Preparation and Compression Resistance of Lightweight Concrete Filled with Lightweight Calcium Carbonate Reinforced Expanded Polystyrene Foam.

Lightweight concrete is widely used in the construction industry due to its low density and high strength. In this paper, lightweight concrete was prepared by a simple two-step method. Firstly, the light calcium carbonate reinforced epoxy macrospheres (LCR-EMS) material was obtained by adhering calcium lighter carbonate powder to the expanded polystyrene foam spheres (EPS) material using the "balling method". In the second step, the LCR-EMS was mixed with water, cement, and the hollow glass microspheres (HGMS) material using the "molding method" to obtain lightweight concrete. The combination of macroscopic photographs and microscopic morphology shows that the LCR-EMS material itself is uniformly encapsulated and well bonded to the matrix. Test results show that the density of the lightweight concrete decreases with an increase in the volume fraction of stacked LCR-EMS, the diameter, and the proportion of HGMS in the matrix, but it decreases with a decrease in the number of layers of LCR-EMS. The compressive strength of lightweight concrete exhibits a completely opposite trend. When three layers of LCR-EMS were used as filler material, the density and compressive strength of the concrete were 1.246 g/cm3 and 8.19 MPa, respectively. The density and maximum compressive strength of lightweight concrete were 1.146 g/cm3 and 6.37 Mpa, respectively, when filled with 8-9 mm-2L-90 svol% of LCR-EMS and 40 wt% of HGMS in the matrix. Compared with lightweight concrete filled with 90% EPS, the density increased by 20% while the compressive strength increased by 300%.

High Hardness, Excellent Hydrophobicity, and Favorable Corrosion Resistance of Plasma-Sprayed FeCrMoSi Amorphous Coatings on 304 Stainless Steel.

The FeCrMoSi amorphous coatings were fabricated on the surface of a 304 stainless steel (SS) base material using atmospheric plasma spraying. A comprehensive investigation was carried out to evaluate the structure, morphology, adhesion to base material, hardness, hydrophobicity, interfacial contact resistance, and corrosion resistance of the coatings. The results show a remarkable hardness of 1180.1 HV, a strong bond strength of up to 64.3 N/mm2, and excellent hydrophobicity with a water contact angle reaching 141.2°. Additionally, in an acidic environment with fluoride ions (0.5 M H2SO4 + 2 ppm HF, 80 °C), the FeCrMoSi amorphous coating demonstrated superior corrosion resistance compared with 304 SS while maintaining similar electroconductibility. Detailed analysis of the structural characteristics and corrosion resistance of FeCrMoSi amorphous coatings provided valuable insights into their mechanics. These promising results signify a bright future for FeCrMoSi amorphous coatings in various industrial sectors, including transportation, petroleum, and electric power industries.

Study of the Compressive Properties of Heavy Calcium Carbonate-Reinforced Epoxy Composite Spheres (HC-R-EMS) Composite Lightweight Concrete.

Lightweight concrete is one of the effective means to solve the problems of structural component weight, energy efficiency, and fire safety in modern civil engineering. Heavy calcium carbonate-reinforced epoxy composite spheres (HC-R-EMS) were prepared by the ball milling method, and HC-R-EMS, cement, and hollow glass microspheres (HGMS) were mixed into the mold by the molding method to prepare composite lightweight concrete. The relationship between the HC-R-EMS volumetric fraction, the initial inner diameter of the HC-R-EMS, the number of layers of HC-R-EMS, the HGMS volume ratio, the basalt fiber length and content, and the multi-phase composite lightweight concrete density and compressive strength was studied. The experimental results show that the density of the lightweight concrete ranges between 0.953-1.679 g/cm3 and the compressive strength ranges between 1.59-17.26 MPa, where the volume fraction of HC-R-EMS is 90%, the initial internal diameter is 8-9 mm, and the number of layers of HC-R-EMS is three. The lightweight concrete can meet the requirements of high strength (12.67 MPa) and low density (0.953 g/cm3). In addition, the addition of basalt fiber (BF) can effectively improve the compressive strength of the material without changing the density of the material. From a micro-level perspective, HC-R-EMS is closely combined with the cement matrix, which is conducive to increasing the compressive strength of concrete. Basalt fibers connect the matrix into a network, improving the maximum limit force of the concrete.

Correction: Wu et al. 3D Thermal Network Supported by CF Felt for Improving the Thermal Performance of CF/C/Epoxy Composites. Polymers 2021, 13, 980.

