Production and properties of porous unfired zircon ceramics

Conclusions We examined the conditions for obtaining porous, uniformed ceramics from zircon. We studied the influence of the concentration and size of the macropores on certain properties of the resulting ceramic. An assessment of these properties suggests that it is prospective to use porous unfired zircon ceramics as heat insulation for high-temperature equipment.Translated from Ogneupory, No. 1, pp. 34–37, January, 1984.     

多孔纳米复合材料的制备及性能研究

用比表面积为1200m^2／g,平均孔径是3．7nm的活性炭作为无机相,用丙烯酰胺作为有机相,制备多孔纳米聚丙烯酰胺一活性炭复合材料,并研究其对酚类化合物的吸附过程。结果表明,经聚合物修饰过的活性炭吸附能力增强,并以化学吸附为主,吸附容量随吸附时间、吸附剂量的增加而增加,最后达到平衡值,吸附过程更适合Freundlich等温吸附方程式。     

Hydrodynamic processes in highly permeable porous cellular materials

The flow pattern in a cell in a layer of a highly porous cellular material is analyzed on the basis of Navier-Stokes equations by the finite-element method. The hydrodynamic resistance of highly permeable porous cellular materials to the transfer of liquid and gaseous media is determined. A comparison with experimental data is made.     

Production of porous materials by dealumination of Ca-A zeolite

Three conventional methods of dealumination were tested on the alumina-rich Ca-A zeolite. The mild acid leaching and the hydrothermal treatment led to mesoporous materials with a sharp distribution of pore size in the 4 nm region. On the other hand, treatment with ammonium hexafluorosilicate resulted in materials with mesopores of 12 nm in size. The latter technique produced the best thermally resistant materials which exhibited also the largest void volume and the highest cation exchange capacity.Presented in part at the Fall Meeting of the Materials Research Society in Boston (U.S.A.), Nov. 28–Dec. 2, 1994.     

Process and quasi-static compressive properties of highly porous palladium bulks

Highly porous palladium bulks with open porosities from 77.8% to 82.0% are prepared by powder metallurgical process with Na₂CO₃ as the filler material. Compressive properties of the prepared porous Pd bulks have been investigated at strain rates of 10⁻³–10⁻¹ s⁻¹. It has been found that the porous Pd bulks first show a short elastic region, then a long and oblique stress yield region, and finally, a densification region where the stress increase rapidly in the nominal stress–nominal strain curves. The effect of strain rate on the compressive properties of the porous Pd bulks is also discussed.     

Effective properties of suspensions,composites and porous materials

Three effective properties of heterogeneous systems are discussed from the viewpoint of rational mechanics and micromechanics: viscosity of suspensions and the tensile modulus and thermal conductivity of solid composites, including porous materials. Rigorous bounds (Voigt–Reuss and Hashin–Shtrikman bounds) are given as well as model relations for prediction and fitting purposes (dilute approximations, power-law relations, exponential relations, Coble–Kingery relations and new relations recently proposed by the authors). The semi-empirical nonlinear relations for the volume fraction (or porosity) dependence, including exponential and power-law relations with and without percolation threshold, are presented in a new systematic way which emphasizes the formal analogies between these relations and might become a useful tool in the future education of materials scientists and engineers.     

Production of highly porous fractal coatings by the plasma-explosion method

Experiments on deceleration of a dense metal plasma obtained under explosive loading of porous specimens have shown that a highly porous coating is formed on the target surface. The coating has a vortex structure; finely dispersed fractal filaments are located on the surface of the vortices. The sprayed surface consists of the recrystallized material of the porous specimen with small admixtures of the target material. In the case of deceleration of a multicomponent plasma, the coating has an analogous structure and consists of the specimen components and target material, which are uniformly distributed over the surface.Institute of Geosphere Dynamics, Russian Academy of Sciences, Moscow 117334. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 110–113, March–April, 1995.     

Preparation of porous spodumene/zircon composite ceramics and its thermal and mechanical properties

Abstract

Porous β-spodumene/zircon (ZrSiO₄) composite ceramics were prepared by addition of zirconia to spodumene mineral using conventional solid reaction methods. The formation of the zircon was investigated by means of the differential scan calorimetry measurements and an X-Ray diffractometer. The microstructure of the composite ceramics was observed through a scanning electron microscope. The results show that the presence of zircon benefited the formation and stability of the porous structure and improved significantly the thermal endurance and mechanical properties of the spodumene matrix. The composites with 10–15% porosity exhibit an excellent thermal shock resistance, a low thermal expansion coefficient of approximately 1·4 × 10^?6 K^?1 in the range of 200–800°C and a high flexural strength about 100 MPa. It is found that the spodumene/zircon composites, widely used as a high temperature structure material, can be synthesised by a cost effective method.     

