Effect of Al_2O_3 on the viscosity of CaO–SiO_2–Al_2O_3–MgO–Cr_2O_3 slags

We investigated the effect of Al_2O_3 content on the viscosity of CaO–SiO_2–Al_2O_3–8wt%MgO–1wt%Cr_2O_3 (mass ratio of CaO/SiO_2is 1.0,and Al_2O_3 content is 17wt%–29wt%) slags.The results show that the viscosity of the slag increases gradually with increases in the Al_2O_3content in the range of 17wt%to 29wt%due to the role of Al_2O_3 as a network former in the polymerization of the aluminosilicate structure of the slag.With increases in the Al_2O_3 content from 17wt%to 29wt%,the apparent activation energy of the slags also increases from 180.85 to 210.23 k J/mol,which is consistent with the variation in the critical temperature.The Fourier-transform infrared spectra indicate that the degree of polymerization of this slag is increased by the addition of Al_2O_3.The application of Iida’s model for predicting the slag viscosity in the presence of Cr_2O_3 indicates that the calculated viscosity values fit well with the measured values when both the temperature and Al_2O_3 content are at relatively low levels,i.e.,the temperature range of 1673 to 1803 K and the Al_2O_3 content range of 17wt%–29wt%in CaO–SiO_2–Al_2O_3–8wt%MgO–1wt%Cr_2O_3 slag.     

Mineral-phase evolution and sintering behavior of MO-SiO2-Al2O3-B2O3 (M=Ca,Ba) glass-ceramics by low-temperature liquid-phase sintering

In this work, network former SiO₂ and network intermediate Al₂O₃ were introduced into typical low-melting binary compositions CaO·B₂O₃, CaO·2B₂O₃, and BaO·B₂O₃ via an aqueous solid-state suspension milling route. Accordingly, multiple-phase aluminosilicate glass-ceramics were directly obtained via liquid-phase sintering at temperatures below 950℃. On the basis of liquid-phase sintering theory, mineral-phase evolutions and glass-phase formations were systematically investigated in a wide MO-SiO₂-Al₂O₃-B₂O₃ (M=Ca, Ba) composition range. The results indicate that major mineral phases of the aluminosilicate glass-ceramics are Al₂₀B₄O₃₆, CaAl₂Si₂O₈, and BaAl₂Si₂O₈ and that the glass-ceramic materials are characterized by dense microstructures and excellent dielectric properties.     

Activity coefficients of NiO and CoO in CaO–Al_2O_3–SiO_2 slag and their application to the recycling of Ni–Co–Fe-based end-of-life superalloys via remelting

To design optimal pyrometallurgical processes for nickel and cobalt recycling, and more particularly for the end-of-life process of Ni–Co–Fe-based end-of-life(EoL) superalloys, knowledge of their activity coefficients in slags is essential. In this study, the activity coefficients of NiO and CoO in CaO–Al_2O_3–SiO_2 slag, a candidate slag used for the EoL superalloy remelting process, were measured using gas/slag/metal equilibrium experiments. These activity coefficients were then used to consider the recycling efficiency of nickel and cobalt by remelting EoL superalloys using CaO–Al_2O_3–SiO_2 slag. The activity coefficients of NiO and CoO in CaO–Al_2O_3–SiO_2 slag both show a positive deviation from Raoult's law, with values that vary from 1 to 5 depending on the change in basicity. The activity coefficients of NiO and CoO peak in the slag with a composition near B =(%CaO)/(%SiO_2) = 1, where B is the basicity. We observed that controlling the slag composition at approximately B = 1 effectively reduces the cobalt and nickel oxidation losses and promotes the oxidation removal of iron during the remelting process of EoL superalloys.     

