Cr2O3 Nanoparticles Research Articles

New catalysts with dual-functionality for cyclohexane selective oxidation

M-Co-TUD-1; a series of the new materials was prepared by applying one-step synthesis procedure based on sol-gel technique. The prepared materials contain 1wt% of cobalt ions and 5wt% of metal oxide (metal = Cr, Cu, Ti, Mn, Bi, V, or Sr) in the TUD-1 mesoporous material. The prepared materials were characterized by using XRD, DRS UV–vis, N2 sorption measurements, ICP elemental analysis, SEM, and HR-TEM. Characterization results showed that all the prepared materials contain isolated Co2+ ions and nanoparticles of Cr2O3, TiO2, MnO, V2O5 or bulky crystals of Bi2O3 and CuO incorporated in the silica matrix. The catalytic performance of the prepared materials was evaluated in liquid phase, free-solvent selective oxidation of cyclohexane to cyclohexanone and cyclohexanol by using TBHP as an oxidant at 70 °C. The prepared materials exhibited higher activity than either Co-TUD-1 or other M-TUD-1. More importantly, a very small concentration of the intermediate; cyclohexyl hydroperoxide (CHHP) was detected. In case of stability, Mn-Co-TUD-1 and Ti-Co-TUD-1 exhibited an excellent stability during the reaction. Moreover, Mn-Co-TUD-1 was successfully recycled up to 4 runs.

Cr2O3 nanoparticles: A promising candidate to improve the mechanical properties and corrosion resistance of Ni-Co alloy coatings

This study was aimed to assess the effects of reinforcement nanoparticles content, on the microstructural features, mechanical properties, and corrosion-related properties of Ni-Co-Cr2O3 nanocomposite coatings. Scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) analysis were employed in order to evaluate the microstructural features and chemical composition of the nanocomposites. Moreover, the microhardness tester and electrochemical impedance spectra (EIS) tests coupled with potentiodynamic polarization measurements were used to investigate the mechanical and corrosion-related properties, respectively. Results demonstrate that albeit the volume fraction of cobalt in coating, average particle size, Cr2O3 nanoparticle content in coating, and microstructural features are of prime significance in determining the mentioned properties of the nanocomposite coatings, Co content is more important. Actually, Cr2O3 nanoparticles serve as suitable nucleation sites for Co particles deposition throughout the microstructure. Thus, combined actions of Cr2O3 nanoparticles incorporation and their optimal content ensures the nucleation of high population of Co particles, which significantly contributes to the improvement in the properties. The Ni-Co-8.9wt%Cr2O3 nanocomposite coating exhibits the superior mechanical and corrosion-related properties.

Electrodeposition and Characterization of Ni–W–Cr2O3 Nanocomposite Coating

In this paper, compact Ni–W and Ni–W–Cr2O3 nanocomposite coatings were deposited on mild steel substrates by DC electrodeposition method. The surface morphology, elemental composition, and structure of the obtained coatings were investigated by scanning electron microscopy, energy dispersive spectrometer, and x-ray diffraction. The corrosion resistance was evaluated by potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy. It is shown that incorporation of Cr2O3 nanoparticles into amorphous Ni–W coating would transform its structure into crystalline and influence its properties. The microhardness of Ni–W–Cr2O3 nanocomposite coatings (717–764 HV0.1) is significantly bigger than that of Ni–W coating (687 HV0.1). In addition, with increase of Cr2O3 addition in the electroplating bath, a tendency of improvement in hardness and corrosion resistance performance is observed. Finally, an excellent Ni–W–Cr2O3 nanocomposite coating with a slightly lower resistance and much higher hardness compared with Ni–W coating is electrodeposited in the bath containing 20 g/L Cr2O3 nanoparticles.

Scanning transmission X-ray microscopy studies of chromium hydroxide hollow spheres and nanoparticles formed by gamma radiation

Amorphous chromium-containing solid nanoparticles and hollow spheres were formed as the intermediate product during the synthesis of Cr2O3 by gamma radiolysis of dichromate solution. Scanning transmission X-ray microscopy (STXM) is applied to investigate the electronic structure and chemical composition of this intermediate product (solid nanoparticles and hollow spheres). The STXM result obtained at O K-edge and Cr L3,2-edge confirms that chromium in the sample exists as Cr3+ and that the solid nanoparticles and hollow spheres are both Cr(OH)3. Combined with other techniques, a mechanism for gamma radiation induced formation of Cr2O3 nanoparticles via Cr(OH)3 intermediates from dissolved dichromate is proposed.

