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Technical Paper 

Reference : TP-GB-RE-LAF-096 

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New Spinel Containing Calcium Aluminate Cement 

for Corrosion Resistant Castables 

C. Wöhrmeyer, C. Parr, H. Fryda, J.M. Auvray, B. Touzo, S. Guichard 

Kerneos SA, Paris, France 

Presented at the Unitecr Conference, Kyoto, Japan, 2011 

Kerneos 

8, Rue des Graviers - 92521 Neuilly sur Seine Cedex, France 

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ABSTRACT 

Changing the microstructure of ladle castables to increase their service life is the target of this 

investigation. To achieve this, a novel Calcium Magnesium Aluminate cement has been developed. 

This new binder brings microcrystalline spinel phases into regions of the microstructure which are 

normally occupied by calcium aluminate phases only. The basis of this new calcium magnesium 

aluminate cement is a novel multiphase clinker with a microstructure of calcium aluminate phases 

embedded in a matrix of microcrystalline magnesium aluminate spinel crystals. The investigation of 

this novel calcium magnesium aluminate as a binder in different types of ladle castables has shown that 

it significantly improves the corrosion and penetration resistance. Both alumina-spinel and aluminamagnesia 

castables resist a large range of ladle slag compositions much better when they contain this 

new calcium magnesium aluminate. 

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1 Introduction 

Castable developments for steel ladles during the 

last three decades have led mainly to aluminaspinel 

and alumina-magnesia systems [1-3] . Also, 

hybrid materials which combine both systems 

have been developed in recent years [4] . It was 

found, for example by Kantani and Imaiida [5] , that 

the best compromise between slag penetration 

and corrosion resistance can be achieved when 

the castable contains about 20-40% magnesium 

aluminate spinel after firing. Furthermore, it 

was discovered that the penetration resistance 

increases when the spinel size was reduced [6] . 

Very fine spinel can be created when magnesia 

is added to the castable and reacts during firing 

with the alumina filler to form spinel. However, 

the magnesia addition often leads to negative 

side effects, for example, problems during dryout 

due to the magnesia hydration and high 

volume increase as a consequence of the spinel 

formation. To limit the expansion to an acceptable 

level, small amounts of silica are often added 

to the dry-mix which creates a small amount of 

liquid phase during firing. That counteracts the 

expansion caused by the spinel formation [3,7] . But 

the silica addition has the negative side effect 

that it significantly reduces the castable strength 

at the ladle service temperature [8] . 

Development work of Falaschi et al. [9] has 

led to a patented method to produce and use 

calcium magnesium aluminate (CMA) as a 

binder in ladle castables. This new method 

opens an economic way to produce microcrystalline 

spinel simultaneously together with 

calcium aluminate inside the same clinker on an 

industrial scale. This can be achieved below the 

sintering temperature of pure spinel and with 

crystal sizes as small as spinel that is generated 

in-situ inside the matrix of an alumina-magnesia 

castable. The hydraulic properties of this new 

cement are described by Assis et al. [10] . The 

impact of this new binder on the service life of 

model ladle castables is the objective of this 

present investigation. 

CA 

CA2 

CA 

CAC grain 

 

CA2 

MA 

MA 

MA 

MA 

CA 

MA 

CA 

CMA grain 

Fig. 1 : Microstructure model of a CAC and a 

CMA grain (medium grain diameter ca. 15 µm). 

2 Experimental Procedure 

2.1 Materials tested 

This study specifically focuses on the wear 

resistance of alumina-spinel and of aluminamagnesia 

ladle castables and their properties 

at high temperatures. Both systems have been 

formulated with pure 70% Al 2 

O 3 

containing 

calcium aluminate cement (CAC) as reference 

and with the new calcium magnesium aluminate 

cement (CMA). In contrast to CAC, the CMA 

consists mainly of microcrystalline magnesium 

aluminate spinel in a multi-component clinker 

(Fig. 1). Besides the spinel, the hydraulic phases 

Calcium mono-Aluminate (CA) and Calcium di- 

Aluminate (CA2) are present and only traces of 

Gehlenite (C2AS). Both cements contain 70% 

Al 2 

O 3 

. The CAC contains 30% CaO, while the 

CMA contains 20% MgO and 10% CaO, only 

(Tab. 1). 

