An innovative energy-saving in-flight melting technology and its application to glass production

The conventional method used for glass melting is air-fuel firing, which is inefficient, energy-intensive and time-consuming. In this study, an innovative in-flight melting technology was developed and applied to glass production for the purposes of energy conservation and environmental protection. Three types of heating sources, radio-frequency (RF) plasma, a 12-phase alternating current (ac) arc and an oxygen burner, were used to investigate the in-flight melting behavior of granulated powders. Results show that the melted particles are spherical with a smooth surface and compact structure. The diameter of the melted particles is about 50% of that of the original powders. The decomposition and vitrification degrees of the prepared powders decrease in the order of powders prepared by RF plasma, the 12-phase ac arc and the oxygen burner. The largest heat transfer is from RF plasma to particles, which results in the highest particle temperature (1810 °C) and the greatest vitrification degree of the raw material. The high decomposition and vitrification degrees, which are achieved in milliseconds, shorten the melting and fining times of the glass considerably. Our results indicate that the proposed in-flight melting technology is a promising method for use in the glass industry.     

An overview on microwave processing of material: A special emphasis on glass melting

Material processing adopting microwave heating has emerged as an alternative tool owing to faster processing, a cleaner environment, and several other advantages. This review provides a summary of recent reports of microwave synthesis of materials. This study reviews the use of microwave energy for application in several material processing technologies apart from food processing. A special emphasis has been made in the processing of glass adopting microwave energy. Melting of glass comprising SiO₂, P₂O₅, B₂O₃ as the main building block has been discussed. It has been revealed that silica, a microwave transparent material as reported earlier, can be heated under microwave heating directly. Microwave absorption of raw materials and different glass system has been discussed. Dielectric properties, particularly loss tangent or loss factor, are presented for some glass composition. Less evaporation of ingredient and low contamination from the crucible wall are noticed during glass melting using microwave heating. Enhanced iron redox ratio (Fe⁺²/∑Fe) in microwave processing may be considered an advantage in the preparation of heat absorbing filter glass. Small-scale glass melting using the microwave heating has a significant impact on energy and time saving. However, the challenges associated with the upscaling glass melting with microwave heating and future scope have been talked about.     

Highlighting of structural units of B2O3–Li2O–P2O5 system under heat treatment

As technology evolves towards the design of small size – high efficiency devices there is a necessity for the development of solid, stable electrolytes that can be fabricated in various shapes. Accordingly, a glass system of xB₂O₃·0.4Li₂O·(0.6 − x)P₂O₅ with 0 ≤ x ≤ 0.6 mol%, was prepared by melting the raw materials at 1200 °C and rapidly cooling the melts at room temperature. The samples were afterwards heat treated to develop crystalline structures, for better identification of the units that build up the network.     

Ultrapure SiO2 and Al2O3 for the preparation of low-loss compound glasses

The application of glass fibers for optical communications requires the preparation of glasses with ultralow transition metal contents. If the glasses are made by melting, raw materials in the form of powders with a purity at least equal to that required for the glass fibers must be available. This paper describes the preparation of ultrapure SiO₂ and Al₂O₃ powders by liquid state hydrolysis of alcoholates.     

Soda-based glass fabricated from Thailand quartz sands doped with silver compound

Yellow colored glass which used for luxury art glass in ancient time was fabricated by the addition of silver compound into the molten glass. It was proved that it was actually silver nanoparticle technology. In this work, the SiO₂–(Na₂O,K₂O)–CaO–B₂O₃–Al₂O₃–MgO glass system was prepared in the laboratory scale based on local quartz sands from Trat Province, eastern area of Thailand as the silica raw material. Various concentrations of silver nitrate were added. After the complete conventional melting process, the bubble-free yellow glasses were yielded. Physical and optical properties such as density, refractive index and optical absorption spectra were measured. Scanning electron microscope coupled with energy dispersive spectroscopy was carried out to study their morphology. The refractive indices and densities were increased as the increase of the silver contents. Electron micrographs showed the presence of silver nanoparticle in the glass matrix. UV–VIS spectra were in good agreement with that found from SEM measurements and corresponded with the universally accepted. It was also showed that the more brilliance on the surface of the glass products was obtained after firing with a gas torch.     

