Mechanism Of Surface Modification Research Articles

Influence of multiple laser impacts on thin leading edges of turbine blade

Laser shock peening is a mechanical surface improvement treatment used to enhance the fatigue life of critical components. This paper investigates the influence of multiple square laser impacts to study their special effect on the diverse mechanical behaviours of the thin leading edge surface of turbine blades. Most works existing in the literature have presented experimental investigations. The originality of our paper is to validate and numerically simulate the proposed model. Indeed, a 3D finite element method of a thin leading edge specimen, Ti–6Al–4V, of a turbine blade is numerically simulated using the ABAQUS software. The mechanical surface modifications (residual stresses, equivalent plastic strains and Johnson–Cook superficial damage) induced by the multiple square laser impact are examined in detail. The main purpose of this investigation is to determine the effects of single-sided and double-sided laser shock peening.

Characterization of surface modification mechanisms for boron nitride films under plasma exposure

The surface modification of a boron nitride (BN) film by plasma exposure was investigated by means of nanoindentation analyses and molecular dynamics simulations. A μm-thick BN film composed of nanoscale sp3-bonded phases in the turbostratic (sp2-bonded) BN domain was prepared on a Si substrate using a reactive plasma-assisted coating system. Then, the BN films were exposed to an inductively coupled Ar plasma under various bias power conditions. The change of the morphology and mechanical properties in the surface region due to the plasma exposure was evaluated with respect to the dependence on the energy of incident Ar ions (Eion). A nanoindentation test under various contact depths identified the formation of a surface plasma-damaged layer (a few nm thick) where the nanoindentation hardness (HIT) was changed in response to the Ar ion irradiation. A molecular dynamics (MD) simulation predicted also the Eion-dependence of the reconstruction of the sp3-bonded phases in a few nm-thick layer on the surface. The presence of a damaged-layer plays an important role in the mechanical properties of the BN/Si structures.

Electro-optical performance of liquid crystal device based on Al-doped SnO fabricated by sol-gel process

ABSTRACTWe demonstrated uniform LC alignment on IB-irradiated aluminium tin oxide (AlSnO) by controlling the annealing temperature. Physico-chemical analyses were carried out to determine the surface modification and uniform LC alignment mechanism as a function of the annealing temperature. IB irradiation induced the breakdown of the chemical bonds of AlSnO, preserving its anisotropic characteristics along the direction of IB irradiation, allowing for uniform alignment of the LC molecules on the reformed surface. However, at annealing temperatures under the boiling point of the solvent, residual solvent remained on the surface, thereby prohibiting uniform LC alignment. Moreover, we obtained good optical transmittance in the visual region and good electro-optical performance. Therefore, the IB-irradiated AlSnO film annealed above 200°C exhibited good potential as an alternative candidate for LC display applications.

Surface modified mechanism of activated carbon fibers by thermal chemical vapor deposition and nitrate adsorption characteristics in aqueous solution

In this study, commercial activated carbon fibers (ACFs) KF1500 was modified by thermal chemical vapor deposition (CVD) method using acetonitrile and steam to adsorb nitrate ions in aqueous solution. Physical properties and surface chemical characteristics of each modified ACF were examined to reveal the surface modification mechanism of modified ACFs. Adsorption kinetics and influence of solution pH were also examined to investigate the adsorption properties. The sample of KF-8ST10-8AN20-9.5HT30-8ST30 showed maximal nitrate adsorption capacity of 0.74 mmol/g at solution pH 3, and surface area was calculated to be 1358 m2/g and 1483 m2/g by Brunauer-Emmett-Teller (BET) method and subtracting pore effect (SPE) method using αs plots, respectively. By means of modification, the quaternary N (or graphitic N) (N–Q) configuration, which is a strong site to adsorb nitrate ion, represented nearly 5 times greater value than that of KF1500. The N–Q configuration reached up to 1.86% in total elemental composition from 0.4% of KF1500. The adsorptive kinetic data of KF-8ST10-8AN20-9.5HT30-8ST30 ACFs were highly well described with pseudo-second-order (R2 = 0.998) model. The adsorption capacity of nitrate decreased rapidly with the increase of the alkalinity in nitrate solution, which indicated that hydroxyl groups rather than nitrate ions in the aqueous solution were more attractive and competitive to the N-Q and other adsorptive sites on the surface of ACFs.

