Effect of Cr₂O₃ on the crystallization, structure, and properties of Ti-bearing blast furnace slag-based glass ceramics

ABSTRACT

The effects of Cr₂O₃ on the crystallization, structure, and properties of Ti-bearing blast furnace slag-based glass ceramics were investigated. The results show that the transition temperature and crystallization temperature decreased with introduction of Cr₂O₃ as a while. Specifically, the crystallization temperature first decreased, then increased with the increase Cr₂O₃ concentration from 0.2 wt% to 0.8 wt%, and finally decreased with further increased in Cr₂O₃ concentration. The crystal phases were identified as anorthite, diopside, and akermanite. As the content of Cr₂O₃ increased to 0.8 wt%, the dendrites gradually decreased and the granular crystals gradually increased. When the Cr₂O₃ concentration further increased, the number of granular crystals gradually decreased and the dendrites gradually accumulated. With the increase of Cr₂O₃ from 0.2 wt% to 0.8 wt%, the structure of the investigated glass gradually depolymerized, while the opposite trend was presented with further increased in Cr₂O₃ content. With increasing Cr₂O₃ content from 0.2 wt% to 2 wt%, the flexural strength values and Vickers hardness values of the glass ceramics first increased and then decreased, and the maximum values of flexural strength and Vickers hardness were obtained as 94.371MPa and 974.43MPa, respectively. The prepared Ti-bearing blast furnace slag-based glass ceramics showed good acid and alkali resistance.

KEYWORDS:

• Ti-bearing blast furnace slag
• Cr₂O₃
• glass ceramics
• crystallization

1. Introduction

Blast furnace slag is an important industrial solid waste produced in the blast furnace ironmaking process [1], which is primarily used to produce building materials with low added values, such as cement, concrete, and bricks [2]. The Ti-bearing blast furnace slag is a by-product of vanadium-titanium-bearing magnetite smelting in blast furnace ironmaking and mainly composed of SiO₂, CaO, MgO, TiO₂, and Al₂O₃ [3]. Since the presence of TiO₂ will reduce the stability of building materials [4], it is typically used to extract titanium. However, the economic value of Ti-bearing blast furnace slag with low-grade TiO₂ (<10 wt%) is rather low. As a result, it is pertinent to develop a method to efficiently and comprehensively utilize low Ti-bearing blast furnace slag.

Glass ceramic is a multiphase material with both a mini-crystal phase and glass phase [5–7]. Glass ceramics possess many remarkable properties, such as excellent mechanical strength, chemical stability, thermal stability, corrosion resistance, and so on [8–16]. The properties of glass ceramics largely depend on crystallization behaviors, such as crystal grain size, quantity, types of main crystal phases, and so on. Various nucleating agents can effectively promote the transformation of glass and refine the crystal grains to achieve bulk crystallization. Examples include Cr₂O₃, TiO,₂ and CaF₂, which can each be added to the glass system to improve the material properties [17–19].

Based on the composition of Ti-bearing blast furnace slag, it is considered a typical silicate material, which can be utilized as a glass ceramic. In addition, according to previous studies [3,7,20,21], TiO₂ can be regarded as a good nucleating agent to control the crystallization behavior of glass ceramics. As a result, the low Ti-bearing blast furnace slag can be a good candidate for the preparation of slag-based glass ceramics [22], where a small amount of TiO₂ in the Ti-bearing blast furnace slag can be the nucleating agent. In our previous work [23], the effects of TiO₂ on the crystallization behavior of Ti-bearing blast furnace slag-based glass ceramics were investigated. The results suggested that it was difficult to achieve three-dimensional crystal growth and two-dimensional crystallization was shown in the sample with 2 wt% TiO₂. To further optimize the crystallization properties of Ti-bearing blast furnace slag-based glass ceramics, an appropriate nucleating agent must be considered. Zhang et al. [24]. showed that adding Cr₂O₃ can accelerate the crystallization of the pyroxene phase, and the prepared glass ceramics showed high strength and good chemical resistance with the introduction of Cr₂O₃. Wang et al. [25] reported that the addition of a small amount of Cr₂O₃ can induce the crystallization of the parent glass, and found that the glass ceramics showed uniform, compact grains, and high bending strength values in the range of 84.6 ~ 101.7 MPa. Back et al. [9] revealed that the crystallization activation energy of SiO₂-Al₂O₃-CaO-MgO based glass ceramics was reduced with the addition of Cr₂O₃. Deng et al. [26] also reported that by increasing the Cr₂O₃ concentration from 1.5 wt% to 2.5 wt%, the two-dimensional crystallization can be changed to three-dimensional crystallization, and the dendrite could be gradually refined. From the above studies, adding a certain amount of Cr₂O₃ can effectively promote crystallization and improve the bending strength, chemical resistance, and so on.

