Preparation Of Composite Materials Research Articles

Preparation and properties of zeolite-fly ash-slag composite porous materials: CO2 adsorption performance and mechanical property.

To solve the environmental problems caused by greenhouse gas emissions, porous materials based on alkaline solid wastes (fly ash and slag) were prepared in this study. Besides, the preparation scheme of the porous materials was optimized through an orthogonal test by taking the compressive strength and static CO2 adsorption capacity as the target parameters. The two target parameters of the porous materials prepared under the optimal ratio are 15.395N and 0.83mmol/g. On the basis of the optimal ratio, zeolite composite porous materials were prepared by adding different types of zeolite, which further improves the CO2 adsorption capacity of the porous materials. Furthermore, the micro-morphologies, CO2 adsorption performances, and mechanical properties of the porous materials were analyzed by a scanning electron microscope (SEM), the Brunauer-Emmett-Teller (BET) method, and a universal testing machine. It is discovered that the addition of different types of zeolite decreases the compressive strength but significantly improves the CO2 adsorption performance as it can promote the specific surface area and the pore volume. Moreover, the best performance is achieved with the addition of 13X zeolite. In this case, the adsorption capacity reaches 2.68mmol/g, about 3.2 times greater than that of the porous materials without zeolite. The CO2 adsorbent proposed in this study, which boasts excellent mechanical property and CO2 adsorption performance, is applicable to goafs and has a bright prospect in the comprehensive utilization of solid wastes and the control of global warming.

Comparison of sawdust bio-composites based on magnesium oxysulfate cement and ordinary Portland cement

This study incorporated sawdust (SD) as a bio-aggregate into magnesium oxysulfate cement (MOSC) and ordinary Portland cement (OPC) for the preparation of composite lightweight materials. The effect of sawdust dosage on the mechanical properties, thermal properties, water absorption, and water resistance of the two bio-composites was investigated. Experimental results revealed that SD-MOSC presented lower density, higher compression strength, and excellent thermal insulation properties than SD-OPC. Thus, MOSC is more suitable as a binder for sawdust aggregates than OPC. Microstructure observation showed that 5 Mg(OH)2·MgSO4·7H2O (5·1·7) phase whiskers preferred to form at the defects of sawdust, indicating that MOSC had better compatibility with sawdust. The increase of sawdust hindered the generation of 5·1·7 phase, resulting in the strength reduction. MOSC-based sawdust bio-composites are a promising material for production of thermal insulation panels and are favorable for environmental protection.

Room-temperature self-healing, high ductility, recyclable polyurethane elastomer fabricated via asymmetric dynamic hard segments strategy combined with self-cleaning function application

It is challenging to prepare room temperature self-healing materials that balance self-healing and mechanical properties. In this study, we introduces a concept of “asymmetric dynamic hard segments” to balance mechanical strength and self-healing properties while ensuring high ductility and recyclability. The introduction of asymmetric dynamic hard segments allows polymer chains to form an amorphous structure and high mobility and enables the dissociation and rapid recombination of multiphase hydrogen bonds. Based on this feature, a simple two-step polycondensation reaction was reported to synthesise a room-temperature-self-healing polyurethane elastomer (PPG-IH-IPDA) with good mechanical strength, good toughness, high ductility and excellent recyclability. The experimental results showed that room-temperature self-healing completely eliminated scratches on PPG-IH-IPDA, and the mechanical properties of the elastomer were fully restored. With the advantageous characteristics of PPG-IH-IPDA, the perfect combination of self-healing and self-cleaning functions leads to the preparation of a superhydrophobic composite material (SHN-SiO2/PPG-IH-IPDA) that shows a contact angle greater than 150°, which enables surface damage self-healing at room temperature. The proposed combination of self-healing and self-cleaning properties provides substantial guidance for the development of versatile materials.

