Partial Impregnation Research Articles

Modelling the Impregnation of a Pressure-Tight Casting

AbstractPressure tightness is important for many die-cast aluminium castings, but the interconnected porosity formed in the aluminium alloy high-pressure die castings (HPDC) can form a network connecting several surfaces of the casting, especially as a result of machining after casting. The resulting potential leakage path can be imagined as a series of discontinuities varying in size over wide limits, where voids of different volumes are connected by channels of smaller cross section. Although vacuum impregnation is often used to ensure pressure-tightness is a robust technology, cavity systems through the casting can still cause leakage after impregnation. This study addresses the issues of the impregnation of discontinuities with a complex geometry. The elementary part of a complex cavity geometry consists of a cavity and a capillary channel. We estimated the limited permeability of the capillary section using a mathematical model based on the Hagen–Poiseuille equation. The calculation results prove that the degree of filling of the cavity with a capillary section is basically a function of the geometrical characteristics of the cavity, primarily the radius of the capillary. If the cavity system also contains a section with a diameter of less than 28 μm, impregnation does not necessarily ensure the gas tightness of the casting. Depending on the radius of the capillary, the impregnation of a cavity of a given volume and connected to the surface through a capillary section of a given length can produce three different results. Above a certain capillary radius, filling is complete, below a certain capillary radius only the capillary itself will contain resin, and between the two limit values, the partial impregnation of the cavity is expected but the capillary section is not filled.

Change in Permeability of Loose Rocks in Partial Impregnation with High-Elastic Polymer

Change in Permeability of Loose Rocks in Partial Impregnation with High-Elastic Polymer

Nondestructive measurement of the capillary water absorption coefficient and water transport behaviors of porous building materials by using single-sided NMR

Capillarity has an important effect on the durability of buildings, and the capillary absorption coefficient is a key parameter to describe the strength of material capillarity. Most of the methods currently used to measure the capillary absorption coefficient of materials can damage the sample or are not accurate enough and need to be improved. This paper proposes a method to measure the capillary absorption coefficient of brick, sandstone, mortar and concrete by using a single-sided nuclear magnetic resonance (NMR) technique, which has the advantages of accuracy, nondestructiveness, continuity and rapidity. The relative error of the capillary absorption coefficient obtained from three repetitions of the experiment ranges from 0 to 5.11%, which is in the range of 0.64%∼1.30% compared with that obtained by the partial impregnation method. This method has great potential for application in in situ testing. This paper also analyzed the water transport behaviors in porous building materials based on the variation in NMR signal intensity in the measured materials and established a water transport model. The model is divided into two stages: the first stage is mainly the one-dimensional rise in moisture in the vertical direction. The second stage is mainly the diffusion of moisture in the horizontal direction, which continuously fills each pore space to saturation. Difficulty in removing air leads to a reduced rate of water absorption in the second stage.

An innovative prestressing system of prestressed carbon fiber sheets for strengthening RC beams under flexure

An innovative prestressing system was developed in this study, which can effectively anchor the prestressed carbon fiber sheets as well as conveniently apply prestress to the carbon fiber sheets. Tensioning tests of the carbon fiber sheet-anchor assemblies were first conducted to verify the anchorage behavior of anchors. Then this prestressing system was used for strengthening reinforced concrete (RC) beams to further verify its feasibility and investigate the effect of the impregnation and curing conditions of the carbon fiber sheets on the flexural strengthening efficiency. The results indicated that the tested ultimate capacity of the carbon fiber sheet-anchor assembly reached 72.1∼97.9% of the theoretical ultimate capacity of the carbon fiber sheet based on different impregnation and curing conditions. The concrete crushing failure and rupture failure of prestressed carbon fiber sheets occurred in the strengthened RC beams. The cracking and yielding loads of the RC beams with prestressed sheets were increased by 56.7∼68.5% and 21.7∼30%, respectively, while those with non-prestressed sheets were increased by 27.3% and 13.7%, respectively. The ultimate load was significantly affected by the impregnation and curing conditions. The prestressed carbon fiber sheets with the uncured full impregnation condition were not superior to the non-prestressed sheets in terms of the ultimate load, whereas the cured full impregnation and partial impregnation conditions were more effective than the uncured full impregnation condition. Finally, theoretical equations were used to calculate the cracking, yielding, and ultimate moments of RC beams strengthened with prestressed carbon fiber sheets.

