Leetsdale, United States
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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.


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.


Compson C.,Almatis Inc. | Rosenberger N.,Almatis Inc. | Spreij M.,Almatis B.V.
CFI Ceramic Forum International | Year: 2013

The ceramics industry encompasses a wide variety of applications, including advanced ceramics, technical ceramics, honeycomb ceramics, spark plugs, high voltage insulators, wear parts and many more. Calcined alumina is a commonly used raw material in all of these ceramic applications due to its robust mechanical, electrical, thermal and chemical properties. These properties are highly dependent on the physical and chemical characteristics of the alumina itself. Therefore, the focus of this research was to evaluate the role of chemical characteristics on the physical and mechanical properties of four commercially available calcined reactive aluminas. Specifically, this work aims to quantify the effect of the trace impurities SiO2 and Na 20, on alumina shrinkage, shrinkage rate, sintered density and flexural strength. © Duravit AG.


Buhr A.,Almatis Inc. | Schnabel M.,Almatis Inc. | Exenberger R.,Voestalpine AG | Rampitsch C.,Voestalpine AG
Proceedings UNITECR 2011 Congress: 12th Biennial Worldwide Conference on Refractories - Refractories-Technology to Sustain the Global Environment | Year: 2011

The paper discusses the difference in the formulation concepts of alumina-spinel (spinel containing) and alumina-magnesia (spinel forming) castables and the influence on their physical properties. The individual property profile will be discussed with respect to the requirements of refractory lining materials for the different zones of a steel ladle.


Schnabel M.,Almatis Inc. | Buhr A.,Almatis Inc. | Kockegey-Lorenz R.,Almatis Inc. | Schmidtmeier D.,Almatis Inc. | Dutton J.,Stourbridge
InterCeram: International Ceramic Review | Year: 2014

The use of monolithic refractories has spread throughout various industries over the past few decades. Today it is common practice to install monolithics in heavy wear areas. In the past, only refractory bricks were used. Unlike bricks, unshaped products require sintering during operational use to obtain their final properties. Applications outside the iron and steel industry are often referred to as "industrial applications". Industrial applications also demand improved castable properties such as better chemical stability, mechanical strength and abrasion resistance in intermediate temperature ranges. The service temperatures in industrial applications are often below 1200°C, so castables do not attain sufficient energy for strong sintering reactions. Matrix properties are important for refractory castables. They determine not only workability and strength, but also performance within an application. By optimising the overall particle size distribution of fine and superfine materials including the binder, better workability can be achieved. In addition, the physical properties of castables can be improved, especially in intermediate temperature ranges. Calcined and reactive aluminas and dispersing additives can also contribute significantly to the improvement of matrix performance with respect to water demand, setting control and strength development.


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.


Zacherl D.,Almatis Inc. | Mcconnell R.,Almatis Inc. | Buhr A.,Almatis Inc. | Schmidtmeier D.,Almatis Inc.
TMS Annual Meeting | Year: 2010

Refractory castables in the aluminum industry as well as chemical and petrochemical industries typically see much lower temperatures than in the steel industry. The maximum temperature is very often in the range of 800 - 1200 °C. Nevertheless these applications can also be very demanding regarding mechanical strength, abrasion resistance, and chemical stability. Mechanical strength of refractory linings is of particular interest at the intermediate temperatures, which do not provide sufficient energy for strong sintering reactions. This paper discusses raw material concepts for high purity silica-free castables for demanding aluminum or petrochemical applications. Bonite, a new dense calcium hexaluminate (CA6) refractory aggregate is introduced for low wettability, high temperature stability and low thermal conductivity of aluminum refractories.


Zacherl D.,Almatis Inc. | Kockegey-Lorenz R.,Almatis Inc. | Buhr A.,Almatis Inc.
TMS Annual Meeting | Year: 2010

The microporous calcium hexaluminate insulating material SLA-92 has been introduced as an alternative to refractory ceramic fiber and other insulating refractory materials. Key properties associated with this product include: high chemical purity, long term high temperature stability up to 1500 °C, low thermal conductivity up to 1500 °C, and high thermal shock resistance. The properties of the new material and various applications in the steel and ceramic industries have been reported in previous papers. The current paper summarizes the industrial application experiences with innovative refractories based on SLA- 92 and discusses potential new applications in various manufacturing as well as energy- related industries.

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