Evolution of plasticized MnO–Al_2O_3–SiO_2-based nonmetallic inclusion in 18wt%Cr-8wt% Ni stainless steel and its properties during soaking process

The properties of MnO–Al_2O_3–SiO_2-based plasticized inclusion are likely to change during soaking process due to its low melting point. In this study, the evolution of the MnO–Al_2O_3–SiO_2-based inclusion of 18 wt%Cr-8 wt%Ni stainless steel under isothermal soaking process at 1250°C for different times was investigated by laboratory-scale experiments and thermodynamic analysis. The results showed that the inclusion population density increased at the first stage and then decreased while their average size first decreased and then increased. In addition, almost no Cr_2O_3-concentrated regions existed within the inclusion before soaking, but more and more Cr_2O_3 precipitates were formed during soaking. Furthermore, the plasticity of the inclusion deteriorated due to a decrease in the amount of liquid phase and an increase in the high-melting-pointphase MnO–Cr_2O_3 spinel after the soaking process. In-situ observations by high-temperature confocal laser scanning microscopy(CLSM) confirmed that liquid phases were produced in the inclusions and the inclusions grew rather quickly during the soaking process. Both the experimental results and thermodynamic analysis conclude that there are three routes for inclusion evolution during the soaking process. In particular, Ostwald ripening plays an important role in the inclusion evolution, i.e., MnO–Al_2O_3–SiO_2-based inclusions grow by absorbing the newly precipitated smaller-size MnO–Cr_2O_3 inclusions.     

Effect of Fe_2O_3 on the crystallization behavior of glass-ceramics produced from naturally cooled yellow phosphorus furnace slag

CaO–Al_2O_3–SiO_2(CAS) glass-ceramics were prepared via a melting method using naturally cooled yellow phosphorus furnace slag as the main raw material.The effects of the addition of Fe_2O_3 on the crystallization behavior and properties of the prepared glass-ceramics were studied by differential thermal analysis,X-ray diffraction,and scanning electron microscopy.The crystallization activation energy was calculated using the modified Johnson–Mehl–Avrami equation.The results show that the intrinsic nucleating agent in the yellow phosphorus furnace slag could effectively promote the crystallization of CAS.The crystallization activation energy first increased and then decreased with increasing amount of added Fe_2O_3.At 4wt% of added Fe_2O_3,the crystallization activation energy reached a maximum of 676.374 k J×mol-1.The type of the main crystalline phase did not change with the amount of added Fe_2O_3.The primary and secondary crystalline phases were identified as wollastonite(CaSiO_3) and hedenbergite(Ca Fe(Si_2O_6)),respectively.     

Low-temperature densification sintering and properties of CaAl_2Si_2O_8 ceramics with MeO·2B_2O_3(Me=Ca,Sr,Ba)

Dense CaAl2Si2O8 ceramics were prepared via a two-step sintering process at temperatures below 1000°C. First, pre-sintered Ca Al2Si2O8 powders containing small amounts of other crystal phases were obtained by sintering a mixture of calcium hydroxide and kaolin powders at 950°C for 6 h. Subsequently, the combination of the pre-sintered ceramic powders with Me O·2B2O3(Me = Ca, Sr, Ba) flux agents enabled the low-temperature densification sintering of the CaAl2Si2O8 ceramics at 950°C. The sintering behavior and phase formation of the CaAl2Si2O8 ceramics were investigated in terms of the addition of the three MeO·2B2O3 flux agents. Furthermore, alumina and quartz were introduced into the three flux agents to investigate the sintering behaviors, phase evolvements, microstructures, and physical properties of the resulting CaAl2Si2O8 ceramics. The results showed that, because of their low-melting characteristics, the MeO·2B2O3(Me = Ca, Sr, Ba) flux agents facilitated the formation of the CaAl2Si2O8 ceramics with a dense microstructure via liquid-phase sintering. The addition of alumina and quartz to the flux agents also strongly affected the microstructures, phase formation, and physical properties of the CaAl2Si2O8 ceramics.     

In situ reaction mechanism of MgAlON in Al–Al_2O_3–MgO composites at 1700°C under flowing N_2

