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In recent years, the morphology control of semiconductor nanomaterials has been attracting increasing attention toward maximizing their functional properties and reaching their end use in real-world devices. However, the development of easy and cost-effective methods for preparing large-scale patterned semiconductor structures on flexible temperature-sensitive substrates remains ever in demand. In this study, vapor post-treatment (VPT) is investigated as a potential, simple and low-cost post-preparative method to morphologically modify gravure-printed zinc oxide (ZnO) nanoparticulate thin films at low temperatures. Exposing nanoparticles (NPs) to acidic vapor solution, spontaneous restructuring pathways are observed as a consequence of NPs tending to reduce their high interfacial energy. Depending on the imposed environmental conditions during the treatment (e.g., temperature, vapor composition), various ZnO thin-film morphologies are produced, from dense to porous ones, as a result of the activation and interplay of different spontaneous interface elimination mechanisms, including dissolution–precipitation, grain boundary migration and grain rotation–coalescence. The influence of VPT on structural/optical properties has been examined via XRD, UV–visible and photoluminescence measurements. Controlling NP junctions and network nanoporosity, VPT appears as promising cost-effective, low-temperature and pressureless post-preparative platform for preparing supported ZnO NP-based films with improved connectivity and mechanical stability, favoring their practical use and integration in flexible devices. [ABSTRACT FROM AUTHOR]

This study presents the development of a highly robust, pressureless, and void-free silver sinter-bonding technology for power semiconductor packaging. A bimodal silver paste containing silver nanoparticles and sub-micron particles was used, with polymethyl methacrylate (PMMA) as an additive to provide additional thermal energy during sintering. This enabled rapid sintering and the formation of a dense, void-free bonding joint. The effects of sintering temperature and PMMA content on shear strength and microstructure were systematically investigated. The results showed that the shear strength increased with rising sintering temperatures, achieving a maximum of 41 MPa at 300 °C, with minimal void formation due to enhanced particle necking facilitated by PMMA combustion. However, at 350 °C, the shear strength decreased to 35 MPa due to cracks and voids at the copper substrate–copper oxide interface caused by thermal expansion mismatch. The optimal PMMA content was found to be 5 wt.%, balancing sufficient thermal energy and void reduction. This pressureless sintering technology demonstrates significant potential for high-reliability applications in power semiconductor modules operating under high-temperature and high-stress conditions. [ABSTRACT FROM AUTHOR]

In this paper, we construct a class of spherically symmetric and self-similar analytical solutions to the pressureless Navier–Stokes equations with density-dependent viscosity coefficients satisfying h (ρ) = ρ , g (ρ) = (− 1) ρ for all > 0. Under the continuous density free boundary conditions imposed on the free surface, we investigate the large-time behavior of the solutions according to various > 1 and 0 < < 1. When the time grows up, such solutions exhibit interesting information: Case (i) If the free surface initially moves inward, then the free surface infinitely approaches to the symmetry center and the fluid density blows up at the symmetry center, or the free surface tends to an equilibrium state; Case (ii) If the free surface initially moves outward, then the free surface infinitely expands outward and the fluid density decays and tends to zero almost everywhere away from the symmetry center, or the free surface tends to an equilibrium state. We also study the large-time behavior of the solutions for = 1 without any boundary conditions. [ABSTRACT FROM AUTHOR]

This paper introduces a novel process, known as pre-solid phase sintering-assisted pressureless infiltration (PSPS-PI), aimed at addressing issues related to the segregation of hard particles and excessive porosity in the manufacturing of lightweight cermet based on TiC. The PSPS-PI process involves compressing a green TiC powder compact with a minor Ni powder addition, followed by vacuum-based solid-phase sintering to create a fully consolidated TiC preform. This study explores the influence of TiC particle size and Ni content on the microstructure and properties of TiC–Cu composites, conducting a comparison with direct pressureless infiltration (D-PI). The results indicate that the high-melting-point Ni element promotes the formation of sintering necks between TiC and Ni, aiding in the consolidation of TiC particles. The stable skeleton ensures that TiC particles remain in their initial positions during subsequent pressureless infiltration, effectively preventing TiC powder segregation. TiC and Ni create a dissolutive wetting system during pressureless infiltration. The formation of the Ni2SnTi intermetallic compound significantly enhances the wettability with Cu alloy, leading to a reduction in porosity and the occurrence of crack defects within the composite. As particle size decreases, the preform's porosity decreases, resulting in a reduced proportion of soft metal binder and lower residual stress. Consequently, finer TiC powder leads to improved cermet hardness and a reduction in the number of micro-crack defects. In general, PSPS-PI allows for the attainment of low porosity, a uniform microstructure, enhanced hardness, and outstanding wear resistance in the lightweight cermet based on TiC with the appropriate TiC particle size (D50 = 10.2 μm), achieving a remarkable hardness of 642.9 (Hv30) and excellent toughness. [ABSTRACT FROM AUTHOR]

