Showing papers on "Mullite published in 1974"
TL;DR: In this paper, the phases in the kaolinite-mullite reaction sequence were reexamined by ir absorption spectrophotometry, with particular attention paid to the controversial intermediate Al-containing phases.
Abstract: The phases in the kaolinite-mullite reaction sequence were reexamined by ir absorption spectrophotometry. Particular attention was paid to the controversial intermediate Al-containing phases. Amorphous materials were leached from fired kaolinite samples with NaOH to help identify crystalline phases. Metakaolinite partially decomposes, releasing amorphous γ-Al2O3 and SiO2, before the “950°C” exothermic reaction in which metakaolinite is completely decomposed. The resulting spinel-type phase, which is associated with amorphous SiO2 and some poorly crystalline “primary” mullite, is γ-Al203 (crystalline) rather than an Al-Si spinel. There is some evidence, however, that a fraction of the γ-Al2O3, may be an Al-Si spinel. At ≥1100°C secondary mullite therefore forms primarily from the γ-Al2O3/amorphous SiO2 reaction and the recrystallization of primary mullite, whereas excess amorphous SiO2 eventually crystallizes as cristobalite.
144 citations
TL;DR: In this paper, single crystals of mullite up to 2 cm in diameter and 6 cm long were grown by the Czochralski method in a nitrogen atmosphere under normal atmospheric pressure with precise programmed control of heating.
48 citations
TL;DR: Diffusion couples, consisting of sapphire and fused silica, which were annealed in the temperature range from 1678� to 2003�C and analyzed by electron beam microprobe, have provided data on the stable phase equilibrium of the silica-alumina system.
Abstract: Diffusion couples, consisting of sapphire and fused silica, which were annealed in the temperature range from 1678° to 2003°C and analyzed by electron beam microprobe, have provided data on the stable phase equilibrium of the silica-alumina system. Under stable equilibrium conditions, the intermediate compound of this system, mullite (3Al2O3 · 2SiO2), melts incongruently at 1828° ± 10°C and its solid solution field extends from 70.5 to 74.0 percent (by weight) alumina. The stable phase diagram is a composite of the two binary eutectic diagrams: silica-mullite in the absence of alumina and silica-alumina in the absence of mullite. Under metastable conditions, mullite melts congruently at ≈ 1890° ± 10°C and its solid solution field extends to ≈ 83.2 percent (by weight) alumina.
48 citations
Patent•
04 Nov 1974TL;DR: Cordierite refractory compositions made from a mixture of talc, clay, calcined kyanite, alumina and water, the composition being such as to result on firing in a body having cordierite as the major crystalline phase as mentioned in this paper.
Abstract: Cordierite refractory compositions made from a mixture of talc, clay, calcined kyanite, alumina and water, the composition being such as to result on firing in a body having cordierite as the major crystalline phase and mullite as the minor crystalline phase and wherein the amount of Na 2 O and K 2 O is not in excess of about 0.14% by weight of the batch dry materials, such compositions being suitable for making a catalyst substrate or support in the form of an extruded multi-tubular refractory body as well as other ceramic bodies such as turbine engine components, heat exchanger cores and furnace ware which have a requirement for high resistance to heat shock and low thermal expansion characteristics.
43 citations
TL;DR: In this paper, it was shown that the mullite-type phase appears to crystallize with an increase in temperature at the expense of a γ-Al2O3 phase, indicating adsorption of Na on the defect spinel structure.
Abstract: Silica-free phases which have a structure similar to that of mullite can be crystallized from gels in the Na2O-Al2O3 and (Na,K)2O-BaO-Al2O3 systems. A gelation step appears to be necessary, since a solid-state reaction between Na2CO3 and Al(OH)3 does not give the mullite-type phase. Crystallization of this phase requires a high alkali content during formation of the gel. A well-crystallized phase is formed at 950°C and is stable to at least 1000°C; at higher temperatures (i.e. 1200°C), β-Al2O3 and corundum are formed. The mullite-type phase appears to crystallize with an increase in temperature at the expense of a γ-Al2O3 phase, indicating adsorption of Na on the defect spinel structure, which is then rearranged to give the mullite-type phases.
33 citations
TL;DR: In this paper, Czochralski grown mullite single crystals have been analyzed by electron microprobe and a small range of solid solution between mullite and Al 2 O 3 was found.
