**2. Features of synthesis of glass-ceramic coatings on stainless steels**

Ferritic and ferritic-martensitic stainless steels are widely used in electrical engineering as heat carriers and metal substrates for the manufacturing of film heating elements (FHE) (**Figure 1**). To insulate the metal substrate from the action of electric current, a dielectric insulation coating is applied to its surface. There are a large number of materials that can be used as electrical insulators at high temperatures. But for the correct choice of technology of a quality coating on the surface of stainless steel, it is necessary to take into account the coefficient of linear thermal expansion (CLTE) and the absence of phase transformations in the structure of the coating material during operation [2].

Due to the compatibility of thermal, physical, and micromechanical properties of stainless steels to the protective coatings, a material based on the fusible glass ceramics of the ZnO-PbO-B2O3 system was proposed as a coating material [3–15].

For the preparation of coatings based on the PbO-ZnO-B2O3 glass-crystal system, mixtures of powders, the compositions of which are shown in **Table 1**, were used. Each mixture was poured into an electrocorundum crucible and melted

#### **Figure 1.**

*Schematic diagram of a film heating element [2]: (1) stainless steel substrate, (2) dielectric layer, (3) resistive element, (4) protective shell, and (5) contact electrodes with current collectors.*


*Technologies of High-Temperature Insulating Coatings on Stainless Steels DOI: http://dx.doi.org/10.5772/intechopen.91334*

#### **Table 1.**

others), ferritic (AISI 430, 430Ti, 439, and others), martensitic (AISI 420, 431, 420F), austenitic-martensitic (AISI 631, AM350), and austenitic-ferritic (AISI 301) stainless steels are distinguished. Chromium ferritic and chromium-nickel austen-

Chromium ferritic stainless steels are the cheapest, but they are inferior to chromium-nickel steels in corrosion resistance. So, AISI 430 steel is stable in acidic environments, but not suitable for welding, because during welding when heated above 900–950°C and rapidly cooled, the grain boundaries become depleted in chromium. With content less than 12% Cr, the electrochemical potential of the steel becomes negative, and it loses its ability to resist corrosion. Under these conditions, AISI 430 steel has a dangerous type of corrosion—intercrystalline corrosion. Stabilization of this steel with titanium or niobium is used to prevent this. It should be noted that σ phase (Fe, Cr) can be formed in high-chromium steels as a result of delamination of the alloyed solid solution into a mixture of α + α<sup>0</sup> phases (where α<sup>0</sup> is σ phase). Due to this, the corrosion resistance of such steels is reduced. In ferritic steels with 20% Cr, the minimum formation time of the σ phase at 600°C is 150 h, and in the steels with 25% Cr at 650°C, it is 15 h. Therefore, when using these steels,

**2. Features of synthesis of glass-ceramic coatings on stainless steels**

Ferritic and ferritic-martensitic stainless steels are widely used in electrical engineering as heat carriers and metal substrates for the manufacturing of film heating elements (FHE) (**Figure 1**). To insulate the metal substrate from the action of electric current, a dielectric insulation coating is applied to its surface. There are a large number of materials that can be used as electrical insulators at high temperatures. But for the correct choice of technology of a quality coating on the surface of stainless steel, it is necessary to take into account the coefficient of linear thermal expansion (CLTE) and the absence of phase transformations in the structure of the

Due to the compatibility of thermal, physical, and micromechanical properties of stainless steels to the protective coatings, a material based on the fusible glass ceramics of the ZnO-PbO-B2O3 system was proposed as a coating material [3–15]. For the preparation of coatings based on the PbO-ZnO-B2O3 glass-crystal system, mixtures of powders, the compositions of which are shown in **Table 1**, were used. Each mixture was poured into an electrocorundum crucible and melted

*Schematic diagram of a film heating element [2]: (1) stainless steel substrate, (2) dielectric layer, (3) resistive*

*element, (4) protective shell, and (5) contact electrodes with current collectors.*

itic steels are the most common in engineering practice [1].

*Engineering Steels and High Entropy-Alloys*

it is desirable to bypass this temperature range.

coating material during operation [2].