Extrinsic Fe3+ Stabilized La1-XSrxCoO3-δ Thin Film Cathode for Enhanced Electrochemical Performance

Perovskite-based La0.6Sr0.4CoO3-δ (LSC) is considered as one of the most promising electrode materials for solid oxide fuel cells (SOFCs). The broad application is, however hindered by its insufficient stability and reactivity at operating conditions. In this study, extrinsic Fe3+ decoration was applied to enhance the electrochemical performance of LSC thin-film electrodes by nearly 4 times. Time-of-flight secondary ion mass spectrometry indicated that the extrinsic Fe3+ can incorporate into LSC lattice and form a thermodynamically preferred (La, Sr)x(Co, Fe)yO3-δ transition phase in the near surface region, thus improving its chemical stability against Sr segregation. X-ray photoelectron spectroscopy suggested the incorporation of Fe can lead to a ~0.2 eV downshift in LSC valance band and facilitate the formation of oxygen vacancies, thus enhancing electrode reactivity. These results can help us understand the mechanism of surface modification, and provide guidance for the rational design of more applicable SOFC electrode materials with higher reactivity and durability.

Titanium surface modifications and their soft-tissue interface on nonkeratinized soft tissues-A systematic review (Review).

In this systematic review, the authors explored the surface aspects of various titanium (Ti) or Ti alloy medical implants, examining the interface formed between the implant and surrounding nonkeratinized soft tissues (periosteum, muscles, tendons, fat, cicatrix, or dura mater). A comprehensive search undertaken in July 2019 used strict keywords in relevant electronic databases to identify relevant studies. Based on the authors' inclusion criteria (restricted to in vivo studies), 19 of 651 publications qualified, all pertaining to animal models. The syrcle's risk of bias tool for animal studies was applied at study level. Given the broad nature of the reported results and the many different parameters measured, the articles under scrutiny were assigned to five research subgroups according to their surface modification types: mechanical surface modifications, oxidative processes (e.g., acid etching, anodization, microarc oxidation), sol-gel derived titania (TiO2) coatings, biofunctionalized surfaces, and a subgroup for other modifications. The primary outcome was a liquid space at the interface (e.g., seroma formation) that was reported in six studies. Machining Ti implants to a roughness between Ra = 0.5 and 1.0 μm was shown to induce soft-tissue adhesion. Smoother surfaces, with the exception of acid polished and anodized Ti (Ra = 0.2 μm), prevented soft-tissue adhesion. A fibroblast growth factor 2 apatite composite coating promoted soft-tissue attachment via Sharpey-like fibers. In theory, this implant-soft tissue interface could be nearly perfect.

The Role of Surface Coatings on the Strain Evolution in Li-Ion Cathode Electrodes during Electrochemical Cycling

Rechargeable Li-ion batteries (LIBs) have been successfully commercialized for portable electronics in the last two decades. Although there has been a great interest to use LIBs in more demanding applications such as electric vehicles, adoption of LIBs has been hindered by capacity loss and poor performance. The current stage of the cathode performance is a limiting factor for the development of higher performance LIBs. Cathode electrodes suffer from significant capacity fade with cycling due to continuous volumetric changes, unstable cathode-electrolyte interface and active material dissolution. Lithium intercalation induces considerable volumetric changes in the electrode and even small strain can cause particle fractures in brittle cathode materials. Surface modification of the cathode electrodes has been used to improve the capacity retention and cycling stability of the electrodes at higher charge/discharge rates by minimizing active material dissolution and stabilizing the electrode-electrolyte surface layer. Although various surface modification techniques were utilized to improve the performance of the electrodes, the underlying mechanism of surface modification has not been elucidated yet. In this work, we investigated the role of surface coatings on the strain generation in lithium manganese oxide (LMO) composite electrodes. Full-field strain measurements based on digital image correlation (DIC) is carried out to measure strain evolution in LMO electrodes1. Scalable electrolysis deposition method was performed to coat LMO particles with Au shell2. LMO composite electrodes were fabricated with a composition of 8:1:1 weight ratio of LMO, carboxymethyl cellulose binder and carbon black. Electrodes were cycled with cyclic voltammetry technique at different scan rates (between 10 and 100μV/s). As expected, composite electrodes expanded during delithiation when lithium is inserted into the electrode and contacted during lithiation when lithium is removed. Capacity was calculated to understand relationship between strain evolution with amount of lithium ions in the electrode at a given scan rate. Interestingly, The LMO electrode without coating undergoes larger strain generation at higher scan rates compared to LMO electrode with surface coatings. Volumetric expansion of LMO (without coating) electrode changes dramatically depending on scan rate whereas strain evolution in the gold-coated LMO electrode is primarily function of capacity, regardless of scan rate. The role of the surface coatings on the mechanical and electrochemical performance of the LMO electrodes will be discussed. References Ö. Ö. Çapraz, S. Rajput, S. White, and N. R. Sottos, Exp Mech, 15, 1182–11 (2018).J. L. Esbenshade, M. D. Fox, and A. A. Gewirth, J. Electrochem. Soc., 162 (1), A26 (2015). Acknowledgement This work was supported as part of the Center for Electrochemical Energy Science (CEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.”