Some technological laws and properties for highly porous ceramic concretes

Conclusions Using ceramic concrete made from zirconia as an example we formulated conditions and established the main technological laws for obtaining highly porous ceramic concretes.We analyzed the composition and microstructure of the ceramic concrete from the point of view of the existence in the system of noncompensated shrinkage. It is shown that for ceramic concrete with a high bond shrinkage during drying and heat treatment, with the purpose of reducing the shrinkage stresses in the system, it is necessary to use multifraction (coarse, medium, and fine) fillers.We show the effectiveness of using, as one of the filler components, removable poreforming additive, based on foamed polystyrol.The optimum region of the grain-size distribution of the components was established; this comes within the true specific volumes in the structure of the shaped ceramic concrete and amounts to 20–30% bond, 20–25% fine (0.1–0.4 mm) and 25–40% coarse (5–10 mm) filler made from waste zirconia foamed ceramics, and 20–25% foamed polystrol (0.63–1.6 mm).We studied certain properties of the resulting materials with a porosity of 60–75% and a compressive strength of 5–20 MPa.Compared with other highly porous materials, for example, foamed ceramics, the highly porous ceramic concretes have technological advantages (much lower water capacity of the shaping system, reduced shrinkage in drying and firing) and also improved operating characteristics, for instance, thermal conductivity, thermal-shock resistance and volume constancy.Translated from Ogneupory, No. 2, pp. 20–25, February, 1984.     

Production and aging of highly porous 17-4 PH stainless steel

This study describes production of highly porous 17-4 PH stainless steel for biomedical implant applications by space holder-sintering technique. 17-4 PH stainless steel powders were mixed with space holder and then compacted. For designing pore properties, both spherical and irregular shaped carbamide with different particle size ranges were used as space holder and removed by water leaching. Porous 17-4 PH steel specimens were sintered at 1,260?°C for 40?min. Boron was used as a liquid phase sintering additive. In addition, sintered specimens were aged in order to increase mechanical properties. Specimens were austenitized at 1,050?°C and then quenched. Quenched specimens were aged at times of 1?C6?h at temperatures between 450 and 570?°C. The pore size and shape of the 17-4 PH stainless steel foams replicated the initial size and shape of the carbamide particles. This suggests that pore properties can be designed by using proper size, shape and content of space holder.     

Some features of the properties of porous and composite materials

A semioctahedral model of the structure of low-porosity materials is proposed. Using this model, the percolation thresholds (critical porosities) for the permeability and the conductivity of these materials are determined. Expressions for the tortuosity of the pore space of granular and cavernous media are refined throughout the range of the permeable porosity, with the critical porosity taken into account. It is shown that porous materials and composites that are partially filled with a liquid are natural gradient materials. It is demonstrated that the properties of filters and membranes can be controlled both by varying the thickness of the permeable material and by modifying (compacting) the surface layer.     

Improvement of the magnetic properties of highly porous open-celled magnets

In the present study, we have investigated the influence of B₂O₃ addition on structural and magnetic properties of hard magnetic BaFe₁₂O₁₉ foams. In the presence of B₂O₃ open-celled foams were successfully fabricated at a calcination temperature of 1300 °C. Magnetization values have been improved by 50% with B₂O₃-addition. Remanence magnetization (M_R), specific magnetization at 1.5 T (M_S) and coercive field (H_c) values were obtained to be 32.7 emu/g, 63.0 emu/g and 2100 Oe, respectively for the 0.5 wt% B₂O₃ containing foams having 30 pores/in. Foams with these magnetic properties have the potential to be used in different areas of technology as permanently magnetic materials.     

Wear properties of new porous carbon materials: Woodceramics

The purpose of this investigation was to analyze the fundamental wear properties of new porous carbon materials Woodceramics. Wear tests were carried out by sliding an alumina ball (R=1.5, 4.0 mm) or hemispherical diamond pin (R=0.075 mm) against a Woodceramics plate (MDF-800), under three lubrication conditions: unlubricated in air, impregnated with base oil, and in water. The specific wear rate was calculated from the profile of the worn surfaces, and the relationship between the specific wear rate and the contact pressure parameter (W/R ²)^1/3 was obtained. Worn surfaces were observed with a scanning electron microscope (SEM) to clarify the microscopic wear mechanisms. The following principal results were obtained: (1) The specific wear rate of Woodceramics increases rapidly with increasing contact pressure parameter (W/R ²)^1/3, under all lubricated conditions; (2) When the contact pressure parameter (W/R ²)^1/3 is less than a certain critical value, the specific wear rate of Woodceramics is less than 10^–8 [mm²/N], which is low enough for practical use; (3) The wear mode of Woodceramics can be classified into the following three modes: large-scale brittle fracture-induced wear (flake formation), small-scale brittle fracture-induced wear (powder formation), and ultra mild wear (ploughing).     

