Barrier Ability Research Articles

Chitosan/CaCO3solvent‐free nanofluid composite membranes for direct methanol fuel cells

Natural polyelectrolyte chitosan (CS) has been considered to be a promising proton‐exchange membrane material for direct methanol fuel cells due to its low cost and excellent methanol barrier ability. To further improve the ionic conductivity and mechanical property of CS, calcium‐carbonate solvent‐free nanofluids (CaCO3‐SF) with unique flow behavior were prepared by an ion‐exchange method, and then used a novel nanofiller to modify CS to fabricate composite membranes. The surface‐grafted organic long chains on the surface of CaCO3nanoparticles could promote the homogeneous dispersion of CaCO3in the CS matrix, and thus improve the interfacial bonding and facilitate the load transfer from the matrix to stiff CaCO3. When the content of CaCO3‐SF was 6 wt%, the tensile strength and fracture elongation of the composite membrane were 28.25 MPa and 17.17%, respectively, which increased by 25% and 36% when compared with those of pure membrane. Moreover, the SO3H groups in the structure of organic long chains could form new proton transport sites, and thus enhance the proton conductivity of the membranes. Consequently, when compared with pure CS membrane (0.0131 S cm−1), incorporation of 6 wt% CaCO3‐SF (0.0250 S cm−1) exhibited about onefold increase of proton conductivity. POLYM. ENG. SCI., 59:2128–2135, 2019. © 2019 Society of Plastics Engineers

Characterization of polylactic acids-polyhydroxybutyrate based packaging film with fennel oil, and its application on oysters

Abstract With the addition of fennel (FEN) oil, a biodegradable film based on polylactic acids (PLA) and polyhydroxybutyrate (PHB) was developed to possess antimicrobial ability. Barrier property and mechanical property tests were performed on three films, including PLA-PHB film, PLA-PHB film integrated with FEN oil (PLA-PHB-FEN) and ethanol vinyl alcohol (EVOH) film, whereby oxygen transmission rate (OTR), water vapor permeation (WVP), tensile strength and elongation at break were gathered. In addition, active properties including releasing, antibacterial and antioxidant abilities were measured. The profile showed that the mechanical properties of PLA-PHB film were comparable to those of EVOH film, except for the oxygen barrier ability. The FEN oil released from PLA-PHB-FEN film significantly inhibited the growth of E.coli and Staphylococcus by 1.2 and 1.3 Log CFU/g, respectively. PLA-PHB-FEN film showed the potential to be compatible with oily food as the maximum release (38.82 μg/mL) of FEN oil took place in fat simulants (65% ethanol). Afterward, the three films were used on the preservation of oysters for empirical tests. The results showed that the abundance of both aerobic and anaerobic bacteria were reduced by 1 Log CFU/g in the packaging of PLA-PHB-FEN film, which was supported by pH value and TVB-N level of oysters. Texture profile analysis and free amino acids quantification were also conducted. The data suggested that the PLA-PHB-FEN film could prolong the shelf-life on oysters for 2–3 days while maintaining their quality compared to EVOH film. This study provides insight into biodegradable packaging by which synthetic packaging could be substituted.

Mechanically robust and highly methanol-resistant sulfonated poly(ether ether ketone)/poly(vinylidene fluoride) nanofiber composite membranes for direct methanol fuel cells

As a key component of direct methanol fuel cells (DMFCs), proton exchange membranes (PEMs) are required to be mechanically robust, methanol-resistant, and conductive to protons. In this work, a novel sulfonated poly(ether ether ketone) (SPEEK) impregnated poly(vinylidene fluoride) (PVDF) electrospun nanofiber membrane was prepared. To avoid the collapse of PVDF fiber framework by the solvent of SPEEK, we designed a SPEEK/solvent/nonsolvent ternary filling system through the cloud point titration curves. Meanwhile, polydopamine (PDA), an extraordinarily adhesive and hydrophilic material, was coated on the surface of PVDF nanofibers to further improve the interface bonding between SPEEK and PVDF. The introduction of PVDF nanofibers completely changed the rigidity of SPEEK thus achieving a 5.4-fold increase of toughness when compared with that of pure SPEEK at dry state. Notably, significantly improved methanol barrier ability was also obtained due to the tortuous methanol crossover pathways caused by the embedded PVDF nanofibers. In the DMFC tests, the ultra-low methanol permeability and relatively high proton conductivity of the obtained composite membrane made it could be operated with 5 M methanol fuel and showed a peak power density of 104.0 mW cm−2, which was higher than the values of 89.3 mW cm−2 (2 M methanol) and 84.0 mW cm−2 (5 M methanol) recorded with commercial Nafion 115 membrane.

