Influence of 3-aminopropyltriethoxysilane/tetraethylorthosilicate mixture pretreatment on the microstructure and corrosion resistance of zeolite coating

Abstract

The influence of silane pretreatment with five different volume ratios (100/0, 75/25, 50/50, 25/75, and 0/100) of 3-aminopropyltriethoxysilane (APTES)/tetraethylorthosilicate (TEOS) on microstructure and corrosion resistance of the hydrothermal synthesized zeolite coatings on the H13 steel substrates was investigated. The surface of the zeolite coatings on the 100/0, 75/25, and 50/50 mixture of the APTES/TEOS pretreated substrates was composed of intergrown rectangular particles. Additionally, pores were observed. A 25/75 mixture of APTES/TEOS pretreatment smoothed the edges and angles of zeolite particles with gel-like materials filled in the pores. In pure TEOS pretreatment, microcracks, and much gel-like materials were observed on the zeolite coating. The electrochemical test revealed that the zeolite coating on a 50/50 mixture of the APTES/TEOS pretreated substrate exhibited the highest corrosion resistance in 3.5 wt-% NaCl solution. This was because a 50/50 mixture of APTES/TEOS pretreatment advantageously promoted development of a dense and thick gel layer, which enhanced the intergrowth of zeolite particles.

Keywords

Silane pretreatment H13 die steel zeolite coating corrosion resistance tetraethylorthosilicate microstructure electrochemical impedance spectroscopy scanning electron microscope

Introduction

H13 steel die parts can easily fail due to surface wear and corrosion from Cl⁻, O^2-, molten aluminium, and other compounds during casting, forging, and hot extrusion. This leads to a decrease in durability and service lifetime [1 –4]. To date, the most effective method to protect H13 steel is surface engineering such as thermochemical treatment [5 –8], laser cladding [9,10], physical/chemical vapour deposition (PVD/CVD) [11], and thermal spraying [12], of which thermochemical treatment can form a compound or diffusion layer with high hardness to improve wear resistance [5,6]. However, the corrosion resistance could not be improved significantly [7,8]. Additionally, the high temperatures involved in its processes can cause size changes and shape distortion in the parts. For a die/mold with high precision requirement, the high-temperature process should be avoided. Whereas other surface treatments, their limitations also are apparent, for example, the unavoidable pores formed during laser cladding can negatively impact corrosion resistance [9,10]; the operation cost of physical/chemical vapour deposition (PVD/CVD) is high [11]. Consequently, the demand for alternative treatment is increasing.

A zeolite coating can potentially protect die/mold steel owing to its good crystallinity, corrosion, and wear resistance [13 –18]. Chow et al. [17] reported that a ZSM-5 zeolite coating on aircraft-grade 4130 steel exhibited higher wear resistance than that imparted by electroplated chromium and cadmium coatings via nano-scratch test. This is attributed to the low modulus and high hardness of zeolite particles. Mitra et al. [19] reported that MTW (ZSM (Zeolite Socony Mobil)−12, BEA (zeolite beta), and MFI (Mobil Five)) zeolite coatings prepared by one-step hydrothermal synthesis on 304 stainless steel plates were continuous and dense; therefore, they could impart higher corrosion resistance. A zeolite coating can be prepared on metal substrate by methods such as dry-gel conversion [20] and hydrothermal synthesis [21,22]. Among them, hydrothermal synthesis is tremendously suitable for die/mold steel because of its low-temperature process (≤200°C), which can advantageously reduce the deformation and distortion of die/mold parts [23].

Because of the high Cr content in H13 steel, it is challenging to hydroxylate its surface. This leads to a weak interaction between the precursor and H13 steel substrate during hydrothermal synthesis [24,25], and thus hinders the growth of zeolite coating on the H13 steel surface. Surface functionalization using different silane coupling groups (e.g. –Cl, –NH₂, –OH) significantly eliminates the problem of reactivity heterogeneity from region to region on metal substrate, and facilitates the deposition of a gel layer and promotes the nucleation of zeolite particles on the substrate, while also improving the compatibility between the substrate surface and zeolite coating [26 –30]. In view of this, silane pretreatment is typically utilized to increase the gas separation performance of zeolite coatings on steel substrates. Chau et al. [26] reported that the pretreatment of a 3-mercaptopropyltrimethoxysilane surfactant enhanced the zeolite coating quality. Huang et al. [27] reported that a 3-chloropropyltrimethoxysilane (CPTES) pretreatment improved the microstructure and gas separation performance of a zeolite coating on porous stainless steel. Martinez et al. [28] prepared a NaA zeolite coating on pre-calcined and then 3-aminopropyltriethoxysilane (APTES)-treated 316 L stainless steel, and the zeolite coating presented an improved crystal intergrowth and separation performance. Single silane pretreatment has been commonly conducted to enhance the separation performance of a zeolite coating on metal substrate; however, the influence of mixed silane pretreatment with higher flexibility on the microstructure and corrosion resistance remains unknown.

