Graphitic Shells Research Articles

Two Birds with One Stone: Broadband Electromagnetic Wave Absorption and Anticorrosion Performance in 2-18GHz for Prussian Blue Analog Derivatives Aimed for Practical Applications.

Nowadays, the exploration of electromagnetic (EM) wave absorbers with anticorrosion to improve the survivability and environmental adaptability of military targets in the harsh environments is becoming an attractive and unavoidable challenge. Herein, through modulation of the metal composition in the precursors, the core@shell structure Prussian blue analog-derived NiCo@C, CoFe@C, NiFe@C, and NiCoFe@C are obtained with excellent EM wave absorption performance. As for NiCoFe@C, ascribed to the coupling effect of the dual magnetic alloy, a minimum reflection loss (RL) of -47.6dB and an effective absorption bandwidthof 5.83GHz are realized, which cover the whole Ku-band. Meanwhile, four absorbers display the lower corrosion current density (10-4 -10-6 A cm-2 ) and larger polarization resistance (104 -106 Ω) under acid, neutral, and alkaline corrosion conditions over uninterrupted 30 days. Furthermore, due to the spatial barrier effect and the passivation effect of the graphitic carbon shell , the continuous salt spray test has little effect on RL performance and inconspicuously changes the surface morphologies of coating, demonstrating its excellent bifunctional performance. This work lays the foundation for the development of metal-organic frameworks-derived materials with both anticorrosion and EM wave absorption performance.

Magnetic carbon nanocomposites via the graphitization of glucose and their induction heating

Carbon nanocomposites containing iron-based nanoparticles are attractive materials for the catalyst supports used for magnetic (induction) heating catalysis. The metallic, soft-magnetic iron nanoparticles provide local heating of the support in an alternating magnetic field and ensure rapid magnetic separation of the nanocomposite particles from reaction suspensions. In this work, magnetic carbon nanocomposites were prepared by annealing the precursor particles consisting of iron-oxide nanoparticles dispersed in a carbohydrate matrix. The annealing was conducted at 600 °C and 750 °C in an Ar atmosphere. At both temperatures the carbothermal reduction of iron oxide to Fe/Fe3C was observed; however, at the lower temperature the rate of reduction and the growth of the nanoparticles were considerably slower. The Fe3C was formed in negligible amounts only after a prolonged period of annealing at 600 °C. A detailed structural analysis showed that the Fe/Fe3C nanoparticles catalyze the graphitization of the carbonaceous precursor material already at 600 °C, resulting in the formation of a graphitic shell that surrounds them. This shell is tight enough to prevent the areal oxidation of the encapsulated Fe nanoparticles; their magnetic properties remained unchanged even after 1 year of storage under ambient conditions. At the higher annealing temperature, the growth of the Fe/Fe3C nanoparticles caused bursting of the graphitic shell and thus partially exposed their surfaces to the atmosphere. All the nanocomposites exhibited ferromagnetic behavior in accordance with their compositions. The nanocomposite that was predominantly composed of a graphitic shell, encapsulated Fe nanoparticles and a negligible amount of Fe3C, showed the highest specific absorption rate (760 W/gFe at 274 kHz), even at a relatively low AC-field amplitude (88 mT).

Core-shell Fe/Fe3C heterostructure@carbon layers anchored on N-doped porous carbon for boosting oxygen reduction reaction

It is still challenging but crucial to plumb non-noble metal-based oxygen reduction reaction (ORR) catalysts with comparable or better performance than benchmark Pt/C catalysts. Herein, we proffer an unconventional core-shell-structured iron-based heterostructure electrocatalyst constructed by a Fe/Fe3C heterostructure nanoparticle core wrapped by a graphitic shell embedded on a conductive N-doped mesoporous graphite skeleton (Fe/Fe3C@NC) via facile pyrolysis of MIL-53(Fe) (MIL = Matérial Institute Lavoisier) and melamine. The Fe/Fe3C@NC catalyst delivers more positive half-wave potential (E1/2) of 0.86 V and a low Tafel slope of 56 mV dec−1 for ORR, outpacing the benchmark Pt/C catalyst, and it also shows remarkable long-term durability and excellent methanol tolerance. The marvelous ORR behaviors can be attributed to its distinctive morphologic structure: the heterostructure can enhance intrinsic ORR activity; the core-shell nanostructure can enhance ORR activities through unique electron transfer between iron species and their conductive carbon shells, which can also act as protective barriers to ensure long-term stability; the high-content pyridinic-N doping can be used as additional active centers; and the abundant mesopores facilitate the diffusion of electrolyte, which can further upgrade ORR activities. This study proffers a strategy to design and fabricate non-noble catalysts with well-designed nanoarchitecture and high catalytic activity.

