Porous Powder Materials Research Articles

Reliable determination of polymeric carbon nitride wettability: A standardized sessile drop method for pressed-tablet samples

The wettability of polymeric carbon nitride (PCN) is an important surface chemical factor affecting its catalytic and separation performance. However, due to the amphipathic characteristics of hydrophilic/lipophilic and porous powder properties, the contact angle (CA) of PCN measured by the common sessile drop method will be interfered by the substrate, resulting in randomness of the results. Herein, the pristine PCNs obtained by thermal polycondensation of different precursors in air or nitrogen atmosphere were used as the wettability research object. The CA of the PCNs was measured by a modified sessile drop method after the traditional powders were replaced by pressed-tablet samples. The influence of sample mass and applied pressure on specific surface area, pore volume, surface morphology and CA of the pressed-tablet samples was investigated carefully, and the optimal experimental conditions were determined. When the sample mass was 0.15 g and the applied pressure was 10 MPa, the measured water CA of PCNs was between 27 ∼ 34°, and the diiodomethane CA is between 24 ∼ 29°. The measurement results showed considerable stability and reproducibility. This improved CA measurement method provides a simple and standardized way to accurately explore the surface chemistry of PCN, and has the potential to be applied to other hydrophilic and/or oleophilic porous powder materials.

Features of Phase Transformations in Porous Powder Materials

Features of Phase Transformations in Porous Powder Materials

Кристаллические микроконусные покрытия на губчатом титане.

For the first time it was shown how to obtain microcone-shaped TiO2structures by means of anodizing of porous powder materials made of titanium sponge. It was established that during anodizing in 10 %Н2SO4+ 0,15 % HF electrolyte along with the growth of the X-ray amorphous nanoporous TiO2film a set of microcones with anatase crystalline structure is formed on the surface of titanium sponge powder particles. Microcones (height is up to 7m, base diameter is up to 5m) consist of multilayer nanoscale structures. Such structures are promising for the manufacture of new nanomaterials for catalytic and sensor devices.

Practical usage of study results of the porous materials weldability from corrosion-resistant steels when creating stamp-welded products with desired properties

It is shown that a significant factor limiting the use of porous powder materials for the manufacture of die-welded products is low tensile plasticity and insufficient weldability. Porous meshing materials (PMM) made of steel 12Cr18Ni10Ti (X10CrNiTi18-10) have the necessary technological and operational properties for the manufacture of permeable die-welded elements. The conditions for the formation of a weld in PMM fusion welding are affected by the porosity and the ratio of the thermal conductivity coefficients along the thickness of the welded edges and in the direction perpendicular to the movement of the welding source. Technologies for argon-arc welding of a heat exchanger-evaporator sleeve, electron-beam welding of filter elements with a housing, which are implemented in the manufacture of preproduction models, have been developed.

Influence of micropores on structural instability of the combustion wave

The article shows examples of visualization of the process of heat transfer by radiation in unstable combustion modes of porous powder materials, which are in good agreement with the results of high-speed video recording and micropyrometry. The mathematical model and the results of calculating the structure of the combustion wave in the Ni-Al system are presented. The contribution of radiative heat transfer at an adiabatic combustion temperature in the range of 810 % and the effect of its trigger shutdown with decreasing temperature were revealed.

Heat utilization system using vacuum insulation container with porous silica powder and phase change materials / chemical heat storage materials

Heat utilization system using vacuum insulation container with porous silica powder and phase change materials / chemical heat storage materials

Evaluating porous polylactide-co-glycolide/bioactive glass composite microsphere powders for laser sintering of scaffolds

While laser sintering (LS) processes are typically optimised towards denser powder beds, our approach is different as we investigate the use of non-dense powder beds made of porous composite powder materials of polylactide-co-glycolide (PLGA) and bioactive glass (BG) 45S5. Powders were produced via solid-in-oil-in-water emulsion with modified BG as porogen and changing PLGA:BG ratios with up to 50 wt% of BG. Characterisation was done using scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), thermal gravimetric analysis (TG), powder packing and flow, particle-size distribution (PSD) and X-ray tomography. The microparticles showed varying degrees of sphericity, porosity and specific surface area (SSA), while the BG porogen could be incorporated into or onto the foamed polymer. Powders were used for LS and gave parts with an overall porosity of ~ 75%. Our special approach might be interesting for multi-material LS for real biomimetic scaffolds with tailored hierarchical pore structures.