In this work, with the aim to improve the corrosion resistance of the zeolite coating and expand the application on the die processing industries, the mixture solution of 3-aminopropyltriethoxysilane (APTES)/tetraethylorthosilicate (TEOS) with different volume ratios was used to pretreat H13 steel, and study its influence on the microstructure and corrosion resistance of the zeolite coating prepared by one-step hydrothermal synthesis.

Materials and methods

Substrate preparation

H13 steel was selected as the substrate, and its chemical composition was as follows (wt-%): C 0.32-0.45, Si 0.80-1.20, Cr 4.75-5.50, Mn 0.20-0.50, Mo 1.10-1.75, Fe in balance. The substrate had a size of 20 × 15 × 2 mm³, and a 2 mm diameter hole was drilled on the edge. Prior to pretreatment, the substrates underwent a polishing process using 80, 320, and 800 # sandpaper, followed by ultrasonic cleaning in an alcohol bath.

The chemical reagents used in the experiment were as follows: APTES (C₉H₂₃NO₃Si, ≥98%) and TEOS (C₈H₂₀O₄Si, ≥98%) were obtained from Macklin Chemical Reagent; tetrapropyl ammonium hydroxide (TPAOH, C₁₂H₂₈NOH, ≥99%) was purchased from Jiuding Chemical Reagent; ethyl alcohol (C₂H₅OH, ≥99.7%) was purchased from Hunan Hui Hong Reagent Co., Ltd.; sodium hydroxide (NaOH, analytically pure) and sodium chloride (NaCl, analytically pure) were obtained from Xilong Chemical Co., Ltd.; distilled water was prepared in the laboratory.

Silane pretreatment

Five volume ratios of APTES and TEOS solution were prepared, and their compositions are listed in Table 1. Prior to use, the solution was aged for 24 h at ambient temperature (10–15°C). The mechanically polished H13 steel substrate was immersed into the solution for 3 min and withdrawn, followed by blow-drying. This process was repeated 3 times, after which the samples were cured at 120°C for 2 h.

Table 1

Chemical compositions of the pretreated silane solution.

Ab.name	APTES/TEOS (%V)	APTES (mL)	TEOS (mL)	H₂O (mL)	Ethanol (mL)
A100/T0	100/0	5	0	4	41
A75/T25	75/25	3.75	1.25	4	41
A50/T50	50/50	2.5	2.5	4	41
A25/T75	25/75	1.25	3.75	4	41
A0/T100	0/100	0	5	4	41

Zeolite coating preparation

The zeolite coating was synthesized on the various volume ratios of APTES/TEOS pretreated H13 steel substrates by hydrothermal synthesis. The solution was prepared using the following molar ratio: TPAOH:NaOH:TEOS:H₂O = 0.16:0.64:1:92, and stirred at ambient temperature (10–15°C) for 5–6 h. In this study, the chemical formula of the zeolite was (SiO₂)₆ H₂O, i.e. silicate-1 zeolite coating. The pretreated substrates were placed vertically on the Teflon-lined stainless steel autoclave using an iron wire, and then placed at 180°C for 20 h. The obtained samples were ultrasonically cleaned in an alcohol bath, followed by blow-drying. The zeolite coatings synthesized on the H13 steel substrates pretreated by 100/0, 75/25, 50/50, 25/75, and 0/100 (in volume ratio (%)) mixture of the APTES/TEOS were named as the ZC-0, ZC-25, ZC-50, ZC-75, and ZC-100 coatings, respectively.

Characterization

The functional group information of the substrate surface after various volume ratios of APTES/TEOS pretreatment was analysed by a Fourier-transform infrared (FTIR, Thermo Fisher Scientific Is-50) spectrometer, during which the spectra were recorded in the wavelength of 500–4000 cm⁻¹ with 2 cm⁻¹ resolution. The morphologies and elemental compositions of the zeolite-coated samples were investigated by scanning electron microscope (SEM, EVOMA10) equipped with an energy dispersive spectrometer (EDS), before which the cross-sectional samples were polished with 320, 800, and 1500 # sandpaper and diamond polishing paste. The phase compositions of the zeolite-coated samples were determined by X-ray diffraction (XRD, D/max 2550 VB, Cu Kα radiation), operated with a scanning 2 θ range of 5–50° and the scan speed of 4°/min.

Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) tests were used to analyse the corrosion resistance of H13 steel and the zeolite-coated samples, before which the surface of the samples were sealed by a mixture of rosin and paraffin except for a 1 cm² exposed area. Both were carried out in 3.5 wt-% NaCl solution at ambient temperature (10∼15°C) using CHI660 electrochemical workstation, wherein the samples served as the working electrode, whereas the saturated calomel electrode (SCE) and platinum plate were used as the reference and counter electrode, respectively. The voltage range and scanning rate of polarization curves were from −1.6 to 0 V [25] and 0.002 V/s, respectively. The EIS tests were conducted at the open circuit potential (OCP), and the frequency was from 100 000–0.01 Hz. In order to decrease the error, the reference electrode should be close to the working electrode as possible. Additionally, the samples with zeolite coatings were immersed into 3.5 wt-% NaCl solution for 30 min to ensure the surface stability prior to test; following the open circuit potential curve (OCP) was tested until it was stable.