The Al–Al_2O_3–MgO composites with added aluminum contents of approximately 0wt%, 5wt%, and 10wt%, named as M_1, M_2, and M_3, respectively, were prepared at 1700°C for 5 h under a flowing N_2 atmosphere using the reaction sintering method. After sintering, the Al–Al_2O_3–MgO composites were characterized and analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results show that specimen M_1 was composed of MgO and MgAl_2O_4. Compared with specimen M_1, specimens M_2 and M_3 possessed MgAlON, and its production increased with increasing aluminum addition. Under an N_2 atmosphere, MgO, Al_2O_3, and Al in the matrix of specimens M_2 and M_3 reacted to form MgAlON and AlN-polytypoids, which combined the particles and the matrix together and imparted the Al–Al_2O_3–MgO composites with a dense structure. The mechanism of MgAlON synthesis is described as follows. Under an N_2 atmosphere, the partial pressure of oxygen is quite low; thus, when the Al–Al_2O_3–MgO composites were soaked at 580°C for an extended period, aluminum metal was transformed into AlN. With increasing temperature, Al_2O_3 diffused into AlN crystal lattices and formed AlN-polytypoids; however, MgO reacted with Al_2O_3 to form MgAl_2O_4. When the temperature was greater than(1640 ± 10)°C, AlN diffused into Al_2O_3 and formed spinel-structured AlON. In situ MgAlON was acquired through a solid-solution reaction between AlON and Mg Al_2O_4 at high temperatures because of their similar spinel structures.     

Reaction mechanism for in-situ β-Si Al ON formation in Fe_3Si–Si_3N_4–Al_2O_3 composites

In this work,Fe_3Si–Si_3N_4–Al_2O_3 composites were prepared at 1300°C in an N_2 atmosphere using fused corundum and tabular alumina particles,Al_2O_3 fine powder,and ferrosilicon nitride(Fe_3Si–Si_3N_4) as raw materials and thermosetting phenolic resin as a binder.The effect of ferrosilicon nitride with different concentrations(0wt%,5wt%,10wt%,15wt%,20wt%,and 25wt%) on the properties of Fe_3Si–Si_3N_4–Al_2O_3 composites was investigated.The results show that the apparent porosity varies between 10.3% and 17.3%,the bulk density varies from 2.94 g/cm~3 and 3.30 g/cm~3,and the cold crushing strength ranges from 67 MPa to 93 MPa.Under the experimental conditions,ferrosilicon nitride,whose content decreases substantially,is unstable;part of the ferrosilicon nitride is converted into Fe_2C,whereas the remainder is retained,eventually forming the ferrosilicon alloy.Thermodynamic assessment of the Si_5AlON_7 indicated that the ferrosilicon alloy accelerated the reactions between Si_3N_4 and α-Al_2O_3 fine powder and that Si in the ferrosilicon alloy was nitrided directly,forming β-Si Al ON simultaneously.In addition,fused corundum did not react directly with Si_3N_4 because of its low reactivity.     

Effect of the CaO/SiO_2 mass ratio and FeO content on the viscosity of CaO–SiO_2–“FeO”–12wt%ZnO–3wt%Al_2O_3 slags

An effective process for recycling lead from hazardous waste cathode ray tubes(CRTs) funnel glass through traditional lead smelting has been presented previously. The viscous behavior of the molten high lead slag, which is affected by the addition of funnel glass, plays a critical role in determining the production efficiency. Therefore, the viscosities of the CaO–SiO_2–"FeO"–12wt%ZnO–3wt%Al_2O_3 slags were measured in the current study using the rotating spindle method. The slag viscosity decreases as the CaO/SiO_2 mass ratio is increased from 0.8 to 1.2 and also as the FeO content is increased from 8wt% to 20wt%. The breaking temperature of the slag is lowered substantially by the addition of FeO, whereas the influence of the CaO/SiO_2 mass ratio on the breaking temperature is complex. The structural analysis of quenched slags using Fourier transform infrared(FTIR) spectroscopy and Raman spectroscopy reveals that the silicate network structure is depolymerized with increasing CaO/SiO_2 mass ratio or increasing FeO content. The [FeO_6]-octahedra in the slag melt increase as the CaO/SiO_2 mass ratio or the FeO content increases. This increase can further decrease the degree of polymerization(DOP) of the slag. Furthermore, the activation energy for viscous flow decreases both with increasing CaO/SiO_2 mass ratio and increasing FeO content.     

