Results of a statistical analysis of the production process of large-sized components from quartz ceramics are presented. The technologies examined are characterized by a long-term stability which makes it possible to reliably control the production process and reach the required level of physicomechanical properties.Progress in advanced sectors of industry, specifically space technology and aircraft engineering, implies the use of materials with superior performance characteristics. Many structural elements for supersonic aircraft are fabricated from refractory, erosion and heat-resistant materials [1]. The typical elements are the leading edges, nose cone ( Fig. 1), nozzles and nozzle guides of rocket engines, etc. High temperature and aerodynamic pressure are factors that may do damage (burn-out, surface fusion, vaporization, and ablation of the material) to aircraft structural elements.Materials that combine specific properties (such as low heat conductivity, high thermal stability, mechanical strength, erosion resistance, ability to transform from the solid or high-viscosity state to a gaseous state, etc.) are capable of meeting stringent performance requirements placed on aircraft structures. No materials that display these useful properties and good fabricability while retaining the original shape and size have been reported in the literature. At present, glass-plastics, sitalls, heat-resisting commercial glasses, and ceramics have found use as heat-protecting structural materials for aerial fairings [2 -4]. Good candidates for this purpose are materials based on quartz glass [5,6]; in particular, they have a nearly 30-years-long history in the production of fairings for hypersonic missiles [7]. However, because of the high viscosity and rather high volatility of silica at temperatures above 2000°C (over 10 3 Pa × sec), the manufacture of engineering components, especially of large size and complex shape, meets with problems [8]. To remedy the situation, a ceramic technology has been developed which made it possible to fabricate components of virtually any size and shape. Here a range of technological factors should be complied with such as the high purity of raw materials, molding technique, granular composition of the semi-finished product, temperature regime, etc.Our goal in this study was to consider factors of prime importance for the technology of large-sized (of base diameter up to 400 mm and height up to 1200 mm) complexshaped fairings made from glass ceramics. Prior to use, the quartz glass was thoroughly treated for purity [10], using in the process a grinding technology (grinding bodies, the lining of the ball mill, water) equally carefully controlled for cleanliness. Generally, a quartz ceramic technology for serial production of fairings should include (i) proper conditioning of raw materials, grinding bodies, and the lining of the ball mill; (ii) grinding of the precursor material; (iii) molding of preforms; (iv) calcination of preforms to meet a set of required properties; (v) machining of t...
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...
The kinetics of thermal degradation of a polyorganosiloxane sealant was studied by the thermogravimetric analysis (TGA) method at three constant heating rates (2, 5, and 20 deg/min). An investigation was also made of the change in shear strength of adhesive joints in the course of heat ageing at temperatures ranging from 250 to 340°C. The data obtained were processed by the non-linear regression method. The process of thermal degradation proceeds in two stages. The first stage has an activation energy of about 140 kJ/mol and is accompanied with increase in the strength of the adhesive layer. The second stage with a higher activation energy (roughly 230 kJ/mol) causes a sharp fall in strength of the adhesive layer. A possible mechanism of the thermal degradation process is discussed.
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