Silicate Coatings Research Articles

Plasma sprayed nano refractory coatings

Nano powders may be reconstituted into micron sized plasma sprayable powders either by using a spray drier or a manual process by employing organic binders to agglomerate them. This paper deals with the synthesis of nano sized alumino-silicate plasma sprayable powders and plasma sprayed coatings prepared from them. Nano sized raw materials involving kyanite and andalusite refractory powders were converted into plasma sprayable powders by using polyvinyl alcohol (PVA) binders. The preparation methodology involved obtaining free flowing, micron sized agglomerated nano –alumino-silicates particles which could be plasma spray coated by using an Atmospheric Spray Coating Facility. About 220 microns thick nano-alumino silicate coatings were deposited on 75 microns thick commercial NiCrAlY bond coat on stainless steel substrates. The challenges involved in plasma spray coating the nano material with low density was in obtaining good deposition efficiency, retaining the nano micro structures and the structural phase composition of the coating. The coatings were evaluated for materials characteristics such as crystal structural phase via XRD, microstructure via SEM and chemical composition via EDS. The microstructure depicted fine grained nano-sized surface morphologies, kyanite and andalusite phase structure, with high potential for application as refractory coatings.

Chemical Stability and Antimicrobial Activity of Plasma-Sprayed Cerium Oxide-Incorporated Calcium Silicate Coating in Dental Implants.

The aim of this study is to investigate the biological activity and antibacterial property of cerium oxide-incorporated calcium silicate coatings (CeO2-CS) in dental implants. In this study, MC3T3-E1 cells cultured on the plastic, Ti-6Al-4V, and the cerium oxide-incorporated calcium silicate coatings (CeO2-CS) coating served as the blank, control, and CeO2-CS groups, respectively. A cell counting kit-8 (CCK-8) and flow cytometry were used to evaluate the biocompatibility. The osteoblastic differentiation of the MC3T3-E1 cells was also analyzed by quantitative real-time polymerase chain reaction analysis. The CCK-8 and counts of colony-forming units (CFUs) were used to detect the antibacterial activity of the coating on Enterococcus faecalis. The study showed that the cerium oxide-incorporated calcium silicate coating (CeO2-CS) has better biocompatibility. Meanwhile, the ALP, OCN, and BSP mRNA expression levels in the CeO2-CS group were significantly upregulated (P < 0.05). The number of viable bacteria and the CFU results were significantly reduced in the CeO2-CS group (P < 0.05). The cerium oxide-incorporated calcium silicate coatings (CeO2-CS) may promote the osteoblastic differentiation of osteoblasts. Meanwhile, the cerium oxide-incorporated calcium silicate coating (CeO2-CS) showed strong antimicrobial activity on E. faecalis, with good biocompatibility.

Assessment of Antifouling Potential of Novel Transparent Sol Gel Coatings for Application in the Marine Environment.

In recent years, there has become a growing need for the development of antifouling technology for application in the marine environment. The accumulation of large quantities of biomass on these surfaces cause substantial economic burdens within the marine industry, or adversely impact the performance of sensor technologies. Here, we present a study of transparent coatings with potential for applications on sensors or devices with optical windows. The focus of the study is on the abundance and diversity of biofouling organisms that accumulate on glass panels coated with novel transparent or opaque organically modified silicate (ORMOSIL) coatings. The diatom assessment was used to determine the effectiveness of the coatings against biofouling. Test panels were deployed in a marine environment in Galway Bay for durations of nine and thirteen months to examine differences in biofilm formation in both microfouling and macrofouling conditions. The most effective coating is one which consists of precursor, tetraethyl orthosilicate (HC006) that has a water contact angle > 100, without significant roughness (43.52 nm). However, improved roughness and wettability of a second coating, diethoxydimethylsilane (DMDEOS), showed real promise in relation to macrofouling reduction.