Flotation of a Low-Grade Zinc Oxide Ore After Surface Modification at High Temperature

There are abundant low-grade zinc oxide ores in Yunnan Province, China, but it is extremely difficult to recover Zn and Pb from them using traditional technology. They are often stockpiled during the exploitation of sulfide ores and high-grade zinc oxide ores and become a kind of solid waste. In this study, a novel methodology using surface modification by sulfidation and reduction at high temperature followed by flotation is proposed. Several factors, such as the sulfur dosage, roasting temperature, coal powder dosage and holding time, that affect the flotation performance of the Zn concentrate were examined in detail, and the optimum process parameters were determined. A flotation concentrate containing 32.1% Zn and 8.0% Pb was obtained with zinc and lead recoveries of 91.3% and 92.3%, respectively. To further interpret the surface modification mechanism of smithsonite, the surface morphology and constituents of the sample before and after reaction were investigated by electron probe microanalysis and thermodynamic calculations. The results showed that zinc sulfide was generated at the outer layer of the zinc oxide mineral after thermal modification, resulting in an improvement of the flotation performance. The purpose of the present study is to apply the surface modification technology previously applied to pure smithsonite to low-grade zinc oxide ore or solid waste to convert them into valuable resources.

Optical measurement of surface topographies with transparent coatings

Manufacturers nowadays have access to state-of-the-art areal surface topography measurement instruments that allow investigation of surface topography at unprecedented levels of detail and over a wide range of scales. However, high value-added products have demanding requirements, pushing measurement technologies to their limits. Therefore, a deeper insight and more comprehensive understanding of performance and behaviour of current areal surface topography measurement solutions is often needed. In this work, we investigate and compare the results when measuring the same surface with different, state-of-the-art areal surface topography measurement solutions involving the principal optical technologies, notably focus variation microscopy, coherence scanning interferometry, imaging confocal microscopy and point autofocus instrument, operated using different set-ups. The test case is a highly engineered surface obtained through a sequence of mechanical and chemical surface modification processes. The surface has complex topographic formations at micrometre and sub-micrometre scales, and is characterised by the presence of a thin transparent layer, notoriously challenging for optical measurement. The topographies reconstructed from measurement are compared both in terms of visual appearance and texture parameters.

Surface modification mechanism of aramid fiber by AACH nanowire recasting and its enhanced modification of TPU

In order to improve the interfacial adhesion with matrix resin, the surface of aramid fibers was recast by surface growth of NH4[Al(OOH)HCO3] (AACH) nanowires. The morphology of aramid fibers before and after treatment was observed by scanning electron microscopy. The infrared and thermal stability of the fibers were tested and the mechanism of surface modification reaction was speculated. The effect of recasting modification on the mechanical properties and thermal stability of TPU resin was further studied. The results show that the roughness of aramid fibers increases obviously after surface recasting, but the thermal stability decreases and the thermal decomposition temperature decreases from 560 °C to 480 °C. At the same time, the interfacial state between surface recasted aramid fibers and TPU resin matrix was significantly improved and the mechanical properties of the composites were further improved. Compared with pure TPU resin, the tensile strength and modulus of the composites increased as 34.3% and 384.0%, respectively, but the elongation at break decreased from 1180.0% to 787.0%.

