Effect of Temperature on Ceramic from Rice Husk Ash - ijens

International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:09 No:09

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Effect of Temperature on Ceramic from Rice Husk Ash M.M. Haslinawati, K.A. Matori, Z.A. Wahab, H.A.A. Sidek, A.T. Zainal Abstract-- Two forms of crystal phase, cristobalite and tridymite contained in RHA ceramic presented in this paper. Raw material (RHA) was going through with thermal treatment in order to produce white ash powder. Later the powder was pelletized using hydraulic press. Then disc shape pellets were sintered at certain temperature (1000-1400°C) in order to observed the effect of sintering temperature on the RHA ceramics. XRD analysis was performed to characterize the phase changing in the RHA ceramics due to their temperature. The results showed that the RHA ceramic sintered at 1000°C contained high percentage of cristobalite and this continues decreasing as the temperature increasing. It seems to be different for tridymite phase where it become greatly appears at higher sintering temperature. This crystal phase can be confirm by their microstructure that performed by SEM.

Index Term-- Microstructure, Phase formation, Rice husk ash, X-ray diffraction.

I. INTRODUCTION Silica (SiO2) is a basic raw material that widely use in many industries. Rice husk (RH) can be considered as suitable energy and silica resource in Asian countries. By heating at higher temperatures, the unburned carbon can be removed from the ashes [1], but this leads to the crystallization of the ash from amorphous silica into cristobalite or tridymite. At lower temperature, the amorphous nature of rice husk ash silica will be occurred [2]. The most common form of crystalline silica found is quartz [3]. But more research has been focused on the formation of cristobalite and tridymite [4]. The transformation has been reported that α-quartz can be form at below 573°C, ß-quartz at 573-870°C, ß-tridymite at 870-1470°C, and ß-cristobalite at 1470-1710°C [5]. The increasing interest to RH requires complete investigation on the effect of heat treatment to their phase and microstructure. Many methods have been developed to produce pure silica from rice husk ash (RHA) in low cost. It has been reported that purity of silica is highly affected from chemical treatment [6]-[9], than thermal treatment [10]. This process not only producing valuable silica powder but also has benefited This work was supported by Malaysian Ministry of Higher Education (MOHE) through Research University Grant Scheme (91477). M.M. Haslinawati (e-mail: [email protected]), K.A. Matori (corresponding author phone: 00603-89466653; fax: 00603-89454454; email: [email protected]), Z.A. Wahab (e-mail: [email protected]), H.A.A. Sidek (e-mail: [email protected]) and A.T. Zainal (e-mail: [email protected]) are with Department of Physics, Faculty of Science, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia.

reducing pollution problem by converting agriculture waste into useful product such as ceramics [11] (silicon carbide, SiC [12] and silicon nitride (Si3N4) [13]), thermal insulation [14], solar technology [8] and electronic semiconductor [15]. However, in semiconductor industrial, silica from RH can be reduced to silicon using metallothermic process with magnesium [16] and calcium [17]. Calcium also undertaken instead of magnesium since it is naturally abundant than magnesium. In this study, the presence of crystalline silica in RHA ceramics sintered at temperature range 1000-1400°C were examined by X-ray Diffraction (XRD). The microstructure of this crystalline silica is also observed. II. MATERIALS AND METHOD A. Raw material Raw materials (RH) were supplied by BERNAS Sdn. Bhd. Tanjung Karang, Malaysia. The procedure for preparation RH powder for the palletizing stage was consisted of washing RH in water in order to remove clay and rock impurities and subsequently dried in an oven at 120°C for 24 h to remove water content. The dried RH then was taken in crucible and placed it in electrical furnace for 1 h at 500°C to get a black ash. The ash then was ground into powder and later heated again at 800°C for 2h for complete combustion (white ash powder). Then the powder was dry milled with zirconia balls for 24 h. The pellets with 12mm diameter were formed. The pellets were then sintered at various temperatures (1000 1400°C) for 2h with heating rate and cooling rate 2°C.

B. Sample Characterization and Analysis Analysis of metallic elements in RH was performed using an inductively coupled plasma (ICP) mass spectrometer. The crystal phases of the sintered RHA pellets were identified by XRD analysis. X-ray Diffractometer (PANAalytical (Philips) X’Pert Pro PW3050/60) with CuKα radiation (Bragg angle 2θ in angular range of 20 to 80°) equipped with a copper x-ray tube and scintillation detector was used. In this paper, FTIR also was performed using Perkin Elmer Spectrum 100 Series with Universal attenuated total reflectance (ATR) Accessory. The microstructures and composition were analyzed by JEOL JSM 6400 Scanning Electron Microscope (SEM) with Oxford Inca Energy 200 EDX. III. RESULTS Table I shows the percentage elements of RHA with silica as the major elements (~93.7%) in agreement with result reported by Mishra and co-workers (1985), who found that RH contains approximately 92-97% of silica. Other metallic elements also present in RHA as minor elements. Fig. 1 shows