16 citations
15 citations
Patent•
23 Oct 1974
TL;DR: In this paper, a process for preparing high purity, submicron, mullite powder (3Al2O3.2SiO2) by hydrolytically decomposing aluminum tris isopropoxide and silicon tetrakis isOPropoxide in the presence of ammonium hydroxide or a very dilute mineral acid is described.
Abstract: A process is provided for preparing high purity, submicron, mullite powder (3Al2O3.2SiO2) by hydrolytically decomposing aluminum tris isopropoxide and silicon tetrakis isopropoxide in the presence of ammonium hydroxide or a very dilute mineral acid. The powder as prepared as well as that subjected to calcination has an orthorhombic crystal structure. Structural bodies of near theoretical density can be fabricated by vacuum hot pressing the powder. Because of its large surface area, the mullite powder is an excellent catalyst and catalyst carrier, especially for hydrocarbon cracking catalysts.
15 citations
TL;DR: In this paper, the Knoop microhardness of one B4C deposit on a mullite substrate was 3,472, which corresponds to a Mohs hardness of approximately 9.32.
8 citations
Patent•
24 Jan 1974
TL;DR: Refractory stone for cladding bottom shaft pt of blast furnaces contains granular basic material of refractory oxides and/or carbides, pref sinter corundum, -mullite, -magnesia, Cr-Magnesia, sillimanite, Zr oxide, and a SiC binder structure as discussed by the authors.
Abstract: Refractory stone for cladding bottom shaft pt of blast furnaces contains (a) granular basic material of refractory oxides and/or carbides, pref sinter corundum, -mullite, -magnesia, Cr-magnesia, sillimanite, Zr oxide and/or SiC, and (b) a SiC binder structure, pref prepd by reacting Si powder with coked electrode pitch and coke powder in deep by-prod coking ovens Si- or FeSi powder used pref contains >70% Si and has 02 mm grain-size
8 citations
Patent•
04 Mar 1974
TL;DR: In this paper, a thermo-chemical bonded refractory product consisting of inactive refractories bonded together by mullite is described. But the product is not suitable for use in a pyro-processing unit.
Abstract: This disclosure concerns a thermo-chemical bonded refractory product which comprises inactive refractory grains bonded together by mullite. The refractory is emplaced in a furnace or other pyro-processing unit by pressing, ramming, gunning, casting, etc. The refractory product is made by mixing inactive refractory grains with a mixture of zircon and alumina powders and a small amount of an alkaline earth oxide catalyst. The catalyst breaks the zircon down into ZrO 2 and SiO 2 at relatively low temperatures. The SiO 2 thus liberated is unusually reactive and reacts with the alumina to form mullite and the ZrO 2 adsorbs the alkaline earth oxide.
TL;DR: In this paper, the authors measured the contact angle of molten zinc drops on fifteen ceramic materials and four metals in high-purity helium and carbon monoxide atmospheres, and found that zinc of 99.9999 percent purity did not wet the oxide materials, glass-type coatings, or graphite.
Abstract: Measurements were made of the contact angle of molten zinc drops on fifteen ceramic materials and four metals in high-purity helium and carbon monoxide atmospheres. Zinc of 99.9999-percent purity did not wet the oxide materials, glass-type coatings, or graphite; all contact angles were greater than 90 deg at 500 to 700°C in helium and 500 to 800°C in carbon monoxide. Materials tested that were most resistant to wetting by zinc were ZnO sinter, glazed fireclay, graphite, and mullite.
23 Jul 1974
TL;DR: The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena as discussed by the authors.
Abstract: The potential of producing the glassy form of selected materials in the weightless, containerless nature of space processing is examined through the development of kinetic relationships describing nucleation and crystallization phenomena. Transformation kinetics are applied to a well-characterized system (SiO2), an excellent glass former (B2O3), and a poor glass former (Al2O3) by conventional earth processing methods. Viscosity and entropy of fusion are shown to be the primary materials parameters controlling the glass forming tendency. For multicomponent systems diffusion-controlled kinetics and heterogeneous nucleation effects are considered. An analytical empirical approach is used to analyze the mullite system. Results are consistent with experimentally observed data and indicate the promise of mullite as a future space processing candidate.
20 Feb 1974
TL;DR: In this paper, the authors presented a program to develop and evaluate mullite fiber with a mean diameter under two microns, which is produced by a blowing process at room temperature from a low viscosity (10-25 poise) solution.