Non-noble, efficient catalyst of unsupported \u03b1-Cr2O3 nanoparticles for low temperature CO Oxidation

Herein, we report the synthesis of chromium oxide nanoparticles, α -Cr2O3 NPs, followed by full characterization via XRD, SEM, XPS, and N2 sorptiometry. The synthesized nanoparticles were tested as catalysts toward the oxidation of CO. The impact of calcination temperature on the catalytic activity was also investigated. CO conversion (%), light-off temperature, T50, data were determined. The results revealed that chromia obtained at low calcination temperature (400 °C) is more active than those obtained at high calcination temperatures (600° or 800 °C) and this is ascribed to the smaller particle size and higher surface area of this sample. The results revealed a superior catalytic activity of Cr2O3 NPs at lower temperature as we reached a complete conversion at 200 °C which is high value in the forefront of the published results of other non-noble catalysts. The high activity of Cr2O3 nanoparticles (T50 as low as 98 °C) where found to be dependent on a careful selection of the calcination temperature. These results may provide effective and economic solutions to overcome one of the major environmental threats.

Modeling of Interactions between the Zebrafish Hatching Enzyme ZHE1 and A Series of Metal Oxide Nanoparticles: Nano-QSAR and Causal Analysis of Inactivation Mechanisms.

The quantitative relationships between the activity of zebrafish ZHE1 enzyme and a series of experimental and physicochemical features of 24 metal oxide nanoparticles were revealed. Vital characteristics of the nanoparticles’ structure were reflected using both experimental and theoretical descriptors. The developed quantitative structure–activity relationship model for nanoparticles (nano-QSAR) was capable of predicting the enzyme inactivation based on four descriptors: the hydrodynamic radius, mass density, the Wigner–Seitz radius, and the covalent index. The nano-QSAR model was calculated using the non-linear regression tree M5P algorithm. The developed model is characterized by high robustness R2bagging = 0.90 and external predictivity Q2EXT = 0.93. This model is in agreement with modern theories of aquatic toxicity. Dissolution and size-dependent characteristics are among the key driving forces for enzyme inactivation. It was proven that ZnO, CuO, Cr2O3, and NiO nanoparticles demonstrated strong inhibitory effects because of their solubility. The proposed approach could be used as a non-experimental alternative to animal testing. Additionally, methods of causal discovery were applied to shed light on the mechanisms and modes of action.

A WO3 nanorod-Cr2O3 nanoparticle composite for selective gas sensing of 2-butanone

The hexagonal (h)-WO3-Cr2O3 nanocomposites with different W/Cr molar ratio of 4:1, 10:1 and 40:1 were prepared by a facile two-step hydrothermal method, and its gas sensing properties were investigated under optimum working temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) were used to characterize the morphology, microstructure and crystallinity of the as-synthesized samples. The hexagonal WO3 nanorods show a better crystallinity than Cr2O3 nanoparticles. When the molar ratio of W/Cr is 10:1, the hexagonal WO3-Cr2O3 nanocomposite shows obvious selectivity toward 2-butanone at 205°C compared with other typical reducing gases, and the response value to 100ppm 2-butanone can reach 5.6. However, there is no selectivity toward 2-butanone when the Cr/W molar ratio is 1:4 and 1:40. Furthermore, hexagonal WO3-Cr2O3 nanocomposites have a short response and recovery time to 5ppm 2-butanone, which is 10s and 80s, respectively. The measured results indicate that hexagonal WO3-Cr2O3 nanocomposite is a potential gas sensing material for monitoring volatile organic compounds (VOCs).