Synergistic effects of antioxidant and silica on enhancing thermo-oxidative resistance of natural rubber: Insights from experiments and molecular simulations

In this work, the thermo-oxidative aging performance of antioxidant N-isopropyl-N′-phenyl-p-phenylenediamine (4010NA)/silica (SiO2)/natural rubber (NR) composite was evaluated by the variations of mechanical properties and chemical structure after aging at 100 °C. Compared with 4010NA/carbon black (CB)/NR composite, there existed significant synergistic effects between 4010NA and SiO2 on improving the thermo-oxidative stability of NR material. Then, by combining the results of experiments and molecular simulations, the synergistic stabilization mechanism in 4010NA/SiO2/NR composite could be attributed to the following comprehensive effects. Firstly, the incorporation of silica was capable of improving oxygen (O2) barrier ability of NR and inhibiting the migration of 4010NA. Secondly, antioxidant 4010NA could be prior to terminate peroxy radicals, and its addition enabled 4010NA/SiO2/NR composite to be of an appropriately high cross-linking density due to a vulcanization accelerated effect. As a result, 4010NA/SiO2/NR composite exhibited more preeminent mechanical properties than 4010NA/NR and 4010NA/CB/NR composites during the thermo-oxidative aging process. This means that the combination of 4010NA and SiO2 can be exploited to prepare high performance NR composite with a facile operation. Furthermore, molecular simulation, as a theoretical method, may contribute to our understanding about structure-properties relationship for NR composite in depth.

Development, modification and characterization of new biodegradable film from basil seed (Ocimum basilicum L.) mucilage.

Biodegradable films from basil seed mucilage (BSM) were formed and modified with several di-carboxylic acid crosslinkers; i.e. tartaric acid (TA), malic acid (MA) and succinic acid (SA) with varying acidity and chemical structures, to enhance mechanical properties and water barrier ability. Basil seeds have a reasonable mucilage content and valuable properties; thus, it has the potential to develop valuable new biodegradable films. We characterized BSM films with the three crosslinkers using Fourier-transform infrared (FTIR) spectra and observed a 1730 cm-1 CO stretching peak, which confirmed ester linkage between the mucilage and crosslinkers. The crosslinked films showed higher gel fraction than native films. The crosslinked films showed better swelling and water vapor permeability with SA than with TA and MA. Crosslinking led to significant improvement in strain at maximum load. Further, the stress maximum load was comparable to that of commercial low-density polyethylene (LDPE) film. Crosslinked films showed additional homogeneous morphology and an increase in thermal degradation temperatures. Crosslinking with dicarboxylic acids improved all the key properties of BSM films, including excellent stress and strain at maximum load, improved barrier capability and thermal properties. Thus, these films showed good potential as biodegradable films, especially for food packaging. © 2019 Society of Chemical Industry.

Preparation and characterization of antioxidant, antimicrobial and pH-sensitive films based on chitosan, silver nanoparticles and purple corn extract

In this study, silver nanoparticles (AgNPs) and anthocyanin-rich purple corn extract (PCE) were incorporated into chitosan to develop active and intelligent food packaging films. The structural, physical and functional properties of chitosan/AgNPs/PCE films were compared with those of chitosan, chitosan/AgNPs and chitosan/PCE films. Spectroscopic analysis showed seven kinds of anthocyanins were present in PCE. Some particles and spots appeared on the surfaces and cross-sections of composite films. Fourier transform infrared and X-ray diffraction analyses suggested the interactions between chitosan and AgNPs were based on coordination effect, whereas the interactions between chitosan and PCE were mainly established through hydrogen bonds. The incorporation of PCE and/or AgNPs remarkably promoted the light and water vapor barrier ability, mechanical strength, antioxidant and antimicrobial properties of chitosan film. Notably, chitosan/AgNPs/PCE film exhibited the highest barrier, mechanical, antioxidant and antimicrobial properties due to synergistic effect between PCE and AgNPs. Besides, chitosan/PCE and chitosan/AgNPs/PCE films could change their colors in different pH buffers because of abundant anthocyanins in PCE. Our results suggested chitosan/AgNPs/PCE film could be used as novel active and intelligent food packaging material in food industry.