Self-Organization of a Bioactive Nanostructured Oxide Layer at the Surface of Sintered Titanium Sponge Powder Subjected to Electrochemical Anodization

Self-ordered nanoporous/nanotubular oxide films are prepared on the surface of porous powder materials of a titanium sponge by electrochemical anodization. By using scanning electron and atomic force microscopies, we establish that anodization of sintered powder of a titanium sponge in an electrolyte containing H2SO4 (10%) and HF (0.15%) yields an X-ray amorphous TiO2 film with a thickness of 250–350 nm and a regular pattern of nanopores and nanotubes with diameters of 30 to 70 nm. Our results confirm that the described method for surface modification of sintered powders of a titanium sponge holds promise in manufacturing bioactive implants.

Analysis of the adequacy and selection of phenomenological models of the elastic properties of porous powder materials

This article offers a phenomenological model of the moduli of elasticity of porous powder materials, which assumes only the deformation of the solid phase volume. The new model correlates the deformable volumes at the shear, tension, and volumetric compression and allows calculating the remaining moduli of elasticity of porous materials by the known values of one modulus of elasticity. It is found that, despite the dispersion of the experimental data, the averaged values of relative Young’s modulus \( E_{r} \) of porous metals and ceramics are identical. A number of theoretical models have been tested based on the averaged reference dependence of \( E_{r} \) on porosity ϕ. The results of calculations for the theoretical models, with the exception of the proposed model, are not consistent with the reference values of the Young’s modulus. The testing of one-dimensional phenomenological models has been provided by the limiting (linear and strongly nonlinear) experimental dependences \( E_{r} (\phi) \). According to the combined test results, the most accurate and versatile model is the new phenomenological one.

Effect of ultrasonic waves on infiltration of dispersed particles into the pores of the powdered material

The article is devoted to the fabrication technology of wares from porous powder materials by filling the metal matrix with various fillers under the effect of ultrasonic waves. Diffusion mechanisms of solid particles of the filler into the pores of the powder material in various cases of particle motion are considered. The mechanical description of particle-motion mechanism in the case of influence of gravity impact and under the joint influence of gravity and ultrasound is presented and filling the pores by solid particles of the infiltrating suspension is interpreted.

ChemInform Abstract: Porous Materials from Titanium Powders: Past, Present, and Future

AbstractReview: 67 refs.

Continual model variant of viscous materials Report 2. Experimental proof

Considering the non-uniform character of viscous flow of hard phase, the continual model of hot deformation of porous powder materials has been checked. The procedure of the phenomenological creep parameter identification for the hard phase of powder materials is described. A particular mechanism of viscous flow of hard phase particles is shown to be realized depending on temperature-force strain conditions. Unlike the cast materi- als the powder material creep process, alongside with volume and boundary diffusion, can be controlled by superficial diffusion as well. In case of the same creep mechanism, the offered continual model allows us to use for powder materials directly the phenomenological constants of cast materials.

An Improved Specimen Preparation of Porous Powder Materials for Transmission Electron Microscopy

An Improved Specimen Preparation of Porous Powder Materials for Transmission Electron Microscopy

Porous Materials from Titanium Powders: Past, Present, and Future

Literature overview and our own results are used to identify the most promising areas of research in the field of titanium porous powder materials (PPMs). The search for possible ways of further reduction in PPM cost is a relevant area. It includes not only the use of sponge titanium powder and titanium sponge as the feedstock but also titanium hydride powder and, in the long term, enriched rutile concentrate. The development of new methods to increase PPM mechanical strength, such as microalloying, use of bisized feedstock, etc., has a great resource-saving potential. Advantages of developing new processes to form and consolidate PPMs from titanium powders are described, including: formation of a gradient porous structure by spark plasma, electric-discharge, selective laser, and microwave sintering and microinjection molding; modification of physicochemical and biochemical properties of PPM pore surface to change functional characteristics; creation of composite PPMs containing isotropically distributed target components such as activators, sorbents, reinforcing additives, etc. It is important to develop PPMs with anisotropic structural properties across the thickness and (or) the area of the porous element distributing a flow of gas or liquid.