**Figure 1.**

**58**

*Chemical compositions of powders for the synthesis of the PbO-ZnO-B2O3 glass-ceramic system-based coatings [2].*

at 1180°C. After holding at this temperature for 60 min, the melt was rapidly cooled to form an amorphous structure and prevent crystallization. The dried granules were ground and sieved to obtain powder fractions with a granule average size of not more than 56 μm. On the basis of the powder obtained, a dielectric paste was made, which was applied to a prepared surface of AISI 420 steel samples and dried at 70°C. For all specimens, standard heat treatment [16–20] was performed with two-step annealing at 380 and 440°C and holding at these temperatures for 45 min. The thermal treatment of the coatings was carried out without a protective atmosphere to activate the formation of oxides.

The coatings were applied to the surface of AISI 420 stainless steel. To determine the adhesion properties, the steel surfaces were treated with three different methods, which allowed obtaining different indices of surface roughness: S1, machine grinding; S2, electrolytic etching; S3, manual grinding [3].

Using the method of interference profilometry, surface profilograms of AISI 420 stainless steel substrates were obtained after various surface treatment methods. From the obtained profilograms using the software "Micron-Gamma," the basic parameters of the roughness of the substrates were calculated, the values of which are given in **Table 2**.

The surface of AISI 420 stainless steel with roughness S1 and S3 is characterized by a nonuniform row structure with gaps and projections of the height of 4.6–5.2 μm (**Figure 2**). The surface of AISI 420 stainless steel with roughness S3 after electrolytic etching has a more uniform structure. The height of the needle projections is uniform and averages 5.3 μm.

Traditional methods do not allow qualitative estimation of quantitative indices of adhesion strength of coatings obtained by the method of thick films, the thickness of which exceeds 100 μm. Because of this, indirect methods of investigation can be used to predict the adhesion strength of such coatings, in particular, the determination of the free surface energy of the substrates on which the coatings are synthesized (**Figure 3**). It is known that the level of surface energy will specify the adhesion properties. This technique allows determining the level of the adhesion


**Table 2.**

*Surface roughness parameters of the AISI 420 steel substrates after various types of grinding operations [3].*

#### **Figure 2.**

*Three-dimensional surface microtopography of AISI 420 steel substrates after various types of grinding operations: (a) machine grinding S1; (b) electrolytic etching S2; (c) manual grinding S3 [3].*

By changing the values of the wetting angle using two calculation methods, the values of the free surface energy components for the substrates S1, S2, and S3 were determined (**Table 3**). The first calculation method [25] gave a large variation of the experimental data, which makes it difficult to predict the physical and mechanical properties of the surface being studied. According to the second calculation method [26], the substrates S1 and S2 have the highest values of the free surface energy. This is confirmed by the fact that the actual contact surface area increases with increasing roughness. This, in turn, will increase the free surface energy indices, which will be reflected in the adsorption component of adhesion.

*Values of wetting angles for AISI 420 stainless steel substrates after machine grinding S1, electrolytic etching S2,*

*and manual grinding S3 depending on the substance of the droplet.*

*Technologies of High-Temperature Insulating Coatings on Stainless Steels*

*DOI: http://dx.doi.org/10.5772/intechopen.91334*

**Lifshitz-van der Waals energy γLW (mJ/m<sup>2</sup> )**

*PbO-ZnO-B2O3 glass crystalline system [3].*

Thus, the formation of the developed surface structure of AISI 420 stainless steel substrates obtained by the surface etching method will provide the maximum level of the free surface energy by forming the largest contact area between the applied dielectric layer and the substrate, which will provide the best level of adhesion

To obtain a high-quality insulation coating on the surface of stainless steels, it is necessary to ensure the maximum homogeneity of its structure in both the thickness and surface area. The surface roughness of such coatings must be within *Rz* = 1–2 μm to provide the required adhesion strength between dielectric and resistive

> **Energy of the electron acceptors γ<sup>+</sup> (mJ/m<sup>2</sup> )**

S1 Method 1 32.3 0.2 2.7 34.2 Method 2 34.8 1.4 4.8 39.9 S2 Method 1 39.2 1.2 0.7 41.0 Method 2 36.9 2.5 1.1 40.2 S2 Method 1 38.2 2.4 0.6 40.6 Method 2 34.9 7.4 0.4 38.2

*Values of the free surface energy constituents for the substrates S1, S2, and S3 and coatings based on the*

**Energy of the electron donors γ (mJ/m2 )**

**Total surface energy γtot (mJ/m<sup>2</sup> )**

uniformity [3].

