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...
The progress of high-temperature technology depends on the development of new materials working at a temperature exceeding 2300 K and requires a systematic study of their properties. Concrete linings are highly effective in the units subjected to thermal stresses and in the gas-dynamic channels (in particular, in the units undergoing thermal shocks and requiring a change in the regime) and, also, in the thermal units incorporating large volumes of intricate linings. The concretes based on aluminum and magnesium oxides are the most widely used high-temperature materials. However, their working temperatures are significantly lower and amount to 1900-2000 K. Under the service conditions involving temperatures close to 2300 K, zirconium dioxide forms the most promising material.This paper deals with a study of the production technology and the properties of a zirconium dioxide based concrete similar to that developed earlier [i, 2]. It incorporates a hydration-hardening (water-setting) binder containing barium aluminate and zirconate. The 2.5-0.5 man fraction (PTsI-2) and the minus 0.5 ran fraction (PTsI-0.5) of the electromelted ZrO 2 that was stabilized with 6% (mole fraction) Y203 (TU 14-8-530-8) were used as the fillers,The barium aluminate-zirconate cement (the binder) [3] was synthesized in one step (simultaneous synthesis of barium aluminate and zirconate was realized by carrying out singlestage firing at 1970 K at the Khar'kovsk Institute of Civil Engineers) and separately (the synthesis of barium aluminate BaAI20 ~ and barium zirconate BaZrO~ was carried out at 1720 and 2000 K, respectively, at the Institute of High-Temperatures). Table 1 shows some of the properties of such binders contain&ng 30% ~ BaAIuO~ and 70% BaZrO 3.The obtained binders are fast-setting and fast-hardening. The setting durations ranging from 50 min up to 1.5 h make it possible to carry out the necessary technological (finishing) operations. The fairly rapid (within 3-7 days) increase of strength permits one to obtain products and specimens attaining satisfactory strength levels within short periods.When developing the ZrO 2 based concrete, we studied the effect of the quantity of the cement consisting of 30% BaAI20 ~ and 70% BaZrO 3 on its strength, density, and porosity. Table 2 gives the composition of the experimental concrete specimens and Fig. 1 shows the variation of their properties.Increasing the cement content of the concrete from 5 up to 20% improves its ultimate compressive strength and apparent density anddecreases its open porosity. Subsequent increase of the cement content up to 25% does not lead to a significant strength gain. It is known that increasing the quantity of cement beyond the required level adversely affects the refractoriness and the strength characteristics of the concretes during their service at high temperatures and, in view of this, subsequent studies were carried out on the No. 4 system.We studied the effect of the content of barium aluminate (from 20 up to 40%) in the cement on the ultimate compressiv...
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