Greater Surface Roughness Research Articles

Molten pool behaviors and printability of tungsten anti-scattering grids with extremely thin wall thickness fabricated via laser powder bed fusion

It is challenging for laser powder bed fusion (LPBF) technique to fabricate metal parts with a wall thickness below 100 μm. This work investigated the critical conditions for achieving extremely thin wall thickness in tungsten grids fabricated via LPBF. Specifically, the impact of low energy density on the printability of tungsten single tracks and grids via LPBF was comprehensively examined. A computational fluid dynamics approach was employed to develop a thermal fluid flow model for single tracks with multilayers in LPBF. The findings demonstrate that at low energy densities, single tracks exhibit four different morphologies, i.e., balling, discontinuity and winding, discontinuity but straightness, as well as continuity and straightness. The simulation model effectively elucidates the continuity of single tracks and provides insights into the governing mechanism of molten pool defects. Due to high thermal diffusion properties of tungsten, the continuity of its track relies on the connection of neighboring molten pools and is sensitive to scanning speed. The tungsten molten pools with low energy density can be categorized into shallow flows affected by surface morphology and deep flows influenced by internal voids of the powder bed. After multi-layer stacking, the track fluctuations and defects in single tracks accumulated into greater surface roughness and deteriorate thin-walled morphology. The critical conditions required for printing extremely thin walls were achieved, ensuring minimal merging of tracks between two layers by maintaining the energy density of 57J/mm3. Based on these findings, an ultra-thin-walled anti-scattering tungsten grid with a wall thickness of 86 μm and a wall roughness below 3.3 μm (Ra) was fabricated by LPBF. This work provides valuable theoretical insights and presents a viable methodology for determining the minimum energy density threshold and wall thickness essential for LPBF processing of thin-walled components.

Experimental investigation into coal wettability changes caused by reactions with scCO2-H2O

Geological CO2 sequestration (GCS) can help mitigate global warming and enhance methane recovery from coal beds. However, few studies have linked the effects of CO2 to surface chemistry changes controlling wetting behavior in deep coal beds. Contact angles (CAs) of CO2/N2-high volatile bituminous coal-water systems were measured under different temperatures and pressures. The surface chemistry and physical structure of coals were characterized to investigate changes in physicochemical properties and their relations with wettability after reactions. For N2 treatment, the time-dependence of static and dynamic CAs were insignificant, ranging within 4°. For gaseous CO2 treatment, the static CAs and the average advancing angles increased slightly. With supercritical (sc) CO2, both the static and dynamic CAs increased significantly, and θadv changed to intermediate-wet (92°). Reactions with minerals exposed to scCO2 resulted in greater surface roughness and heterogeneity, greater contact angle hysteresis and more surface sites occupied by scCO2 rather than H2O. Increases in hydrophobic functional groups and decreases in hydrophilicity were shown by FTIR spectra, reflecting the shedding of polar oxygen-containing functional groups, reduction of hydrogen bonds, and increasing percentage of hydrocarbons. XRD patterns obtained following scCO2-treatment showed that crystallite growth and molecular polymerization were higher toward graphite-like. The calculated structural parameters of functional groups and crystallites both showed elevated coal rank. Changes in crystallite structure, notably higher carbon content and decreased negative surface charge, are unfavorable for water-wetting. This study contributes to understanding surface chemistry changes responsible for decreased wettability during CO2-enhanced coal bed methane recovery and GCS in coal reservoirs.