Durability of Coatings Based on Sol Silicate Paint

The results of the study provide information on the resistance of coatings based on the solof silicate paint in the process of freezing and thawing. It was found, that coatings based on sol silicatepaints are characterized by a higher resistance compared of silicate coatings. It is shown, that thecoatings withstood 50 cycles of alternate freezing and thawing. The surface energy of the coatingswas calculated using the critical surface tension of the fluid at the interface with the solid. Thedispersion contribution in the intermolecular interaction between the particles of the coatings wasestimated. The values of the surface tension of the coatings and the values of the dispersioncomponent of the surface energy of the coatings — the complex Hamaker constant — are calculated.It was revealed, that after testing a decrease in the values of the Hamaker constant is observed. It wasestablished, that after testing for frost resistance, the values of the Hamaker constant for coatingsbased on sol of silicate paint are higher compared to coatings based on silicate paint.

Рецензии и отзиви: Рецензия на Учебник „Декоративни глазури – изкуство и технология“ от д-р инж. Васил Харизанов

This textbook is based on many years of practice, research and teaching work of the author in the field of decorative ceramic glazes. It is an original intersection of theory and artistic approach. It is a kind of manual, fully adapted to the needs of ceramists and designers of ceramic products. The theory of vitreous coating and the practice of creating decorative glazes is brought together. Both the basic properties of glaze melt and the variety of raw materials used in modern practice are presented as well as useful guidelines for the right choice of material and the technological process. Аn Information about the regimes of thermal treatment is also provided. The testing methods used in glaze production technology are included as well. Thanks to its scientific and practical orientation, the textbook can be used as a comprehensive methodological guide in the process of obtaining new glazing coatings or modifying existing ones. It is аdressed to students who are trained in the specialties “Design of Porcelain and Glass” and “Ceramics” at the National Academy of Art, as well as for all who are interested in the technology of vitreous silicate coatings.

Microscale distribution of trace elements: a methodology for accessing major bearing phases in stream sediments as applied to the Loire basin (France)

The threat of trace elements (TE) stored in sediments depends on total concentrations, their chemical form, and also on the type of TE–particle association and their resultant stability. The present study aimed at identifying the major TE-bearing phases in river sediments and quantifying their in situ concentrations once total concentrations of TE had been determined in order to understand potential TE mobility and ensuing environmental risk during early diagenesis mechanisms and the sediment cascade. Several TE-enriched layers of sediment cores were selected in a polymetallic-contaminated river basin (Loire basin, France). Selected samples were taken from up- and downstream areas far from sites of specific mining, or heavy industrial or urban activities. They thus represent non-site-dependent sediments which were not modulated or controlled by specific mineralogy or anthropogenic activities. Detailed microscale investigation techniques (SEM, EPMA, and μSXRD) were used to characterize directly the complex TE–solid phase association within river sediments. Despite Bi, Cd, and Hg representing the highest enrichment of the studied sediment layers, these elements were not detected at a microscale and only ubiquitous TE such as As, Cu, Pb, and Zn could be quantified on polished thin sections (EPMA quantification limit = 1000 mg kg−1, n = 111). Three mineralogical groups were evidenced by PCA, EPMA, and μSXRD data. (i) Fine-grained aggregates of aluminosilicates were frequently detected, appearing multiphased in organic matrices. They were mostly enriched with Zn and Pb without any As or Cu. (ii) (Mn, Ti)-rich Fe oxyhydroxides were predominantly SEM observed, either as isolated grains, silicate coatings, or included in aggregates. They represented the highest detected in situ concentrations for all the studied TE. And finally, (iii) Mn-rich particles were not frequently observed with SEM but when present were characterized by the highest TE concentrations. Phosphates, carbonates, and S-rich particles (sulfides and/or sulfates) were also determined by PCA as a potential mineralogical group. However, due to their very low TE concentrations and frequency, they could not be considered representative of a TE-bearing mineralogical group. This fine sorting classification, combining different techniques at the particle scale, was used to visualize and quantify complex mineralogy and particle associations of TE-bearing phases in river bed sediments under no specific mineralogical control. It represents an interesting approach to understand TE mobility during sediment cascade and post-depositional processes in sediments.