Structural and magnetic properties of carbon-encapsulated Fe/Fe3C nanoparticles

Carbon-encapsulated iron-cementite (Fe/Fe3C) magnetic nanoparticles were synthesized by an up-scalable solid-state pyrolysis method using iron phthalocyanine as a precursor. The dependence of the structure, morphology and magnetic properties on the pyrolysis conditions is presented. The nanocomposite contains nanoparticles made of cementite with a small fraction of iron, with an average diameter of 15 nm embedded in an amorphous carbon matrix.A 3 nm thick graphite shell is formed on the surface of the particles. The volume fraction of α-Fe increases almost linearly on increasing pyrolysis temperature: from 0.5% for the sample synthesized at 800 °C up to 11% for a 900 °C pyrolysis temperature, resulting in an increase of the saturation magnetization from 14.0 to 17.74 Am2/kg and a decrease of the coercivity from 49.34 to 10.74 kA/m.

Upcycled synthesis and extraction of carbon‐encapsulated iron carbide nanoparticles for gap Plasmon applications in perovskite solar cells

AbstractAn effective method for obtaining large amounts of metal nanoparticles (NPs) encapsulated by carbon layers through upcycling from floating‐catalyst aerosol chemical vapor‐deposited carbon nanotubes is demonstrated. NPs with diameters of less than 20 μm are selectively extracted from the synthesized carbon assortments through sonication, centrifugation, and filtration. The particles show an aggregation behavior owing to the π–π interaction between the graphitic carbon shells surrounding the iron carbides. By controlling the degree of the aggregation and arrangement, the light scattering by the gap‐surface plasmon effect in perovskite solar cells is maximized. Application of the NPs to the devices increased the power conversion efficiency from 19.71% to 21.15%. The short‐circuit current density (JSC) trend over the particle aggregation time accounts for the plasmonic effect. The devices show high stability analogue to the control devices, confirming that no metal‐ion migration took place thanks to the encapsulation.image

Lubrication and anti-wear behavior of duplex annealed nanodiamonds/PEO coating on Ti6Al4V: Functional mechanism of structural transformation

Titanium alloys have been widely used due to its low density, high strength and excellent corrosion resistance, but the poor tribological properties restrict its engineering application. Nanodiamond particles provide excellent lubrication and high wear resistance due to the unique physical-chemical properties, but the mismatched mechanical properties severely restrict the solid lubrication application of nanodiamond for titanium alloys. In this study, plasma electrolytic oxidation coatings were firstly prepared on Ti6Al4V substrates, and core-shell annealed nanodiamond particles obtained by high-temperature annealing at 1300 °C with nanodiamond core and graphitic outer shell were deposited on the PEO coatings. The plasma electrolytic oxidation-annealed nanodiamond coatings led to a 46.67 % and 96.13 % reduction of coefficient of friction and wear volume comparing to plasma electrolytic oxidation coatings. Annealed nanodiamond with unique core-shell structure can reduce the abrasion of friction pairs; and the friction-induced structural transformation of annealed nanodiamond particles in the top-layer tribofilm further enhanced the lubrication and wear-resistance. The proposed lubrication mechanism has implications for the development of novel nanomaterials with core-shell structure and duplex coating systems for engineering applications.

Synthesis of metal phosphides encapsulated within defect carbon: A sulfur-tolerant and acid-resistant catalyst for selective hydrogenation

A universal strategy to synthesize metal phosphides (MPs, M = Ni, Co, Cu, Fe, Pd, Pt, Ru) nanoparticles encapsulated in 2D defect-rich graphitic carbon shell (MPs@C-PPS) using P- and C-rich polymeric phosphide (PPS) as the precursor was brought out. Characterization results demonstrate that the thickness of the carbon shell on different MPs nanoparticles ranges from 1 to 7 nm, which can be adjusted by changing the Ni/P molar ratio. Some cracks and irregular defects are observed in carbon layers, which can selectively permeate small hydrogen molecules and block the passage of larger organic molecules. In catalytic performance test, the as-synthesized Ni2P@C-PPS exhibited excellent selectivity in alkynes semihydrogenation and high anti-sulfur poisoning and anti-acid corrosion capability in hydrogenation reactions. Mechanism exploration indicates that selective permeability of the carbon shell is the key to improving catalyst robustness.