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Both binders have been ground to a specific 

surface area of approx. 4000 cm 2 /g (Blaine) 

with a median grain size d50 for both cements 

of about 15 µm. 

Model castables as shown in Tab. 2 have 

been used to carry out this investigation. Two 

different types of model castables have been 

selected. Castables MA1 and MA2 use prereacted 

sintered spinel. Castables M1 and M2 

contain free sintered MgO (Periclase) which 

reacts to form spinel in-situ during castable 

firing. Castables MA1 and M1 use CAC as the 

binder while MA2 and M2 apply the new CMA 

binder. The amount of binder has been chosen 

in a way that the overall CaO content of all 4 

castables amounts to 1.7%, thus all 4 castables 

are Low Cement Castables (LCC). The spinel 

content after firing is in all cases around 23%. A 

polycarboxylate ether (PCE) has been chosen 

to efficiently deflocculate the castables at a 

very low amount of mixing water. The amount 

of water and PCE has been adjusted in order to 

achieve the same initial fluidity for all 4 recipes. 

Table 2 : Alumina-spinel (MA) and aluminamagnesia 

(M) model castables with CAC and 

with CMA cement. 

Castable MA1 MA2 M1 M2 

Binder system CAC CMA CAC CMA 

Tabular Alumina 0-6 mm 60 61 75.5 70 

Reactive Alumina 11 11 11 8 

Sintered Spinel 0-1 mm 13 10 

Sintered Spinel



Page : 5/9 

2.2 Experimental apparatus and method 

Chemistry and mineralogy have been 

determined by using the XRF and the XRD- 

Rietveld methods. The permanent linear 

change has been measured after firing samples 

for 3h at the indicated test temperature. Hot 

modulus of rupture has been determined 

according to European standard EN 993-7. 

Dried samples have been heated up to the 

test temperature with 5 K/min and have been 

kept 30 min at test temperature prior to the 

hot modulus measurement. Further thermophysical 

properties have been studied using 

110°C dried cylindrical samples in the test 

furnace as specified in EN 993-8. Unlike in the 

Refractoriness under Load measurement, the 

samples have been heated up with a load of 

only 0.05 MPa up to 1550°C to measure the 

thermal expansion. At 1550°C the samples 

have been kept for 1h before being cooled down 

to 1000°C. Then, at 1000°C, a load of 0.2 MPa 

has been applied and the samples heated up 

again to study the refractoriness under load. 

The corrosion and penetration resistance 

against different slags was tested in a laboratory 

rotary kiln according to ASTM C874-99. The 

test specimens were prepared using a bigger 

mixer then those for the physical properties. 

The higher mixing energy in that mixer allowed 

a further reduction of water. For castables MA1 

and MA2 3.9% water and for M1 and M2 4.0% 

water was sufficient. The vibrated samples were 

then cured for 24h at 20°C, dried at 110°C, and 

then pre-fired for 5h at 1550°C. 

The specimens were installed in the laboratory 

rotary kiln where they were heated up to 1550°C 

again and kept at that temperature for 30 minutes 

prior to the first addition of 900g of slag. 1.7kg/h 

of fresh slag was introduced into the kiln during 

the following 5h at 1550°C. The furnace rotated 

at a constant speed of 2½ rpm. The furnace 

was tilted 3º axially towards an oxy-acetylene 

flame burner at the lower end of the kiln. The 

slag pellets were charged into the upper end 

of the tilted rotary kiln. This way, the molten 

slag washed over the lining, finally dripping off 

at the lower end of the furnace. Two different 

slags with compositions as shown in Tab.3 were 

used. The diameters of the specimens before 

and after the test were measured to quantify 

the degree of wear. Corrosion tests were also 

conducted in a laboratory induction furnace. 

The specimens of the test castables lined the 

wall of the furnace which was charged with 

steel and covered with the slags, as shown in 

Tab.3. The test temperature was 1600°C. The 

steel contained 0.08% C, 1.9% Si, 0.3% Mn, 

0.01% S, and 0.02% P. The wear was quantified 

by determining the ratio between the original 

cross sectional area of the specimens and the 

remaining cross sectional area after the test. The 

areas were measured using an image analyzing 

software. Furthermore, SEM techniques were 

used to study the microstructure of the castables 

and to quantify the penetration depth of slag. 

