Determination of the ultimate tensile strength of ceramics up to 2500 K in the environment of combustion gases

Abstract

Determining the strength of high-temperature materials at a temperature exceeding 2000 K is an important problem. In particular, we note that very few studies have been carried out for determining the high-temperature strength of these materials in oxidizing media.We designed and installed a simple device (equipment) for determining the mechanical properties of the materials (in particular, oxide ceramics) including the tensile properties at 1700-2500 K in the environment of combustion gases.The device is fitted with an oxygen-gas burner* and consists of a ceramic channel (Fig~ I) that is sectionally constructed using sliced bricks of zirconia (zirconium dioxide) refractories having a granular structure. The test specimens % are freely accommodated in the channel and their fixing is carried out outside the channel. In view of the fact that the temperature at the ends of the specimen does not exceed 1000~ metallic clamps can be used for gripping. Heating is carried out using the oxygen-gas burner having a variable coefficient of excess oxidant (~ = 0.5-1.5); the maximum consumption of the combustion gases amounts to 2 g/sec.In view of the relatively low ultimate tensile strength of ceramics in the 2000-2500 K range (usually, it does not exceed 1-2 N/mm=), it is quite easy to obtain the required loads (for example, sand or metallic balls can be used). At 1700-2000 K, it is advisable to use more complex attachments (including a tensile testing machine).Using the developed device, we determined the temperature dependence of the ultimate tensile strength Otn s of the dumbbell-shaped specimens (Fig. 2) obtained from a water-cured zirconia concrete (hydration-hardened zirconium dioxide-based concrete) (WZC) containing 80% (weight contents) electromelted ZrO 2 of two fractions and 20% cement produced from a mixture

Tensile strength of a water-setting (hydration-hardening) zirconium dioxide based concrete in the 300?2300 k range

“…At higher temperatures, the measurements were carried out using a high-temperature testing unit [3] in an atmosphere consisting of the products of combustion of propane in oxygen maintaining the coefficient of excess oxidant at 0.9-1.0 and keeping a heating rate of approximately 50 K/min, and a loading rate of 60 N/min. At higher temperatures, the measurements were carried out using a high-temperature testing unit [3] in an atmosphere consisting of the products of combustion of propane in oxygen maintaining the coefficient of excess oxidant at 0.9-1.0 and keeping a heating rate of approximately 50 K/min, and a loading rate of 60 N/min.…”

High-refractory concretes for lining high-temperature units. A study of the high-temperature tensile strength of zirconium dioxide based hydration hardening (water setting) concretes

“…In view of this, it is necessary to study the strength of ZHC at high temperature (in particular, the ultimate tensile strength that characterizes the efficiency of the lining most completely).The aim of this paper was to obtain, for the first time, the data concerning the ultimate tensile strength Otn s of ZHC up to a temperature of 2100 K and to reveal the main factors affecting it.As a rule, a lining is under nonisothermal conditions, i.e., temperature gradients exist across its thickness.Under the operational conditions of gasdynamic installations, the mechanical integrity of the lining is determined mainly by the variation of the pressure of the gaseous atmosphere that leads to the development of destructive forces (fracture), vibration, and weight.For the purpose of rough evaluations, a value of approximately 0.i N/mm 2 can be taken as the permissible ultimate tensile strength oPtn s of the material of the lining.Testing was carried out using tensile specimens whose working portion (gauze length) was maintained under isothermal conditions.In order to obtain a plot depicting the functional relationship Otn s (T) over the maximum possible temperature range, we measured the isothermal ultimate tensile strength of ZHC using a 1231U-I0 industrial universal testing machine (up to 1400~ in air) and a specially designed high-temperature testing unit (from 1400 to 2100 K) [2].The aforementioned special unit is fitted with gas-oxygen burners (in order to attain temperatures up to 2600 K in the atmosphere of combustion gases) and consists of a ceramic channel made from a zirconium dioxide refractory having a granular structure in which test specimens are mounted vertically.The end portions of the specimens remain outside the channel.This arrangement makes it possible to use relatively cold metallic grips.Dumbbell shaped specimens of ZHC were obtained by hand-ramming. Their subsequent setting was carried out in air for a period of not less than 7 days.…”