Friction properties of new porous carbon materials: Woodceramics

Woodceramics are new porous carbon materials obtained from wood or woody materials impregnated with phenol resin, and carbonized in a vacuum furnace at high temperature. Woodceramics have several superior characteristics from the viewpoints of engineering materials and ecological materials: they are hard and strong, have porous structure and low density, are made from natural resources, do not cause environmental pollution, and are cheap to manufacture. This paper describes the fundamental friction properties of Woodceramics in sliding contact with several materials. Woodceramics made of medium density fiberboard (MDF) and beech impregnated with phenol resin and carbonized in a vacuum furnace at 800°C and 2000°C were rubbed against alumina, silicon nitride, bearing steel and diamond by using a reciprocating friction apparatus. Experiments were carried out unlubricated in air, impregnated with base oil and in water, at several normal loads and sliding velocities. The following principal results were obtained: (1) The friction coefficient is around 0.15, under all three lubrication conditions; (2) The friction coefficient slightly decreases and then stays constant with increasing normal load; (3) The friction coefficient is not affected by sliding velocity; (4) Woodceramics have a good self-lubricity.     

Sol-gel and SPS combined synthesis of highly porous wollastonite ceramic materials with immobilized Au-NPs

Here we present a prospective method of sol-gel synthesis of highly porous wollastonite ceramic powders with controlled macroporous structure (mean pore size ~160 nm) and immobilized gold nanoparticles (particle size is less than 50 nm). The method's distinction is based on using the colloidal template (micelles of "core-shell" polymer latex) both as a poreforming agent and as nanoreactors for nanoparticle synthesis in the system wollastonite/Au-NPs. We revealed the impact of template thermal removal on the morphology of nanostructured wollastonite. We also optimized thermal treatment to obtain defect-free macroporous calcium silicates. Template functionalization by size stabilized gold nanoparticles with their following immobilization into the porous volume of synthesized wollastonite has been described. Besides, an original nonstandard method of combined sol-gel (template) synthesis and spark plasma sintering (SPS) is suggested to obtain the wollastonite ceramic compounds with bimodal pore size distribution (100–500 nm and not less than 1 µm), high mechanical strength (compressive strength limit ~120 MPa) and containing immobilized Au-NPs. Peculiarities of biporous silicate framework formation has been studied using two types of poreforming agents (templates) of various origin, shape and size, introduced during different stages of sol-gel and SPS processes. These templates are organoelemental polymer latex of “core-shell” type and nonorganic carbon filler. Developed approaches are innovative and provide to make new materials with unique characteristics and functional properties as bone-like structure, mechanical stability, antibacterial and anti-inflammatory effects and etc. The materials meet all the biomaterials requirements and are in high demand by modern medicine.     

Processing,properties and applications of highly porous geopolymers: A review

Geopolymers, possessing a semi-crystalline three-dimensional inorganic network generated by the dissolution and reaction of a solid alumino-silicate source with an activating solution, have attracted increasing attention from both academia and industry because of their unique and favorable characteristics. This review deals with the synthesis, characterization and potential applications of porous geopolymers, realized through different processing routes. Firstly, the processing approaches are divided into five categories: (i) Direct foaming, (ii) Replica method, (iii) Sacrificial filler method, (iv) Additive manufacturing, and (v) Other methods. Their microstructure, porosity and properties are compared and discussed in relation also to the different processing routes. This review highlights the fact that porous geopolymers are promising low-cost candidates for technologically significant applications such as catalyst supports or membranes, filtration of liquid or gases, adsorption and insulation. This review aims at summarizing the main published results and fostering further investigations into developing innovative ways to generate components with improved properties.     

Synthesis and properties of porous carbon materials from natural cryptocrystalline graphites

The applicability of cryptocrystalline graphites as porous carbon materials was studied. The properties of the resulting products were examined with the use of various physicochemical methods of analysis.     

Preparation and properties of porous carbon materials based on fallen leaves

The properties of porous carbon materials prepared by the thermolysis and activation of fallen leaves pretreated with alkali metal ions were studied. A regression model was proposed to relate the sorption activities of the resulting materials toward iodine and methylene blue with the surface properties of these materials.     

Production and properties of highly oriented polypropylene by die drawing

A comprehensive examination of the die-drawing behavior of polypropylene has been carried out, examining the effects of draw temperature, haul-off speed, and initial billet size. A range of oriented products was obtained and characterized, primarily by the determination of Young's modulus at room temperature, the maximum modulus being 20 GPa for a draw ratio R_A of 23.2. Using a large-scale machine, it was found possible to produce drawn products at speeds up to 2 m min^?1 at a draw temperature of 155°C and R_A of 19.3. The dynamic mechanical behavior of several drawn materials was studied over the temperature range ?30 to +80°C. It was of particular interest that the β relaxation was found to be absent in samples of high draw ratio.