Nc Materials Research Articles

Y/Co-MWCNT nanocomposite conjugated Nafion modified glassy carbon electrode for sensitive detection of thiourea chemical by electrochemical approach

In this approach, we develop noble electrochemical sensor probe using binary Yttrium oxide/Cobalt oxide nanomaterials conjugated with functionalized-multiwalled carbon nanotube (f-MWCNT) for the sensing of Thiourea (TU; Thiocarbamide 2-Thiourea; CH4N2S). Y2O3/Co3O4 functionalized MWCNT nanocomposites have been prepared using direct solid state chemical technique and characterized using various techniques. Additionally, powder XRD, UV/vis., SEM, BET, and FTIR were used to assess the crystallinity, band-gap energy, surface morphology, surface area, and functional properties of the synthesized Y/Co-MWCNT NC materials respectively. The electrochemical activity of the proposed sensor was further assessed through electrochemical EIS, LSV, and CV. The glassy carbon electrode (GCE) was constructed using the prepared Y/Co-MWCNT NCs by incorporating 5% Nafion to fabricate the electrode for the examination of electrochemical sensor analyses and performances in the phosphate buffer solution (PBS). The modified electrode was successfully detected TU in PBS at a pH of 6.5, showcasing remarkable electrocatalytic activity. The recommended sensor probe (Y/Co-MWCNT NCs/GCE) demonstrated linearity within a concentration range of 7.0 × 10–10 − 3.1 × 10−9 molL−1, a detection limit of 2.8 × 10−8 mmolL−1 and sensitivity of 5.85 × 10−3 µAmM-1cm-2. The selectivity of the newly prepared probe for thiourea detection was also evaluated in the presence of various chemicals and interfering agents. The spiked real water samples demonstrated an impressive recovery value when employing the proposed method. A new route is introduced utilizing binary metal oxides intercalated functionalized MWCNTs nanocomposites through reliable electrochemical approaches, aimed at enhancing safety in ecological and environmental domains on an extensive measure.

The non-carbonaceous nature of Earth’s late-stage accretion

Constraining the origin of Earth’s building blocks requires knowledge of the chemical and isotopic characteristics of the source region(s) where these materials accreted. The siderophile elements Mo and Ru are well suited to investigating the mass-independent nucleosynthetic (i.e., “genetic”) signatures of material that contributed to the latter stages of Earth’s formation. Studies contrasting the Mo and Ru isotopic compositions of the bulk silicate Earth (BSE) to genetic signatures of meteorites, however, have reported conflicting estimates of the proportions of the non-carbonaceous type or NC (presumptive inner Solar System origin) and carbonaceous chondrite type or CC (presumptive outer Solar System origin) materials delivered to Earth during late-stage accretion (likely including the Moon-forming event and onwards). The present study reports new mass-independent isotopic data for Mo, which are presumed to reflect the composition of the BSE. A comparison of the new estimate for the BSE composition with new data for a select suite of NC iron meteorites is used to constrain the genetic characteristics of materials accreted to Earth during late-stage accretion. Results indicate that the final 10 to 20 wt% of Earth’s accretion was dominated by NC materials that were likely sourced from the inner Solar System, although the addition of minor proportions of CC materials, as has been suggested to occur during accretion of the final 0.5 to 1 wt% of Earth’s mass, remains possible. If this interpretation is correct, it brings estimates of the genetic signatures of Mo and Ru during the final 10 to 20 wt% of Earth accretion into concordance.

Guanine biomolecule derived nitrogen-doped carbon for efficient oxidative dehydrogenation performance

Biomolecule self-assembly shows great potential in the preparation of ordered functional materials. Here, we prepare a gauzy NC material via water guiding guanine biomolecule self-assemble, which exhibits the better ethylbenzene conversion (∼50%), styrene selectivity (∼91%) and long-term stability (>40 h) in ODH of ethylbenzene to styrene than that of guanine solid self-assembly produced NC (38% conversion vs. 88% selectivity) sample. The study shows that water not only facilitates guanine biomolecule self-assembly to form more stable octamer structure but restrains vertical growth of guanine, and resultant NC-1000-12 h holds high density active sites and outstanding oxidation resistance, thus enhancing NC catalytic performance. Overall, current work provides a new understanding on preparation of highly efficient NC materials through supramolecular self-assembly strategy.

