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Long B.,University of Science and Technology Beijing | Long B.,Almatis Inc. | Xu G.-Y.,University of Science and Technology Beijing | Li Y.,University of Science and Technology Beijing | Buhr A.,Almatis Inc.
International Journal of Minerals, Metallurgy and Materials | Year: 2016

Three different castables based on the Al2O3–MgO–CaO system were prepared as steel-ladle purging plug refractories: corundum- based low-cement castable (C-LCC), corundum-spinel-based low-cement castable (C-S-LCC), and corundum-spinel no-cement castable (C-S-NCC) (hydratable alumina (ρ-Al2O3) bonded). The fracture behavior at room temperature was tested by the method of “wedge-splitting” on samples pre-fired at different temperatures; the specific fracture energy Gf ′ and notched tensile strength σNT were obtained from these tests. In addition, the Young’s modulus E was measured by the method of resonance frequency of damping analysis (RFDA). The thermal stress resistance parameter R′′′′ calculated using the values of Gf ′, σNT, and E was used to evaluate the thermal shock resistance of the materials. According to the microstructure analysis results, the sintering effect and the bonding type of the matrix material were different among these three castables, which explains their different fracture behaviors. © 2016, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.


Zacherl D.,Almatis Inc. | Long B.,Qingdao Almatis | Wang Z.,Wuhan University of Science and Technology | Buhr A.,Almatis Inc.
Proceedings of the Unified International Technical Conference on Refractories, UNITECR 2013 | Year: 2014

CT10SG is a special calcined alumina which has high water retaining property and is ideal to add stickiness to gunning mixes. CT10SG as a new plasticiser was studied in high performance gunning mixes as replacement for conventional plasticizer such as soft clay and silica fume. Matrix slurries and laboratory test bars from the gunning mixes were investigated at Wuhan University of Science and Technology. The matrix study showed that the slurry containing CT10SG had an equivalent rheological behaviour when compared to that with traditional plasticisers. Tabular alumina based gunning mix with CT10SG displayed good consistency and stickiness, high volume stability (low permanent linear change), high hot modulus of rupture and good slag resistance. © 2014 The American Ceramic Society.


Long B.,University of Science and Technology Beijing | Long B.,Almatis Inc. | Xu G.-Y.,University of Science and Technology Beijing | Andreas B.,Almatis Inc.
International Journal of Minerals, Metallurgy and Materials | Year: 2017

Three different castables were prepared as steel-ladle purging-plug refractory materials: corundum-based low-cement castable (C-LCC), corundum–spinel-based low-cement castable (C-S-LCC), and no-cement corundum–spinel castable (C-S-NCC) (hydratable alumina ρ-Al2O3 bonded). The properties of these castables were characterized with regard to water demand/flow ability, cold crushing strength (CCS), cold modulus of rupture (CMoR), permanent linear change (PLC), apparent porosity, and hot modulus of rupture (HMoR). The results show the CCS/CMoR and HMoR of C-LCC and C-S-LCC are greater than those of the castable C-S-NCC. According to the microstructure analysis, the sintering effect and the bonding type of the matrix material differ among the three castables. The calcium hexaluminate (CA6) phase in the matrix of C-LCC enhances the cold and hot mechanical strengths. In the case of C-S-LCC, the CA6 and 2CaO·2MgO·14Al2O3 (C2M2A14) ternary phases generated from the matrix can greatly increase the cold and hot mechanical strengths. In the case of the no-cement castable, sintering becomes difficult, resulting in a lower mechanical strength. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.


