SUBMITTED BY:ABHINAV SRIVASTAVA

M. Tech. 3rd Semester Department of Ceramic Engineering Institute of Technology

Banaras Hindu University, Varanasi -221005

Synthesis and STUDIES ON CORDIERITE BASED ultra low high alumina cement cASTABLES

project guideDR. Vinay Kumar

Co- SupervisorpRof. g.n. agarwal

CONTENT

S. No. CHAPTERS

1. INTRODUCTION

2. LITERATURE REVIEW

3. OBJECT OF THE PRESENT INVESTIGATION

4. EXPERIMENTAL

5. RESULTS & DISCUSSIONS

6. PLAN FOR FUTURE WORK

7. REFERENCES

INTRODUCTION

What are Refractory Castables?Refractory Castables are fabricated with the help

of optimum mixture’s of different refractory aggregate fractions along with suitable bond materials and microfine additives.

Why Castables?Castable Refractories include:

Absence of joint structure. Better Resistance to Corrosion and Abrasion. Better thermo-mechanical-resistant properties. Low thermal conductivity and energy savings in the

formulation of materials.

Why low cement?

The traditional castable with 10-12% cement content not only needs high curing time but also represents strength retrogression in the intermediate temperature range during heating of castable refractories.

Apart from these, development of low temperature melting phases severely deteriorate the physiochemical properties at higher temperature.

LITERATURE REVIEW

Cordierite Cordierite (2MgO-2Al2O3-5SiO2) mineral, occurs in very

small quantities. Has properties such as low thermal expansion coefficient

(α = (1–2) ×10−6 0C−1), low dielectric constant (ε = 5–6) and high specific resistivity (ρ >1014 Ω.cm), and high chemical and mechanical durability.

Best suited to applications that require low thermal expansion coefficient (2×106 0C-1 to 6×106 0C-1) and outstanding thermal shock resistance.

These materials are extensively used as refractory products, electro ceramics, tableware, and catalyst carriers.

Cordierite has begun to replace Al2O3 as a substrate material for semiconductor packaging.

Ternary Phase Diagram of CaO-MgO-Al2O3

Calcium Aluminate Cement The use of Portland cement as bond material in

castable is restricted to cover temperature range (<4000C), and it releases free lime when heated above 6000C.

High Alumina Cement or CAC by virtue of their purity and high alumina content, increase the temperature of formation of a eutectic and therefore, can effectively be used as a binder in high temperature refractory applications.

CAC have sufficient refractoriness and mechanical strength during continuous heating or in frequent heating or cooling cycles.

OBJECT OF THE PRESENT INVESTIGATION

One of the objectives of the present work is to prepare calcium aluminate cement at low temperature with the identification and characterization of various calcium aluminate cement phases with varying temperature ranges. Further these phases will be studied for their initial and final setting time, and the cement with lowest initial and final setting will be utilized with cordierite powder for the synthesis of Cordierite based castables.

The cordierite material has to be prepare using the chinaclay (Al2Si2O5(OH)4), alumina gel, silica and magnesia (AR Grade). The microsilica content is to be varied in the castable and its effect will be studied on the characteristic of the cordierite based castables.

EXPERIMENTAL

EQUIPMENTS AND MATERIALS

Apparatus used in the investigation are: Globar furnace (up to 1400°C) Hydraulic Press for making pellets (up to 30

tonnes) Screw gauge and Vernier calipers for

determination of shrinkage of the samples after sintering.

Electronic balance Boiling water bath

RESULTS & DISCUSSIONS

Determination of Initial & Final setting time of the Calcium aluminate Cement:

Standard consistency of a cement paste is defined as consistency which will permit the Vicat Plunger to a point 5 to 7 mm. from the bottom of the Vicat mould. By using the Vicat apparatus the standard consistency of the cement was found out.

Since 400 gms of cement requires 112 cc of water. So, 100 gms of cement will require

(112×100)÷400 = 28 cc of water.Using above calculated consistency the

initial and final setting times were calculated for cement paste fired at different temperatures.

S.N

O.

Temperature 0C

Initial

Setting

Time

Final

setting

time

1. 12000C 56 min. 7hr. 22

min.

2. 12500C 49 min. 7hr. 10

min.

3. 13000C 47 min. 6hr. 45

min.

