Composition and structural evolution of basalt melt during homogenization

Zhang P., Feng Z., Guo J., Zheng Y., Yuan P.

Hou Y., Zhang S., Dang J., Guo J., Zhou H., Lü X.

Currently, the Al2O3 content in the high-alumina slag systems within blast furnaces is generally limited to 16wt%–18.5wt%, making it challenging to overcome this limitation. Unlike most studies that concentrated on managing the MgO/Al2O3 ratio or basicity, this paper explored the effect of equimolar substitution of MgO for CaO on the viscosity and structure of a high-alumina CaO–MgO–Al2O3–SiO2 slag system, providing theoretical guidance and data to facilitate the application of high-alumina ores. The results revealed that the viscosity first decreased and then increased with higher MgO substitution, reaching a minimum at 15mol% MgO concentration. Fourier transform infrared spectroscopy (FTIR) results found that the depths of the troughs representing [SiO4] tetrahedra, [AlO4] tetrahedra, and Si–O–Al bending became progressively deeper with increased MgO substitution. Deconvolution of the Raman spectra showed that the average number of bridging oxygens per Si atom and the $$X_{\rm{Q}^{3}}/X_{\rm{Q}^{2}}$$ ( $$X_{\rm{Q}^{i}}$$ is the molar fraction of Qi unit, and i is the number of bridging oxygens in a [SiO4] tetrahedral unit) ratio increased from 2.30 and 1.02 to 2.52 and 2.14, respectively, indicating a progressive polymerization of the silicate structure. X-ray photoelectron spectroscopy (XPS) results highlighted that non-bridging oxygen content decreased from 77.97mol% to 63.41mol% with increasing MgO concentration, whereas bridging oxygen and free oxygen contents increased. Structural analysis demonstrated a gradual increase in the polymerization degree of the tetrahedral structure with the increase in MgO substitution. However, bond strength is another important factor affecting the slag viscosity. The occurrence of a viscosity minimum can be attributed to the complex evolution of bond strengths of non-bridging oxygens generated during depolymerization of the [SiO4] and [AlO4] tetrahedral structures by CaO and MgO.

Fareez U.N., Loudiy A., Erkartal M., Yilmaz C.

ABSTRACTElectromagnetic wave (EMW) radiation pollution is getting more severe as result of the advancement of electronic technology. Researching shielding materials with superior EMI (electromagnetic interference) shielding characteristics is therefore crucial. Basalt fibers (BFs) have been an emerging candidate in the fiber‐reinforced polymer (FRP) category due to their favorable mechanical and chemical properties, along with being favorites in sustainability and having low production costs. Therefore, due to the rising need for cheaper and efficient alternatives in the EMI shielding industry, the EMI shielding is covered in terms of BF composite materials and their properties in this review, starting with the EMI shielding mechanism and followed by how BF composites affect the EMI properties. This review then covers the post‐treatments of BF composites and, finally, the factors of the composites that affect the EMI properties. Moreover, the EMI shielding applications in which BFRPs are used are comprehensively discussed as well. This review aspires to bridge an understanding between EMI shielding as a material property and the BF composites that are developed to aid in the EMI shielding application.

Atalie D., Chen Z., Li H., Liang C., Gao M., Cheng X., Ma P.

This study addresses the need for high-performance and sustainable air filters by developing a bio-based, high-efficiency particulate air (HEPA) filter. Current HEPA filters often rely on non-biodegradable materials, creating environmental burdens. In this paper, we presented a HEPA filter fabricated from natural basalt fiber (BF) and nanocellulose fiber. The developed filter featured a sandwich structure with electrospun nanocellulose fiber deposited onto a base BF layer, followed by a second BF layer and heat treatment. Various techniques were employed to characterize the obtained sample, and the results showed that the nonwoven BF fabric significantly reduced the pressure drop of the filter by up to 60 %. The nanocellulose fiber played a crucial role in achieving a remarkable filtration efficiency of 99.99 % for PM

Guo J., Zhou H., Hou Y., Zhang S., Dang J., Lv X.