**Constituents of surface energy**

**Table 3.**

**61**

**Figure 4.**

#### **Figure 3.**

*General view of the desktop of the KSV Attension Theta optical tensiometer (a) and the droplet along with the calculated wetting angles (b) [3].*

strength in the coating-substrate system if the actual contact area between them is known [21–24].

To predict the adhesion strength of the dielectric coating to the substrate, the surface topography of the prepared substrates was investigated, and the values of the free surface energy were calculated for them. Optical tensiometry was used to calculate the free surface energy with the measurement of wetting angles between the test surface and droplets of substances: water, glycerol, formamide, ethylene glycol, diiodomethane, and bromonaphthalene [3]. **Figure 4** shows the change in the wetting angles for the substrates after various surface treatments, depending on the type of drip fraction of the substance applied to the surface.

The substrates S1 and S2 have the highest average values of the wetting angles. This testifies to the dependence of the wetting angle not only on the physicochemical properties of the droplet but also on the roughness and microtopography of the surface.

*Technologies of High-Temperature Insulating Coatings on Stainless Steels DOI: http://dx.doi.org/10.5772/intechopen.91334*

#### **Figure 4.**

*Values of wetting angles for AISI 420 stainless steel substrates after machine grinding S1, electrolytic etching S2, and manual grinding S3 depending on the substance of the droplet.*

By changing the values of the wetting angle using two calculation methods, the values of the free surface energy components for the substrates S1, S2, and S3 were determined (**Table 3**). The first calculation method [25] gave a large variation of the experimental data, which makes it difficult to predict the physical and mechanical properties of the surface being studied. According to the second calculation method [26], the substrates S1 and S2 have the highest values of the free surface energy. This is confirmed by the fact that the actual contact surface area increases with increasing roughness. This, in turn, will increase the free surface energy indices, which will be reflected in the adsorption component of adhesion.

Thus, the formation of the developed surface structure of AISI 420 stainless steel substrates obtained by the surface etching method will provide the maximum level of the free surface energy by forming the largest contact area between the applied dielectric layer and the substrate, which will provide the best level of adhesion uniformity [3].

To obtain a high-quality insulation coating on the surface of stainless steels, it is necessary to ensure the maximum homogeneity of its structure in both the thickness and surface area. The surface roughness of such coatings must be within *Rz* = 1–2 μm to provide the required adhesion strength between dielectric and resistive


#### **Table 3.**

*Values of the free surface energy constituents for the substrates S1, S2, and S3 and coatings based on the PbO-ZnO-B2O3 glass crystalline system [3].*

strength in the coating-substrate system if the actual contact area between them is

*General view of the desktop of the KSV Attension Theta optical tensiometer (a) and the droplet along with the*

*Three-dimensional surface microtopography of AISI 420 steel substrates after various types of grinding operations: (a) machine grinding S1; (b) electrolytic etching S2; (c) manual grinding S3 [3].*

To predict the adhesion strength of the dielectric coating to the substrate, the surface topography of the prepared substrates was investigated, and the values of the free surface energy were calculated for them. Optical tensiometry was used to calculate the free surface energy with the measurement of wetting angles between the test surface and droplets of substances: water, glycerol, formamide, ethylene glycol, diiodomethane, and bromonaphthalene [3]. **Figure 4** shows the change in the wetting angles for the substrates after various surface treatments, depending on

The substrates S1 and S2 have the highest average values of the wetting angles. This testifies to the dependence of the wetting angle not only on the physicochemical properties of the droplet but also on the roughness and microtopography of the

the type of drip fraction of the substance applied to the surface.

known [21–24].

*calculated wetting angles (b) [3].*

**Figure 3.**

**Figure 2.**

*Engineering Steels and High Entropy-Alloys*

surface.

**60**

layers. It should be noted that the glass-ceramic coating should have a minimum porosity to obtain perfect electrophysical characteristics, in particular, the breakdown voltage and electrical strength.