Detecting Visible to Near-Infrared II Light via CsPbBr3 Nanocrystals/Y6 Heterojunctions.

In the endeavor to develop advanced photodetectors (PDs) with superior performance, all-inorganic perovskites, recognized for their outstanding photoelectric properties, have emerged as highly promising materials. Due to their unique electronic structure and band characteristics, the majority of all-inorganic perovskite materials are not sensitive to near-infrared (NIR) light. Here, we demonstrate the fabrication of a high-performance broadband PD comprising CsPbBr3 perovskite NCs/Y6 planar heterojunctions. The incorporation of Y6 not only facilitates charge transfer from CsPbBr3 NCs to Y6 for enhancing photodetection performance under visible illumination but also broadens the absorption spectrum range of the whole device toward the NIR regime. As a result, the heterojunction PD exhibits a photo-to-dark-current ratio above 105, a dynamic range of 149.5 dB, and an impressive lowest detection limit of incident power density of 1.6 nW/cm2 under 505 nm illumination. In the NIR regime, where photon energy is below the bandgap of CsPbBr3, electron-hole pairs can still be produced in the Y6 layer even when illuminated at 1120 nm. Consequently, photodetection is uniquely possible in PDs that incorporate heterojunctions when the illumination wavelength is longer than 565 nm. At 850 nm, the heterojunction device is capable of detecting light with power densities as low as 1.3 μW/cm2 corresponding to a LDR of 99.8 dB. The exceptional performance is attributed to the creation of a heterojunction between CsPbBr3 NCs and Y6. These findings propose a novel approach for developing broadband PDs based on perovskite NC materials.

Efficient synthesis of glycerol carbonate by doping metallic copper in palladium-catalyzed glycerol system for carbonylation reaction

The synergistic effect between copper and palladium promotes electron transport by using ZIF-8-derived Cu–NC materials to support palladium nanoparticles, which plays a crucial role in the ringing of glycerol carbonate.

Hierarchically structured electrode materials derived from metal-organic framework/vertical graphene composite for high-performance flexible asymmetric supercapacitors

Low conductivity of metal-organic frameworks limits their applications in electrochemical energy storage and conversion. To overcome this shortcoming, we synthesized the zeolitic imidazolate framework-67 on the vertical graphene (VG) surface with abundant defects grown on carbon cloth (ZIF-67-VG-CC). Based on “one-for-two” strategy, the Co3O4 nanoparticles (Co3O4-VG-CC) and nanoporous carbon (NC-VG-CC) can be derived from ZIF-67-VG-CC via selective pyrolysis in the controlled atmospheres. In the hierarchically structured Co3O4-VG-CC and NC-VG-CC, the Co3O4 nanoparticles with a size of 20 nm and N-doped porous carbons were uniformly dispersed on the VG surface, as confirmed by electron microscopies. Both the Co3O4-VG-CC and NC-VG-CC yield high specific capacitance and excellent rate capability. After assembling these two electrodes to make an asymmetric supercapacitor, the Co3O4-VG-CC//NC-VG-CC delivered a maximum energy density of 43.75 Wh/kg at a power density of 5.2 kW/kg as well as excellent cycling stability with 91.5 % specific capacitance retained after 20,000 charge-discharge cycles. All these results should be ascribed to that the VG sheets possess their high electrical conductivity and 3D network structure, and provide the hierarchical supports for the uniform distribution of the ZIF-67-dervied Co3O4 nanoparticles and NC materials, which are beneficial to the fast electron and ion transfer in the electrodes.

Transition Metal−N/Graphene for advanced Lithium–Sulfur Batteries: A first principles study

Developing highly efficient anchoring materials with strong adsorption to lithium polysulfides to suppress ‘shuttling effect’ is crucial to address the short cycling life issue of lithium sulfur batteries. Herein, we systematically investigated transition metal, nitrogen co-doped graphene as host materials for sulfur cathode via first-principles study. The computation results reveal that TM2–NC materials have higher adsorption energy to lithium polysulfides than TM–NC materials. Fe2–NC is one of the most promising anchoring materials, where robust Fe–S and N–Li bonds ensure the stable adsorption of all LiPSs.