A multiscale study of the influence of aggregate type on adhesion at the asphalt–aggregate interface

In order to examine the influence of aggregate type on the asphalt–aggregate interface, the adhesion performance between asphalt and aggregate was investigated at three scales. The pull-out test was conducted on asphalt and three kinds of aggregates at the macroscale to directly estimate the adhesion performance between them. At the microscale, the surface energies between asphalt and limestone, basalt, and andesite were examined through a surface energy experiment, and then the adhesion and debonding work were assessed. At the nanoscale, the interfacial behavior between six mineral compositions (SiO2, CaO, MgO, Al2O3, Fe2O3, and Na2O) of these aggregates and asphalt was determined using molecular dynamics simulation. The correlation of adhesion work at the microscale and nanoscale was further explored to unveil the bonding mechanisms between asphalt and aggregate. The macroscale results indicate that the adhesion force of andesite is slightly greater than that of limestone, probably because andesite has a greater surface roughness than limestone. The microscale results show the best adhesion and water stability between asphalt and limestone. The finding further explains that alkaline aggregates exhibit superior interfacial adhesion to asphalt. The nanoscale results show that the adhesion work of alkaline oxides with asphalt is more significant than that of acidic oxides with asphalt. Limestone and basalt have better adhesion to asphalt due to higher alkaline oxide content, while andesite has poorer adhesion to asphalt due to lower alkaline oxide and higher SiO2 content. The interfacial adhesion work increases from the microscale to the nanoscale by a factor of 2.91–4.75.

Incipient Dissolution of Emplaced Forsterite and Fayalite Records the Effects of Climate, Mineral Composition, and Crystallographic Orientation

To investigate the effects of environment, composition, and crystal orientation on incipient surface alteration of forsterite and fayalite in a natural environment, polycrystalline forsterite and fayalite samples were emplaced in Mg/Fe-rich and Al-poor ultramafic soils under subarctic (Tablelands in Newfoundland, Canada; 3.9 ⁰C and ∼120 cm precipitation/year), Mediterranean (Klamath Mountains, California;≤12.8 ⁰C and ∼101-118 cm precipitation/year), and desert (Pickhandle Gulch, Nevada; ∼14.1 ⁰C and ∼14.4 cm/year) climates for one year. Incipient alteration after one year was examined using scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, X-ray photoelectron spectroscopy, and visible and near-infrared reflectance spectroscopy.Alteration features on forsterite surfaces included flat-bottomed pits with steeply dipping walls likely developing on grain faces and representing surface retreat of individual grains and lining features likely developing along grain boundaries. Mg-leached surface layers formed under acidic to slightly alkaline conditions while Mg-enrichment was observed under alkaline conditions. Flat bottomed pit formation preferentially occurs on surfaces within 30° of perpendicular to the b-axis (on the [010] plane) of the olivine crystal lattice. Depth of flat-bottomed pits on forsterite surfaces follows the order Klamath Mountains > Tablelands >> Pickhandle Gulch, reflecting the importance of environmental conditions. Warm, wet, and relatively acidic conditions enhanced forsterite dissolution over cold, wet, and slightly alkaline conditions, with minimal alteration observed under hot but arid and alkaline conditions. Greater surface roughness on flat-bottomed pit floors on Klamath Mountain forsterite surfaces are consistent with less-saturated soil-pore water reaction conditions.In contrast, fayalite disks buried in the Klamath Mountains show no evidence for etch-pit formation despite the warm, wet, and slightly acidic conditions. Elevated Fe/Si ratios from X-ray photoelectron spectroscopy measurements and evidence of M-OH bonds in visual and near infrared spectra are consistent with formation of a Fe-enriched hydroxylated layer limiting fayalite surface area available for water-rock interaction and retarding fayalite dissolution during aqueous alteration under oxidizing conditions. These results differ from previous laboratory experiments that show enhanced dissolution of fayalite relative to forsterite, showing the effect of natural, oxic, unsaturated weathering zones. These results will be helpful for interpreting observations of this widely studied mineral, including from the planet Mars.

High Emissivity MoSi2-SiC-Al2O3 Coating on Rigid Insulation Tiles with Enhanced Thermal Protection Performance.