Partially dehydrated zinc hydroxide sulfate nanoplates reinforced coating for corrosion protection

In this work, partially dehydrated zinc hydroxide sulfate nanoplates are synthesized by facile chemical bath deposition together with subsequent heat dehydration. The nanoplates exhibit well-defined hexagonal plate structure with smooth surface and no visible defects can be observed. Then, the corrosion protection performance of the nanoplates-embedded fluorocarbon coatings was investigated in 3.5 wt% NaCl aqueous solution. It turns out that the well dispersed nanoplates greatly enhance the protection ability of composite coatings. Once electrolyte permeates into the coating matrix and reaches the surfaces of nanoplates, the nanoplates can actively trap water molecules and ions (Cl− and Na+) therein through phase transition behavior, thus inhibiting the diffusion of electrolyte to the interface between coating and substrate. Meanwhile, the concomitant swelling of nanoplates blocks the diffusion of corrosive media, thus further enhancing the protection performance. The multi-functions of this material impart superior passive barrier and active barrier abilities to polymer coating.

Preparation and characterization of active and intelligent packaging films based on cassava starch and anthocyanins from Lycium ruthenicum Murr

Lycium ruthenicum Murr. is a functional food with abundant anthocyanins. Since anthocyanins can change colors under different pH conditions, pH-sensitive packaging films were developed based on cassava starch and L. ruthenicum anthocyanins (LRA). Effect of LRA content on the physical, structural, antioxidant and pH-sensitive properties of starch-LRA films were evaluated. In addition, starch-LRA films were applied to monitor the freshness of pork. Spectroscopic analysis showed LRA contained six kinds of anthocyanins. The incorporation of LRA significantly enhanced the water vapor and ultraviolet-visible light barrier ability, tensile strength and antioxidant potential of starch film. Moreover, the barrier, antioxidant and pH-sensitive properties of starch-LRA films were closely related with LRA content. However, the thermal stability of starch film was not affected by LRA. Fourier transform infrared and X-ray diffraction analyses revealed intermolecular interactions (hydrogen bonds) formed between starch and LRA in the films. Starch-LRA films are pH-sensitive and could change their colors in different buffer solutions (pH 2–13). When applied to monitor the freshness of pork, starch-LRA films exhibited remarkable color variations with the quality change of pork. Our results suggested starch-LRA films could be used as active and intelligent packaging films in food industry.

Co-sputtering Co–Ti alloy as a single barrier/liner for Co interconnects and thermal stability enhancement using TiN metal capping

Scaling of interconnect dimensions is becoming increasingly difficult due to the fast rise in line/via resistance. To alleviate this problem, Co is a high-potential alternative material of Cu or W in metallization schemes. In this work, Co interconnects is imitated, where Co1−xTix is proposed as single barrier/liner to replace conventional thick TiN/Ti bilayer structure, reserving more available space for interconnect metal to achieve overall lower line resistance. The samples with and without Co1−xTix or TiN metal capping were fabricated in attempt to optimize the whole interconnects. Meanwhile, the properties of these films with different stacking structures were comprehensively studied through material analysis instruments. In order to further evaluate the barrier ability of Co1−xTix single layer, the capacitance–voltage (C–V) and current–voltage (I–V) characteristics of MOS capacitors after thermal stress (TS) as well as bias thermal stress (BTS) were analyzed elaborately. Obtained results indicate that Co1−xTix single barrier/line is effective to enhance adhesion property and to restrain Co diffusion into SiO2 dielectric, and TiN metal capping is also indispensable for Co interconnects to improve thermal stability and to prevent Co oxidation.