On glass formation for a Na2O·4TeO2 melt: Effect of melting temperature, time, and raw material

The effect of melting temperature, time, and the type of raw material, NaNO₃ or Na₂CO₃, as a source for Na₂O on the glass formation for a Na₂O·4TeO₂(NT₄) melt was investigated. Melting with NaNO₃ at 750°C for a short time (15 min) produced a glass that is slightly more chemically durable and more resistant to crystallization than glasses melted at a higher temperature (800°C), or for a longer time (60 min), or using Na₂CO₃. A thin surface layer (<1.5 nm) that contains some nitrogen and a higher concentration of bridging oxygen is suspected to be the reason for the higher chemical durability and higher resistance to crystallization for this glass. However, melting at 800°C for 60 min produced a glass, whose properties were independent of the type of raw material, NaNO₃ or Na₂CO₃, used.     

Crystallization of glasses obtained by recycling goethite industrial wastes to produce glass-ceramic materials

Goethite waste, originated in the hydrometallurgy of zinc, was characterized and recycled, in combination with raw materials, for producing glass-ceramic (GC) materials. Four base compositions were prepared with an Fe₂O₃ content ranging from 15 to 25 wt%. The mixtures were melted at 1400–1450 °C and quenched to obtain the glass. The nucleation and crystallization temperatures and the activation energy of the crystallization process were determined by differential thermal analysis. The glass samples were nucleated at 660 °C for times ranging from 1 to 4 h and crystallized at 800–900 °C for 1 to 4 h. X-ray diffraction and fluorescence analysis were performed on the glasses and GC samples and the crystalline phases characterized. The percentage of crystallinity was determined as a function of the temperature and duration of the thermal treatment. The fractional factorial experimental approach was carried out on the 20 wt% Fe₂O₃ composition with the aim of evaluating the influence of the nucleation temperature and time, the crystallization temperature and time and the presence of a reducing agent on the glass devitrification process.     

Preparation of glass fibres of the ZrO2-SiO2 and Na2O-ZrO2-SiO2 systems from metal alkoxides and their resistance to alkaline solution

Glass fibres of the ZrO₂-SiO₂ and Na₂O-ZrO₂-SiO₂ systems containing up to 33 wt% ZrO₂ were prepared by a non-melting technique using zirconium n-propoxide, sodium methoxide and silicon tetraethoxide as raw materials. The mixed alkoxide solutions were exposed to moist air for hydrolysis. The fibrous gels were drawn from these solutions in the course of hydrolysis, and converted to the corresponding oxide glass fibres by heating at 500 to 700° C. It was found that chemical durability of the fibres toward alkaline solution increased with ZrO₂ content. The weight loss due to the corrosion by 2 N NaOH solution at 96° C for 4 h was around 14 mg dm^–2 for the fibres containing 17 to 26 wt% ZrO₂, which was comparable to the alkali-resistant glasses so far obtained by the conventional melting technique. The glass fibres containing 33 wt% ZrO₂ showed higher resistance.     

Optimization of the LENS Rapid Fabrication Process for In-Flight Melting of Feed Powder

A model for in-flight melting of feed-powder particles propelled through a laser beam in the Laser-Engineered Net Shaping (LENS) process has been developed. The model is next incorporated in an optimization analysis to determine optimum LENS process parameters (laser power, particle velocity, and the angle between the laser-beam axis and particle trajectory), which maximize the probability for in-flight particle melting while ensuring the absence of melting of the surface of the substrate. A simple model, based on solution of the thermal energy conservation equation, is also developed to determine the laser-power threshold for melting of the substrate surface. The optimization analysis is then applied to Inconel 625 Ni-Cr-Mo superalloy. The results show that by maximizing the laser power and the residence time of the particles in the laser beam (increases with reductions in particle velocity and particle trajectory angle), the probability for in-flight particle melting can be greatly increased, i.e. relatively coarse (–30/+40 mesh size) particles can be melted by propelling them through the laser beam.     