High emissivity coatings with sol as the binder have the advantages of room temperature curing, good thermal shock resistance, and high emissivity; however, only silica sol has been used in the current systems. In this study, aluminum sol was used as the binder for the first time, and MoSi2 and SiC were used as emittance agents to prepare a high emissivity MoSi2-SiC-Al2O3 coating on mullite insulation tiles. The evolution of structure and composition at 1000-1400 °C, the spectral emissivity from 200 nm to 25 μm, and the insulation performance were studied. Compared with the coating with silica sol as a binder, the MoSi2-SiC-Al2O3 coating has better structural uniformity and greater surface roughness and can generate mullite whiskers at lower temperatures. The total emissivity is 0.922 and 0.897, respectively, at the wavelength range of 200-2500 nm and 2.5-25 μm, and the superior emissivity at a low wavelength (<10 μm) is related to a higher surface roughness and reduced feature absorption. The emissivity reduction related to the oxidation of emittance agents at a high temperature (-10.2%) is smaller than that of the silica-sol-bonded coating (-18.6%). The cold surface temperature of the coated substrate is 215 °C lower than the bare substrate, suggesting excellent thermal insulation performance of the coating.

In English

Features of interfacial adsorbate/adsorbent phenomena depend on several factors: particulate morphology, texture, and structure of adsorbents, molecular weight, shape, and polarity of adsorbates; as well as prehistory of adsorbents pretreated under different conditions. All these factors could affect the efficiency of practical applications of not only adsorbents but also polymer fillers, carriers, catalysts, etc. Interactions of nonpolar nitrogen, hexane, benzene, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water with individual (silica, alumina), binary (silica/alumina (SA)) and ternary (alumina/silica/titania, AST) nanooxides were studied using experimental and theoretical methods to elucidate the influence of the morphological and textural characteristics and surface composition of the materials on the adsorption phenomena. The specific surface area SX / ratio (X is an adsorbate) changes from 0.7 for hexane adsorbed onto amorphous silica/alumina SA8 with 8 wt. % Al2O3 (degassed at 200 °C) to 1.9 for acetonitrile adsorbed onto pure fumed alumina (treated at 900 °C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of organic molecules interacting with surfaces characterized by certain set and amounts of various active sites, as well as due to changes in the accessibility of pore surface for probe molecules of different sizes. Larger SX / &gt; 1 values are observed for complex fumed oxides with larger primary nanoparticles, greater surface roughness, hydrophilicity, and Brønsted and Lewis acidity of a surface. Both polar and nonpolar adsorbates can change the morphology and texture of aggregates of oxide nanoparticles, e.g., swelling of structures, compacted during various pretreatments, upon the adsorption of liquids. The studied effects should be considered upon practical applications of adsorbents, especially “soft” fumed oxides.

Spray deposited pristine and Mo doped WO3 thin films for acetaldehyde gas sensing at room temperature

In this paper, pure WO3 and molybdenum-incorporated WO3 were directly deposited in the form of thin films on the glass substrate. The films were deposited through the spray pyrolysis technique, and their gas sensing properties, structural, optical, electrical, and morphological properties were altered by adding a dopant to the pristine WO3. A direct, one-step approach is used to deposit metal oxide semiconductor materials as thin films, which enhances the ability to detect gas. A novel gas sensing response for acetaldehyde gas detection was observed from Molybdenum doped WO3 thin film at 25 °C. On investigating the sensing performance of both films for various volatile organic compounds (VOC), a high response (54.55 %) towards acetaldehyde was achieved for 2 % molybdenum-doped WO3 film. The XRD analysis demonstrated that the synthesized films are crystalline with triclinic phase. Decrease in crystallite size increases the grain boundaries that enhance the sensing response. The absorption spectra of UV–Visible spectroscopy showed an apparent change of increase in the absorbance and decrease in the optical band gap on addition of the dopant to the pure WO3 thin film. Filamentous structured porous thin films are discovered to have larger voids and greater surface roughness from FE-SEM and AFM, which aids in the adsorption of gas molecules. Mo-doped WO3 thin films showed a strong sensing response due to larger grain boundary scattering and wide pores abetting for more gas adsorption.

Behaviour of the Peri-Implant Soft Tissue with Different Rehabilitation Materials on Implants.

