Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Concentration on Density and Structure of (CaO-SiO<Subscript>2</Subscript>)-xAl<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag

The effect of Al₂O₃ concentration on the density and structure of CaO-SiO₂-Al₂O₃ slag was investigated at multiple Al₂O₃ mole percentages and at a fixed CaO/SiO₂ ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al₂O₃ content was less than 15 mole pct, density decreased with increasing Al₂O₃ content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al³⁺ ion as a network modifier.     

Effect of heat treatments on <Emphasis Type="Italic">In-Situ</Emphasis> Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiAl<Subscript>3</Subscript> composites produced from squeeze casting of TiO<Subscript>2</Subscript>/A356 composites

In-situ Al₂O₃/TiAl₃ intermetallic matrix composites were fabricated via squeeze casting of TiO₂/A356 composites heated in the temperature range from 700 °C to 780 °C for 2 hours. The phase transformation in TiO₂/A356 composites employing various heat-treatment temperatures (700 °C to 780 °C) was studied by means of differential thermal analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). From DTA, two exothermic peaks from 600 °C to 750 °C were found in the TiO₂/A356 composites. The XRD showed that Al₂O₃ and TiAl₃ were the primary products after heat treatment of the TiO₂/A356 composite. The fabrication of in-situ Al₂O₃/TiAl₃ composites required 33 vol pct TiO₂ in Al and heat treatment in the range from 750 °C to 780 °C. The hardness (HV) of the in-situ Al₂O₃/TiAl₃ composites (1000 HV) was superior to that of nonreacted TiO₂/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO₂/A356 composites to 250 MPa for Al₂O₃/TiAl₃ composites. It decreased rapidly because pores occurred during the formation of Al₂O₃ and TiAl₃. The activation energy of the formation of Al₂O₃ and TiAl₃ from TiO₂ and A356 was determined to be about 286 kJ/mole.     

A reinvestigation of phase equilibria in the system Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>-ZnO

The phase equilibria and liquidus temperatures in the binary SiO₂-ZnO system and in the ternary Al₂O₃-SiO₂-ZnO system at low Al₂O₃ concentrations have been experimentally determined using the equilibration and quenching technique followed by electron probe X-ray microanalysis. In the SiO₂-ZnO system, two binary eutectics involving the congruently melting willemite (Zn₂SiO₄) were found at 1448±5 °C and 0.52±0.01 mole fraction ZnO and at 1502±5 °C and 0.71±0.01 mole fraction ZnO, respectively. The two ternary eutectics involving willemite previously reported in the Al₂O₃-SiO₂-ZnO system were found to be at 1315±5 °C and 1425±25 °C, respectively. The compositions of the eutectics are 0.07, 0.52, and 0.41 and 0.05, 0.28, and 0.67 mole fraction Al₂O₃, SiO₂, and ZnO, respectively. The results of the present investigation are significantly different from the results of previous studies.     

Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-4 Wt Pct Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramic Compound

Different amounts of LiF were added to an Al₂O₃-4 pct Nb₂O₅ basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb₃O₇F, but also to the absence of LiAl₅O₈. The preferential interaction of LiF with Nb₂O₅, instead of Al₂O₃, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.     

Evaluating the Diffusion Coefficient of Sulfur in Low-Silica CaO-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag

The chemical diffusion coefficient of sulfur in the ternary slag of composition 51.5 pct CaO-9.6 pct SiO₂-38.9 pct Al₂O₃ slag was measured at 1680 K, 1700 K, and 1723 K (1403 °C, 1427 °C, and 1450 °C) using the experimental method proposed earlier by the authors. The P_\textS2 P_{{{\text{S}}_{2} }} and P_\textO2 P_{{{\text{O}}_{2} }} pressures were calculated from the Gibbs energy of the equilibrium reaction between CaO in the slag and solid CaS. The density of the slag was obtained from earlier experiments. Initially, the order of magnitude for the diffusion coefficient was taken from the works of Saito and Kawai but later was modified so that the concentration curve for sulfur obtained from the program was in good fit with the experimental results. The diffusion coefficient of sulfur in 51.5 pct CaO-9.6 pct SiO₂-38.9 pct Al₂O₃ slag was estimated to be in the range 3.98 to 4.14 × 10⁻⁶ cm²/s for the temperature range 1680 K to 1723 K (1403 °C to 1450 °C), which is in good agreement with the results available in literature     

Effect of CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-MgO slags on the formation of MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> inclusions in ferritic stainless steel

