In this study, cavitation erosion tests were conducted on different materials such as pure aluminium (99% aluminium) and 1045 steel which were used as “vibratory” specimens, whereas untreated 6082 ...aluminium alloy, 304 stainless steel and 4340 steel were used as “stationary” specimens. A first set of tests was conducted using only tap water where a lower wear rate was observed. On the other hand, a second set of tests was carried out adding silicon carbide particles to the tap water which led to increase of the erosion wear rate. It helped to evaluate the performance of all the tested materials at different testing conditions.
High speed camera was used to analyse the bubble formation in the radiating surface of the horn made of 2024 aluminium alloy. In these videos, it was possible to observe that the bubble formation was similar to the cone-like bubble structure (CBS) observed in other cavitation studies. Additionally, high speed videos were obtained as abrasive particles were used to conduct the tests. In these, it was possible to observe how abrasive particles were moving along the two surfaces, staying in the clearance to cause higher wear damage on both surfaces. The “stationary” specimen was located at a 1mm distance with respect to the position of the “vibratory” specimen which was attached to the radiating surface. Optical microscopy was used to identify the wear mechanisms which were characterized by a pitting action when only tap water was used whereas some scratches and irregular indentations similar to those observed in abrasive wear were seen on the surfaces with abrasive particles.
•Size, cell shape and cellular architecture of mesocarp tissue control apple firmness•Stiffness and complexity of cell wall were the main biomechanics of apple tissues•Cellulose fibers and pectic ...agglomerate size explain some differences in apple firmness•Principal component analysis was successful in classifying the studied apple cultivars.•A simplified model for firmness prediction of some apples was obtained by multivariate analysis
A study of the physicochemical, structural, nanomechanical properties at macro, micro and nanometric scales was carried out to determine which features have the greatest influence on the firmness of selected apple cultivars (Golden Delicious, Granny Smith, Gala and Red Delicious). Physicochemical assays, microscopy techniques, image analysis, nanoindentation and spectroscopy were used to characterize the properties of the four selected apples. The data were analyzed using principal component analysis, Pearson analysis and multiple linear regression to classify apple cultivars. These techniques were also used to identify which physicochemical, micro, and nanostructural as well as nanomechanical features were most associated with apple firmness. This allowed for the creation of a mathematical model (R2 = 0.97) for the prediction of apple firmness from evaluated variables. It was determined that the cellular architecture, stiffness of cell walls and crystallinity index of cellulose fibers were the most important factors in explaining the variability of firmness in the studied apples. This research provides novel and valuable information for understanding the role of cellular architecture, micro and nanostructure, as well as nanomechanical properties in the firmness of the studied cultivars.
The objective of this study was to evaluate the effect of the presence of calcium oxalate (CaOx) crystals on the micromechanical properties of sclerenchyma tissue from the pecan nutshell (Carya ...illinoinensis). The microstructure of the cross-section nutshell was examined using light microscopy (LM) and atomic force microscopy (AFM). Using an instrumented indentation system, indentation tests with maximum loads of 500 mN were made on the biological material where the variables studied were the number of crystals present in the evaluated area and the size of individual crystals. Microscopic analysis revealed that the pecan nutshell consists of sclerenchyma tissue with multiple CaOx crystals randomly distributed throughout the material, exhibiting prismatic shapes and various sizes. The results of the indentation tests showed that the examined areas where there were crystals (1, 2 or up to 3) presented values of hardness and elastic modulus significantly higher (P < 0.05) compared to the sclerenchyma (without crystals). Likewise, there were no significant differences (P > 0.05) between the values of the micromechanical properties of the areas evaluated as a function of the number of crystals. On the other hand, it was observed that the size of the crystals did not show a direct correlation with the mechanical properties evaluated as expected. In conclusion, the biomineralization phenomenon is a successful strategy designed by nature to improve the rigidity of the pecan nutshell, where the CaOx crystals strengthen the structure by increasing the micromechanical properties.
•The effect of CaOx crystals on the micromechanical properties of the sclerenchyma from the pecan nutshell were evaluated by indentation tests.•The CaOx crystals increased the hardness (≈20%) and elastic modulus (≈13%) of the sclerenchyma tissue locally.•There were no significant differences between the values of the micromechanical properties evaluated as a function of the number of crystals.•The size of the crystals did not show a direct correlation with the mechanical properties.•CaOx crystals strengthen the structure of the pecan nutshell, demonstrating that they fulfill a mechanical function.
► R. communis seeds were dried by fluidized bed at high temperatures (80–110°C). ► Modelling of drying kinetics applied to a non-studied material was conducted by empirical models. ► Diffusion ...approach model was the best model to describe drying behaviour of seeds. ► The dependences of moisture ratio, drying rate, effective moisture diffusivity and energy activation were studied with respect to temperature. ► The study of fluidized bed drying of R. communis seeds provides information useful for food and energetic industries.
