•Sealing ability of different sol-gel coatings for the PEO layer on AA2024.•Electrochemical evaluation of the duplex coatings via SVET and EIS techniques.•The crucial role of compactness, ...hydrophobicity, and impregnation for the sol-gel sealing.•PSG-ZT illustrated the best sol-gel sealing for the PEO layer.•Insufficient sealing and hydrophilic properties of the PSG-AP for the PEO coating.
Owing to the inherent porosity of the coatings produced through the PEO process, the application of sol-gel coatings as a post-treatment has drawn immense attention thanks to their eco-friendly and reliable protective characteristics. Various parameters affect their performance, and the type of sol-gel precursors plays a significant role. In this study, various sol-gel precursors were used to prepare four types of PEO/sol-gel coating systems followed by an investigation of their sealing ability and corrosion resistance properties on AA2024 alloy. The corrosion prevention performance of the coatings was studied by electrochemical impedance spectroscopy (EIS) along with Scanning Vibrating Electrode Technique (SVET) analyzes. Some chemical characterization tests, such as Fourier Transform Infrared Spectroscopy (FT-IR) and rheology measurement, affirmed the influence of the sol-gel chemical composition on its compactness and the network viscosity. The distinctive sealing ability of different sol-gel coatings for the defects and pore filling of the PEO layer was visualized by Scanning Electron Microscope (SEM). To this end, different sol-gel formulations and various sol-gel network properties accordingly caused dissimilar sealing features for the PEO pores and, subsequently, the corrosion resistance of the duplex PEO/sol-gel coating is widely dependent on the used sol-gel precursors.
Nanostructured Nb doped TiO2 were prepared by a novel Sol-Gel method using new N‐methyldiethanolamine‐modified precursors of Ti (IV) and Nb(V). Co-hydrolysis of Ti(IV) and Nb(V) precursors in ...suitable ratio resulted in the introduction of atomically dispersed Nb cation, along with the formation of small Nb oxo clusters homogenously dispersed within the TiO2 matrix. Characterizations showed a progressive decrease of the crystallinity as well as an increase in the defects and the BET surface areas of the TiO2 nanoparticles with the Nb doping. Upon Nb doping, gas phase calorimetry of NH3 and CO2 adsorption, evidenced the acidity but also the basicity increase. The aqueous phase dihydroxyacetone conversion increased significantly over Nb/TiO2 as compared to undoped TiO2. However, upon increasing the Nb doping, the base-catalyzed pathway, which forms hexoses from DHA, became the prevailing mechanism at the expense of the usual acid-catalyzed pathway leading to formation of Pyruvaldehyde.
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•Sol-Gel synthesis of Nb-doped TiO2 of extremely high Nb dispersion within TiO2 matrix using new precursors of Ti and Nb•Enhanced BET surface areas and acid-base properties were determined by gas phase calorimetry of CO2and NH3 adsorption.•Nb-doped TiO2 catalyzes hexoses formation from DHA by aldolic condensation.
ZrO2 thin films were deposited on quartz substrates from 10wt.%, 20wt.% and 40wt.% solutions of Zirconium-n-butoxide in isopropanol by sol–gel dip-coating technique. Higher concentrated sols of ...20wt.% and 40wt.% exhibited faster gelation, where as 10wt.% sol remained stable for two months and films synthesized from this sol remained transparent and continuous even for 12 coatings. Ellipsometric study revealed that refractive index of the films increased with increase in sol concentration which is ascribed to the decrease in porosity. X-ray diffraction study showed that a tailoring of grain size from 7.9 to 39.2nm is possible with increase in sol concentration. Atomic force microscopy studies showed a change in growth mode from vertical to lateral mode with increase in sol concentration. The film surface revealed positive skewness and high kurtosis values which make them favorable for tribological applications. The average optical transmittance in the visible region is highest (greater than 90%) for the film deposited from 10wt.% sol. The optical band gap decreased from 5.74 to 5.62eV with increase in the sol concentration. Photoluminescence (PL) spectra of the films exhibit an increase in the emission intensity with increase in sol concentration which substantiates better crystalline quality of the film deposited from 40wt.% sol and increase in oxygen vacancies. The “Red shift” of the PL spectra with increase in sol concentration originates from the increase in the grain size with sol concentration which makes it suitable for generation of solid state lighting in light emitting diode.