After synthesis and heat treatment, the obtained glass-ceramic coatings have a dark gray color with shades of green and are smooth to the touch. Small projections and gaps are observed along the entire area of the formed coating. No defects in the form of pores, gas bubbles, or residues of non-smelted sealant (SC, sital cement) powder have been detected. The thickness of the coatings ranges from 90 to 105 μm.

To evaluate the microgeometry parameters of the surface structure for each synthesized coating, the surface topography was investigated in five sections of the surface with a section area of 0.55 0.75 mm2 . Surface profilograms of the coatings were obtained using the interference profilometer (**Figure 5**).

Structural and geometric parameters of the surface roughness of the coatings, the values of which are given in **Table 4**, were calculated from the obtained profilograms using the Micron-Gamma software. According to **Table 4**, the values of *Rz* parameter of the surface roughness are 2.11, 1.87, 1.63, and 2.14 μm for the investigated coatings SC 100-1, SC 90-1, SC 88, and SC 90, respectively.

The study of three-dimensional topography of the surface of the formed coatings by the method of interference profilometry testifies to the presence of identical fragments of their structure, regardless of the microtopography of the substrate surface (**Figure 6**).

Coatings based on powders SC 100-1, SC 90-1, SC 88, and SC 90 have a homogeneous structure with shallow round gaps and needle projections of height 0.8–1.1 μm.

Such surface microtopography of the dielectric coating will guarantee correspond-

*Three-dimensional microtopography of the surfaces of functional coatings based on glass crystalline materials of grades (a) SC 100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 on AISI 420 stainless steel substrates [3].*

**Average distance based on the 10 highest peaks and lowest valleys over the entire sampling length** *R***Z, μm**

SC 100-1 0.55 2.11 2.29 1.01 SC 90-1 0.49 1.87 2.21 1.01 SC 88 0.41 1.63 1.82 1.00 SC 90 0.57 2.14 2.29 1.01

*Parameters of surface roughness of coatings SC 100-1, SC 90-1, SC 88, and SC 90 [3].*

*Technologies of High-Temperature Insulating Coatings on Stainless Steels*

**Maximum height of the profile** *R***max, μm**

**Average step of peaks along the mean line** *S***m, μm**

**2.1 Microstructure of functional coatings based on glass crystalline materials**

The dendritic component has been revealed in the surface layers of the dielectric coatings using a scanning electron microscope (**Figure 7**). This is a positive feature because it is the crystalline component of the microstructure of the PbO-ZnO-B2O3 system coating that is responsible for the proper functional properties of the insulation layer [4]. The largest dendritic crystals are observed in the structure of SC 100-1 and SC 90 coatings. As the coatings of SC 100-1 and SC 90 grades have the highest surface roughness compared to the other two coating grades, it can be assumed that the growth rate of dendritic crystals will affect the final surface

It should be noted that the presence of an amorphous phase in the amount of more

thermophysical characteristics of coatings while increasing the dielectric strength [4].

than 15% will cause a significant deterioration of the micromechanical and

ingly high adhesion strength of the applied resistive layer [1–3].

roughness parameters of the coatings.

**Marking Arithmetical mean**

**Table 4.**

**Figure 6.**

**63**

**deviation of the assessed profile** *Ra***, μm**

*DOI: http://dx.doi.org/10.5772/intechopen.91334*

**Figure 5.**

*Surface profilograms of synthesized functional coatings based on glass crystalline materials of grades (a) SC 100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 on AISI 420 stainless steel substrates [3].*

*Technologies of High-Temperature Insulating Coatings on Stainless Steels DOI: http://dx.doi.org/10.5772/intechopen.91334*


**Table 4.**

layers. It should be noted that the glass-ceramic coating should have a minimum porosity to obtain perfect electrophysical characteristics, in particular, the break-

After synthesis and heat treatment, the obtained glass-ceramic coatings have a dark gray color with shades of green and are smooth to the touch. Small projections and gaps are observed along the entire area of the formed coating. No defects in the form of pores, gas bubbles, or residues of non-smelted sealant (SC, sital cement) powder have been detected. The thickness of the coatings ranges from 90 to 105 μm. To evaluate the microgeometry parameters of the surface structure for each synthesized coating, the surface topography was investigated in five sections of the

Structural and geometric parameters of the surface roughness of the coatings,

The study of three-dimensional topography of the surface of the formed coatings by the method of interference profilometry testifies to the presence of identical fragments of their structure, regardless of the microtopography of the substrate

Coatings based on powders SC 100-1, SC 90-1, SC 88, and SC 90 have a homogeneous structure with shallow round gaps and needle projections of height 0.8–1.1 μm.

