Hydrofluoric Research Articles

Correlation between the micro-shot peening coverage and surface microstructural evolution and fluoride-induced corrosion behavior in Monel 400 alloy

This study examines the influence of micro-shot peening (MSP) on Monel 400 alloy, focusing on surface microstructural evolution and fluoride-induced corrosion behavior compared to its solution annealed (SAed) counterpart. MSP treatments were conducted at various surface coverages (100%, 200%, 500%, 1000%, 1500%, and 2000%). Characterization encompassed microhardness, surface roughness, grazing incidence x-ray diffraction (GI-XRD), field emission scanning electron microscopy (FE-SEM) with electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). With increasing the MSP coverage to 2000%, the surface crystallite size decreased from approximately ∼30 µm in the SAed sample to 60 nm. TEM analysis emphasized dislocation slip and formation of dislocation structures as the primary mechanisms for the grain refinement. However, the 2000% coverage exhibited microcrack formation, compromising its hydrofluoric (HF) corrosion resistance. Electrochemical tests revealed severe localized corrosion in all MSP-treated samples except the 1500% coverage, which exhibited a minimum passive current density of 0.2–1.0 µA/cm2. Inductively coupled plasma optical emission spectroscopy (ICP-OES) of immersion solutions showed lower copper and nickel ion concentrations (<150 ppm) in the 1500% MSP-treated sample, indicating its enhanced corrosion resistance. X-ray photoelectron spectroscopy (XPS) identified NiO, NiF2, CuO, CuF2, and Cu(OH)2 phases in SAed and 1500% MSPed samples, with a higher concentration of copper oxide (CuO) in the corrosion film of the 1500% MSP-treated sample, contributing to its superior corrosion resistance.

Coal quality enhancement by using bio extracts of carissa carandas fruits in combination with Hydro Fluoric acid

ABSTRACT This paper addresses the imperative need for environmentally sustainable beneficiation technologies tailored for low-rank coals, constituting about 50% of global coal deposits. The focus is on recent advancements in bio-beneficiation methods for sub-bituminous coals in thermal power stations, employing ”bio extract of Carissa carandas fruits” with lower concentrations of Hydrofluoric acid. The objective is to enhance coal quality by reducing ash content and adjusting mineral composition to mitigate clinker formation during combustion. The research investigates simultaneous coal treatment with bio extract and low-concentration Hydrofluoric acid. While traditional beneficiation techniques, such as physical, chemical, and physicochemical methods, have been extensively used, a research gap is identified in green methods utilizing biomaterial extracts to remove/reduce metal oxides from coal and the need to regulate the silica-to-alumina ratio in coal composition, for resolving the issue of clinker formation. The investigation demonstrates the bio extract’s efficacy in leaching alumina, iron oxide, and alkali/alkaline earth metal oxides from coal, significantly reducing ash content. Consequently, there is a remarkable increase in coal’s gross calorific value post bio-beneficiation, accompanied by a significant reduction in sulfur content in addition to the decrease in tendency of clinker formation of coal during combustion. This study is a significant contribution to the field of environmentally friendly coal beneficiation and to reduce the tendency of clinker formation during combustion.

Evaluation of zirconia surfaces and shear bond strength after acid–etching with ultrasonic vibration

