintering process. In this work, a novel technique, i.e. combustion synthesis assisted water atomization (CSAWA) method, was invented to synthesize supersaturated Al₂O₃/ZrO₂ solid solution powders. The huge cooling rate supplied by CSAWA greatly improved the solubility of Al³⁺ in ZrO₂ lattice. Subsequently, the synthesized powders underwent a solid solution precipitation process. The ultra-fine ZrO₂ nanoparticles and Al₂O₃ matrix are precipitated from metastable phase, and the ZrO₂ nanoparticles are uniformly dispersed in Al₂O₃ matrix. Simultaneously, the powders were densified and formed compact ZTA ceramics. Together with detailed microstructure, phase composition, interface characteristic, mechanical properties, as well as the toughening mechanisms were collaboratively outlined. CSAWA-SSPP not only produces impressive comprehensive properties, but also much lower costs and simpler process than currently methods, which opens up a new route to industrially produce nano-ZTA ceramics with high performance.     

泡沫陶瓷的研究进展

介绍了泡沫陶瓷的特性、制造工艺、用途及在冶金工业中的应用。指出除现有的堇青石质、氧化铝质、堇青石－氧化铝质过滤器外，还开发了氮化硅质、碳化硅质、氧化铝质产品。     

泡沫陶瓷材料的研究进展

介绍了泡沫陶瓷的特性、制造工艺，并列举了泡沫陶瓷在几个方面的主要应用。指出了当前陶瓷材料的研究热点和今后发展需要解决的问题。     

Strengthening porous silicon-nitride ceramics

Translated from Steklo i Keramika, No. 7, pp. 18–19, July, 1992.     

A flexible porous copper-based metal-organic cage for carbon dioxide adsorption

A metal-organic cage (termed FJI-C9) based on six square-shaped Cu₂(CO₂)₄ paddle-wheel building units and eight flexible 1,3,5-trimethyl-2,4,6-tris(3-phenoxymethyl)benzoic acid (TTBA) linkers has been constructed. The porous FJI-C9 containing large cage of 1.5 nm shows high CO₂ adsorption uptake.     

A review of 3D printed porous ceramics

Three-dimensional (3D) printing of ceramics has gained widespread attentions in recent years. Many excellent reviews have reported the printing of ceramics. However, most of them focus on printing of dense ceramics or general ceramic aspects, there is no systematical review about 3D printing of porous ceramics. In this review paper, the 3D printing technologies for fabricating of porous ceramic parts are introduced, including binder jetting, selective laser sintering, direct ink writing, stereolithography, laminated object manufacturing, and indirect 3D printing processes. The techniques to fabricate hierarchical porous ceramics by integrating 3D printing with one or more conventional porous ceramics fabrication approaches are reviewed. The main properties of porous ceramics such as pore size, porosity, and compressive strength are discussed. The emerging applications of 3D printed porous ceramics are presented with a focus on the booming application in bone tissue engineering. Finally, summary and a perspective on the future research directions for 3D printed porous ceramics are provided.     

Analysis of steric mass-action model for protein adsorption equilibrium onto porous anion-exchange adsorbent

The ion-exchange equilibrium of bovine serum albumin (BSA) to an anion exchanger, DEAE Spherodex M, has been studied by batch adsorption experiments at pH values ranging from 5.26 to 7.6 and ionic strengths from 10 to 117.1 mmol/l. Using the unadjustable adsorption equilibrium parameters obtained from batch experiments, the applicability of the steric mass-action (SMA) model was analyzed for describing protein ion-exchange equilibrium in different buffer systems. The parametric sensitivity analysis was performed by perturbing each of the model parameters, while holding the rest constant. The simulation results showed that, at high salt concentrations or low pHs close to the isoelectric point of the protein, the precision of the model prediction decreased. Parametric sensitivity analysis showed that the characteristic charge and protein steric factor had the largest effects on ion-exchange equilibrium, while the effect of equilibrium constant was about 70%-95% smaller than those of characteristic charge and steric factor under all conditions investigated. The SMA model with the relationship between the adjusted characteristic charge and the salt concentration can well predict the protein adsorption isotherms in a wide pH range from 5.84 to 7.6. It is considered that the SMA model could be further improved by taking into account the effect of salt concentration on the intermolecular interactions of proteins.     

