Abstract—The magnesia-chrome brick which have long been

used in the burning zone of rotary cement kilns but the considerable amount of water soluble, hexavalent chromium ion has been reported for used this bricks. So, magnesia-chrome bricks are being replaced with chrome-free brick mainly of magnesia -spinel type. Due to the progress with Cr-free lining, together with the reduction of cement production,such problems as instability of the cement coating, corrosion resistance of brick and, etc., wich affect the stability of kiln operation, and require further improvement. In this research, the positive effect of TiO2 addition on the coating ability and corrosion resistance of basic brick is reported. Thus, 0, 2, 4, and 6 wt.%TiO2 ratios were used in the blend(grain size distribution in the blend was 1-4mm, 0-1mm and <75 μm) and the optimum sintering temperature was about 1410 �C. After the production of bricks, the coating test and corrosion resistance was carried out against raw meal cement. Microstructural analysis and phase identification were done by scanning electron microscopy with energy dispersive X-ray analyzer (SEM/EDS), also, mineral phases present in the samples were determined at room temperature by using X-Ray diffraction. The results indicated that the properties of the samples were positively affected by TiO2 addition. So, according to experimental results showed coating and corrosion resistance with using TiO2 were improved against raw cement meal.

Index Terms—Chrome-free brick, Coating, Corrosion, Magnesium-Titanate, Spinel

I. INTRODUCTION Magnesia-chromite bricks have been standard lining for

the hot kiln zones since ~ 1940. Their properties such as coating and corrosion resistance are mainly determined by the use of refractory grade chrome ores[1]. The bonding of the bricks strongly influences the performance of a magnesia-chromite refractory lining. In the so-called direct bonded magnesia bricks, the grains are bonded tightly to the surrounding matrix. In general, the presence of alkalis in oxidizing atmosphere can degenerate the chrome -ore of magnesia-chromite bricks. The reaction is accompanied by the formation of toxic hexavalent chromates[2]-[3].

Recently, an increase in environmental concerns has pushed each company to strive for zero-emission status and/or to achieve the environmental isocertification.

Hence, chrome-free bricks of magnesia-spinel type for rotary cement kilns have been developed[4]. For cement kilns refractories, MgO-oversaturated spinel are preferred as

Manuscript received May 13, 2012; revised July 13, 2012. The authors are with the Department of Materials Engineering, Science

University, Tehran, Iran.

their eutectic of 2135 C is much higher than the burning temperature of cement (1450 C). Because of different thermal expansion coefficients between spinel and the magnesia matrix a microcrack system exists in the brick, which results the addition of alumina and titania(TiO2) to a magnesia composition and the spinel is formed during the brick firing by an in-situreaction[5]. Magnesia-spinel bricks are highly thermal shock resistant (not sensitive against reducing /oxidizing conditions, but are attacked by thermal overload [6]. On the other hand, spinel forms low-melting phases with the result of a premature wear. To overcome this problem, latest development are directed at an increasing use of MgO-TiO2 products[7]. To use magnesia-spinel bricks, which were developed for transition zone,which the beneficial property of non-adherence of cement clinker, in the burning zone, the properties of coating adherence and corrosion resistance must be improved.[8-9] In this paper reports the results for Cr-free brick used in focus area of rotary cement kilns, together with the development of an improved brick with lower thermal conductivity.

II. EXPERIMENTAL PROCEDURE The raw materials for this study were Chinese dead burned

magnesia, Czech sintered magnesia, tabular Alumina from Alcoa Company and Chinese magnesia-rich spinel listed in “Table I”. High purity TiO2 from Merck company (100808), as with an average size, d50, of <3µm was used.

TABALE I: CHEMICAL COMPOSITIONS OF RAW MATERIAL

Four samples were prepared by addition of 0-6 wt.% TiO2

and MgCl2 using as a binder to the main raw materials which are given in “Table Ⅱ”.

Particle size distribution were 1-4 mm, <1 mm and<75µm. All raw materials were mixed following the standard commercial practice. The compositions after mixing, were shaped by hydraulic press with 1200 Kg.Cm-2 pressure to form bricks (198×200 m m). The bricks were dried at 110 ºC for 24 h, and then sintered in gas kiln at 1410 ºC for 52 h.

S. Ghanbarnezhad, M. Bavand-Vandchali, A. Nemati and R. Naghizadeh

Coating Ability and Corrosion Resistance of Basic Brick with TiO2 for Rotary Cement Kilns

OxideRaw Material (%)

MgO

CaO Al2

O3 Fe2

O3 SiO2 L.O.