To evaluate the effect of surface reaction process after hydrofluoric (HF) acid etching using ultrasound and the shear bond strength (SBS) of resin cement to zirconia polycrystal (Y-TZP) ceramic. Y-TZP ceramic sheets were divided into rinsing group (Group P), ultrasonic cleaning group (Group C), and ultrasonic reaction + rinsing group (Group CP), and all the groups were treated for 5, 10, 20, 30, 40, 50, and 60 min, respectively. The surface morphology, elements distribution, roughness, and wettability of the ceramic sheets in each group were observed. The SBS of ceramic-resin bonding specimens was tested after immersion and after cooling-heating cycles, respectively. Octahedral and spiculate products were observed on the surface of Y-TZP that was etched with HF acid in Group P. The amount of these products increased over time. In contrast, only a few octahedral products remained on the surface of Y-TZP in Groups C and CP. Within the same reaction time, the surface reaction of the CP group was stronger than that of the other two groups, accompanied by a more uniform morphology. The shear force in Group C was the lowest, and the shear force reduction in Group CP was the least after cooling-heating cycling, with statistically significant differences (P< 0.05). After the reaction time exceeded 30 min, the shear force in each group decreased instead of increasing. Octahedral and spiculate acid etching products on the surface of HF acid-etched Y-TZP can enhance the bonding force of zirconia. Ultrasonic cleaning would drive the exfoliation of acid etching products from the sample surface, leading to the decrease of the bonding force. The acid etching with ultrasonic vibration can accelerate the HF acid etching process of Y-TZP ceramics, which is conducive to improving the bond strength to resin and durability.

Effect of Combined Application of Hydrofluoric and Phosphoric Acids and Active Irrigation with a Microbrush on Shear Bond Strength of Lithium Disilicate Ceramics to Enamel.

This study assessed the effect of combined application of hydrofluoric (HF) acid and phosphoric acid (PA) and active irrigation (AI) with a microbrush on shear bond strength (SBS) of lithium disilicate (LDS) ceramics to enamel. This in vitro study was conducted on 40 extracted teeth that received enamel preparation with a #12 cylindrical bur. Forty IPS e.max LT rods (3mm diameter, 6mm height) were fabricated and randomly assigned to four groups (n = 10) for surface treatment with 5% HF (group 1), 5% HF and AI with a microbrush for 20 seconds (group 2), 5% HF and 32% PA (group 3), and 5% HF and 32% PA plus AI with a microbrush for 20 seconds (group 4). Silane and Choice 2 cement were used for bonding rods to enamel. The SBS was measured by a universal testing machine. Data were analyzed by two-way analysis of variance (ANOVA), Bonferroni, and Chi-square tests (alpha = 0.05). Group 4 had the highest SBS, and group 1 had the lowest SBS (P < 0.05). Group 2 had a significantly higher SBS than group 1, and group 4 had a significantly higher SBS than group 3. AI with a microbrush significantly increased the SBS (P < 0.05), but the application of PA caused no significant change in SBS (P > 0.05). The interaction effect of PA and AI on SBS was not significant (P > 0.05). The application of PA in addition to 5% HF acid caused no significant change in the SBS of LDS ceramic to enamel. However, AI with a microbrush significantly increased the SBS.

Ultrathin Feldspathic Ceramic Veneers: A Pilot SEM Evaluation of Etched Intaglio Surfaces.

Ultrathin ceramic veneers are a viable therapeutic option to manage esthetic challenges in the anterior zone. Proper conditioning of the intaglio surface of porcelain veneers is essential to achieve an adequate bonding. In clinical practice, this is typically done with chemical etching using an acid-containing agent, such as hydrofluoric acid. While it is well established that the etching effect is dependent on etching time and the acid concentration, little is known about the impact of etching time and the veneer fabrication method. The purpose of this pilot study was to evaluate, using scanning electron microscopy (SEM), the effect that different etching-time protocols have on the intaglio surface characteristics of ultrathin ceramic veneers fabricated with either the platinum foil technique or the refractory die technique. Several replicas of an ultrathin feldspathic ceramic veneer for a maxillary central incisor were fabricated. Individual specimens were processed according to different intaglio surface-etching protocols: no etching, etching for 90 seconds, etching for 120 seconds, and etching for 150 seconds (9.6% hydrofluoric acid used for all etching groups). It was observed that the 120-second etching protocol resulted in a favorable microroughness surface pattern in the platinum foil group. This pattern was comparable to that obtained by etching for 90 seconds with hydrofluoric acid the intaglio surface of veneers fabricated with the refractory die technique. Increasing the etching time to 150 seconds did not result in a more favorable roughness pattern.