Synthesis of Graphite-Encapsulated Ni Micro- and Nanoparticles Using Liquid-Phase Arc Discharge

In this work, the synthesis of nickel particles encapsulated in a few-layer graphene shell was carried out using the method of electric arc discharge in the liquid phase, in various media: deionized water, alcohol, and toluene. Nickel and graphite were used as electrodes. The study was carried out to analyze how various liquids, acting as a cooling medium and a source of carbon, affect the formation of a protective shell around metal particles. Raman studies, analysis of X-ray diffraction data, and scanning electron microscopy confirmed the formation of spherical encapsulated nickel particles in all types of liquid media. It was found out that the use of toluene as a cooling medium increased the number of particles with a graphite shell and allowed obtaining micro- and nanoparticles covered with monolayer graphene. The absence of oxygen in the composition of toluene, in contrast with alcohol and especially water, prevents the oxidation of nickel particles during the synthesis. This fact, along with the initial basic hexagonal carbon structure of toluene, makes it a good medium for the formation of metal particles covered with a protecting graphite shell as a result of arc discharge in the liquid phase.

Development and characterization of AA6063 matrix composite reinforced with B4C, graphite and groundnut shell powder

In due course of time, the role of natural reinforcement for Aluminium matrix composites (AMCs) composite manufacture has gained the interest of many researchers. It is cost-effective and at the same time environmentally friendly as it helps in the use of certain disposable or pollution creating substances. The manufacturing of various automotive parts, biomedical, and aerospace parts can be done by using these naturally occurring fibers or particulates. An effort has been made to study the effect of such industrial waste on the Aluminium metal matrix composite and evaluate it in terms of characterization. A comparison has also been made with solid lubricant reinforcement and compares wear for both types of composite. The focus of this study is on the characterization of the AA 6063 reinforced hybrid composite with desired material produced using stir casting. The AA 6063 is fabricated with the composition of B4C + Graphite (Gr.) and B4C + Groundnut Shell Powder (GSA) composition. The hybrid composite constituting hybrid composite of two types has been formed i.e. Al6063 + 6 %B4C + 4 %Gr and Al6063 + 6 %B4C + 3 %GSA. FeSEM images revealed the homogenous composition of the reinforcement particles. A tribological study revealed the average wear rate of 67.14 µm for Al6063 + 6 %B4C + 3 %GSA and 60.02 µm Al6063 + 6 %B4C + 4 %Gr. Microscopic images of the worn samples of composite reveal that both show good wear resistance, more for Gr. reinforced composite followed by SBA, the reason being the self-lubricating property of the Gr. reinforced hybrid composite. Thus as a result it can be cost-effective to find certain automotive applications where strength to weight ratio is a key factor to look at.

Microstructure of onion-like carbon fabricated in vacuum by annealing ND

The relationship between annealing temperature, holding time and the structure of Onion-like carbon (OLC) in a certain atmosphere was the key to the industrial preparation of OLC. OLCs with various structures were fabricated in a vacuum by annealing detonation nanodiamond (ND) in the conditions of 900–1600 °C/0–2 h/30 °C·min −1 /1.0 × 10 −1 Pa. XRD, Raman, HRTEM, TG-DSC, and FTIR were used to characterize the composition, bond types, microstructure, thermal stability and surface adsorption properties of OLCs. It had been shown that increasing the annealing temperature or extending the holding time increases the graphite content and the average grain size of OLCs and decreases the average ND core size of OLCs. The annealing temperature determined whether the ND core was present in the OLC, and the holding time allowed the OLC to reach the stable phase. When the annealing temperature was less than 1400 °C, the OLC mostly existed in spherical and elliptic structures and had an ND core inside. The ND core in the OLC cannot vanish even if the holding time was extended. When the temperature exceeds 1400 °C, OLC mostly existed in ellipse and polygon structures and did not have an ND core inside. OLC without ND core had higher oxidation resistance and lower adsorption capacity due to the integrity of its concentric graphite shell structure. This work provided a feasible method for batch preparation of OLC with a controllable structure. • Batch preparation of OLC with controllable structure. • The direct relationship between the annealing parameters and the grain size, shell number, interlayer space, residual diamond core size and graphite content of OLC was investigated systematically and detailedly. • The mechanism and trade-off of annealing parameters effects on the microstructure and composition of OLC were revealed.