A pH-sensitive self-healing coating for biodegradable magnesium implants

Self-healing coatings have attracted attention on surface modification of magnesium alloys, as it can recover the barrier ability of the coatings from corrosion attack. Nevertheless, previous works on this aspect are not suitable for biomedical magnesium alloys owing to the lack of biocompatibility. In this study, we fabricated a self-healing coating on biomedical Mg-1Ca alloy by compositing silk fibroin and K3PO4. PO43− ions act as corrosion inhibitor, while K3+ ions help to regulate the secondary structures of silk fibroin. The scratch test, scanning vibrating electrode technique (SVET), and electrochemical impedance spectroscopy (EIS) provide comprehensive results, confirming the pH-sensitive self-healing capacity of the composite coating. Moreover, cells’ (MC3T3-E1) multiple responses including spreading, adhesion, proliferation, and differentiation illustrate the preferable biocompatibility as well as the osteogenic activity of the coating. These primary findings might open new opportunities in the exploration of self-healing coatings on biomedical magnesium alloys. Statement of significanceBiomedical magnesium alloys surface modifications have been studied for years, which however the biomedical self-healing coatings were rarely involved. In this work, silk fibroin and phosphate (K3PO4) were composited to fabricate coating on biomedical magnesium alloys. The coating not only owned the self-healing ability with pH sensitivity, but also endowed the substrate preferable corrosion resistance as well as osteogenic activity. This work gives a new insight into surface modification for biomedical Mg alloys.

Highly smooth, stable and reflective Ag-paper electrode enabled by silver mirror reaction for organic optoelectronics

Cellulose paper can be exploited for future electronics due to its flexibility, versatility, and low cost. However, the rapid fabrication of paper electrodes with a smooth surface and durability remains a challenge. In this paper, we report the fabrication of conductive, smooth and stable Ag electrodes on common printing paper through solution-processed silver mirror reaction. The rough cellulose substrate was modified with polypropylene to form an interconnected two-network structure yielding a super-flat surface and significantly better mechanical performance than paper or plastic. Based on the modified paper, a controllable spin-coating silver mirror reaction process was developed to form a smooth silver coating. The obtained Ag-paper electrode has a surface roughness without big particles over 50 nm and a strong barrier ability against moisture and solvents, while retaining the features of common cellulose paper. The successful solution-processed application of organic solar cells and organic light-emitting diodes based on silver electrode is demonstrated, showing the material’s potential in future flexible electronics.

Golden Exosomes Selectively Target Brain Pathologies in Neurodegenerative and Neurodevelopmental Disorders.

Exosomes, nanovesicles that are secreted by different cell types, enable intercellular communication at local or distant sites. Alhough they have been found to cross the blood brain barrier, their migration and homing abilities within the brain remain unstudied. We have recently developed a method for longitudinal and quantitative in vivo neuroimaging of exosomes based on the superior visualization abilities of classical X-ray computed tomography (CT), combined with gold nanoparticles as labeling agents. Here, we used this technique to track the migration and homing patterns of intranasally administrated exosomes derived from bone marrow mesenchymal stem cells (MSC-exo) in different brain pathologies, including stroke, autism, Parkinson's disease, and Alzheimer's disease. We found that MSC-exo specifically targeted and accumulated in pathologically relevant murine models brains regions up to 96 h post administration, while in healthy controls they showed a diffuse migration pattern and clearance by 24 h. The neuro-inflammatory signal in pathological brains was highly correlated with MSC-exo accumulation, suggesting that the homing mechanism is inflammatory-driven. In addition, MSC-exo were selectively uptaken by neuronal cells, but not glial cells, in the pathological regions. Taken together, these findings can significantly promote the application of exosomes for therapy and targeted drug delivery in various brain pathologies.

A highly resistant structure between the cuticle and the cortex of human hair. II. CARB, a penetration barrier.

We previously reported that a chemically resistant structure is present at the interface between the cuticle and the cortex of human hair. The goal of this study was to identify the position of that structure and to clarify its barrier ability. Untreated, partially and completely decuticled hair fibres were characterized. The correlation between the number of cuticle layers and the penetration depth of a dye into the cortex was microscopically investigated. In addition, similar measurements were performed using hair with a denatured cell membrane complex. The penetration depth of the dye into the cortex showed no statistically significant correlation with the number of cuticle layers in the case of partially decuticled hair fibres (the number of cuticle layers ranged from one to four). Penetration of the dye proceeded drastically just when the last cuticle layer was lost, but denaturation of the cell membrane complex did not affect the depth of penetration. That suggested that the penetration barrier at the interface between the cuticle and the cortex is not the cell membrane complex, but rather is the resistant structure previously reported. It was observed that a thin layer structure is located beneath the endocuticle of the innermost cuticle cell layer, only in the range where the cuticle borders the cortex. It is thought that this is the structure in question. These results demonstrate that a highly resistant structure located at the interface between the cuticle and the cortex of human hair acts as a penetration barrier. We propose that structure be named CARB, cuticle anchored resistant base.