A case study on energy and exergy analyses for an industrial-scale vertical roller mill assisted grinding in cement plant

In this study, the analyses of energy and exergy were implemented for an industrial-scale vertical roller mill (VRM) of Kerman Momtazan Cement Company (KMCC) of Iran. The energy and exergy analyses demonstrated the first law efficiency of the VRM is 62.1%, while the second law efficiency of the VRM is 34.6%. Comparing to the widely applied ball milling, the second law efficiency is 16.4% higher for the VRM than the ball mill. Results also showed when the classifier rotor speed increases from 53 to 65 rpm, the particle size of the product decreases from P_90µm = 18.2% to P_90µm = 10.8%, but the power consumption of the VRM unit increases from 19.7 to 22.3 kWh/t of raw materials. Finally, the power consumption of the VRM unit compared with 14 raw mill units around Iran and the international best available technology (IBAT). The results demonstrated that the VRM unit consumes around 81% (9.75 kWh/t of raw materials), and 36% (5.8 kWh/t of raw materials) more energy to grind raw material than the IBAT unit and domestic best raw mill (DBRM), respectively.     

Synthesis of soluble polyimide/silica–titania core–shell nanoparticle hybrid thin films for anti-reflective coatings

In this study, researchers prepared polyimide/silica–titania core–shell nanoparticle hybrid thin films (PI/SiO₂–TiO₂) from soluble fluorine-containing polyimide, colloidal silica, and titanium butoxide. The soluble polyimide with carboxylic acid end groups (6FDA–6FpDA–4ABA–COOH) could condense with titanium butoxide to provide organic–inorganic bonding, and thus prevent macrophase separation. TGA and DSC analysis showed that the decomposition temperature of hybrid materials increased with an increase in the content of silica–titania nanoparticles within the hybrid films. FTIR spectra indicated that the imidization was complete and the cross-linking Ti–O–Ti network formed. HRTEM and HRSEM images showed that the size of the core–shell nanoparticles were 18–20 nm. The thickness of titania shell on the silica is about 2.5 nm. The n&k and UV–Vis analysis showed that the prepared hybrid films had good optical properties and a high refractive index of 1.735. Researchers applied the prepared PI/SiO₂–TiO₂ hybrid thin films to develop a three layer antireflective (AR) coating on the glass and PMMA substrate. Results showed that the reflectance of the AR coating on the glass and PMMA substrate at 550 nm was 0.356 and 0.495%, respectively. The transparency was greater than 90% for both AR coatings on the glass and PMMA substrates.     

Penetration impact resistance of hybrid composites based on commingled yarn fabrics

The penetration impact resistance of hybrid composites based on commingled yarn fabrics was investigated. The commingled yarn fabrics were composed of E-glass fibres (GF) and thermoplastic fibres blended together within the fibre bundles. Various thermoplastic fibres such as polypropylene (PP), polyamide (PA) and modified polyethylene terephthalate (mPET) were studied. Various resin matrices with different cure cycles were studied such as Quickcure polyester, Cycom X823 RTM epoxy, and Shell Epikote 828 epoxy resin. Depending on the crystalline melting temperature (T_m) of the thermoplastic fibres, the hybrid composites can be categorised as fibre-hybrid composites or matrix-hybrid composites. Fibre-hybrid composites refer to those in which the thermoplastic fibres remain in the fibre form after curing, for example the GF–PP and GF–PA hybrid composites. For matrix-hybrid composites, the thermoplastic fibres melt and dissolve into the thermosetting matrix during curing such as the GF-mPET hybrid composites. The results from the penetration impact showed that the total absorbed energy of the fibre-hybrid composites were significantly higher than for the plain glass composites. Plastic deformation in the thermoplastic fibres is the key factor that improves the absorbed energy of the hybrid composites. When the thermoplastic fibres dissolved into the thermosetting matrix as in matrix-hybrid composites, the total absorbed energy was similar to that of the plain glass fibre composites. This suggests that the total absorbed energy is dependent on the properties of the fibres rather than the matrix. However, the fibre-hybrid composites showed slight differences in the total absorbed energy for different matrices. The differences are thought to be related to the differences in the bonding between the thermoplastic fibres and the thermosetting matrix which have yet to be investigated.     