Carbon defects promoting syngas into liquid fuels over Fe3C@C catalysts

A Fe3C@C catalyst with defect-rich graphite shell exhibits C5+selectivity of 70.1% and CH4selectivity of 9.0%.

Structure and Raman Spectra of Exotic Carbon Microcrystals from Meteoritic Dust of Chelyabinsk Superbolide.

The Chelyabinsk superbolide, the largest in XXI century, which exploded on 15 February 2013 over snowy fields of Southern Urals was a historic event not just only because of its massive scale and explosive power. High-temperature, high-pressure conditions in the front shock wave caused intense ablation of the asteroid material and formation of huge amount of meteoritic dust dispersed in the atmosphere during the flyby. Massive snowfalls just few days before and after the event conserved precipitated meteoritic dust in thin layer of snow which was collected and studied later. The most intriguing and challenging material discovered in the dust was closed-shell 10-70 µm exotic polygonal graphitic carbon microcrystals of undisclosed nature. Using optical and electron microscopy and Raman spectroscopy the atomic structure of closed-shell microcrystals was thoroughly studied and their graphitic nature was revealed. It was found that some of the particles formed by multilayer graphitic polygonal shells have extensive hollows inside. Comparative microscopic and spectroscopic analysis of meteorite exotic carbon microcrystals with different graphite species, carbon onions, and diamond revealed two distinctively different closed-shell carbon particles. The first type of the particles can be attributed to carbon onions with characteristic graphite nanocrystalline basic structural units (BSU) of 49 nm lateral size and less and, probably, BSU heteroatomic termination necklace with oxygen content comparable to 1.1% and more. It was shown that the second type of unique graphitic carbon particles of a convex shape and perfect hexagonal symmetry with lateral dimensions of 14 µm correspond to multiply twinned closed-shell graphite microcrystals with polyhexacyclooctadecane (-C18-)n core wrapped by multiple layers of carbon honeycombs with low (<1%) content of oxygen termination necklace.

Magnetic coupling in cm-scale buckypapers of self-organized Fe/Fe3C-filled carbon nano-onions: A controlled chemical vapour deposition approach

We report the selective nucleation and growth of cm-scale thin buckypaper-films of carbon nano-onions (CNOs) filled with nanocrystalline Fe 3 C and α-Fe ferromagnetic phases. The presented result was achieved by sublimation and pyrolysis of 20 to 100 mg of ferrocene in an Ar flow of 10 ml/min under conditions of low-carbon-supply pyrolysis. The high reproducibility of the presented method opens-up new directions for industrial applications of these nanomaterials. We highlight the observation of an unusual D-band splitting, indicative of a defect-induced structural transition within the graphitic shells of the CNOs. The morphological and structural properties of the buckypapers were investigated by employing scanning and transmission electron microscopy (SEM, TEM, HRTEM) together with X-ray diffraction (XRD). The magnetic properties were investigated by employing electron paramagnetic resonance (T-EPR) at T ~ 300 K, 200 K, 150 K, 100 K and 77 K in the field range from 0 to 500 mT. We highlight the presence of broad π-electron signals, with significant shift of the g-factor parameter as the temperature was decreased from T ~ 300 K to ~77 K. A possible coupling between the iron-based nanocrystal phases was found at T ~ 300 K, at g-factor ~ 20.

