Sol Gel Alumina Research Articles

Process Yield and Device Stability in Sol-Gel Alumina Passivation Layer-Based GFETs

Process Yield and Device Stability in Sol-Gel Alumina Passivation Layer-Based GFETs

Nanocrystalline Sulfided NiMoW Catalyst Supported on Mesoporous Aluminas for the Hydrodesulfurization of 4,6-Dimethyldibenzothiophene

Tri-metallic NiMoW catalysts prepared by impregnating mesoporous aluminas (pore sizes of ~9 nm and surface areas of ~225 m2/g) obtained by sol-gel (NiMoW/Al) and hydrothermal (NiMoW/AlHYDT) processes were investigated in the hydrodesulfurization (HDS) of thiophene and 4,6-dimethyldibenzothiophene (4,6-DMDBT) at H2 pressures of 1 MPa and 5.0 MPa, respectively. The supports and catalysts were characterized by N2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). The NiMoW/AlHYDT catalyst, which was the most active in both test HDS reactions, was characterized by a pore size of 7.5 nm, whereas the pore size of the catalyst on sol-gel alumina (NiMoW/Al) was only 4.8 nm. Moreover, the NiMoW/AlHYDT catalyst exhibited reduction peaks shifted to a lower temperature during TPR, indicating weaker metal support interactions, a higher degree of Mo (79%) and W (48%) sulfidation, and an optimal layer slab length distribution of Mo(W)S2 nanocrystals preferentially between 2–4 nm with an average layer stacking of 1.7 compared to the NiMoW/Al counterpart.

Seed layer engineering for crack-free sol–gel Alumina deposition on GFETs

Low-cost and low thermal budget-based spin-coated sol–gel Alumina was explored as a dielectric/passivation layer for graphene field effect transistor (GFET). Post thermal annealing, the crack was observed in the sol–gel Alumina layer exactly above the graphene channel. The possible mechanism of crack could be graphene lateral restoring movement due to (i) the Thermal Expansion Coefficient (TEC) difference between graphene and adjacent layers and (ii) shrinkage stress generated during the solvent removal process. Based on the crack formation phenomenon, a combination of different annealing schemes (low thermal budget deep ultraviolet (DUV) annealing) and seed layer engineering (thickness and different deposition schemes) were carried out. Finally, a novel two-step seed layer deposition method with DUV annealing was proposed and demonstrated to resolve the crack issue successfully and also able to retain the Dirac point in the electrical characteristics.

Parameter optimization for enhancing tribological properties of sol–gel alumina and aluminum silicate-coated aluminum alloy: Grey–Taguchi method

The degradation of materials by wear is reduced by the wet chemical technique, where a thin film is coated over the surface susceptible to wear. The sol–gel coating method is one of the wet chemical techniques normally employed to improve tribological and anti-corrosive properties. This paper deals with evaluating tribological properties such as coefficient of friction, volumetric wear loss, and corrosive stability of alumina and aluminum silicate-coated aluminum alloy A356. The coating parameters affecting the tribological properties are identified and the experiments are designed using Taguchi orthogonal array and optimized using the Grey relation analysis technique. The tribological characteristics at room temperature are evaluated using a pin on disc tribometer. Among the sol–gel coating parameters chosen for minimizing the effect of wear and coefficient of friction between surfaces, the temperature for heat treatment and pH of the sol–gel are identified as the critical parameters that affect the tribological characteristics. The corrosive stability of the samples has been evaluated by corrosion current, corrosion potential, and corrosive stability methods. It is found that tribological properties and corrosive stability are improved for the coated sample compared with the uncoated sample. It is also observed that alumina coating provides better tribological properties and aluminum silicate coating provides better corrosive stability.

Ruthenium hydrides encapsulated in sol-gel glasses exhibit new ultrafast vibrational dynamics.