Nanocomposites made from thermoplastic linear poly(urethane-siloxane) and organoclay: Composition impact on the properties

Thermoplastic poly(urethane-siloxane)/organoclay nanocomposites (TPU NCs) with different hard segment content (20?55 wt. %) were prepared by in situ polymerization in the presence of organically modified montmorillonite as a nanofiller (Cloisite 30B; 1 wt. %). Hydroxyl-terminated ethoxypropyl- poly(dimethylsiloxane) was used as soft segment, while 4,4'-methylenediphenyl diisocyanate and 1,4-butanediol were the hard segment components. The study of the influence of the hard segment content on the functional properties of TPU NCs was performed by Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), water contact angle and water absorption tests. The results revealed that TPU NCs with the increasing hard segment content exhibit higher values of degree of microphase separation, melting temperature of the hard segments, degree of crystallinity, storage modulus (except for TPU NC-55), but lower thermal stability and hydrophobicity. TPU NC films were hydrophobic and their free surface energy was in the range from 17.7 to 24.9 mJ m-2. This work highlights how the composition of TPU NCs would affect their functional properties and provide an additional composition intended for designing advanced TPU NC materials for special biomedical applications.

An Electrochemical Sensor Based on a Nitrogen-Doped Carbon Material and PEI Composites for Sensitive Detection of 4-Nitrophenol.

A glassy carbon electrode (GCE) was modified with nitrogen-doped carbon materials (NC) and polyethyleneimine (PEI) composites to design an electrochemical sensor for detecting 4-nitrophenol (4-NP). The NC materials were prepared by a simple and economical method through the condensation and carbonization of formamide. The NC materials were dispersed in a polyethyleneimine (PEI) solution easily. Due to the excellent properties of NC and PEI as well as their synergistic effect, the electrochemical reduction of the 4-NP on the surface of the NC–PEI composite modified electrode was effectively enhanced. Under the optimized conditions, at 0.06–10 μM and 10–100 μM concentration ranges, the NC–PEI/GCE sensor shows a linear response to 4-NP, and the detection limit is 0.01 μM (the signal-to-noise ratio is three). The reliability of the sensor for the detection of 4-NP in environmental water samples was successfully evaluated. In addition, the sensor has many advantages, including simple preparation, fast response, high sensitivity and good repeatability. It may be helpful for potential applications in detecting other targets.

High‐Sensitivity Tunable Bloch Surface Waves’ Biosensor Using Nanocomposite Cap Layer

The advantage of the high versatility of the nanocomposite (Nc) materials in modeling photonic structure devices is exploited to design an optical biosensor based on Bloch surface waves (BSWs) to probe different biomolecular species. The suggested biosensor is constituted by two periods of low and high refractive indices (RIs) of alternate dielectric materials SiO2 and TiO2 capped by Ag−TiO2 Nc layer operating under the Kretschmann configuration and using p‐polarized incident light. Herein, the biosensor performances are theoretically investigated in a wide range of the sensing medium RI [1.33, 1.61] using selected operating wavelengths 455, 465, 480, 500, and 600 nm to deviate a large dielectric loss of the Ag−TiO2 Nc layer. The results show that the structure sustains BSW for each wavelength in separate domains of the sensing medium RI conferring to the proposed biosensor a potential for the high‐sensitive multiwavelength detection of different biomolecular entities.

Synergy Photodegradation of Basic Dyes by ZnO/Bi2O3 Nanocomposites under Visible Light Irradiation

