GLAZES USING E-GLASS FIBERS WASTE

Vasilica Dima1,a, Adrian Volceanov1,b, Mihai Eftimie1, Adriana Petrescu2, Maria Ionescu2, Nicolae Ziman3, Enikö Volceanov4

1 University POLITEHNICA Bucharest, Faculty of Applied Chemistry and Materials Science, 1

Polizu street, zip 011061, Bucharest, Romania, phone +40-21-4023996 2 IMA-METAV SA, 67-77 Biharia street, Bucharest, Romania

3 FAIMAR, 104 Bucharest blvd , Baia Mare, Romania 4 Metallurgical Research Institute, 30 Mehadiei street, Bucharest, Romania

a vasilica.dima@gmail.com, b avolceanov@gmail.com Keywords: frits, glazes, E-glass fibers waste, table ware ceramics.

Abstract. The main purpose of the paper is to present results of experiments concerning E-glass

fibers waste with a content of 7% B2O3 for obtaining glazes for tableware ceramics, as well as to

study the consequences upon fabrication technology.

The results are encouraging and make possible the use of E-glass fibers waste for preparation

of vitreous glazes.

1. Introduction

The turning into account of the potential of E-glass fibers waste through their usage in frits

and glazes by taking the advantage of oxide composition (B2O3 content is about 7%), of energy

content of a glass and ecological effects, as well, represents strong arguments for their study and

finding of optimum solutions, both technical and economical [1-4]. The approached subject is of

present interest, namely the capitalization of some industrial waste in fabrication of products.

This target represents a major priority from the viewpoint of environment protection and

sustainable development but also an economical priority for energy saving and raw materials

management by using the advantage of the chemical composition of E-glass, presence of boron

oxide and energy content of the glass.

2. Experimental part

2.1 Selection of compositions with appropriate properties

In a first stage [4] a mathematical program was developed to model and calculate the linear

thermal expansion coefficient of the glazes to be selected, having as reference value the thermal

expansion coefficient of the tableware ceramic body ( 300

50α = 71.6 .10

-7 K

-1) to yield good glaze –

ceramic mismatch. In this way 10 compositions of glazes were selected for which the thermal

expansion coefficients fulfilled the conditions for an acceptable glaze-ceramic mismatch, which

appears when the support’s thermal expansion coefficient is greater than that of the glaze with about

6 - 15% [2]. The amount of E-fibers waste ranging as 70 % - 97 % assures for glazes a 5.31 – 7.35

% B2O3 content [5], and can be seen in Table 1.

Table 1 - Batch oxide composition of glazes

Batch oxide composition [% gr.] Sample

SiO2 Al2O3 Fe2O3 CaO MgO R2O B2O3

1 A, B 57.23 18.43 0.28 14.34 2.32 2.07 5.31

2 A, B 57.21 17.00 0.23 15.33 2.47 2.06 5.68

3 A, B 57.20 15.58 0.17 16.32 2.62 2.04 6.06

4 A, B 58.32 15.59 0.21 15.36 2.46 2.37 5.68

5 A, B 53.82 15.00 0.03 19.62 3.14 1.02 7.35

(A) - ground fibers waste, (B) ground frit; R = Na, K

Advanced Materials Research Vols. 39-40 (2008) pp 663-666Online available since 2008/Apr/08 at www.scientific.net© (2008) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.39-40.663

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2.2 Experimental glazes

Based on the results of mathematical modelling optimal compositions were selected and used

to carry out experiments for glazes, by introducing different amounts of glassy waste processed as

ground frit (B), or ground fibers waste (A), both having the same composition of E-glass and a

specific surface area of 3500 – 4200 cm2/g.

Before melting the wettability of samples was determined for mixtures of raw materials in

order to get information on temperature dependence of wetting angle (i.e. the adhesion to ceramic

substrate), as another criterion for selecting glaze compositions, respectively. Feldspar (0-20 % gr.)

and kaolin (3-15 % gr.) was added to the batch as regular raw materials used for glaze preparation.

The batches were prepared by mixing and homogenization of components. Samples were obtained

by pressure moulding and shaped as cylinders (height 3 mm).

2.2.1. Determination of wettability

Wettability is involved in several stages of glass and glaze fabrication process. During the

glazing of ceramic products, at glaze-ceramic substrate contact, the adhesion can be enhanced by

heating glass until the wetting angle, θ, becomes small enough. The wettability angle is used as a

wetability measure and it represents the angle between the tangent at the liquid-gas separation

surface with the solid-liquid separation surface, always containing the liquid phase.

Figure 1 - The wettability angle

The wettability increases with the decrease of the wettability angle. If θ < 90° the liquid wets

the solid (Fig. 1a) and if θ >90° the liquid does not wet the solid (Fig. 1b). In our case the wetting

angle reached values about 30°. Each sample was disposed on the ceramic support and then inserted

in the refractory tube of a horizontal oven. The wetting ability vs. temperature was observed by

measuring the θ angle on a cathetometer with bevel angle. The heating rate was 3°C/min.

To control this process one must determine accurately the dependence of wetting ability (i.e.

wetting angle) of glaze as function of temperature. Therefore, it is necessary to consider the

behaviour at higher temperature of selected glaze compositions, in order to estimate critical

temperature points (e.g. softening point) and of wettability to a given substrate. These properties are

critical for glazing process.

The wetting angle θ was recorded for each step of 10°C in the temperature range 1100 –

1280°C, through the evolution of sample’s shape versus temperature and the softening points were

set up for the temperatures at which the edges of samples were rounded. The upper limit of 1280°C

was chosen as a result of the fact that the firing temperature of glazes for the given ceramic

substrate is around 1200°C. The experimental values are given in Fig. 2.