Electrical conductivity optimization of the Na_3AlF_6–Al_2O_3–Sm_2O_3 molten salts system for Al–Sm intermediate binary alloy production

Metal Sm has been widely used in making Al–Sm magnet alloy materials. Conventional distillation technology to produce Sm has the disadvantages of low productivity, high costs, and pollution generation. The objective of this study was to develop a molten salt electrolyte system to produce Al–Sm alloy directly, with focus on the electrical conductivity and optimal operating conditions to minimize the energy consumption. The continuously varying cell constant(CVCC) technique was used to measure the conductivity for the Na_3 AlF_6–AlF_3–LiF–MgF_2–Al_2O_3–Sm_2O_3 electrolysis medium in the temperature range from 905 to 1055°C. The temperature(t) and the addition of Al_2O_3(W(Al_2O_3)), Sm_2O_3(W(Sm_2O_3)), and a combination of Al_2O_3 and Sm_2O_3 into the basic fluoride system were examined with respect to their effects on the conductivity(κ) and activation energy. The experimental results showed that the molten electrolyte conductivity increases with increasing temperature(t) and decreases with the addition of Al_2O_3 or Sm_2O_3 or both. We concluded that the optimal operation conditions for Al–Sm intermediate alloy production in the Na_3 AlF_6–AlF_3–LiF–MgF_2–Al_2O_3–Sm_2O_3 system are W(Al_2O_3) + W(Sm_2O_3) = 3wt%, W(Al_2O_3):W(Sm_2O_3) = 7:3, and a temperature of 965 to 995°C, which results in satisfactory conductivity, low fluoride evaporation losses, and low energy consumption.     

Acting mechanism of F,K,and Na in the solid phase sintering reaction of the Baiyunebo iron ore

<正>The effect of F,K,and Na on the solid phase reaction of the Baiyunebo iron ore was investigated by differential thermal analysis (DTA) and X-ray diffraction(XRD).It has been identified that alkaline elements K and Na in the Baiyunebo ore instigate the formation of low melting point compounds Na_2SiO_3 and Na_2O·Fe_2O_3 and the generation of molten state in the solid phase sintering.Element F in the Baiyunebo ore facilitates the formation of cuspidine compound 3CaO·2SiO_2·CaF_2 in the solid phase reaction.The cuspidine compound is kept in solid as one of the final products through the entire sintering process due to its high melting point.In the sintering process,CaF_2and SiO_2 react with CaO first and form 3CaO·2SiO_2·CaF_2 and 3CaO·2SiO_2,so the formation of ferrites,Na_2O·Fe_2O_3,and 2CaO·Fe_2O_3 is inhibited.     

Influence of CeO_2 addition on the preparation of foamed glass-ceramics from high-titanium blast furnace slag

Foamed glass-ceramics doped with cerium oxide(CeO_2)were successfully prepared from high-titanium blast furnace slag by one-step sintering.The influence of CeO_2 addition(1.5wt%–3.5wt%)on the crystalline phases,microstructure,and properties of foamed glass-ceramics was studied.Results show that CeO_2 improves the stability of the glass phase and changes the two-dimensional crystallization mechanism into three-dimensional one.XRD analysis indicates the presence of Ca(Mg,Fe)Si_2O_6 and Ca(Ti,Mg,Al)(Si,Al)_2O_(6 )in all sintered samples.Added with CeO_2,Ti CeO_4 precipitates,and crystallinity increases,leading to increased thickness of pore walls and uniform pores.The comprehensive properties of foamed glass-ceramics are better than that of samples without CeO_2.In particular,the sample added with a suitable amount of CeO_2(2.5wt%)exhibits bulk density that is similar to and compressive strength(14.9 MPa)that is more than twice of foamed glass-ceramics without CeO_2.     

In situ(α-Al_2O_3+ZrB_2)/Al composites with network distribution fabricated by reaction hot pressing

In situ(α-Al_2O_3+ZrB_2)/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis(DTA) was used to study the reaction mechanisms in the Al–Zr O2–B system. X-ray diffraction(XRD) and scanning electron microscopy(SEM) in conjunction with energy-dispersive X-ray spectroscopy(EDX) were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechanical properties was investigated. The results show that the optimum sintering parameters to complete reactions in the Al–Zr O2–B system are 850°C and 60 min. In situ-synthesized α-Al2O3 and Zr B2 particles are dispersed uniformly around Al particles, forming a network microstructure; the diameters of the α-Al2O3 and Zr B2 particles are approximately 1–3 μm. When the size of Al powder increases from 60–110 μm to 150–300 μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of reinforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of the in situ(α-Al2O3–Zr B2)/Al composites from Hv 163 to Hv 251.     