(1) Background: Mucointegration seems to gain interest when talking about success in the maintenance of dental implants. As we well know, collagen fibres cannot be inserted due to the lack of root structure on the implant surface, so the structural integration of peri-implant tissues that provide a firm seal around implants seems to be of interest when it comes to ensuring the survival of dental implants. To achieve a good epithelial barrier, the physicochemical characteristics of the surfaces of the restorative materials are of vital importance; therefore, the objective of this study is to analyse the histological behaviour of the peri-implant soft tissues in three different restorative materials. (2) Methods: Histological analysis of biopsied peri-implant keratinised mucosa, inflammatory epithelium and connective tissue in contact with a reinforced composite (BRILLIANT Crios), a cross-linked polymethylmethacrylate (TELIO CAD), and a hybrid ceramic (Vita Enamic), restored on a customised Atlantis-type abutment (Dentsply Sirona) between 60 and 180 days after restoration. (3) Results: A greater number of cells per mm2 of keratinised epithelium is observed in the reinforced composite, which could indicate greater surface roughness with greater inflammatory response. In this way, the greater number of lymphocytes and the lateral cellular composition of the inflammatory cells confirm the greater inflammatory activity towards that material. The best material to rehabilitate was hybrid ceramic, as it shows a better cellular response. (4) Conclusions: Knowing the limitations of the proposed study, despite the fact that greater inflammation is observed in the reinforced composite relative to the other materials studied, no statistically significant differences were found.

Effect of cathode material on the morphology and osseointegration of TiO2 nanotube arrays by electrochemical anodization technique

Titanium (Ti) has been one of the most widely used materials for biomedical implants owing to its suitable bulk and surface properties. To control the risk of tissue infection and implant failure, titanium dioxide nanotubes (TNTs) have been frequently grown on Ti surface via electrochemical anodization (EA), which is a cost-effective process offering tunable TNTs structures with ease. In the present work, the role of counter electrodes in affecting the microstructure and surface properties of TNTs was investigated. To study this less-highlighted parameter systematically, platinum (Pt), graphite (Gp), and stainless steel (SS) were selected as representatives. The use of Pt and Gp cathodes led to TNTs with typical circular morphology, while those produced with the SS cathode displayed hexagonal-shaped tubes. Moreover, TNTs fabricated with SS cathode exhibited particle debris on the surface at the expense of some portion of its tube length. This morphology, however, resulted in greater surface roughness and hydrophilicity. The highly complicated surface microstructure played a major role in facilitating the growth of bone-forming apatite during osseointegration.

Tribo-sanitizer: A portable and self-powered UV device for enhancing food safety

Food safety is of constant major concern worldwide. Each year, hundreds of millions of people fall ill due to consuming contaminated food, and the resulting economic loss runs into hundreds of billions of dollars. To mitigate these issues, we developed Tribo-sanitizer, which utilizes a freestanding rotational triboelectric nanogenerator (FSR-TENG) to convert mechanical energy into sustainable, low-cost or free electricity that powers an ultraviolet-C (UVC) lamp for food-safety applications. Thanks to the air gap in its circuit – a design inspired by a natural phenomenon, lightning, which can lead to electrical breakdown of air – the optimal FSR-TENG can generate a high voltage output of more than 4,000 V. This high electrical output, in turn, enables brighter illumination of the UVC lamp. Tribo-sanitizer’s decontamination efficacy was evaluated against a gram-positive bacterial strain (Listeria monocytogenes) and a gram-negative one (Escherichia coli O157:H7) inoculated in a liquid buffer, on a polymer widely used in the food-packaging industry, and on two types of fresh produce. Tribo-sanitizer achieved a 5.03-log reduction and a 5.95-log reduction for E. coli O157:H7 in buffer solution and on polyethylene terephthalate (PET), respectively, in line with the 5-log reduction recommended in government guidelines for microbial control. The log reductions for L. monocytogenes in buffer solution and on PET were 4.36 and 3.81, respectively. Lesser effectiveness was observed with the apples and romaine lettuce, likely due to these fresh produce samples’ greater surface roughness as compared to PET, one of the most widely used polymers for the construction of food packaging and drinks bottles. Our results also demonstrate that biomechanical motions can provide Tribo-sanitizer with sufficient power to achieve bacterial inactivation, demonstrating its excellent potential for use in low-resource settings. With further improvements, it could help mitigate severe food-safety problems around the world, leading to a more secure and sustainable food system.