In the original article [...].

Carbon Fiber/Phenolic Composites with High Thermal Conductivity Reinforced by a Three-Dimensional Carbon Fiber Felt Network Structure.

The formation of highly thermally conductive composites with a three-dimensional (3D) oriented structure has become an important means to solve the heat dissipation problem of electronic components. In this paper, a carbon fiber (CF) felt with a 3D network structure was constructed through the airflow netting forming technology and needle punching. The carbon fiber/phenolic composites were then fabricated by CF felt and phenolic resin through vacuum impregnation and compression molding. The effects of CF felt content and porosity on the thermal conductivity of carbon fiber/phenolic composites were investigated. The enhancement of carbon skeleton content promotes the conduction of heat inside the composites, and the decrease of porosity also significantly improves the thermal conductivity of the composites. The results indicate that the composites exhibit a maximum in-plane thermal conductivity of 1.3 W/mK, which is about 650% that of pure phenolic resin, showing that the construction of 3D thermal network structure is conducive to the reinforcement of thermal conductivity of composites. The method can provide a certain theoretical basis for constructing a thermally conductive composite with a three-dimensional structure.

Diode-pumped Tm3+,Ho3+ co-doped GAGG mode-locking laser near the 2.1µm wavelength region.

In this paper, a laser diode (LD) pumped passive mode-locking Tm,Ho:GAGG laser based on a semiconductor saturable absorber mirror (SESAM) is reported. By adjusting the group delay dispersions inside the laser cavity and transmissions of the output couplers (OCs), a shortest pulse duration of 10.84 ps at 2089.9 nm is achieved, the average output power is 33.17 mW and the laser runs at a 83.01 MHz repetition rate. A maximum average output power of 66.43 mW is also obtained at 2089.9 nm with a pulse duration of 16.56 ps by using an OC of 3%. To the best of our knowledge, this is the first report on the mode-locking Tm,Ho:GAGG laser.

Study on Preparation and Properties of Ultrahigh Molecular Weight Polyethylene Composites Filled with Different Carbon Materials.

The development of ultrahigh molecular weight polyethylene (UPE) has been restricted due to its linear structure and low thermal conductivity. In this paper, graphene oxide (GO) was prepared by the modified Hummers method, and then UPE/reduced graphene oxide (rGO) powder was prepared by reduction with hydrazine hydrate. UPE/natural graphite (NG), UPE/carbon nanofiber (CNF), and UPE/rGO are prepared by hot compression molding. With the increase of thermally conductive fillers, the high density of the composite makes the thermal conductivity of the crystal structure more regular and the thermal conductivity path increases accordingly. Both TGA and SEM confirmed the uniform dispersion of carbon filler in epoxy resin. Among the three composites, UPE/NG has the best thermal conductivity. When the NG filling content is 60 phr, the thermal conductivity of the UPE/NG composite is 3.257 W/(mK), outperforming UPE/CNFs (0.778 W/(mK) and pure UPE (0.496 W/(mK) by 318.64 and 556.65%, respectively. UPE/CNFs have the best dielectric properties. Comparison of various carbon fillers can provide some references for UPE's thermal management applications.

Polyethylene Glycol-Calcium Chloride Phase Change Materials with High Thermal Conductivity and Excellent Shape Stability by Introducing Three-Dimensional Carbon/Carbon Fiber Felt.

The low thermal conductivity and poor shape stability of phase change materials (PCMs) have seriously restricted their applications in energy storage and energy saving. In this paper, poly(ethylene glycol)-calcium chloride/carbon/carbon fiber felt (PEG-CaCl2/CCF) PCMs were fabricated by a liquid-phase impregnation-vacuum drying-hot compression molding method with carbon/carbon fiber felt as the three-dimensional (3D) thermal skeleton and PEG-CaCl2 as the polymer PCM matrix. PCMs were heated and compressed by the compression confinement method to improve the contact area between 3D skeleton carbon fibers. The carbon fibers in PCMs presented a 3D (X-Y-Z) network structure and the fiber arrangement was anisotropic, which were beneficial to improve the thermal conductivity of PCMs in the fiber direction. The compression confinement can improve the contact area between the fibers in the 3D skeleton. As a result, the thermal conductivity of PEG-CaCl2/CCF PCMs can reach 3.35 W/(m K) (in-plane) and 1.94 W/(m K) (through-plane), about 985 and 571% of that of PEG-CaCl2, respectively. Due to the complexation of PEG and CaCl2 and the 3D skeleton support of carbon fiber felt, PCMs have excellent shape stability. The paper may provide some suggestions for the preparation of high thermal conductivity and excellent shape stability PCMs.