Zr2AC MAX phases are ternary carbide family with layered structures combining of the outstanding characteristics of metals and ceramics. This review study provides an overview of Zr2AC MAX phase formation mechanisms, applications, and the correlation between Zr2AC MAX phase formation mechanisms and performance in applications such solar coatings, oxidation resistance, high temperature applications, and nuclear applications. Zr2InC MAX phase has low friction and wear materials that can be used for variety applications for significant technology such as electrical spinning connections and rotating bearings. More examples, the Zr2SnC MAX phase uses for self-healing of cracks and oxidation resistance. The Zr2PbC MAX phases are elastic and electrically anisotropic in nature and appropriate for high temperature applications, optoelectronic devices, and coating materials. Studying the optical characteristics of the Zr2SeC has shown its potential for application as a shielding material in order to decrease the heating of solar. The Zr2SC is suitable for use in high-temperature technologies, such as thermal barrier coating material TBC. The Zr2AlC phase is the most attractive among all non-synthesizable ternary MAX phases, particularly for the nuclear industry. There are a lot of challenges during fabrication of the MAX phase, including synthesis temperature, the MAX phase purity, and the secondary phase (impurities). In harsh external conditions, the defect density has a substantial impact on the MAX phase's stability and thus, the methods of defect formation and migration have a considerable impact on the phases' radiation resistance and self-healing capabilities.

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects when electric current passes through the underdeveloped inter-particle contacts. Until now, inter-particle interactions during pressureless SPS have been studied mainly for particles of the same material. In this work, we focused on the interactions between particles of dissimilar materials in mixtures of micrometer-sized Fe and Al powders forming porous compacts during pressureless SPS at 500-650 °C. Due to the chemical interaction between Al and Fe, necks of conventional shape did not form between the dissimilar particles. At the early interaction stages, the Al particles acquired shell morphology. It was shown that this morphology change was not related to the influence of electric current but was due to the Kirkendall effect in the Fe-Al system and particle rearrangement in a porous compact. No experimental evidence of melting or melt ejection during pressureless SPS of the Fe-Al mixtures or Fe and Al powders sintered separately was observed. Porous FeAl-based compacts could be obtained from Fe-40at.%Al mixtures by pressureless SPS at 650 °C.

Low-temperature and pressureless silver (Ag) sintering was applied to a 1200 V/200 A silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module with a Ag-finished silicon nitride active metal-brazed substrate, and the results were evaluated for applicability in electric and hybrid electric vehicles. The sintering was performed at 220–240°C, 90 min in vacuum under nitrogen gas conditions; the bonding strength, bonding layer thickness (BLT), void content, and densification of the as-sintered Ag joints were 39 MPa, 71.4 µm, 2%, and 90.5%, respectively. The shear strength, BLT, densification, and microstructure of the Ag-sintered joints were compared before and after the thermal cycling test (− 50–150°C, 1100 cycles, TCT) and high temperature storage test (200°C, 1000 h, HTST). To simultaneously compare the electrical properties of the SiC power module with lead (Pb)-free solder joints, the same SiC MOSFET power module was manufactured using a Sn-3.0Ag-0.5Cu (SAC305) Pb-free solder. The shear strength and densification after TCT and HTST were 35.5 MPa and 39.7 MPa, as well as 92.8% and 94.8%, respectively. The on-resistance and total switching efficiency of the SiC power module with the Ag-sintered joint were also compared to those of the SAC305 solder joint module, which evinced maximum values of 7.3 mΩ and 10.7 mJ that were superior to those of 8.5 mΩ and 11.3 mJ for the SAC305 solder joint, respectively. Under the same measurement conditions, the maximum generated current and voltage values are lower than those of the solder joint module, so it is envisaged that stable power module operation is realizable for long-term use. The Ag-sintered joint surpassed the SAC305 solder interconnects in terms of the electrical and mechanical reliability of the power module. When a SiC wide band gap device was used, it was discovered that Ag sintering was superior to Pb-free solder interconnects to increase the power conversion efficiency of the power module. [ABSTRACT FROM AUTHOR]