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Table 3 : Slag compositions (Slag B: BOFslag, 

Slag A: Al-killed steel slag). 

Al 2 

O 3 

SiO 2 

FeO MnO CaO MgO 

Slag B 2 15 19 6 53 5 

Slag A 30 5 0.8 0.2 57 7 

3 Results and discussion 

3.1 Thermo-physical castable properties 

The difference between the castables with preformed 

spinel (MA1, MA2) and those with in-situ 

spinel formation (M1, M2) can easily be seen 

in Fig.2. While both MA1 and MA2 keep high 

volume stability, those with free MgO (namely 

M1 & M2) show a significant permanent linear 

change after firing at 1550°C due to the insitu 

spinel formation. However, mix M2, which 

contains less free MgO than M1, shows lower 

expansion. 

Permant Linerar Change 

(%) 

MA1 (CAC) MA2 (CMA) M1 (CAC) M2 (CMA) 

2,0 

1,5 

1,0 

0,5 

0,0 

-0,5 

800 1200 1350 1550 

Temperature (°C) 

is applied on the sample during the first heatup 

and during 1h soaking at 1550°C followed 

by cooling to 1000°C. After this pre-firing 

procedure, the application of a load of 0.2 MPa 

results in an excellent refractoriness under load 

with a T 2 

of 1680°C for the CMA containing M2. 

While the silica free castables MA1 and MA2 

show very high hot modulus of rupture (HMOR), 

the values are quite low in the case of M1 and 

M2 at 1350°C and 1550°C respectively (Fig. 4) 

due to the silica content. However, the lower 

permanent expansion of M2 and the presence 

of microcrystalline spinel in CMA leave space 

for further recipe optimization with respect to 

silica and periclase content to optimize this 

formulations’ hot properties. 

3.2 Castable microstructures 

SEM micrographs of polished matrix samples 

fired at 1550°C are shown in Fig. 5. Matrix 

samples are derived from the castable 

formulations given in Table 2 after the removal 

of any aggregate coarser than 300 µm. 

The pores in the CAC containing mixes are 

significantly bigger than the pores in the 

CMA containing mixes. Furthermore, the 

microcrystalline phases of spinel and calcium 

aluminate are more homogeneously distributed. 

Whereas in the case of CAC, a certain area 

in the microstructure is occupied by calcium 

aluminates alone, the corresponding area 

is occupied by ultra-fine spinel and calcium 

aluminate phases in the CMA containing mixes. 

Fig. 2 : Permanent linear change of castables. 

The measurement of the thermo-physical 

properties as shown in Fig.3 also indicates 

that the permanent expansion with M2 is lower 

than with M1 when only a load of 0.05 MPa 

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DL/Lo (%) 

DL/Lo (%) 

Fig. 3 : Thermo-physical properties of 

model. castable M1 (CAC) and M2 (CMA). 

Test procedure: see section 2.2. 

HMOR (MPa) 

2,0 

M1 (CAC) 

1,5 

1,0 

0,5 

0,0 

-0,5 

-1,0 

-1,5 

-2,0 

0 400 800 1200 1600 


2,0 

M2 (CMA) 

1,5 

1,0 

0,5 

0,0 

-0,5 

-1,0 

-1,5 

-2,0 

0 400 800 1200 1600 


30 

25 

20 

15 

10 

5 

0 


1000 1350 1550 


Fig. 4 : Hot modulus of rupture of model 

castables. 

100 µm 

MA1 ((CAC)) 

MA2 ((CMA)) 

Fig. 5 : Matrix microstructure of model 

castables with CAC and CMA (1550°C, 3h). 

3.3 Thermo-chemical castable properties 

The following results show quite clearly that the 

CMA containing systems achieve both better 

corrosion and penetration resistance to slags. 