A thermodynamic equilibrium between the Fe-16Cr melts and the CaO-Al₂O₃-MgO slags at 1823 K as well as the morphology of inclusions was investigated to understand the formation behavior of the MgO-Al₂O₃ spinel-type inclusions in ferritic stainless steel. The calculated and observed activities of magnesium in Fe-16Cr melts are qualitatively in good agreement with each other, while those of aluminum in steel melts exhibit some discrepancies with scatters. In the composition of molten steel investigated in this study, the log (X _MgO/X _{Al 2}O₃) of the inclusions linearly increases by increasing the log [a _Mg/a _Al ² ·a _O ² ] with the slope close to unity. In addition, the relationship between the log (X _MgO/X _{Al 2}O₃) of the inclusions and the log (a _MgO/a _{Al 2}O₃) of the slags exhibits the linear correlation with the slope close to unity. The compositions of the inclusions are relatively close to those of the slags, viz. the MgO-rich magnesia-spinel solid solutions were formed in the steel melts equilibrated with the highly basic slags saturated by CaO or MgO. The spinel inclusions nearly saturated by MgO were observed in the steel melts equilibrated with the slags doubly saturated by MgO and MgAl₂O₄. The spinel and the Al₂O₃-rich alumina-spinel solid solutions were formed in the steel melts equilibrated with the slags saturated by MgAl₂O₄ and MgAl₂O₄-CaAl₂O₄ phases, respectively. The apparent modification reaction of MgO to the magnesium aluminate inclusions in steel melts equilibrated with the highly basic slags would be constituted by the following reaction steps: (1) diffusion of aluminum from bulk to the metal/MgO interface, (2) oxidation of the aluminum to the Al³⁺ ions at the metal/intermediate layer interface, (3) diffusion of Al³⁺ ions and electrons through the intermediate layer, and (4) magnesium aluminate (MgAl₂O₄ spinel, for example) formation by the ionic reaction.     

Reactive synthesis of <Emphasis Type="Italic">in-situ</Emphasis> ZrAl<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al composites

In this work, a reactive synthesis process is proposed to obtain ZrAl₃-Al₂O₃ particulate-reinforced aluminum matrix composites. The process involves the in-situ formation of Al₂O₃ and ZrAl₃ from Al-ZrO₂ green compacts. Upon compact heating, it is found that reduction of ZrO₂ by molten aluminum occurs at temperatures above 750 °C, leading to the development of ZrAl₃ and Al₂O₃ phases. Thermodynamically, it is found that the reduction of zirconium oxide is driven mainly by the dissolution of Zr in molten aluminum. Because the solubility of Zr in liquid aluminum is extremely small, the formation of ZrAl₃ is favored after relatively small Zr dissolutions. The first Zr-Al intermetallics to form at the lowest temperatures seem to be metastable, as infered from the measured atom ratios for Al : Zr of 2.83 : 1. At increasing temperatures, the reaction comes into completion, resulting in the formation of equilibrium intermetallic ZrAl₃ phases. The results obtained from differential scanning calorimetry (DSC) indicate that by increasing the scanning rates, both the reaction temperature and the exothermic peak intensity also increase. Alternatively, it is found that by reducing the amount of ZrO₂ in the green compact, the in-situ reaction temperatures also shift toward higher values.     

Alumina Solubility in KF-NaF-AlF<Subscript>3</Subscript>-Based Low-Temperature Electrolyte

KF-NaF-AlF₃-based electrolyte is a promising low-temperature electrolyte for aluminum reduction. Alumina solubility in molten KF-NaF-AlF₃-based electrolyte was determined as a function of the melt composition and temperature by measuring the weight loss of a rotating corundum disk and by using a LECO RO500 oxygen analyzer (LECO Corporation, St. Joseph, MI). The investigated temperature range is 1023 K to 1073 K (750 °C to 800 °C), and the total cryolite molar ratio (CRt = ([KF] + [NaF])/[AlF₃]) is 1.3 to 1.5; the content of NaF ranges from 0 mol pct to 50 mol pct. The effect of temperature, CaF₂, and LiF on alumina solubility is discussed as well.     

Phase-equilibrium data and liquidus for the system “MnO”-CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> at Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> of 0.55 and 0.65

Phase-equilibrium data and liquidus isotherms for the system “MnO”-CaO-(Al₂O₃+SiO₂) at silicomanganese alloy saturation have been determined in the temperature range of 1373 to 1723 K. The results are presented in the form of the pseudoternary sections “MnO”-CaO-(Al₂O₃+SiO₂) with Al₂O₃/SiO₂ weight ratios of 0.55 and 0.65. The primary-phase fields have been identified in this range of conditions.     

