ZIRCONIA REFRACTORIES

• 1 Outline of physical properties of zirconium ore.
• 2 Mention of zirconia laboratory ware and method of manufacture.
• 3 Manufacture and physical properties of zirconia brick.
• 4 Zirconia cement and its uses.

     

SOME EXPERIMENTS ON CRYSTAL GROWTH AND SOLUTION IN GLASSES*

Experiments, which included the development of methods of measuring the linear rates of crystal growth and crystal solution and a study of surface crystallization, were conducted on commercial-type glasses. A method of studying interdiffusion of two glasses of similar composition is described but no conclusions were reached. It was found that (a) the rate of crystal growth is constant until the crystallization zones from the opposite surfaces meet and (b) the curve of crystal solution is continuous with that of crystal growth as the temperature is raised above the liquidus temperature. The results indicate that dust in the atmosphere is a major contributing factor promoting surface devitrification.     

添加熔铸锆刚玉微粉锆英石捣打料的烧结性和抗蚀性

采用行星磨微细化的熔铸锆刚玉微粉(fused corundum zirconia micropowder,mp-FAZS)改善玻璃窑池底用锆英石捣打料的烧结性和抗蚀性.测试1 350 ℃渣蚀48 h坩埚侵蚀深度等性能,结合显微结构观察,讨论含5%～25%(质量分数)mp-FAZS,1 200～1400 ℃烧结后样品的显气孔率、侵蚀深度与mp-FAZS含量和烧结温度的关系.结果表明:添加mp-FAZS能明显改善捣打料的烧结性和抗蚀性,25%mp-FAZS,1400 ℃烧结样品显气孔减少高达34%,侵蚀深度下降近5倍.mp-FAZS助烧和抗蚀机制主要为mp-FAZS中的玻璃相和高表面能促进捣打料烧结性以及由FAZS、斜锆石和刚玉相所形成的侵蚀界面能够提高其抗蚀性.     

SOME CONSIDERATIONS IN THE PRODUCTION OF FUSED MULLITE FOR REFRACTORIES *

The principles of the process of fusing ceramic materials for abrasives and refractories are now rather generally known. The benefits to be derived from the additions of fused materials to a refractory are likely to be (1) an increase of chemical resistance owing to the greater density and lower permeability, (2) an increase of load-bearing value of the product, and (3) a control of the kind and number of crystalline materials present in the grain as well as the proportion of glass contained. The term “flux” is not necessarily correctly used in connection with such fused materials, because it often applies only to a constituent which changes the proportions of the crystalline phases and does not affect the refractoriness or glass content.     

REACTION BETWEEN COPPER REVERBERATORY SLAG AND REFRACTORIES*

Small slag cylinders placed on top of different refractory brick were heated at 1300° and 1400°C. Depth and width of reaction and diffusion zones were measured, and thin sections through the penetrations mere studied.     

SPECIFIC HEATS OF CHROME AND MAGNESIA REFRACTORIES*

The previous work in the field is surveyed, the method of preparing the samples is described, and chemical, petrographic, and screen analyses and photomicrographs of the samples are presented. Specific-heat determinations were made by the method of mixtures in a calorimeter using carbon tetrachloride; the calorimeter and the auxiliary equipment are described; and the procedures for determining the heat capacity of the calorimeter system and for the specific heats of the test samples are given in detail. The results are summarized, tabulated, and compared with published data. In addition to the bibliography of the papers mentioned in the article, an additional section (Section B), which served as a background for the study, is included.     

GLOST KILN REFRACTORIES*

Saggers for glost placing must give good life and avoid harmful secondary effects on the ware. Low thermal expansion is the most necessary property but, if carried too far, may cause the fault known as pin chipping. This defect, however, is compensated by low expansion in the pin itself. The system sagger-pin-ware should be adjusted to minimize tensile stresses in cooling.     

THE THERMAL CONDUCTIVITY OF SOME REFRACTORIES1

The problem of measuring the thermal conductivity of materials up to high temperatures has been studied, especially in regard to the sources of error. This investigation has shown that many of the previous determinations of thermal conductivity may have had little precision due to a lack of appreciation of the errors involved. The values of thermal conductivity for a number of refractories are given, as obtained by a new type of apparatus designed to eliminate to a considerable extent the errors of measurement. However, it is believed that these values may have an error as high as ± 25 % for the better heat conductors; so there is still much work to be done in developing a method for measuring thermal conductivity with the precision usual in other physical measurements.     