In this work, facile pressureless sintering process is explored to manufacture the promising Cr2AlC MAX phase material, using three elemental powders as starting materials. The powders are mixed in a molar ratio of Cr:Al:C = 2:1.2:1, and ball-milled for particle refinement and homogenization. The powder mixture is sintered at differing temperatures from 1000 to 1400°C without applying pressure. Highly pure Cr2AlC MAX phase is obtained from sintering at 1200°C. The Cr2AlC compound shows laminated microstructures and high crystal quality. At other temperatures, significant amounts of secondary phases are observed. The optimized Cr2AlC compound exhibits a metallic behavior and superior oxidation resistance. The simple manufacturing method of Cr2AlC MAX phase developed in this work may also be applied for fabrication of a wider range of MAX phases. [ABSTRACT FROM AUTHOR]

The silicon carbide (SiC) ceramics containing multilayer graphene derived from graphite exfoliation were successfully prepared by pressureless sintering, and the effect of graphene content on the sintering behaviours, microstructure, mechanical, tribological, electrical and thermal properties was investigated in detail. The bulk density, bending strength and hardness of the composite ceramics gradually decrease with the increase of graphene content, but the friction, conductance and thermal conductance properties are improved obviously. When the graphene content reaches 5 wt-%, the dry friction coefficient of 0.22, electrical conductivity of 2724.14 S−1 m−1 and thermal conductivity of 8.5 W (m−1 K−1) can be obtained, indicating good comprehensive mechanical, tribological, electrical and thermal properties. This multilayer graphene reinforced silicon carbide ceramic is a promising seal material instead of SiC seal materials containing graphite to be applied in next-generation mechanical seals. [ABSTRACT FROM AUTHOR]

Pressureless sintering of B 4 C with MoSi 2 (5–30 wt%) as a sintering aid was carried out at 1600–2260 °C in vacuum. The phase compositions, relative density, microstructures and mechanical properties of the obtained ceramic composites were investigated. Results indicate that MoSi 2 can react with B 4 C to in-situ form Mo 2 B 5 and SiC below 1600 °C. Mo 2 B 5 will gradually transform to MoB 2 with the further increasing temperature. Liquid-phase sintering of B4C is realized at about 2150 °C and the formed liquid phase fills the pores in the matrix, enhancing the densification of the composites. The relative density, fracture toughness and hardness of the samples with 30 wt% MoSi 2 sintered at 2260 °C reach 96.5%, 3.98 MPa m1/2 and 28.1 GPa, respectively. The high-toughness second phases and the coexistence of transgranular and intergranular fracture have a synergistic effect on improving the overall fracture toughness of the ceramic composites. [ABSTRACT FROM AUTHOR]

Abstract In order to overcome interfacial delamination of pressureless sintered nanosilver as die attachment on the ENIG finish, we tried to clarify the densification and interfacial diffusion behavior of sintering nanosilver paste on Au finish. Two different electroless nickel immersion gold (ENIG-1, ENIG-2) and one electroplated nickel gold (electrolytic Au) were compared in the aspects of mechanical, thermal performance, and microstructures. Delamination was found at the as-sintered Ag in the vicinity of Ag/Au interface in the ENIG-1. It was likely that too much Ag atoms was diffused into the ENIG-1, the left Ag atoms of the Ag-NPs in the vicinity of the interface are not sufficient to be densified as a robust sintered Ag joint at the higher temperatures. Electron backscattered diffraction (EBSD) results confirmed that the grain size, the high angle grain boundary, and the (111) texture lead to the rapid non-densifying diffusion of the Ag atoms with the ENIG. We proposed a modified sintering profile and the rougher ENIG-2 with thinner Au finish to reduce the non-densifying diffusion. The performance, and microstructures of the sintered Ag on the ENIG-2 confirmed that it is reasonable to enhance the sintered Ag on ENIG by reducing the rapid non-densifying diffusion at above 150 °C. Highlights • Interfacial delamination of pressureless sintered Ag on the ENIG finish was solved. • Rapid non-densifying diffusion of Ag atoms leads to interfacial delamination. • Grain size, angle, and (111) texture contribute to non-densifying diffusion. • A modified sintering profile could reduce non-densifying diffusion successfully. [ABSTRACT FROM AUTHOR]