Detection of Porosity in Impregnated Die-Cast Aluminum Alloy Piece by Metallography and Computer Tomography

The porosity of die-cast aluminum alloys is a determining factor for the quality of the product. In this paper, we studied the porosity of a selected part of a die-cast AlSi9Cu3(Fe) compressor part by computer tomography and metallography. In the case of this part, the achievable resolution by CT, a non-destructive testing method, was 30 μm—this method could not detect smaller cavities. Based on metallographic analysis, the percentage of defects larger than 30 μm ranges from 10 to 30% of the total number of defects, which represents 75–95% of the defective area (area ratio). Impregnation with methacrylate resin (used to seal cavities to prevent leakage) can be detected with UV-illuminated optical microscopic examination on metallographically prepared specimens. As confirmed by scanning electron microscopy, partial filling and partial impregnation can occur in a system of shrinkage cavities.

Ir–Ru Electrocatalysts Embedded in N‐Doped Carbon Matrix for Proton Exchange Membrane Water Electrolysis

AbstractMore active electrocatalysts for H2 and O2 evolution reactions, efficient membranes, and robust porous transport layers (PTL) are required for designing advanced proton exchange membrane water electrolysis (PEMWE) systems. An N‐doped carbon matrix is introduced in this study to surpass the existing Ti PTLs. One‐step pyrolysis results in the carbonization of polyaniline films to the N‐doped carbon matrix, simultaneous formation of desiccation cracks and IrxRuy nanoparticles, and partial impregnation of the synthesized particles into the carbon matrix. The embedded IrxRuy nanoparticles are firmly bound to the surface of the carbon matrix, inhibiting the dissolution and detachment of the nanoparticles during the O2 evolution reaction (OER). The cracks in the carbon matrix allow the steady transport of the produced O2, comparable to conventional PTLs. After optimizing the Ir and Ru contents of the nanoparticles based on the electrocatalytic performance, Ir88Ru12 embedded in the N‐doped carbon matrix is found to be the most suitable catalyst for enhancing the OER performance of the PEMWE system with negligible degradation. These findings can potentially contribute to the industrial application of PEMWE. Relevant electrochemical systems with membrane electrode assemblies, such as fuel cells and CO2 reduction systems, can be modified using the suggested structure.

Towards low polymer content transparent composites via novel integration engineering

Abstract The high polymer and low wood content of current transparent wood has limitation in the mechanical strength and hence obstruct green sustainable transition of the building industry. In this study, a novel method for manufacturing transparent wood was reported by minimizing the usage of polyethylene glycol using partial impregnation followed by a densification approach. The delignified wood was firstly partially impregnated by polyethylene glycol, and subsequently compressed to eliminate pores for the compressed transparent wood, providing the strong hydrogen bonds and dense structures for transparent wood. The wood content of the novel compressed transparent wood was dramatically increased to 64%, compared with the uncompressed transparent wood of 25%. Additionally, the obtained compressed transparent wood demonstrated satisfactory optical transmittance, suitable thermal energy storage, and superior mechanical strengths owing to the formation of densely packed microstructures. This novel, sustainable, and low-cost transparent wood was easy to be manufactured while having increased mechanical and energy-saving characteristics compared to those available in the existing market.