4. 13500C 29 min. 6hr. 5 min.

5. 14000C 27 min. 5hr. 50

min.

Determination of Initial & Final setting time of the Calcium aluminate Cement fired at different temperatures

Determination of Initial & Final setting time of the Calcium aluminate Cement fired at different temperatures

XRD’S OF CALCIUM ALUMINATE CEMENT

PERCENTAGE LINEAR CHANGE WITH VARYING WT. % OF MICROSILICA SINTERED AT 1300 0C FOR 2 HOURS:

S. No.Soaking

Time% Linear Shrinkage

0 Weight% Microsilica

1 Weight % Microsilica

1. 10 2.05 2.60

2. 30 2.15 2.70

3. 50 2.40 2.90

4. 100 2.50 3.00

Percentage linear Change with varying wt. % of microsilica sintered at 13000C for 2 hours:

BULK DENSITY WITH VARYING WT. % OF MICROSILICA SINTERED AT 13000C FOR 2 HOURS:

S. No.

Soaking Time

Bulk Density

0 Weight % Microsilica

1 Weight %

Microsilica

1. 10 2.28 2.34

2. 30 2.39 2.45

3. 50 2.50 2.56

4. 100 2.57 2.63

Bulk Density with varying wt. % of microsilica sintered at 13000C for 2 hours:

S. No. Temperature 0C

Apparent Porosity

0 Weight% Microsilica

1Weight %

Microsilica

1. 1300 24 19

APPARENT POROSITY WITH VARYING WEIGHT % OF MICROSILICA SINTERED AT 13000C FOR 2 HOURS:

The determination of initial and final setting time of the calcium aluminate cement shows a decrease in its value by increasing the firing temperature. Which predicts that more the amount of Calcium Hexaluminate phase is formed the less is the setting time of the cement paste.

The XRD graphs show and confirm the formation of calcium hexaluminate, dicalcium aluminate, and tricalcium aluminate phases.

DISCUSSIONS

The PLC test presents the expansion behaviour of high alumina low cement cordierite based castable with and without addition of microsilica content. In both the systems the sintering shrinkage is detected due to (1) CA2 formation around 11000C, (2) the spinel formation in the 1200-13000C, (3) the CA6 formation at temperatures higher than 12500C. The span of percentage linear shrinkage decreases with the minor 1% addition of microsilica content.

Similar results are obtained when the Bulk Density tests were performed. The minor 1% addition of microsilica in the ultra low cement cordierite castable increases its bulk density giving it more strength in low temperature applications. The apparent porosity has subsequently decreased when the microsilica doped pellet was sintered at 13000C for 2 hours.

PLAN FOR FUTURE WORK

The future plan is to study the physical and thermal properties of prepared cordierite material and its addition in castable with varying grain size of magnesia.

Study will also be done to observe the effects of microsilica addition in cordierite based castables.

Other proposed plans include studying various phases of cordierite and its ultra low cement castables by XRD technique and to determine their grain size distribution and microstructure by SEM.

REFERENCES

S. Mukhopadhyay, P.K. DasPoddar, Effect of preformed and in situ spinels on microstructure and properties of low cement castable, Ceram. Int. 30 (3) (2004) 369–380.

Emre Yalamac¸ Sedat Akkurt, Additive and intensive grinding effects on the synthesis of cordierite, Science Direct (2005).

Zagorka Acimovic, Ljubica Pavlovic, Ljiljana Trumbulovic, Ljubisa Andric & Milan Stamatovic, Synthesis and characterization of the cordierite ceramics from nonstandard raw materials for application in foundry, Science Direct (2002).

Lj. Trumbulovi & Lj. Andric, Synthesis and Characterization of Cordierite from Kaolin and Talc for Casting Application, Vol. 31, No 1, 2003 FME Transactions.

E.Y. Sako, M.A.L. Braulio a, D.H. Milaneza, P.O. Brantb & V.C. Pandolfelli, Microsilica role in the CA6 formation in cement-bonded spinel refractory castable, Science Direct (2009).

M.A.L. Braulio a, P.O.C. Brant b, L.R.M. Bittencourt b, V.C. Pandolfelli, Microsilica or MgO grain size: Which one mostly affects the in situ spinel refractory castable expansion, Science Direct (2009).

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