The Clinical Potential of 3D-Printed Crowns Reinforced with Zirconia and Glass Silica Microfillers

The development of 3D-printed crown resin materials with improved mechanical and physical properties is an area of growing interest in dentistry. This study aimed to develop a 3D-printed crown resin material modified with zirconia glass (ZG) and glass silica (GS) microfillers to enhance overall mechanical and physical properties. A total of 125 specimens were created and divided into five groups: control unmodified resin, 5% either ZG or GS reinforced 3D-printed resin, and 10% either ZG or GS reinforced 3D-printed resin. The fracture resistance, surface roughness, and translucency parameter were measured, and fractured crowns were studied under a scanning electron microscope. The results showed that 3D-printed parts that were strengthened with ZG and GS microfillers demonstrated comparable mechanical performance to unmodified crown resin but resulted in greater surface roughness, and only the group that contained 5% ZG showed an increase in translucency. However, it should be noted that increased surface roughness may impact the aesthetics of the crowns, and further optimisation of microfillers concentrations may be necessary. These findings suggest that the newly developed dental-based resins that incorporate microfillers could be suitable for clinical applications, but further studies are necessary to optimise the nanoparticle concentrations and investigate their long-term clinical outcomes.

The effects of aspect ratio of cellulose nanocrystals on the properties of all CNC films: Tunicate and wood CNCs

In this study, the physicochemical, mechanical, and thermal properties of films made from cellulose nanocrystals (CNCs) obtained from two sources – wood and tunicate - and their hybrids were investigated. It was found that different morphologies affect the properties of CNC films. Specifically, the surface morphology of tunicate CNC (TCNC) films differed significantly from wood CNC (WCNC) films, and the structure of hybrid CNC (HCNC) films was also different. Compared to wood CNC-containing films, tunicate CNC films exhibited significantly higher BET surface areas, superior thermal properties, greater surface roughness, and very low (≈1 wt.%) dispersibility in water due to their ability to form long-range connectivity. The average BET surface area of TCNC films was measured at 91.9 ± 2.1 m2/g, and this value decreased with the addition of WCNCs to the film structure. The pore diameter also decreased from 11.362 nm for TCNC films to 0.437 nm for WCNC films, indicating the filler effect of WCNCs on the TCNC films. The chiral nematic phase exhibited by WCNC films was confirmed by their iridescent appearance, as observed through cross-sectional SEM images. The TS for TCNC and HCNC3 was measured at 185.2 ± 10.5 MPa and 182.9 ± 13.7 MPa, respectively, which were the highest values among the samples. The lowest TS value of 113.1 ± 9.5 MPa was observed in the WCNC films. A similar decline was observed in the EB values, from 1.76 ± 0.37% for TCNC to 0.9 ± 0.22% for WCNC. This study provides information and knowledge useful for understanding the impact of biomass source on the properties of CNC films for a variety of purposes, including packaging materials, biodegradable coatings, flexible electronics, and membrane applications.

Influence of Tool Rotation and Surface Roughness on the Shear Strength of Nylon 6 - SS 304 Dissimilar Joint Resulted by Friction Lap Welding

This research was conducted to investigate the effect of variations in tool rotation and surface roughness towards shear strength on the newly developed friction lap welding (FLW) for dissimilar joints between stainless steel (SS) 304 and Nylon 6 plates. Under constant welding traverse speed at 30 mm/min, the variation of tool rotation used were 1100 and 2200 rpm and surface roughness of 0.32; 1.25; and 1.88 μm initially obtained from different surface modification methods. The shear test was conducted at FLW dissimilar joint based on AWS D8.9-97 standard. The results showed that the shear stress increased along with the higher tool rotation and at the greater surface roughness. The highest shear strength value was found at the tool rotation of 2200 rpm and surface roughness of 1.88 μm with 9.447 MPa. The tool rotation may produce a higher heat input as well as an effect on the value of nylon hardness. On the other hand, rougher SS surfaces provide a larger area for the interfacial adhesive bond between nylon and metal; therefore, they can act as an interlocking site when the shear loading was applied. These phenomena were also confirmed by fracture morphology and microscopic image analysis.