At ambient temperature (10∼15°C), the samples with a 1 cm² exposed area were immersed into 3.5 wt-% NaCl solution for 1680 h, during which its surface variations were recorded via a digital camera. Prior to the immersion test, the H13 steel substrates were polished with 80, 320, and 800 # sandpaper and ultrasonically cleaned in an alcohol bath.

Results and discussion

Characteristics of zeolite-coated samples

Surface analysis

Figure 1 shows the surface morphologies of ZC-0, ZC-25, ZC-50, ZC-75, and ZC-100 coatings on the H13 steel substrate. As shown in Figure 1(a), the ZC-0 coating comprises intergrown and rectangular zeolite particles with different sizes and orientations. Several pores also appear on the surface, which are caused by incomplete intergrowth between adjacent zeolite particles. Although the particles of the ZC-25 coating in Figure 1(b) are smaller than that in Figure 1(a), the quantity of pores increases. As for ZC-50 coating in Figure 1(c), it shows a well-intergrown structure between adjacent zeolite particles. Consequently, few pores are presented on the surface. Further increasing the TEOS volume ratio (APTES/TEOS = 25/75), the edges and corners of zeolite particles on the ZC-75 coating become much smoother (Figure 1(d)). By the insert in Figure 1(d), gel-like materials can be observed. When applying pure TEOS pretreatment (APTES/TEOS = 0/100), as shown in Figure 1(e), several microcracks are presented, and the pores vanish. The primary reason for the surface cracks was due to thermal stress caused by a significant mismatch of thermal expansion coefficients between gel-like materials and zeolite particles.

Figure 1

Surface morphologies of (a) ZC-0, (b) ZC-25, (c) ZC-50, (d) ZC-75, and (e) ZC-100 coatings.

Table 2 shows the chemical element content of points 1–6 in Figure 1. The Si and O were the primary elements of zeolite framework. The presence of C components was ascribed to the structure-directing template (SDT) of TPAOH in the zeolite framework. As shown in Table 2, the C content of point 5 at zeolite particles is lower than that of point 6 at gel-like materials. This was because the gel-like materials were formed by the condensation of the silanol groups (≡Si-OH), obtained from TEOS hydrolysis [18].

Cross-sectional analysis

Figure 2 shows the cross-sectional morphologies and thickness variations of ZC-0, ZC-25, ZC-50, ZC-75, and ZC-100 coatings on the H13 steel substrates. As shown in Figure 2(a–e), micropores with different sizes were distributed within the zeolite coating, wherein the ZC-50 coating (Figure 2(c)) has the least micropores. At the same time, there are no apparent separation or microcracks at the interface between the H13 steel substrate and zeolite coatings. Notably, the ZC-25 coating (Figure 2(b)) shows a discontinuous characteristic, which is due to the weakly intergrown zeolite particles exfoliating during the mechanical polishing process. The thickness of ZC-0, ZC-25, ZC-50, ZC-75, and ZC-100 coatings is 15.35 ± 0.68, 7.6 ± 0.95, 6.32 ± 0.41, 7.05 ± 0.58, and 9.68 ± 0.78 μm, respectively, displaying a tendency of first decreasing and then increasing with increased TEOS content (Figure 2(f)).

Figure 2

Cross-sectional morphologies of (a) ZC-0, (b) ZC-25, (c) ZC-50, (d) ZC-75, and (e) ZC-100 coatings; (f) the thickness variation of the five zeolite coatings.

Phases analysis

Figure 3 shows the XRD patterns of the zeolite-coated samples. A strong martensite (α′-Fe) peak at 44.66° of 2 θ (PDF#65-4899) was observed on zeolite-coated samples due to the penetration of X-ray. At the same time, the peaks presentation of ZSM-5 zeolite (PDF#44-0009) indicated that the various volume ratios of APTES/TEOS pretreatment did not change the phase of the zeolite coating.

Figure 3

XRD diffraction patterns of the five zeolite-coated samples.

Influence of silane pretreatment on zeolite coatings

Figure 4 shows the FTIR spectra of the various volume ratios of APTES/TEOS pretreated H13 steel substrates. The weak peaks around 2850 and 2927 cm⁻¹ can be ascribed to -CH of the ≡Si-(CH₂)₃-NH₂ in APTES, or incompletely hydrolysed ≡SiOC₂H₅ in TEOS [31]. For APTES-pretreated specimen, the significant peak around 1020 cm⁻¹ corresponds to the stretching of Si-O-Si in the silane film [30,32,33]. The strong peaks at 1472 and 1556 cm⁻¹ are assigned to the vibration of –NH₂ groups [31,34], whereas that at 1630 cm⁻¹ is related to the silanol groups (≡Si-OH). For the mixed APTES- and TEOS- pretreated specimens, the Si-O-Si peak around 1020 cm⁻¹ gradually decreases with the increased volume ratio of TEOS. At the same time, the Si-O-Si peak of the 50/50 mixture of APTES/TEOS pretreated substrate is much wider, suggesting better cross-linking in the formed film. For pure-TEOS-pretreated specimen, a strong peak corresponding to hydrogen bonded –OH groups at 3209 cm⁻¹, and a strong peak corresponding to –CH at 1440 cm⁻¹ can be observed.