*Surface profilograms of synthesized functional coatings based on glass crystalline materials of grades (a) SC*

*100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 on AISI 420 stainless steel substrates [3].*

the values of which are given in **Table 4**, were calculated from the obtained profilograms using the Micron-Gamma software. According to **Table 4**, the values of *Rz* parameter of the surface roughness are 2.11, 1.87, 1.63, and 2.14 μm for the

investigated coatings SC 100-1, SC 90-1, SC 88, and SC 90, respectively.

. Surface profilograms of the coatings

down voltage and electrical strength.

*Engineering Steels and High Entropy-Alloys*

surface (**Figure 6**).

**Figure 5.**

**62**

surface with a section area of 0.55 0.75 mm2

were obtained using the interference profilometer (**Figure 5**).

*Parameters of surface roughness of coatings SC 100-1, SC 90-1, SC 88, and SC 90 [3].*

**Figure 6.**

*Three-dimensional microtopography of the surfaces of functional coatings based on glass crystalline materials of grades (a) SC 100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 on AISI 420 stainless steel substrates [3].*

Such surface microtopography of the dielectric coating will guarantee correspondingly high adhesion strength of the applied resistive layer [1–3].

#### **2.1 Microstructure of functional coatings based on glass crystalline materials**

The dendritic component has been revealed in the surface layers of the dielectric coatings using a scanning electron microscope (**Figure 7**). This is a positive feature because it is the crystalline component of the microstructure of the PbO-ZnO-B2O3 system coating that is responsible for the proper functional properties of the insulation layer [4]. The largest dendritic crystals are observed in the structure of SC 100-1 and SC 90 coatings. As the coatings of SC 100-1 and SC 90 grades have the highest surface roughness compared to the other two coating grades, it can be assumed that the growth rate of dendritic crystals will affect the final surface roughness parameters of the coatings.

It should be noted that the presence of an amorphous phase in the amount of more than 15% will cause a significant deterioration of the micromechanical and thermophysical characteristics of coatings while increasing the dielectric strength [4].

fraction of pores in the structure of the SC 90-1-based glass-ceramic material coating is 4.1%, in contrast to the coating SC 100-1, the average porosity of which

of the PbO-ZnO-B2O3 system with BaO oxide in quantities up to 1.7%, which reduces the temperature of formation of the amorphous glass material in the synthesis stage, which in turn causes acceleration of the sublimation processes of

organic solvents and accelerates the crystallization process [4].

*Quantitative analysis of the porosity of coatings SC 100-1 and SC 90-1.*

**Parameter Coating based on SC 90-1**

*DOI: http://dx.doi.org/10.5772/intechopen.91334*

*Technologies of High-Temperature Insulating Coatings on Stainless Steels*

The difference in the structure of the coatings can be explained by the alloying

**powder**

Number of pores per field of view 157 88 Volume fraction of pores, % 4.1 19.7 Specific surface of pores 0.031 0.047 Mean chord length of pores, μm 5.3 16.9 Average distance between pores, μm 126.5 69.1 Fractal dimension 1.07 1.56 Form factor 0.867 0.825 Compact factor 0.989 0.935 Stretching factor 0.815 0.734 Cutting factor of the contour 0.867 0.859

**Coating based on SC 100-1 powder**

The microstructural analysis of the polished transverse sections of the synthesized coatings on AISI 420 steel substrates was carried out. Using energy dispersive X-ray spectroscopy (EDS), it was found that no diffusion or transition zones are formed between the applied coatings and the substrates. This is evidenced by a sharp drop in the content of lead in the place where the coating is bonded to the substrate (**Figure 9**). This indicates a significant influence of electrochemical processes (double electric layer) during the formation of a strong adhesion of the synthesized glass crystalline coatings of the PbO-ZnO-B2O3 system with the

*The local EDS microanalysis of the coating based on the glass crystalline material of SC 90-1 grade by the depth*

*of the layer showing the distribution of elements (a) Fe, (b) Cr, (c) Si, and (d) Pb.*

is 19.7%.

