Crystallization of fusion cast ceramics and glass-ceramics

The most important single factor responsible for the largely different microstructure and properties of glass-ceramics as compared with fusion cast ceramics is the viscosity conditions during crystallization. Whereas cast ceramics crystallize from liquids almost always in a very fluid condition, i.e., viscosity less than a 10³ poise, the controlled nucleation and crystallization of glass normally takes place at viscosities greater than 10⁸ poise, usually between 10⁹ and 10¹² poise.Crystallization of ceramic materials from a melt is a time-temperature-pressure dependent process. Factors such as high volume expansion, crystal orientation, solid solution and exsolution control the resulting microstructure and properties of these brittle materials. Non-equilibrium conditions play a major role in affecting the microstructure. The importance of additions of one or more components to each of the following basic ceramic systems will be discussed: (1) ZrO₂-Al₂O₃-SiO₂, (2) Al₂O₃, (3) MgO, (4) carbides, and (5) borides.Glass ceramics are crystalline materials formed through controlled devitrification of glass. The sequence of nucleation, crystal growth, and phase transformation occurring during the thermal treatment of such glasses can be controlled to produce unique microstructures and properties. This is reviewed for several basic composition areas: (1) SiO₂-Al₂O₃-Li₂O (spodumene), (2) SiO₂-Al₂O₃-MgO (cordierite), (3) SiO₂-Al₂O₃-MgO-K₂O-F (mica), and (4) SiO₂-Al₂O₃-CaO-MgO-Fe₂O₃ (basalt).     

Thermoanalytical characteristics of powders in dental cast investment

The present study examined the thermal properties of phosphate-bonded investments, a gypsum-bonded investment and an experimental investment powder when the basic powders were heated to high temperatures by simultaneous differential thermal analysis (DTA) and thermogravimetry (TG). The phosphate-bonded investments showed values of about 59 kcal mol^–1 (247 kJ mol^–1) (thermal decomposition of NH₄H₂PO₄) and about 11 kcal mol^–1 (46 kJ mol^–1) (formation of NH₄MgPO₄). Thermal reactions occurred clearly on the DTA-TG curves for the investment powders, using powders of NH₄H₂PO₄, and MgO with NH₄H₂PO₄/MgO = 1 as main components in the investment.     

Thermophysical characteristics of fusion thermal tracers

The results of an investigation into the thermophysical characteristics of fusion thermal tracers used for determining the temperature fields of heated surfaces are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 5, pp. 802–803, November, 1974.     

Thermal expansion characteristics of cast Cu based metal matrix composites

Like any other metal/alloy, copper and its alloys also soften at elevated temperatures. Reinforcing with ceramic or carbon fibres is one of the suggested solutions to overcome this. Very limited literature is available on Cu based metal matrix composites (MMCs); none of these pertain to liquid phase fabrication. Hence, a systematic investigation was carried out on MMCs based on copper, with alumino-silicate fibres and carbon fibres as reinforcements. The MMCs thus produced exhibit a uniform distribution of reinforcement in the matrix. Coefficient of thermal expansion (CTE) values are lower than that of pure copper.     

Ethyl-silicate-bonded refractories

The manufacture of Ethyl Silicate from Silicon Tetrachloride and Ethanol is described. Difficulties with control of pollution and plant corrosion make an alternative Ethyl Silicate manufacture by the direct reaction between silicon and Ethanol very attractive. The chemistry of Ethyl Silicate bonding of refractory materials is summarised with reference to reaction mechanisms and the principal uses of Ethyl-Silicate-bonded refractories are outlined. Nozzles of various sizes and types, also well-blocks, are used in sliding-gate systems for the casting of steel. A new Orifice Ring with container has been developed for use in the Glass industry. Some other types of Ethyl-silicate-bonded refractories include Burner Blocks, Furnace parts, Crucibles and Insulation components.     

Study on hardness and microstructural characteristics of sand cast Al-Si-Cu alloys

In this study, the influence of Cu content on the hardness and microstructural characteristics of sand cast Al-Si-Cu alloys have been investigated. Al-Si alloys with 2% and 5% Cu have been utilized for this purpose. Solidification of Al-Si-Cu alloys have been realized by melting in a gas furnace with a crucible and casting in green sand molds at 690°C. The solution treatment has been performed at 500°C for 7 h and then specimens were quenched in water. The samples have been aged at 190°C for 15 h to observe the effect of aging on mechanical properties.     

Emissivity of aluminosilicate refractories

Experimental data was obtained on the dependence of the emissivity of refractories on temperature and chemical composition.Translated from Imzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 3, pp. 406–411, September, 1987.     

Hydrodynamic characteristics of the liquid-metal blanket of fusion reactors

A theoretical method of determining the hydraulic resistance of liquid-metal blankets of fusion reactors is presented along with numerical results.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 2, pp. 229–235, February, 1990.     

Ageing characteristics of cast Zn-Al based alloy (ZnAl7Cu3)

Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich phase and four phase transformation, + T + , were detected during ageing at 150°C. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich and phases.     

Surface characteristics of tubercle mass and graphitic residue in cast iron water pipelines

Graphitic residues from cast iron water mains were characterized by surface area measurements. The surface areas were about 4–5 times higher than those determined for reference graphite Samples. Their capacity to retain water equalled that of activated charcoal. Adsorption properties were examined by using methylene blue and rhodamine B. Under the conditions employed, methylene blue behaved as a cationic species whereas rhodamine B seemed to have little charge effects. Ferric iron was found to adsorb on graphitic residues in a pH-dependent manner. Surface characteristics of tubercle material that overlyes graphitized areas in cast iron pipes were examined by scanning electron microscopy. A high degree of particle aggregation was observed and the size distribution varied with the crystallinity of the tubercle components.     

Structure and tribological characteristics of a cast heterogeneous alloy before and after laser treatment

The positive influence of laser treatment on the formation of the structure of the surface layer of a Fe– Cr–Cu–C–Ti cast alloy and its tribological characteristics under conditions of boundary lubrication is shown.