Figure 4

FTIR spectra of the H13 steel substrates at various volume ratios after APTES and TEOS pretreatment: (a) 500–2000 cm⁻¹ and, (b) 2500–4000 cm⁻¹.

In summary, during the aging process under neutral condition, the alkoxy groups on APTES easily hydrolysed to silanol groups (≡Si-OH) via the reaction equation of (1). In contrast, TEOS exhibited weaker hydrolysis ability, resulting in only partial conversion of alkoxy groups to silanol groups (≡Si-OH). Subsequently, when the H13 steel substrate underwent the silane pretreatment and curing process, a thin silane film was formed by intermolecular condensation among the silanol groups (≡Si-OH), and between the silanol groups (≡Si-OH) and the hydroxyl groups related to element Fe on the substrate via the reaction equations of (2)–(3) [29,31, 35 –37]. As for element Cr, there may be a specific interaction between the amino –NH₂ groups on the hydrolysed APTES and oxide of Cr on the substrate [37]. Based on above analysis, the schematic structures of the films formed on the substrates by solutions of APTES, a 50/50 mixture of APTES/TEOS, and TEOS pretreated substrate are shown in Figure 5. (1) (2) (3)

Figure 5

Bonding methods of the silane layer with the H13 steel substrate.

where the ≡Si-OC₂H₅ represents the APTES or TEOS.

Formation mechanism of zeolite coatings

During the hydrothermal synthesis, the zeolite coating started with the deposition of a gel layer by intermolecular condensation among the Si(OH)₄ molecules, and between the Si(OH)₄ molecules and the functional groups (–NH₂ or –OH) on the substrate surface; afterwards, the zeolite nuclei, formed via the interconnection of the Si(OH)₄ molecules in the form of a cage-like structure under the effect of the SDT of TPAOH, were attracted and anchored onto the gel layer via the hydrogen bond, and then intergrew to form the zeolite particles layer [18]. As shown in Figures 4 and 5, various volume ratios of APTES/TEOS pretreatment caused the types and distribution difference of functional groups on the substrate surface, which would exert influence on the formation of gel layer, and the nucleation ratio and growth of zeolite particles. For the pure TEOS and 25/75 mixture of APTES/TEOS pretreatment, lots of alkoxy groups were present on the H13 steel surface, which did not react with the silanol groups (≡Si-OH) in hydrothermal-synthesized solution, and possibly resulted in the gel layer being discontinuous and porous. This unfavourably attracted, anchored, and grew the zeolite nuclei. Therefore, on one hand, the massive Si(OH)₄ molecules near the substrate/liquid interface continuously copolymerized to form gel-like materials around zeolite particles (Figure 1(e,d)); on the other hand, the zeolite nucleated and grew in a higher Si(OH)₄ /SDT ratio, that is, their zeolite particles had the lower C content of zeolite particles (Table 2). Influenced by these, the particles of ZC-75 coating grew insufficiently and their edges and angles were much smoother (Figure 1(d)), and the particles number of ZC-100 coating was fewer (Figure 1(e)). As shown in Figure 5(b), a 50/50 mixture pretreatment of APTES/TEOS offered a silane film with fewer alkoxy groups. This advantageously generated a dense and thick gel layer (as proved by the fitting results of R_g in Table 4), strongly attracting and anchoring the zeolite nuclei, and then significantly increasing the intergrowth degree between adjacent zeolite particles, as shown in Figure 1 and Figure 2(c). Introducing a small amount of TEOS, that is, the APTES/TEOS = 75/25, possible led to the reactivity heterogeneity between the hydroxyl group rich and the amine group rich region on the substrate surface during hydrothermal synthesis. This easily caused lots of micropores formed on the gel layer, leading to it being less dense (as proved by the fitting value of R_g in Table 4). Additionally, these micropores greatly lowered the intergrowth degree between adjacent zeolite particles, as shown in Figure 1(b) and Figure 2(b). While for the pure APTES pretreatment, the -NH₂ groups on the substrate surface bonded with the Si(OH)₄ molecules in the synthesized solution via the silazane-based reaction, and formed the NH₃ [29]. This increased the pH value near the substrate/liquid interface because of the formation of NH₃ [29], with this decreasing the copolymerization ability of Si(OH)₄ to form dense and thick gel layer, and then intergrowth degree between adjacent particles, as shown in Figure 1(a) and Figure 2(a).

Table 2

Main element contents (wt-%) of the zeolite coated samples in Figure 1.