CHARACTERIZATION OF SAGO PALM-CARBON FIBRE REINFORCED EPOXY HYBRID COMPOSITES

Natural fibers are potential alternatives to synthetic fibers. Sago palm is a new type of natural fiber and has the potential same as other existing natural fibers. In this study, the mechanical properties of sago palm/carbon fiber reinforced with epoxy hybrids were studied. Impact tests were conducted to study the impact properties of sago palm-carbon fiber-reinforced X hybrid composites. The hybrid composites contain woven sago palm fiber and carbon fiber reinforced with epoxy resin produced by the vacuum compaction method. Each sample was prepared with different volume fractions such as 40%, 64%, and 91% of composition sago palm fiber. After the preparation of composite material, mechanical properties tests were studied on the prepared sample. In addition, by using Scanning Electron Microscope Tests, the failure mode is investigated. It can be concluded that 40% of sago palm fiber contains the best impact behavior compared to 64% and 91% of sago palm fiber loading because it’s high in impact resistance.

Facile and scalable synthesis of mesoporous composite materials from coal gasification fine slag for enhanced adsorption of malachite green

The recycling of the solid wastes produced in the industrial process and converting them into functional materials with unique structures are of great significance for the sustainable development of human society. In this study, a facile and scalable synthesis method was designed for the preparation of mesoporous composite materials from waste coal gasification fine slag using K2CO3 as a mild chemical additive to chemically recombine SiO2 and Al2O3. At a fine slag to K2CO3 mass ratio of 1:1, a mesoporous composite material (OMB-KB) mainly composed of faujasite-Na and amicite was obtained, which possessed a uniformly porous and loose structure with a specific surface area of 40.26 m2/g and the pore size range of 2–50 nm. Metals inherited from the raw slag and various chemical groups existed on the surface of OMB-KB, making the materials have unique surface chemical properties. OMB-KB exhibited ultra-high adsorption performance on malachite green (MG), and the adsorption capacity reached 7218.31 mg/g when 0.01 g of OMB-KB and 300 ml of MG solution with a concentration of 300 mg/L were used for the adsorption at 298K. The increase of pH was beneficial to the adsorption of cationic MG, and the removal efficiency reached an excellent state at pH ≥ 6. The good fitting of the pseudo-second-order kinetic model and the Freundlich isotherm model suggested that the adsorption process was dominated by chemisorption. The thermodynamic analysis showed that the adsorption of OMB-KB to MG was endothermic, entropy-increasing and entropy-controlled. The adsorption of MG by the material was realized through the exchange interactions between cations, as well as the electrostatic attraction and van der Waals forces between –OH groups and MG. Meanwhile, the oxygen-containing groups and π-electrons in the carbon layer could also adsorb MG molecules by electrostatic attraction.

Preparation and application of composite phase change materials stabilized by cellulose nanofibril-based foams for thermal energy storage

The leakage issue and inferior heat conduction of organic phase change materials (PCMs) limit their actual applications. In the present study, cellulose nanofibril (CNF)-based foams were prepared as the porous scaffolds for polyethylene glycol (PEG) and paraffin wax (Pw) to prevent their leakage, and multiwalled carbon nanotubes (CNTs) were incorporated to improve the heat transfer performance. The prepared foams had low density (<67.3 kg/m3) and high porosity (>94.5 %). Selective chemical modifications of nanocellulose foams enhanced their shape-stability and compatibility with PCMs. The highly porous foam structure and favorable compatibility resulted in high PCM loading levels (93.63 % for PEG and 91.77 % for Pw) and negligible PCM leakage (<2 %). CNTs improved the heat transfer performance of PCMs, as evidenced by the improved thermal conductivities and boosted temperature rises during solar heating. Meanwhile, the composite PCMs exhibited improved thermal stability over the control. PEG-based composite PCM exhibited a phase change enthalpy of 143 kJ/kg with a melting temperature of 25.2 °C; Pw-based composite PCM exhibited a phase change enthalpy of 184 kJ/kg with a melting temperature of 53.4 °C. Novel PCM sandwich structures based on these composite PCMs and a thermoelectric generator were designed and displayed promising potential for solar energy harvesting and utilization.

Improving the Energy Storage Performance of All-Polymer Composites By Blending PVDF and P(VDF-CTFE).