Modeling of structurization processes and mechanical properties of porous powder materials

A new approach to the formation of the mechanical properties of iron-based powder materials is proposed. The approach is based on model ideas on the structurization of bulk powder mixtures under compacting pressure. It is established that as the porosity increases (decreases) within the range 5–25 %, the structure of compacted powder mixtures (compacts) alternates between mesostructural and submesostructal states.

Modelling of Recrystallization Curves of Porous Copper-Titanium Powder Materials

In this paper, modelling and plotting of recrystallization curves of copper-titanium powder materials with titanium content of 0.5%, porosity 5% and 10%. The mathematical model that describes an influence of temperature, degree of deformation, strain rate, initial grain size and porosity to grain size after deformation has developed. The interconnection of deforming parameters and structure has presented by function of several variables with analytical expression obtained by method of undetermined coefficients based on experimental data. Theoretical recrystallization curves for copper-titanium powder materials with different porosity have plotted. It has established that porosity decelerates the kinetics of structure formation during dynamical softening of porous powder materials.

Thermal evolution and sintering of chondritic planetesimals

The major aim of this study is to assess the effects of sintering of initially porous material on the thermal evolution of planetesimals, and to constrain the values of basic parameters that determined the structure and evolution of the H chondrite parent body. A new code is presented for modeling the thermal evolution of ordinary chondrite parent bodies that initially are highly porous and undergo sintering by hot pressing as they are heated by decay of radioactive nuclei. The pressure and temperature stratification in the interior of the bodies is calculated by solving the equations of hydrostatic equilibrium and energy transport. The decrease of porosity of the granular material by hot pressing due to self-gravity is followed by solving a set of equations for the sintering of powder materials. For the heat conductivity of granular material we combine recently measured data for highly porous powder materials, relevant for the surface layers of planetesimals, with data for heat conductivity of chondrite material, relevant for the strongly sintered material in deeper layers. To demonstrate the capability of our new model, the thermal evolution of the H chondrite parent body was reconstructed. The model starts with a porous body that is later compacted first by 'cold pressing' at low temperatures and then by 'hot pressing' for temperatures above \approx 700 K, i.e., the threshold temperature for sintering of silicates. The thermal model was fitted to the well constrained cooling histories of the two H chondrites Kernouve (H6) and Richardton (H5).

Determination of the corrosion rate of powder materials by electrochemical methods

The application of polarization and impedance measurements to determine the corrosion rate of porous materials and those infiltrated with copper, produced by powder metallurgy, in neutral chloride electrolyte is examined. The determination of the corrosion rate of porous powder materials per true surface area in view of their heterogeneity is described.

MODELING OF PLASTIC DEFORMATION OF POROUS POWDER MATERIALS

In the present study the model of plastic deformation of porous powder materials (PPM) is described and numerically simulated. This model enables prediction of change of fundamental technological parameters of PPM in plastic deformation conditions, i.e. porosity, pore size, specific surface and mechanical properties. Porous media is described by unit cells consisting of eight powder particles. The parameters of unit cell (the distance between the centers of particles, the angles of the array and the dimensions of interparticle connections) form the model of porous material and define its technological characteristics. The model takes into account the effect of deforming anisotropy on PPM properties. Calculations are performed in nonorthogonal coordinates connected with unit cell. In the case of uniaxial straining obtained numerical results have shown good agreement with the experimental results.

Densification model for porous metal powder materials: Z.Y. Zhou et al. (South China University of Technology, Guangdong, China.) J. Mater. Process. Technol., Vol 129, 2002, 385–388

Densification model for porous metal powder materials: Z.Y. Zhou et al. (South China University of Technology, Guangdong, China.) J. Mater. Process. Technol., Vol 129, 2002, 385–388