Arc-integration of graphite-coated plasmonic satellite-magnetic core nanoassembly: Efficient tailoring of nanostructure/functionality for catalysis of pollutants

Most magnetoplasmonic nanoassemblies with tunable geometries are commonly fabricated by the wet assembly approach, which is greatly restricted by the high complexity and severe conditions. This study applied a facile one-step arc discharge to fabricate graphite-encapsulated magnetic core-gold satellite (FeAu@G) nanoassembly with tailorable morphologies (35.5–58.8 nm of magnetic cores with 4.91- 0.335 nm of shells, and 4.63–9.01 nm of Au satellites with 1–4 graphite layers of shells) and tunable surface functionalization (hydrophobization, amination). The specific formation processes of graphite shells (i.e., dissolution-reprecipitation-graphitization for shells over magnetic cores, deposition-graphitization for shells over Au satellites) is essential to generate this unique nanoassembly. An storage-dependent consuming time for the removal of Cr(VI) by aminated FeAu@G presented an excellent negative linearity with [Au wt.%]/[Au satellite diameter]3. The reusability of aminated FeAu@G could be significantly aroused by the radio-frequency plasma treatment with an enhancement of 198–894 %. Hydrophobic FeAu@G could converse nitroaromatics recycled with an excellent negative linearity of catalytic activity values to the diameter of Au satellites. This work unlocks a versatile platform to design and produce magnetoplasmonic nanoassemblies with ideal complex nanostructures and surface functionality.

Confined high-entropy-alloy nanoparticles within graphitic shells for synergistically improved photothermal conversion

High-entropy-alloy nanoparticles (HEA-NPs) have exhibited great potential in solar steam generation, in which their photothermal conversion performances can be optimized through the interband transition (IBTs) between the composing elements. In this work, the HEA-NPs were in-situ confined in the multi-layer graphitic shells (HEA@CNPs) by the arc-discharged plasma approach to achieve a synergistic improvement in the solar steam generation performances. It can be recognized that the graphitic shells not only serve as optical absorbers but also improve the surface temperature ascribed to their low thermal conductivities. The numerical simulation reveals that the electric fields can be accumulated in the graphitic shells over the wavelength regions of 1000 to 2500 nm. As a result, the most optimized FeCoNiTiVCrMnCu@C nanocapsules demonstrated an evaporation rate of 2.66 kg m−2h−1 under one sun irradiation with an energy conversion efficiency of 98%, and the surface temperature can increase to ∼105 °C within 90 s, demonstrating an effective solar steam generation performance. The present study indicates an insight into the synergistic optical absorption behaviors between HEA-NPs and graphitic shells, and the nanocapsules could be expanded to other solar-thermal conversion applications.

Ru-optimized geometric sites of cations in CoFe/CoFe2O4 electrocatalysts with graphitic carbon shells for boosting water oxidation

Rational fabrication of an electrocatalyst with excellent stability, conductivity, and activity is urgently demanded for oxygen evolution reaction (OER). In this work, Ru-regulated hierarchical CoFe/CoFe2O4 nanoparticles with graphitic carbon shells were successfully fabricated via self-assembling and vapor reduction strategies. Our investigation uncovers high concentrations of octahedral Co3+ sites in electrocatalysts can be triumphantly acquired via moderate Ru doping, which could give rise to excellent electrocatalytic activities during OER. In addition, the design of CoFe alloys and graphitic carbon shells can compensate for the weak conductivity of cobalt ferrites. Based on the intrinsic stability, improved conductivity and activity, the as-prepared electrocatalyst yields a low overpotential of 237 mV at 10 mA cm−2 and a small Tafel slope of 47 mV dec−1 in 1.0 M KOH electrolyte, exhibiting outstanding electrocatalytic activities for OER.

Role of Hydrogen Flow Rate for the Growth of Quality Nanodiamonds via Microplasma Technique

Nanodiamonds (NDs) were prepared by utilizing a microplasma facility. Ethanol and Argon mixture was decomposed in microplasma for the formation of NDs. In order to stabilize the NDs growth, the Hydrogen was added in the mixture during the growth process. Hydrogen flow rate was changed from 1 to 5 L/min to find out the optimum flow rate for the growth of stabilized NDs. The experiments were also performed without the introduction of Hydrogen for the comparison. TEM and Raman analysis confirm that the highest quality diamonds are obtained at Hydrogen flow rate of 3L/min. In the case of Hydrogen, the SAED patterns reveal the presence of pure diamond phases which in turn envisages the etching of graphitic shell. TEM micrographs reveal that the size of NDs produced at 3 L/min Hydrogen flow rate ranges from 1~20 nm which is much smaller than that of without Hydrogen (4-32 nm). EDX spectra also disclose the Carbon peak with a maximum intensity for 3 L/min flow rate. UV-Visible and PL spectroscopy analysis indicate the presence of Nitrogen-Hydrogen defect centers. However, a decrease in defect density at 3L/min indicates the production of improved quality NDs. FTIR also verifies the removal of graphitic shell around NDs at 3 L/min flow rate. Moreover, high hydrogen flow rates effectively incorporate nitrogen vacancy (NV) defects. Prepared NDs offer emerging applications in optoelectronic systems, biomedical nanodevices and nanoscale sensors for electric field, magnetic field & temperature.