Development of Wear-Resistant Cu-10Cr-3Ag Electrical Contacts with Nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Dispersion by Mechanical Alloying and High Pressure Sintering

Cu-10Cr-3Ag (wt pct) alloy with nanocrystalline Al₂O₃ dispersion was prepared by mechanical alloying and consolidated by high pressure sintering at different temperatures. Characterization by X-ray diffraction and scanning electron microscopy or transmission electron microscopy shows the formation of nanocrystalline matrix grains of about 40 nm after 25 hours of milling with nanometric (<20 nm) Al₂O₃ particles dispersed in it. After consolidation by high pressure sintering (8 GPa at 400 °C to 800 °C), the dispersoids retain their ultrafine size and uniform distribution, while the alloyed matrix undergoes significant grain growth. The hardness and wear resistance of the pellets increase significantly with the addition of nano-Al₂O₃ particles. The electrical conductivity of the pellets without and with nano-Al₂O₃ dispersion is about 30 pct IACS (international annealing copper standard) and 25 pct IACS, respectively. Thus, mechanical alloying followed by high pressure sintering seems a potential route for developing nano-Al₂O₃ dispersed Cu-Cr-Ag alloy for heavy duty electrical contact.     

Thermal diffusivity measurements of some synthetic CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> slags

In an attempt to systematize the knowledge of the heat conduction of liquid silicates, the effective thermal diffusivities of some synthetic slags containing CaO, Al₂O₃, and SiO₂ have been measured, using the three-layer laser-flash method on a differential scheme in the temperature range of 1625 to 1825 K. The effective thermal diffusivities measured, which are a combination of the phononic and photonic heat-transfer mechanisms, were found to increase with increasing temperature for all the presently investigated slags. The slag compositions were chosen in such a way that the changes in the effective thermal diffusivities would reflect the changes in the structure of the slags. It was observed that, at a CaO/Al₂O₃ molar ratio of 4.42, an increase of the SiO₂ content had very little effect on the effective thermal diffusivity values. On the other hand, addition of SiO₂ to a slag with the CaO/Al₂O₃ molar ratio of 2.59 resulted in a significant increase in the effective thermal diffusivity. The addition of Al₂O₃ to slags with a constant CaO/SiO₂ molar ratio resulted in a marked increase in the effective thermal diffusivity. Both these trends indicate that there might be an influence of the network formation in silicate melts on the effective thermal diffusivity.     

Investigation into the solubility of nanopowders of the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system in the aqueous medium at various pH

Nanopowders of ZrO₂–Y₂O₃–CeO₂ and ZrO₂–Y₂O₃–CeO₂–Al₂O₃ systems are investigated with the purpose of studying the influence of pH of the dispersed medium on the solubility of nanopowder particles of a complex composition in an aqueous medium after membrane filtration and centrifugation to further prepare the stable dispersions necessary for toxicological investigations of nanoparticles. Concentrations of elements remaining in a supernatant after the sample preparation, which includes membrane filtration and centrifugation, are measured by inductively coupled plasma optical emission spectroscopy. It is established that that the largest aggregative stability of the nanopowder dispersion without the Al₂O₃ additive corresponds to the optimal range of pH 5.5–9.5, while with the Al₂O₃ additive, it is region pH 7.0. The results evidence that, when dispersing these powders, the hydrosol of yttrium oxyhydroxide, which is dissolved at pH < 6.0, is formed. When dissolving in water of the powder with the Al₂O₃ additive in the neutral medium, aluminum hydroxide is formed; in the acidic medium (pH < 6), it is replaced by main soluble aluminum salts; and in the alkali medium (pH > 7), amphoteric aluminum hydroxide is dissolved because of the formation of aluminates.     