Multiparametric Quantitative Analysis of Photodamage to Skin Using Optical Coherence Tomography.

Ultraviolet (UV) irradiation causes 90% of photodamage to skin and long-term exposure to UV irradiation is the largest threat to skin health. To study the mechanism of UV-induced photodamage and the repair of sunburnt skin, the key problem to solve is how to non-destructively and continuously evaluate UV-induced photodamage to skin. In this study, a method to quantitatively analyze the structural and tissue optical parameters of artificial skin (AS) using optical coherence tomography (OCT) was proposed as a way to non-destructively and continuously evaluate the effect of photodamage. AS surface roughness was achieved based on the characteristic peaks of the intensity signal of the OCT images, and this was the basis for quantifying AS cuticle thickness using Dijkstra's algorithm. Local texture features within the AS were obtained through the gray-level co-occurrence matrix method. A modified depth-resolved algorithm was used to quantify the 3D scattering coefficient distribution within AS based on a single-scattering model. A multiparameter assessment of AS photodamage was carried out, and the results were compared with the MTT experiment results and H&E staining. The results of the UV photodamage experiments showed that the cuticle of the photodamaged model was thicker (56.5%) and had greater surface roughness (14.4%) compared with the normal cultured AS. The angular second moment was greater and the correlation was smaller, which was in agreement with the results of the H&E staining microscopy. The angular second moment and correlation showed a good linear relationship with the UV irradiation dose, illustrating the potential of OCT in measuring internal structural damage. The tissue scattering coefficient of AS correlated well with the MTT results, which can be used to quantify the damage to the bioactivity. The experimental results also demonstrate the anti-photodamage efficacy of the vitamin C factor. Quantitative analysis of structural and tissue optical parameters of AS by OCT enables the non-destructive and continuous detection of AS photodamage in multiple dimensions.

Annealing effect on the structural and optoelectronic properties of Cu-Cr-O thin films deposited by reactive magnetron sputtering using a single CuCr target

Abstract The aim of this study is to explore the structural and optoelectronic properties of Cu-Cr-O thin films when processed by the magnetron sputtering method using a single equimolar CuCr alloy target. These films were then post-annealed in a controlled Ar atmosphere at 500°C to 800°C for 2 h. The as-deposited Cu-Cr-O thin film consisted of an amorphous phase and exhibited extremely poor optoelectronic properties. After annealing was conducted at 500°C, monoclinic CuO and spinel CuCr2O4 phases were simultaneously formed in the film. Upon increasing the annealing temperature to 600°C, the CuCr2O4 phase reacted completely with the CuO phase and transformed into the delafossite CuCrO2 phase, possessing optimal optoelectronic performance. It has an electrical resistivity of 41 Ω-cm and a light transmittance of 49.5%, making it suitable for p-type transparent conducting electrodes. A further increase in annealing temperature resulted in larger grains and greater surface roughness and void density, which, in turn, degraded the optoelectronic performance.