Laminated Transparent Woods with Adjustable Optical and Enhanced Mechanical Properties

AbstractTransparent wood is promising for energy‐saving buildings, but its poor mechanical properties in transverse direction dramatically limit its applications. To resolve the problem, a novel processing technology is developed to fabricate laminated transparent woods. Various kinds of transparent woods are prepared by stacking partially impregnated woods in different styles and then compressing them. The wood template contents in these transparent woods are significantly increased by the partial impregnation compared with traditional full impregnation. The influence of lamination structures on the properties of the transparent woods is also evaluated. As the number of laminate layers increases from one to three, the optical transmittance reduces from ≈70% to 44%, respectively, while the haze increases from 32% to 66%. The isotropy of scatter light distribution could be achieved by controlling lamination structures for more uniformity in indoor illumination. The mechanical properties of the transparent woods are dramatically enhanced, and the highest tensile and flexural strength can reach 134.0 and 192.3 MPa, respectively. Additionally, the direction‐dependence of mechanical strength is reduced by cross‐laminating. The adjustable optical features, excellent mechanical strengths, and low thermal conductivity endow the prepared transparent woods a promising candidate for energy‐efficient buildings applications.

AUTOMATED CALCULATIONS IN THE DEVELOPMENT OF ENERGY-EFFICIENT DESIGNS OF FURNACES FOR ALUMINUM SCRAP REMELTING

The analysis of operational thermal conditions of the furnaces for aluminum scrap remelting is given. It was established that it is necessary to choose refractory materials with aluminum oxide content more than 85 % and the thickness of the thermal insulation should ensure the temperature of the external surfaces not higher than 50 °C when designing the furnaces for lining. On the basis of relevant methods packages of application programs have been developed for design calculations of lining and thermal insulation considering thermal conductivity change of individual layers as a result of their complete or partial impregnation with molten aluminum; calculations of energy balances; the selection of external heating devices with electric or flame heating. The power of the external heat source, the amount of heat spent on heating the scrap to the melting temperature, melting and overheating the melt to the working temperature and heat loss have been taken into account in the energy balance. The heat balance equation is used for determination of the melting time for electrically heated furnaces or the power of burner devices at the desired melting time. In the design calculations, the necessary thicknesses of lining and heat-insulating materials are chosen for all elements of enclosure. With appropriate calculations in dialog mode, it is also possible to change materials and their thickness quickly in case of exceeding the allowable operating temperatures of these materials. Options of using electric tape or wire heaters made of nichrome or EI-626 steel were considered during external heating devices calculations. Flame heating can be implemented using gas burners or liquid fuel nozzles. Further variant calculations based on the developed methods and software made it possible to create a furnace design with a capacity of 600 kW with reduced energy and operating costs for the melting process. Bibl. 14, Fig. 1, Tab. 1.

Cold Spray Metallization of Hybrid Thermoplastic - Thermoset Fiber Reinforced Composite

Surface metallization is amongst the recent trends in the polymer and polymer matrix composites (PMCs) research industries to improve the electrical and thermal properties and exploit the subsequent utilization in the aerospace sector. Specifically, polymer matrix composites have been subjected to the limitations in form of high temperature exposure and substrate deterioration. The present study encompasses a new strategy in the manufacturing and metallization process. The first stage in the manufacturing of hybrid thermoplastic-thermoset composite was the hot compaction which comprised of primary preform preparation enabling the partial impregnation of the thermoplastic resin through the fabric reinforcement layer. The subsequent stage entailed the preform vacuum bagging and conducting catalyzed thermoset resin impregnation. The vacuum resin infusion step included a cocuring cycle to generate a fiber reinforced composite comprising of thermoplastic and impregnated thermoset resin with improved adhesion. Resin flow front movement was analyzed during the resin infusion process. Composite metallization was achieved through cold spray (CS). CS process parameters influence on the coating quality and characterization of laminates through microstructural analysis and results have been reported. The hybrid composite with thermoset resin through thickness and in-plane impregnation was achieved with the intact adherent thermoplastic layer after the curing cycle. In the CS metallization, the effective operative window of stand-off distances (SoD) and temperature has been determined.