Biodegradable and active nanocomposite pouches reinforced with silver nanoparticles for improved packaging of chicken sausages

Abstract This study reports the development of biodegradable PVA-montmorillonite K10 clay nanocomposite blend films with in situ generated ginger extract mediated silver nanoparticles. Photo-assisted method using sunlight irradiation was adopted for the rapid and eco-friendly in situ generation of ginger extract mediated silver nanoparticles in the composite. FTIR, XRD and SEM analysis were conducted to confirm the generation of AgNPs. The nanocomposite blend film had clear antimicrobial activity against common food borne pathogens S. Typhimurium and S. aureus. It also had superior mechanical properties, water resistivity and light barrier ability compared to control films. Indoor soil burial test revealed the nanocomposite blend would degrade completely within 110 days. The nanocomposite blend film was then fabricated into novel packaging pouches and found to be highly efficient in reducing the microbial burden in chicken sausage samples, compared to control polyethylene pouches, signifying its potentiality in extending the shelf life of chicken meat products.

Aluminum-Magnesium Hydroxycarbonate/Azo Dye Hybrids as Novel Multifunctional Colorants for Elastomer Composites.

This study presents the preparation and characterization of new organic-inorganic pigments based on aluminum-magnesium hydroxycarbonate (LH) and azo dyes. Solvent resistance studies, XRD, SEM, and TGA confirmed the successful formation of hybrid pigments, which were characterized in terms of their physicochemical properties. The new hybrid pigments were applied in acrylonitrile-butadiene (NBR) and ethylene-propylene (EPM) rubber composites and cured with sulfur and peroxide curing systems, respectively. The mechanical properties, dispersion quality, and flame-retardant properties of the NBR/hybrid and EPM/hybrid pigment composites were determined by dynamic mechanical analysis (DMA), SEM, and microscale combustion calorimetry (MCC). Complex experimental investigations revealed that the layered nature of hybrid pigments could improve the barrier ability and flame retardancy of elastomer composites. In comparison to unmodified aluminum-magnesium hydroxycarbonate, the modified LH dye structures contributed to significantly decrease the heat release rate and the total heat release of the NBR and EPM composites, offering a new approach to imparting low flammability to elastomer materials.

Mechanical properties of whey protein concentrate based film improved by the coexistence of nanocrystalline cellulose and transglutaminase

Whey Protein Concentrate (WPC) has been researched as food packaging materials in recent years. However, WPC films own the drawbacks on the barrier ability to water vapor and mechanical properties. In the presented work, Transglutaminase (TGase) and different concentrations of nanocrystalline cellulose (NCC) (0–15% wt. of WPC) were incorporated into the WPC matrix to prepare WPC-NCC composite film, their transmittance, mechanical properties, water vapor permeability and microstructures were investigated and compared with that of WPC films. Results illustrated that NCC as fillers in the protein network blended with WPC markedly improved the mechanical properties. The tensile strength of composite film increased from 1.3 to 3.15 MPa as NCC increased to 15% wt. of WPC. Moreover, TGase took a promoted effect on mechanical properties. The composite film achieved a maximal elongation value of 86.7% when TGase was added at 9 U/g of WPC. SDS-PAGE confirmed that TGase positively facilitated the formation of the protein polymers. FTIR analysis observed conformational changes caused by TGase in the films and implied the interaction between WPC and NCC. Results suggest NCC and TGase have a synergy effect on mechanical properties of WPC based film, and TGase-crosslinked WPC-NCC composite film can be applied as an alternative packaging material.