A Mechanistic Study of Surfactants, Particles, and Polymers on Foam Stabilization

Foam stabilization by mixtures of Bentonite, Xanthan Gum (XG) as stabilizers, and surfactants such as Sodium Dodecyl Sulfate (SDS) and Hexadecyltrimethyl Bromide (CTAB) were mechanistically investigated. Surface modification, adsorption properties and foaming characteristics of both surfactants were compared. Both possess dissimilar surface modification mechanisms namely the hydrophobic interaction mechanism for SDS and ion-pair mechanisms for CTAB. SDS generates foam of 21 % longer half-life and 17 % better foamability as compared to CTAB. Both Bentonite-stabilized and XG-stabilized SDS foam showed improvement of half-life of up to 10000 folds and 50000 folds. A reduction in foamability of up to 24% and 40% for Bentonite and XG respectively were observed. With increasing stabilizers concentration, viscosities across different shear rates and the elastic moduli (G’) across different frequencies increase due to the increasing particles adsorption density on the air/water interface. Bentonite acts as a better synergist to SDS in foam formation as it has less viscosifying tendencies as compared to XG. It is also able to sufficiently improve SDS foam properties.

Morphology and Surface Chemistry of Gas-Wetting Nanoparticles and Their Effect on the Liquid Menisci in Porous Media

The transformation of the liquid menisci at pore throats is of great importance for mitigating the liquid-blocking of condensate reservoirs. Here, we reported a super gas-wetting peanut-like nanoparticle which can facilitate the liquid menisci to transform from concave shape to convex shape by coating a super gas-wetting adsorption with high surface roughness. The morphology and surface chemistry of gas-wetting nanoparticles were investigated by SEM, AFM, and XPS analysis. The mechanism of surface modification was further explored by TEM; the adsorption layer coated on the nanoparticle surface can be recognized as monolayer absorption. The gas-wetting model is recommended as the combination of the Wenzel model and Cassie-Baxter model, which is in close agreement with the results of AFM and contact-angle measurements. Core flooding visualization was performed to identify the of gas-wetting alteration on the transformation of liquid menisci in porous media. Results showed that the addition of gas-wetting nanoparticles could decrease the liquid saturations by inducing the transformation of liquid menisci in the pore throat. Additionally, a unique amoeba effect and miscibility can synergistically improve the mobility of the oil phase, further enhancing the oil recovery.

Research of Bioproof Materials at Superficial Modification of Wood

The mechanism and conditions of surface modification of wood by phosphorous-containing and siliceous organic compounds have been studied. Wood has the ability to absorb moisture from the air, and the moisture content of wood produces a significant effect on the physical and mechanical properties of wood. Traditional water-repellent agents of lignocellulosic materials are Organic Silicon Compounds (OSC). Our research is aimed at developing a “soft” silylation technology, in which the degree of chemical modification is negligible, and the content of chemically bound Si amounts to ~ 1%. As silylating agents, alkylhydride siloxanes, alkoxysilanes were used. From alkylhydride siloxanes, polyethylhydride siloxane (PEHS) and polymethylhydride siloxane (PMS) with different n-polymerization degrees were used. Activating hydrophilic additives were ammonium fluoride, potassium fluoride and titanates. The treatment of wood with salts, with the subsequent treatment with OSCs facilitated the penetration of OSCs into the wood while the processes of “soft” silylation proceeded. “Soft” silylation of wood with polyalkylhydride siloxanes proceeds in the presence of catalyst additives, the degree of silylation is low and depends on the nature of the additives. The dependence of distribution of OSCs in the wood on the nature of the additives is evidenced by the method of scanning electron microscopy. Phosphorous-containing organic compounds (FOC) have a high penetrating ability, while completely filling the intercellular structure of the wood. With the sequential impregnation of the wood with FOCs and OSCs, organic silicon compounds enter the intercellular space of the wood, with dense spongy OSC deposits, which in some places completely fill the internal cavities of cellular tubes of the wood. As FOC, for example, a 40% solution of trichloroethylphosphate (TCEP) was used. Decaying of wood over time starts from the surface, since there are no diffusive limitations in the sorption process. Surface modification of wood can increase its durability due to increased biological stability and hydrophobic behaviour, which will ensure a long-lasting protection. Long-lasting protection is due to the formation of covalent bonds of wood (cellulose) with a modifier. Wood samples after surface “soft” modification with FOCs and OSCs were tested for hydrophobic behaviour and biological stability. The samples were tested in the climate chamber with irrigation of the samples with water in a mode of -30°C to +40°C. To determine the hydrophobic behaviour, the limiting wetting angle was determined. The biological stability was determined by the growth of testing cultures of the fungi Aspergillus, Penicillium, Trihoderma and some others according to GOST 9.048-89. The amount of the data obtained allows to make a conclusion about the nondurable decrease in water absorption capacity during surface modification of wood with OSCs. Long-lasting biological and water resistance is achieved only in cases when surface application of OSCs is carried out on the pre-phosphorylated wood. Phosphorylation thus leads to the formation of covalent bonds. The compounds developed were successfully used for 10-15 years to preserve the monuments both of wooden architecture and the buildings and structures made of stone, bricks, and concrete.