In this work, by analyzing the crystallization behavior and properties of prepared glass ceramics with different additions of Cr₂O₃, the effects of Cr₂O₃ on the Ti-bearing blast furnace slag-based glass ceramics were investigated. This study provides theoretical and technical support for the efficient and comprehensive utilization of low Ti-bearing blast furnace slag.

2. Experimental

2.1. Sample preparation

Ti-bearing blast furnace slag was obtained from an iron and steel plant in China, which was the main raw material in preparation of glass ceramics. As shown in Table 1, the chemical compositions were characterized by X-ray fluorescence spectroscopy (XRF) (Polish PANalytical B.V., Axios Advanced).

Table 1. Chemical composition of the original Ti-bearing blast furnace slag (wt%)

	CaO	SiO2	Al2O3	TiO2	MgO	Fe2O3	Cr2O3	Others
wt%	35.00	31.83	13.54	6.71	6.13	1.35	0.02	5.42

The CaO/SiO₂ mass ratio of the original Ti-bearing blast furnace slag was about 1.1, which was higher than that of ordinary silicate-based glass ceramics, so the chemical reagent SiO₂ was added to adjust the CaO/SiO₂ to 0.5. At the same time, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1.1 wt%, and 2 wt% Cr₂O₃ were added, respectively. The chemical compositions of the glass ceramics were shown in Table 2. After accurate weighing, the specimens were placed in an agate mortar and ground for 30 minutes until uniformly mixed. Then, the powder specimens were placed into a corundum crucible, in a high-temperature tube furnace to melt. The temperature was then increased from room temperature to 1500°C in air and held for 4 hours. After that, the specimens were taken out and quenched with water to obtain the basic glasses, which were identified by X-ray diffraction (XRD) (PANalytical X^’Pert Powder, Spectris Pte, the Netherlands), as shown in Figure 1.

Figure 1. XRD patterns of the water-quenched samples with different contents of Cr₂O_3.

Table 2. Chemical composition of Ti-bearing blast furnace slag-based glass ceramics (wt%)

Sample	CaO	SiO2	Al2O3	TiO2	MgO	Fe2O3	Others	CaO/SiO2	Cr2O3
S0	25.33	50.66	9.80	4.85	4.44	0.98	3.94	0.50	-
S1	25.41	50.82	9.77	4.96	4.46	0.92	3.46	0.50	0.20
S2	25.33	50.66	9.74	4.94	4.44	0.92	3.47	0.50	0.50
S3	25.26	50.52	9.72	4.93	4.43	0.91	3.43	0.50	0.80
S4	25.18	50.36	9.69	4.91	4.42	0.91	3.43	0.50	1.10
S5	24.95	49.90	9.60	4.87	4.38	0.90	3.40	0.50	2.00

Afterward, 1 wt% polyvinyl alcohol and 5 wt% zinc stearate and pure water were used as binders. An FYD-30 electric powder compactor was used to press the basic glass into the cylinder with a diameter of 8 mm and cuboid with dimensions of 50x6x6 mm for mechanical property detection. The pressed samples were heated to 600°C for 1 h in a high-temperature tube furnace. The transition temperatures (T_g) of the investigated glasses were determined using differential scanning calorimetry (DSC) (449F3, NETZSCH, Germany). The nucleation temperature was estimated to be 800°C, which is normally 50 ~ 100°C greater than the T_g of glasses [5,27].