NOTES ON REACTION BETWEEN MgO AND VARIOUS TYPES OF REFRACTORIES *

Samples of high-heat duty, superduty, 60% Al₂O₃, 70% Al₂O₃, 90% Al₂O₃, fused-alumina, kaolin base, kyanite base, chrome magnesite, silicon carbide, zircon, and chrome-magnesite compositions were tested for reaction with MgO at temperatures of 2200°, 2600°, and 2800°F. (1205°, 1425°, and 1540°C.). Silicon carbide and zircon refractories showed a slight reaction at 2800°F. and none at 2600°F. or at 2200°F. Commercial grades of firebrick containing 60% or more of Al₂O₃ in contact with powdered magnesia showed no reaction up to 2800°F.     

EXPERIMENTS WITH AN ACCELERATED WEATHERING TEST FOR PORCELAIN ENAMELS*

Experiments were conducted on porcelain enamels using the accelerated weather test developed at the National Bureau of Standards. A comparison of results indicates this test to be a promising solution to the problem of the rapid determination of the weather resistance of porcelain enamel.     

CHEMICAL AND MINERALOGICAL CHANGES IN STACK AND HEARTH REFRACTORIES OF A BLAST FURNACE*

Refractory samples removed from the lining of a blast furnace exhibiting normal behavior were analyzed for chemical and mineralogical changes. The changes observed in the lining of this furnace are discussed and their probable effect upon the refractory life is indicated; On the basis of the findings, suggestions are made regarding blastfurnace refractory practice.     

SECONDARY EXPANSION OF HIGH-ALUMINA REFRACTORIES*

Several mixtures of raw and calcined diaspore and bauxite with raw and calcined fire clays were prepared and fired at 2700°F. Specimens were refired at higher temperatures, and the linear changes were determined. Bodies composed of high-alumina grog and fire clay expand in the refire, whereas specimens of fire-clay grog that are bonded with ground raw diaspore exhibit shrinkage. The cause of the secondary expansion and shrinkage of these bodies is discussed.     

ELECTRICAL RESISTIVITY OF SPECIALIZED REFRACTORIES*

Tests were made of the electrical resistivity of twelve commercially used special refractory brick at temperatures up to 1300°C. Standard 9-inch brick were tested using apparatus which is standard equipment and readily obtainable. Temperature lag was eliminated by constant heating over a prolonged period of time at given temperatures. Results obtained indicate a decrease in resistivity with prolonged heating for some classes of refractories. Those refractories composed of minerals of the same petrographic classification appear to undergo the least change.     

CHARACTERISTICS OF ZIRCON PORCELAIN*

The manufacturing characteristics, properties, uses, and future possibilities of zircon porcelain are discussed. Any of the usua1 manufacturing processes may be used, but special glazes must be employed because zircon absorbs normal glazes: The typical properties (approximate values) are (a) linear expansion, 4.5 × 10^-6 per °C., (b) thermal conductivity, 0.012 (normal porcelain, 0.004), (c) tensile strength, 13,000 Ib. per sq. in., (d) compressive strength, 100,000 Ib. per sq. in., (e) modulus of elasticity, 25 × 10⁶ Ib. per sq. in., (f) thermal-shock resistance, good, (g) power factor at 1 mc., 0.001, and (h) dielectric constant, 9.     

DEVELOPMENT OF OPACITY IN ZIRCONIA ENAMELS*

Opaque zirconia-bearing enamels are divided into two general types, namely, those whose opacity is due (1) to the undissolved residue of the zirconia added in the raw batch and (2) to the crystallization of a zirconia compound during firing. These enamels are described and illustrated. The quantity, identity, and appearance of the materials causing opacity in representative samples of each group of enamels are given.     

SOME EFFECTS OF COAL ASH ON REFRACTORIES1

The action of coal ash on the following types of refractories was studied: (1) high diaspore brick, (2) fireclay refractories with very little quartz, (3) fireclay refractories with considerable quartz, (4) refractories containing a mixture of diaspore and fireclay, and (5) andalusite refractories. The tests were carried out in a rotary test furnace at temperatures ranging from 1500 to 1600°C. The phases present in the coal-ash refractory slag were identified by means of the petrographic microscope and consisted of magnetite, mullite, and glass. The effects of time of slag action and slagging temperature were studied.