In this work, low-pressure synthesis of carbon spheres from resorcinol and formaldehyde using an autoclave is presented. The influence of reaction time and process temperature as well as the effect of potassium oxalate, an activator, on the morphology and CO2 adsorption properties was studied. The properties of materials produced at pressureless (atmospheric) conditions were compared with those synthesized under higher pressures. The results of this work show that enhanced pressure treatment is not necessary to produce high-quality carbon spheres, and the morphology and porosity of the spheres produced without an activation step at pressureless conditions are not significantly different from those obtained at higher pressures. In addition, CO2 uptake was not affected by elevated pressure synthesis. It was also demonstrated that addition of the activator (potassium oxalate) had much more effect on key properties than the applied pressure treatment. The use of potassium oxalate as an activator caused non-uniform size distribution of spherical particles. Simultaneously higher values of surface area and total pore volumes were reached. A pressure treatment of the carbon materials in the autoclave significantly enhanced the CO2 uptake at 25 °C, but had no effect on it at 0 °C.

Highly reliable sintering technologies operating in extreme conditions are being extensively researched nowadays to improve the efficiency of power modules based on silicon carbide (SiC) devices for use in electric vehicles. In this study, the strength of silver (Ag) sintered joints used in SiC/direct bonded copper (DBC) was recorded at 21.9-23 MPa, at a pressure of 0.2 MPa and zero pressure, at 210°C using 83 wt.% and 88 wt.% Ag paste. Al2O3 and AlN DBCs with copper and Ag finishes were used. The inter-diffusion of the Cu-Ag and the Ag-Ag sintered interfaces contributed to increasing bonding strength. Based on the relationship between bonding layer thickness and densification in the pressurized and pressureless sintering conditions, if densification was at least 93%, the strength of the Ag joint strength was as high as 23.8 MPa. From the results of a simulation of thermal deformation based on the mismatch in the coefficients of thermal expansion of materials without considering heat transfer, the Al2O3 DBC material (rather than AlN) exhibited a small and dispersed deformation of the SiC/DBC sintered module. We also observed that Al2O3 DBC was favorable in terms of warpage. [ABSTRACT FROM AUTHOR]

It is significant to attach power devices on low-cost copper (Cu) substrates by pressureless silver-sintering in air. The Cu surface in direct-bond-copper (DBC) substrates could have a wide range of surface roughness due to the various processing techniques. It is crucial to find out how the surface roughness influences the bonding strength of the sintered-silver (Ag) die-attachment. In this study, we did die-attach on Cu substrates with surface roughness R a  = 0.15–8.41 µm and R z  = 1.22–50.97 µm by pressureless sintering of nanosilver paste in air. When the surface roughness ( R a of 0.65 μm) is slightly larger than the silver nanoparticles (diameter of 0.6 μm), the high shear strength in excess of 50 MPa was achieved, likely due to both strong metallic bonds and mechanical interlock. This work could help to prepare DBC substrates with optimized surface roughness to accommodate the viscosity, the particle size, and the sintering shrinkage of the silver paste for well using the sintered-Ag die-attach technology. [ABSTRACT FROM AUTHOR]

A two-stage sintering process was successfully used to sinter FeAl to densification levels of just above 95% at a temperature of 1300°C. In the first stage, mixed iron and aluminium powders were synthesised at 750°C via self-propagating high-temperature synthesis (SHS) to form brittle and porous Fe2Al5. Then the pellets were crushed and milled to various sizes and mixed with iron powders in the nominal composition of FeAl40 and pressurelessly sintered at a higher temperature to obtain a higher densification by taking advantage of the less violent exothermic reaction of Fe2Al5 and Fe. The intermediate and end products in SHS and sintering were characterised by SEM/EDX and XRD. The porosity level of the final FeAl40 product was controlled by the heating rate and powder size, which was also strongly influenced by the temperature, holding time and the ratio of the two powders. [ABSTRACT FROM AUTHOR]