The first exothermic peak temperature of DSC was used as the crystallization temperature to prepare glass ceramics. The specimens were held at 800°C for 2 h and then heated to its crystallization temperature for 1.5 h at a heating rate of 5°C/min to obtain the glass ceramics. The specific preparation process of Ti-bearing blast furnace slag-based glass-ceramics was shown in Figure 2.

Figure 2. The specific preparation process of Ti-bearing blast furnace slag-based glass-ceramics

2.2. Characterizations and measurements

The parent glass powders were examined by DSC in air from room temperature to 1300°C at a heating rate of 5°C/min to obtain the transition temperature and crystallization temperature. The crystallization phases of glass ceramics were identified by XRD. In addition, scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS) (JSM-7800 F, JEOL, Japan) was used to observe the distribution of crystal phase and morphology of the prepared glass ceramics. The structures of the parent glasses were analyzed using a Raman spectrometer (HORIBA Jobin Yvon S.A.S, France) at room temperature in the range of 200–1500 cm⁻¹. The microhardness-tester (MH-5 L, Shanghai, China) was used to measure the Vickers hardness with a measuring force of 300 N and a load time of 15 s, and the Vickers hardness values were obtained by calculating the average of five detection values. The flexural strength of glass ceramics was detected by the electronic universal material testing machine (CMT4303, MTS, American) with a span of 40 mm and descending speed of 0.5 mm/min. Afterward, the flexural strength values of the glass ceramics were calculated by the equation according to GB/T 6569–2006, as shown in equation (1)(1) ${\sigma }_f=(3FL)/\left(2b{d}^2\right)$(1) :

(1) ${\sigma }_f=(3FL)/\left(2b{d}^2\right)$(1)

where ${\sigma }_f$ is the flexural strength (MPa), F is the maximum load (N) and L is the lower span of fixture (mm). Also, b and d are the width and height of the sample (mm), respectively. The flexural strength values were obtained by calculating the average of five measurements.

The density was determined using equation (2)(2) $\rho =m_0/\left(h\ast \pi \ast r^2\right)$(2) :

(2) $\rho =m_0/\left(h\ast \pi \ast r^2\right)$(2)

where ρ is the density of the glass ceramics, $m_0$ is the mass of the glass ceramics, $h$ is the height of cylindrical sample, and $r$ is the radius of the cylindrical sample.

Moreover, after immersing the glass ceramics in 5% H₂SO₄ and 5% NaOH solutions for 24 hours, the changes in surface and weight before and after were observed to determine the acid and alkali corrosion resistance of the glass ceramics. The chemical stability was calculated by weighing the samples before corrosion (m₀) and after corrosion (m₁):

(3) $\mathrm{K}\left(\mathrm{\%}\right)=100m_1/m_0$(3)

3. Results and discussion

3.1. Thermal analysis of glass ceramics

Figure 3 shows the DSC curves of Ti-bearing blast furnace slag-based glass samples with different Cr₂O₃ contents at a heating rate of 5°C/min. The transition temperature (T_g) and crystallization temperature (T_p) have been determined as the endothermic and exothermic peak temperatures, respectively, as marked in Figure 3. The transition temperature and crystallization temperature decreased with the introduction of Cr₂O₃ as a while. Specifically, the crystallization temperature first decreased with the introduction of Cr₂O₃, then increased with the increase Cr₂O₃ concentration from 0.2 wt% to 0.8 wt%, and finally decreased with further increases in Cr₂O₃ concentration.

Figure 3. DSC curves of the parent glasses with different contents of Cr₂O_3.