Manufacturing and metallization of hybrid thermoplastic-thermoset matrix composites

Metallization is a common strategy employed to enhance the electrical and thermal conductivity of polymer matrix composite materials. Nevertheless, metallic deposition on polymer-based materials is challenging due to the inherent limitations related to high temperature exposure of the substrate. In this article, a new technique for the manufacturing of composite laminates and the subsequent metallization by cold spraying of metallic powder is presented. The composite manufacturing route is based on the production of thermoplastic-thermoset hybrid substrates and consisted of two main stages: in the first stage the partial impregnation of a reinforcement textile by a thermoplastic film was promoted by hot pressing compaction. Afterwards, the prepared lamina was vacuum bagged with other reinforcing layers and impregnated by the thermoset catalyzed resin by a vacuum infusion process. Finally, the thermoset and thermoplastic layers were co-cured to increase the adhesion of the substrate with the thermoplastic film. The metallization of composite laminate was obtained through the cold spraying technique, depositing powders on the thermoplastic surface layer. The effect of processing parameters on the coating deposition, quality and microstructure was reported and discussed.

Experimental determination on the capillary water absorption coefficient of porous building materials: A comparison between the intermittent and continuous absorption tests

The liquid water transfer in porous building materials has a great influence on the hygrothremal properties of the materials. The capillary water absorption coefficient a key parameter characterizing the water absorption capability of porous building materials, which is essential to the simulations of moisture transfer. However, the traditional standard measurement (partial impregnation method) which has been widely used today has some disadvantages, such as human error and discontinuous testing. In this paper, an improved continuous measurement method, which is still based on the partial impregnation strategy, was proposed, featuring continuous and automatic data acquisition during the adsorption tests without interruption by an operator. As a typical porous building material, autoclave aerated concrete (AAC) featuring lightweight and high porosity was taken as an example to study the effects of the method on the measured results of capillary water absorption coefficient. Comparisons were made between the results of traditional standard and continuous measurement methods. It was shown that this improved continuous method avoids the process of intermittent sample extraction and weighing, making it more convenient than the standard method. The continuous method was deemed to have the advantages of high precision, simple operation, and high repeatability.

Micro-level mechanisms of fiber waviness and wrinkling during hot drape forming of unidirectional prepreg composites

Fiber misalignment in composites in the form of in-plane waviness and out of-plane wrinkling, is a major defect arising from processes such as hot drape forming. This work studies the micro-level mechanisms of forming in-plane fiber waviness and out-of-plane wrinkling. An out-of-autoclave unidirectional prepreg system by SOLVAY (CYTEC), CYCOM 5320/T650-35 was used to conduct multiple forming experiments and study the effects of various parameters including forming temperate and lay-up sequence. The effect of partial impregnation, or ‘Engineered Vacuum Channels’, in out-of-autoclave prepreg systems on the intra-ply separation/slippage and consequently fiber misalignment was studied and found to be a significant contributor to micro-level mechanisms. Cross sectioning and microscopy of the parts and examination of the end termination profiles were used to analyze the effect of forming parameters on ply end-shortening and consequently fiber misalignment.

THE STRENGTH OF CONCRETE FOUNDATIONS, PUMPING UNITS IN THE IMPREGNATION OF THEIR OILS AND OIL

The article presents the results of measurements of the strength of concrete foundations, pumping units, operated in the ground with partial impregnation with oil, in conditions of high vibration exposure for more than 30 years. The research was carried out during the examination of designs of the bases pumping units located in the main oil pumping stations. The analysis of the fundamental articles in the studied direction from the experience of examination of such objects. On the basis of visual inspection when measuring concrete strength the presence of the impregnation of concrete with oil. In the majority of cases examined impregnation of designs of the bases of the oil occurred through the soil. Considered the strength of concrete as the aerial parts of the foundations (with the opening facing) and the underground part of the Foundation (with the pits to the soles).Given the use of two methods for the determination of concrete strength: the of chipping and shock-pulse method. In this study the measurement of concrete strength at 20 the foundations of the pumping units by the method of separation with shear fracture – no less than 5 of the test object and the shock-pulse method – at least 20 trials per object. Shows the dependencies of the measurement results and the other method depending on the impregnation of concrete with oil. The analysis of factors affecting the strength of concrete when saturated with oil. A comparison of the conclusions of the study with data from other studies shows the presence of different results, which demonstrates the relevance of the complex work including the testing of various types of concrete, taking into account temperature regimes, the type of impregnating oil, vibration exposure, the concentration of oil products, the time of exposure to petroleum products on concrete, massive structures and methods for determining concrete strength.