In the induction furnace, the corrosion of the 

CMA containing mixes was around 50% lower 

than the CAC containing reference mixes. With 

CMA, the castables resisted both of the tested 

slags better than CAC (Fig. 6). A similar trend is 

visible in the rotary kiln where the improvement 

was in the range of 20% when changing from 

MA1 to MA2 resp. and from M1 to M2 (Fig. 7). In 

all cases, the iron oxide rich slag B caused more 

corrosion than slag A. With respect to wear, 

castable M2 shows the best performance while 

penetration is the lowest with MA2 even with the 

iron rich slag B (Fig. 8). This can be of great 

advantage not only in the ladle wall and floor but 

also for functional pre-cast products that often 

need adhering slag and remaining steel to be 

cleaned from the working surface by burning 

oxygen lances. This can create aggressive ironrich 

slags which CMA will resist better than CAC. 

The lowest corrosion with the typical ladle slag 

A was observed with CMA based castable M2. 

This type of spinel forming and spinel containing 

hybrid castable could have great advantage in 

the ladle wall and bottom. 

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Corroded cross section area (%) 

16 

14 

12 

10 

8 

6 

4 

2 

0 

Slag B 

Slag A 


Fig. 6 : Corrosion of model castables in 

laboratory induction furnace. 

Wear (mm) 

16 

14 

12 

10 

8 

6 

4 

2 

0 

Slag B 

Slag A 


Fig. 7 : Corrosion of model castables in 

laboratory rotary kiln with two different slags. 

4 Conclusions 

CMA, the new calcium magnesium aluminate 

cement significantly increases the corrosion 

and penetration resistance of castables for 

steel ladle applications. This achievement is 

based on an innovative microstructure which 

brings microcrystalline spinel to places within 

the matrix microstructure that are normally 

occupied by calcium aluminate phases only. With 

CMA, smaller pores are formed, explaining the 

improved penetration resistance. Homogeneous 

distribution of the microcrystalline spinel inside 

the CMA grains within the castable matrix 

enhances the in-situ life of both spinel containing 

and spinel-forming castables. 

5 Acknowledgements 

We would like to thank the Kerneos laboratories 

in France and China, the Wuhan University 

of Science and Technology, China, the ITMA 

institute, Spain, the ICAR institute, France, and 

the BCMC institute, Belgium, for the support of 

this study. 

1000 

Slag B 

Slag A 

Penetration (µm) 

800 

600 

400 

200 

0 


Fig. 8 : Slag penetration of model castables in 

laboratory rotary kiln. 

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6 References 

[1] T. Yamamura et al.: Development of 

alumina-spinel castables for steel ladles. 

Taikabutsu 42, 8 pp 427-434 (1990). 

[2] S. Asano et al.: Mechanism of slag 

penetration in alumina-spinel castable for 

steel ladle: Taikabutsu 43, 4, pp 193-199 

(1991). 

[3] H. Naaby, O.Abbildgaard, G. Stallmann, C. 

Wöhrmeyer and J. Meidell: Refractory wear 

mechanisms and influence on metallurgy, 

37 th Int. Colloquium on Refractories, 

Aachen, Germany, pp. 198-204 (1994). 

[4] K.H. Dott: Monolithic ladle lining at SSAB 

Tunnplåt in Luleå, Sweden. RHI Bulletin, 1, 

pp 34-37 (2008). 

[5] T. Kanatani, Y. Imaiida: Application of an 

alumina-spinel castable to the teeming ladle 

for stainless steelmaking. UNITECR’93, pp 

1255-1266, (1993). 

[6] M. Nakashima, T. Isobe, S. Itose: 

Improvement in corrosion of alumina-spinel 

castable by adding ultra fine spinel powder. 

Taikabutsu, 52,2, pp 65-72, (2000). 

[7] T. Bier, C. Parr, C. Revais, M. Vialle : Spinel 

forming castables : Physical and chemical 

mechanisms during drying. Refractories 

Application 4, pp 3-4, (2000). 

[8] Y.C. Ko: Development and production of 

Al2O3-MgO and AlsO3-spinel castables for 

steel ladles. Mining and Metallurgy, Taipei, 

47, 1, pp 132-140. 

[9] J.P. Falaschi et al. : Liant du type clinker, 

utilisation et procede de fabrication d’un 

tel liant. Demand de brevet d’invention, 

FR2788762A1, (1999). 

[10] G. Assis et al.: Castables with improved 

corrosion resistance for steel making 

applications, Unitecr’11, (2011). 

Kerneos 


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