The performance of the product components in application greatly depends on the morphological parameters and inherent capabilities of the material. In the present study, Al-ZrB2 composite is made out of powder metallurgy route. Incremental weight% (0, 2, 4 and 6 wt%) of ZrB2 were added into Al matrix to produce different composites. Composites were prepared by cold axial compaction followed by pressureless sintering at 550 °C for 1 h in controlled atmosphere (Ar gas). Hardness increased with the amount of ZrB2 in the composite. To enhance the properties further, composites were deformed at 25, 400 and 500 °C respectively. The size, shape and orientation of the grains in the deformed composites were analyzed and correlated with the mechanical properties. The mechanical adhesion of ZrB2 particle with the Al matrix was examined in different composites during different temperature conditions of deformation process. The fracture strain of the composites decreased with increase of ZrB2 in the composite. [ABSTRACT FROM AUTHOR]

This short note concerns the formal limit presented in [J. Comput Phys 230 (2011), 8057-8088] and [Actes colloquia Rouen (2012)] between the compressible Euler equations with singular pressure (soft model) and the pressureless Euler system with unilateral constraint (hard model). These soft and hard models with maximal constraint on the density are used to reproduce congestion phenomena. In this paper, we are interested in the question how the different regions (congested and non-congested regions) fit together and how the transition occurs when congestion first develops in the initial system namely the compressible Euler equation with singular pressure. We shall develop a formal solution by matched asymptotics and show that a shock front may separate the congested region from the outside non-congested region. This, in some sense, shows that to justify the formal limit between the two models (soft and hard Euler systems), the shock fronts formation has to be considered and mathematically analyzed. [ABSTRACT FROM AUTHOR]

Silver sintering joining technology provides lead-free die attachment with excellent thermal conductivity and compatibility with high-temperature (≥300 °C) applications. However, sintering affordable micron-scale silver particles requires high temperature and the assistance of high pressures, which can damage chips and increase the manufacturing cost. In this article, we achieved the low-temperature, pressureless sintering of micron-scale silver particles by employing an active Ag 2 O additive as a bridge among the micron-scale silver particles. The Ag 2 O was reduced in situ to nanoscale silver to activate the surface of the micron-scale silver particles, resulting in the rapid diffusion and densification of silver particles at low temperature. An optimized composition of Ag-10% Ag 2 O exhibited a bonding strength of over 40 MPa at only 180 °C without any additional pressure. The results suggest that affordable micron-scale metal particles can be sintered using a suitable activating additive under an energy-efficient and eco-friendly fabrication process. [ABSTRACT FROM AUTHOR]

High compacted aluminum nitride (AlN) substrates were prepared by aqueous tape casting. Aluminium dihydrogen phosphate was used to modify AlN particle surface from hydrolysis during casting process. The absolute value of zeta potential for the AlN particle treated by Al(H2PO4)2was 60mv at pH = 9. The slurry suitable for tape casting was prepared which possessed shear-thinning behavior and appropriate viscosity. The results showed that the green tapes own excellent properties including high bulk density, uniform pore distribution and low porosity. The samples were fired at 1700°C (lower than melting point of Pt) with pressureless sintering process which can be used to fabricate complex device. [ABSTRACT FROM PUBLISHER]

We present a new hydrodynamic model for the interactions between collision-free Cucker-Smale flocking particles and a viscous incompressible fluid. Our proposed model consists of two hydrodynamic models. For the Cucker-Smale flocking particles, we employ the pressureless Euler system with a non-local flocking dissipation, whereas for the fluid, we use the incompressible Navier-Stokes equations. These two hydrodynamic models are coupled through a drag force, which is the main flocking mechanism between the particles and the fluid. The flocking mechanism between particles is regulated by the Cucker-Smale model, which accelerates global flocking between the particles and the fluid. We show that this model admits the global-in-time classical solutions, and exhibits time-asymptotic flocking, provided that the initial data is appropriately small. In the course of our analysis for the proposed system, we first consider the hydrodynamic Cucker-Smale equations (the pressureless Euler system with a non-local flocking dissipation), for which the global existence and the time-asymptotic behavior of the classical solutions are also investigated. [ABSTRACT FROM AUTHOR]

