Fluoride Etchants Research Articles

Facile synthesis of MXene from MAX phase via Hydrothermal method using a mild etchant

The present study explains an effective and efficient synthesis of MXene (Ti3C2TX) from MAX phase (Ti3AlC2) via hydrothermal method in presence of a mild etchant that is an affordable, safe, easy to handle and environmentally friendly approach. The successful synthesis of MXene from MAX phase was explained on the basis of shifting of (002) plane towards lower angle with significantly enhancement in the corresponding FWHM of the peak, which demonstrates the enhanced interlayer spacing of MXene sheets. The lower intensity of peak corresponding to (104) plane shows removal of aluminum layer from MAX phase with a very small quantity of aluminum content as analyzed from X-ray diffractogram and EDS spectrum. The enhanced interlayer spacing are also clearly visible in FESEM images and comes out to be an average of ∼42 nm. The elemental distribution mapping shows the purity of MXene with fluorine as a functional group because of using mild fluoride etchant. The optical and electrochemical properties also support the synthesis of efficient and high purity MXene. The synthesized MXene can be proven as a promising material for a wide variety of applications from environmental remediation to electrochemical sensing and energy storage, leading to their increasing popularity in the research and scientific field.

Comparative Study of Zeolite L Etching with Ammonium Fluoride and Ammonium Bifluoride Solutions

AbstractA commercial zeolite L is subjected to chemical etching with aqueous solutions of NH4F and NH4HF2 to generate secondary porosity. The derived samples are characterized by X‐ray diffraction, N2 adsorption, scanning, and transmission electron microscopy, 27Al MAS NMR, thermogravimetric analysis, and their acid sites are quantified by FTIR spectroscopy of adsorbed basic probe molecules. The catalytic properties of the pristine and modified zeolites are evaluated in the dealkylation of 1,3,5‐triisopropylbenzene. Tuning the etching conditions allows to generate hierarchical zeolites without losing micropore volume. Furthermore, both fluoride etchants do not change the acid properties of the zeolite substantially, which is confirmed by chemical composition analysis (ICP‐OES) and by FTIR spectroscopy of pyridine. The dissolution rate of zeolite L is much faster with NH4HF2 than NH4F. The set of experimental data shows that the 1 wt% NH4HF2 solution is an efficient etchant able to generate mesopores without affecting the parent zeolite properties as lower amounts of fluoride source are required than with concentrated (20–40 wt%) NH4F solutions.

Effects of a fluoride etchant and a phosphate primer on bonding of veneering composite to Ti–6Al–4V alloy for CAD/CAM restorations

PurposeTitanium abutments and superstructures are commonly veneered or covered with esthetic materials. The present investigation was carried out to evaluate the effects of an experimental surface treatment using etchant and primer on bond strength between a resin composite and Ti–6Al–4V alloy. MethodsDisk-shaped Ti–6Al–4V alloy was machine milled, the surface was air abraded with alumina, and the alloy was chemically etched with 5wt% ammonium hydrogen fluoride (F-etch) for 30s. A phosphate primer (MDP-primer) was applied to the bonding area, and then a resin composite, with or without milled-fiber resin composite (FRC), was veneered on the specimen. Shear bond strengths were determined after thermocycling for 20,000 cycles. Bond strength data were analyzed by means of ANOVA and a multiple comparison test (α=0.05). The surface of Ti–6Al–4V alloy was observed using a scanning electron microscope before and after the etching procedure. ResultsNo-FRC/F-etch/MDP-primer exhibited the highest bond strength (28.2MPa), followed by No-FRC/No-etching/MDP-primer (24.2MPa), FRC/F-etch/MDP-primer (19.9MPa), FRC/No-etching/MDP-primer (17.8MPa), No-FRC/No-etching/No-primer (13.6MPa), while FRC/No-etching/No-primer (2.5MPa) resulted in the lowest value. Microphotographs showed that numerous micro and nano pits were created on the Ti–6Al–4V alloy surface modified with F-etch. ConclusionsThe bond strength between Ti–6Al–4V alloy and the veneering resin composite was the highest when the alloy surface was modified with alumina blasting, fluoride etchant, and phosphate primer successively.

The same etchant produces both near-atomically flat and microfaceted Si(100) surfaces: The effects of gas evolution on etch morphology

The effects of H2 gas evolution during the etching of silicon surfaces by aqueous ammonium fluoride (NH4F) solutions were investigated by scanning tunneling microscopy, atomic force microscopy, optical microscopy, and noncontact profilometry. If H2 bubbles, a reaction product, were removed from the etching surface or if their coalescence was suppressed, near-atomically flat surfaces were produced. Otherwise, the etched surface developed significant roughening on many length scales with several characteristic morphological features, including nested, nearly-concentric circular etch pillars, circular etch pits, and faceted micropits. Mechanisms for the production of all three types of features are proposed. Chemical and physical means of suppressing bubble-induced surface roughening are presented. These results explain the conventional wisdom that aqueous fluoride etchants roughen Si(100) surfaces, in part by promoting the formation of Si{111} microfacets. Although some conditions promote the formation of a high density of {111}-faceted micropits (areal densities of 30%–50% were observed), microfacet formation is not inherent to the atomic-scale reactions. Instead, the microfacets are a direct result of gas evolution during the etching reaction.

Nanostructure formation via print diffusion etching through block copolymer templates

The present work demonstrates nanoscale etching of silicon with standard aqueous fluoride etchants running through the hydrophilic domains of a vertically aligned copolymer template. The delivery of etchants was unprecedentedly achieved by an etchant-solution-saturated agarose gel stamp, a technique we call print diffusion etching. Three-dimensional nanoprotrusion features with controllable shapes and sizes (about 20 nm) were formed. To prove that the block copolymers serve to direct the silicon surface morphology by controlling the spatial location of the reaction as well as concentration of reagents, the same etching steps both on silicon and PS-b-PEO (polystyrene-block-polyethyleneoxide) templates were carried out for comparison. The mechanism of the nanoprotrusion formation was elucidated, and the morphology evolution vs. etching time studied.