A micro‐Raman spectroscopic study of Cr(OH)3 and Cr2O3 nanoparticles obtained by the hydrothermal method

Cr2O3 nanoparticles, widely used in the industry, can be obtained by calcination of the nanoparticles synthesized via the hydrothermal method. The chemical nature and the morphology of as‐prepared and calcined nanoparticles are investigated by scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. Our results indicate that the as‐prepared nanoparticles mainly consist of amorphous and hydrated Cr(OH)3, with only minor amounts of Cr2O3. By contrast, and as already known before, calcined nanoparticles consist of Cr2O3. We also demonstrate the effect of inappropriately chosen experimental conditions, because the use of laser intensities above 0.7 mW during the Raman experiments causes a local heating and thus induces the transformation of Cr(OH)3 into Cr2O3. The correlation between the laser power and a local heating is further corroborated by thermogravimetric analyses, which show that upon increased temperature, Cr(OH)3 first dehydrates and then partially condensates to the intermediate CrO(OH) form, to finally attain the crystalline form of Cr2O3 at about 409 °C. Copyright © 2017 John Wiley & Sons, Ltd.

Bacterial community and molecular ecological network in response to Cr2O3 nanoparticles in activated sludge system

The potential environmental risks of chromium oxide nanoparticles (Cr2O3 NPs) have caused great concerns. However, their possible impacts on activated sludge process are very limited. In this study, we carried out long-term exposure experiments to evaluate the influence of Cr2O3 NPs on wastewater nutrient removal, bacterial community and molecular ecological network (MEN) in the sequencing batch reactor (SBR). It was found that 1 mg/L Cr2O3 NPs increased the effluent concentrations of NO3−-N and TP from 6.5 to 15.4 mg/L, and 0.6–2.7 mg/L, indicating the serious deterioration of denitrification and phosphorus removal. Cr2O3 NPs significantly decreased the bacterial richness in terms of the number of different OTUs (626 OTUs in Cr2O3 samples and 728 OTUs in controls). Detrended correspondence analysis (DCA) showed that the overall taxonomic structure of bacterial community was altered at Cr2O3 NPs in activated sludge systems. Further analysis revealed that three genera related to denitrification (Desulfovibrio, Pseudomonas and Hyphomicrobium) and two genera related to phosphorus removal (Accumulibacter and Rhodobacter) decreased significantly, which was consistent with the observed influences of Cr2O3 NPs on denitrification and phosphorus removal. MEN analysis showed that the overall architecture of the network under Cr2O3 NPs was substantially alerted. β-Proteobacteria, playing an important role in nutrients removal, had less complex interactions in the presence of Cr2O3 NPs, which may be associated with the deterioration of denitrification and phosphorus removal. This study provides insights into our understanding of shifts in the bacteria community and their MEN under Cr2O3 NPs in activated sludge systems.

Investigation of Annealing Temperature on Structural and Morphological Properties of Cr2O3 Nanoparticles for Humidity Sensor Application

Cr2O3 nanoparticles have been prepared for precipitation technique at reaction temperature 50 °C. The prepared samples were annealed different temperatures at 500,700 and 1000 °C. Synthesized powders were characterized as X-ray diffraction, optical, transmission electron microscope, SEM with EDAX, humidity sensor, FTIR. The annealing temperature has been found to be playing a crucial role in the controlling particle size. XRD study shows the rhombohedral crystal structure of highly preferential orientation along (1 0 4) direction. FTIR reveals that the presence Cr–O bonds in the structure. The TEM images show that the size of NPs of Cr2O3 varied from 26 to 60 nm with average crystalline size 43 nm. UV–visible spectrum shows the absorption band of Cr2O3 nanoparticles at 400 nm. The humidity sensor of the Cr2O3 nanoparticles was studied by two temperature method. 1000 °C annealed Cr2O3 nanoparticles show better sensing properties and exhibits good linearity in response than 500 °C. SEM images show the clusters and agglomeration of nanoparticles. EDAX spectrum confirms the presence of Cr2O3 nanoparticles. Each samples have been characterized as sensing materials to determine relative humidity in the range of 20–90%. The humidity sensing property increased with increasing of annealing temperature and the resistance was decreased.