Selective extraction of aliphatic amines by functionalized mesoporous silica-coated solid phase microextraction Arrow

Mesoporous silica-coated solid phase microextraction (SPME) Arrow systems were developed for capturing of low-molecular-weight aliphatic amines (LMWAAs) from complicated sample matrices. Specifically, silicas of type MCM-41, SBA-15 and KIT-6 were chosen as substrates to afford size-exclusion selectivity. They possess ordered multidimensional pore-channel structures and mesopore sizes between 3.8 and 8.2 nm. Their surface acidity was enhanced by grafting them with a layer of titanium hydrogenphosphate (-TP). This enhanced the chemical selectivity for basic LMWAAs. The siliceous coatings increased the extraction of ethylamine, diethylamine (DEA) and triethylamine (TEA) by factors of 18.6–102.5, 4.8–10.8 and 2.6–4.0, respectively, when compared to the commercial SPME Arrow with polydimethylsiloxane/divinylbenzene coating. Among them, the MCM-41 and MCM-41-TP coated SPME Arrows demonstrated exceptional selectivity towards LMWAAs that were quantified by gas chromatography-mass spectrometry (GC-MS). The total peak area ratios of LMWAAs/ten competing compounds were 25.4 and 36.3, respectively. The extraction equilibrium was reached within 20–30 min. The MCM-41 and MCM-41-TP derived SPME Arrows gave very similar results (18.4 ± 2.1–376 ± 12 ng g−1 to DEA and TEA) when applied to urban mushroom samples. SPME Arrow with MCM-41 coatings followed by GC-MS was applied also to the analysis of atmospheric air and urine samples resulting in high selectivity due to the size and mesoporous structure of the functionalized silica, and its chemical interactions with the LMWAAs.Graphical abstractScheme of synthesis of the MCM-41 silicas, and the preparation of solid phase microextraction Arrow coatings. They were employed for selective capturing of aliphatic amines from complex sample matrices, followed by gas chromatography-mass spectrometry.

Revisiting aqueous alkaline silicates as precursors for sol‐gel optical coatings

AbstractAlkaline silicates are well‐known soluble silica derivatives already widely used for industrial purposes. Nevertheless, their applications for the elaboration of functional optical coatings have largely been discarded by the sol‐gel community who mainly focused on alkoxide precursors. The objective of this work is to reconsider the alkaline silicates sol‐gel chemistry, targeting optical coatings of a few hundreds of nanometers. The structures of Li+, Na+, and K+ silicate coatings are discussed on the basis of spectroscopic characterizations. We show that a simple washing process allows a postdeposition removal of most alkaline ions, thus preventing the efflorescence effect and improving the aqueous stability of the films. Finally, several examples are shown for the application of alkaline silicates in the elaboration of functional optical coatings following conventional sol‐gel chemistry.

POLYSILICATE BINDER FOR SILICATE PAINTS

Information is given on the structure and properties of a polysilicate binder obtained by mixing a silicic acid sol with a liquid glass. It was found that the introduction of a silicic acid sol in a liquid glass promotes an increase in the fraction of high-polymer fractions of silicic anions. An increase in the sol content promotes an increase in the fraction of high-polymer fractions of silicic anions. The results of the kinetics of the change in the silica content in the monomeric form in the potassium and sodium polysilicate solution are given. It was found that the dependence of the silica content in the monomeric form in the early stages of the interaction of the silicic acid sol with liquid glass is extremely extreme. It has been shown that when the potassium liquid glass is mixed with silica sol, the formation of silica in the monomeric form proceeds more slowly at the initial stage than in the sodium liquid glass. The results of studying the structure of polysilicate solutions by the method of violation of total internal reflection are presented. IR-spectroscopy revealed a shift in the band corresponding to Si-O-Si vibrations to the region of higher frequencies compared to liquid glass, which indicates a higher degree of polymerization of silica. The presence of silica in the polysilicate binder polymeric species is established, which ensures an increase in the stability of silicate coatings. Information on the properties of silicate composition with the use of polysilicate film-forming and coatings based on it is given. The composition is intended for interior and exterior walls of buildings.