Block Copolymer Templated Etching on Silicon

The use of self-assembled polymer structures to direct the formation of mesoscopic (1-100 nm) features on silicon could provide a fabrication-compatible means to produce nanoscale patterns, supplementing conventional lithographic techniques. Here we demonstrate nanoscale etching of silicon, applying standard aqueous-based fluoride etchants, to produce three-dimensional nanoscale features with controllable shapes, sizes, average spacing, and chemical functionalization. The block copolymers serve to direct the silicon surface chemistry by controlling the spatial location of the reaction as well as concentration of reagents. The interiors of the resulting etched nanoscale features may be selectively functionalized with organic monolayers, metal nanoparticles, and other materials, leading to a range of ordered arrays on silicon.

Comparison of Four Fluoride Etchants in Bonding between Titanium and a Self-curing Luting Agent

The purpose of the present study was to investigate the efficacy of four different fluoride etchants in titanium bonding. The etchants were aqueous solutions of 5 wt% sodium fluoride (NaF), ammonium fluoride (NH4F), sodium hydrogen fluoride (NaFHF), and ammonium hydrogen fluoride (NH4FHF). Cast specimens of commercially pure titanium were air-abraded with alumina, etched for 30 seconds, and then primed with a phosphate primer. An acrylic rod was bonded to the specimen with a tri-n-butylborane-initiated self-curing luting agent. Shear bond strengths were determined before and after 10,000 thermocycles. Regarding pre-thermocycling bond strength, there were no significant differences among the etchants. After thermocycling, there was a decrease in bond strength for all groups. Nonetheless, the bond strengths of NaFHF and NH4FHF were significantly higher than those of NaF, NH4F, and non-etched control. In terms of bonding durability between resin and titanium, it was significantly improved when the titanium surface was microscopically roughened with alumina blasting and etching using NaFHF or NH4FHF.

Effect of an acidulated fluoride etchant on bonding between titanium and two luting materials

Adhesive bonding between resin and titanium is useful for resin-bonded prostheses. The purpose of this study was to investigate the efficacy of an etchant, consisting of ammonium hydrogen fluoride (AHF) and phosphoric acid (PA), in titanium bonding. Cast specimens of commercially pure titanium were air-abraded with alumina and etched for 30 s, after which a primer (ALP) was applied. An acrylic rod was bonded to the specimen with one of the two luting agents being examined (Super-Bond QUICK and Panavia F2.0). Shear bond strengths were determined following 10,000 thermocycles. When Panavia F2.0 was applied, neither the etchant nor the ALP primer showed significant effect on bond strength. The postthermocycling bond strength of Super-Bond QUICK was significantly improved with the use of an etchant and ALP primer. Although microscopic observation revealed that considerable numbers of submicron pits were created on the specimens etched using AHF with PA, no significant difference in bond strength was detected in the application of AHF, with or without PA. The present findings suggested that the improved bonding durability was due to the micromechanical retention between the resin and the microscopically roughened titanium surface.

Effects of a fluoride etchant on resin bonding to titanium-aluminum-niobium alloy.

This investigation was carried out in order to evaluate ammonium hydrogen fluoride (AHF) and cupric chloride (CC) as components of a metal etchant. The surface of cast titanium-aluminum-niobium (Ti-6Al-7Nb) was air-abraded with alumina, etched for 10 s, and rinsed with water. A phosphate or a thiophosphate primer was applied to the bonding area, and an acrylic rod was bonded to the specimen with a tri-n-butylborane-initiated self-curing luting agent. Shear bond strengths were determined after thermocycling (4 degrees C and 60 degrees C) for 10,000 cycles. The average bond strength was significantly influenced by thermocycling, AHF, and primer, but was not influenced by CC. The maximum average bond strengths were obtained when the etchant consisted of 5mass% AHF, with and without 0.3mass% CC. Microphotographs showed that numerous micropits were created on the etched surface, suggesting increased micromechanical retention. In conclusion, chemical etching with 5mass% AHF significantly improved the durability of resin bonding to Ti-6Al-7Nb.

Comparison of acidulated phosphate fluoride gel and hydrofluoric acid etchants for porcelain-composite repair

Hydrofluoric acid etches porcelain to produce a porous surface visible under scanning electron microscopy when compared to an acidulated phosphate fluoride gel. Some investigators have suggested the greater porosity of the hydrofluoric acid etch produces a greater composite-to-porcelain bond. This investigation tested that assumption with two common fluoride etchants. The etched surfaces were first viewed under scanning electron microscopy to ensure that a characteristic etch was achieved. Both etchants yielded bond strengths that produced, cohesive failure of all samples. This suggested that the intraoral use of hydrofluoric acid is no more effective than the less dangerous acidulated phosphate fluoride gel.

Fabrication of micromachined silicon tip transducer for tactile sensing

The tunneling vacuum diode was employed to construct a novel displacement transducer for tactile sensing. High sensitivity of the emission current to variations of cathode–anode separation is the most important feature. The device was fabricated on a silicon wafer. The device components are a single tip or an array of tips made by wet etching, and a metal anode diaphragm. Nitric acid-ammonium fluoride etchant is used at room temperature to etch the silicon tips, with an easily controlled etch rate and excellent uniformity. A unique sacrificial layer technique creates and controls the spacing between cathode tip and anode diaphragm. Highly sensitive responses of the device current to different force loads on the anode diaphragm are presented.