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International Journal of Basic & Applied Sciences IJBAS-IJENS Vol:09 No:09

the XRD pattern of RHA ceramics sintered at 1000- 1400°C for 2 h revealed that the presence of crystalline phases. Cristobalite and tridymite were observed after sintering at 1000°C. A weak peak of tridymite at 20.7° accompanied with a strong peak of cristobalite at 21.8° and an additional weak peak at 28.4°, 31.3° and 36.0° can be seen in Fig. 1. While after sintering at 1300°C and 1400°C tridymite phase occurred at 20.6°, 23.4° and 31.4° along with cristobalite phases and included the most intense peak at 21.9°. It confirmed that the reaction sintering process can effectively transform phase from cristobalite into tridymite. These results can be evidence that RHA ceramics start the transformation from amorphous silica to cristobalite accompanied with a small amount of tridymite. Shinohara and Kohyama in 2004 [18] found at higher temperature or after a long sintering time, the proportion of tridymite increased, whereas the proportion of cristobalite decreased in agreement with the result found in this study. The studies on samples structure using IR spectroscopy were carried out in the wavenumber range 280-4000cm-1. However the spectra in the wavenumber region 300-1100 cm-1 are presented for the samples 800ºC, 1000ºC, 1200 ºC, 1400ºC in Fig. 2 respectively. A characteristic shoulder in the region 1000-1100cm-1 appeared in all samples which corresponded to the presence of structural siloxane bond, Si-O-Si asymmetry stretching vibration. For the all samples, the band at around 700-800 cm-1 was due to the symmetric stretching mode of the Si-O-Si bond. A very weak band at 617cm-1, which is characteristic of the crystalline cristobalite occurred for the all samples except. The band around 450-464cm-1 is due to Si-OSi bending vibration. Fig. 3(a-e) presented the surface morphology of RHA ceramics sintered at 1000-1400°C. Fine pores and grains were observed at 1100°C and above. Although the grain particle is not spherical and irregular, but it shown evidently the amount of pores decreased with increasing sintering temperature. DISCUSSIONS The present study revealed the phase analysis of RHA ceramics that formed by sintering. Two crystalline form of silica in RHA ceramics were cristobalite and tridymite. Silica of RHA is amorphous form at low temperature 700°C and 800°C [19] while crystalline silica occurred at temperature above 900°C. It is believed that the crystalline silica of ceramic RHA is correlated with their microstructure and also their composition. The temperature of crystalline phase is occurred because of the presented of potassium (K 2O) in the RHA. It has been reported that the higher concentrations of potassium is the favored for the major crystallization of tridymite [18]. Tridymite is the silica polymorph with lowest density and it is the only silica phase that able to accommodate interstitial K+ cations into its big cavities [20]. To investigate the composition, the EDX analysis (Table II) of RHA ceramics performed on the same area used in the morphological analysis (Fig. 3). The results confirm the presence of silica with highest percentage, while other metallic elements such as K, Mg, and Ca also presented as minor IV.

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elements. K+ cation is noted as the major impurities. The crystalline nature of RHA ceramics can be confirmed by their microstructure. Crystalline increased as the temperature increased, and that effected of the grain growth. At temperature 1000°C, the grain of the particle is not completely developed, but at 1200°C and above, the grain can be clearly shown as the crystalline increased. It can be explained that sintering process provides energy to encourage the particle to bond together in order to remove the porosity. At the same time the particle will be shrinking. The XRD, SEM and EDX results revealed that RHA ceramic sintering at 900°C and above consist mainly of crystal phase. As clearly shown in Fig. 1-3 progressive increased of sintering temperature cause changes in the surface condition and crystal phase in ceramic. Therefore, the important factor in crystal formation is the heat treatment temperature. V. CONCLUSIONS Ceramics produced from RHA were well analyzed by XRD, FTIR, SEM and EDX. The XRD revealed the changes in crystal phase due to sintering temperature. SEM is useful tool to follow structural changes that occur at the surface of ceramics. The morphology analysis of RHA ceramics showed that the microstructure of samples were related to the phase of crystal occurred. On the other hand, EDX analysis confirm the composition of elements contain in RHA ceramics. VI. ACKNOWLEDGEMENT The researchers gratefully acknowledge the financial support for this study from Malaysian Ministry of Higher Education (MOHE) through Research University Grant Scheme (91477). TABLE I The composition of RHA

Weight (%)

Element 1100°C

1200°C

1300°C

O

59.00

54.40

51.60

Si

38.64

44.04

47.87

K

0.68

0.98

Ca

1.11

0.58

0.53 -

Mg

0.57

-

-

TABLE II Results of EDX analysis

Element

Percentage

SiO2

93.67

K2O

1.82

Al2O3

1.45

CaO

1.30

MgO

0.57

Na2O

0.54

Fe2O3

0.47

MnO

0.09

CuO

0.05

ZnO

0.04 IJENS

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Fig. 1. XRD pattern for pellets sintered at temperature range (1000-1400ºC). Fig. 2. FTIR spectra of pellets with different sintering temperature

(a)

(b)

(c)

(d)

(e) Fig. 3. SEM images of the pellets after (a) 1000°C, (b) 1100°C, (c) 1200°C, (d)1300°C, (e) 1400°C 2hours sintering

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