Ceramic and fibrous materials based on quartz glass with controlled porosity (0 to 90%) and technologies for fabrication of complex-shaped components developed at the Tekhnologiya Research and Production Enterprise are described. Properties of structural ceramic and heat-protecting fibrous radio transparent materials for use in aerospace and aircraft technologies are reported. Techniques for improving the strength of thin-walled ceramic shells operating under heavy-duty conditions are described.Development of aerospace technology has stimulated a search for ceramic materials that would combine high thermal stability, low heat conductivity, and constancy of dielectric properties over a wide range of temperatures and frequencies. The materials had to be resistant to optical, highfrequency and ionizing radiation and be operable in vacuum and in oxidizing and reducing media. These requirements were adequately met by materials based on amorphous silicon oxide (quartz glass) that could be prepared by a ceramic technology using powdered or fibrous raw products.Ceramic materials based on quartz glass are a relatively recent addition to the class of inorganic materials [1,2]. Studies that were conducted in the U.S.A. and the USSR in the late 1950s have led to a range of structural and heat-protecting materials differing in properties and manufacturing technologies. A conventional classification was proposed: vacuum-dense ceramics (open porosity P = 0), structural (P = 5 -15%) and porous (P = 20 -25%) ceramics, high-porosity heat-protecting materials (P = 60 -95%), unfired ceramics, SiO 2 -based modified materials, laminated ceramic composites, and ceramic castables.The increased interest in materials based on amorphous silicon oxides stems from three factors:1. The unique set of dielectric, thermophysical, and chemical properties; as regards parameters such as thermal stability, radio transparency over a wide range of temperatures and frequencies, and heat protecting properties, these materials have no analogs, which makes them unmatched in research and technology.2. Ease of fabricability, large reserves of raw materials in many countries over the world, and readily available, simple technological equipment. Practically any established method in ceramic engineering can be used to treat quartz ceramics; the low shrinkage at drying and sintering temperatures (0.5 -2.0%) makes it possible to fabricate large-size components without buckling and strain.3. These materials have much room left for further updating and modifying to obtain products with high reliability and tailored properties.By properly modifying the treatment of raw materials and semi-finished products, molding techniques, and drying regimes, a technology was developed for materials and components with porosity varying from 0 to 90% [3].Properties of ceramic and fibrous inorganic materials based on quartz glass are summarized in Table 1. For ceramic materials, the basic technology is aqueous slip casting in plaster molds followed by sintering, and for fibrous ma...
Results of theoretical and experimental studies of the process of aqueous slip casting of complex-shaped ceramic components using plaster molds are given. A technology for manufacture of complex-shaped homogeneous high-quality preforms from quartz ceramics such as aerial fairing shells is proposed.The casting of aqueous slip into plaster molds is a currently employed technique for shaping thin-walled ceramic components, for example, aerial fairing shells [1,2]. The buildup of a preform on the surface of a complex-profile mold involves two major processes:-capillary suction of the liquid phase of the slip by the plaster mold and movement of slip particles towards the mold and their deposition on the mold surface;-deposition of slip particles on the mold surface under the action of gravity.One of the two processes becomes prevailing depending on the density, viscosity and grain composition of the slip. A judicious trade-off between these parameters is a major concern in developing a technology for shaping preforms. With the former process predominant, a more dense and uniform packing of particles is achieved, and the preform shape exhibits higher strength characteristics.Apart from the capillary suction and gravity forces, a slip particle is subjected to the buoyancy force of liquid phase (static lift) and to the viscous force of the medium. The particle's velocity vector is controlled by the direction and intensity of all the forces involved. With allowance for Stokes' law the equation of motion of a particle towards the curved surface of a mold takes the formwhere m is the mass of the particle; V p is the velocity of motion of the particle towards the preform surface; V f is the speed of water filtration; r is the radius of the particle; h is the viscosity of the medium (the slip); q is the horizontal slope of the tangent to the curved surface of the preform; P g is the gravity force, P g = mg; P a is the buoyancy force, P a = m 0 g; r is the particle density; r 0 is the slip density; m 0 is the slip mass; m = r(4pr 3 /3); m 0 = r 0 (4pr 3 /3).Equation (1) describes the transient motion of a particle from the state of rest to a fully established quasi-stationary motion when the inertial force on the left side of the equation can be neglected. According to [3], one has the solution V V P P r V g r g a p f f = + -+ -6 2 9 2 0 p h q = r r h q cos ( ) cos . (2) Allowing for 2 8 2 0 gr V g ( ) r r h -=(V g is the gravitational deposition velocity of a slip particle), expression (2) can be written asThe particle velocity V p is a major factor controlling the preform buildup rate; by analogy with Eq. (3), the preform buildup rate for a curved surface can be written aswhere h f is the portion of the wall thickness that was built up by capillary filtration of water in the plaster mold; h g is the
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