Temperature dependence of the refractive index of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Na<Subscript>2</Subscript>O-SiO<Subscript>2</Subscript> melts: Role of electronic polarizability of oxygon controlled by network structure

Refractive indexes for the Al₂O₃-Na₂O-SiO₂ system have been measured using an ellipsometer for a wavelength of 632.8 nm over a wide temperature range (1100 to 1800 K). Two kinds of sample were used: xAl₂O₃-(40-x)Na₂O-60SiO₂ and yAl₂O₃-yNa₂O-(100-2y)SiO₂, where x ranged between 6 and 20 mol pct and y between 12.5 and 25 mol pct. In the former samples, the temperature coefficient of refractive indexes changed from negative to positive on increasing the concentration of Al₂O₃. In the latter samples, the refractive indexes increased monotonically with decreasing concentration of SiO₂, and the temperature coefficient was always positive. It has been found that the temperature dependence of refractive indexes in these melts is determined by the coefficient of thermal expansion, which would be relevant to the degree of polymerization of the melts. In addition, the electronic polarizability of oxygen derived from the refractive indexes increased with increasing temperature in each melt. This suggests that the basicity of the alumino-silicate melts increases as temperature increases. The positive temperature coefficient of the electronic polarizability of oxygen can be attributed to an increase in the distance between cation and oxygen ion due to thermal expansion. The dependence of the electronic polarizability of oxygen on the concentration of Al₂O₃ has also been discussed in terms of the electronic polarizabilities of three types of oxygen contained in the melts. This article is based on a presentation given in the Mills Symposium entitled “Metals, Slags, Glasses: High Temperature Properties & Phenomena,” which took place at The Institute of Materials in London, England, on August 22–23, 2002.     

Long-term oxidation of an as-cast Ni<Subscript>3</Subscript>Al alloy at 900 °C and 1100 °C

The oxidation behavior of a cast nickel aluminide alloy, IC221M, was examined after long-term aging in air for up to 16,600 hours at 900 °C and 5000 hours at 1100 °C. The oxidation products were identified using X-ray diffraction and energy-dispersive X-ray (EDX) spectroscopy with multivariate statistical analysis. At 900 °C, NiO dominates the oxidation products initially, but at longer times, NiAl₂O₄ spinel and Al₂O₃ predominate and remain stable for times up to 16,600 hours. Cross-sectional observation confirmed that a continuous surface oxide that is mostly a mixture of Al₂O₃ and NiAl₂O₄ protects the base metal. In its initial stages, the oxidation process at 1100 °C is qualitatively similar to that at 900 °C but with faster kinetics. However, as aging proceeds, NiO spalls freely from the surface, and a protective continuous oxide scale does not form. The oxidation mechanism can be qualitatively understood by the selective oxidation mechanism maps developed by Giggins and Pettit. An erratum to this article is available at .     

Electrical conductivity of NaF-AlF<Subscript>3</Subscript>-CaF<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> melts

The electrical conductivity of NaF-AlF₃-Al₂O₃ melts with a CaF₂ concentration of 5 wt % is measured at a continuously varying cell constant when the molar cryolitic ratio CR = [NaF]/[AlF₃] changes from 1.2 to 2.0 [1, 2]. The experimental data are used to obtain a regression equation to describe the dependence of the electrical conductivity of the melts under study on CR, the alumina content, and temperature {χ] = f(CR, [Al₂O₃], T)}.     

Kinetics of Reduction of CaO-FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-MgO-PbO-SiO<Subscript>2</Subscript> Slags by CO-CO<Subscript>2</Subscript> Gas Mixtures

Kinetics of the reaction of lead slags (PbO-CaO-SiO₂-FeO _x -MgO) with CO-CO₂ gas mixtures was studied by monitoring the changes in the slag composition when a stream of CO-CO₂ gas mixture was blown on the surface of thin layers of slags (3 to 10 mm) at temperatures in the range of 1453 K to 1593 K (1180 °C to 1320 °C). These measurements were carried out under conditions where mass transfer in the gas phase was not the rate-limiting step and the reduction rates were insensitive to factors affecting mass transfer in the slag phase. The results show simultaneous reduction of PbO and Fe₂O₃ in the slag. The measured specific rate of oxygen removal from the melts varied from about 1 × 10^?6 to 4 × 10^?5 mol O cm^?2 s^?1 and was strongly dependent on the slag chemistry and its oxidation state, partial pressure of CO in the reaction gas mixture, and temperature. The deduced apparent first-order rate constant increased with increasing iron oxide content, oxidation state of the slag, and temperature. The results indicate that under the employed experimental conditions, the rate of formation of CO₂ at the gas-slag interface is likely to be the rate-limiting step.     