Hou Y., Zhang S., Dang J., You Z., Lv X.

This study investigated the impact of BaO/Al2O3 molar ratio on the electrical conductivity and Al coordination state of CaO–MgO–SiO2–Al2O3–BaO slag using four-electrode technique and 27Al MAS-NMR spectroscopy, respectively. With an increasing BaO/Al2O3 molar ratio from 0.14 to 0.36, BaO preferentially participated in charge compensation of Al3+, which facilitated the transition from AlO5 and AlO6 structures to AlO4 structure and increased the stability of AlO4 tetrahedra, thus enhancing the slag’s polymerization and reducing its electrical conductivity. However, once the compensation achieved equilibrium, remaining BaO was involved in depolymerizing the tetrahedral structure and promoting the formation of AlO5 and AlO6 structures. Consequently, the decreased degree of polymerization and increased concentration of free ions together led to an increase in electrical conductivity. However, the increased migration resistance due to the large radius of Ba2+ ion is responsible for the electrical conductivity minimum near the molar ratio of 0.43.

Hou Y., Zhang S., Guo J., Zhou H., Lv X.

This study investigated the effects of equimolar substitution of BaO for CaO and Al2O3 for SiO2 on the viscosity and structure of CaO-SiO2-MgO-Al2O3-BaO slag. In slags containing 2 mol.% Al2O3, introducing BaO disrupted the bridging oxygen bonds, leading to an increase in non-bridging oxygen and the depolymerization of the tetrahedral structure. Consequently, viscosity decreased with increased BaO substitution. However, for slags with 5 mol.% Al2O3, the synergistic effects of preferential charge compensation by Ba2+ for Al3+ and structural depolymerization by BaO led to the initial stabilization of tetrahedral structures, followed by destabilization. This resulted in the viscosity first increasing and then decreasing with higher BaO substitution levels. With the gradual replacement of SiO2 by Al2O3, a significant increase in [AlO4] tetrahedra relative to the decrease in [SiO4] tetrahedra could be observed. Concurrently, a reduction in free oxygen and non-bridging oxygen content was observed, ultimately leading to an increase in viscosity.

Dou H., Wang Y., Bai J., Kong L., Bai Z., Li H., Guo Z., Li W.

The slow dissolution process of zirconium oxide (ZrO2) limits the efficient and energy-saving production of zirconium-rich basalt fibers with excellent alkali resistance for fiber-reinforced concrete. Therefore, it is necessary to investigate the optimum homogenization conditions to produce high-performance zirconium-rich basalt fibers. In this study, quenched zirconium-rich glasses and zirconium-rich fibers with the addition of 7 wt% ZrO2 at different homogenization temperatures and time were prepared. The quenched melt structure was characterized by XRD and FTIR, and followed information about the melt structure obtained by Gaussian curve fitting of the FTIR spectra. The results indicated that obvious ZrO2 crystals appeared in the melts and fibers with homogenization temperature below 1500 °C and time below 4 h. The degree of polymerization of zirconium-rich basalt melt was found to increase with increasing homogenization temperature and time, meanwhile the tensile strength and production stability of zirconium-rich fibers increased with increasing the degree of polymerization. The optimum homogenization temperature and time for zirconium-rich basalt fibers were concluded to be 1580 °C and 10 h, and the corresponding tensile strength is 1799 MPa and 1761 MPa, respectively. By diffusion experiment of ZrO2 in basalt melt with altered major component content, it was found that the Ca, Mg, Na, and Fe significantly facilitated the melting of ZrO2 into basalt melt by XRD and EDS. It was mainly attributed to the charge-compensating effect of metal cations on the [ZrO6] octahedra, which promoted the homogenization of ZrO2 in basalt melt.

Al-Rousan E.T., Khalid H.R., Rahman M.K.

