Porous Middle Layer Research Articles

Ablation behavior of CVD-TaC coatings with different crystal structures for C/C composites under oxyacetylene flame

TaC coatings with four kinds of crystal structures were prepared on carbon/carbon composites by chemical vapor deposition. The surface morphologies, microstructure transformation, and ablative behaviors of TaC coated C/C specimens were investigated. Results show that the coatings with acicular crystal structure exhibit better ablation resistance with lower ablation rates, especially the needle-piled sample. The bistratal structure composed of dense glass layer and compact TaC layer is beneficial for maintaining the integrity of acicular samples after ablation. But the formation of lamella grains and porous middle layer is the main factor for the damage and even exfoliation of the columnar specimens.

Dynamic response of functionally graded plates with a porous middle layer under time-dependent load

A dynamic analytical solution for a simply supported, rectangular functionally graded plate with a porous middle layer under time-dependent load based on a refined third-order shear deformation theory with a cubic variation of in-plane displacements according to the thickness and linear/quadratic transverse displacement is presented. The solution achieved in the trigonometric series form and rests on the Green's function method. Two porosity types and their influence on material properties, and mechanical behavior are considered. The network of pores is assumed to be empty or filled with low-pressure air, and the material properties are calculated using the power-law distribution idealization. Numerical calculations have been carried out to demonstrate the accuracy of the kinematic model for the dynamic problem, the effect of porosity, thickness of porous layers, power-law index, and type of loading on the dynamic response of an imperfect functionally graded material plate.

Rapid structural evolution and bone inducing mechanism of the multilayer coating with silicon-doped hydroxyapatite crystals on the microwave water steaming-hydrothermally treated titania coating

To reveal the formation mechanism of new bone tissues induced by the multilayer titania coating with silicon-doped hydroxyapatite (Si-HA), plasma electrolyte oxidation (PEO) and microwave steam-hydrothermal treatment (MG) were performed to form Si-HA nanorods rapidly on the PEO coating. In the present work, the length and diameter of Si-HA nanorods on the MG-treated PEO coating for 10 min (PEOMG10) were smaller than that those treated for 60 min (PEOMG60). The microstructure of the multilayer coating, including the porous middle layer containing anatase nanocrystal cluster, the middle anatase layer, Si-HA nanocrystals, and the outermost layer that grew Si-HA nanorods, was revealed by transmission electron microscopy (TEM). The in vitro mineralization test indicates that the PEOMG60 sample exhibits excellent apatite-inducing ability because of its high degradation. The in vivo animal experiment showed that the PEOMG10 implant has high interfacial bonding strength and excellent osseointegration interface status. The fracture for the PEOMG10 implant occurred at the interface between the coating and the bone side owing to its good interface status. The present study can expand the widespread applications of the titania-based hydroxyapatite composite materials for repairing hard tissues and teeth filling.

Static analysis of functionally graded plates with a porous middle layer based on higher order shear deformation theory with linear/quadratic transverse displacement

In this article, we present an analytical solution for an imperfect functionally graded plate based on higher order shear deformation theory with cubic variation of in-plane displacements according to thickness and linear/quadratic transverse displacement. The developed solution is used to analyze the static responses of a plate with a porous layer to mechanical loading. Two porosity types and their influences on material properties, displacement, and stress behaviors are considered. The network of pores is assumed to be empty or filled with low-pressure air, and the material properties are calculated using power-law distribution idealization in terms of the volume fractions of constituents. The computed results are presented to illustrate the accuracy of the proposed solutions based on comparisons to previously reported analytical and numerical solutions in the literature. We also analyzed the effects of different volume fractions and thicknesses of porous layers on the mechanical loading and mechanical behavior of the imperfect functionally graded plate.

Lithium salts as leachable corrosion inhibitors and potential replacement for hexavalent chromium in organic coatings for the protection of aluminum alloys

Lithium salts are being investigated as leachable corrosion inhibitor and potential replacement for hexavalent chromium in organic coatings. Model coatings loaded with lithium carbonate or lithium oxalate demonstrated active corrosion inhibition and the formation of a protective layer in a damaged area during neutral salt spray exposure. The present paper provides an abridged overview of the initial studies into this novel inhibitor technology for the active corrosion protection of aluminum alloys. Coating defects were investigated by microscopic techniques before and after exposure to corrosive conditions. Scanning electron microscopy analysis of cross-sections of the coating defect area demonstrated that the protective layer comprises a typical three-layered structure, which included a dense layer near the alloy surface, a porous middle layer, and a flake-shaped out layer. Potentiodynamic polarization measurements obtained with a microcapillary cell positioned in the coating defect area and electrochemical impedance spectroscopy confirmed the corrosion protective properties of these protective layers. The long-term corrosion inhibition of the lithium-based coating technology was tested in industrial coating systems.

An investigation of the corrosion inhibitive layers generated from lithium oxalate‐containing organic coating on AA2024‐T3 aluminium alloy

The protective film formed in a defect by leaching of lithium oxalate from model organic coatings during neutral salt spray exposure has been investigated. A scribed area of about 1 mm width was introduced on the coated AA2024‐T3 aluminium alloy. The scribed area was examined before and after exposure in neutral salt spray environment for 4, 8, 24 and 168 h by scanning and transmission electron microscopies. It was found that the lithium oxalate was able to leach from the organic coating during neutral salt spray exposure and it promoted the formation of a film that provided effective corrosion protection to the alloy. The typical film morphology consists of three different layers, including a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. Variation of the film morphology was also observed at different locations of the scribed alloy surface, which may be related to the difference of local concentration of lithium species. Electron energy loss spectroscopy detected lithium, aluminium and oxygen in the film. Although the film showed the varied morphologies in different regions of the scribed area, the alloy substrate was protected from corrosion when the film was formed. Copyright © 2016 John Wiley & Sons, Ltd.