I B.D

g.Cm-

3

China Magnesia 97.20

1.20 0.20 0.32 0.70 0.38 3.28

Czech magnesia Magnesia-Rich Spinel Tabular Alumina

89.90 33.00

2.95

0.10

64.0

0

99.5

7.00

0.80

0.5

0.00

0.65

3.32

3.28

3.55

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Journal of Medical and Bioengineering (JOMB) Vol. 1, No. 1, September 2012

and Research Branch,Islamic Azad

For coating test, the bricks was coated with disk form of raw cement clinker and sintered in 1400 -1450 � C for 6 h and for corrosion resistance, the bricks was cut crucible forms and filled by raw cement clinker. Then, put at 1400-1450 C for 6 h in lab kiln which in “TABLE Ⅲ”. are indicated the chemical composition of the raw cement clinker.

TABLE Ⅱ: FORMULATION OF THE MIXTURES

TABLE Ⅲ: THE CHEMICAL COMPOSITION OF THE RAW CEMENT CLINKER

III. EXPERIMENTAL APPARATUS AND METHOD Chemical composition of raw cement clinker was done by

X-ray Fluorescence from PHILIPS company (PW1606). The microstructure of polished was investigated under SEM, Vega//Tescan which equiped with an energy-dispersive spectroscope. For mineral phases distinguishing was used X-ray diffraction from PHILIPS company (PW 3710).

IV. RESULTS AND DISCUSSION

A. Coating Test and the Study Given that, in between the magnesia- spinel bricks and

coat, βC2S-rich phase is formed and this phase in 725 �C transmitted to γC2S and this reaction is associated with a 10% volume expansion. Thus, this phenomenon is caused the downfall of coating that dusting is also called [10.]

“Fig 1”. Shows the coating images the brick with addition of TiO2 (B.S2, B.S4, B.S6). It is observed, titania can be improved the coating ability.

Because CaO in the cement clinker Reacts with TiO2 in the brick and is formed Calcium -Titanate phase, the phase is increased the linkage potency between brick and coating. Already as mentioned, sintering of calcia proceeded with the progress of densification induced by particle growth similar to that of magnesia. As a factor of this densification, the formation of solid solution by diffusion of titania into calcia, identical with the magnesia, and the formation of low temperature melting compounds, namely calcium-titanates (CaO. TiO2, 3CaO.2TiO2) are considered to take place.

However, as for the formation of solid solution, the difference of ionic radius is large, namely, Ca2+ 0.099 nm and

Ti4+ 0.068 nm, so there seems to be little possibility for the formation of solid solution by titanium. Furthermore, with respect to their melting points, the relative sintering temperature of calcia (m.p. 2570 � C) was higher than that of magnesia (m.p. 2800 �C)[11], so the titania was more effective for of the coating. This feature is attributed to the fact that solid solution formation is more difficult in calcia and the melting temperature of calcium titanate is higher than magnesium titanate.

Fig. 1. coating images the bricks of the samples, a)B.S2, b) B.S4, c)B.S6

The magnesium-titanate phase are able to create the sturdy contacts between magnesia-spinel and magnesia in the matrix, consequently, it makes the strength to be increased. The same phases by X-ray diffraction patterns are shown in “Fig 2”.

Fig . 2. X-ray diffraction patterns of these samples after sintering in 1410 �C

As shown in “Figs 3 and 4” when using an electron

microscopic by backscatter electron (SEM/BSE) to analyze of the microstructure specimens (B.S2, B.S6) and microchemical analysis by energy dispersive X-ray analysis (SEM/EDS)of the sample B.S2, it is observed that the magnesium-titanate spinel and calcium-titanate is formed at the matrix.

B. Corrosion Resistance study For this study, the bricks was cut crucible forms and filled

by raw cement clinker. Then, put at 1400-1450 ̊ C for 6 h in lab kiln.

Magnesia-spinel bricks reacts with the cement material. This bricks, which naturally contain Al2O3 from compounds of the CaO-Al2O3-SiO2 system: these cause substantial corrosion of the bricks because of their relatively low melting points and the low viscosity of the produced liquid phase. Therefore, TiO2 will be added and to improve the corrosion resistance of these sorts bricks[12]. As another approach TiO2 additives were supposed to accelerate the growth of the coating layer on hot face of the brick, as it is expected that such additives form CaO- TiO2 compounds of rather high

Samples Raw material (wt.%)

B.S0 B.S2 B.S4 B.S6

Magnesia 90> 90> 90< 90< Spinel Alumina Titania

5≤ ≤2 0

5≤ ≤2 2

5≤ ≤2 4

5≤ ≤2 6

Oxide (%)

SiO2

Al2O3

Fe2O3(t)

CaO

Na2O

K2O

Clinker

14.9

5

2.62

2.77

41.5

7

0.29

0.51

Oxide (%)

MgO

TiO2

MnO

P2O5

SO3

L.O.I

Clinker

1.65

0.157

0.072

0.08

0

0.22

3

34.68

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Journal of Medical and Bioengineering (JOMB) Vol. 1, No. 1, September 2012

melting points.