	O	C	Si
point 1	51.3	29.7	17.2
point 2	51.7	26.8	19.9
point 3	40.8	23.1	31.9
point 4	46.7	15.9	36.1
point 5	44.2	15.0	36.7
point 6	43.2	12.4	39.6

Corrosion resistance of zeolite-coated samples

Potential polarization curve

Figure 6 shows the potential polarization curves of the H13 steel substrate and zeolite-coated samples. The corresponding fitted results are listed in Table 3. As shown in Figure 6 and Table 3, the I_corr of six samples are arranged as follows: H13 steel substrate (4.53 × 10⁻⁶A·cm⁻²) > ZC-25 coating (6.97 × 10⁻⁸A·cm⁻²) > ZC-100 coating (6.23 × 10⁻⁸A·cm⁻²) > ZC-0 coating (5.34 × 10⁻⁸A·cm⁻²) > ZC-75 coating (4.61 × 10⁻⁸A·cm⁻²) > ZC-50 coating (2.27 × 10⁻⁸A·cm⁻²), from which it is discovered that the I_corr values of the zeolite-coated samples are about two orders of magnitude lower than that of the H13 steel substrate. This indicates that the zeolite coating has excellent corrosion resistance. Additionally, a pitting potential was present on the H13 steel substrate, ZC-0, ZC-25, and ZC-100 coatings. This can be ascribed to the defects on the zeolite particles layer, like pores and microcracks (as shown in Figures 1(a, c, and d)), allowed the electrolyte solution to penetrate and reach the gel layer, leading the gel layer beneath this portion first degraded to form defects [31].

Figure 6

Potential polarization curves of the H13 steel substrate and the zeolite-coated samples in 3.5 wt-% NaCl solution.

Table 3

Fitted results of potential polarization curves.

Sample	E_corrvs.SCE (V)	I_corr (A·cm⁻²)	Pitting potential (V/SCE)
H13 steel	−0.85	4.53 × 10⁻⁶	−0.39
ZC-0	−0.75	5.34 × 10⁻⁸	−0.31
ZC-25	−1.03	6.97 × 10⁻⁸	−0.25
ZC-50	−0.97	2.27 × 10⁻⁸	–
ZC-75	−0.83	4.61 × 10⁻⁸	–
ZC-100	−0.86	6.23 × 10⁻⁸	−0.12

Electrochemical impedance spectroscopy tests

Figure 7 shows the Bode curves of the H13 steel substrate and zeolite-coated samples. As shown in Figure 7(a), the low-frequency impedance modulus of the H13 steel substrate is 1.05 × 10³ Ω·cm², indicating its poor corrosion resistance. For the zeolite-coated samples, the Bode curves in Figure 7(b–f) show two-time constants, separately at high (∼10^4.5Hz) and low frequency (∼10⁰Hz). The time constant at high frequency was attributed to the outside barrier effect of the zeolite particles layer, while that at low frequency was related to the interfacial gel layer. The impedance modulus at 0.01Hz (│Z│_0.01) reduces with the increased immersion time, indicating the gradual failure to the coating. The values of │Z│_0.01 in Figure 7(b–f) are 2.41 × 10⁵, 5.34 × 10⁵, 1.01 × 10⁶, 1.18 × 10⁶, and 5.06 × 10⁵ Ω·cm² at 1 h, and decrease to 2.36 × 10⁴, 1.01 × 10⁴, 2.95 × 10⁵, 1.03 × 10⁵, and 3.40 × 104 Ω·cm² after 600 h of immersion, respectively.

Figure 7

Bode curves of (a) H13 steel substrate, (b) ZC-0, (c) ZC-25, (d) ZC-50, (e) ZC-75, and (f) ZC-100 coatings in 3.5 wt-% NaCl solution.

The equivalent circuit model [25] in Figure 8 was used to fit the electrochemical impedance data, where the R_s represented the solution resistance; QPE_z and R_z represented the constant phase element and resistance caused by the zeolite particles layer; W_s represented the impedance caused by the diffusion behaviour; and QPE_g and R_g represented the constant phase element and resistance caused by the gel layer, respectively.

Figure 8

Equivalent circuit model used to fit the EIS data of the five zeolite coatings.

The fitted results are listed in Table 4. First, the values of R_z and W_s decreased with the increased immersion time, indicating the gradual failure of the zeolite particles layer. For ZC-0, ZC-25 and ZC-50 and ZC-100 coatings, it was owing to the defects, like the pores on ZC-0, ZC-25, and ZC-50 coatings (Figure 1(a–c)) or microcracks on ZC-100 coating (Figure 1(e)), allowed the penetration of corrosion media; while for ZC-75 coating, it can be ascribed to that the gel-like materials, as shown in Figure 1(e), would degrade when exposed to NaCl solution [30]. Second, the ZC-50 coating shows the highest R_z value because of its best-intergrowth of zeolite particles (Figure 1 and Figure 2(c)). Similarly, it can be inferred that the weakly intergrown zeolite particles (Figure 1 and Figure 2(b)) endowed the lowest value of R_z to ZC-25 coating. last, the R_g values of all zeolite coatings were higher than that of R_z, indicating the interfacial gel layer provided better corrosion protection [25]. As shown in Table 4, the ZC-50 coating has the highest value of R_g after 600 h of immersion in 3.5% NaCl solution, indicating its gel layer is the densest. Additionally, the R_g value continuously decreased with the increased immersion time, such as the R_g value of ZC-50 coating decreased from 8.76 × 10⁶ Ω·cm² to 1.04 × 10⁶ Ω·cm², indicating the interfacial gel layer was not consistently stable during the immersion test. This was ascribed to the siloxane groups of Si-O-Si or Si-O-Me (Me represented the metal elements) was hydrolysed, and then formed the Me-OH and Si-OH groups when exposed to corrosive media [31].

