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was different. For the cement bonded mix, the wet out time was around 40 s and wet mixing time a total of 4 min. While for the Alphabond 300 mix, the wet out time was 2 min, resulting in a longer wet mixing time of a total of 6 min. Longer mixing time for the hydratable alumina containing mix is important for both the laboratory test and in practical application. Insufficient mixing may, in practice, cause overdosing of water, which will significantly deteriorate the castable. In industrial applications, 2-4 % of Alphabond 300 is recommended for such mixes to avoid a too high water demand with higher Alphabond 300 contents.


All castables were adjusted by appropriate water addition to achieve a vibration flow value of around 200 mm. This Figure is that which is typically required for proper installation. Mixes were casted into molds 40x40x160 mm for the testing of general physical properties, and 100x100x75 mm for the wedge splitting test. Smaller molds of 25x25x125 mm were used for casting sample bars for HMoR testing [9]


. After curing and drying the sample


bars were then fired at different temperatures with a holding time of 5 h. The cold modulus of rupture (CMoR), cold crushing strength (CCS), bulk density, open porosity and permanent linear change were then tested.


Castable recipe


Tabular alumina T60/T64 3 - 6 mm 1 - 3 mm


0.5 - 1 mm


0.2 – 0.6 mm 0 – 0.5 mm 0 – 0.2 mm 0 – 0.02 mm


Spinel (AR 78)


0.5 - 1 mm 0 – 0.5 mm


0 - 0.045 mm


Reactive Alumina CL 370


Binder


CA-14 M cement Alphabond300


Additives ADS 3/ADW 1 Water demand 1 3.9 1 4.1 1 4.2 1 4.7


Table 1: Composition of cement and hydratable alumina Alphabond 300 bonded castables (additives on top of 100% sum)


Microstructures of the samples were examined using a scanning electron microscope (FEI-SIRION, operated at 5 kV) equipped with an energy- dispersive X-ray spectrometer. The mineral phases were identified by X-ray diffraction (XRD; Rigaku D/DMAX-RB) using Cu Kα


radiation (40 kV, 20 mA,


λ = 0.15406 nm) in the 2θ angular range from 10 to 100°and with a scan speed of 2°/min.


For purging plug refractory materials in general, the chemical composition will be very close to the angle of corundum (α-Al2


O3 diagram Al2 O3 -MgO-CaO [15] low cement castable), MgO (10~20% of spinel (MgO.


due to the low amounts of CaO (low or ultra- Al2


O3, 6Al2 A8 ) in the ternary phase MA) equals (CA6


to 2~5% MgO), and the high amount of corundum. In thermodynamic equilibrium, the phases of the purging plug at a high service temperature in the range of 1600 to 1700°C will be corundum, spinel, and CaO. ), with the peritectic melting point at 1850°C [16,17]


O3 Iyi et al. [19] reported the two ternary compounds C2 .


. Göbbels et al. [18] M2


A14 and CM2


and as


metastable phases at high temperature in the ternary system. The existence of metastable ternary compounds was confirmed by the studies of De Aza et al. [17]


mol [20]


Figure 2: (a) Schematic of the wedge-splitting test and (b) a typical load– displacement curve [11]


July 2018 Issue


After each heat in the steel ladle, some residual liquid steel will remain on the bottom until the ladle is tilted. This steel can freeze at the top of the purging plug, or may infiltrate into the slits of the purging plug. Oxygen lancing is a conventional way to melt and blow away the residual steel on top of the purging plug and to open the slits of the purging plug. In the oxygen lancing process, the hot iron will react with oxygen to form iron oxide in a strongly exothermic reaction, e.g. for FeO ∆f . FeOx


H0 is -272.0 kJ/ will react with refractory at very high temperatures. Therefore


it is necessary to study the chemical reaction between the iron oxide and the purging plug material.


ENGINEER THE REFRACTORIES 17 2 5 5 4


3. Thermodynamic analysis by FactSage 3.1 Overview of the refractory and slag system


7


10 9


13 7


10 9


13 13 7


10 9


13


C2S26 C5S26 C5S0 A4S26 %


%


25 18 6


10


25 18 6


7


15 7


%


20 20 10 10


%


25 18 6


8


Technical Paper


The wedge splitting test (Figure 2) was conducted at Montanuniversitaet Leoben, and three samples of each material were used in order to prove repeatability. The applied wedge splitting test is suitable for determining the specific fracture energy of refractories by specimens with sufficiently large dimensions [10,11]


G′f and nominal notch tensile strength σNT Eqs (1) and (2).


. After the wedge splitting test, the specific fracture energy can be obtained according to


The Young’s moduli of the samples were measured by resonance frequency of damping analysis (RFDA, IMCE in Belgium) at Montanuniversitaet Leoben. The samples were cast into bars of 25 mm × 25 mm × 125 mm. After curing at 20°C for 24 h and drying at 110°C for 24 h, all samples were pre-fired at 350°C for 5 h. Young’s moduli of the samples were measured after pre-firing at 350°C, 1250° and 1500°C respectively.


The equation used to calculate the characteristic length (lch) is shown in Eq.(3), where G′f modulus, and σNT


represents the specific fracture energy, E is Young’s is the nominal notch tensile strength [10,11]


the double area of the projection of the fracture surface, R′′′′ equals lch In the present paper, lch


investigated materials. σNT = Fmax (1 + 6γ/h)/bh


lch = G′fE/σ2 R′′′′ = γE/σ2


NT NT


(1) (2)


(3) (4)


For thermal shock resistance testing, quenching in water was carried out according to the Chinese national standard YB/T 376.1-1995[14]


. Samples


were pre-fired at 400 and 1650°C respectively with a holding time of 5 h. Samples were held at 1100°C for 20 min and then immersed into running water for 3 min. The above process was considered as one cycle. Residual CMoR was tested after one and three cycles, and compared to the starting CMoR.


. Thermal shock


resistance parameter R′′′′ can be calculated according to Eq.(4), where γ is the specific surface fracture energy [11,12,13]


. Since γ is the energy relative to /2.


is used to compare the thermal shock resistance of


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