PSI - Issue 42

Shahin Takht Firouzeh et al. / Procedia Structural Integrity 42 (2022) 1069–1073 Shahin Takht Firouzeh / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction

Ceramic filter materials made of carbon-bonded alumina (Al 2 O 3 -C) are implemented to reduce the inorganic and non-metallic inclusions from the metal melt. A cleaning e ffi ciency of more than 95% at the metal matrix was reported in Emmel and Aneziris (2012). More environmentally friendly approaches using Lactose-Tannin (L-T) based systems have recently been investigated, see Wu et al. (2022). Due to the high importance of mechanical properties at service temperatures, a high temperature study of Al 2 O 3 -C was conducted using ball-on-three-ball (B3B) tests, cf. Zielke et al. (2016). Moreover, mechanical properties Al 2 O 3 -C were investigated in various studies, e.g. Zielke et al. (2017, 2020). With the development of the new lactose-tannin based filter materials in the Collaborative Research Center(CRC) 920, the material behavior at high temperatures is yet to be studied. The application of a miniaturized Brazilian Disc Test (BDT) to Al 2 O 3 -C at room temperature was studied in Takht Firouzeh et al. (2022). Elastic properties of the bulk material were identified using a digital image correlation (DIC) technique in combination with numerical meth ods. To study the high temperature filter material behavior using BDT, the selected test and specimen configuration was applied on Al 2 O 3 -C and two lactose-tannin based materials. The test took place at 1200 ◦ C. Due to the known crack path on ring-shaped specimens, simulation of the specimen failure using cohesive zone model was possible. Cohesive material parameters and the resulting fracture toughness was studied by fitting the simulation outputs to the experimental data. Al 2 O 3 -C is mainly used for the filtration of steel melts due to their high shock resistance. The fine grained mi crostructure of Al 2 O 3 -C consists of 99.8%-pure alumina (Martoxid MR 70, Martinswerk, Germany, d 90 ≤ 3 . 0 µ m) and various carbon sources given as modified coal tar pitch powder (Carbores ® P, Ru¨ tgers, Germany, d 90 ≤ 0 . 2 mm), fine natural graphite (AF 96 / 97, Graphit Kopfmu¨hl, Germany, 96.7wt% carbon, 99.8wt% ≤ 40 µ m), and carbon black powder (Luvomaxx N-911, Lehmann & Voss & Co., Germany, ≥ 99.0 wt.% carbon, > 0.01 wt.% ash content, primary particle size of 200 − 500 nm). For the lactose-tannin based slurry, Carbores ® P is replaced with the white lactose powder (Mivolis Milchzucker, DM-Markt, Germany) and the orange tannin powder (Quebracho-Extrakt ATO, Otto Dille, Germany). The di ff erence between two lactose-tannin based slurries is their lactose to tannin ratio of 5:1 and 3:1. The chemical composition of the slurry for Al 2 O 3 -C, Al 2 O 3 -L-T-5:1 and Al 2 O 3 -L-T-3:1 is given in Table 1. The obtained slurry from these components and deioinized water is poured to the specimen blocks. The heating rate for coking procedure of Al 2 O 3 -C is 0 . 8 ◦ Cmin − 1 until T max = 800 ◦ C, then 180 min of dwell time at T max followed to a free cooling. For L-T specimens coking temperature was T max = 1000 ◦ C with a rate of 0 . 8 ◦ Cmin − 1 and 30 min of dwell time for every 100 ◦ C followed by a 3 hour dwelling time at the T max before it was cooled to room temperature. Carbores ® P for Al 2 O 3 -C, and lactose and tannin for L-T binder systems are the binding phase which enables alumina to get bonded in the carbon matrix. After some evaporation from the mixture the materials are obtained with approx imately 40% porosity. Cylindrical pieces are drilled out of the specimen block using a diamond hollow drilling bit. The final diameter after the drilling process is 9 . 8 mm. The specimens are then cut to their final length of 6 . 0 mm. The diameters of the holes for the specimens are 1 . 5 mm, which are obtained through drilling. The schematic view of the test specimens is given in Figure 1. 2. Investigated Material and Specimen Preparation

Fig. 1. Geometry of the BDT specimen and view onto the specimens before and after the failure. The curved cracks on the right hand side figure are secondary cracks forming after the vertical crack.