Table 4

Fitted results of the EIS data for five coatings.

Sample	Time/h	QPE_z-Q/F·cm⁻²	QPE_z-N	R_z/Ω·cm²	QPE_g-Q/F·cm⁻²	QPE_g-N	R_g/Ω·cm²	W_s /Ω·cm²
ZC-0	1	6.57 × 10⁻⁹	1.00	3112	1.02 × 10⁻⁵	0.52	4.94 × 10⁵	4.80 × 10⁴
	240	1.25 × 10⁻⁸	1.00	1561	2.97 × 10⁻⁵	0.60	7.86 × 10⁴	1.57 × 10⁴
	480	1.19 × 10⁻⁷	0.95	685	4.93 × 10⁻⁵	0.67	2.51 × 10⁴	5.16 × 10³
	600	1.22 × 10⁻⁷	0.97	507	6.29 × 10⁻⁵	0.62	2.42 × 10⁴	1.36 × 10³
ZC-25	1	1.87 × 10⁻⁸	1.00	3061	9.50 × 10⁻⁶	0.60	1.57 × 10⁶	4.46 × 10⁴
	240	2.64 × 10⁻⁸	1.00	532	8.95 × 10⁻⁵	0.57	1.68 × 10⁴	3.34 × 10³
	480	5.81 × 10⁻⁷	0.88	276	1.83 × 10⁻⁴	0.71	1.33 × 10⁴	1.67 × 10³
	600	6.60 × 10⁻⁷	0.86	251	2.06 × 10⁻⁴	0.76	1.16 × 10⁴	1.14 × 10³
ZC-50	1	1.03 × 10⁻⁹	1.00	7245	5.50 × 10⁻⁶	0.54	8.76 × 10⁶	2.91 × 10⁶
	240	1.17 × 10⁻⁹	1.00	6523	4.78 × 10⁻⁶	0.53	1.69 × 10⁶	2.14 × 10⁵
	480	1.21 × 10⁻⁹	1.00	5643	6.55 × 10⁻⁶	0.48	1.05 × 10⁶	2.13 × 10⁵
	600	1.26 × 10⁻⁹	1.00	5371	9.38 × 10⁻⁶	0.43	1.04 × 10⁶	1.85 × 10⁵
ZC-75	1	1.37 × 10⁻⁹	1.00	4274	9.24 × 10⁻⁷	0.67	8.82 × 10⁶	1.24 × 10⁵
	240	4.31 × 10⁻⁹	1.00	3219	4.48 × 10⁻⁶	0.51	5.32 × 10⁶	1.17 × 10⁵
	480	4.67 × 10⁻⁹	1.00	3056	3.85 × 10⁻⁶	0.51	4.98 × 10⁶	1.05 × 10⁵
	600	1.45 × 10⁻⁸	1.00	1096	9.06 × 10⁻⁶	0.49	5.91 × 10⁵	8.96 × 10⁴
ZC-00	1	6.48 × 10⁻⁹	1.00	3271	9.67 × 10⁻⁶	0.66	5.66 × 10⁵	8.59 × 10⁴
	240	9.03 × 10⁻⁹	1.00	2606	4.11 × 10⁻⁵	0.42	8.08 × 10⁴	7.08 × 10⁴
	480	1.46 × 10⁻⁸	1.00	1706	5.31 × 10⁻⁵	0.39	7.24 × 10⁴	5.01 × 10⁴
	600	5.91 × 10⁻⁸	1.00	958	5.47 × 10⁻⁵	0.41	6.63 × 10⁴	3.65 × 10⁴

Immersion test

Figure 9 shows the surface variations of the H13 steel substrate and zeolite-coated samples in 3.5 wt-% NaCl solution at ambient temperature (10∼15°C). For the H13 steel substrate, its surface was severely corroded and covered by rust at 600 h. While for the zeolite-coated samples, the surface of the samples with the ZC-0, ZC-25, ZC-75, and ZC-100 coatings got yellow, and several corrosion pits were also observed at 1680 h. However, the surface of the ZC-50 coating maintained its original lustre, and few corrosion pits were observed at 1680 h.

Figure 9

Digital photos of the H13 steel substrate and zeolite-coated samples after immersing in 3.5 wt-% NaCl solution.

The electrochemical and saline immersion tests demonstrated that the zeolite coating greatly enhanced the corrosion resistance of the H13 steel substrate. The reason for this is, on one hand, the zeolite particle is composed of [SiO4]- unit, which has stable chemical property and thus presents high resistance to corrosion media [18,25]. On the other hand, the gel layer between the zeolite particles and the H13 steel substrate can further prevent the corrosion media from penetrating into the substrate, reducing the corrosion rate [18, 25]. Also, it was concluded that the ZC-50 coating had the best corrosion resistance for long time. This was possibly attributed to that the 50/50 mixture of APTES/TEOS pretreatment enabled the formation of a dense and thick interfacial gel layer, which significantly helped to increase the intergrowth degree between adjacent zeolite particles. Consequently, the corrosion media was much more difficult to penetrate through the zeolite coating to corrode the H13 steel substrate.