Phosphonium-Based Ionic Liquid Electrolyte in Combination with Silicon Anodes and LiNi0.5-XMn1.5+XO4 Cathodes for Lithium Ion Batteries

Ionic liquids, like bis(fluorosulfonyl)imide (FSI) ionic liquids, are promising solvents for lithium ion batteries due to their high thermal stability and wide electrochemical window. The performance of ionic liquid electrolytes is however hampered by the low conductivity at room temperature, but the high thermal stability allows for operation at elevated temperatures, at which the conductivity is significantly improved.Electrolytes based on LiFSI and ionic liquids of the cations; pyrrolidinium (PYR13 +), and phosphonium (P111i4 +), with FSI anions, have been shown to exhibit stable cycling at room temperature, and good rate performance for cells composed of silicon anodes and LiFePO4 cathodes at 60 °C [1,2]. The lithium ion mobilities, relative to standard carbonate electrolytes, were determined from the limiting current densities at room temperature and 60 °C. Significant differences in the temperature dependence of the transport properties were revealed, with a considerable increase in the lithium ion mobility from 20 to 60 °C for electrolytes based on P111i4FSI. The best rate performance at 60 °C was demonstrated for the P111i4FSI based electrolyte, with discharge capacities around 1000 mAh/gSi at a 2C rate [2]. The improved performance was attributed to a combination of the improved lithium ion mobility and formation of a more conductive solid electrolyte interphase (SEI) for this electrolyte.In view of the excellent high temperature performance of P111i4FSI, including high thermal stability and a large electrochemical window [1,2], this electrolyte has been selected for further studies as electrolyte for high voltage LiNi0.5-xMn1.5+xO4 (LNMO) cathodes. LiNi0.5-xMn1.5+xO4 (LNMO) is an attractive candidate as a next generation Li-ion battery (LIB) cathode material because it has a high energy density, due to the high operating voltage, and a relatively low cost (Co-free) compared to alternative cathode chemistries. However, the stability of LNMO is not yet satisfactory for commercial applications, especially in full-cell configuration with graphite as the anode material, and at elevated temperatures. One challenge is the transition metal (TM) dissolution, which poisons the graphite anode by degrading the solid electrolyte interface (SEI) [4]. The TM dissolution is affected by the formation of hydrofluoric (HF) acid in carbonate-based electrolytes utilizing the LiPF6 salt [3]. Additionally, the decomposition processes occur with an increased rate at elevated temperatures [4,5]. Another challenge is the side reactions occurring at the high operating voltage, which limits the coulombic efficiency. Previous works have indicated that the carbon conductive additive is more prone to side reactions than the LNMO active material [6].Here, we present a study on the phosphonium-based ionic liquid P111i4FSI, with two different salt concentrations: 0.79 m LiFSI and 3.0 m LiFSI, as an alternative electrolyte for LIBs with an LNMO cathode.The focus of the research is to study the side reactions separately on the carbon conductive additive, and on the LNMO active material. Carbon conductive additives differing in structure and particle size are studied. The electrolyte is tested both in half-cell and full-cell configuration with a graphite anode, as well as at room temperature and elevated temperatures. Using 0.79 m LiFSI P111i4FSI results in similar capacity retention, but higher coulombic efficiencies after 200 cycles in half-cells at room temperature compared to 1 M LiPF6 in 1:1 EC:DEC (v/v). Post-mortem characterization is carried out with SEM, TEM, Raman spectroscopy, and FT-IR.