Vibrational dynamics were measured by IR pump-probe spectroscopy and two-dimensional IR spectroscopy for triruthenium dodecacarbonyl and the undecacarbonyl hydride that forms when it is encapsulated in an alumina sol-gel glass. For comparison, a triruthenium undecacarbonyl hydride salt was also synthesized and studied in neat solution to identify the potential influence of the confined solvent environment on the dynamics experienced by carbon monoxide ligands. The vibrational lifetime was found to be significantly decreased for both hydride species relative to the dodecacarbonyl compound. Conversely, spectral diffusion of the CO vibrations was measured to be faster for the parent compound. The most significant dynamic changes occurred upon transformation from the starting compound to the hydride, while only minor differences were observed between the dynamics of the freely dissolved and sol-gel encapsulated hydrides. The results suggest that the structural change to the hydride has the largest impact on the dynamics and that its improved catalytic properties likely do not originate from confined solvent effects.

Evaluation of hybrid sol-gel alumina coating for electrical resistance applications

In an electric motor, bearing plays a vital role in the performance and reliability which fails frequently due to electrical pitting. To avoid this issue, the bearing can be coated with insulation material. In this present investigation, hybrid sol-gel coating was carried out on bearing steel by dip-coating method. The hybrid sol-gel was prepared using aluminium isopropoxide and calcined alumina powder. The ratio of Sol-Gel to calcined alumina and thickness of the coating was optimized to attain a crack-free surface coating. The crack behaviour was studied. The characterization of Hybrid Sol-Gel was carried out using Fourier-transform infrared spectroscopy and the surface morphology was observed using an optical microscope. The electrical resistance of the coating was measured using an insulation resistance tester. The crack-free surface coating of 40 microns was achieved at a low sol-gel to calcined alumina ratio. The electrical resistance of the coating is found suitable for bearing application. The thermodynamically stable hybrid sol-gel i.e., α alumina -ϒ alumina coating surface is proposed for electrical insulation coating.

Reactive SPS for sol–gel alumina samples: Structure, sintering behavior, and mechanical properties

This work presents a fast and direct controlled routine for the fabrication of fully dense alumina based on the reactive spark plasma sintering (reactive-SPS) of boehmite (γ-AlOOH) nano-powders obtained by the sol–gel technique. The evolution of the transition aluminas during sintering has been studied. Some boehmite powders were seeded with α-Al2O3 particles prior to the gelation. Boehmite seeded powders exhibited a direct transition to α-Al2O3 at 1070 °C, enhancing the transformation kinetics and lowering the required temperature by more than 100 °C. For comparison, other samples were prepared by previously annealing the seeded and unseeded boehmite powders. Thus, α-Al2O3 powders were obtained and were sintered by standard-SPS. A detailed structural and mechanical characterization is presented, comparing the hardness and indentation fracture resistance for different grain sizes and porosities. Both the reactive-SPSed samples and the standard-SPSed samples showed a high hardness (18–20 GPa), whereas the reactive-SPSed samples exhibited a lower indentation fracture resistance due to a large grain size (∼10 μm). Improvements of this procedure for obtaining smaller grain size are discussed. In summary, the presented technique brings a revolutionary fast method for the fabrication of fully dense alumina, as this process reduces the time and temperature required for alumina densification.

A novel microfluidic system for the sensitive and cost-effective detection of okadaic acid in mussels.

Okadaic acid (OA) is produced by marine dinoflagellates and it can be easily accumulated in shellfish, causing intoxications when consumed by humans. Consequently, there is a need for sensitive, reliable and cost-effective methods to detect OA in real samples. In this work, we developed a novel and affordable microfluidic system to detect OA based on the protein phosphatase 1 inhibition colorimetric assay. This enzyme was immobilized in a microfluidic chamber by physisorption in an alumina sol-gel. The results show good enzyme stability over time when maintained at 4 °C. The developed system was sensitive for OA standard solutions, presenting a limit of detection (LOD) of 11.6 nM over a large linear range (43.4 to 3095.8 nM). Our method revealed an LOD as low as 0.2 μg kg-1 and a linear range between 1.47 and 506 μg kg-1 for extracted mussel matrix, detecting OA concentrations in contaminated mussels much lower than the regulated limit (160 μg kg-1). The enzyme stability and reusability along with the simplicity and low cost associated with microfluidics systems make this method very interesting from a commercial point of view.