Fig. 3. SEM/BSE of the specimens a) B.S2 and b) B.S6 after sintering in 1410

�C

Fig. 4. Microchemical analysis by energy dispersive X-ray analysis (EDS) of

the sample B.S2

It is reported that these additives effectively contribute to

increase the high temperature strength of the bricks by forming spinels, by forming minerals of rather high melting points and by accelerating the sintering of the brick.

“Fig. 5” shows the images of the bricks to compare the

corrosion resistance. It is obvious; the sample B.S2 has the best properties in total test.

Fig. 5. The images of the bricks a)B.S0, b)B.S2, C)B.S4 and d)B.S6 after

corrosion resistance being tested

V. CONCLUSIONS The results showed that with addition TiO2 and reactions

between MgO-TiO2 it has reinforced the microstructure of brick.

The cation vacancy was increased and the reaction between materials was improved.

Meanwhile, TiO2 improved the coating ability and corrosion resistance of the bricks.

ACKNOWLEDGMENT The authors would like to thank Pars Refractories

Company for their support in conducting this study.

REFERENCES [1] P. Bartha and H. J. Klischat, “Present state of the refractory lining for

cement kilns,” CN-Refractories, 1999, vol. 6, no. 3, pp. 31–38. [2] D. J. Bray, “Toxicity of chromium compounds formed in refractories,”

Ceram. Bull, 1985, vol. 64, no. 7, pp. 1012–1016. [3] M. O. Driscoll, “Price temper steel market promise,”Industrial

Minerals, 1994, vol. 324, pp. 35–49. [4] H. Komats, M. Arai, and S. Ukawa, “Current and future status of

chrome -free bricks for rotary cement kilns,” Taikabutsu Overseas, 1999, vol. 19, no. 4, pp. 3–9.

[5] P. Bartha and H. J. Klischat, “Classification of magnesia bricks in rotary cement kilns according to specification and serviceability,” ZKG Intern, 1994, vol. 47, no. 10, pp. 277–280.

[6] H. Makino et al, “The application of MgO-TiO2-Al2O3 aggregates for chrome-free refractories,” Journal of the technical association of refractories, Japan, vol. 24, no. 4, pp. 259, 2004.

[7] R. Lodha, C. O. Troczynski, and G. Oprea, “Magnesia-rich chromium -free spinel-bonded basic refractories,” UB ceram, Departmant of Material Engineering of British Columbia, Advances in refractories V-The Michel Rigaud Symposium , 2011.

[8] Refractories Handbook, The technical Association of refractories, Japan, 1998.

[9] H. Iwadoh et al, United State Patent, U.S.A. Dec, vol. 15, 1992. [10] R. Sarkar, A. Ghosh, and S. K. Das, “Reaction sintered magnesia rich

magnesium aluminate spinel,” effect of alumina reactivity. Ceram Int, 2003, pp.407-411.

[11] F. Ozeki, Y. Kajita, T. Honda, and S. Ota, “Chrome-free basic for cement rotary kilns,” Journal of the technical association of refractories , Japan, vol. 21, no. 2, pp.78-84, 2001.

[12] Y Kajita, F. Ozeki, and T. Honda, “The persent and future of chrome-free linings for rotary cement kilns,” Journal of the technical association of refractories, Japan, vol. 20, no. 4, pp. 266-270, 2000.

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Solmaz Ghanbarnezhad is a first Author. She was born in 1984 in Bandar –Anzali, Iran. Education: M.S,. In Ceramic Engineering, in the Department of Materials Engineering, Science & Research Branch, Islamic Azad University, Tehran, Iran, 2012. Thesis: The effect of TiO2 on physical, mechanical, thermo-mechanical properties, coating and corrosion resistance of chrome-free basic brick.

B.S,. In Ceramic Engineering, Maybod University, Islamic Azad University,Yazd, Iran,2006.

Ali Nemati is Corresponding Author. He is Assoc.Prof. in the university. Education: Ph.D., In Materials Science and Engineering (Ceramic major) Case Western Reserve University, Cleveland , Ohio, USA, 1994. Dissertation: The effects of Ce Doping on the PTCR effects of Barium Titanate. Advisors: Professor M.R. DeGuire & Professor M.

Tabib Azar. M.S., In Ceramic, Iran University of Science and Technology, Tehran, Iran, 1988. Thesis: Stabilization and Transformation Toughening in Zirconia Ceramics. B.S., In Ceramic, Iran University of Science and Technology, Tehran, Iran, 1985. PROFESSIONAL AFFILIATIONS: Iranian Ceramic Society,(member & a member of Board of the Society). Iranian Metallurgical Society, (member). Center of excellence in Adv. Eng. Materials, ( Head and member). Member of Biomedical Research Center of Sharif. American Ceramic Society (Former member- While living in the USA).

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Journal of Medical and Bioengineering (JOMB) Vol. 1, No. 1, September 2012