Ricinus communis or castor oil seed is an agricultural product which possesses a large amount of proteins and lipids that could be useful in food and energy industries. Drying process can be helpful to conserve the castor oil seed during long storage periods, for this reason in this research, the drying kinetics of castor oil seeds during fluidized bed drying at a constant air velocity of 7m/s and high air temperatures (80, 90, 100, 110°C) were studied. Six empirical mathematical models were selected to describe and compare the drying characteristic of R. communis seeds at previous described conditions. Drying rate constants, coefficients and statistical parameters were determined by non-linear regression analysis. Among the tested models used to describe the drying kinetics of castor oil seeds, the diffusion approach model was selected as the best one. The moisture loss from the seeds was described by the Fick's diffusion equation, and based on the obtained results the effective moisture diffusivity was estimated, getting a value in the range from 8.21×10−10 to 2.61×10−9m2/s. The relationship between the temperature and the effective moisture diffusivity was described adequately by means of Arrhenius-type equation. An activation energy value of 41.41kJ/mol was obtained. The findings allow the successful simulation of R. communis seeds fluidized bed drying between 80 and 110°C. This study provides information to dry castor oil seed by fluidized bed at high temperatures that could be useful for biofuel production.
•Thermosonication was the best method for extracting phenolic compounds.•Thermosonic extract was the most effective method for inactivating Campylobacter jejuni.•The Gompertz model was the most ...suitable to fit C. jejuni kinetics.•AFM confirmed structural and nanomechanical effects of chill extracts on C. jejuni.•C. jejuni exposed to chili extracts had high Young's modulus values.
Campylobacter jejuni is a pathogen bacterium that causes foodborne gastroenteritis in humans. However, phenolic compounds extracted from natural sources such as capsicum pepper plant (Capsicum annuum L. var. aviculare) could inhibit the growth of C. jejuni. Therefore, different extracts were prepared using ultrasonic extraction (USE), conventional extraction (CE) and thermosonic extraction (TSE). C. jejuni was then exposed to chili extracts to examine the antimicrobial effect and their growth/death bacterial kinetics were studied using different mathematical models. Atomic force microscopy was applied to investigate the microstructural and nanomechanical changes in the bacteria. Extracts obtained by TSE had the highest phenolic content (4.59 ± 0.03 mg/g of chili fresh weight FW) in comparison to USE (4.12 ± 0.05 mg/g of chili FW) and CE (4.28 ± 0.07 mg/g of chili FW). The inactivation of C. jejuni was more efficient when thermosonic extract was used. The Gompertz model was the most suitable mathematical model to describe the inactivation kinetics of C. jejuni. Roughness and nanomechanical analysis performed by atomic force microscopy (AFM) provided evidence that the chili extracts had significant effects on morphology, surface, and the reduced Young’s modulus of C. jejuni. The novelty of this work was integrating growth/death bacterial kinetics of C. jejuni using different mathematical models and chili extracts, and its relationship with the morphological, topographic and nanomechanical changes estimated by AFM.
•Porosity of calcified chicken eggshell was examined by AFM and image processing.•The palisade layer exhibits the highest degree of porosity and largest thickness.•Bubble pores in all layers have ...mainly circular shapes and similar sizes.•A gradient of porosity along the cross-section of calcified eggshell was observed.
In this work, the porosity of the layers of calcified chicken eggshell (vertical crystal layer VCL, palisade layer PL and mammillary layer ML) was evaluated using atomic force microscopy (AFM) and image processing (IP). AFM topographic images were obtained from different locations for each layer and along the cross-section of calcified eggshell. Roughness parameters, surface area values, pore size and shape, surface porosity, area occupied by pores and pore density were obtained from AFM and IP. It was observed that the thickest layer (PL) exhibited the highest degree of porosity (surface porosity = 2.75 ± 1.68%, pore density = 162 ± 60 pores/μm2) when compared to the other two layers. In general, the pores located in all layers (“bubble pores”) had circular shape and similar sizes. Measurements revealed a porosity gradient along the cross-section which varied with position, i.e., increasing surface porosity from the VCL towards the region of the PL closer to the ML, and decreasing surface porosity from this location towards the ML innermost surface. This suggests that the calcified eggshell has a sandwich-like structure where porosity may influence gas exchange and mechanical properties. The combination of AFM with IP presented here provides a simple and precise method to study porosity in calcified chicken eggshell, and this methodology could be used to examine other types of porous biological materials.