Spectroscopic Study of Sol-Gel Entrapped Triruthenium Dodecacarbonyl Catalyst Reveals Hydride Formation.

Triruthenium dodecacarbonyl exhibits increased catalytic activity toward hydrogenation reactions when encapsulated in alumina sol-gels. In this study, we demonstrate structural and electronic changes induced by the encapsulation process. Fourier transform infrared (FTIR) spectroscopy reveals that the carbonyl vibrational modes dramatically red shift during aging in the sol-gel glass. These shifts are attributed to the formation of the metal hydride: [HRu3(CO)11]-. A comparison to the FTIR spectrum of synthesized [NEt4][HRu3(CO)11] confirms this assignment. XPS studies show that the Ru 3d5/2 peak of [HRu3(CO)11]- also shifts to lower binding energy, consistent with an increased electron density on the Ru nuclei compared to Ru3(CO)12 and confirmed by density functional calculations. This study should open the door to further investigations into the hydride's role in the previously observed catalytic activity. To the best of our knowledge, this is the first study to identify the presence of [HRu3(CO)11]- in the alumina sol-gel.

Effect of Sol-Gel Alumina Biocomposite on the Viability and Morphology of Dermal Human Fibroblast Cells.

This paper is the continuation of our previous work on the ability of biocomposites based on sol-gel alumina (boehmite) to promote skin recovery from burns and atrophic scars. The present study describes the increasing of the cytoplasma volume and the number of filopodias of HDF cells, which for the first time indicates their proliferation on the alumina itself and on alumina-based biocomposite. Studies in vivo confirm the efficiency of the composite in the treatment of atrophic scars.

Grindability studies of thermomechanically processed advanced high strength steel using sol-gel and fused alumina grain-based grinding wheels

Advanced high strength steels have excellent strength-to-weight ratio and are widely used for automotive and structural applications. Grinding is commonly used as a final machining process for these materials to achieve the required dimensional tolerance and surface quality. In this work, the grindability of as-received microstructure of ferrite-pearlite and in-house developed ferrite-bainite-martensite steels using polycrystalline white fused alumina and microcrystalline sol-gel alumina grinding wheels under flood and minimum quantity lubrication conditions is studied. Grindability of these steels was evaluated based on the wheel wear, grinding forces, force ratio, specific cutting energy, surface roughness (Ra), and surface morphology. The sol-gel alumina wheel was observed with higher wear flat area and forces under all the grinding conditions as compared with white fused alumina wheel. The white fused alumina wheel exhibited higher force ratio values for all the grinding conditions than the sol-gel alumina wheel. The energy required per unit volume of material removal is lower for the white fused alumina wheel in both the steels under flood and minimum quantity lubrication conditions. This is due to the retention of sharpness of abrasive grains by self-sharpening for white fused alumina wheel than the sol-gel alumina. The presence of fractured, melted, and hollow chips on the ferrite-pearlite and ferrite-bainite-martensite steels under both the grinding condition confirms the change in material removal mechanism with the presence of higher wear flat area of the sol-gel alumina wheel. Based on the obtained results, the white fused alumina wheel was found to be a suitable grinding wheel for grinding of both the steels under all grinding conditions compared to the sol-gel alumina wheel.

Sol-gel alumina coating of wire mesh packing

Wire mesh packings have seen increasing applications to multiphase processes in recent years. Despite the high surface area, open structure and thermal and chemical resistance, wire mesh packings have a complex geometry which hinders some chemical applications, including changes of surface properties through application of a uniformly adhesive coating. In this work, the sol-gel deposition method of alumina coating ceramics was investigated for the first time on stainless steel wire mesh by using Dixon rings as example. The kinetics of deposition during the hydrolysis and polycondensation was followed for a range of initial composition of the coating such as the ratios of Al2O3 to water, acid content, polyethyleneimine binder content and the number of deposition cycles. Well-adhered alumina with a thickness up to 20 μm was successfully deposited. The molar ratios of acid to alumina and alumina to water of 0.25 and 0.01, respectively, 48 h of the aging time, 96 h of the mixing time and 2.1 g/L of polyethyleneimine binder formed a free of cracks coating of controlled thickness alumina on the Dixon rings.