Micrometer-sized Ag particles adsorb substantial oxygen above 200^\circC. A dispersion of these particles in alcohol can be successfully used as a die-attach material by sintering the Ag particles to form a soft porous bonding layer. Since the low-temperature sintering of micrometer-sized Ag particles is unlikely to involve the nanometer size effect associated with melting, it was considered that the low-temperature sintering between Ag layers of micrometer thickness would occur in air. The contact surface of a light emitting diode die and a glass substrate were both coated with an Ag sputtered layer of 2 \mum in thickness. The Ag–Ag direct bonding proceeded by sintering above 200^\circC in air. The bonding strength of the Ag–Ag direct bonding exceeded that of the low-temperature sintering of micrometer-sized Ag particles, and the bonding strength depended on oxygen concentration in the sintering atmosphere. On the Ag sputtered surface of the glass substrate, a substantial morphology change was observed by heating the Ag sputtered layer in air. It was supposed that this morphology change was caused by abnormal grain growth of Ag in the Ag sputtered surface. It is concluded that low-temperature sintering of Ag materials is accelerated by the abnormal grain growth of Ag with oxygen adsorption near the Ag surface. [ABSTRACT FROM PUBLISHER]

Synthesis of silicon carbide agricultural waste-derived activated carbon composite nanomaterials is demonstrated at heating rates of 25–100°C up to 1600°C in vacuum. The synthesis technique utilizes a novel free-pressureless spark plasma sintering (FPSPS) process. Improved macroscopic structural integrity is achieved through the development of SiC nanowire networks and preliminary specific surface area values of 69m2 g−1 are measured, exhibiting potential application in catalyst support and adsorption applications. The advantages and potential of FPSPS processing for this material system are discussed. [Copyright &y& Elsevier]

Abstract: In this work, a novel simple method is presented to synthesize highly pure Ti3AlC2 powder by heating 2TiC/Ti/Al (molar ratio) powder system between 1300°C and 1400°C for 15–30min in flowing argon atmosphere. 2TiC/Ti/Al is selected as the raw material because of its much lower exothermal quantity than elemental 3Ti/Al/2C powder system in reacting process. The purity of Ti3AlC2 is not sensitive to the final temperature, soaking time or raw material scale. Its content is maintained around 97wt.%, even though the scale of mixed raw materials vary from 5g to 1000g. The synthesized samples can be easily ground into powders with a mean particle size of 4.9μm. Synthesis mechanism shows that both Ti2AlC and Ti3AlC2 will generate from the reaction among TiC, Ti and Al below 1200°C. Above 1300°C, Ti2AlC will continue to react with TiC and generate Ti3AlC2. The formation of Al liquid phase above 660°C is considered as a promoting factor in the reacting process. [Copyright &y& Elsevier]

The use of Fe2Al5–FeAl2 prealloyed powders and heating rates >150 K min-1 overcomes the formation of density restricting Kirkendall porosity in the Fe–Al system. X-ray diffraction, electron probe micro analysis and differential thermal analysis suggest that the absence of a persistent liquid, experienced when liquid phase sintering with elemental powders, is overcome. Homogenisation is greater during heating at a rate of 20 K min-1 than for 150, 250 or 400 K min-1 and homogenous Fe3Al forms across the compact at temperatures below the melting point of the liquid forming constituent, indicating that a liquid will not form under such processing conditions. The maximum density achieved under the processing conditions in the present study is 92% of theoretical density. The presence of large pores shortly after liquid formation suggests that the remaining porosity is largely due to powder agglomeration during mixing. [ABSTRACT FROM AUTHOR]

This paper addresses the difficult problem of predicting service life in pressureless underground plastics pipes applications. Lifetime in such applications is generally determined by thermooxidative behaviour, which is governed principally by the type and amount of two classes of stabiliser: primary antioxidants and thio-synergistics. Ageing studies in water at 95°C have indicated that, for polypropylene (PP), mechanical performance is not influenced by exposure for up to six months (longer term trials are in progress). Despite this, aging in water can have a significant effect on the thermoxidative life of PP, by extracting antioxidant additives. As in pressurised pipe applications, determination of the combined effects of oxygen and water extraction is key to useful predictions of durability. In an attempt to improve life assessment, polypropylene plaques have been aged in contact with water at 95°C to determine the fitting parameters for Fickian diffusion. The residual stabiliser was measured directly by high-performance liquid chromatography (HPLC) and indirectly, using oven aging. Parameters have been determined for three phenolic primary antioxidants widely used in polyolefin pipes. Direct analysis by HPLC was found to give much lower scatter and hence is proposed as the more reliable method. A methodology is proposed to predict the lifetime of polyolefin pipe materials for underground sewerage applications avoiding the need to make tests on pipes. [ABSTRACT FROM AUTHOR]