Reaction mechanisms between molten CaF_2-based slags and molten 9CrMoCoB steel

Investigating the reaction mechanism between slag and 9CrMoCoB steel is important to develop the proper slag and produce qualified ingots in the electroslag remelting(ESR) process. Equilibrium reaction experiments between molten 9CrMoCoB steel and the slags of 55 wt%CaF_2–20 wt%CaO–3 wt%MgO–22 wt%Al_2O_3–xwt%B_2O_3(x = 0.0, 0.5, 1.0, 1.5, 2.0, 3.0) were conducted. The reaction mechanisms between molten 9 CrMoCoB steel and the slags with different B_2O_3 contents were deduced based on the composition of the steel and slag samples at different reaction times. Results show that B content in the steel can be controlled within the target range when the B_2O_3 content is 0.5 wt% and the FeO content ranges from 0.18 wt% to 0.22 wt% in the slag. When the B_2O_3 content is ≥1 wt%, the reaction between Si and B_2O_3 leads to the increase of the B content of steel. The additions of SiO_2 and B_2O_3 to the slag should accord to the mass ratio of [B]/[Si] in the electrode, and SiO_2 addition inhibits the reaction between Si and Al_2O_3.     

Microstructure and properties of Ag–Ti_3SiC_2 contact materials prepared by pressureless sintering

Ti_3SiC_2-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti_3SiC_2 substrate was measured by the sessile drop method. The Ag–Ti_3SiC_2 composites were prepared from Ag and Ti_3SiC_2 powder mixtures by pressureless sintering. The effects of compacting pressure(100–800 MPa), sintering temperature(850–950°C), and soaking time(0.5–2 h) on the microstructure and properties of the Ag–Ti_3SiC_2 composites were investigated. The experimental results indicated that Ti_3SiC_2 particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10 wt%Ti_3SiC_2 had a relative density of 95% and an electrical resistivity of 2.76 × 10-3 mΩ?cm when compacted at 800 MPa and sintered at 950°C for 1 h. The incorporation of Ti_3SiC_2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti_3SiC_2 reinforcement, suggesting its potential application in electrical contacts.     

Bioactivity analysis of the Ta(Ⅴ) doped SiO_2–Ca O–Na_2O–P_2O_5 ceramics prepared by solid state sintering method

The main objective of the study was to control the degradation rate of material at a higher degradation rate improving the chemical stability of the material. Ta is known to have good chemical resistance, biocompatibility and show no adverse biological response. In the present study, Si O_2–Na_2O–Ca O–P_2O_5 bioceramics with different Ta_2O_5 contents was prepared by solid state sintering method at 1000 °C. The as-sintered ceramics were subjected to immersion studies in stimulated body fluid(SBF) for 21 days under static condition and characterized by XRD, FTIR, SEM, and AAS. The findings of the research indicate that the addition of Ta_2O_5 controlled degradability, and all samples showed sufficient bioactivity.     

Effect of Y_2O_3 content in the pack mixtures on microstructure and oxidation resistance of B–Y modified silicide coating

B–Y modified silicide coatings were prepared on Nb–Si based alloy by pack cementation at 1300 ℃ for 10 h. The effect of Y_2O_3 content in the pack mixtures on microstructure and oxidation resistance of the coatings was investigated. The results show that the four coatings have similar structures, which possess a(Nb,X)Si_2 outer layer and a(Nb,X)_5Si_3 transitional layer. Y_2O_3 content in the pack mixtures has an obvious effect on the Si content in the coating. The mass gains of the coatings prepared with 0.5, 1, 2 and 3 wt% Y_2O_3 in pack mixtures are 2.33, 1.96, 2.05 and 2.86 mg/cm~2 after oxidation at 1250 ℃ for 100 h, respectively. The coating prepared with 1 wt% Y_2O_3 exhibits the best oxidation resistance due to the formation of a dense glass-like borosilicate scale.     