Environmental problems caused by organic pollutants can be resolved by semiconductor photocatalysts. Using the strategies of doping hydrothermally, Zinc oxide/Bismuth oxide nanocomposites (ZnO/Bi2O3 NCs) comprising of different proportions of BiO for the applications of basic dyes and were tested for antibacterial activity. The average crystallite sizes of these, metal oxide nanocomposites were ranging from 12 nm to 29 nm. UV-Visible diffuse reflectance spectra were used to determine the optical energy bandgap (Eg) of about 2 to 2.82 eV of the NCs for different proportions of the metal oxides. Square-like morphology of ZnO NPs and ZnO/Bi2O3 NCs were observed in the Scanning Electron Microscopy (SEM). This morphological structure along with its high surface area attributes to the promotion of degrading organic pollutants in dyeing wastewater along with decolorization. The Photoluminescence (PL) emission intensity of ZnO/Bi2O3 NCs suggests a lower recombination rate of photogenerated charge carriers leading to enhanced photocatalytic activity. Visible light-driven photodegradation of MB, MG, and R6G by 0.5M ZnO: 0.5M Bi2O3 resulted in high rate constants of 8.5×10-3/min, 6×10-3/min, and 9×10-3/min. The hybrid ZnO/Bi2O3 NC materials showed immense antibacterial activity against gram-positive bacterium S. aureus and the gram-negative bacterium E. coli with an inhibition zone of 6mm and 5mm respectively which was comparable to the standard, chloramphenicol. A desired predominant gram-positive bacterial inhibition unwraps a new way for enhanced antibacterial agents. The heterojunction at the interface between Bi2O3 and ZnO could efficiently reduce the recombination of photoinduced electron-hole pairs and thereby enhancing the photocatalytic and antibacterial activity of ZnO/Bi2O3 heterostructures. This study reveals that ZnO/Bi2O3 NCs as a promising candidate for the photocatalytic and antibacterial treatment of dye effluent.

Grain size dependent microstructure and texture evolution during dynamic deformation of nanocrystalline face-centered cubic materials

Evolution of microstructure and texture in nanocrystalline (nc) face-centered cubic materials subjected to high-strain-rate compression are investigated. Three nc materials, differing in grain size or stacking fault energy, namely, 27 nm Ni, 70 nm Ni, and a 27 nm NiCo alloy are deformed under high strain rates (8000–23000 s−1) using the split-Hopkinson pressure bar technique. The transmission Kikuchi diffraction technique and discrete-crystal plasticity finite element (D-CPFE) simulations are used to evaluate structural evolution. Experimental results show that grain growth and grain refinement occurred in samples with small and large initial grain sizes, respectively, while all deformed materials evolve to a (110) texture. The D-CPFE simulations, built for grain-size dependent nc deformation with no fitting parameters, reveal that partial dislocation slip caused faster texture evolution than full dislocation slip. Comparison between experimental and simulation results suggests that the (110) texture is mainly generated by combined full and partial dislocation slip in the 27 nm and 70 nm Ni samples, and by partial dislocation slip alone in the NiCo alloy. Deformation twinning made almost no contributions to the observed texture evolution. Grain-boundary-mediated deformation facilitates grain coarsening, while partial dislocation activities help to promote dynamic stabilization and further refinement of the nano-grains. The highly coupled evolution of microstructure and texture during dynamic deformation is controlled by a synergy of grain size and strain rate effects.

Biomass waste-derived porous carbon efficient for simultaneous removal of chlortetracycline and hexavalent chromium

SummaryThe simultaneous removal of mixed containments of antibiotics and heavy metals is still a big challenge in wastewater treatment. Herein, we report the successful synthesis of N-doped porous carbon (abbreviated as NC) from straw waste through the Maillard reaction to activate sp3-sp2 conversion efficient for the simultaneous removal of chlortetracycline (CTC) and hexavalent chromium (Cr(VI)). In 200 min, 96.9% of Cr(VI) was reduced into Cr(III) and 93.1% of CTC was oxidatively degraded. Reactive substances (e.g., h+, e−1, ⋅OH, and ⋅O2-) were verified for the photocatalytic reactions. Besides, the possible degradation intermediates of CTC were analyzed with ultra performance liquid chromatography-mass spectrometry (UPLC-MS/MS), and the mechanism of photocatalytic degradation of CTC was then proposed. The synthesized bifunctional NC materials could also be applied for the similar system; this will open the door for promising practical applications.

Ultrastrong nanocrystalline binary alloys discovered via high-throughput screening of the CoCr system

Nanocrystalline (nc) alloys are stronger than their coarse-grained versions. Here, we report ultrastrong alloys, discovered via high-throughput screening of the nc CoCr33-69 materials library. The nc materials library was fabricated using magnetron co-sputtering. The alloys consist of textured, columnar structures with grain size in the nanometric regime. We found that the texture and phase composition can be tailored by changing the Cr concentration. In the investigated region of the nc CoCr system, a relatively broad spectrum of yield strength, determined via micropillar compression tests, was found ranging from 1.41 GPa up to 3.64 GPa. The remarkable strength increment was caused by a chemically- and thermally-driven phase and microstructure evolution of the system. The strongest alloys were found in the regions containing the δCoCr phase, which was considered previously as metastable. Density functional calculations revealed that the δCoCr phase is more energetically favourable in Cr-rich regions compared to single-phase simple solid solutions (HCP, BCC). Experimental results showed that the range of its occurrence is wider than previously thought, i.e. after annealing the δCoCr phase was found above 44 at. % of Cr. We demonstrate that systematic screening of materials libraries can boost the discovery of new materials with outstanding properties.