Conclusions

A zeolite coating was synthesized on the H13 steel substrate pretreated by 100/0, 75/25, 50/50, 25/75, and 0/100 (in volume ratio (%)) mixture of the APTES/TEOS. SEM images showed the zeolite coating on the 100/0, 75/25, and 50/50 mixture of the APTES/TEOS- pretreated substrate was composed of incompletely intergrown particles. Additionally, the 50/50 mixture of APTES/TEOS pretreatment led to the formation of zeolite coating with least porosity. On application of the 25/75 mixture of APTES/TEOS pretreatment, the adjacent particles of the zeolite coating lacked sufficient intergrowth, and their edge and angle became smoother. Additionally, the pores between adjacent particles were filled with gel-like materials. Several cracks caused by the thermal stress between the zeolite particles and gel-like materials were observed on the pure-TEOS-pretreated substrate. The electrochemical and immersion tests showed the zeolite coating, synthesized on the 50/50 mixture of the APTES/TEOS-pretreated substrate, had the best corrosion resistance in 3.5 wt-% NaCl solution. It had the lowest value of I_corr and the highest value of │Z│_0.01 for a long time.

Footnotes

Acknowledgement

This work was supported by the National Key Research and Development Program of China (grant 2017YFB0306301).

Disclosure statement

No potential conflict of interest was reported by the author(s).

References

Ding

, Yang

, Li

, . Failure analysis of H13 steel die for high pressure die casting Al alloy. Eng Failure Anal. 2021;124:105330. doi:10.1016/j.engfailanal.2021.105330

Wang

, Jia

, Ji

, . Determining the wear behavior of H13 steel die during the extrusion process of pure nickel. Surf Eng. 2011;28(8):581–586.

Chang

, Tang

, Tai

, . Effect of liquid oxy-nitriding at various temperatures on wear and molten aluminum corrosion behaviors of AISI H13 steel. Corros Sci. 2021;178:109088. doi:10.1016/j.corsci.2020.109088

, Shivpuri

, Rapp

RA.

Effects of molten aluminum on H13 dies and coatings. J Mater Eng Perform. 1995;4(2):175–181. doi:10.1007/BF02664111

Demir

, Gündüz

, Erden

, . Influence of the heat treatment on the microstructure and machinability of AISI H13 hot work tool steel. Int J Adv Manuf Technol. 2018;95(5-8):2951–2958. doi:10.1007/s00170-017-1426-3

Krelling

, Milan

JCG

, Da costa

CE.

Tribological behaviour of borided H13 steel with different boriding agents. Surf Eng. 2015;31(8):581–587. doi:10.1179/1743294414Y.0000000423

Fernandes

FAP

, Heck

, Picone

, . On the wear and corrosion of plasma nitrided AISI H13. Surf Coat Technol. 2020;381:125216. doi:10.1016/j.surfcoat.2019.125216

Chen

, Wang

, Fan

, . Combat molten aluminum corrosion of AISI H13 steel by low-temperature liquid nitrocarburizing. J Alloys Compd. 2019;776:702–711. doi:10.1016/j.jallcom.2018.10.298

Ding

, Liu

, Wang

, . Corrosion and wear performance of stellite alloy hardfacing prepared via laser cladding. Prot Met Phys Chem Surf. 2020;56(2):392–404. doi:10.1134/S2070205120020069

10.

Yan

, Yang

, Wang

, . Surface roughness optimization and high-temperature wear performance of H13 coating fabricated by extreme high-speed laser cladding. Opt Laser Technol. 2022;149:107823. doi:10.1016/j.optlastec.2021.107823

11.

Batista

JCA

, Joseph

, Godoy

, . Micro-abrasion wear testing of PVD TiN coatings on untreated and plasma nitrided AISI H13 steel. Wear. 2001;249(10-11):971–979. doi:10.1016/S0043-1648(01)00833-X

12.

Zhou

, Wang

, He

, . Microstructure and wear resistance of Fe-based amorphous metallic coatings prepared by HVOF thermal spraying. J Therm Spray Techn. 2010;19(6):1287–1293. doi:10.1007/s11666-010-9556-2

13.

, Yang

, Wu

, . Synthesis of corrosion-resistant MFI-type zeolite coatings by solid-conversion secondary growth without solvent. Microporous Mesoporous Mater. 2021;311:110714. doi:10.1016/j.micromeso.2020.110714

14.

Pande

, Parikh

PA.

Novel application of ZSM-5 zeolite: corrosion-resistant coating in chemical process industry. J Mater Eng Perform. 2013;22(1):190–199. doi:10.1007/s11665-012-0226-z

15.

Xing

, Chen

, Yu

, . Microstructure and corrosion performance of zeolite/MAO-coated Al alloy. Sur Eng. 2020;36(2):167–174. doi:10.1080/02670844.2019.1627016

16.

Song

, Jing

, Wang

, . Corrosion-resistant ZSM-5 zeolite coatings formed on Mg–Li alloy by hot-pressing. Corros Sci. 2011;53(5):1732–1737. doi:10.1016/j.corsci.2011.01.047

17.