Organic film capacitors have incredibly high power density and have an irreplaceable position in pulsed power systems, high-voltage power transmission networks and other fields. At present, the energy storage density and energy storage efficiency of organic film capacitors are relatively low, resulting in excessive equipment volume. The performance of organic film capacitors is determined by polymer materials, so it is crucial to develop a polymer composite with high energy storage density and high charge-discharge efficiency. Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-CTFE)) is incorporated into the polyvinylidene fluoride (PVDF) matrix by solution blending. The successful preparation of the all-polymer composite material solves the problems of low breakdown electric field strength, low discharge energy density, and low charge-discharge efficiency of high-dielectric ferroelectric materials. The discharge energy density of the PVDF/P(VDF-CTFE) (70/30) film is more than twice that of pure PVDF due to the increase of phases α and γ and the decrease of crystallinity. Under the breakdown electric field (380kV mm-1 ), PVDF/P(VDF-CTFE) (70/30) film also has an ultrahigh energy storage efficiency of 64%. The relationship between the structure and properties of composite materials is investigated in this study, which has important implications for the development of capacitors with high energy storage density.

Physico-Chemical Properties of Alkali Treated Cellulosic Fibers from Fragrant Screw Pine Prop Root

ABSTRACT The purpose of this study is to characterize alkali-treated fibers from the prop root of fragrant screw pine (FSP) plant in order to determine their suitability as a substitute for man-made fiber in preparation of lightweight bio-based composite materials. The physical, chemical, mechanical, morphological, and thermal properties of alkali-treated FSP fibers (AFSPF) were reported and compared to those of other natural fibers used as reinforcement in polymer composites. Cellulose content (80.53 wt.%), wax content (0.21 wt.%), density (1.41 g/cm3), tensile strength (619–1038 MPa), and young’s modulus (23–41 GPa) of AFSPF were determined. Thermal analysis (TGA and DTG) confirms the thermal stability of these fibers up to 257°C. The characterized properties demonstrate that AFSPF can be used as reinforcement in the preparation of polymer-based bio-composites for applications requiring low weight and high specific strength that meet technical and environmental requirements.

Large-Scale Production of Rectorite Nanosheets and Their Co-Assembly with Aramid Nanofibers for High-Performance Electrical Insulating Nanopapers.

Compared with raw rectorite microplatelets (RMs), rectorite nanosheets (RNs) have considerably greater application prospects in the preparation of advanced composite materials because of their larger aspect ratio, higher surface reactivity, and intrinsically superior mechanical and physical properties. However, the difficulty in the efficient preparation of RNs significantly limits their large-scale applications. Here, a scalable poly(vinylpyrrolidone)-assisted stirring approach is developed to prepare ultrathin RNs from the abundant natural RMs. A higher production rate (≈0.675g h-1 ) is achieved compared with that of most other nanosheets. Additionally, instead of using conventional time- and energy-consuming high-speed centrifugation, an efficient poly(dienedimethylammonium chloride)-assisted sedimentation strategy is proposed here to rapidly separate the exfoliated RNs from the RN dispersion. Then, the RNs are co-assembled with aramid nanofibers (ANFs) into large-scale nacre-mimetic ANF-RN nanopapers with considerably enhanced mechanical, electrical insulating, and high-temperature-resistantproperties compared with pure ANF nanopapers and ANF-RM micropapers. Moreover, these properties are superior to those of previously reported ANF-based nanopapers and commercial insulating micropapers.

Cobalt Ferrite Particles Produced by Sol-Gel Autocombustion and Embedded in Polysilane: An Innovative Route to Magnetically-Induced Fluorescence Composites.

Fluorescence detection is currently one of the commonly used techniques worldwide. Through this work, the preparation and optical properties of an interesting composite material are discussed. It is shown that encapsulating cobalt spinel ferrite (CoFe2O4), obtained by the sol-gel autocombustion method, into poly[diphenyl-co-methyl(H)]silane matrix leads to fluoromagnetic particles (PSCo) with intriguing optical properties. Transmission electron microscopy, combined with energy-dispersive X-ray analysis, showed 500 nm large spherical structures containing a core (around 400 nm in diameter) composed of magnetic ferrite particles, surrounded by a thin layer of semiconductive fluorescent polymer. The as-obtained material exhibited ferrimagnetic properties. The FTIR spectrum confirmed that the Si-H functionality of the polysilane was preserved. UV spectroscopy combined with molecular modeling studies indicated that the magnetic core had a strong influence on the intramolecular electron transitions characteristic of the σ-conjugated polysilane. Further analysis by steady-state fluorescence spectroscopy revealed that the internal magnetic field strongly enhances the polysilane emission. This property will be further investigated in the future in order to develop new detection devices.

Composite TiO2-based photocatalyst with enhanced performance.