**Table 5.**

substrate surfaces.

**Figure 9.**

**65**

#### **Figure 7.**

*Surface microstructure of dielectric coatings based on glass crystalline materials of grades (а) SC 100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 [4].*

To evaluate the porosity of coatings based on glass crystalline materials of SC 100-1 and SC 90-1 grades, their microstructure after polishing was investigated (**Figure 8**). They are found to contain a large number of pores of different sizes, unevenly distributed in the bulk of the coatings. The formation of pores can be explained by the uncontrolled process of sublimation of organic solvents (butyl acetate, amyl acetate) during synthesis at temperatures of 250–350°C.

Quantitative analysis of the porosity of synthesized coatings based on SC 90-1 and SC 100-1 powders was carried out (**Table 5**). It was found out that the volume

#### **Figure 8.**

*The microstructure of coatings based on glass crystalline materials of grades (a) SC 100-1 and (b) SC 90-1 after polishing [4].*


*Technologies of High-Temperature Insulating Coatings on Stainless Steels DOI: http://dx.doi.org/10.5772/intechopen.91334*

#### **Table 5.**

To evaluate the porosity of coatings based on glass crystalline materials of SC 100-1 and SC 90-1 grades, their microstructure after polishing was investigated (**Figure 8**). They are found to contain a large number of pores of different sizes, unevenly distributed in the bulk of the coatings. The formation of pores can be explained by the uncontrolled process of sublimation of organic solvents (butyl

*Surface microstructure of dielectric coatings based on glass crystalline materials of grades (а) SC 100-1,*

Quantitative analysis of the porosity of synthesized coatings based on SC 90-1 and SC 100-1 powders was carried out (**Table 5**). It was found out that the volume

*The microstructure of coatings based on glass crystalline materials of grades (a) SC 100-1 and (b) SC 90-1*

acetate, amyl acetate) during synthesis at temperatures of 250–350°C.

**Figure 7.**

**Figure 8.**

**64**

*after polishing [4].*

*(b) SC 90-1, (c) SC 88, and (d) SC 90 [4].*

*Engineering Steels and High Entropy-Alloys*

*Quantitative analysis of the porosity of coatings SC 100-1 and SC 90-1.*

fraction of pores in the structure of the SC 90-1-based glass-ceramic material coating is 4.1%, in contrast to the coating SC 100-1, the average porosity of which is 19.7%.

The difference in the structure of the coatings can be explained by the alloying of the PbO-ZnO-B2O3 system with BaO oxide in quantities up to 1.7%, which reduces the temperature of formation of the amorphous glass material in the synthesis stage, which in turn causes acceleration of the sublimation processes of organic solvents and accelerates the crystallization process [4].

The microstructural analysis of the polished transverse sections of the synthesized coatings on AISI 420 steel substrates was carried out. Using energy dispersive X-ray spectroscopy (EDS), it was found that no diffusion or transition zones are formed between the applied coatings and the substrates. This is evidenced by a sharp drop in the content of lead in the place where the coating is bonded to the substrate (**Figure 9**). This indicates a significant influence of electrochemical processes (double electric layer) during the formation of a strong adhesion of the synthesized glass crystalline coatings of the PbO-ZnO-B2O3 system with the substrate surfaces.

#### **Figure 9.**

*The local EDS microanalysis of the coating based on the glass crystalline material of SC 90-1 grade by the depth of the layer showing the distribution of elements (a) Fe, (b) Cr, (c) Si, and (d) Pb.*

## **2.2 X-ray structural studies of functional coatings based on glass crystalline materials**

The diffraction pattern of the coating based on the SC 100-1 powder (**Figure 10**) confirms the fact of the formation of a crystalline structure during synthesis. It shows pronounced peaks corresponding to lead and zinc as pure chemical elements. The shape and height of the peaks indicate the presence of crystalline phases in the volume of the coating.