X-ray photoelectron spectroscopy analysis of the effect of photoresist passivation on InGaZnO thin-film transistors

Bottom-gate InGaZnO (IGZO) thin-film transistors (TFTs) with EOC photoresist (PR) passivation were fabricated. Compared to the unpassivated IGZO TFT with a mobility of 6.71 cm2 V−1 s−1, a hysteresis of 2.42 V and a poor bias stress stability, the PR-passivated IGZO TFT showed good electrical characteristics with a higher mobility of 8.85 cm2 V−1 s−1, a lower hysteresis of 0.06 V and a more reliable stability (△Vth = 0.36 V) under positive gate bias stress (PBS). The effect of PR passivation on the performance of IGZO-TFT was investigated by x-ray photoelectron spectroscopy (XPS), systemically. The result of XPS spectra of the O 1s core levels indicate that PR passivation effectively suppressed the adsorption/desorption effect on IGZO surface, resulting in fewer unstable states and higher electrical stability. Furthermore, XPS depth profile experiments show that the proportion of elements on the film surface changed and the IGZO surface was In-rich after PR passivation, enhancing the mobility. The PR passivation with low temperature (100 °C) process exhibited good dielectric quality and excellent barrier ability against water and oxygen molecules. Therefore, it may be a good candidate for high-mobility and high-stability flexible TFTs in future.

Natural Biomaterial-Based Edible and pH-Sensitive Films Combined with Electrochemical Writing for Intelligent Food Packaging.

An edible and pH-sensitive film combined with electrochemical writing was developed by using gelatin, gellan gum, and red radish anthocyanins extract for intelligent food packaging. The composite film showed an orange red-to-yellow color change in the pH range of 2-12. The tensile strength, ductility, and barrier abilities to ultraviolet (UV) light and oxygen of the films were improved as the concentration of red radish anthocyanins increased. Multicolor patterns were successfully drawn on the films by using the electrochemical writing method. The composite films, which acted as gas sensors, presented visible color changes in the presence of milk and fish spoilage, while the written patterns were well-preserved. Accordingly, this composite film with written patterns could be an easy-to-use indicator with great potential for monitoring food spoilage as a part of an intelligent packaging system.

TiO2 nanorod arrays on the conductive mica combine photoelectrochemical cathodic protection with barrier properties

Oriented rutile TiO2 nanorod arrays (TiO2 NRA) were elaborately grown on the conductive mica (C-mica) with Sb-SnO2 seed crystal by a hydrothermal strategy to achieve TiO2 NRA/C-mica composites. The as-obtained samples were characterized by X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy and photo-electrochemical measurements. Compared with TiO2 NP/mica, TiO2 NRA/C-mica coated film exhibits more excellent physical barrier ability in the dark, and an enhanced photo-induced current density as well as a more negative photo-potential shift in the light, indicating remarkable photo-cathodic protection for 304 stainless steel (304SS). The distinctive 1D-2D architecture of TiO2 NRA/C-mica facilitates the transmission and separation of photo-induced electron-hole pairs. Furthermore, it's the first time that the TiO2 NRA/C-mica hybrid film is found to possess continuous and stable cathodic protection for the 304SS over a long period in the dark.

Synergistic effect of hydrophobic film and porous MAO membrane containing alkynol inhibitor for enhanced corrosion resistance of magnesium alloy

Magnesium and magnesium alloys have important applications in aviation, electronic devices, medical equipment, and automotive industries, while the corrosion is a common and real problem that must be solved for these applications. In this paper, a novel and effective anti-corrosive composite coating on AZ31 Mg alloys was prepared by the combination of micro-arc oxidation (MAO) layer, corrosion inhibitor and hydrophobic wax film technologies. And among these, the MAO treated micro- and nanopores as the container of corrosion inhibitor and the solid hydrophobic wax as the multifunctional sealing isolating agent. The morphology and phase composition of the resulting composite coatings were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively, indicating the successful synthesis of the organic-inorganic composite coating. The potentiodynamic polarization and electrochemical impedance spectroscopy measurements showed that compared with the MAO membrane covered Mg alloys, the organic-inorganic composite coating has superior corrosion resistance with the a lower corrosion current (5.764 × 10−9 A/cm2) and a higher protection efficiency (99.7%) after immersion in 3.5 wt% NaCl solution, attributing to the synergistic effect of effective inhibition of inhibitor and the physical barrier ability of hydrophobic film and MAO membrane. This simple and low cost strategy to fabricate organic-inorganic composite anticorrosion coatings would have promising applications in the corrosion protection of the light metals and their alloys.