Titanium films were deposited on AISI 316L stainless steel substrates by D.C. unbalanced magnetron sputtering, the substrate temperature and deposition time were changed. In this study, the ...structural characterization was conducted by scanning electronic microscopy (SEM), spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and atomic force microscopy (AFM). Furthermore, mechanical properties were obtained by nanoindentation. Adhesion and wear behavior were evaluated through progressive load scratch test (PLST) and pin-on-disk test, respectively. Titanium films thicknesses within a range of 2.5–4.2μm were obtained, different XRD Ti peaks such as (002), (102) and (103) were identified. Values estimated for hardness were between 7.2 and 8.4GPa, and for Young's modulus they were 126–162GPa. Tensile cracks, compressive and gross spallation failure mechanisms were found with scratch tests. Preferred oriented sample only showed cracks, with a critical load of 2.6N, and exhibited a better wear ratio (~1.5×10−4), which is about two times better than substrate steel. This study provides evidence of how a preferred oriented Ti (002) film exhibits better hardness, adhesion and wear properties.
•Heating the substrate caused a strong preferred (002) orientation in one sample.•Preferred oriented sample presented the best scratch resistance.•Wear behavior information of titanium films with different deposition parameters.•Lower wear ratio obtained with preferred (002) orientation.
In the present work a comprehensive characterization of the hierarchical architecture of the walnut shell (Juglans regia L.) was carried out using scanning electron microscopy (SEM), atomic force ...microscopy (AFM) and confocal laser scanning microscopy (CLSM). Furthermore, micromechanical properties (hardness, HIT and elastic modulus, EIT) of plant tissues were evaluated at cell wall level by applying the instrumented indentation technique (IIT). The complex architecture of the material was described in terms of four hierarchical levels (HL): endocarp (H1), plant tissues (H2), plant cells (H3) and cell wall (H4). Our findings revealed that the walnut shell consists of a multilayer structure (sclerenchyma tissue, ST; interface tissue, IT; porous tissue, PT; and flattened parenchyma tissue, FPT), where differences in the microstructure and composition of plant tissues generate parallel gradients along the cross-section. The indentation tests showed a functional gradient with a sandwich-like configuration, i.e., a lightweight and soft layer (PT, HIT = 0.04 GPa) is located between two dense and hard layers (ST, HIT = 0.33 GPa; FPT, HIT = 0.28 GPa); where additionally there is an interface between ST and PT (IT, HIT = 0.16 GPa). This configuration is a successful strategy designed by nature to improve the protection of the kernel by increasing the strength of the shell. Therefore, the walnut shell can be considered as a functionally graded material (FGM), which can be used as bioinspiration for the design of new functional synthetic materials. In addition, we proposed some structure-property-function relationships in the whole walnut shell and in each of the plant tissues.
•The hierarchical architecture and micromechanical properties of the walnut shell were characterized.•Parallel gradients (microstructure, composition, mechanical properties) through the cross-section of the biological material were observed.•The walnut shell exhibits a sandwich-like configuration.•Structure-property-function relationships were proposed in the whole walnut shell and in each of the plant tissues.•The walnut shell can be considered as a functionally graded material (FGM).
Nanomechanical properties of fruit determine macroscopic firmness. Young's modulus (YM) of apple tissue obtained by atomic force microscopy (AFM) at cellular level and its correlation with other ...macroscopic physical parameters are used to evaluate ripening when apples were stored at 25°C during 40days. The YM of the tissue decreased from 0.96±0.42MPa (first day) to 0.11±0.06MPa (last day). The best linear correlation of YM was obtained with firmness (F) which decreased from 21.15±0.79N to 12.74±0.34N. Also various physical parameters obtained as peel color difference (ΔE) from 57.80±0.97 to 66.51±0.71, environmental electron microscopy (ESEM) such as entropy: Ent (from 8.67±0.12 to 9.60±0.17) and fractal dimension: FD (from 2.67±0.05 to 2.75±0.03) changed as well. Significant correlations (P<0.05) were found between YM, F, ΔE, Ent and FD using Pearson analysis. Predictive models to evaluate YM from F, ΔE, Ent, FD were obtained by multiple linear regression, R2>0.95 was found.
The study of the nanomechanical properties of fruit cells by AFM may provide insight into internally fruit properties and how changes in these properties over time influence the quality of the fruit. The determination of cell/tissue mechanics could be used to follow changes in the nanomechanical properties that occur during the processing and storage of climacteric fruits such as apples. The study of the nanomechanical properties of plant cells as well as their correlation with other useful food properties such as firmness, peel color and image texture could lead to a better understanding of the ripening process. Mathematical models to predict cell mechanical properties at the nanometric level through food quality parameters could be an innovation in food engineering and be a novel tool in evaluating the quality of apples. Benefits of the methods herein could be extended to address current issues, such as extending the storage life of other climacteric fruits and predicting nanostructural modifications to the cells when they are physically modified or chemically treated.
•Young's modulus values of apple tissue showed a wide distribution during the ripening.•Young's modulus and firmness steadily decrease and maintained a linear correlation.•Image texture parameters of ESEM images correlated with nanomechanical properties.•Young's modulus of apple tissue can be predicted from typical food quality parameters.
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