Basalt fiber-reinforced concrete (BFRC) is relatively a new type of fiber-reinforced concrete, which has demonstrated good mechanical performance. Several types of fibers such as steel, glass, and carbon fibers, are used to improve the performance of plain concrete. However, basalt fibers (BF) are being considered superior to these because of their comparable mechanical strength, higher durability than glass fibers, lesser cost than carbon fibers, sustainability due to abundant raw material, and environment-friendly production process. Hence, the number of studies on BFRC are increasing over the years. This review paper covers the properties of BF and BFRC. The effects of BF length and dosage are discussed in detail in term of fresh, hardened, and durability properties of BFRC, followed by highlighting some areas for future research. It is concluded that BF can potentially replace the other conventional fibers which are being used in the industry.

Dou H., Bai J., Lu H., Zhang T., Kong L., Bai Z., Li W.

The low alkali resistance of basalt fiber limits its utilization in the strong alkaline environment such as cement and concrete as the reinforcing material. Adding additive in the basalt rocks is the feasible method to enhance the alkali resistance. However, it is necessary to develop the efficient additive for basalt fiber. In this work, the effect of TiO2 on the preparation condition, alkali resistance and mechanical properties of basalt fiber was investigated. The preparation conditions were studied by DSC, XRD and high-temperature rotational viscometer. Then the corrosion behavior of TiO2-basalt fibers in NaOH solution was studied via SEM/EDX, FIB/SEM and FTIR. The results indicated that the viscosity of basalt melt decreased significantly with the increasing TiO2 content from 0% to 2%, but the crystallization tendency was not changed with TiO2 below 2%, the upper limit for TiO2 addition. The tensile strength increased by 20–60% because Ti4+ promoted Al3+ into the network structure and intensify the polymerization by entering the network structure as network precursor in the form of [TiO4]. Meanwhile, TiO2 in the basalt fibers formed insoluble titanium hydroxide, so the weight loss of TiO2-basalt fibers in NaOH solution was reduced up to 50%. Through FIB/SEM/EDX, the corrosion of basalt fiber in alkali condition is controlled by ion diffusion. The outward diffusion of Fe, Mg and Ti to the surface of fiber formed the insoluble layer, so the rate of substitution reaction between the OH− and basalt fibers was slowed down, but it also leaded to the non-uniform corrosion.

Li Y., Zhang J., He Y., Huang G., Li J., Niu Z., Gao B.

In order to further broaden the application scope of basalt fiber reinforced concrete (BFRC), prolong service life in complex environment, master development status and sort out development needs, the durability of BFRC in complex environment was systematically summarized. First of all, the reason and damage mechanism of concrete deterioration in a variety of harsh environment are analyzed and grasped. Secondly, the strengthening mechanism of basalt fiber (BF) structure in permeability, carbonization, sulfate erosion, alkali environment, freeze-thaw cycle and high temperature is reviewed in detail, and the strengthening effect and performance of BFRC are discussed from the perspective of macroscopic properties and microscopic pore structure. The addition of BF reduces the generation and development of early microcracks in concrete structures, promotes the densification of structures on a microscopic scale. What's more, the permeability, carbonation resistance, acid and alkali corrosion resistance, frost resistance and high temperature resistance of concrete structures can be significantly improved. Finally, the problems in the current research are summarized and research ideas to cope with the environmental complexity are proposed to provide a research basis for BFRC to maintain excellent performance in the actual complex application scenarios. This paper focuses on the strengthening effect of basalt fiber on cement-based materials, and mainly introduces its strengthening effect and action mechanism from several aspects in the figure.

Yang C., Liu Z., Tong X., Guo L., Miao S., Jiang L., Li Y., Li H., Liu C.

In this study, basalt from a base in Hebei, China, was selected as the raw material. Water-quenched basalt glasses and basalt fibers were prepared at different homogenization times and temperatures. The water-quenched glass structure was characterized by XRD and a Raman spectrometer followed by fitting of their Raman spectra by Gaussian curves to obtain information about melt structure. The fiber performance was characterized by fiber strength meter and fiber fineness meter. The results demonstrate that homogenization time and temperature had significant effects on the structure of basalt melt. The degree of polymerization of the melt increased with increasing homogenization time and decreased with increasing homogenization temperature. The fiber strength increased with increasing the degree of polymerization. As the homogenization time and temperature increased, coefficients of variation of fiber strength and fiber diameter decreased, indicating enhanced fiber stability.