► ZrO2 thin films were deposited on quartz substrates by sol-gel method. ► Control of grain size with sol concentration. ► Microstructure studies showed a change in growth mode from vertical to lateral mode. ► The optical band gap decreased with increase in grain size and sol concentration. ► Dependence of photoluminescence on particle size leads to tailoring emission colour.
We show that the polycondensation of chiral sol-gel precursors can be efficiently followed up by optical rotation measurements. Three silanes were studied, namely, the hexaethoxysilane derivatives of
...l
-threonine,
l
-isoleucine, and dimethyl-
l
-tartrate. Two main sol-gel polycondensation mechanisms were identified, namely, linear kinetics product growth and second-order cluster–cluster growth. Dynamic light scattering measurements are used to support the proposed mechanisms.
Highlights
The polycondensation of chiral sol-gel precursors is efficiently followed up by optical rotation.
The chiral hexaethoxysilanes of L-threonine, L-isoleucine and dimethyl-L-tartrate, are studied.
Two sol-gel mechanisms were identified: linear-kinetics and second-order cluster-cluster growth.
This paper reviews the use of organofunctional trialkoxysilane sol-gel precursors as contemporary fi nishing agents for the chemical modification of textile fires. The structures of organofunctional ...trialkoxysilanes are presented and compared to those of other silicon-based organic-inorganic hybrid materials. We describe the steps in the application procedure and the polysilsesquioxane coating fabrication on the surface of textile fibres. The functionalities, e.g., water and oil repellency, flame retardancy, antimicrobial properties, electrical conductivity and anti-static properties, are discussed in relation to the chemical structures of the precursor organic moiety, mechanisms and principals of the coating activity and its washing fastness. The most important published scientific results on organofunctional trialkoxysilanes applications to the surface of textile fibres are discussed with an emphasis on the creation of a multicomponent coating with multifunctional protective properties.
Non-aqueous reactions of aluminum isopropoxide with 8-hydroxyquinoline (Hq = HONH
6
C
9
) in 1:1, 1:2 and 1:3 molar ratios in anhydrous benzene yield complexes of the type q
n
Al(OPr
i
)
3−n
{where ...n = 1 (
1
), n = 2 (
2
), n = 3 (
3
)}. Progress of the reactions were monitored by estimating liberated 2-propanol in benzene-2-propanol azeotrope by oxidimetric method. All the products were fluorescent green powders, sparingly soluble in CHCl
3
. They were characterized by elemental analysis, FT-IR and (
1
H,
13
C and
27
Al) NMR studies. The ESI mass spectral studies indicate dimeric nature for (
1
) and (
2
) and monomeric nature for the compound (
3
). The XRD spectra of (
1
–
3
) showed crystalline nature with the average particle size of 45, 32 and 27 nm respectively, as evaluated from
Debye
–
Scherrer equation.
The XRD spectrum of (
3
) also suggests the formation of β-crystalline polymorphs of Alq
3
. The SEM images appear to indicate granular morphology for (
1
) and formation of cylindrical shaped rods for (
2
) and (
3
). Sol–gel hydrolysis of (
1
), (
2
) or (
3
) in presence of a strong acid as well as of the precursor, Al(OPr
i
)
3
,without acid or base catalyst, followed by sintering at 950 °C yielded tetragonal primitive phase of nano-sized δ-alumina in all the cases, as reflected by their powder X-ray diffraction pattern. The IR, SEM and EDX studies also support the formation of transition alumina.
In recent years, there has been increased interest in the use of inorganic UV blocking nanoparticles for photostabilization of wood surfaces. Photostability and moisture uptake properties of wood ...veneers coated with a combination of hybrid inorganic-organic thin sol-gel films and organic light stabilizers was investigated. The light stabilizers were applied by brushing, and the thin sol-gel films were deposi-ted on the wood surface by dipping in a sol prepared from a mixture of methyltrimethoxysilane, hexadecyltrimethoxysilane, and aluminum isopropoxide precursors. Although the sol-gel film improved the moisture resistance of the wood veneers, it showed mixed results on photostability. Under light and spray conditions in a Weather-Ometer™, specimens treated with a combination of sol-gel thin film and a UV absorber, tris-resorcinol triazine and an acrylic self-crosslink-ing binder, or treated with lignin stabilizer/tris-resorcinol triazine/acrylic self-crosslinking binder showed good overall weathering performance. Under permanent light conditions in the Weather-Ometer™, specimens treated with a combination of sol-gel thin film, a lignin stabilizer, and a water soluble UV absorber – namely: (2-hydroxyphenyl)-benzotriazole – revealed a good overall weathering performance. This study has demonstrated the feasibility of using a combination of organic light stabilizers and sol-gel deposits of hybrid inorganic-organic thin films to improve weathering resistance of softwood substrates.