In Situ Upregulating Heat Shock Protein 70 via Gastric Nano-Heaters for the Interference of Helicobacter pylori Infection.

Taking inspiration from the mechanism of Helicobacter pylori infection can lead to innovative antibacterial ways to fight antibiotics resistance. Herein, a gastric nano-heater iron-cobalt alloy shielded with graphitic shells (FeCo@G) is developed to interfere with H. pylori infection under an alternating magnetic field. FeCo@G shows a high and stable specific loss power (SLP = 534.1 W g-1) in the acidic environment and provides efficient magnetothermal stimulation in the stomach. Such stimulation upregulates the cytoprotective heat shock protein 70 (HSP70) in gastric epithelial cells, which antagonizes the infection of H. pylori. This finding is further supported by the transcriptomic analysis verifying the upregulation of HSP70 in the stomach. Moreover, the nano-heater shows a high inhibition rate of H. pylori in vivo with good biocompatibility; 95% of FeCo@G is excreted from the mouse's gastrointestinal tract within 12 h. In summary, FeCo@G allows magnetothermal therapy to be used in harsh gastric environments, providing an approach for the therapy against H. pylori.

Lignin-derived hierarchical porous flower-like carbon nanosheets decorated with biomass carbon quantum dots for efficient oxygen reduction

Excavating and developing efficient and economical non-metallic nanomaterial catalysts for oxygen reduction reactions (ORR), which are vital for fuel cells, but is still challenging. Here, we synthesize a nitrogen-doped hierarchical porous flower-like carbon nanosheets decorated with nitrogen-doped carbon quantum dots. The hierarchically porosity heteroatom-doped flower-like carbon nanosheets are first synthesized using MgO as hard template, KOH/NaOH as activator, lignin/urea as carbon/heteroatom source, and then lignin-based carbon quantum dots (CQDs) fabricated via microwave hydrothermal are compounded with carbon nanosheets after a one-step hydrothermal treatment. Benefitting from the interconnection of its 3D graphite shell network, abundant active sites, high specific surface area, and multi-scale pore structure, the n-HPFN@CQDs exhibits favorable ORR activity and stability in 0.1 mol KOH media. Compared with commercial Pt/C, the assembled Zn-air batteries using n-HPFN@CQDs as electrode catalysts exhibit comparable discharge performance. This work synthesized a novel and green biomass-based carbon composite materials achieving high-performance for energy conversion applications.

Core-shell sp3@sp2 nanocarbon for adsorption of anionic and cationic organic dyes: Effect of the graphitization of nanocarbon

Developing suitable and efficient adsorbents to remove organic dyes from wastewater become a hot topic. Herein, core-shell sp3@sp2 nanocarbons (ND-700, ND-900, ND-1100 and ND-1300), consisting of diamond core and graphitic shell with variable sp2/sp3-carbon ratio, were prepared by annealing nanodiamonds (NDs) at various temperatures (700–1300 °C). The increased graphitization degree of the nanocarbons with the increase of annealing temperature was confirmed by X-ray diffraction (XRD) and high-resolution Transmission Electron Microscopy (HRTEM). Sequentially, these nanocarbons were utilized as solid adsorbents to remove anionic methylene orange (MO) and cationic methylene blue (MB). Results show that although all of the nanocarbons are positively charged, the nanocarbons with higher graphitization (ND-1100, ND-1300) exhibit higher adsorption performance for both MB and MO. This can be attributed to the forming of π-π interaction between the graphitic surface and aromatic rings within the dye molecules. The ND-700 exhibits little adsorption for cationic MB for its low graphitization as well as electrostatic repulsion. The adsorption of MO and MB on ND-700 and ND-1300 in the binary MO/MB system was also investigated, respectively. Results show that the ND-1300 could adsorb MO and MB efficiently and simultaneously, and ND-700 exhibits selective adsorption for MO from the binary system.