Liquid CO2 processing of solid polylactide foam precursors

Diffusion of CO2 in polylactide was modelled by assuming the diffusion coefficient to depend on CO2 concentration, c, according to D[ c] = D[0]exp[ Ac], where D[0] and A are empirical constants, with the aim of optimizing impregnation of nominally amorphous and semicrystalline polylactide/CO2-based precursors for physical foaming. Numerical simulations provided a consistent description of desorption at different temperatures, T, from polylactide impregnated with liquid CO2 at 10℃ and 5 MPa, and D[0, T] could be represented analytically using Arrhenius or Williams–Landel–Ferry-type expressions, allowing interpolation and extrapolation. Sorption was argued on this basis to involve a step-like diffusion front, such that the CO2 content of a plate of thickness l increased as ( D[0] t)1/2 l−1 F[ Aco], where co is the value of c at saturation and F is a function of Aco only. A major practical concern with polylactide/CO2 precursors is that the glass transition temperature, Tg, decreases strongly with c, so that amorphous polylactide saturated with CO2 at 10℃ and 5 MPa degasses spontaneously at room temperature and pressure. However, it was inferred from the models and confirmed experimentally that partial impregnation in liquid CO2 for relatively short times could provide a relatively rapid means of preparing precursors with a roughly uniform CO2 content of around 0.1 g/g that were stable with respect to rapid CO2 loss on heating to room temperature. The resulting precursors gave satisfactory foam morphologies and densities on foaming at 100℃. Moreover, it was also possible to adapt the impregnation conditions so as to obtain partially foamed structures from semicrystalline polylactide under these conditions, in spite of its tendency to undergo cold crystallization during impregnation in liquid CO2, which suppressed expansion of saturated specimens at 100℃.

Pore space analysis of cement-based materials by combined Nitrogen sorption – Wood’s metal impregnation and multi-cycle mercury intrusion

Abstract The analysis of pore space is crucial for a profound understanding of transport and mechanical properties of porous materials. Cement-based materials have a broad pore size distribution ranging from micro- to macro-pores. The analysis of this kind of pore space therefore becomes difficult. Because the resolution of image based methods is limited, indirect analysis methods like Nitrogen sorption or mercury intrusion porosimetry (MIP) are often applied. The standard MIP results in an underestimation of large pores because of its intrinsic limitation due to ink-bottle type pores (i.e., pores that are connected to the surface by smaller neck entrances only). The adsorption of Nitrogen seems to be less influenced by such connectivity effects, but the analysis of pores larger than about 100 nm is not possible. To overcome these limitations, in this study pores were selectively filled with Wood’s metal. The liquid metal (at elevated temperature) is intruded into the samples by applying different pressure regimes and then re-solidified in place. The partial impregnation with this metal allowed the analysis of non-ink-bottle type pore space in a subsequent Nitrogen sorption experiment and its comparison with an empty pore system. Furthermore, Mercury intrusion experiments with an additional pressurization–depressurization cycles (multi-cycle-MIP) were performed. The pore size distributions and pore volumes as calculated from Nitrogen sorption data are then compared with MIP and multi-cycle MIP data.

ドライ炭素繊維シートの引張性能向上に関する検討

The purpose of this study is to improve tensile behavior of no-impregnated (dry) carbon fiber sheets. First, tensile tests of dry carbon fiber sheets with different spans are carried out and it is confirmedthat the tensile strength is only about 30-40% of that of carbon fiber reinforced polymer (CFRP) sheets. Then, two countermeasures by means of partial impregnation with epoxy resin and hybridization with PBO (Poly-para-phenylene-benzo-bis-oxazole) fiber sheets which present high performance in energy absorption are examined to improve the tensile strength of dry carbon fiber sheets. Through a series of experiments, it is realized that the tensile strength ratios of dry carbon fiber sheets with a combination of the two countermeasures to CFRP sheets can be enhanced into 60-70%.