Protective Film Formation on AA2024-T3 Aluminum Alloy by Leaching of Lithium Carbonate from an Organic Coating

An investigation into corrosion inhibition properties of a primer coating containing lithium carbonate as corrosion inhibitive pigment for AA2024 aluminum alloy was conducted. It was found that, during neutral salt spray exposure, a protective film of about 0.2 to 1.5 μm thickness formed within the area where an artificial defect was introduced by scribing through the coating to the base alloy. This film showed a multilayered structure consisting of a relatively compact layer near the alloy substrate, a porous middle layer and a columnar outer layer. The thicknesses of the layers varied, as a consequence of the difference in the local concentration of lithium species leaching from the primer coating. The presence of the film in the scribed area significantly reduced corrosion of the alloy, with little consumption of the metal substrate within the scribed area during neutral salt spray exposure. Furthermore, the presence of the protective film resulted in a significant increase of impedance modulus, measured after the salt spray exposure.

The corrosion protection of AA2024-T3 aluminium alloy by leaching of lithium-containing salts from organic coatings.

Lithium carbonate and lithium oxalate were incorporated as leachable corrosion inhibitors in model organic coatings for the protection of AA2024-T3. The coated samples were artificially damaged with a scribe. It was found that the lithium-salts are able to leach from the organic coating and form a protective layer in the scribe on AA2024-T3 under neutral salt spray conditions. The present paper shows the first observation and analysis of these corrosion protective layers, generated from lithium-salt loaded organic coatings. The scribed areas were examined by scanning and transmission electron microscopy before and after neutral salt spray exposure (ASTM-B117). The protective layers typically consist of three different layered regions, including a relatively dense layer near the alloy substrate, a porous middle layer and a flake-shaped outer layer, with lithium uniformly distributed throughout all three layers. Scanning electron microscopy and white light interferometry surface roughness measurements demonstrate that the formation of the layer occurs rapidly and, therefore provides an effective inhibition mechanism. Based on the observation of this work, a mechanism is proposed for the formation of these protective layers.

Measuring residual stress and its influence on properties of porous ZrO2/(ZrO2+Ni) ceramics

Ceramic–metal functionally graded materials (FGMs) have been extensively used in aerospace engineering where high strength and excellent heat insulation materials are desired. However, their performance highly depends on the internal residual stress, which is generated inevitably due to the thermal mismatch of ceramic and metal. In this paper, based on the nanoindentation test, the field distribution of the residual stress of porous ZrO2/(ZrO2+Ni) ceramic–metal FGMs is measured. The residual stress field measured by nanoindentation agrees qualitatively with the finite element simulation results. Then a constitutive relation is established to investigate the effects of residual stress on the macroscopic deformation behavior of porous ZrO2/(ZrO2+Ni) FGMs, which agrees well with the bending and compression experiments. It is found that residual stress can improve both the flexural strength and stiffness of the porous ZrO2/(ZrO2+Ni) FGMs, by densifying and compensating the tensile stress of the porous middle layer (ZrO2) during the bending process, respectively. However, it has no obvious influence on the ultimate compressive strength of the porous ZrO2/(ZrO2+Ni) FGMs, but mainly influences its initial stage of elastic deformation in the compressive behavior.

Thermal and hydraulic analysis of multilayered asphalt pavements as active solar collectors

The fulfillment of current environmental aims like reducing fossil fuel consumption or greenhouse gas emissions entails the development of new technologies that enable the use of cleaner, cheaper and renewable energies. Furthermore, the need to improve energy efficiency in buildings encourages scientists and engineers to find new ways of harvesting energy for later uses.The use of asphalt pavements as active solar collectors is introduced in this article. Several authors have studied the use of roads as an energy source before. However, a new technology is presented in which a multilayered pavement with a highly porous middle layer is used instead of a solar collector with an embedded pipe network. These collectors are fully integrated within the road infrastructure and may offer low cost solar energy for water heating.The paper includes a brief comment on the state-of-the-art. Then, a broad methodology is presented in which data, materials and procedures needed to run the tests are fully described. Finally, the results of the laboratory tests are stated and discussed.The prototype used in the laboratory provided excellent thermal efficiency. However, these good results contrast with the low flow rate levels registered during the tests. Thus, although this technology seems to be very promising, new experimental tests should be performed before an effective application is possible.

SEPARATION OF PROPANE FROM PROPANE/NITROGEN MIXTURES USING PDMS COMPOSITE MEMBRANES BY VAPOUR PERMEATION

This study deals with polydimethylsiloxane (PDMS)/polyvinylidene fluoride (PVDF) composite membranes for propane separation from propane/nitrogen mixtures, which is relevant to the recovery of propane in petroleum and chemical industry. The surface and cross-section morphology of PDMS/PVDF composite membranes was observed by scanning electron microscope (SEM). The surface morphology of PDMS/PVDF composite membranes is very dense. There are three layers, the thin dense top layer, finger-like porous middle layer and sponge-like under layer in the cross-section SEM image of PDMS/PVDF composite membranes. The effects of the types of cross-linking agents and pressure on the membrane permselectivity were investigated. The permeability of nitrogen was independent of feed pressure. However, the permeability of propane increased with the pressure increasing for all membranes. The membrane cured by a tri-functional crosslinker with attached vinyl groups had better performance than the tetra-functional one, in both ...