Synthesis of Titanium Carbide MXene Nanosheets by Ecofriendly Technique for Strontium Ion Adsorption

2D titanium carbide (Ti3C2Tx, where Tx indicates the surface termination) MXene nanosheets are synthesized by etching the Ti3AlC2 MAX phase using two kinds of etchants: potassium hydroxide (KOH) base and hydrofluoric (HF) acid. This study aims to reduce the environmental side effects caused by the etchant in fabricating MXene nanosheets to extract strontium ions (Sr2+) from nuclear wastewater. Ti3C2Tx MXene synthesized using alkaline KOH etchant shows a 99% Sr2+ removal rate, which is much higher than that synthesized using the conventional HF etchant (82%). The enhanced Sr2+ removal rate associated with KOH etching is explained by unique surface termination, which offers more active adsorption sites for Sr2+ by the partial hydrolysis of TiC bonds on the surface of MXene nanosheets.

Assessing the catalytic performance of Cu@Ln (Eu, Sm)-N-C composites as bifunctional electrocatalysts using mesoporous silica-protected calcination

Synthesis of a composite with high technical performance and low cost instead of Platinum-based electrocatalysts has become an investigation hotspot to develop fuel cells and storage technologies. So, in the current investigation, three new bifunctional electrocatalysts incorporating lanthanides into Zeolitic Imidazolate Framework (ZIF)-8 are fabricated and assessed. First, by using a facile protocol, three trimetallic composites consisting of Europium (Eu), Samarium (Sm), Copper (Cu), and ZIF-8 are prepared, and the fabricated samples are labeled as EuCu-ZIF, SmCu-ZIF, and SmEuCu-ZIF. Next, in order to eliminate the irreversible fusion and quick aggregation of metal nanoparticles through the high-temperature carbonization process, the mesoporous-silica-protected calcination technique is investigated. After the Hydrofluoric (HF) etching process, the Cu@Ln (Eu, Sm)-N-C electrocatalysts are formed. Based on the fabricated samples, the Cu@Eu-N-C electrocatalyst exhibited the best Oxygen Reduction Reaction (ORR) performance with an onset potential of −0.06 V vs Ag/AgCl. Additionally, the electron transfer number for this composite is found to be 3.68. The GCD experiments show that the Cu@Eu-N-C electrode has the greatest specific capacitance, measuring 431 F g−1 when tested at 1 A g−1. It is deduced that the introduction of Eu3+ and Sm3+ as metal ions in the ZIF-8 catalyst led to an improvement in defects in the carbon matrix and mass transfer, illustrating the fabricated catalysts have an acceptable efficiency for ORR and storage applications. Indeed, due to the use of metallic ions (Ln and Cu), highly effective active sites were formed, resulting in an outstanding improvement in ORR efficiency. Also, it was found that with the use of mesoporous-silica protection for the fabricated samples, there is a remarkable improvement in the onset potential and specific capacitance parameters.

Study the Effect of Hydrofluoric (HF) Concentration on the Topography of the Porous Silicon Layer Prepared by Sunlight Photochemical Etching (SLPCE)

Silicon nanocrystals have a vast range of potential applications, from improving the efficiency of solar cells and optoelectronic devices to biomedical imaging and drug delivery, wastewater treatment, and antibacterial activities. In this study a photochemical etching technique was used to create layers of porous silicon on a donor silicon wafer with orientation (111) and resistivity equal to 1‑10 ohm·cm. The process involved focusing sunlight onto the samples using a telephoto lens with a suitable focal length of 30cm and a diameter of 90 mm, which provided sufficient energy to complete the chemical etching. By using a constant etching time of 60 minutes and different concentrations of hydrofluoric acid (ranging from 25% to 40%), layers with varying properties were obtained. The resulting surfaces were studied using the atomic force microscope (AFM), revealing the formation of different nanostructures and particles with varying shapes, sizes, and thicknesses depending on the preparation conditions. The average size of the particles was found to be 90.43nm at a concentration of 40% acid, while decreasing to 48.7nm at a concentration of 25% HF acid.

Argon Plasma Treatment Effects on the Micro-Shear Bond Strength of Lithium Disilicate with Dental Resin Cements.