TiO2 is the most studied photocatalyst because of its non-toxicity, chemical stability, and low cost. However, the problem of TiO2 is its low activity in the visible region of the spectrum. In this study, we focused on the preparation of composite photocatalytic materials with altered light absorption properties. TiO2 P25 and various metal oxides were mechanically joined by ball-milling and immobilized on glass plates. The prepared samples were evaluated based on their ability to degrade NO in gas phase. The formation of undesirable byproducts was also investigated. Four best performing composites were later chosen, characterized, and further evaluated under various conditions. According to their performance, the metal oxide additives can be divided into three groups. P25/Fe2O3 showed the most promising results-an increase in overall deNOx activity under modified ISO conditions and altered selectivity (less NO2 is formed) under both simulated outdoor and simulated indoor conditions. On the other hand, P25/V2O5 composite showed negligible photocatalytic activity. The intermediate group includes P25/WO3 and P25/ZnO photocatalysts, whose performances are similar to those of pristine P25.

Antimicrobial ceramic foam composite air filter prepared from Moroccan red clay, phosphate sludge waste and biopolymer

The COVID-19 pandemic has highlighted the importance of air sterilization and disinfection. Besides the regular cleaning and disinfection of surfaces it is at least as important to reduce the number of airborne microorganisms as they are known to play an important role in the spreading of different infections.Herein, we report a facile preparation of a porous air filter ceramic composite material, suitable for the effectively eliminating airborne microorganisms. The antimicrobial activity of the ceramic foam could be attributed to a thin chitosan biopolymer layer immobilized on the ceramic surface. Furthermore, as the ceramic foam was prepared on phosphate sludge waste and Moroccan red clay basis, this research opens new routes towards the valorization of solid industrial or mining wastes or other yet unused abundant materials, as well.

Synergistic Effect of Work Function and Acoustic Impedance Mismatch for Improved Thermoelectric Performance in GeTe-WC Composite.

The preparation of composite materials is a promising methodology for concurrent optimization of electrical and thermal transport properties for improved thermoelectric (TE) performance. This study demonstrates how the acoustic impedance mismatch (AIM) and the work function of components decouple the TE parameters to achieve enhanced TE performance of the (1-z)Ge0.87Mn0.05Sb0.08Te-(z)WC composite. The simultaneous increase in the electrical conductivity (σ) and Seebeck coefficient (α) with WC (tungsten carbide) volume fraction (z) results in an enhanced power factor (α2σ) in the composite. The rise in σ is attributed to the creation of favorable current paths through the WC phase located between grains of Ge0.87Mn0.05Sb0.08Te, which leads to increased carrier mobility in the composite. Detailed analysis of the obtained electrical properties was performed via Kelvin probe force microscopy (work function measurement) and atomic force microscopy techniques (spatial current distribution map and current–voltage (I–V) characteristics), which are further supported by density functional theory (DFT) calculations. Furthermore, the difference in elastic properties (i.e., sound velocity) between Ge0.87Mn0.05Sb0.08Te and WC results in a high AIM, and hence, a large interface thermal resistance (Rint) between the phases is achieved. The correlation between Rint and the Kapitza radius depicts a reduced phonon thermal conductivity (κph) of the composite, which is explained using the Bruggeman asymmetrical model. Moreover, the decrease in κph is further validated by phonon dispersion calculations that indicate the decrease in phonon group velocity in the composite. The simultaneous effect of enhanced α2σ and reduced κph results in a maximum figure of merit (zT) of 1.93 at 773 K for (1-z)Ge0.87Mn0.05Sb0.08Te-(z)WC composite for z = 0.010. It results in an average thermoelectric figure of merit (zTav) of 1.02 for a temperature difference (ΔT) of 473 K. This study shows promise to achieve higher zTav across a wide range of composite materials.

Natural and Synthetic Polymer Fillers for Applications in 3D Printing—FDM Technology Area

This publication summarises the current state of knowledge and technology on the possibilities and limitations of using mineral and synthetic fillers in the field of 3D printing of thermoplastics. FDM technology can be perceived as a miniaturised variation of conventional extrusion processing (a microextrusion process). However, scaling the process down has an undoubtful drawback of significantly reducing the extrudate diameter (often by a factor of ≈20–30). Therefore, the results produced under conventional extrusion processing cannot be simply translated to processes run with the application of FDM technology. With that in mind, discussing the latest findings in composite materials preparation and application in FDM 3D printing was necessary.