Low-temperature densification sintering and properties of CaAl2Si2O8 ceramics with MeO·2B2O3 (Me=Ca,Sr, Ba)

Dense CaAl2Si2O8 ceramics were prepared via a two-step sintering process at temperatures below 1000°C. First, pre-sintered CaAl2Si2O8 powders containing small amounts of other crystal phases were obtained by sintering a mixture of calcium hydroxide and kaolin powders at 950°C for 6 h. Subsequently, the combination of the pre-sintered ceramic powders with MeO·2B2O3 (Me=Ca, Sr, Ba) flux agents enabled the low-temperature densification sintering of the CaAl2Si2O8 ceramics at 950°C. The sintering behavior and phase formation of the CaAl2Si2O8 ceramics were investigated in terms of the addition of the three MeO·2B2O3 flux agents. Furthermore, alumina and quartz were introduced into the three flux agents to investigate the sintering behaviors, phase evolvements, microstructures, and physical properties of the resulting CaAl2Si2O8 ceramics. The results showed that, because of their low-melting characteristics, the MeO·2B2O3 (Me=Ca, Sr, Ba) flux agents facilitated the formation of the CaAl2Si2O8 ceramics with a dense microstructure via liquid-phase sintering. The addition of alu-mina and quartz to the flux agents also strongly affected the microstructures, phase formation, and physical properties of the CaAl2Si2O8 ce-ramics.     

Microstructure and mechanical properties of reaction-bonded B_4C–SiC composites

Reaction-bonded B_4C–SiC composites are highly promising materials for numerous advanced technological applications. However,their microstructure evolution mechanism remains unclear. Herein, B_4C–SiC composites were fabricated through the Si-melt infiltration process. The influences of the sintering time and the B_4C content on the mechanical properties, microstructure, and phase evolution were investigated. X-ray diffraction results showed the presence of SiC, boron silicon, boron silicon carbide, and boron carbide. Scanning electron microscopy results showed that with the increase in the boron carbide content, the Si content decreased and the unreacted B_4C amount increased when the sintering temperature reached 1650°C and the sintering time reached 1 h. The unreacted B_4C diminished with increasing sintering time and temperature when B_4C content was lower than 35 wt%. Further microstructure analysis showed a transition area between B_4C and Si,with the C content marginally higher than in the Si area. This indicates that after the silicon infiltration, the diffusion mechanism was the primary sintering mechanism of the composites. As the diffusion process progressed, the hardness increased. The maximum values of the Vickers hardness, flexural strength, and fracture toughness of the reaction-bonded B_4C–SiC ceramic composite with 12 wt% B_4C content sintered at 1600°C for 0.5 h were about HV 2400, 330 MPa, and 5.2 MPa·m~(0.5), respectively.     

Suspension calcination and alkali leaching of low-grade high-sulfur bauxite:Desulfurization,mineralogical evolution and desilication

To enable the utilization of low-grade and high-sulfur bauxite, the suspension calcination was used to remove the sulfur and the activate silica minerals, and the calcinated bauxite was subjected to a desilication process in Na OH solution under atmospheric pressure. The desulfurization and desilication properties and mineralogical evolution were studied by X-ray diffraction, thermogravimetry–differential thermal analysis, scanning electron microscopy, and FactSage methods. The results demonstrate that the suspension calcination method is efficient for sulfur removal: 84.21% of S was removed after calcination at 1000°C for 2 min. During the calcination process, diaspore and pyrite were transferred to α-Al_2O_3, magnetite, and hematite. The phase transformation of pyrite follows the order FeS_2 → Fe_3O_4 → Fe_2O_3, and the iron oxides and silica were converted into iron silicate. In the alkali-soluble desilication process, the optimum condition was an alkali solution concentration of 110 g/L, a reaction time of 20 min, and a reaction temperature of 95°C. The corresponding desilication ratio and alumina loss ratio were 44.9% and 2.4%, respectively, and the alumina-to-silica mass ratio of the concentrate was 7.9. The Al_2O_3·2SiO_2, SiO2, and Al_2O_3 formed during the calcination process could react with Na OH solution, and their activity decreased in the order of Al_2O_3·2 SiO_2, SiO_2, and Al_2O_3.