Preparation and characterization of epoxy-silica hybrid materials by the sol-gel process

A transparent organic-inorganic epoxy/silica hybrid material was prepared by epoxy resin, functionalized-epoxy resin, which was partially functionalized by 3-aminopropyl triethoxylsilane(APTES), and highly reactive polysilcic acid (PSA), which was prepared through hydrolysis and condensation of metasilicate salt. The properties of hybrid materials such as impact strength, tensile strength, glass transition temperature (T_g), thermogravimetric temperature (TGA), and thermal effect of the hybrid materials were studied. The size of PSA particles in THF measured by dynamic light scattering technique, ranged from 10–28 nm. The results of experiment indicated that modified epoxy resin possed better roughness than that of the pure epoxy resin. The structure of the hybrid materials was characterized by FT-IR spectroscopy and 29SiNMR spectroscopy.     

Preparation and properties of sintered glass–ceramics containing Au–Cu tailing waste

Au–Cu tailings (ACTs) are gold mining industry by-products that require further treatment before disposal to alleviate polluting the environment such as landfill, plant cover or using material production. This study focuses on the preparation and properties of a material called glass–ceramics that was prepared by a melting method with ACT, as raw materials, and without additional nucleating agents. The nucleation and crystallization temperature of the base glasses were determined by differential scanning calorimetry (DSC). The microstructure and properties of the glass–ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), a bending strength test, a microhardness test, linear thermal expansion coefficient, and a wear-and-tear test, thereby obtaining the best optimum formula composition and the process parameters. The results show that the utilization of ACT can be up to 77.56 wt.%, which can make good use of ACT and develop decorated glass–ceramics with perfect properties. Two crystalline phases are diopside ((Mg_0.6Fe_0.2Al_0.2) Ca(Si_1.5Al_0.5)O₆) and hedenbergite (Ca(Fe_0.821Al_0.179) (SiAl_0.822Fe_0.178O₆)) which are formed in the glass–ceramic samples. The obtained glass–ceramics show the properties of maximum bending strength of 209.6 MPa, density of 3.23 g/cm³, hardness of 1008.7 kgf/mm² and wear resistance of 0.039 mg/g.     

Effect of in-flight particle oxidation on the phase evolution of HVOF NiTiZrSiSn bulk amorphous coating

Bulk amorphous NiTiZrSiSn feedstock was sprayed using a high velocity oxy-fuel spraying process. In order to evaluate the amorphous formability in view of chemical instability, the oxygen to hydrogen gas flow rate ratio was changed at the constant total gas flow rate. Flame gas enthalpy was increased with the O₂/H₂ gas ratio. In-flight particle melting state was improved with the increase of oxidizer flow rate. Accordingly, porosity as well as unmelted particle size and density were decreased. For the amorphous phase fraction within an as-sprayed coating, it was decreased with the oxygen flow rate. From the thermal analysis and X-ray diffraction, the effects of O₂/H₂ gas ratio on the crystallization of HVOF sprayed bulk amorphous NiTiZrSiSn could be divided into two categories. One is due to the solid-state crystallization during flight along the low gas enthalpy flame. The other results from the destabilization of bulk amorphous feedstock due to the chemical composition change resulting from in-flight particle oxidation at the higher oxygen gas flow rate. Oxidation degree was different from the O2/H2 gas ratio and it had influences on the glass formability [ΔTx] and crystalline phase. Increase of oxide phase fraction was parallel to that of γ-Ni solid solution.     

Microstructure of low temperature processed CNFs/glass nanocomposites

Carbon nanofibers/glass (CNF/G) nanocomposites were obtained from a glass powder of low melting point and pristine CNFs. Green bodies containing from 0 to 22 % (v/v) of CNFs were sintered under nitrogen atmosphere in the 550–700 °C temperature range with different holding times. A fully microstructure characterization, by means of Hg porosimetry and N₂ adsorption, was carried out for understanding the CNFs/G composites behavior during the sintering process. This understanding is required to optimize the microstructural design of CNFs/glass nanocomposite materials. During sintering two different and simultaneous phenomena occur the matrix crystallization and the pore formation. The glass matrix crystallization temperature decreases from 650 to 550 °C, when CNFs concentration increases to 22 % (v/v). The glass matrix produces the CNFs degradation and generates gaseous species which lead to homogeneous or foamy materials. This depends on the CNFs concentration and thermal treatment conditions. Foamy nanocomposites present pore size distributions with pores <0.1 and close to 20 μm. The glass matrix wets the CNFs and produce their degradation been of 1 % of carbon loss in all nanocomposites.     