Effect of Preparation Technique on the Performance of Ni and Ce Incorporated Modified Alumina Catalysts in CO2 Reforming of Methane

Performances of modified sol–gel alumina (MSGA) based catalysts, synthesized in an inert atmosphere and activated by Ni and Ce were investigated in CO2 reforming of methane. Two different incorporation methods were used to dope Ce into the structure of the catalysts: (i) simultaneous impregnation of Ce together with Ni (Ni–Ce@MSGA), (ii) one-pot synthesis of Ce incorporated alumina support material (Ni@Ce-MSGA). In the second case Ni was impregnated on the Ce-MSGA support. Synthesized catalysts were characterized using TPR, XRD, N2 adsorption/desorption, pyridine adsorbed DRIFT, CO2-TPD techniques. These analyses showed that the synthesized catalysts possessed reduced Ni particles, as well as mesoporous structure, Lewis acid sites and moderate basicity. The modified sol–gel alumina and modified sol–gel Ce-MSGA supported catalysts showed stable activity in CO2 reforming of methane. Ce incorporation improved catalytic activity of the synthesized catalysts and reduced the occurrence of reverse water gas shift reaction. Ni–Ce@MSGA catalyst decreased the CO2/CH4 conversion ratio much higher than Ni@Ce-MSGA catalyst. Coke analysis were determined using TGA/DTA, XRD, and SEM analysis. Especially, simultaneous impregnation of Ce and Ni catalyst inhibited coke deposition significantly due to lattice oxygen of ceria. However, coke deposition over Ni@Ce-MSGA catalyst was higher than Ni@MSGA catalyst since Ni@Ce-MSGA catalyst has higher nickel crystal size than that of Ni@MSGA catalyst.

Removal of Aluminosilicate Bond and Process Optimization on Recovery of Sol Gel Alumina Abrasive Grain from Abrasive Industry Waste

Sol-gel alumina abrasive grains are used in high cutting speed and high material removal process. The need of sol gel alumina abrasive grain is huge. So, the waste generated from the grinding process is also high. In grinding operation, flange portion of the grinding wheel is unused and dumped as waste. Recovery of abrasive grains from this unspent portion adds wealth. This study deals with recovery and re-use of sol gel alumina abrasive grains. Chemical method is opted to recover the sol gel abrasive grains. Based on previous studies, the process parameter such as solid liquid ratio, lump size, immersion time and stirring speed were selected as the control factors and extraction efficiency of sol gel alumina abrasive is considered as response parameter. The experimental results show that major influencing control factor sequence were lump size> solid liquid ratio > stirring speed and > immersion time. The optimal combination for the maximum sol gel alumina grain recovery will be smaller lump size, maximum solid liquid ratio, maximum stirring speed and intermediate immersion time. Apart from that, the surface features of the recovered abrasive grains are studied by scanning electron microscopy. The elements during chemical washing process are observed using energy-dispersive spectroscopy (EDS). Recovered grains from this process can also be reused in the grinding wheel production. This is the feasible and economical method for recovering the sol gel alumina grains from the spent grinding wheel waste.

Internal Cylindrical Grinding Process of INCONEL® Alloy 600 Using Grinding Wheels with Sol-Gel Alumina and a Synthetic Organosilicon Polymer-Based Impregnate.