An Evaluation of the Colour Stability and Surface Roughness of High Translucency Zirconia Dental Ceramic after Immersion in Different Acidic Media: An In-vitro Study

Introduction: Demand for increasingly appealing metal-free ceramic restorations drives research. With its exceptional mechanical and biological properties, zirconia crown outperforms other traditional ceramic materials. With outstanding mechanical and biological qualities, zirconia has several therapeutic applications. Temperature, environment, diet, and smoking habits all affect colour and surface roughness of dental restorations. Aim: To investigate the colour stability and surface roughness of high translucency monolithic zirconia following immersion in various acidic solutions. Materials and Methods: This in-vitro study was conducted at Yenepoya Dental College, Mangalore, Karnataka, India. Duration of the study was 6 months, from December 2019 to June 2020. Thirty rectangular samples from a CAD (computer-aided Design)/ Computer Aided Manufacturing (CAM) machined Zirconia blank with 10x8x1 mm dimensions was sintered at 1350°C, tested for colour stability (E) and surface roughness prior to immersion (R). Classified into Groups CO (coffee), TO (tobacco) and CA (citric acid medium). Colour stability and surface roughness were re-evaluated post immersion on all samples using spectrophotometers and profilometer respectively. A significant difference in surface roughness and colour stability between the test groups was assessed using the paired-t test. The data was analysed using Statistical Package for Social Sciences (SPSS) version 24.0. Results: Colour stability and surface roughness variations between the baseline value and three groups were found to be unaltered by different acidic media. The intergroup comparison of spectrophotometric analysis between the three groups had a standard deviation of 0.422 for citric acid medium, 0.316 for Coffee medium and 0.422 for Tobacco medium with an overall p-value of 0.804. The intergroup comparison of profilometric analysis had a standard deviation of 0.316 for Citric acid medium, 0.00 for Coffee medium and 0.00 for Tobacco medium with an overall p-value of 0.381. The paired-t-test study showed that immersion in different acidic media had little effect on surface roughness of samples with a p-value of 0.343 but it was under clinically acceptable range. Conclusion: According to the present study, high translucency monolithic zirconia had greater colour stability when treated with citric acid, followed by tobacco and then with coffee media, whereas, zirconia in coffee media had greater surface roughness, followed by tobacco, and then with citric acid media. However, both the results were clinically acceptable, indicating a 10 year lifespan when properly glazed.

Highly‐durable hydrophobic and adhesive coatings fabricated from graphene‐grafted methacrylate copolymers

AbstractThe demand for highly‐durable protective coatings for use in extreme environments is continually growing, however, poor durability and adhesion restricted their practical applications. Herein, we prepared a novel solution‐processable graphene‐based copolymer for fabricating highly‐durable protective coatings. The random‐structured copolymer GO‐g‐(PMMA‐co‐PMPS) was prepared by graphene‐based initiator (GO‐g‐Cl) initiating methyl methacrylate (MMA) and 3‐methacryloxypropyltrimethoxysilane (MPS) via surface‐initiated atom transfer radical polymerization (SI‐ATRP). The copolymers rendered the coatings with high transmittance (~95%), high hydrophobicity (water contact angles = 113.8 ± 2.13°), and strong adhesion (1.26–1.38 MPa). Tetrahydrofuran (THF)‐casted coating surface presented a higher Si content and greater surface roughness than that cast from dimethyl carbonate (DMC), yielding more hydrophobic coating than those cast from DMC. The coatings could be coated on different substrates (glass, aluminum, and sandstone); and besides, the structures and performance of the coatings remained unchanged, even exposing to acid/alkali, salt, and ultraviolet light irradiation. These high‐performance properties make the GO‐based copolymers ideal candidates for fabricating high‐durability protective coatings.

The effect of phytosphingosine associated with tooth brushing on color change, surface roughness, and microhardness of dental enamel - an in vitro and in situ study.