Modifications to the refractive indices of meso-structured organic–inorganic films caused by variations in the mole fraction of precursors in ethanolic solutions were investigated. The refractive ...indices were dependent on the mole fraction of C
16
TMS (hexadecyltrimethoxysilane) and of the C
16
TMS/TMOS (tetramethoxysilane) (1/1) mixture in ethanol. The dependency was determined to be nonlinear, and the phenomenon was attributed to self-assembly caused by the long alkyl groups (C
16
) on the C
16
TMS. Changes in the maximum decreasing rate of d
n
/d
x
values (d
n
/d
x
)
max
—for d
n
/d
x
estimation, the curves from Fig.
1
were associated with a polynomial; using a dedicated program, d
n
/d
x
was calculated; maximum values of d
n
/d
x
were taken into account and were included in Table
1
) were used to distinguish the behavior of alcoholic precursor mixtures. In the case of using pyrene as a fluorescent probe, the ratio between two peaks from the pyrene emission spectra (I
1
/I
3
) strongly decreased as hydrophobic micro-surroundings formed due to the self-assembly process. The UV–VIS spectra of a cationic dye solution, R6G, was studied because dilute solutions of the dye in equilibrium form measurable ratios of dimers and monomers. The absorbance was modified as micro-surroundings with different polarities were formed. These three methods demonstrated that nano-structuration was present prior to the occurrence of the sol–gel process. The combination of C
16
TMS with other alkyltrialkoxysilane precursors having hydrocarbon chain lengths between C
1
and C
8
provided further evidence for a nonlinear dependence of the refractive indice and fluorescence spectra of pyrene. The properties of the final hybrids obtained by the sol–gel process were significantly affected by the precursor hydrocarbon chain lengths. DSC, XRD and FTIR measurements were used to show the plasticizing phenomena of C
16
as other alkyltrialkoxysilanes (i.e., C
1
–C
8
) were added.
Fig. 1
Variation of the refractive index with the mole fraction of the precursor mixtures
Table 1
Properties of the initial precursor mixtures and resultant hybrids
Sample no.
Precursor
Initial mixtures (dn/dx)
max
Final hybrids
TGA (ΔG/T
max
)
DSCT
c
(°C)
CA (°)
FT-IR
XRD
0–200 °C
200–500 °C
500–700 °C
Residue (%)
λ
SiOSi
/λ
cyclic
λ CH
2
(ν
as
/ν
s
) (cm
−1
)
A
cyclic
/A
SiOSi
d (Å)
19
C
16
TMS
0.52
1.06/66.51
59.68
24.34
14.88
60.1
110.40
1,114/1,023
2,919/2,851
0.804
36.2
21
C
16
TMS/TMOS = 1/1
0.30
2.57/85.68
47.61
11.82
38.00
57.1
110.78
1,124/1,061
2,921/2,851
0.880
48.8
24
TMOS
0.02
6.62/95.77
4.99/365.19; 448.94
1.84/516.55
86.56
51.73
1,125/1,068
0.910
25
C
16
TMS/TMOS = 1/4
0.12
3.60/
24.58
16.54
55.28
54.3
111.91
1,126/1,065
2,924/2,854
0.697
37.1
26
C
16
TMS/MTMS = 1/4
0.11
0.94/164.39
32.83
14.90
51.33
11.0
112.18
1,133/1,031
2,926/2,855
1.119
0
27
C
16
TMS/VTMS = 1/4
0.19
0.26
21.00
19.97
58.77
17.0
111.55
1,128/1,046
2,925/2,854
1.190
28
C
16
TMS/PTMS = 1/4
0.17
0.93
41.10
21.14
36.83
13.7
112.44
1,118/1,062
2,926/2,855
1.00
29
C
16
TMS/OTMS = 1/4
0.27
0.28
56.06
23.09
20.57
−28.6
93.74
1,124/1,038
2,924/2,854
1.27
ΔG, weight loss; T
max,
highest temperature for the decomposition process; CA, contact angle; T
c
, critical temperature
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