The development of modern jet engines would not be possible without dynamically developed nickel–chromium-based superalloys, such as INCONEL® The effective abrasive machining of above materials brings with it many problems and challenges, such as intensive clogging of the grinding wheel active surface (GWAS). This extremely unfavorable effect causes a reduction in the cutting ability of the abrasive tool as well as increase to grinding forces and friction in the whole process. The authors of this work demonstrate that introduction of a synthetic organosilicon polymer-based impregnating substance to the GWAS can significantly improve the effects of carrying out the abrasive process of hard-to-cut materials. Experimental studies were carried out on a set of a silicon-treated small-sized sol–gel alumina 1-35×10×10-SG/F46G10VTO grinding wheels. The set contained abrasive tools after the internal cylindrical grinding process of INCONEL® alloy 600 rings and reference abrasive tools. The condition of the GWAS after the impregnation process was studied, including imaging and measurements of its microgeometry using confocal laser scanning microscopy (CLSM), microanalysis of its elemental distribution using energy dispersive X-ray fluorescence (EDXRF), and the influence of impregnation process on the grinding temperature using infrared thermography (IRT). The obtained results confirmed the correctness of introduction of the impregnating substance into the grinding wheel structure, and it was possible to obtain an abrasive tool with a recommended characteristic. The main favorable features of treated grinding wheel concerning the reduction of adhesion between the GWAS and grinding process products (limitation of the clogging phenomenon) as well as reduction of friction in the grinding process, which has a positive effect on the thermal conditions in the grinding zone.

Modelling the wear evolution of a single alumina abrasive grain: Analyzing the influence of crystalline structure

The grinding process is continuously adapting to industrial requirements. New advanced materials have been developed, which have been ground. In this regard, new abrasive grains have emerged to respond to the demands of industry to reach the optimum combination of abrasive-workpiece material, which allows for both the minimization of wheel wear and increased tool life. To this end — and following previous experimental works — the present study models in 3D the wear behavior of Sol-Gel alumina abrasive grain using Discrete Element Methods. It is established that the alumina behaves as a ductile material upon contact due to the effect of high temperature and pressure. This model reproduces the third body generation in the contact, taking into account the tribochemical nature of the wear flat, which is the most harmful type of wear in the grinding process. The evolution of the wear during a complete contact is analyzed, revealing similarities in the wear of white fused alumina (WFA) and Sol-Gel (SG) alumina. However, the SG abrasive grain suffers less wear than the WFA under the same contact conditions. The proposed wear model can be applied to any abrasive-workpiece combination.

A new sol‐gel route alumina for selective oxidation of H2S to sulphur

AbstractIn this study, a new synthesis method was developed for the production of modified sol‐gel alumina (SG‐M) for the selective oxidation of H2S to elemental sulphur. The catalytic activity of this modified alumina without any active metal incorporation was then compared with the activity of commercial alumina (alumina‐com) for H2S selective oxidation. The N2 adsorption‐desorption isotherm showed that the SG‐M alumina synthesized in this work has a mesoporous structure with well‐defined hysteresis loops. Both alumina materials showed a γ‐Al2O3 crystalline phase with an amorphous structure in their crystal structure. The surface acidity of the alumina materials was determined using pyridine‐adsorbed FTIR analyses, and both alumina showed Lewis acid sites on their surfaces. The catalytic activity tests were performed at 250°C using a feed ratio of O2/H2S:0.5. The complete conversion of H2S over SG‐M was achieved during 400 minutes of reaction time. However, the commercial alumina lost its activity at earlier reaction times. Lewis acid sites and surface hydroxyl groups caused the alumina to be active in H2S selective catalytic oxidation, and the formation of Al‐S bonds, observed when the H2S conversion fell, caused a decrease in the catalytic activity of the alumina materials. A high sulphur yield (≥95%) was obtained over SG‐M, even though there was no active metal incorporation and even in the presence of excess oxygen. Considering the catalytic activities, the new sol‐gel alumina synthesized in this work is superior to commercial alumina. It was concluded that, as a catalyst without any active metal, SG‐M is a promising catalyst in H2S selective oxidation to sulphur.

Effect of the CuAl2O4 and CuAlO2 Phases in Catalytic Wet Air Oxidation of ETBE and TAME using CuO/γ-Al2O3 catalysts.