Insights into the modification for improving the surface property of calcium sulfate whisker: Experimental and DFT simulation study

In order to improve the compatibility and dispersion of anhydrous calcium sulfate whiskers (ACSW) in polymer composites, the treatment for surface modification was studied with aqueous solution sodium stearate (SS, C17H35COONa) at hot temperature. The surface modification mechanism between stearate and ACSW was carried out by experimental and density functional theory (DFT) simulation. The surface property of modified anhydrous calcium sulfate whiskers (M-ACSW) became hydrophobic by changing the water contact angle with the calcium sulfate whisker (CSW) from 0° to 132°. The TEM and TG results proved the adsorption of stearate on M-ACSW surface, which was further confirmed by FTIR and XPS. The experimental and DFT simulation outcomes for the mechanism were interpreted by taking the reaction of the carboxyl group of stearate with Ca2+ ions to form calcium stearate on the whisker surface. Their long alkyl chains of stearate coated on the surface of whisker made ACSW improve the surface with a hydrophobic property. Thus, here it is provided details of a novel method of modifier selection for CSW and its interaction mechanism with the crystal surface.

Tool Wear Reduction Effect of Oil-Immersion Treatment and its Surface Modification Mechanism

This study describes a new surface treatment method that involves immersing sintered cutting tools into a high-pressure, high-temperature processing liquid. Cutting experiments were performed, and the results show that oil-immersion treatment helps reduce tool wear. However, this treatment limits the applications of treated carbide tools, e.g., they become unsuitable for heavy-cutting conditions. After the cutting test, surface analyses of the treated carbide tools were performed using FT-IR, SEM, EPMA, and XPS to verify the effect of oil-immersion treatment on tool-wear reduction. FT-IR analysis showed that, following oil-immersion treatment, trace quantities of the coolant remained on the tool surface, which could be readily removed by ultrasonic cleaning. Despite the removal of the processing liquid, the tool subjected to oil immersion exhibited less wear than the non-treated tool. SEM and EPMA examinations revealed that oil-immersion treatment reduced the amount of cobalt on the tool surface, forming sulfur deposits. EPMA analysis indicated that less cobalt binder was found on the surface after oil-immersion treatment, suggesting that the reduction in the amount of cobalt caused tungsten carbide particles to be exposed.

Optimization of the stream finishing process for mechanical surface treatment by numerical and experimental process analysis

The stream finishing process represents an efficient mass finishing process capable in mechanical surface modification. In order to generate a deeper understanding of the cause-effect relationships, normal forces, material removal and surface topography were analyzed and correlated for varied process parameters of disc-shaped AISI 4140 specimens. Local resolution of tangential velocities of the particles and normal forces on the workpiece’s surface were simulated using the discrete element method for defined process parameter configurations and were correlated with experimental results. A deep process understanding is accomplished enabling the process design for efficient surface smoothing and improved residual stress depth distribution.

Ultrafast dynamics and subwavelength periodic structure formation following irradiation of GaAs with femtosecond laser pulses

A theoretical investigation of the ultrafast processes and dynamics of the excited carriers upon irradiation of GaAs with femtosecond (fs) pulsed lasers is performed in conditions that induce material damage and eventually surface modification of the heated solid. A parametric study is followed to correlate the produced transient carrier density with the damage threshold for various pulse duration values {\tau}p (it increases as ~ at relatively small values of {\tau}p while it drops for pulse durations of the order of some picoseconds) based on the investigation of the fundamental multiscale physical processes following fs-laser irradiation. Moreover, fluence values for which the originally semiconducting material demonstrates a metallic behaviour are estimated. It is shown that a sufficient number of carriers in the conduction band are produced to excite Surface Plasmon (SP) waves that upon coupling with the incident beam and a fluid-based surface modification mechanism lead to the formation of sub-wavelength periodic structures orientated perpendicularly to the laser beam polarization. Experimental results for the damage threshold and the frequencies of induced periodic structures show a good agreement with the theoretical predictions.