Amorphous silica wastes for reusing in highly porous ceramics

The paper analyzes a solution in green manufacturing of foamed or cellular ceramics. The objective of this study was to determine the technical solution for rice husk ash and “tales” of mixed glass cullet reusing based on the specific properties of these materials for creation of spherical holes inside ceramic using the process of coalescence of cellular glass. The paper reports on experimental results obtained from the production of lightweight cellular glass granules produced using glass cullet and rice husk ash. Lightweight cellular glass granules were mixed with clay, pressed and fired in air at 920°C. Clay sintering and the formation of ceramic were followed with the coalescence of cellular structure of glass granules and with the formation of spherical hollows inside the matrix. Density and strength of the fired ceramic bodies were determined. It is observed that the lightweight ceramics with density 900 ÷ 920 kg/m³ possess a compressive strength of about 5 MPa that is acceptable for bricks or tiles manufacture. The utilization of amorphous silica waste for lightweight ceramics manufacture helps in reducing waste disposal concerns and costs associated, and also transforms the waste into an alternative raw material with added value, moreover making the final product cheap.     

A BiVO4 photoanode grown on porous and conductive SnO2 ceramics for water splitting driven by solar energy

The transformation of solar energy into chemical energy stored as hydrogen fuel underlies the water splitting process into O₂ and H₂ in photo-electrochemical (PEC) cells. This a potentially promising technology to generate renewable and clean energy. To make this technology commercially viable, the engineering of appropriate low-cost and robust photo-electrode materials and substrates is needed. In this study, we introduce BiVO₄-photoelectrodes grown on conductive bulk SnO₂–Sb₂O₅ ceramics acting as porous substrate. For these photoelectrodes, the value of photocurrent density of 1.1 mA/cm² was achieved in 0.1 M NaOH electrolyte at 1.23 V vs. RHE (reversible hydrogen electrode) under LED light (λ = 455 nm). This PEC performance of these BiVO₄ photoelectrodes is reached in spite of using a simple and low-cost deposition technique, where the BiVO₄-precursor is delivered to the bulk porous ceramic substrate as a nebulized aerosol in air-flow at room temperature. The high porosity of the ceramic substrate permits some permeation of the aerogel into the pores to a depth of several micrometers to provide a 3D-growth of the BiVO₄-coating on conductive SnO₂ grains. The film thickness of the BiVO₄ on individual grains is approximately 100 nm. This construction of the photoelectrode leads to an effective interface with good absorption of solar radiation and good electron harvesting. The bulk ceramics assure favorable conditions for electron collection and charge transport, which results in a good PEC performance with this type of photoanode.     

A nitride whisker template for growth of mullite in SiC reticulated porous ceramics

Silicon carbide reticulated porous ceramics (SiC RPCs) were fabricated by polymer replica technique. The effects of nitride whisker template on the growth of mullite, the strut structure and mechanical properties of SiC RPCs were investigated. Prepolyurethane (PU) open-cell sponge was first coated by SiC slurry consisting of SiC, reactive Al₂O₃, microsilica and Si powder, then it was nitridized at 1400 °C in a flowing N₂ atmosphere to prepare SiC preforms. Subsequently, these preforms were treated by vacuum infiltration of alumina slurry and fired at 1450 °C in air. The results showed that Si₂N₂O whiskers grew on the surface and in the matrix of SiC preforms after nitridation. The diameter of struts in SiC RPCs increased after vacuum infiltration process because alumina slurry was easily adhered by the surface nitride whiskers. In addition, such whiskers inside the strut of SiC preforms acted as the template to promote the growth of column-liked mullite in SiC RPCs. The mechanical properties and thermal shock resistance of SiC RPCs were greatly improved due to the special interfacial characteristics of multi-layered struts as well as better interlocked column-liked mullite in SiC skeleton.     

生物SiC多孔陶瓷的研究进展

介绍了生物SiC多孔陶瓷的研究现状,并对生物碳模板的分类、制备方法进行了详尽的叙述,同时对生物SiC多孔陶瓷的各项性能进行了综述,最后对生物SiC多孔陶瓷的发展趋势作了总结。