This paper studies Cu/Al2O3 catalysts, synthesized in two ways: copper deposit in the synthesis of alumina (sol gel) and incipient impregnation stabilized at 400 °C. The materials were characterized by X‐ray diffraction studies, nitrogen physisorption, temperature programmed reduction of H2, dehydration of isopropanol, scanning electronic microscopy, transmission electronic microscopy, which were evaluated in the liquid phase oxidation reaction of ethyl tert‐butyl ether and tert‐amyl methyl ether. The formation of CuAl2O4 and CuAlO2 in the samples synthesized by sol gel, led to a modification of the texture, thus resulting in an expansion of the specific area of the materials. CuAl2O4 and CuAlO2 have been identified by DRX from a content of 10 % Copper, the first showed the highest intensity with this technique. In the same way, these species favor the presence of Lewis acid sites; this is reflected in the materials with (Di‐isopropyl Ether) DIPE of 96.7 % and 91.1 % for the samples SAlCu5 and SAlCu15 respectively. The catalytic activity of the materials prepared by sol gel is in the function of the number of surface acid sites, the smaller particle size of the Cu and the surface of the contact, in the case of the ETBE meanwhile for TAME the activity was based mainly on the strength of the present acid sites. With impregnated materials, the activity is attributed to the smaller particle size of the Cu and the greater strength of the surface acid sites in the solid. The formation of spinel species inhibits the leaching phenomenon in the reaction milieu.

Corrosion Performance of Nano-Alumina Coatings over Anodized Aluminum Alloy by Dip Coating Method

Alumina coatings are widely used to enhance the wear, abrasion, and corrosion resistance of metal components. This investigation aims at studying the alumina sol-gel coating on the anodized aluminum alloy surface using a dip coating technique. A stable alumina coating was deposited over the anodized aluminum surface using oxime-modified aluminum(III) isopropoxide as sol-gel precursor. The scanning electron microscopy image of the coated anodized sample suggests deposition of a uniform and crack-free aluminum coating. The corrosion resistances of bare, anodized, and coated anodized aluminum alloy samples were investigated by electrochemical impedance spectroscopy and potentiodynamic polarization in 3.5 wt % aqueous NaCl solution. An appreciable shifting was observed in the equilibrium corrosion potential (Ecorr) and the corrosion current density (icorr) values of both anodized and coated anodized samples: i.e. Ecorr: from –1377.11 mV (anodized) to –711.54 mV (coated anodized) and icorr: from 80.37 μA/cm2 (anodized) to 0.090 μA/cm2 (coated anodized). The results clearly indicate the corrosion resistive behavior of nano-alumina coatings.

Dibenzothiophene Hydrodesulfurization over P-CoMo on Sol-Gel Alumina Modified by La Addition. Effect of Rare-Earth Content

Alumina-lanthana (La at 1, 3, or 5 wt%) supports were prepared by sol-gel from Al alkoxide sol where La(NO3)3 was added. Annealed (550 °C) xerogels were characterized by N2 physisorption, thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy- energy dispersive spectroscopy (SEM-EDS), CO2-adsorption studied in IR region, Raman and ultraviolet-vis (UV-vis) spectroscopies. The texture of amorphous binary matrices of high La dispersion was adequate to applications in catalysts for middle distillates hydrodesulfurization (HDS). Generally, the amount and strength of surface basic sites increased with La content in solids. Mo (at 2.8 at. nm−2) and Co (at Co/(Co+Mo) = 0.3) were deposited over carriers by one-pot simultaneous impregnation in the presence of PO43− (P2O5/(NiO+MoO3) = 0.2 mass ratio). Calcined (400 °C) Co-Mo-P impregnated precursors had decreased basicity as to that of corresponding carriers, suggesting strong La-deposited species interaction. As La content in carriers increased Mo=O Raman stretching vibrations shifted to lower wave-numbers (949 to 935 cm−1) suggesting octahedral molybdates coordination change to tetrahedral. Although La at the lowest concentration (1 wt%) enhanced dibenzothiophene, HDS (~38% higher as to the Al2O3-supported formulation) desulfurization was significantly diminished at augmented content. Presence of hardly sulfidable tetrahedral Mo originated during impregnation at basic conditions in pores of La-modified carriers seemed to dictate observed behavior. Rare earth content in formulations enhanced selectivity to biphenyl.