Chow

, Bedi

, Yan

, . Zeolite as a wear-resistant coating. Microporous Mesoporous Mater. 2012;151:346–351. doi:10.1016/j.micromeso.2011.10.013

18.

Chen

, Chen

, . Improvement of the wear and corrosion resistance of nitrocarburized H13 steel using hydrothermal-synthesized zeolite coating. Surf Coat Technol. 2022;447:128866. doi:10.1016/j.surfcoat.2022.128866

19.

Mitra

, Wang

, Cao

, . Synthesis and corrosion resistance of high-Silica Zeolite MTW, BEA, and MFI coatings on steel and aluminum. J Electrochem. Soc. 2002;149:B472–B478. doi:10.1149/1.1507784

20.

Changjean

, Chiang

AST

, Tsai

TC.

Anti-corrosion zeolite film by the dry-gel-conversion process. Thin Solid Films. 2013;529:327–332. doi:10.1016/j.tsf.2012.09.037

21.

Madhusoodana

, Das

, Kameshima

, . Microwave-assisted hydrothermal synthesis of zeolite films on ceramic supports. J Mater Sci. 2006;41(5):1481–1487. doi:10.1007/s10853-006-7490-y

22.

Zhang

, Wang

, Liu

, . Factors affecting the synthesis of hetero-atom zeolite Fe-ZSM-5 membrane. Sep Purif Technol. 2003;32(1–3):151–158. doi:10.1016/S1383-5866(03)00028-5

23.

Katariya

, Jana

, Parikh

PA.

Corrosion inhibition effectiveness of zeolite ZSM-5 coating on mild steel against various organic acids and its antimicrobial activity. J Ind Eng Chem. 2013;19(1):286–291. doi:10.1016/j.jiec.2012.08.013

24.

Honkanen

, Hoikkanen

, Vippola

, . Characterization of silane layers on modified stainless steel surfaces and related stainless steel–plastic hybrids. Appl Surf Sci 2011;257(22):9335–9346. doi:10.1016/j.apsusc.2011.05.058

25.

Huang

, Hao

, ChangJean

, . Growth of MFI zeolite film as corrosion protection layer of aluminum alloy. Microporous Mesoporous Mater. 2015;217:71–80. doi:10.1016/j.micromeso.2015.05.045

26.

Chau

JLH

, Tellez

, Yeung

, . The role of surface chemistry in zeolite membrane formation. J Membr Sci. 2000;164(1–2):257–275. doi:10.1016/S0376-7388(99)00214-8

27.

Huang

, Liu

, Wang

, . Covalent synthesis of dense zeolite LTA membranes on various 3-chloropropyltrimethoxysilane functionalized supports. J Membr Sci. 2013;437:57–64. doi:10.1016/j.memsci.2013.02.058

28.

Galeano

, Cornaglia

, Tarditi

AM.

NaA zeolite membranes synthesized on top of APTES-modified porous stainless steel substrates. J Membr Sci. 2016;512:93–103. doi:10.1016/j.memsci.2016.04.005

29.

Huang

, Liu

, Caro

, . Iso-butanol dehydration by pervaporation using zeolite LTA membranes prepared on 3-aminopropyltriethoxysilane-modified alumina tubes. J Membr Sci. 2014;455:200–206. doi:10.1016/j.memsci.2013.12.075

30.

Huang

, Wang

, Caro

Seeding-free synthesis of dense zeolite FAU membranes on 3-aminopropyltriethoxysilane-functionalized alumina supports. J Membr Sci. 2012;389:272–279. doi:10.1016/j.memsci.2011.10.036

31.

Toorani

, Alifkhazraei

, Mahdivian

, . Effective PEO/silane pretreatment of epoxy coating applied on AZ31B Mg alloy for corrosion protection. Corros Sci. 2020;169:108608. doi:10.1016/j.corsci.2020.108608

32.

Zhou

, Yin

, Fu

YW.

Self-assembling silicon carbide@Kh550 onto carbon fiber for tribological applications. Ceram Int. 2020;46(14):23236–23244. doi:10.1016/j.ceramint.2020.06.108

33.

Qin

, Zang

, Bai

, . Dual functionalization of aligned silicon nanowires by APTES and nano-Ag to achieve high response to rarefied acetone at high ambient humidity. J Mater Sci: Mater Electron. 2021;32(1):908–922. doi:10.1007/s10854-020-04868-5

34.

Karade

, Sharma

, Dhavale

, . APTES monolayer coverage on self-assembled magnetic nanospheres for controlled release of anticancer drug Nintedanib. Sci Rep. 2021;11(1):5674. doi:10.1038/s41598-021-84770-0

35.

Calabrese

, Bonaccorsi

, Proverbio

Corrosion protection of aluminum 6061 in NaCl solution by silane–zeolite composite coatings. J Coat Technol Res. 2012;9(5):597–607. doi:10.1007/s11998-011-9391-5

36.

Wang

A simple, rapid and Low-cost 3-aminopropyltriethoxysilane (APTES)-based surface plasmon resonance sensor for TNT explosive detection. Anal Sci. 2021;37(7):1029–1032. doi:10.2116/analsci.20N028

37.

Plueddemann

ED.

Silane coupling agents. New York: Plenum Press; 1991.