Adhesion Behavior of Escherichia coli on Plasma-Sprayed Zn and Ag Co-incorporated Calcium Silicate Coatings with Varying Surface Roughness

Our previous work demonstrated the good biocompatibility and bactericidal activity of a plasma-sprayed Zn and Ag co-incorporated calcium silicate ceramic coating (Ag-Ca2ZnSi2O7), namely Ag-HT. In this work, we evaluated the influence of the surface roughness of Ag-HT coatings for Escherichia coli adhesion behavior, considering that surface topography is an important factor that regulates bacterial responses to biomaterials. Surface characteristics of as-sprayed and satin-finished Ag-HT coatings were investigated by scanning electron microscopy and measured using a surface roughness tester. Bacterial adhesion experiments showed that the number of viable E. coli cells on the as-sprayed or satin-finished coating surfaces was substantially lower than on the Ti-6Al-4V control surface, which can be explained by the antimicrobial effect of Ag and/or Zn. Moreover, the density of E. coli on the as-sprayed Ag-HT coating was considerably lower than on the satin-finished derivative. We attribute this difference to the fact that the as-sprayed coating surface was relatively smooth at a scale comparable to the size of an individual bacterium, while the satin-finished surface was slightly rough at this length scale and thus favored bacterial adhesion.

Improved osteogenesis of boron incorporated calcium silicate coatings via immunomodulatory effects.

Osteoimmunology has revealed the importance of a favorable immune response for successful biomaterial-mediated osteogenesis. Boron-incorporated calcium silicate (Ca11 Si4 B2 O22 , B-CS) coating has been reported as a potential candidate for improving osteogenesis in orthopedic applications in vitro. However, relatively little is known about its effects on the immune response and subsequent osteogenesis. In this work, the immunomodulatory properties of the B-CS coating and its specific mechanism of action were explored. We found that the B-CS coating decreased M1 polarization and converted macrophages to the M2 phenotype via restraining the toll-like receptor signaling pathway, thus inducing a significant reduction in pro-inflammatory cytokines and an increase in anti-inflammatory cytokines. Moreover, the B-CS coating inhibited osteoclastogenesis and osteoclastic activities by downregulating osteoclastogenic genes and inhibiting the RANKL/RANK system. BMP2 and VEGF were also significantly upregulated by macrophages and bone mesenchymal stem cells, leading to activation of the BMP2 signaling pathway and subsequent upregulation of osteogenesis-associated genes, finally promoting osteogenic differentiation. These findings show that the B-CS coating could be a promising coating material for hip and knee implants. Furthermore, incorporation of the element boron into bioceramic coatings could be a good strategy in the design of bone biomaterials with beneficial immune responses. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 12-24, 2019.

Exposing Sustainable Mortars with Nanosilica, Zinc Stearate, and Ethyl Silicate Coating to Sulfuric Acid Attack

Obtaining durable materials that lengthen the service life of constructions and thereby contribute to sustainability requires research into products that improve the durability of cementitious materials under aggressive conditions. This paper studies the effects of sulfuric acid exposure on four mortar types (control mortar, mortar with nanosilica, mortar with zinc stearate, and mortar with an ethyl silicate coating), and evaluates which of them have better performance against the acid attack. After 28 days of curing, the samples were exposed to a sulfuric acid attack by immersing them in a 3% w/w of H2SO4 solution. Physical changes (mass loss, ultrasonic pulse velocity, open porosity, and water absorption), and mechanical changes (compressive strength) were determined after the sulfuric acid exposure. A scanning electron microscope (SEM) was used to characterize the morphology of the surface mortars after the exposure. The control mortar had the highest compressive strength after the acid attack, although of the four types, the zinc stearate mortar showed the lowest percentage of strength loss. The zinc stearate mortar had the lowest mass loss after the acid exposure; moreover, it had the lowest capillary water absorption coefficient (demonstrating its hydrophobic effect) both in a non-aggressive environment and acid attack.