Long B.,University of Science and Technology Beijing | Xu G.,University of Science and Technology Beijing | Buhr A.,Almatis Inc. | Jin S.,University of Leoben | Harmuth H.,University of Leoben
Ceramics International | Year: 2017

This paper completes the investigations performed on cement- and no-cement bonded refractory materials for steel ladle purging plugs. In addition to the thermodynamic evaluations and detailed material descriptions given in a previous paper, this paper focuses on the fracture behaviour of the materials. The influence of low and high pre-firing temperatures on the fracture behaviour is investigated. Differences in the microstructure of cement- and hydratable alumina-bonded castables with and without spinel can explain their different mechanical properties and fracture behaviour especially after pre-firing at elevated temperatures. When comparing cement- with no-cement bonded materials for applications in steel ladle purge plugs, both concepts have advantages and disadvantages. The much higher hot modulus of rupture of the cement bonded materials, especially in combination with spinel, is advantageous for the required erosion resistance in this application. With regard to corrosion resistance against the iron oxide-rich slag created during the oxygen lancing of the purging plugs, the calcia-free no-cement bonded materials would be advantageous. The more ductile, less brittle fracture behaviour of the no-cement system even after high temperature pre-firing should provide advantages with respect to the cracking and spalling behaviour of the hot face during use. Based on this investigation it would appear to be worthwhile testing hydratable alumina bonded corundum-spinel materials in industrial applications for steel ladle purging plugs. © 2017 Elsevier Ltd and Techna Group S.r.l.


Braulio M.A.L.,Federal University of São Carlos | Rigaud M.,University of Montréal | Buhr A.,Almatis Inc. | Parr C.,Kerneos Inc. | Pandolfelli V.C.,Federal University of São Carlos
Ceramics International | Year: 2011

Due to their high corrosion resistance to basic slags, either pre-formed or in situ spinel (MgAl2O4) containing refractory castables are nowadays widely used as steel ladle linings. Nevertheless, whereas the pre-formed spinel castables present high volumetric stability and a well-known processing technology, the in situ spinel castables still require further understanding due to the challenges related to magnesia hydration and their expansive behaviour at high temperatures. Therefore, the objective of this paper is to review the knowledge already available for high-alumina spinel-containing castables (preformed and in situ) in order to provide a support for novel technological developments in the area. The main variables considered are the spinel content and grain size, the effect of calcium aluminate cement and hydratable alumina on the general castables' properties, the influence of different alumina and magnesia sources and the silica fume content. Nowadays research subjects, including the use of mineralising compounds, the addition of nano-scaled particles and the evaluation of the effect of expansion under constraint will also be addressed, pointing out alternatives for the design of high-performance alumina-magnesia refractory castables. © 2011 Elsevier Ltd and Techna Group S.r.l.


Rosenberger N.,Almatis Inc. | Compson C.,Almatis Inc. | Atria J.,Almatis Inc.
CFI Ceramic Forum International | Year: 2015

In order to find the best suitable processing route for laboratory scale experiments for alumina powder and binder evaluation a comparative study on granules produced with different techniques was performed. The results are compared to CT 3000 SDP from regular Almatis pro-duction, which achieves unique performance in terms of thermal reactivity and resulting excellent mechanical strength.


Lawrence A.K.,Lehigh University | Kundu A.,Lehigh University | Harmer M.P.,Lehigh University | Compson C.,Almatis Inc. | And 2 more authors.
Journal of the American Ceramic Society | Year: 2015

The concept of grain-boundary complexions has been extended to specialty alumina powders with the goal of deconvoluting the effects of second phase and complexion transitions on microstructure evolution. Two powder compositions with significantly different impurity levels were examined to study the effect of second phase content. The changes in grain size distribution after postsintering annealing for the two compositions were analyzed in order to identify complexion transitions. An analysis technique was developed using probability plots to separate distinct populations of grains of different size regimes. There was evidence of multiple transitions in each material as evidenced by multiple grain size populations. A higher amount of second phase in one powder suppressed the effects of the transitions making the microstructural inhomogeneities less pronounced. © 2015 The American Ceramic Society.