Therefore, it can be concluded that crystallization was promoted as the introduction of Cr₂O₃ as a while. However, it was slightly inhibited as the Cr₂O₃ concentration increased from 0.2 wt% to 0.8 wt%, and then was slightly promoted again as a further increase in Cr₂O₃ concentration. Two observed exothermic peaks were observed in the DSC curves for all samples, indicating that there were at least two successive crystallization events. It can be observed that T_g was approximately 720 ~ 750°C. Therefore, in this work, the nucleation temperature was estimated to be 800°C in this work, which was normally 50 ~ 100°C greater than T_g of glasses. The actual T_p of each glass was applied as the crystallization temperature for the preparation of glass ceramics.

3.2. Crystal phase and morphological analysis

The crystal phases of the prepared glass ceramics were identified by XRD, as shown in Figure 4. There were anorthites, ordered (CaAl₂Si₂O₈), diopside (Ca_0.959Ti_0.041) (Mg_{0. 987}Al_0.013) (Si_1.905Al_0.095O₆) and akermanite, syn(Ca₂MgSi₂O₇) crystals co-precipitated. It can be seen that part of titanium has entered into the crystal of diopside and the chromium has entered into glass phase. The relative intensity of CaAl₂Si₂O₈ was the strongest, indicating that it was the primary crystal of the prepared glass ceramics. With increasing Cr₂O₃ concentration, no obvious change was observed. Therefore, the introduction of Cr₂O₃ did not change the main crystals of Ti-bearing blast furnace slag-based glass ceramics.

Figure 4. X-ray diffraction patterns of Ti-bearing blast furnace slag-based glass ceramics

Figure 5 shows the SEM results of the polished Ti-bearing blast furnace slag-based glass ceramics. Apparently, the distributions between the glassy phase and the crystal phase were relatively uniform. The results of EDS point detections showed that the crystal phase in the glass ceramics was CaAl₂Si₂O₈. As shown in the example of 0.2 wt% Cr₂O₃, shown in Figure 6, this is consistent with the XRD results. Other phases were not identified which may be due to their low content and/or small size. As can be observed from Figure 5(a–c), the crystals were interlaced with each other in the form of dendrites and embedded in the glass ceramics. In addition, it can be observed that the size of dendrites in the glass ceramic with no introduction of Cr₂O₃ was much smaller than that of additional Cr₂O₃. As Cr₂O₃ content increased from 0.2 wt% to 0.8 wt%, the dendrites gradually decreased and granular crystals gradually increased. When the Cr₂O₃ concentration is increased to 0.8 wt%, the dendrites almost change to granular crystals, and the crystal size was obviously decreased to less than 1 μm. However, with increase in Cr₂O₃ concentration, the number of granular crystals gradually decreased, and the dendrites gradually accumulated again via aggregation.

Figure 5. SEM images of the polished Ti-bearing blast furnace slag-based glass ceramics. (a)S0, (b)S1, (c)S2, (d)S3, (e)S4 and (e)S5

Figure 6. SEM image of sample with 0.2 wt% Cr₂O₃, with EDS analysis overlaid on the photographs

This can suggest that the addition of 0.2 wt% Cr₂O₃ can promote the dendrites in glass to grow up quickly, while the morphology of the main crystals was transformed into granular crystals and the size of the crystals was refined with further increase in Cr₂O₃ concentration from 0.2 wt% to 0.8 wt%. Also, with further increase in Cr₂O₃ concentration, crystallization was promoted again to cause the presence of greater size of dendrites.