This study evaluated the in vitro and in situ effects of phytosphingosine (PHS) associated with tooth brushing on color stability, surface roughness, and microhardness of dental enamel. Sixty-four specimens of bovine teeth (6 × 6 × 2mm) were separated into 8 groups (n = 8): S + TB: PHS (spray) + tooth brushing; TB + S: tooth brushing + PHS (spray); I + TB: PHS (immersion) + tooth brushing; TB + I: tooth brushing + PHS (immersion); TB: tooth brushing; S: PHS spray; I: immersion in PHS solution, and Saliva: immersion in saliva. Tooth brushing simulation (Mavtec, Brazil) was performed (356rpm on 3.8cm area by the toothbrush - Soft Tek) for 1, 7, 15, and 30days. PHS remained in contact with specimens for 15min. The specimens were evaluated before and after tooth brushing for color alteration (Easy Shade, VITA), and surface roughness (Model SJ-201P Mitutoyo), and Knoop microhardness (HMV-2, Shimadzu Corporation). For the in situ analyses, 8 participants were recruited and received an intraoral device with 6 fragments of bovine enamel (6 × 6 × 2mm). The properties evaluated were the same as those of the in vitro study. Participants were randomized following best results of in vitro tested protocols, for 15days: TB, TB + S, I + TB. Data obtained by in vitro (two-way ANOVA, Tukey, p < .05) and in situ (one-way ANOVA, Tukey, p < .05) studies were analyzed. The in vitro study showed that greater color change was found after 30days. The greatest differences in surface roughness occurred between the initial value and after 1day. Regarding microhardness, the highest values occurred after 15 and 30days, which showed similar results. The in situ study showed greater color changes for the TB and I + TB, and greater surface roughness changes for TB as well as a similar increase in microhardness for the PHS protocols, which were higher than TB. Phytosphingosine leads to an increase in performance regarding color stability, surface roughness, and microhardness when applied. In general, the application of PHS after brushing showed a positive impact on its performance. Phytosphingosine proved to be interesting for compound prevention formulations in the dentistry field.

Effect of different fibers on small-strain dynamic properties of microbially induced calcite precipitation–fiber combined reinforced calcareous sand

Microbially induced calcite precipitation (MICP)–fiber combined reinforcement through the addition of fibers during the MICP process is a novel, natural, and green technique for foundation improvement, which can effectively enhance the mechanical properties of cemented soil. However, the small-strain dynamic properties of this method remain unexplored. The effects of different polyester fiber and hemp fiber contents (0%, 0.1%, 0.2%, and 0.4%) on the dynamic properties of the MICP–fiber combined reinforced calcareous sand under small-strain conditions were studied using resonant column tests, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The maximum dynamic shear modulus of the MICP–fiber combined reinforced calcareous sand under small-strain increases with the fiber content; the stiffness degradation rate of the dynamic shear modulus ratio of the test sample increases with the addition of two types of fibers, and the addition of hemp fibers greatly boosts the increase rate of the damping ratio. The SEM results indicate that excessive fibers distributed between the sand particles occupy the nucleation sites of bacteria, hinder the bonding between sand particles, and ultimately affect the dynamic shear modulus parameters of the sample. The AFM results show that the hemp fiber has much greater surface roughness than the polyester fiber. Therefore, the change rate of the damping ratio of the hemp fiber-doped MICP–fiber combined reinforced calcareous sand is much greater than that of the polyester fiber-doped sample. This is the first report on the basic mechanism of the small-strain dynamic properties of the MICP–fiber combined reinforced calcareous sand with different fiber contents and types. Furthermore, it provides a new theoretical basis for related research on improving the dynamic properties of sand thus reinforced.

Improvement in Bending Strength of Silicon Nitride through Laser Peening.

This study aimed to improve the bending strength and reliability of ceramics using laser peening (LP). In the experiment, LP without coating (LPwC) and with coating (LPC) were applied to silicon nitride (Si3N4) under various conditions. The surface roughness, residual stress, and bending strength were then measured for the non-LP, LPwC, and LPC specimens. The results show that the LPwC specimen had a greater surface roughness but introduced larger and deeper compressive residual stress when compared with the non-LP and LPC specimens. In addition, the bending strength of the LPwC specimen was higher and scatter in bending strength was less compared with the non-LP and LPC specimens. This may be attributed to the transition of the fracture initiation point from the surface to the interior of the LPwC specimen because of the compressive residual stress introduced near the surface. Thus, it was demonstrated that the application of LP is effective in improving the strength and reliability of ceramics.