Improvement in different properties of the permalloy by nano-Cr2O3 incorporation

This paper deals with the study of improvement in different properties of the Ni–Fe alloy matrix by incorporation of Cr2O3 nanoparticles. Ni–Fe/Cr2O3 nanocomposite coatings were electrodeposited from ethylene glycol bath at several current densities using nickel sulfamate and ferrous sulfate. The coatings were characterized by powder X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy, and atomic force microscopy. Although a change in the surface morphology from fine granular to coarse granular was observed on the incorporation of Cr2O3 nanoparticles, surface roughness of the composite coatings was found lower than the alloy at the optimum current density. At lower current density, preferred orientation of the coating was found along (111) plane while at higher current densities it was along (200) plane. An improvement in the microhardness of the Ni–Fe alloy was recorded (>900 HV) after the nano-Cr2O3 incorporation. Despite incorporation of ceramic particles above 5 wt%, lower electrical resistivity and higher corrosion resistance of the alloy matrix were retained in the nanocomposite coatings. The deposits have shown soft magnetic characteristics.

Enhancement of gas sensing properties by the functionalization of ZnO-branched SnO2 nanowires with Cr2O3 nanoparticles

Complex metal oxides such as functionalized branched nanowires (NWs) are a new category of nanocomposites with unique properties for gas sensing applications. In the present work, we studied the gas sensing properties of Cr2O3-functionalized ZnO-branched SnO2 NWs, inspired by their high surface area and numerous resistive points. These NWs were studied and compared with pristine SnO2 NWs and ZnO-branched SnO2 NWs. To prepare the functionalized NWs, ZnO-branched SnO2 NWs were sputter-coated with a Cr layer and then annealed at 500°C to produce isolated Cr2O3 NPs on the ZnO branches. Results of X-ray diffraction, scanning electron microscopy, and lattice-resolved transmission electron microscopy collectively showed that Cr2O3-functionalized ZnO-branched SnO2 NWs were successfully formed. Cr2O3 functionalization was found to greatly improve the sensors’ response to NO2 gas. Furthermore, the sensors’ good selectivity was demonstrated by testing them in the presence of various interfering gases. The underlying gas sensing mechanisms are discussed herein in detail. We believe that the Cr2O3-functionalized ZnO-branched SnO2 NWs reported herein are promising sensors for the highly sensitive and selective detection of NO2 gas.

Synthesis, FTIR Studies and Optical Properties of Aluminium Doped Chromium Oxide Nanoparticles by Microwave Irradiation at Different Concentrations

In this exposure, pure and aluminium (Al)doped chromium (III) oxide (Cr2O3) nanoparticles are synthesized by simple solvothermal microwave irradiation (SMI) technique. SMI technique is simple and low cost; it has the future to be produced on a huge scale. The effect of dopant (Al) concentration on the structural behavior of Cr2O3 nanoparticles was examined by X-ray diffraction. The average crystallite size of the synthesized nanoparticles was measured from XRD patterns using Scherrer equation and was decreased from 14.56 nm 10.86 nm with the increasing Al concentration in Cr2O3 from 0 to 5% (in steps of 0, 1, 2, 3, 5). Morphologies and compositional elements of the synthesized nanoparticles were observed by the field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) spectroscopy, respectively. The optical property of the samples was measured by ultraviolet - visible (UV-Vis.) absorption spectroscopy. The observed optical band gap value ranges from 2.12 eV to 1.90 eV for Al doped nanoparticles and was red shifted in comparison with that of the pure Cr2O3 (3.483 eV).

Evaluation of the spectroscopic ellipsometry and dielectric properties of Cr2O3 nanoparticles doped PVDF thin films for future application of organic ferroelectric junctions

Here, we report the synthesis of Cr2O3 nanoparticles via ethylene glycol assisted microwave approach. Thin films of Cr2O3 nanoparticles doped Poly(vinylidene fluoride) (PVDF), at a variety concentrations (0.01–0.09wt%), were prepared by spin-coating technique on quartz substrate with thickness of 200nm. The influence of the concentrations of Cr2O3 nanoparticles on the structural, morphological, optical and dielectric properties of the PVDF is examined. The optical properties of the Cr2O3/PVDF thin films were examined by the ellipsometry and fitted by Forouhi–Bloomer model. The doping of PVDF by 0.05wt% of Cr2O3 nanoparticles showed an enhancement of the index of refraction compared to the neat PVDF. A remarkable enhancement of the dielectric constant was achieved when the PVDF film doped with 0.05wt% of Cr2O3 nanoparticles with 35 orders of magnitude compared to the neat PVDF film, owing to the Maxwell–Wagner–Sillars polarization effect. This results in an enhancement of the ferroelectric properties of the PVDF by increasing its remnant polarization from 8.7μC/cm2 to 12.1μC/cm2. These superior properties may enable the developed Cr2O3/PVDF films to be a potential candidate in the field of organic ferroelectric random access memory junctions.

