The immersible quartz--ceramic nozzles produced by the Podolsk Refractories Plant (PRP) for continuous steelcasting machines (CSCM) are important components on the durability of which the stability and smoothness of the continuous process of casting and the character of the crystallization of the steel ingot depend to a considerable extent. The manufacture of the nozzles from quartz glass by slip casting is a labor-intensive and expensive process for which reason it is important that they are quality-tested without the destruction of a certain number for the purpose of obtaining specimens. Such a method would be important because it would permit the testing of all products and not merely a representative sample.The All-Union Institute of Refractories and PRP investigated a nondestructive method of controlling the porosity and density variation of the nozzles for the purpose of determining the influence of the porosity on their service behavior.The porosity of the nozzles was tested by a microwave phase method (using uhf waves) [1, 2]. The method is based on the utilization of the relation between the specific inductive capacitance ~ of the medium and its general porosity P [3]. For quartz ceramic the relation between ~ and P is expressed by the equationwhere 60 is the specific inductive capacitance for a nonporous quartz ceramic (P = 0) and equals 3.81 [5,6].In the phase method of control described here the measured quantity is fl, the advance of the phase of the electromagnetic wave passing through the tested product, i.e., the phase change of the refracted wave caused by its passage through the product. For an inorganic dielectric medium the relation between fi and s is described by the equation [7] = -~-()/~ --1) d.( 2) where s is the length of the electromagnetic wave in free space and d the measurement base (the depth of the examination zone).With regard to Eq. (1), therefore, a well-defined functional relation exists between the advance of the electromagnetic wave and the porosity of the dielectric medium. However, in the case of products like quartz nozzles with their complex configuration and dimensions, the diffraction phenomena may produce a masking effect so that the character of the relation between fl and ~ (P) may differ from that described by Eq. (2).To determine the relation between fi and P in the various examination zones of the quartz nozzles, a comparison and statistical analysis were carried out of the relation between ~ and P in the examination zones of the nozzles. The porosity was determined by the standard method (GOST 2409-67) for specimens prepared from the examination zones. The quantity fi was measured with an INF-2 instrument [8] at wavelength ~ = 3.93 cm using horn antennas with an opening of 2.4 • 2.4 cm. The nozzles were examined in the various zones ( Fig. 1) in the direction of the diametral axis of the plane-polarized wave. The vector of the electric displacement was oriented in the direction of the center axis of the nozzle. The transmission base d was represented by the combi...

666.762.2.017:620~!79oi T. I. Litovskaya, and S. P. Shmitt-FogelevichThe formation of cristobalite during the preparation of articles made from quartz ceramic leads to the emergence of cracks in the articles and to a loss of strength [i] as a result of the ~ + B cristobalite transition on cooling.As a result, the properties of the articles are degraded in use.It is therefore necessary to eliminate as far as possible the supply to the customer of products in which a critical amount of cristobalite has been formed.Sometimes the formation of cristobalite leads to cracks which emerge on the surface of the article.In that case defective articles can be revealed by visual inspection.Since the reasons for the formation of cristobalite may vary and be associated with very slight and unrecorded deviations in the production process, the output of articles in which the concentration of cristobalite goes beyond permissible limits is random in character.At the present time there are no inspection methods which make it possible to reveal~ reliably and immediately, those articles which contain cristobalite.Normally under laboratory conditions the concentration of cristobalite is determined using an x-ray method [2] but for several reasons this cannot be used for production control.According to [3,4] as well as from some theoretical considerations, the emergence of cristobalite must produce a change in the dielectric properties of a quartz ceramic. This fact may be used as the basis of a method which makes it possible to organize on-line production control of the concentration of cristobalite in the articles.The aim of the studies described in the present paper was to investigate the dependence of the dielectric properties, porosity, and density, on the phase composition of the ceramic.The studies were carried out on cylindrical specimens made by a slip-casting method. As the starting materials we used vitreous silica with a mass fraction of SiO2 > 99%. The specimens were fired in a furnace with silicon carbide heaters at a heating rate of 200~ with a 3-h dwell.It was possible to produce specimens with different concentrations of cristobalite by changing the firing temperature between I150~and 1300~ The open porosity (Pop) and apparent density (Papp) of the specimens were determined in accordance with GOST 2409-80; the concentration of cristobalite was determined using an x-ray method.Samples were prepared by quartation down to 2-5 g and milling in a chalcedony mortar to particles <0.063 nun. The measurement error in the concentration of crystalline phase depends on the amount and extent of defectiveness in the cristobalite [2].The dielectric properties of the specimens were studied in the UHF range at wavelengths of % = 3.935 and 0.884 cm.The measurements at % = 3.935 cm were carried out in an INF-2 instrument [5] using horn-type antennae with an aperture of 2.4 x 2.4 cm; the measurements at X = 0.884 cm were carried out in equipment assembled from standard units in accordm~ce with the diagram in Fig. i; horn antennae with an ...

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