Ceramic wastes as alternative raw materials for Portland cement clinker production

The cement industry has for some time been seeking procedures that would effectively reduce the high energy and environmental costs of cement manufacture. One such procedure is the use of alternative materials as partial replacements for fuel, raw materials or even clinker. The present study explores the reactivity and burnability of cement raw mixes containing fired red or white ceramic wall tile wastes and combinations of the two as alternative raw materials.The results showed that the new raw mixes containing this kind of waste to be technically viable, and to have higher reactivity and burnability than a conventional mix, providing that the particle size of the waste used is lower than 90 μm. The mineralogical composition and distribution in the experimental clinker prepared were comparable to the properties of the clinker manufactured with conventional raw materials. Due to the presence of oxides such as ZnO, ZrO₂ and B₂O₃ in tile glazing, the content of these oxides was higher in clinker made with such waste. The mix of red and white ceramic wall tile waste was found to perform equally or better than each type of waste separately, a promising indication that separation of the two would be unnecessary for the purpose described above.     

Radome health management based on synthesized impact detection,laser ultrasonic spectral imaging,and wavelet-transformed ultrasonic propagation imaging methods

A radome must not only withstand various forces during operation, but also provide a window for electromagnetic signals. A radome is generally a composite sandwich structure. Much of the damage to radomes is barely visible to the naked eye on the outer surface, but is severe internally. In this study, a radome health management strategy consisting of in-flight damage event detection and ground damage evaluation processes is proposed. A radome health management system, composed of an on-board subsystem and a ground subsystem, was developed to realize the strategy. An in-flight event detection system was developed based on acoustic emission (AE) technology. A built-in amplifier-integrated PZT sensor was used, and the minimum impact energy that the on-board subsystem can detect was determined. The AE sensor was then switched to an ultrasonic receiver. A scanning laser ultrasonic technology was combined with the ultrasonic receiver to develop a ground nondestructive evaluation subsystem. For in situ damage visualization, laser ultrasonic frequency tomography and wavelet-transformed ultrasonic propagation imaging algorithms were developed in this study. To demonstrate the robustness of the ground subsystem, a damage was generated by 5.42 J impact in a glass/epoxy radome with honeycomb core, and the impact image of 25 mm in diameter invisible outside could be visualized with the combination of ultrasonic spectral imaging (USI) and wavelet-transformed ultrasonic propagation imaging (WUPI), which made the propagation of only the damage-related ultrasonic modes visible.     

Influence of weldlines on tensile properties of hybrid acrylonitrile butadiene styrene (ABS) composites filled with short glass fibres (GF) and glass beads (GB)

The present study investigated the effect of weldlines on tensile strength and modulus of injection moulded ABS polymer reinforced with both short fibres (GF) and spherical glass beads (GB). It was observed that tensile strength and modulus of ABS/GF/GB hybrids increased with increasing the concentration total of glass in the hybrid as well as the concentration of glass fibres in the hybrid (χ _GF ). Results indicated that tensile strength and modulus of ABS/GF/GB hybrids obey the rule-of-mixtures. The presence of weldlines had a negative effect on tensile properties of ABS/GF/GB hybrids. Although tensile strength and modulus of ABS/GF/GB hybrids were reduced in the presence of weldlines, nonetheless both increased with increasing the total concentration of the glass particles and χ _GF . The observed linearity of weldline strength and modulus with χ _GF indicated that these properties like their unweld counterparts can be expressed by simple rule-of-mixtures. It was noted also that weldline integrity factor for tensile modulus and strength decreased with increasing χ _GF and the total concentration of the glass particles in the hybrids. Weldline integrity values indicated that hybrid tensile strength was more affected by the weldlines than hybrid modulus.     

Nucleation kinetics of a Li2O·2SiO2 glass based on a liquid model

A liquid model was proposed wherein crystal embryos should exist in equilibrated melts at temperatures even above the melting point or liquidus temperature and the number density of embryos should decrease as the melting temperature increases. Crystallization behavior of a Li₂O·2SiO₂ glass was studied. Secondary heat-treatment (600 °C for 20–60 min) of the Li₂O·2SiO₂ glass induced different number of crystals depending upon the melting temperature in the range 1040°–1300 °C and duration of heat-treatment t. The number density of crystals N decreased with increasing temperature of melting. The number density of pre-existing embryos was estimated from (N – t) diagram and was found consistent with what the proposed model claims.