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In order to improve the high-temperature performance of mullite ceramic materials, mullite ceramic bodies were placed in closed containers with AlF3 · 3H2 powder and kept at 1 600 °C for 6 h. AlF3 · 3H2O reacts with O2 to produce gaseous compounds AlOF and F, which penetrate into the bodies, promote Al2O3 and SiO2 to form mullite whiskers, and strengthen the mullite ceramic materials. The results show that the mullite ceramics have enhanced hot strength, increased bulk density and declined apparent porosity by adding a certain amount of AlF3 · 3H2 in a closed container. When the addition of AlF3 · 3H2 is 6%, the bulk density of the ceramic material reaches the maximum and the apparent porosity is the lowest; and when the addition of AlF3 · 3H2 is 8%, the hot strength of the material is the highest. [ABSTRACT FROM AUTHOR]

The liquid metal infiltration of carbon preformed with copper and its alloys is already an established and well-known process. It is extensively used by the electronic industry to produce heat sinks of power electronics and electric contacts and sliding electric contacts. The advantage of the process is its ability to produce near net shape components with high volume fractions of carbon at a relatively low price. The process is carried out in a vacuum and with low applied pressure. However, a strong dependence on the temperature of infiltration and its precise control is significant for the sound final product. For certain pair carbon matrix–copper alloys, different results could be obtained according to the infiltration temperature. If the temperature is too low, the solidification may occur prior to complete infiltration (high final porosity). When the temperature is too high, undesirable reactions may occur at the fiber–matrix interface (e.g., corrosive carbides). Therefore, there are still a lot of scientific papers pushing this technology to new directions and over old limits. Publications inside scientific journals within this field deal with composite materials for sliding electrical contact and electrical contact materials, sealing materials, parts of brake disks, pantograph strips for high-speed railways, other electric and mechanical applications and even for wall surface shields in future fusion devices. The present paper reviews used carbon preforms, copper alloys, technological parameters, properties of prepared composites prepared via infiltration during the last 12 years. It can be stated that 1/3 of the papers were published within the last 3 years. Moreover, renewed interest in this low-cost technique could be expected within the next few years due to climate programs and increasing prices of the energy resources. [ABSTRACT FROM AUTHOR]

The liquid metal infiltration of carbon preformed with copper and its alloys is already an established and well-known process. It is extensively used by the electronic industry to produce heat sinks of power electronics and electric contacts and sliding electric contacts. The advantage of the process is its ability to produce near net shape components with high volume fractions of carbon at a relatively low price. The process is carried out in a vacuum and with low applied pressure. However, a strong dependence on the temperature of infiltration and its precise control is significant for the sound final product. For certain pair carbon matrix–copper alloys, different results could be obtained according to the infiltration temperature. If the temperature is too low, the solidification may occur prior to complete infiltration (high final porosity). When the temperature is too high, undesirable reactions may occur at the fiber–matrix interface (e.g., corrosive carbides). Therefore, there are still a lot of scientific papers pushing this technology to new directions and over old limits. Publications inside scientific journals within this field deal with composite materials for sliding electrical contact and electrical contact materials, sealing materials, parts of brake disks, pantograph strips for high-speed railways, other electric and mechanical applications and even for wall surface shields in future fusion devices. The present paper reviews used carbon preforms, copper alloys, technological parameters, properties of prepared composites prepared via infiltration during the last 12 years. It can be stated that 1/3 of the papers were published within the last 3 years. Moreover, renewed interest in this low-cost technique could be expected within the next few years due to climate programs and increasing prices of the energy resources.

Abstract Highly conducting and lightweight wires can be created based on carbon nanotube (CNT) assembly materials, where the inter-tube electron transport plays a key role. Here we report a gas infiltration of bromine to improve the electrical properties of CNT fibers, owing to the enhanced inter-tube electron hopping. Although Br infiltration is mainly a physical absorption process, with just a little fraction to form covalent bonding with the defect of CNTs, it can induce electron transfer from CNT to Br. Together with the densification effect, there are more pathways for interfacial electron transport between the CNTs. As a result, the infiltration efficiently increases the electrical conductivity from 2.66 × 105 to 1.63 × 106 S/m, by 6-fold. Based on the high performance stability, the composite fiber can be used as lightweight and functional conductor for wearable smart devices. Graphical Abstract Highlights • Bromine infiltration increases the electrical conductivity of carbon nanotube fiber. • Interfacial electron transfer from carbon to bromine makes carbon nanotubes p-doped. • Bromine-infiltrated carbon nanotube fiber can be used as a functional wire. [ABSTRACT FROM AUTHOR]

To investigate the effect of pore pressure distribution on fracture behavior of rock in gas fracturing, nitrogen fracturing experiments on the sandstone are performed under different gas filtration conditions. Results indicate that the breakdown pressure of the sandstone reduces with the decreasing amount of gas filtration. In no gas filtration case, the breakdown pressure value of the sample decreases by 69.98 and 45.6% in comparison to no gas invasion case and gas filtration case, respectively. The failure pattern of the sandstone sample is determined by borehole pressure and pore pressure, and it is mainly controlled by borehole pressure at high injection rate and controlled by pore pressure at low injection rate. In addition, pore pressure can promote microcracks initiation and high pore pressure distribution contributes to generating complex multifractures network. Furthermore, in order to popularize the experimental results to the field application, a method of special graded particles is proposed to temporarily plug induced and natural fractures during fracturing process and then prop these fractures after fracturing. The method is expected to improve fracturing efficiency and increase production of oil and gas in practical application. [ABSTRACT FROM AUTHOR]

When a porous solid is subjected to both gas infiltration and heat transfer, thermal stresses are generated in such a solid. In the previous reports, fundamental theory for a porous solid under such a complex situation was developed, and then a thermal stress problem for a porous solid with a flat boundary surface subjected to a concentrated loading was solved completely. In this study, thermal stress problem for a porous infinite solid subjected to a point loading is investigated. A method of solution based upon displacement potential and Fourier integral transform techniques is applied to solve the problem as well as the way used in the previous report. Complete closed form of gas pressure, solid temperature, displacement and thermal stress field in the infinite porous media are presented. It was found that the asymptotic behavior around a point load is strongly affected by gas permeability and pressure of gas phase.

A novel approach of a gas pressure infiltration technique is presented for the synthesis of Co-Continuous Ceramic Composite (C4). SiC foams of varying pore sizes were infiltrated with aluminium AA5083. Optical examination revealed that the SiC foams contained open cells with a network of triangular voids. The number of pores-per-inch (PPI) in the foams was found to depend on the strut thickness and pore diameter. The compressive strengths of two foam configurations, 10 and 20 PPI, were estimated to lie between 1–2 MPa. After infiltration, the compressive yield strength of the resulting C4 was observed to increase to 126 MPa and 120 MPa, respectively, for the 10 and 20 PPI C4. Additionally, the infiltration of ceramic foam with the AA5083 alloy resulted in an increase in strength of 58–100 times when compared with plain ceramic foam. The failure modes of the composites in compression were analyzed by crack propagation and determining the type of failure. The study revealed that shear failure and vertical splitting were the predominant mechanisms of compression failure, and that the fabricated C4 is advantageous in mechanical properties compared to the plain ceramic foam. This study, therefore, suggests the use of C4 composites in armour applications. [ABSTRACT FROM AUTHOR]