The low bond strength of lithium disilicate (LD) ceramics to dental resin cements remains a critical issue for dental applications because it leads to frequent replacement and causes tooth tissue destruction and consumption. The objective of this study was to examine the effects of atmospheric non-thermal argon plasma (NTP) treatment on LD to improve its micro-shear bond strength (μSBS) with dental resin cements because LD mostly experiences shear stress for its commonly used dental applications as crowns or veneers. Argon plasma treatment was performed on hydrofluoric (HF) acid-etched LD surfaces, and then commercial resin cements were subsequently applied to the treated LD surfaces. The plasma treatment significantly reduced the water contact angle of the LD surface to less than 10° without changing the surface morphology. The μSBS test was performed with cement-bonded LD samples after 24 h and 30 days, as well as after 1000 cycles of thermal cycling. The test results show that, as compared with the untreated controls, 300 s of plasma treatment significantly improved the LD-resin cement bond strength by 59.1%. After 30 days of storage in DI water and 1000 cycles of thermal cycling, the plasma-treated LD samples show 84.2% and 44.8% higher bond strengths as compared to the control samples, respectively. The plasma treatment effect on LD surfaces diminished rapidly as the bond strength decreased to 25.5 MPa after aging in the air for 1 day prior to primer and cement application, suggesting that primers should be applied to the LD surfaces immediately after the plasma treatment. These results demonstrate that, when applied with caution, plasma treatment can activate LD surfaces and significantly improve the SBS of LD with dental resin cements in both short-term and long-term periods.

Design mode filtering interferometer using etched double clad fiber

Abstract Mode filtering technique is one of the most desired techniques in optical fiber communication systems, especially for multiple input multiple output (MIMO) coherent optical communications that have mode-dependent losses in communication channels. In this work, a special type of optical fiber sensing head was used, where it utilizes DCF13 that is made by Thorlabs and has two numerical apertures (NA’s). One is for core and 1st cladding region, while the 2nd relates the 1st cladding to the 2nd cladding. Etching process using 40 % hydro-fluoric (HF) acid was performed on the DCF13 with variable time in minutes. Investigation of the correlation between the degree of etching and the refractive index (RI) profile of double-clad fibers for low order linearly polarized (LP) modes is the focus of this work research. The used software programs to simulate the effect of etching are Comsol Multi-Physics V6 and Optigrating V4.2.2. It is seen that the optimum case that gave highest cladding power to core power ratio is the case of etching for 10 min, which can be used for detection applications. This ratio greatly affects the sensitivity of the system.

High-Sensitivity Seawater Salinity Sensing With Cladding Etched Fiber Bragg Grating Technology

Seawater salinity is an essential parameter to show the basic hydrological information of the ocean. Cladding etched fiber Bragg grating (CE-FBG) technology has potential in seawater salinity sensing because of its high sensitivity to surrounding refractive index. Here, we fabricated the different CE-FBG salinity sensing elements by using hydrofluoric (HF) acid based wet chemical etching. We encapsulated a CE-FBG and a bare FBG (B-FBG) into a salinity sensor to realize simultaneous measurement of seawater salinity and temperature. Various sensing characteristics of the CE-FBG, including salinity and temperature sensitivity, response time, hysteresis, repeatability, and long-term stability were investigated systematically. The salinity and temperature measurements of the CE-FBG sensor were highly consistent with those of the electronic salinometer, which indicates that fiber optic salinity sensor provides a new means for salinity measurement. Together, our results demonstrate the great potential of the CE-FBG salinity sensor for high sensitivity, long-term, and quasi-distributed seawater salinity monitoring.