Epoxy Composites with High Thermal Conductivity by Constructing Three-Dimensional Carbon Fiber/Carbon/Nickel Networks Using an Electroplating Method.

Heat dissipation problem is the primary factor restricting the service life of an electronic component. The thermal conductivity of materials has become a bottleneck that hinders the development of the electronic information industry (such as light-emitting diodes, 5G mobile phones). Therefore, the research on improving the thermal conductivity of materials has a very important theoretical value and a practical application value. Whether the thermally conductive filler in polymer composites can form a highly thermal conductive pathway is a key issue at this stage. The carbon fiber/carbon felt (CF/C felt) prepared in the study has a three-dimensional continuous network structure. The nickel-coated carbon fiber/carbon felt (CF/C/Ni felt) was fabricated by an electroplating deposition method. Three-dimensional CF/C/Ni/epoxy composites were manufactured by vacuum-assisted liquid-phase impregnation. By forming connection points between the adjacent carbon fibers, the thermal conduction path inside the felt can be improved so as to improve the thermal conductivity of the CF/C/Ni/epoxy composite. The thermal conductivity of the CF/C/Ni/epoxy composite (in-plane K∥) is up to 2.13 W/(m K) with 14.0 wt % CF/C and 3.70 wt % Ni particles (60 min electroplating deposition). This paper provides a theoretical basis for the development of high thermal conductivity and high-performance composite materials urgently needed in industrial production and high-tech fields.

3D Thermal Network Supported by CF Felt for Improving the Thermal Performance of CF/C/Epoxy Composites.

The heat generated by a high-power device will seriously affect the operating efficiency and service life of electronic devices, which greatly limits the development of the microelectronic industry. Carbon fiber (CF) materials with excellent thermal conductivity have been favored by scientific researchers. In this paper, CF/carbon felt (CF/C felt) was fabricated by CF and phenolic resin using the "airflow network method", "needle-punching method" and "graphitization process method". Then, the CF/C/Epoxy composites (CF/C/EP) were prepared by the CF/C felt and epoxy resin using the "liquid phase impregnation method" and "compression molding method". The results show that the CF/C felt has a 3D network structure, which is very conducive to improving the thermal conductivity of the CF/C/EP composite. The thermal conductivity of the CF/C/EP composite reaches 3.39 W/mK with 31.2 wt% CF/C, which is about 17 times of that of pure epoxy.

Carbon Fiber Reinforced Multi-Phase Epoxy Syntactic Foam (CFR-Epoxy-Hardener/HGMS/Aerogel-R-Hollow Epoxy Macrosphere(AR-HEMS)).

Because the aerogel has ultra-low density and good impact resistance, the aerogel material, epoxy-hardener system, and expandable polystyrene beads (EPS) were used to prepare the lightweight aerogel reinforced hollow epoxy macro-spheres (AR-HEMS). The multi-phase epoxy syntactic foam (ESF) was manufactured with the epoxy-hardener system, HGMS (EP-hardener-HGMS), and AR-HEMS by "the compression modeling method." In this experiment, in order to enhance the strength of the ESF, some different kinds of the carbon fiber (CF) were added into the EP-hardener-HGMS system (CFR-EP). The influence of the volume stacking fraction, inner diameter, and layer of the AR-HEMS and the content and type of the CF in the EP-HGMS (CFR-EP) system on the compressive strength of the ESF were studied. Weighing the two factors of the density and compressive strength, the ESF reinforced by 1.5 wt% CF with 90% AR-HEMS has the better performance. This kind of the ESF has 0.428 g/cm3 nd 20.76 Mpa, which could be applied in 2076 m deep sea.

Epoxy composite with high thermal conductivity by constructing 3D-oriented carbon fiber and BN network structure.