Lu Z., Jiang M., Pan Y., Xian G., Yang M.

This study focused on the durability of basalt fibers, glass fibers, basalt-fiber-reinforced polymer (BFRP) bars, and glass-fiber-reinforced polymer (GFRP) bars in an artificial seawater. The specimens were immersed in the artificial seawater at 20, 40, and 60°C; the specimen immersed in distilled water at a temperature of 60°C was also used as a reference. The tensile strength of the monofilament basalt fibers and glass fibers immersed in the seawater for 90 days at a temperature of 60°C decreases by 61% and 59% respectively, showing the most significant degradation; the brittleness of the fibers also increases due to the decomposition of their sizing agent. The chloride ions in the seawater are beneficial to enhancing the resistance of the composites to moisture absorption. In addition, the tensile strength retention of the fiber-reinforced polymer (FRP) bars is higher than that of the fibers due to the protection by the epoxy resin. The mechanical properties of the FRP bars immersed in the seawater improve after removing their moisture. The mechanical performance of the BFRP bars is inferior to that of the GFRP bars due to their higher water absorption and weak bonding between the basalt fibers and the polymer matrix.

Wang Z.T., Luo H.J., Zhang J., Chen H.W., Zhang L., Wu L.L., Jiang H.

Basalt fiber is widely applied in composite materials. Recent years, it has a new application in filter bags. But commercial sizing agent always decomposes at 300 °C, which limits the application of basalt fiber above 300 °C. To solve this problem, in this study, a water-soluble polysiloxane sizing agent was synthesized and used to coat basalt fiber to improve its heat resistance. TG-DSC results showed the polysiloxanes starts to decompose at 370 °C. SEM and AFM results indicated that the surface of the fiber was wrapped by an organic coating. Abrasion tests showed friction factors of basalt fibers were decreased by the coating. XPS study showed there was a chemical connection between the layer and surface. Results of contact angles showed the surface energies of the fiber have increased after coated. Mechanical tests showed the breaking force of the coated basalt fiber could be maintained above 76% at 300 °C, which was 3.8 times that of unsized fiber, and kept above 49% at 400 °C, which was 2.4 times that of unsized fiber.

Wang Q., Zhang Q., Luo L., Yan T., Liu J., Ding L., Jiang W.

• The tensile strengths of BFs at high temperatures were studied • BFs with higher IRIs retained better tensile strengths at high temperatures • A CaO-based crystal layer was formed on the surface of BFs • BFs with lower IRIs formed more ferric tetrahedral structures at high-temperature Iron plays an important role in enhancing the tensile strength of basalt fibers (BFs); however, the origins of tensile-strength variation at high temperatures are not well understood. In this work, we prepared BFs with different iron reduction indices (IRI = Fe 2+ /Fe total ) and explored the effects of high temperature and IRI on tensile strength. The results show that BFs with higher IRIs retained better tensile strength after high-temperature treatment at 600°C for 1 h. The surface morphology was analyzed by scanning electron microscopy to observe the nanocrystalline layers on the surface of BFs with higher IRIs, and the main composition of the crystals was CaO. The formation of nanocrystalline layers increased the tensile strength of the BFs. Moreover, results from transmission 57 Fe Mössbauer spectroscopy and Fourier transform infrared spectroscopy indicate that BFs with lower IRIs formed more ferric tetrahedral structures (Fe 3+ (tet)) after high-temperature treatment, which depolymerized Si(Al)-O-Si(Al) tetrahedral structures, resulting in lower tensile strength. A better understanding of the origin of microstructures in different iron coordination states and the tensile strength of BFs at high temperatures will assist in the development of advanced iron-bearing glass fiber products suitable for high-temperature environments.