Fluoride ion and hydrofluoric acid detection via silicon nanosheet field-effect transistor sensor

Fluoride ion (F–) and hydrofluoric (HF) acid are widely used, but they are highly toxic to the health and the natural environment. Sensors based on the field-effect transistor (FET) are commonly considered for chemical applications due to their small size and simple fabrication method. However, there has not been reported on the FET-based sensor for detecting F– ion and HF acid in the literature. Here, we demonstrate F– and HF acid sensors based on the FET, enabling sensitive detection in a small form factor. In particular, our FET sensor incorporates silicon nanosheet (SN) as the channel structure and polycrystalline lanthanum fluoride as a sensing membrane. Therefore, the fabricated sensor presents high responsivity (SR[M]) of 455.7 %/log[F–] for F– and high SR[M] of 392.4 %/log[HF] and has extremely low limit of detection of 10.20 ppb for F– and 32.04 ppb for HF acid. Moreover, it shows a good selectivity over other ions such as CO32–, NO3–, PO43–, and SO42– and a low hysteresis current of 0.81 %. Finally, the performance of our HF sensor has been excellently demonstrated by the fabricated real-time HF sensor system and exhibits negligible error (less than 5 %) comparable to a commercial one.

Evaluation paste removal method and bond strength between resin cement and lithium disilicate ceramic: An in vitro study

Statement of problemAfter the use of evaluation paste, residue can remain on the bonding surface. However, how adhesion to lithium disilicate ceramic is affected is unclear. PurposeThe purpose of this in vitro study was to determine the effectiveness of lithium disilicate cleaning after contamination with an evaluation paste and before the application of a resin cement. Material and methodsRectangular lithium disilicate (IPS e.max CAD) specimens were obtained with a simulated milled surface, crystallized, etched with 5% hydrofluoric (HF) acid, and contaminated with an evaluation paste. The cleaning methods tested were air-water spray (SPRAY), 37% phosphoric acid (HPO), ultrasonic bath (ULT), cleaning paste (IVOC), and a conventional surface treatment (HF + silane–HF+SIL). The control (CTRL) group was not contaminated. After silane had been applied, resin cement cylinders were fabricated and light polymerized. Half of the cylinders (n=56) were tested for microshear bond strength at baseline (24 hours), and the other half after 210 days of water storage and 25 000 thermal cycles. Surface roughness, failure analysis, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were performed. Statistical analysis was performed with the Kruskal-Wallis and Mann-Whitney tests for surface roughness and the 2-way ANOVA and Bonferroni post hoc tests for bond strength (α=.05). ResultsAt baseline, only SPRAY did not restore the bond strength compared with CTRL. After aging, the bond strengths of SPRAY and IVOC were lower than of CTRL (P<.05); no significant difference was found between CTRL, HPO, ULT, and HF+SIL (P>.05). EDS demonstrated the presence of carbon in the SPRAY and ULT groups, probably remnants of the evaluation paste. SEM analysis identified such remnants in the SPRAY group only. ConclusionsFor optimal bond strength between lithium disilicate and resin cement after evaluation paste use, cleaning the ceramic surface with 37% phosphoric acid, ultrasonic bath, or with hydrofluoric acid worked best.