To determine the chemical homogeneity of the coatings, a local EDS microanalysis was performed. It was detected lead, zinc, and boron oxides in all types of synthesized coatings in various proportions depending on the location of the analysis.

In the coatings based on SC 90-1, SC 88, and SC 90 powders, BaO and SiO2 oxides were found. Due to the low accuracy of the EDS method when detecting light elements, including boron oxide, the volume fraction of each of the oxides in the coating structure could not be estimated correctly.

X-ray photoelectron spectroscopy (XPS) was used to determine the qualitative and quantitative chemical composition of coatings, as it allows doing this more accurately and detecting all chemical elements except hydrogen and helium. This technique is based on obtaining XPS spectra by irradiating a material with a beam of X-rays (Al Kα) while simultaneously measuring the kinetic energy and number of electrons that escape from the top 0 to 10 nm of the coating being analyzed. To improve the reliability of the results obtained, the evaluation of the chemical composition was performed in three different areas on the sample surfaces. According to the investigation results, experimental diffraction patterns were constructed (**Figure 11**).

It was revealed that the elemental compositions of the synthesized coatings correspond to the compositions of the original powders within the error of the device (2%). As an example, the chemical composition of the synthesized coating based on sital cement of SC 90-1 grade is as follows: 75.3 wt% PbO, 11.6 wt% ZnO, 8.5 wt% B2O3, 2.1 wt% SiO2, 0.8 wt% Al2O3, and 1.7 wt% BaO. Besides, unwanted phases of 0.15% BaSO4, 1.02 % (ZnS + ZnF2), and 0.28% B4C, which could be formed during prolonged isothermal holding and interaction of powder particles with residues of nitrocellulose lacquer, were detected. To avoid the formation of these phases, it is necessary to increase the annealing temperature to accelerate the crystallization process and simultaneously reduce the holding time. However, it

should be remembered that the final crystallization temperature should not exceed

*Experimental X-ray patterns of the surfaces of coatings based on glass crystalline materials of grades (a) SC*

The ion-plasma sputtering as one of the CVD technique methods was chosen as an alternative method of synthesizing protective insulating coatings on stainless steels. As materials for the sputtering, it is advisable to use pure compounds based on nitrides and oxides of metals, which have a wide range of functional properties

The most optimal materials for application to the surfaces of ferritic and ferriticmartensitic stainless steels are coatings of magnesia (MgO), alumina (Al2O3), titanium dioxide (TiO2), and aluminum nitride (AlN) (**Table 6**). It should be noted that the thermal conductivity of beryllium oxide (BeO) is nine times higher than of the listed materials. Thus, it can significantly increase the power of FHE on stainless steel substrates. However, the use of BeO is hampered by its high cost and toxicity during processing. Traditionally, this or that type of ceramics is obtained by sintering oxide or nitride powders at various temperatures. However, high-energy methods of surface engineering are promising when forming dielectric layers on the surfaces of various structural materials. The properties of the layers synthesized in this way, which are given in various literary sources, differ significantly and depend

Magnesium oxide is the only oxygen compound of magnesium. It exists in only one modification and crystallizes in a cubic system. The crystalline form of MgO is called periclase. It has a potassium salt lattice with a parameter of 0.42 nm. By its chemical properties, MgO is a basic oxide, and, as a consequence, it combines with

the glass spill temperature more than two times (in our case up to 520°C).

*100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 obtained by X-ray photoelectron spectroscopy.*

*Technologies of High-Temperature Insulating Coatings on Stainless Steels*

*DOI: http://dx.doi.org/10.5772/intechopen.91334*

**3. Formation of insulating coatings by plasma chemical vapor**

**deposition (CVD)**

on a method used to form these layers.

[27–31].

**67**

**Figure 11.**

*Technologies of High-Temperature Insulating Coatings on Stainless Steels DOI: http://dx.doi.org/10.5772/intechopen.91334*

**Figure 11.** *Experimental X-ray patterns of the surfaces of coatings based on glass crystalline materials of grades (a) SC 100-1, (b) SC 90-1, (c) SC 88, and (d) SC 90 obtained by X-ray photoelectron spectroscopy.*

should be remembered that the final crystallization temperature should not exceed the glass spill temperature more than two times (in our case up to 520°C).