As electronic devices tend to be integrated and high-powered, thermal conductivity is regarded as the crucial parameter of electronic components, which has become the main factor that limits the operating speed and service lifetime of electronic devices. However, constructing continuous thermal conductive paths for low content particle fillers and reducing interface thermal resistance between fillers and matrix are still two challenging issues for the preparation of thermally conductive composites. In this study, 3D-oriented carbon fiber (CF) thermal network structures filled with boron nitride flakes (BN) as thermal conductive bridges were successfully constructed. The epoxy composite was fabricated by thermal conductive material with a 3D oriented structure by the vacuum liquid impregnation method. This special 3D-oriented structure modified by BN (BN/CF) could efficiently broaden the heat conduction pathway and connected adjacent fibers, which leads to the reduction of thermal resistance. The thermal conductivity of the boron nitride/carbon fiber/epoxy resin composite (BN/CF/EP) with 5 vol% 10 mm CF and 40 vol% BN reaches up to 3.1 W m-1 K-1, and its conductivity is only 2.5 × 10-4 S cm-1. This facile and high-efficient method could provide some useful advice for the thermal management material in the microelectronic field and aerospace industry.

Preparation and Mechanical Properties of Carbon Fiber Reinforced Multiphase Epoxy Syntactic Foam (CF-R-Epoxy/HGMS/CFR-HEMS Foam).

Short carbon fiber (CF), epoxy-hardener (EP-hardener), and expanded polystyrene (EPS) beads were used to prepare CF-reinforced hollow epoxy macrospheres (CFR-HEMS) by the "rolling ball method". The multiphase epoxy syntactic foam (ESF) was prepared with CFR-HEMS, the EP-hardener system, and hollow glass microspheres (HGMS) by the "compression modeling method". In this experiment, the influences of the stacking volume fraction, wall thickness, and inner diameter of the CFR-HEMS and HGMS types and contents in the EP-hardener system on the properties of the ESF were studied. In addition, CFs with different meshes were used to reinforce hollow epoxy macrospheres (HEMS) to study the effect of different kinds of CFs on the compressive strength of the ESF. During the mixing of the EP-hardener and HGMS (EP-hardener-HGMS), 300 AW CFs with different contents were added to the system to enhance the compressive strength of the ESF. The CFR-HEMS spherical wall was combined tightly with the EP-hardener-HGMS system by a scanning electron microscope (SEM). The ESF, which has better properties relatively in the experiment, can be used in 2673 m deep water and provide 490 kg/m3 buoyancy, which can be of help in the preparation of buoyancy materials in detection systems and oil extraction systems in the deep sea.

The Effect of Laser Power on the Properties of M3B2-Type Boride-Based Cermet Coatings Prepared by Laser Cladding Synthesis.

Boride-based cermet can serve as a good protective coating for low-corrosion and wear-resistant materials, such as carbon steels, due to their mechanical and chemical properties. In this study, M3B2 (M: Mo, Ni, Fe, and Cr) boride-based cermet coatings were fabricated on Q235 steel with mixed powders of Mo, B, Ni60, and Cr by laser cladding synthesis, and the effects of laser power on the properties of the cermet layer were investigated. Three laser powers (2200, 2500, and 2800 W) were used at the same scanning speed. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analysis confirmed that all the coatings were composed of M3B2-type borides and {Fe, Ni} alloys. The micro-hardness, corrosion, and frictional experiments showed that the cermet coatings enhanced the corresponding performances of the Q235 steels at the three laser powers. However, the micro-hardness of the coatings decreased as the power increased, and the maximum micro-hardness value was 1166.3 HV (Vickers Hardness). The results of the corrosion and frictional experiments showed that the best performance was obtained at a laser power of 2500 W, followed by 2800 and 2200 W.

Development and Mechanical Characterization of HGMS-EHS-Reinforced Hollow Glass Bead Composites.

Hollow glass microsphere-reinforced epoxy hollow spheres (HGMS-EHSs) were prepared by a "rolling ball method" using expanded polystyrene beads, HGMSs, and epoxy resin (EP). The three-phase epoxy syntactic foam (epoxy/HGMS-EHS-HGMS composite) was fabricated by combining HGMS-EHS as a lightweight filler with EP and HGMS by a "molding method". The HGMS-EHS and epoxy curing agent systems were well mixed by scanning electron microscopy. Experiments show that higher HGMS-EHS stack volume fraction, lower HGMS-EHS layer number, higher HGMS-EHS diameter, lower HGMS-EHS density, higher HGMS volume fraction, and lower HGMS density result in a decrease in the density of the three-phase epoxy syntactic foam. However, the above factors have the opposite effect on the compressive strength of the three-phase epoxy syntactic foam. Therefore, in order to obtain the "high-strength and low-density" three-phase epoxy syntactic foam, the influence of various factors should be considered comprehensively to achieve the best balance of compressive strength and density of the three-phase epoxy syntactic foam. This can provide some advice for the preparation of buoyancy materials for deep sea operations.