3.3. Structural analysis of parent glasses

The structure of the glass is a deeply related to its properties. The Raman spectra for CaO-Al₂O₃-SiO₂-TiO₂-Cr₂O₃ glasses at room temperature were recorded to investigate the parent glass structure. According to previous studies [28–30], the characteristic peaks within the 800–1100 cm⁻¹ region included the main information on silicate-based glasses. Therefore, the present Raman spectra within 800–1100 cm⁻¹ region were deconvoluted by assuming the Gaussian-Deconvolution method similar to the method by Mysen et al. [31]. The [SiO₄] tetrahedron structural units can be separated into five types – Qⁱ (i = 0,1,2,3,4, where i represents the number of bridge oxygen per SiO₄ tetrahedra) from the previous reports [17,28,30,32]. Therefore, the best-fit simulations with the minimum correlation coefficient r² ≥ 0.995 were applied, as shown in Figure 7(a–f) [29,32]. It was observed that there were an intense band at about 890 cm⁻¹ which was attributed to the vibrations of Ti-O-Si or Ti-O-Ti [29,33]. The other strong band located at about 1035 cm⁻¹ was corresponded to Q³ and a relatively weak band near 930 cm⁻¹ and 1 000 cm⁻¹ were referred to as Q¹ and Q² structure based on previous study [34]. It can be seen that the intensity of Q³ gradually decreased with the content of Cr₂O₃ increasing from 0 wt% to 0.8 wt%, while it was increased with further increase in Cr₂O₃ concentration.

Figure 7. Deconvolved results of Raman spectra for the parent glasses with different Cr₂O₃ contents. (a)S0, (b)S1, (c)S2, (d)S3, (e)S4 and (f)S5

A summary of the deconvolution results was shown in Table 3. The results suggested that the main structure unit in Ti-bearing blast furnace slag-based glass was the sheet (Q³). The ratio of dimer (Q¹) and chain (Q²) gradually increased, while the ratio of Q³ gradually decreased as the Cr₂O₃ content increased from 0 wt% to 0.8 wt%. However, the relative intensities of Q³ increased with constantly increasing Cr₂O₃ concentration.

Table 3. Deconvolved results of Raman spectra for the parent glasses

Sample number	Percentage of each unit (%)
	Q^1	Q^2	Q^3
S0	17.75	13.68	68.57
S1	23.09	15.09	61.82
S2	28.21	16.70	55.08
S3	30.06	21.69	48.24
S4	19.59	20.33	60.08
S5	20.10	25.52	54.38

Based on some studies [29,35], the average number of bridging oxygen atoms of each sample can be estimated by the area ratio of each structural unit (Q⁰, Q¹, Q², and Q³) multiplied by the number of bridging oxygens, as shown in Figure 8. It was clear that the amount of bridging oxygen reached a minimum as Cr₂O₃ content is 0.8 wt%. According to previous study [17], the increase in bridging oxygen caused the silicate structure to polymerize. Therefore, with the increase of Cr₂O₃ from 0 wt% to 0.8 wt%, the structure of the investigated glass was gradually depolymerized, while the opposite trend was presented with further increase of Cr₂O₃. The decrease of the sheet (Q³) reduced the degree of polymerization of CaO-Al₂O₃-SiO₂-TiO₂-Cr₂O₃ glasses. As a consequence, when the content of Cr₂O₃ was 0.8 wt%, it contributed to the formation of a simple silicon-oxygen group, which can provide excellent kinetic conditions for crystallization, so that the crystallization temperature was the lowest at 8 wt% Cr₂O₃ [17]. Moreover, the simple silicon-oxygen group of glass can promote nucleation and crystallization. As the concentration increased to 0.8 wt%, the number of nuclei formed gradually increased, and the growth spaces of the nuclei restricted to each other during crystallization so that the crystal grain size was gradually decreased. As a result, the dendrites were gradually changed to a smaller sized granular crystal and the surface of the glass ceramics became denser. With a further increase in Cr₂O₃, crystallization was inhibited, and the dendrites were precipitated again by another increase in Q³.