Evaluation of Chemical Mechanical Polishing-Based Surface Modification on 3D Dental Implants Compared to Alternative Methods

Chemical mechanical polishing (CMP) has been introduced in previous studies as a synergistic technique to modify the surface chemistry and topography of titanium-based implants to control their biocompatibility. In this study, the effectiveness of CMP implementation on titanium-based implant surface modification was compared to machined implants, such as baseline and etching and biphasic calcium phosphate (BCP) particle-based sand blasting treatments, in terms of the surface chemical and mechanical performance. Initially, a lab-scale 3D CMP technique was developed and optimized on commercial dental implant samples. The mechanical competitiveness of the dental implants treated with the selected methods was examined with the Vickers microhardness test as well as pull-out force and removal torque force measurements. Furthermore, the surface structures were quantified through evaluation of the arithmetic mean roughness parameter (Ra). Subsequently, the surface chemistry changes on the treated implants were studied as wettability by contact angle measurement, and surface passivation was evaluated through electrochemical methods. In each evaluation, the CMP treated samples were observed to perform equal or better than the baseline machined implants as well as the current method of choice, the BCP treatment. The ability to control the surface topography and chemistry simultaneously by the use of CMP technique is believed to be the motivation for its adaptation for the modification of implant surfaces in the near future.

Enhanced piezoelectric output of the PVDF-TrFE/ZnO flexible piezoelectric nanogenerator by surface modification

In this paper, ZnO nano-particles (NPs) were modified by adding a dispersant (n-propylamine, PA) and a silane coupling agent (1H, 2H, 1H, 2H, Perfluorooctyltriethylsilane, PFOES) simultaneously. Further, the PVDF-TrFE/modified ZnO composite films with high crystallinity and large specific surface area were prepared, which acted as the active layer of the piezoelectric nanogenerator (PENG). Four species of films, pure PVDF-TrFE, PVDF-TrFE/ZnO, PVDF-TrFE/ZnO@PA and PVDF-TrFE/ZnO@PA@PFOES were marked P-0-0-0, P-Z-0-0, P-Z-P-0 and P-Z-P-P, respectively. The crystalline phases of the films were determined by Fourier infrared spectroscopy (FT-IR) and wide-angle X-ray diffraction (WXRD). Scanning electron microscope (SEM), Laser scanning confocal microscope (LSCM), Atomic force microscope (AFM) and water contact angle (WCA) measurements were employed to analyze the surface morphology of the films. The thermal properties of the materials were characterized with a differential scanning calorimeter (DSC). From the FTIR spectra and WXRD pattern, it was notable that the modified ZnO NPs promoted the crystallization of β-phase. The results showed that the crystallinity of P-Z-P-P was increased by 36.12% compared to P-0-0-0. Combined with the results of SEM, LSCM and AFM, it can be concluded from WCA that modified ZnO NPs can increase the specific surface area of the film. The piezoelectric strain constant d33 value of P-Z-P-P film was 73.5% higher than that of P-0-0-0 film, and the output voltage value of ITO/P-Z-P-P/Au PENG increased 24.4% than that of ITO/P-0-0-0/Au PENG. After 1000 cycles of testing, the output voltage of the ITO/P-Z-P-P/Au PENG has been maintained at 2.40 V, indicating that the generator exhibited the high mechanical endurance. By clarifying the mechanism of surface modification, it can be concluded that enhanced piezoelectric output of the PENG is contributed to both higher β-phase content and larger charge collecting area by surface modification.

Inhibiting efflorescence formation on fly ash–based geopolymer via silane surface modification

Efflorescence can be a critical issue for the application of alkali-activated fly ash–based geopolymer products, especially when the products are in a moist environment. In this study, a new method was explored to inhibit efflorescence of fly ash–based geopolymer via silane surface modifications. After the modification, the surface of the geopolymer was transformed from hydrophilic to hydrophobic, with a water contact angle of 144.1°, and the capillary absorption and diffusion of water were significantly suppressed; and as a consequence, the soluble alkali ion leaching was reduced. Analysis by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and size-exclusion chromatography demonstrated that the selected silane is attached successfully onto the surface of the fly ash–based geopolymer via chemical bonding instead of via physical absorption. A possible reaction mechanism for the silane surface modification of the fly ash–based geopolymer is proposed.