A pressureless low-temperature Cu-embedded intermetallic joint for interconnects is fabricated using a Cu-based mixed paste containing different amounts of SAC305 (SAC) particles. The highest joint's shear strength reaches 24.2 MPa. The average of the shear strength is 19.2 (±4.3) MPa, which is also high for pressureless solid-state bonding. After a solid-state interdiffusion bonding process, the joint is composed of an intermetallic-compound (IMC) shell and the Cu core particles. TEM analysis indicates a coherent interface between the core and shell. The ductile Cu phase mixed with brittle IMC in the joint enhances its strength. This study validates that void fraction in the joints is not the sole factor that affects the joint's properties. A mathematical model proves that the IMC thickness and IMC interfacial areas make significant contributions for robust interconnects. • Pressureless and low-temp. interconnect is achieved by solid-state interdiffusion. • Interconnects have Cu-embedded intermetallic microstructure. • TEM analysis indicates a coherent interface between Cu core and Cu 3 Sn shell. • A model proves the IMC thickness and interfacial areas affect joint's properties. [ABSTRACT FROM AUTHOR]

Pressureless sintering is not considered feasible for the preparation of TiAl-based intermetallics from elemental powders due to the Kirkendall effect. When the compacts are sintered without pressure, swelling and surface cracking occur in the billets. Porous billets are obtained, which cannot be further used. Nevertheless, pressureless sintering is still worth investigating because of lower cost and easier operation. In this study, a two-step pressureless sintering process was developed to prepare the TiAl-based intermetallic preforms. The first step was to eliminate the aluminum particles in the billets through a solid-state sintering procedure to prevent the aluminum from melting and to suppress the formation of the Kirkendall pores by sintering with a constrained mold. The second step was to make the billets homogenized and densified by a high-temperature sintering procedure. Results show that the billets sintered with constrained molds are dense and crack free after the first step. Then, the billets are densified in the second step. Therefore, the application of constrained molds makes pressureless sintering feasible in the preparation of the TiAl-based intermetallics from the elemental powders. The microstructure is fully transformed from the aluminum and titanium compacts to the TiAl-based intermetallics after this two-step pressureless sintering process. [ABSTRACT FROM AUTHOR]

In this work, low-pressure synthesis of carbon spheres from resorcinol and formaldehyde using an autoclave is presented. The influence of reaction time and process temperature as well as the effect of potassium oxalate, an activator, on the morphology and CO2 adsorption properties was studied. The properties of materials produced at pressureless (atmospheric) conditions were compared with those synthesized under higher pressures. The results of this work show that enhanced pressure treatment is not necessary to produce high-quality carbon spheres, and the morphology and porosity of the spheres produced without an activation step at pressureless conditions are not significantly different from those obtained at higher pressures. In addition, CO2 uptake was not affected by elevated pressure synthesis. It was also demonstrated that addition of the activator (potassium oxalate) had much more effect on key properties than the applied pressure treatment. The use of potassium oxalate as an activator caused non-uniform size distribution of spherical particles. Simultaneously higher values of surface area and total pore volumes were reached. A pressure treatment of the carbon materials in the autoclave significantly enhanced the CO2 uptake at 25 °C, but had no effect on it at 0 °C. [ABSTRACT FROM AUTHOR]