Abstract: Results are presented of a program to develop and evaluate mullite fiber with a mean diameter under two microns. The two micron fiber is produced by a blowing process at room temperature from a low viscosity (10-25 poise) solution. The blown fiber was evaluated for dimensional stability in thermal cycling to 1371 C, and was equivalent to the 5 micron spun B and W mullite fiber. An additive study was conducted to evaluate substitutes for the boron. Three levels of chromium, lithium fluoride, and magnesium were added to the standard composition in place of boron and the fiber produced was evaluated for chemical and dimensional stability in thermal cycling to 1371 C. The magnesium was the most chemically stable, but the chrome additive imparted the best dimensional stability.
TL;DR: The property indices of pure-mullite specimens are high and approach those of pureoxide products, i.e., creep, volatility and the coefficient of thermal expansion are low, the high-temperature strength is good, spalling resistance is satisfactory, and electrical resistance high.
Abstract: The property indices of pure-mullite specimens are high and approach those of pure-oxide products, i.e., creep, volatility and the coefficient of thermal expansion are low, the high-temperature strength is good, spalling resistance is satisfactory, and electrical resistance high. These quality indices are degraded with the addition of impurities.
TL;DR: In this article, the deformation properties of high-alumina refractories were investigated and it was shown that creep in a reducing medium (containing up to 8% CO) is greater than in an oxidizing medium, viz.
Abstract: An investigation of the deformation properties of high-alumina refractories showed that creep in a reducing medium (containing up to 8% CO) is greater than in an oxidizing medium, viz. by a factor of 1.3 for mullite products, 1.7 for mullite-corundum specimens, and 2.2 for commercial grade mullite-corundum refractories.
TL;DR: In this article, it was shown that the mullite-type phase appears to crystallize with an increase in temperature at the expense of a γ-Al2O3 phase, indicating adsorption of Na on the defect spinel structure.
Abstract: Silica-free phases which have a structure similar to that of mullite can be crystallized from gels in the Na2O-Al2O3 and (Na,K)2O-BaO-Al2O3 systems. A gelation step appears to be necessary, since a solid-state reaction between Na2CO3 and Al(OH)3 does not give the mullite-type phase. Crystallization of this phase requires a high alkali content during formation of the gel. A well-crystallized phase is formed at 950°C and is stable to at least 1000°C; at higher temperatures (i.e. 1200°C), β-Al2O3 and corundum are formed. The mullite-type phase appears to crystallize with an increase in temperature at the expense of a γ-Al2O3 phase, indicating adsorption of Na on the defect spinel structure, which is then rearranged to give the mullite-type phases.
01 Feb 1974
TL;DR: The characteristics of cordierite type compositions and the relationship between thermal expansion and raw materials, processing, and gross composition are examined in this paper, where other possible support materials are reviewed briefly.
Abstract: The characteristics of cordierite type compositions and the relationship between thermal expansion and raw materials, processing, and gross composition are examined. Other possible support materials are reviewed briefly. These included mullite, zircon, beryl, spodumene, aluminum titanate, silicon nitride, and other low expansion compositions. Raw material cost, processing, and reactivity with the catalysis are discussed for these materials.
TL;DR: In this article, the phases in the kaolinite-mullite reaction sequence were reexamined by ir absorption spectrophotometry, with particular attention paid to the controversial intermediate Al-containing phases.
Abstract: The phases in the kaolinite-mullite reaction sequence were reexamined by ir absorption spectrophotometry. Particular attention was paid to the controversial intermediate Al-containing phases. Amorphous materials were leached from fired kaolinite samples with NaOH to help identify crystalline phases. Metakaolinite partially decomposes, releasing amorphous γ-Al2O3 and SiO2, before the “950°C” exothermic reaction in which metakaolinite is completely decomposed. The resulting spinel-type phase, which is associated with amorphous SiO2 and some poorly crystalline “primary” mullite, is γ-Al203 (crystalline) rather than an Al-Si spinel. There is some evidence, however, that a fraction of the γ-Al2O3, may be an Al-Si spinel. At ≥1100°C secondary mullite therefore forms primarily from the γ-Al2O3/amorphous SiO2 reaction and the recrystallization of primary mullite, whereas excess amorphous SiO2 eventually crystallizes as cristobalite.