A thermal microactuator made by partial impregnation of polyimide with paraffin

We have fabricated and tested thermal, paraffin-impregnated polyimide actuators, utilizing the large volume increase associated with the solid-to-liquid phase transition of paraffin. In the bimorph-like device, the top layer was made porous by ion track technology. Stochastically distributed pores of various lengths (95, 70, 45 and 20 µm) and various lateral coverages (5–45%) were filled with paraffin by liquid substitution or from vacuum, and sealed with epoxy. Actuators, 125 µm thick, 35 mm long and 7 mm wide, have been characterized with respect to tip deflection and load-carrying capacity with one end rigidly clamped. Loaded with 0.6 g or about ten times their own weight at their free end, about 50% of the maximum stroke (17 mm) was still attained.

Effect of needle density on the mechanical properties of fiber-reinforced polypropylene composites

The partial impregnation textile preform consisting of chopped-strand, long glass fiber and nonwoven polypropylene (PP) has been prepared by needle-punching to improve fiber–matrix distribution before processing. These unconsolidated textile preforms were then preheated and hot-pressed for consolidation and formation. A multichannel recorder was used to determine the completion of impregnation on multilayer glass fiber-reinforced PP, which could significantly reduce the required consolidation time. The effect of needle density on their impregnation has studied by scanning electron microscopy and optical microscopy, along with mechanical analysis. The increasing needle density up to 400 st/cm2 has increased the flexural modulus, but the impact strength decreased. The optimal needle density contained proper flexural and impact properties is 50–100 st/cm2, consistent with the observations from scanning electron microscopy and optical microscopy. A similar phenomenon is also observed by using nonwoven maleic-anhydride-modified polypropylene (mPP) instead of unmodified PP. However, the effect of needle punching on flexural and impact properties is not significant in mPP, which is probably due to better adhesion between glass fiber and mPP matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2169–2176, 1999

Massive sulfide chimneys from the east pacific rise at 7°24's and 16°43's

Massive sulfide chimneys from two hydrothermal fields at 7°24'S and 16°43'S on the East Pacific Rise were investigated using microscopic and chemical methods. The studies reveal three stages of growth for chimneys derived from black smokers in both locations: I. Euhedral, partially porous aggregated Fe‐sulfides crystallized at high temperatures (> 300°C), building the central vent II. Clogging of mesh‐structured (spongy) central conduit by idiomorphous base metal sulfides; percolation of solutions through porous chimney walls; partial solution of initial precipitates (S isotope disequilibrium!), quenching in outer portions of chimney walls, cementation with inward growth of front; late stage (150–100°C) epithermal impregnation of early (partially friable) precipitates by layered colloidal and laminated fine‐grained sulfide specimens III. Emanation of fluids at the chimney base or from secondary vents branching off the chimney; direct seawater mixing and precipitation of quenched sulfides on the outer shell of the initial central vent with partial impregnation of walls Stages II and III likely proceed simultaneously, provided the entire smoker builds in a single fluid‐expulsion event, with a slow temperature decrease of emanating fluids. None of these cycles is marked by the concentration of specific chemical elements; pyrite, chalcopyrite, and sphalerite are most abundant, and ubiquitous in various forms in all portions of the smokers. Marcasite occurs laminated, interlayered with gel‐pyrite. Multivariate factor analysis reveals a preferred accumulation of As, Cr, and Ni in the crystal lattice of iron sulfides, while chalcopyrite scavenges Se, Hg, and Bi. Sphalerite tends to concentrate Cd, Au, Ag, Ge, Pb, Mn, Ga, and In. Chemical disequilibrium is common among sulfides due to remobilization of early precipitates, “contamination”; by later‐stage hydrothermal solutions, and quenching.