Preparation and Performance Analysis of Form-Stable Composite Phase Change Materials with Different EG Particle Sizes and Mass Fractions for Thermal Energy Storage.

The low thermal conductivity and leakage of paraffin (PA) limit its wide application in thermal energy storage. In this study, a series of form-stable composite phase change materials (CPCMs) composed of PA, olefin block copolymer (OBC), and expanded graphite (EG) with different particle sizes (50 mesh, 100 mesh, and 200 mesh) and mass fractions are prepared by melt blending. OBC as a support material could reduce PA leakage during melting, and EG as a thermally conductive filler can improve the thermal performance of PCMs. The microstructure characteristics and chemical and thermal properties of prepared CPCMs are tested and analyzed. The results show that PA/OBC and EG have good compatibility, and there is no chemical reaction with each other to generate new substances. Thermal conductivity can be significantly improved by adding EG, and it is greatly enhanced with the increase in EG particle size at the same EG mass fraction. Simultaneously, the addition of EG increased the melting temperature of CPCMs and decreased the solidification temperature as well; meanwhile, the values of melting temperature and solidification are also reversed for CPCMs compared to PA/OBC. There is an optimal content of EG to balance the thermal conductivity and heat storage capacity for CPCMs. The addition of OBC can provide a stable geometric construction, and the leakage will be further improved with the increase in EG content. Finally, the melting time of CPCMs containing EG-50, EG-100, and EG-200 with 4 wt % EG is shortened by 52.9, 41.1, and 37.5%, respectively, compared with PCMs without EG in the heat storage and release experiments. Also, the CPCMs with EG-50 have better thermal performance compared with the CPCMs of EG-100 and EG-200.

Discharged Titanium Oxide Nanotube Arrays Coated with Ni as a High‐Performance Lithium Battery Electrode Material

Transition metal oxides are in high demand as electrode materials for alkali metal‐ion batteries due to high theoretical capacity. However, low electron transfer kinetics and slow ion migration lead to poor cycle stability and rate performance of the transition metal oxide electrode. Herein, TiO2 nanotube arrays coated with Ni (Ni/TiO2NTs) are fabricated by using predischarge‐electrodeposition method and subsequent calcination under H2/N2. In the Ni/TiO2NTs composite, TiO2NTs and Ni nanoparticles play the role of framework and coating layer, respectively. The as‐prepared Ni/TiO2NTs composites have a high specific surface area and a unique tubular structure, which facilitates the quick penetration of the electrolyte into the tubes and reduces the lithium ions’ diffusion distance. The incorporation of Ti3+ and metallic nickel in the hydrogenated TiO2NTs also increases conductivity. Besides, the spin‐polarized surface capacitance of Ni0 nanoparticles causes the magnetic changes that generate an extra lithium‐ion storage capacity. The Ni/TiO2NTs composite electrode maintains a high capacity of 507 mA h g−1 after 100 cycles at 0.2 A g−1. Here, the predischarge‐electrodeposition provides a new route for the preparation of composite materials.

Preparation of Graphene Nanosilver Composites for 3D Printing Technology

At present, graphene in two-dimensional carbon nanomaterials is a material with excellent properties. Its preparation technology and application prospects are very wide. The most common one is the chemical redox method, which can make graphite into graphite oxide dispersed in water. Graphene oxide obtained by the Hummers method has a wrinkled structure. In order to broaden the application field of graphene and give full play to its excellent properties, the current research on graphene mainly focuses on the preparation and application of functional composite materials as a matrix material or reinforcement material. Due to its special two-dimensional structure, it has a large specific surface area, good biocompatibility, and stable physical and chemical properties, making it an excellent nanoparticle carrier. The graphene-supported silver nanoparticles can effectively prevent the aggregation and stacking between particles, improve the electrochemical performance of the composite material, and expand its application range. In this article, the assisted preparation of graphene nanosilver composites by 3D printing technology (three-dimensional printing) was studied. 3D printing technology is a rapid prototyping technology that emerged in the 1980s. 3D printing technology is based on discrete stacking and realizes rapid processing of models by directly outputting data from the printing device. In this article, a new type of graphene oxide (GO) was prepared by the modified Hummers method. In the case of NaOH aqueous solution as a catalyst, silver nitrate and GO were used as precursors, and XRD, infrared spectrum, Raman spectrum, and other methods were used. The crystal structure and morphology of Ag/rGO under different conditions were studied, thus revealing the growth of silver particles and the changes of oxidized functional groups under different conditions. It was found that the intensity of the two peaks in the GNs-Ag-2 Raman spectral curve was seven times that of the GNs peak.