Simulator Aids Design, Analysis of Acidizing Jobs With Fluoroboric Acid

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 205893, “Novel Simulator for Design and Analysis of Matrix Acidizing Jobs With Fluoroboric Acid in Sandstone Reservoirs,” by Mohammed Qamruzzaman, SPE, Mandeep Khan, and Dhirendra C. Roy, SPE, ONGC, et al. The paper has not been peer reviewed. _ Matrix acidizing with fluoroboric acid (HBF4) has gained special attention because of its deeper penetration of in-situ generated hydrofluoric (HF) acid and stabilization of formation fines by binding them to the pore surface. While numerous mathematical models exist in the literature for design and evaluation of conventional mud acid treatments, few attempts have been made in developing a laboratory-validated model that can do so for fluoroboric acid treatments. The complete paper presents a novel mathematical model that has been developed that takes into account the chemical kinetics and equilibrium aspects of important reactions and fluid flow inside the reservoir rock. Mathematical Modeling Because the complete paper contains numerous equations, it is essential for understanding the authors’ description of their mathematical model. The authors identify three benefits of their approach from a modeling point of view. First, it reduces the total number of chemical reactions taking place, which greatly simplifies computational complexity while maintaining reasonable accuracy. Second, the inclusion of separate chemical reactions for silica gel precipitation may require fixing the average value of stoichiometric coefficients for reactions between HF/hexafluorosilicic acid (H2SiF6) and slow- and fast-reacting minerals. This becomes challenging to do beforehand, especially when different types of clays are present with relatively equal proportions in the reservoir. Third, all resulting nondimensional numbers can be estimated easily by measuring effluent acid concentration during coreflooding. The following assumptions have been incorporated into the model: - The reservoir and core are assumed to be homogeneous and isotropic. - Flow is assumed to be one-dimensional. - All fast-reacting minerals are grouped together as a single fast-reacting mineral. - All slow-reacting minerals are grouped together as single slow-reacting mineral. - The reaction of HF with fast- and slow-reacting minerals is assumed to be first-order with respect to HF. - Changes in porosity are small and diffusion/gravity/thermal effects are neglected. Laboratory Studies Laboratory studies were performed on sandstone core samples from a prominent payzone in northeastern India to generate data for model validation. Core plugs of 1.5-in. diameter were taken from the same block to prevent mineralogical heterogeneities. Samples were characterized with X-ray diffraction (XRD) analysis and porosity measurements. This payzone was selected because it consists of a diverse range of minerals. Thus, a model that can be validated with the coreflooding from this sample could, in principle, apply to any other sandstone reservoir.

The potential of sodium carbonate and Tiron extractions for the determination of silicon contents in plant samples—A method comparison using hydrofluoric acid digestion as reference

For the determination of silicon (Si) contents in plant materials several methods are in use, but as all of these methods exhibit specific advantages and drawbacks, none of them has become prevalent. Alkaline chemicals are widely used to extract Si from plant samples, because this method is comparably simple, fast, and cheap. However, a comprehensive method comparison between different alkaline extractions to different plant organs is still missing, as well as understanding of the relationship between Si content quantified with those methods and soil silicon availability. In our study we performed two different alkaline (sodium carbonate (Na2CO3) and Tiron) extractions to determine Si contents in husk and straw samples of winter wheat (Triticum aestivum). Results obtained from hydrofluoric (HF) acid digestion were used as reference as this method is assumed to completely dissolve Si in a plant material. We evaluated the efficacy of simple, single-step Na2CO3 and Tiron extractions in relation to complex, multistep HF extractions and analyzed the relationships between Si and phytolith contents in plant samples and plant available Si concentrations in corresponding soil samples. Irrespective of the plant material used (husk or straw) we found Tiron to be more efficient in Si extraction compared to Na2CO3. While Na2CO3 extractions systematically underestimated Si contents in the tested plant materials, the results of Tiron extractions were comparable to the results of HF digestions, at least for husk samples. Phytolith contents in plant samples were strongly positively correlated to Si contents obtained from extractions, especially in husk samples. Plant available Si in soil samples was also reflected best in husk Si contents. Based on our results we recommend the use of Tiron for the extraction of Si from plant materials as this method provided more reliable results compared to the Na2CO3 extraction.

IMPACT OF HYDROFLUORIC (HF) ACID TREATMENT ON MORPHOLOGICAL AND CHEMICAL STRUCTURE OF AGRICULTURAL WASTES

Acid, base and/or water treatments expand biomass utilisation by reducing ash contents and improving energy density and higher heating values. Dilute acid treatment results in negative impacts on the physiochemical structure of biomass. This study aimed to analyse the effects of hydrofluoric (HF) acid (5% w/w) on the morphological and chemical structure of Wheat Straw (WS), Cotton Stalk (CS) and Rice Husk (RH). Scanning Electron Microscopy (SEM) exposed physical changes after treatment, and Fourier Transform Infrared (FTIR) spectroscopy was used to evaluate the changes in available functional groups in the composition of biomass samples. Dilute HF resulted in pronounced changes in morphology and chemical functional groups of all biomasses. Proximate analysis showed carbonaceous material is also affected; the increment in volatiles (9.27%, 7.7% and 6.9% for RH, WS and CS, respectively) and fixed carbon was observed while ash contents reduced. Furthermore, the influence of all samples on the thermal processing of biomass is compared.&#x0D; Keywords: biomasses, acidic pretreatment, ash contents, morphology, aromaticity