Lawrence A.K.,Lehigh University | Kundu A.,Lehigh University | Harmer M.P.,Lehigh University | Compson C.,Almatis Inc. | And 2 more authors.
Journal of the American Ceramic Society | Year: 2015

The concept of grain-boundary complexions has been extended to specialty alumina powders with the goal of deconvoluting the effects of second phase and complexion transitions on microstructure evolution. Two powder compositions with significantly different impurity levels were examined to study the effect of second phase content. The changes in grain size distribution after postsintering annealing for the two compositions were analyzed in order to identify complexion transitions. An analysis technique was developed using probability plots to separate distinct populations of grains of different size regimes. There was evidence of multiple transitions in each material as evidenced by multiple grain size populations. A higher amount of second phase in one powder suppressed the effects of the transitions making the microstructural inhomogeneities less pronounced. © 2015 The American Ceramic Society.


Frueh T.,Pennsylvania State University | Kupp E.R.,Pennsylvania State University | Compson C.,Almatis Inc. | Atria J.,Almatis Inc. | Messing G.L.,Pennsylvania State University
Journal of the American Ceramic Society | Year: 2016

To determine how grain-boundary composition affects the liquid phase sintering of MgO-free Bayer process aluminas, samples were singly or co-doped with up to 1029 ppm Na2O and 603 ppm SiO2 and heated at 1525°C up to 8 h. Na2O retards densification of samples from the onset of sintering and up to hold times of 30 min at 1525°C compared to the undoped samples, but similar to the as-received, MgO-free Al2O3, Na2O-doped samples sinter to 98% density with average grain sizes of ~3 μm after 8 h. Increasing SiO2 concentration significantly retards densification at all hold times up to 8 h. The estimated viscosities (20-400 Pa·s) of the 0.3 to 1.8 nm thick siliceous grain-boundary films in this study indicate that diffusion greatly depends on the composition of the liquid grain-boundary phase. For low Na2O/SiO2 ratios, densification of Bayer Al2O3 at 1525°C is controlled by diffusion of Al3+ through the grain-boundary liquid, whereas for high Na2O/SiO2 ratios, densification can be governed by either the interface reaction (i.e., dissolution) of Al2O3 or diffusion of Al3+. Increasing Na2O in SiO2-doped samples increases diffusion of Al3+ and Al2O3 solubility in the liquid, and thus densification increases by 1%. Based on these findings, we conclude that Bayer Al2O3 densification can be manipulated by adjusting the Na2O to SiO2 ratio. © 2016 American Ceramic Society.


Long B.,University of Science and Technology Beijing | Andreas B.,Almatis Inc. | Xu G.,University of Science and Technology Beijing
Ceramics International | Year: 2016

The influence of iron oxide in the phase relationships of Al2O3-MgO-CaO and Al2O3-MgO purging plug refractory material has been studied by the thermodynamic analysis tool FactSage. Results showed that the system without CaO to be advantageous on the onset temperature of liquid phase, and on the liquid content at defined chemical composition and temperature. Therefore, CaO negatively influences the iron-rich slag resistance of the purging plug material. Analysis of used purging plugs proved the thermodynamic results. They showed that spinel solid solution and calcium hexaluminate as stable phases were formed in the reaction with iron oxide slag.Corundum-spinel castables with and without calcium aluminate cement were investigated in the laboratory to compare the relevant technical properties. In the cement bonded castable, the curing and drying strength are increased by increasing the cement content. However high cement addition requires higher water demand, which results in higher open porosity and a lower hot modulus of rupture (HMoR). In the CaO-free, no-cement castable with hydratable alumina binder, the water demand is slightly higher when compared to the ultra-low cement castable. However, the curing and drying strength are still slightly higher for the no-cement castable. As there is no significant difference in HMoR with various hydratable alumina binder additions, low dosage of such binder in the range of two to four percent is normally recommended to avoid excessive water addition. Cement bonded castables (with CaO) show some advantages to the no-cement castable (non-CaO) regarding HMoR, however the no-cement castable could have advantages regarding the iron-rich slag resistance and thermal shock resistance. © 2016 Elsevier Ltd and Techna Group S.r.l.

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