Effects of local fiber discontinuity on the fatigue strength parameter at the fiber inclusion corner in fiber-reinforced composites

Abstract To comprehend the fatigue failure mechanism at the fiber discontinuity in fiber-reinforced composites, it is necessary to evaluate the local mechanical behaviors. The fatigue strength depends on the stress distribution at the fiber inclusion corner. An improved advanced finite element method (IAFEM) is proposed for the stress intensity factor (SIF) analysis at the fiber inclusion corner. In the IAFEM, the element stiffness matrix of singular inclusion corner element (SICE) is obtained, and the singular elastic field at the tip of the fiber inclusion is determined. The effects of load direction, fiber distribution, fiber geometry, and material properties on SIFs are analyzed numerically using the IAFEM. The difference in stress field distribution between two-dimensional and three-dimensional fiber inclusions is discussed. The IAFEIM and calculation results can provide reference for fatigue strength analysis and preparation of composite materials.

Long-term antimicrobial effect of polylactide-based composites suitable for biomedical use

This work deals with the preparation and characterization of antimicrobial polymeric composite materials based on polylactide, which is currently widely investigated to produce temporary implants. Polylactide was blended with antimicrobial fillers: silver, hexadecylpyridinium or hexadecyltrimethylammonium bromides anchored on vermiculite or graphene oxide matrices in an amount of 1% wt. The prepared samples were characterized by conventional methods, further they were exposed to degradation tests in physiological saline conditions and characterized for their antimicrobial properties using common pathogen microorganisms. It has been proven that the prepared polylactide composites change their antimicrobial effects after being in physiological saline of pH 7 and 9 for 0–6 months. The weight of the composites changed by about 10%, and antimicrobial properties were growing over time. The effectiveness of the composites was confirmed for 6 months at minimum. Therefore, they are suitable for the preparation of temporary stents, catheters or implants suitable for fracture fixation.

Preparation of high-performance thermal insulation composite material from alkali-activated binders, foam, hollow glass microspheres and aerogel

• Physical foaming, hollow glass microspheres and aerogel were used for AAB. • CMC minimized foam and slurry delamination and improved foaming effect. • KH550 treated hollow glass microspheres showed enhanced the interfacial bonding. • PE100-hydrophobic aerogel had extern hydrophilic and internal hydrophobic effect. Herein, a high-performance thermal insulation composite material was prepared by adding physical foaming agent (FA), hollow glass microspheres (HGMs) and aerogel (AG) with alkali-activated binders (AABs) as the matrix. The results of orthogonal experiments revealed that AG has the greatest effect on thermal conductivity, followed by the effect of FA and HGMs. The thermal conductivity value of AABs was reduced from 0.6057 to 0.0870 W/(m·K) at an AG dosage of 4 g (42.48 kg/m 3 ) in the single factor experiments. The effect of compressive strength followed an order of: HGMs < FA < AG. Under the temperature condition of 400–800 °C, the FA exacerbated the linear shrinkage of the sample, HGMs inhibited the linear shrinkage at 400 °C and 600 °C, and exacerbated it at 800 °C, while AG inhibited the linear shrinkage. X-ray diffraction and scanning electron microscopy analyses revealed that the sample maintained stable performance below 800 °C. Orthogonal experiment results concluded that the optimal level combination was 6 g FA, 6 g HGMs and 3 g AG (A6B6C3) and exhibited the minimal thermal conductivity (0.0434 W/(m·K)). The compressive strength of A6B6C3 at 30 °C was 0.38 MPa, which gradually increased with temperature, reaching the maximum of 0.79 MPa at 800 °C. This composite can meet the thermal insulation, mechanical and high temperature resistance properties. In addition, accredited to simple preparation process, short curing period, and low cost, this approach can be deemed of great significance for applications in composite thermal insulation materials in nuclear power plants and other key areas.