Modeling of the solubilities of NiO/NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and FeO/FeAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in cryolite melts at 1300 K

Experiments to measure the solubilities of NiO/NiAl₂O₄ and FeO/FeAl₂O₄ were performed, and the results confirmed existing literature values. The solubilities of NiAl₂O₄ and FeAl₂O₄ in Al₂O₃-saturated cryolite melts at 1300 K were modeled thermodynamically in terms of the Ni-containing complexes Na₂NiF₄ and Na₄NiF₆, and the Fe-containing solutes FeF₂, Na₂FeF₄, and Na₄FeF₆. The experimental solubility data were fitted to multiple simultaneous equilibria. Equilibrium constants and ΔG _f ⁰ values for the formation reactions of the these solutes were thereby estimated. The solubilities of NiO/NiAl₂O₄ and FeO/FeAl₂O₄ and solute distributions in Al₂O₃-undersaturated cryolite melts were calculated for a number of melt compositions from the present model. The existence of several competitive solute species is inherent to highly buffered ionic cryolite solutions where the traditional log-log methodology had previously failed to identify dominant single solutes. In such solutions, individual solutes of oxides are not likely to dominate over a wide composition range so that a more global modeling is required. The principal solute species identified in the present study exhibit reasonable three-dimensional (3-D) anion geometries.     

Microstructural Evolution and Mechanical Properties of Nanointermetallic Phase Dispersed Al<Subscript>65</Subscript>Cu<Subscript>20</Subscript>Ti<Subscript>15</Subscript> Amorphous Matrix Composite Synthesized by Mechanical Alloying and Hot Isostatic Pressing

The structure and mechanical properties of nanocrystalline intermetallic phase dispersed amorphous matrix composite prepared by hot isostatic pressing (HIP) of mechanically alloyed Al₆₅Cu₂₀Ti₁₅ amorphous powder in the temperature range 573 K to 873 K (300 °C to 600 °C) with 1.2 GPa pressure were studied. Phase identification by X-ray diffraction (XRD) and microstructural investigation by transmission electron microscopy confirmed that sintering in this temperature range led to partial crystallization of the amorphous powder. The microstructures of the consolidated composites were found to have nanocrystalline intermetallic precipitates of Al₅CuTi₂, Al₃Ti, AlCu, Al₂Cu, and Al₄Cu₉ dispersed in amorphous matrix. An optimum combination of density (3.73 Mg/m³), hardness (8.96 GPa), compressive strength (1650 MPa), shear strength (850 MPa), and Young’s modulus (182 GPa) were obtained in the composite hot isostatically pressed (“hipped”) at 773 K (500 °C). Furthermore, these results were compared with those from earlier studies based on conventional sintering (CCS), high pressure sintering (HPS), and pulse plasma sintering (PPS). HIP appears to be the most preferred process for achieving an optimum combination of density and mechanical properties in amorphous-nanocrystalline intermetallic composites at temperatures ≤773 K (500 °C), while HPS is most suited for bulk amorphous alloys. Both density and volume fraction of intermetallic dispersoids were found to influence the mechanical properties of the composites.     

Mechanism and rate of reaction of Al<Subscript>2</Subscript>O,Al, and CO vapors with carbon

During the production of aluminum by carbothermic reduction, large quantities of Al₂O and Al vapor are generated. For the process to be economical, the aluminum and energy associated with these species must be captured and used in the process. This is accomplished by reacting them with carbon to form Al₄C₃. The mechanism and rate of the reactions of gas containing Al and Al₂O with various forms of carbon was studied. The Al₂O-Al-CO gas was generated by reacting an Al₄C₃-Al₂O₃ melt with carbon at high temperatures (2000 °C to 2050 °C). The gas then reacted with carbon at lower temperatures (1900 °C to 1950 °C). The only form of carbon that reacted extensively, forming Al₄C₃, was wood charcoal; with other forms of carbon, such as metallurgical coke and petroleum coke, primarily only Al₂O₃ condensed on the surface formed. The rate of formation of Al₄C₃ on wood charcoal was found to be controlled by the diffusion of Al₂O and Al through the Al₄C₃ product layer, and their effective diffusivities were estimated to be 0.82 and 1.31 cm²/s, respectively. Over 90 pct of the carbide is formed by Al₂O and only 10 pct by Al vapor. When an Al₄C₃-Al₂O₃ dense slag was formed on the charcoal at lower temperatures (1920 °C to 1930 °C) and then reacted at a higher temperature, it appears that the slag and carbon reacted to form Al₄C₃ relatively fast. The volume of Al₄C₃ formed is much greater than that of the original carbon. It is believed that this is the reason the other forms of carbon with lower porosity (25 pct vs 60 pct) did not react significantly. Any amount of Al₄C₃ formed would quickly fill the pores of the more dense carbon, stopping any further reaction.