Figure 8. Effects of Cr₂O₃ content on the number of the average bridging oxygen

3.4. Properties of Ti-bearing blast furnace slag-based glass ceramics

Figure 9 showed the measurement results of the flexural strength of Ti-bearing blast furnace slag-based glass ceramics. With the introduction of Cr₂O_3, the flexural strength showed a slight decrease. Then, as the concentration of Cr₂O₃ further increased from 0.2 wt% to 2 wt%, the flexural strength values initially increased and then decreased, reaching a maximum of 94.371 MPa when the Cr₂O₃ content was 0.8 wt%. According to a previous study [1], uniform crystal distribution and small size crystals can enhance the flexural strength. When the content of Cr₂O₃ increased from 0.2 wt% to 0.8 wt%, the size of the crystal was smaller, and the distribution was uniform, thus leading to enhanced flexural strength. When the content of Cr₂O₃ increased from 0.8 wt% to 2 wt%, the size of the crystal gradually increased and the microstructure became loose and the flexural strength values decreased accordingly. While the greater flexural strength for the sample with no addition of Cr₂O₃ may be due to its evenly distributed small dendrites in glass.

Figure 9. The change of the flexural strength of glass ceramic with different Cr₂O₃ contents

The Vickers hardness values for the glass ceramic samples with different Cr₂O₃ concentrations are presented in Figure 10. The Vickers hardness values increased first and then decreased with the concentration of Cr₂O₃ increasing from 0.2 wt% to 2 wt%. Furthermore, when the content of Cr₂O₃ is 0.8 wt%, the Vickers hardness value reached a maximum hardness of 974.43 MPa. When the Cr₂O₃ content is 0.8 wt%, the largest number of small-sized granulate crystals were formed in the glass ceramics and uniformly distributed, and the glass ceramics have excellent Vickers hardness values.

Figure 10. The change of the Vickers hardness of glass-ceramic with different Cr₂O₃ contents

Therefore, it can be concluded that Cr₂O₃ can promote nucleation and crystallization with a low content (≤0.8 wt%). The crystallization temperature can be decreased, and the crystal size can be refined as the concentration of Cr₂O₃ increased from 0.2 wt% to 0.8 wt% due to the role of depolymerization on the silicate glass network. With further increase in Cr₂O₃ content, the opposite trend was obtained due to the highly polymerized structure. Additionally, the small-sized granulate crystals can enhance the flexural strength and Vickers hardness of Ti-bearing blast furnace slag-based glass ceramics.

In summary, this research demonstrated that a certain amount of Cr₂O₃ can promote the precipitation of crystals and generate crystallite to improve the related mechanical performance of glass ceramics.

To analyze the corrosion resistance properties of the prepared glass ceramics, the glass ceramic samples were immersed in 5% H₂SO₄ and 5% NaOH solutions for 24 h, as shown in Figure 11. It can be seen that the glass ceramics showed a certain amount of fading after soaking in 5% H₂SO₄ solution for 24 hours. However, no obvious changes were found on the surface of the samples after soaking in 5% NaOH solution for 24 hours.

Figure 11. The surface condition of the glass ceramics before and after the acid and alkali resistance test

The weight changes of glass ceramics before and after the acid and alkali corrosion test are listed in Table 4. The mass loss of samples in acid was less than 2%, and in an alkaline environment was less than 1%. As a result, the prepared glass ceramics have good acid and alkali resistance properties, especially the alkali resistance properties. In addition, the densities of the prepared glass ceramic were measured and shown in Table 4. The densities are in the range of 2.65–2.80 g/cm³, which was similar range with other slag-based glass ceramics reported by previous studies [24,36,37],

Table 4. Density, Acid, and Alkali Resistance of the glass ceramics with different contents of Cr₂O_3.