Easy functionalization process applied to develop super‐hydrophobic and oleophobic properties on ASTM 1200 aluminum surface

Super‐hydrophobic and oleophobic surfaces on ASTM 1200 H14 aluminum alloy substrates were achieved by chemical etching followed by deposition of organically modified silicate (ORMOSIL) coatings synthesized through sol‐gel method. The chemical etching using FHH solutions (FeCl3 + HCl + H2O2) was adapted for the studied aluminum alloy by varying the concentration of iron (III) chloride and the etching time in order to increase the surface roughness of the material. This chemical etching produces rough surfaces exhibiting superficial square pores with edges about 1 to 2 μm. The chemical modifications with ORMOSIL solutions based on 1H,1H,2H,2H‐perfluorooctyltriethoxysilane (PFOTES) and hexadecyltrimethoxysilane sol‐gel precursors induced water contact angles about 154° and 150°, respectively, and sliding angles smaller than 5°, on the previously optimized etched surface. Moreover, the surface modification with ORMOSIL based on PFOTES reached also an oleophobic character with an oil contact angle about 136° due to air entrapment in the surface roughness at the oil‐aluminum interface. Finally, ORMOSIL coatings produced with varied concentrations of PFOTES and tetraethoxyorthosilane precursors proved that the super‐hydrophobic and oleophobic properties can be maintained with an important decrease of the PFOTES precursor, which should significantly decrease the cost production of such functional surfaces and could favour its mechanical durability.

Phase evolution of reactive sputtering synthesized holmium silicate coatings

AbstractHolmium silicates are promising environmental barrier coatings (EBCs) materials for Si‐based non‐oxide ceramics due to their excellent thermal and mechanical properties. In the present work, the phase evolution of holmium silicate coatings synthesized by reactive sputtering was systematically studied. The monosilicate crystallized in an X1‐Ho2SiO5 phase at 1000°C and transformed to an X2‐Ho2SiO5 phase at 1200°C. The phase transition is not problematic for the coating process because the X1‐ and X2‐Ho2SiO5 phases have similar coefficients of thermal expansion (CTEs). For the holmium disilicates, the stoichiometry obviously influenced polymorphic phase evolutions. Relatively Ho2O3‐rich compounds promoted the formation of γ‐Ho2Si2O7 phase at lower temperatures. This study on phase evolution vs temperature and stoichiometry can provide a guideline to optimize the processing and the properties of advanced holmium silicate EBCs.

Influence of phase composition on thermal aging behavior of plasma sprayed ytterbium silicate coatings

In this study, ytterbium silicate coatings with different phase compositions were designed by controlling Yb2O3/SiO2 ratio and fabricated by atmospheric plasma spray (APS) technique. Thermal aging behaviors such as microstructure evolution and thermomechanical properties were focused, and the influence of phase composition was analyzed. Results showed that obvious grain growth and defect reduction occurred, and the thermomechanical properties were significantly modified after thermal aging. The larger reduction in defects and greater increase in elastic modulus, Vickers hardness and coefficient of thermal expansion took place in the Yb2O3-rich coatings containing Yb2O3 and Yb2SiO5 phases. The bigger grains and transgranular cracks were formed and the greater increase in thermal conductivity took place in the SiO2-rich coatings containing Yb2SiO5 and Yb2Si2O7 phases. The relationship among microstructure evolution and variation of thermomechanical properties was analyzed. The results of this study may provide a reference for design and application of rare-earth silicates as environmental barrier coatings (EBCs).

Low infrared emissivity of the Cr39Ni7C/inorganic silicate coatings with excellent heat-resistant

Low infrared emissivity coatings with good heat-resistant property are prepared by using Cr39Ni7C powders and inorganic silicate as filler and binder, respectively. The effects of ball-milling time and heating temperatures on both the microstructure and crystallinity of Cr39Ni7C powders as well as the infrared emissivity of the coatings are detailedly explored. The results show that large spherical Cr39Ni7C particles change into smaller flakey particles gradually with ball-milling time extending to 70 h. Meanwhile, crystallinity of Cr39Ni7C powders enhances with temperature increasing from 300 °C to 700 °C. Contributed by the small flakey particles and enhanced crystallinity, the Cr39Ni7C coating could possess low emissivity value of 0.59 at room temperature, and it further reduces to 0.55 with the temperature rising up to 600 °C. Additionally, good thermal stability is obtained due to the SiOSi space network structure and the SiOM bonding between the coatings and substrates.