Chromium Isotopic Evidence for Mixing of NC and CC Reservoirs in Polymict Ureilites: Implications for Dynamical Models of the Early Solar System.

Nucleosynthetic isotope anomalies show that the first few million years of solar system history were characterized by two distinct cosmochemical reservoirs, CC (carbonaceous chondrites and related differentiated meteorites) and NC (the terrestrial planets and all other groups of chondrites and differentiated meteorites), widely interpreted to correspond to the outer and inner solar system, respectively. At some point, however, bulk CC and NC materials became mixed, and several dynamical models offer explanations for how and when this occurred. We use xenoliths of CC materials in polymict ureilite (NC) breccias to test the applicability of such models. Polymict ureilites represent regolith on ureilitic asteroids but contain carbonaceous chondrite-like xenoliths. We present the first 54Cr isotope data for such clasts, which, combined with oxygen and hydrogen isotopes, show that they are unique CC materials that became mixed with NC materials in these breccias. It has been suggested that such xenoliths were implanted into ureilites by outer solar system bodies migrating into the inner solar system during the gaseous disk phase ~3-5 Myr after CAI, as in the "Grand Tack" model. However, combined textural, petrologic, and spectroscopic observations suggest that they were added to ureilitic regolith at ~50-60 Myr after CAI, along with ordinary, enstatite, and Rumuruti-type chondrites, as a result of breakup of multiple parent bodies in the asteroid belt at this time. This is consistent with models for an early instability of the giant planets. The C-type asteroids from which the xenoliths were derived were already present in inner solar system orbits.

In-situ pyrolysis of Taihu blue algae biomass as appealing porous carbon adsorbent for CO2 capture: Role of the intrinsic N

An environment-friendly, cost-effective, and facile N self-doping porous carbon (NC) were prepared through in-situ pyrolysis of nitrogen abundant Taihu blue algae biomass for CO2 uptake. It was found that the CO2 sorption capacity of porous carbon prepared through carbonization at 800 °C with KOH activation (N-C-800) exhibit higher CO2 uptake capacity of 4.88 (1 bar and 0 °C) and 2.76 mmol/g (1 bar and 25 °C) respectively, with the CO2/N2 selectivity of N-C-800 attaining 39.3. Besides, the adsorption capacity of N-C-800 remained stable even after 7 repeated cycles, with a slight loss of nearly 6%. Moreover, total graphitic N (Ntg) sources from the intrinsic N in N-C-800 is not only higher than other agro-sourced porous carbon materials, but the graphitic N performed a sound correlation with the CO2 uptake capacity. Combining experiments with Density Functional Theory (DFT) calculations, higher adsorption energy of N-C-800 (−13.6 kJ/mol, comparing with −6.9 kJ/mol of N-free carbon framework) would render the efficient adsorption of CO2 molecular onto the graphitic N site. The current study not only provides a new option for the reclamation of Taihu blue algae biomass as N self-doping material, but a proof-of-concept investigation employing NC materials as an appealing candidate for CO2 capture.

Effect of ZnO/Ag Nanocomposites Against Anionic and Cationic Dyes as Photocatalysts and Antibacterial Agents