Samples	Density (g.cm^−3)	Acid Resistance (%)	Alkali Resistance (%)
S0	2.79 ± 0.10	98.44 ± 0.10	99.94 ± 0.10
S1	2.76 ± 0.10	98.94 ± 0.10	99.94 ± 0.10
S2	2.72 ± 0.10	99.36 ± 0.10	99.95 ± 0.10
S3	2.72 ± 0.10	99.39 ± 0.10	99.94 ± 0.10
S4	2.67 ± 0.10	98.87 ± 0.10	99.95 ± 0.10
S5	2.75 ± 0.10	98.13 ± 0.10	99.94 ± 0.10

The prepared glass ceramics showed excellent properties, such as flexural strength, acid resistance, alkali resistance for the samples with no addition and 0.8 wt% addition of Cr₂O₃, as shown in Table 5. The maximal flexural strength of the investigated blast furnace slag glass-ceramic reached 109.58 MPa. The introduction of Cr₂O₃ induced a slightly decrease in flexural strength and an increase in hardness. On the whole, the flexural strength of the current blast furnace slag-based glass-ceramics is slightly higher than that of others but lower than that of AOD slag-based glass-ceramics. The slag-based glass ceramics showed excellent acid and alkali corrosion resistance [5,38,39].

Table 5. Comparison of main properties of glass-ceramics prepared with better properties with those of others’ works

Samples	Flexural strength (MPa)	Hardness (MPa)	Acid Resistance (%)	Alkali Resistance (%)
S0	109.58	882.66	98.44 ± 0.10	99.94 ± 0.10
S3	94.37	974.43	99.39 ± 0.10	99.94 ± 0.10
Blast furnace slag-based [38]	89.00	-	-	-
AOD slag-based [39]	137.93	-	99.92	99.99
Blast furnace slag-based [5]	102.20	-	99.72	99.67

4. Conclusion

Herein, the effects of Cr₂O₃ on the crystallization behaviors, microstructure, mechanical properties, and physicochemical properties of Ti-bearing blast furnace slag-based glass ceramics were investigated. The following conclusions can be drawn:

1) The transition temperature and crystallization temperature decreased with the introduction of Cr₂O₃ as a while. Specifically, the crystallization temperature first decreased with the introduction of Cr₂O₃, then increased with the increase Cr₂O₃ concentration from 0.2 wt% to 0.8 wt%, and finally decreased with further increases in Cr₂O₃ concentration.

2) The crystal phases of Ti-bearing blast furnace slag-based glass ceramics are identified as anorthite, ordered (CaAl₂Si₂O₈), diopside ((Ca_0.959Ti_0.041)(Mg_0.987Al_0.013) (Si_1.905Al_0.095O₆)) and akermanite, syn(Ca₂MgSi₂O₇). The main crystal phases of glass ceramics show negligible changes with increasing Cr₂O₃ content. As the content of Cr₂O₃ increased to 0.8 wt%, the dendrites gradually decreased and the granular crystals gradually increased. When the Cr₂O₃ concentration further increased, the number of granular crystals gradually decreased and the dendrites gradually accumulated.

3) The main structure unit in Ti-bearing blast furnace slag-based glass was the sheet Q³. With the increase of Cr₂O₃ from 0 wt% to 0.8 wt%, the structure of the investigated glass was gradually depolymerized, while the opposite trend was presented with further increase in Cr₂O₃ content. The relationship between the structure and crystallization of the prepared glass ceramics was discussed.

4) With increasing Cr₂O₃ content from 0.2 wt% to 2 wt%, the flexural strength values and Vickers hardness values of the glass ceramics first increased and then decreased. When the content of Cr₂O₃ was 0.8 wt%, the maximum values of flexural strength and Vickers hardness were obtained as 94.371MPa and 974.43MPa, respectively. The greater flexural strength of the sample with no addition of Cr₂O₃ may be due to it’s evenly distributed small dendrites in glass. The prepared Ti-bearing blast furnace slag-based glass ceramics showed good acid and alkali resistance, especially alkali resistance. The recommended content of Cr₂O₃ was 0.8 wt% for the addition of Ti-bearing blast furnace slag-based glass ceramics.

Acknowledgments

This work was supported by National Training Program of Innovation and Entrepreneurship for Undergraduates (202010611041).

Disclosure statement

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

Additional information

Funding

This work was supported by the National College Students Innovation and Entrepreneurship Training Program [202010611041].