2.2.2. Batch preparation and melting of samples

The compositions selected for their good wetting behaviour (small wetting angles at firing

temperature) were used to study the melting behaviour, to set up the melting parameters and for

experimental determination of their thermal expansion coefficients in order to assess the glaze –

ceramic mismatch. The melts were obtained in alumina crucibles, in an electrical oven with

superkanthal heating elements within the temperature range 1300 – 1350°C for 3 hours plateau. The

obtained melts were homogeneous, clear and fluid, easy to mould in graphite forms for sample

preparation to be used in thermal expansion determinations.

2.2.3. Thermal expansion coefficient

To estimate glaze – ceramic substrate mismatch for the given ceramic tableware there were

determined the thermal expansion curves with a differential Weiss dilatometer, for a temperature

rate increase of 2°C/min. up to 700°C (around 650°C all the studied glazes featured the glass

664 Glass – The Challenge for the 21st Century

transition). The standard material of the differential dilatometer was fused silica. The construction

of the apparatus did not make possible to measure the glaze – ceramic mismatch in a single run.

3. Results and discussion

The wettability data have been used for plotting the variation of wetting angle versus

temperature. The required firing temperature of glazes on the ceramic substrate is 1200°C, so a

comparative analysis of glaze samples at this temperature is given in Fig. 2. This lead to the

conclusion that only certain compositions (3 B; 4 A,B; 5 A,B) are suitable and interesting for

melting.

Figure 2 -Values of wetting angle for studied glazes at 1200°C

Variation of thermal expansion coefficients with temperature brings valuable information for

analysis of glaze – ceramic mismatch of studied glazes as shown in Fig. 3.

Thermal expansion

0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0 100 200 300 400 500 600 700

Temperature [C]

∆∆ ∆∆l/l 0

Body

Sample 3b

Sample 4a

Sample 4b

Sample 5b

Figure 3 - Dependence on temperature of thermal expansion coefficients

At higher temperature (400–600°C) thermal expansion coefficients of glazes are lower than

that for ceramic substrate that allows, at cooling of glaze–ceramic body system within this critical

domain for glaze, to develop a slight compressive stress with a positive effect upon glazed product.

At temperatures even lower, when the ratio between the thermal expansion coefficients of

ceramic substrate and glaze must be kept within narrow limits, the differences between the curves

of thermal expansion of ceramic body (as given) and selected glazes are small and thus having a

good influence upon the finite glazed product.

The following aspects were emphasized:

- melting angle decreases when increasing the proportion of glassy waste (samples 5A and 5B

have a higher content of waste as compared with samples 1A and 1B), regardless of how the waste

Advanced Materials Research Vols. 39-40 665

is introduced in the raw mixture as frits or ground fibres; it shows an increase of wettability;

- the wetting angle is smaller for the samples with frit (samples B) then that for those with

ground fibers, showing a higher wettability.

The obtained data confirm some known aspects, namely:

- both fibers waste and ground frit represent melted glass already bearing energy and

therefore, their increased proportion in glaze compositions leads to lower melting temperatures;

- the frit, obtained by remelting of glassy waste followed by quenching, has a structure with a

higher energy content that makes it more reactive in comparison with fibers waste even if ground at

the same specific surface area as frit.

Experiments were conducted for ceramic tableware products using glazes with ground frit on

an industrial processing line [5]. Industrial products samples were analysed with scanning electron

microscopy (HITACHI S 2600 N) at glaze substrate interface [5], confirming the important role of

the interface in providing the glaze – substrate mismatch. A strong interface between ceramic

substrate and glaze is another factor for a good mismatch. The formation of this bonding interface

layer is a consequence of melted glaze diffusion within the surface layers of ceramic substrate and

exhibits an intermediate thermal expansion that diminishes the action of stress at the interface.

Figure 4 - SEM micrograph at interface between glaze with E-frit and ceramic body

The micrographs emphasize a strong interface between ceramic support and glaze. Melted

glaze penetrates into ceramic pits, dissolves some constituents of ceramic body and favours

formation of fine crystals, so yielding a joining layer that ensures a good glaze-substrate mismatch.

Conclusions

The results emphasise the possible use of E-glass fibers waste for preparation of vitreous

glazes. The waste of E-glass fibres represents an effective option for frit and glaze preparation to be

used for other ceramic products such as tableware, ceramic sandstone. Possible advantages are: (a)

addition of valuable components (B2O3, Al2O3, CaO) in glaze composition; (b) raw materials and

energy saving, environment friendly products; (c) high B2O3 content of E-glass fibers recommend

their use in frits and glazes free of PbO considered as highly toxic material.

References

[1] R.Eppler, D. Eppler: Glazes and Glass Coatings, The Amer. Ceram. Soc., Ohio, (2000), p. 239

[2] M. Preda, Ceramics and Refractories, Ed. Printech, (in Romanian) (2001), p. 220

[3] R.Eppler, M.Obstler: Understanding Glazes, The Amer. Ceram. Soc., Ohio, (2005), p. 71

[4]A. Volceanov, M. Eftimie, V. Dima, A. Petrescu, M. Ionescu, S. Enescu, Design and Modelling

of optimum glaze compositions based on glass fibers waste, Academic Days Symposium,

Timisoara, Romania, (2005)

[5]. Research Contract no. 1 RELANSIN - New technology for processing recyclable resources of

glass fibres for vitreous glazes, (2004)

666 Glass – The Challenge for the 21st Century

Glass – The Challenge for the 21st Century 10.4028/www.scientific.net/AMR.39-40 Glazes Using E-Glass Fibers Waste 10.4028/www.scientific.net/AMR.39-40.663

DOI References

[1] R.Eppler, D. Eppler: Glazes and Glass Coatings, The Amer. Ceram. Soc., Ohio, (2000), p. 239

doi:10.1023/A:1009089023367