Comparison of the Micro-Shear Bond Strength of Resin Cements to CAD/CAM Glass Ceramics with Various Surface Treatments.

This study aimed to compare the effect of acid etching, sandblasting, or silica coating on the micro-shear bond strength of dual-cured resin cements to computer-aided design and computer-aided manufacturing (CAD/CAM) glass ceramic materials. Feldspathic, lithium disilicate, and zirconia-reinforced CAD/CAM ceramics were divided into four groups: control group (C), no surface treatment; hydrofluoric (HF) group, 5% HF acid-etched; sandblasting (SB) group, abraded with 50 µm aluminum oxide (Al2O3) particles; silica-coated (CJ) group, abraded with 30 µm silica-modified Al2O3 particles. Roughness values were obtained by using a profilometer. The cements were condensed on the surface-treated specimens and a micro-shear bond test was conducted. The ceramic material (p < 0.001) and surface treatment type (p < 0.001) significantly affected the micro-shear bond strength values. HF acid etching can be recommended for the surface pretreatment of feldspathic, lithium disilicate, and zirconia-reinforced CAD/CAM ceramics. Better bond strengths can be obtained with HF acid etching than with sandblasting and silica coating.

Evolution Regularity of Continuous Surface Structures Shaped by Laser-Supported Fictive-Temperature Modifying

The influence of residual heat on the fictive temperature modification zone of fused silica for different CO2 laser scanning time intervals was investigated to precisely control the profiles of hydrofluoric (HF) acid-etched fused silica surface, which were formed by the increasing HF acid-etching rate for fused silica with increasing fictive temperature induced by CO2 laser scanning. The surface profiles of HF acid-etched fused silica treated by different scanning time intervals of CO2 laser were measured by a stylus profilometry, and experimental results indicate that the CO2 laser scanning time intervals intensively influence the HF acid-etched surface profiles of fused silica. The increasing depth of surface profiles treated by shorter scanning time intervals shows that the fictive temperature modification zone significantly expands. Numerical simulations of the fictive temperature modification zone induced by different scanning time intervals indicate that the residual heat of CO2 laser scanning with shorter time intervals leads to a dramatical increase in the fictive temperature modification zone. By adjusting the residual heat of CO2 laser scanning intervals, various surface profiles of fused silica can be obtained by HF acid-etching of fused silica.

Epitaxial lift-off method for GaAs solar cells with high Al content AlGaAs window layer

The epitaxial GaAs substrate lift-off (ELO) technique is widely used to produce thin film III–V semiconductor optoelectronic devices. However, the hydrofluoric (HF) acid used in the process forbids the incorporation of active AlGaAs device layers with high Al content due to its selective etching. In this work, a new ELO method is presented, which allows for the protection of AlGaAs layers against the HF acid attack. The method is used here to prepare and analyse thin film GaAs solar cells containing Al0.85Ga0.15As window layer. We employ a sacrificial GaAs buffer and device perimeter pre-processing that covers the exposed edges with back contact metals and electroplated Cu. A comparison of the epitaxially lifted GaAs solar cells with identical cells prepared by substrate etching demonstrates identical photovoltaic figures of merit and confirms the viability of the AlGaAs protection approach. In addition to applications in thin film photovoltaics, this ELO method can be applied to solid-state lasers and single-photon emitters employing AlGaAs-based Bragg reflectors, among other III–V semiconductor optoelectronic devices.