The impact of trivalent oxide nanoparticles on the microstructure and performance of magnesite-dolomite refractory bricks

In this research, the impact of trivalent oxide nanoparticles on the microstructure and performance of the magnesite-dolomite refractory bricks was examined. Up to 4 wt% Fe2O3, Al2O3, and Cr2O3 nanoparticles were added to the specimens as additives. Physical and mechanical properties such as bulk density (BD), apparent porosity (AP), hydration resistance (HR), and cold crushing strength (CCS) were examined. XRD and SEM analysis were used to detect the ceramic phase's formation and microstructure analysis, respectively. Results show that the use of Fe2O3, Al2O3, and Cr2O3 nanoparticles improve the physical and mechanical properties of the MgO-CaO materials. Also, it revealed that specimens contain Fe2O3 and Al2O3 nanoparticles improve hydration resistance through the liquid phase sintering mechanism by formation some low melting phases such as C2F(2CaO·Fe2O3), C3A(3CaO·Al2O3), and C12.A7(12CaO·7Al2O3). However the specimens contain Cr2O3 nanoparticles improve the hydration resistance through the solid state sintering mechanism by formation phases such as CaCr2O4 and MgCr2O4. In general, hydration resistance improvement trend of the MgO-CaO specimens includes trivalent nanoparticles is Al2O3<Fe2O3< Cr2O3.

Synthesis of Co(II) and Cr(III) salicylidenic Schiff base complexes derived from thiourea as precursors for nano-sized Co3O4 and Cr2O3 and their catalytic, antibacterial properties

This study focuses on the synthesis of Co(II) and Cr(III) Schiff base complexes obtained from thiourea. The complexes were synthesized by template method and characterized by elemental analysis (CHNS), FT-IR, UV–vis spectroscopy, conductivity measurement and magnetic moment. The spectroscopic studies suggested the octahedral and square-pyramidal structures for Co(II) and Cr(III) complexes, respectively. Then the complexes were used as precursors for preparation of Co3O4 and Cr2O3 nanoparticles via solid-state thermal decomposition without using a catalyst, toxic solvent, template or surfactant and complicated equipment, which makes it efficient, one-step, simple and environment-friendly. The chemical structure of the metal oxides is studied by FT-IR, XRD and SEM. To investigate the applications of the synthesized complexes, in the next step, the complexes were screened for antibacterial activity against clinically important bacteria such as Escherichia coli, Staphylococcus aureus, and Bacillus subtilis. The Cr(III) and Co(II) complexes showed good biological activity against all the tested bacteria. Also, the catalytic activities of the complexes were studied in toluene using non-toxic hydrogen peroxide as the oxidant. The results showed that Co(II) complex has catalytic activity for oxidation of toluene, but Cr(III) complex did not show any catalytic activity.

