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

Abstract

Zirconium dioxide based hydration hardening concretes (ZHC) [i] containing aluminatezirconate binders can serve as good materials for making the linings exposed to high-temperatures, in particular, in the 2000-2300 K range, where using corundum is absolutely impossible. 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.The composition of the concrete is as follows:80% filler consisting of electromelted ZrO 2 (the 2-0.5 mm fraction 50% and the minus 0.5 mm fraction 30%) and 20% cement consisting of 6% aluminate binder and 14% BaZrOao The body was set using 3.5-4% water (above 100% charge).A barium-alumina cement (BAC) (that was produced at the Pilot Plant of the Scientific-Research Institute of Cement) was used as the aluminate binder.It contains 80% BaAI=O4; other barium aluminates and impurities, in particular, SiO 2 (2%) and AI203 (5-8%), account for the remaining 20%.Shaped specimens having a cross section measuring 25 x 25 mm in the region of failure (their open porosity amounted to 13-17%) were preheated for 5 h in a furnace at a temperature corresponding (equal) to the temperature of the subsequent testing.Using t...