Engineering efficient, strong and cost-effective nanoparticles with strong inhibitory activities are the growing need at present. Using the strategies of doping, Zinc oxide/Silver nanocomposites (ZnO/Ag NCs) namely 0.9 M ZnO: 0.1 M Ag, 0.7 M ZnO: 0.3 M Ag and 0.5 M ZnO: 0.5 M Ag were synthesized hydrothermally. The average crystallite sizes for the ZnO/Ag NCs were 31 nm, 29 nm and 23 nm. The band gap energy (Eg) for the ZnO/Ag NCs was estimated to be 3.09 eV, 3.12 eV and 3.18 eV using Tauc’s plot. Grain-like morphological images was observed in the Scanning Electron Microscopy (SEM), which helps in effective promotion of degrading methyl orange (MO), methylene blue (MB) and crystal violet (CV) under visible light irradiation with a rate constant of 5 × 10–3/min, 16.6 × 10–3/min and 4 × 10–3/min respectively. This superior photocatalytic decomposition of dye are ascribed to smaller particle size, high surface area, the ability to absorb visible light and the efficient charge separation associated with the synergetic effects of appropriate amounts of ZnO and Ag in the prepared samples. In addition, the antibacterial efficacy of the NCs is observed as 90 and 100% for 75 μl. These hydrothermally synthesized synergistic NCs can be designed for large-scale fabrication of NC materials for potential applications in photocatalytic and antibacterial activity.

Review of thermo‐kinetic correlation during grain growth in nanocrystalline materials

AbstractNanocrystalline (NC) materials exhibit many unique properties over their coarse‐grained counterparts due to the high grain boundary density and the small grain size, but they are too difficult to be used in engineering environment because of the poor thermal stability. With regard of this, two strategies are previously proposed to enhance the thermal stability (or impede the grain growth) of NC materials, that is, the thermodynamic and the kinetic approaches. Recent investigations increasingly support that the two approaches may be physically interacted and acted on each other, and they can be treated together within a unified thermo‐kinetic framework. This paper reviews the progress in the investigation of thermo‐kinetic correlation during grain growth in NC materials. First, the theoretical models to describe the concept of the thermo‐kinetic correlation and the grain growth equations developed based on the thermo‐kinetic correlation are reviewed. Second, experimental and simulated evidences to support the coexistence of thermodynamic and kinetic effects are summarized. Third, the potential application of thermo‐kinetic correlation is analyzed and discussed. This paper shows that the stabilization of NC materials can be tailored by the selection of the suitable strategies. Finally, several directions that require further exploration are identified.

Multilayering process of electrodeposited nanocrystalline iron–nickel alloys for further strengthening

Effect of multilayering on the tensile property in nanocrystalline (nc) iron–nickel (Fe–Ni) alloys was studied to obtain a clue to further strengthening of nc materials. Multilayering electrodeposition process of nc Fe–Ni alloys with different Ni contents was investigated using an electrolyte which mainly composed of nickel sulfamate and iron chloride. The Ni content in the obtained nc Fe–Ni alloys increased with increasing current density of the electrodeposition. The multilayered structure with 3–11 layers composed of nc Fe–34 mass% Ni alloy (Invar alloy) and nc Fe–46 mass% Ni alloy (non-Invar alloy) were obtained alternatively applying two different current densities at predetermined time intervals. The average thickness of individual Invar alloy layer in the multilayered specimens with 3–11 layers was changed from 19.2 to 6.0 μm. The tensile strength in the multilayered nc Fe–Ni alloy specimens was increased ranging from 1.47 to 2.24 GPa with decreasing thickness of Invar alloy layers and increasing number of multilayer interface. The possible mechanism of the strengthening in the multilayered nc Fe–Ni alloy specimens was discussed based on the results of the hardness–distance profile near the interface between the Invar alloy and non–Invar alloy layers.

Creep and Superplasticity: Evolution and Rationalization

Detailed studies on the creep behavior of materials are of scientific and practical significance. From a scientific point of view, data obtained from such studies are critical to the characterization of creep behavior in terms of deformation mechanisms. From a practical point of view, information inferred from such studies is useful because of its relevance to many design considerations. Over the past several decades, much progress has been made in rationalizing the creep behavior of metals and solid‐solution alloys. Such progress is extended to understanding the creep behavior of new classes of materials such as powder metallurgy (PM) Al alloys, discontinuous SiC composites, superplastic alloys, and high‐entropy alloys (HEAs). Progress in micrograin superplasticity (1 μm < d < 10 μm, where d is the grain size) has been applied to the emergence of high strain rate (HSR) superplasticity using ultrafine‐grained alloys (0.3 μm < d < 1 μm). The concept of creep is utilized to develop a deformation mechanism for nanocrystalline (nc) materials (d < 100 nm). Using the details of this mechanism, it is possible (1) to explain why the behavior of nc material is not superplastic and 2) to predict a transition from superplastic behavior to nc behavior.