the present study evaluated the effect of the Spark Plasma Sintering (SPS) and Pressureless Sintering (PLS) methods on the physical and mechanical properties of ZrO 2 -bearing Lithium Silicate (ZLS) glass-ceramics. SPS and PLS methods were used for fabricating of the zirconia-bearing Lithium Silicate glass-ceramics. Several sintering temperatures were applied in order to achieving the best mechanical and physical properties in both methods. For this purpose, the particle size measurement of the glass powder was performed. Field Emission Scanning Electron Microscope (FESEM) was carried out for evaluation of the microstructure. X-ray diffraction (XRD) was used to investigate the amorphous or crystalline state of the samples. Fourier Transform Infrared Spectroscopy (FTIR) was used for the investigation of the chemical bonds. Flexural strength, Vickers microhardness, fracture toughness, and physical properties such as bulk density, water absorption, and the apparent porosity of the samples were measured. It is possible to fabricate ZLS glass-ceramics by the SPS method at a sintering temperature approximately 350 °C lower than the sintering temperature of the PLS method. Results of the SPS showed SGC, 550 °C (SPS Glass Ceramic sintered at 550 °C) had the highest flexural strength (255.10 ± 15.44 MPa), fracture toughness (3.15 ± 0.62 MPam1/2), Vickers microhardness (7.96 ± 0.13 GPa) and bulk density (2.63 ± 0.02 g/cm3); the lowest water absorption (0.11 ± 0.12) and, apparent porosity (0.25 ± 0.32). Results of the PLS showed PLGC, 900 °C (PLS Glass Ceramic sintered at 900 °C) had the flexural strength (160.27 ± 12.69 MPa), the highest Vickers microhardness (7.22 ± 0.67 GPa) and bulk density (2.53 ± 0.03 g/cm3); the lowest water absorption (0.15 ± 0.21) and, apparent porosity (0.39 ± 0.54). According to the XRD patterns and FESEM images, SGC, 550 °C has Li 2 Si 2 O 5 spherical nanocrystals (approximately 50–100 nm diameters). Different sintering temperatures in the SPS and PLS methods have an obvious effect on the microstructure, mechanical, and physical properties of ZrO 2 -bearing Lithium Silicate (ZLS) glass-ceramics. Sintering temperature was decreased in SPS compared to the PLS method and nanocrystals of Li 2 Si 2 O 5 formed. [ABSTRACT FROM AUTHOR]

Objective: the present study evaluated the effect of the Spark Plasma Sintering (SPS) and Pressureless Sintering (PLS) methods on the physical and mechanical properties of ZrO 2 -bearing Lithium Silicate (ZLS) glass-ceramics., Method: SPS and PLS methods were used for fabricating of the zirconia-bearing Lithium Silicate glass-ceramics. Several sintering temperatures were applied in order to achieving the best mechanical and physical properties in both methods. For this purpose, the particle size measurement of the glass powder was performed. Field Emission Scanning Electron Microscope (FESEM) was carried out for evaluation of the microstructure. X-ray diffraction (XRD) was used to investigate the amorphous or crystalline state of the samples. Fourier Transform Infrared Spectroscopy (FTIR) was used for the investigation of the chemical bonds. Flexural strength, Vickers microhardness, fracture toughness, and physical properties such as bulk density, water absorption, and the apparent porosity of the samples were measured., Results: It is possible to fabricate ZLS glass-ceramics by the SPS method at a sintering temperature approximately 350 °C lower than the sintering temperature of the PLS method. Results of the SPS showed SGC, 550 °C (SPS Glass Ceramic sintered at 550 °C) had the highest flexural strength (255.10 ± 15.44 MPa), fracture toughness (3.15 ± 0.62 MPam 1/2 ), Vickers microhardness (7.96 ± 0.13 GPa) and bulk density (2.63 ± 0.02 g/cm 3 ); the lowest water absorption (0.11 ± 0.12) and, apparent porosity (0.25 ± 0.32). Results of the PLS showed PLGC, 900 °C (PLS Glass Ceramic sintered at 900 °C) had the flexural strength (160.27 ± 12.69 MPa), the highest Vickers microhardness (7.22 ± 0.67 GPa) and bulk density (2.53 ± 0.03 g/cm 3 ); the lowest water absorption (0.15 ± 0.21) and, apparent porosity (0.39 ± 0.54). According to the XRD patterns and FESEM images, SGC, 550 °C has Li 2 Si 2 O 5 spherical nanocrystals (approximately 50-100 nm diameters)., Significance: Different sintering temperatures in the SPS and PLS methods have an obvious effect on the microstructure, mechanical, and physical properties of ZrO 2 -bearing Lithium Silicate (ZLS) glass-ceramics. Sintering temperature was decreased in SPS compared to the PLS method and nanocrystals of Li 2 Si 2 O 5 formed., (Copyright © 2020 Elsevier Ltd. All rights reserved.)