SYNTHESIS, CHARACTERIZATION AND ANTIBACTERIAL ACTIVITIES OF CHROMIUM OXIDE NANOPARTICLES AGAINST KLEBSIELLA PNEUMONIAE

Objective: This paper consists of synthesis of chromium oxide (Cr2O3) nanoparticles by sol-gel technique, their characterization and investigation of antibacterial activity of these nanoparticles against pathogenic bacteria by measuring zone of inhibition, colony forming units and optical density on solid agar media as well as in liquid medium.Method: The Cr2O3 nanoparticles were synthesized by sol-gel technique using TEOS as precursor. The synthesized chromium oxide nanoparticles were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, UV-Visible spectroscopy and transmission electron microscopy (TEM) techniques. The antibacterial effect of these chromium oxide nanoparticles against Klebsiella pneumoniae was investigated both on the solid agar plates and in liquid medium supplemented with different concentrations of Cr2O3 nanoparticles. The antibacterial activity of chromium oxide nanoparticles was also compared with the antibacterial activities of the standard antibiotics such as ampicillin, chloramphenicol, penicillin G, streptomycin, sulphatriad and tetracycline which were taken in the form of hexa discs.Results: Average particle size of the Cr2O3 nanoparticles was found to be 24.0 nm. It was observed that Klebsiella pneumoniae is resistant to the penicillin G and ampicillin but Cr2O3 nanoparticles shows good antibacterial property. The minimum inhibitory concentration (MIC) of Cr2O3 for Klebsiella pneumoniae is 2.5 mg/ml. The bacterial growth was monitored by measuring zone of Inhibition, colony formation unit (CFU) and optical density (OD) method.Conclusion: Sol-gel technique is a convenient and easy technique for the synthesis of metal nanoparticles. Nanosized Cr2O3 particles showed an effective antibacterial activity against Klebsiella pneumoniae. Therefore, chromium oxide nanoparticles due to its low manufacturing cost and high effectiveness in antimicrobial properties may find wide applications in various industries to address safety issues.

Cr2O3 nanoparticle-functionalized WO3 nanorods for ethanol gas sensors

Pristine WO3 nanorods and Cr2O3-functionalized WO3 nanorods were synthesized by the thermal evaporation of WO3 powder in an oxidizing atmosphere, followed by spin-coating of the nanowires with Cr2O3 nanoparticles and thermal annealing in an oxidizing atmosphere. Scanning electron microscopy was used to examine the morphological features and X-ray diffraction was used to study the crystallinity and phase formation of the synthesized nanorods. Gas sensing tests were performed at different temperatures in the presence of test gases (ethanol, acetone, CO, benzene and toluene). The Cr2O3-functionalized WO3 nanorods sensor showed a stronger response to these gases relative to the pristine WO3 nanorod sensor. In particular, the response of the Cr2O3-functionalized WO3 nanorods sensor to 200ppm ethanol gas was 5.58, which is approximately 4.4 times higher that of the pristine WO3 nanorods sensor. Furthermore, the Cr2O3-functionalized WO3 nanorods sensor had a shorter response and recovery time. The pristine WO3 nanorods had no selectivity toward ethanol gas, whereas the Cr2O3-functionalized WO3 nanorods sensor showed good selectivity toward ethanol. The gas sensing mechanism of the Cr2O3-functionalized WO3 nanorods sensor toward ethanol is discussed in detail.

Doped poly(m-phenylenediamine) (PmPDA): A new precursor for Cr2O3 nanoparticles

Poly(m-phenylene diamine) has been synthesized and characterized by physical and spectral techniques. The effect of doping Cr, Co and Ni ions on the spectral, thermal and optical properties has been studied. Optical band gap measurements indicated that, doped polymers have wider optical band gap than the pure one. The effect of doping on the thermal stability differs according to the doped metal ion. The doped with Cr ions poly(m-phenylenediamine) has been used as a precursor of mesoporous Cr2O3 nanoparticles, which have been also characterized by XRD and HR-TEM.

MgO–CaO–Cr2O3 composition as a novel refractory brick: Use of Cr2O3 nanoparticles

At this study the effect of Cr2O3 nanoparticles (up to 3wt.%) on the physical and mechanical properties of MgO–CaO refractory composition with emphasis on the hydration resistance improvement have been investigated. Specimens pressed at 90MPa then were sintered at 1650°C for 5h in an electric furnace. Properties such as bulk density, apparent porosity, cold crushing strength and hydration resistance were examined. The crystalline phases and microstructure characteristics of sintered specimens were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS), respectively. Results shown that add of the 1.5wt.% Cr2O3 nanoparticles have the best results i.e. increased the bulk density (3.41g/cm3), cold crushing strength (848kg/cm2), hydration resistance (1.5%) and decreased apparent porosity (5.58%), respectively. The mechanism of specimens hydration resistance improvement are: (i) decreasing the amount of free CaO and MgO with converted to high hydration resistance phases such as CaCr2O4 and MgCr2O4 phases, (ii) promotion of the densification as well as (iii) modification of the microstructure.