Influence of phase composition on microstructure and thermal properties of ytterbium silicate coatings deposited by atmospheric plasma spray

In this study, ytterbium silicate coatings with different compositions were designed by controlling the Yb2O3/ SiO2 ratio and fabricated by atmospheric plasma spray. The microstructure and thermal properties of these coatings were characterized. Results showed that the Yb2O3-rich coatings contained Yb2O3 and Yb2SiO5 phases, which were characterized by Yb2O3 columnar grains, obvious interfaces between splats and many microcracks. The SiO2-rich coatings were composed of Yb2SiO5 and Yb2Si2O7 phases, which were composed of well bonded splats with many spherical pores. The Yb2O3-rich coatings had higher coefficient of thermal expansion values and lower thermal conductivities than the SiO2-rich coatings. The SiO2-rich coatings presented much better thermal cycling resistance than the Yb2O3-rich coatings. The relationship among phase composition, microstructure and thermal properties of ytterbium silicate coatings was analyzed. The results of this study may provide some clues for designs and applications of rare-earth silicates as environmental barrier coatings.

Sol-infiltrated multilayer SiC/yttrium silicate coatings for imparting enhanced oxidation resistance to C-SiC composites

Yttrium silicate coatings are applied on C-SiC composites for advanced aerospace structural applications at high temperatures. The Air Plasma Spray (APS) method is widely used for the deposition of yttrium silicate coatings. However, the oxidation resistance offered by the APS-deposited coating is limited by the inherent porosity and micro-cracks in the coating. The present study demonstrates the effective sealing of the pores and micro-cracks in the APS coating by impregnation with yttrium silicate sol followed by sintering at 1400 °C. The cyclic oxidation behavior is comparatively assessed at 1300 and 1500 °C in air for the C-SiC composite samples applied with multilayer coatings comprising combinations of CVD SiC/APS yttrium silicate/sol infiltrated yttrium silicate coatings. The lone SiC coated and the SiC/APS yttrium silicate coated samples exhibited rapid decrease in weight. On the contrary, the SiC/APS coated samples infiltrated with yttrium silicate sol exhibited significantly improved oxidation resistance. The weight loss during oxidation was prevented after infiltration of the yttrium silicate sol at a higher vacuum level of 1 mbar, which effected in better healing of the pores in the APS coating and formation of a dense yttrium silicate scale on the surface.

A performance comparison of protective silicate-coated lead and non-coated lead electrodes in various kind electrolytes of gel valve-regulated lead-acid battery

A novel silicate-based protective film was formed on negative electrodes and compared of the performance in various electrolyte systems of lead-acid batteries. The sodium silicate-based coating for the negative electrode component of a gel valve-regulated lead-acid (gel-VRLA) battery was applied for the first time in the literature. The battery system was produced by sodium silicate-coated negative electrodes and lead oxide positive electrodes in various kinds of electrolyte. Electrochemical characterization of cells and battery prototypes were done by cyclic voltammetric (CV) analysis, electrochemical impedance spectroscopic (EIS) analysis, and cyclic charge-discharge tests. The surface morphologies of silicate-coated electrodes were investigated by scanning electron microscopic analysis after cyclic voltammetric analysis and charge-discharge tests. The coating of silicate on the surface of negative electrodes increased the corrosion resistance of a VRLA battery according to the Tafel polarization curves. Indeed, sulfation on the negative electrode component of the battery have significantly reduced with silicate coatings of them. Besides, the prepared novel silicate-based protective film have increased the battery performance of a VRLA. Silicate-based coatings for electrodes can be used for industrial battery production for many different battery types due to their amazing anti-corrosion properties in acidic media.

Fire-proof silicate coatings with magnesium-containing fire retardant

A formula for an environmentally friendly and safe fire-proof paint was developed based on a potassium silicate aqueous solution with addition of a magnesium-containing fire retardant. The predominant use in paint of magnesium-containing fire retardant such as hydromagnesite compared to brucite and magnesite was demonstrated. It was established that a paint containing 5.5 wt% of hydromagnesite provides the first group of fire resistance for a wooden surface. The high fire resistance of the paint with this formula is proven by the high intumescence ratio (150%) and low weight losses (8.4%) after tests in a ceramic tube. When the paint is heated, a gradual loss of weight is detected, which is related to the characteristics of the hydromagnesite structure and helps to obtain an effectively foamed protective layer that prevents the diffusion of combustible gases and flame.