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EFFECT OF ZIRCONIA ON THE CHEMICAL DURABILITY OF SODA-LIME-GLASSES.

Byline: M. Saadet, K. Javed, W. A. Shah and M. B. Bhatty

ABSTRACT

Meltings were made in clay crucibles in which ZrO2 was progressively substituted in a selected soda lime silica glass. Durability of each sample was determined by weight loss method. Chemical durability showed that with gradual substitution of ZrO2 in glass, the resistance of the glass to chemical attack was increased and gradually reduced the extraction of alkali to a least value near to zero.

Key words: Zirconia, chemical durability, weight loss, soda lime glass.

INTRODUCTION

Glass is often thought of as an "inert" material - Although some glasses have high corrosion resistance as compared to common glasses. But actually glass products are chemically reactive to some extent, this chemical reactivity of glass depends upon (i) composition of glass (ii) type of material contained in it (iii) temperature of the liquid contained in it (iv) time of storage (v) previous history of glass e.g. mode of production and annealing. Glass containers are commonly used for storing and packing for food, pharmaceuticals and chemical products, while in laboratory many reactions involving very corrosive materials are commonly carried out in glassware. Glass equipment is also used for the chemical processes in industry where exceptional durability is required. Pharmaceutical solutions required bottles of good durability for storage.

Similarly, the glass windows, lenses and other optical units may be affected by atmospheric vapors, which will produce a dimming or fogging of the surfaces due to extraction of alkalies (Mclellan and Shand, 1984). Glass equipments subjected to the action of usually corrosive materials particularly at high temperatures may show surface wear. HCl has proved to be the most corrosive among the common acids, excluding HF, while H2SO4 and HNO3 have little action on most glasses. The temperature at which glass is exposed to reagents is very important (Stadler and David, 2000). Above 60oC extent of attack is high for all reagents. Water usually attacks much less vigorously than alkali but attack of water quickly becomes the attack of alkali as alkali is extracted from the glass into the solution to the take part in the reaction. Attack of alkali is much more vigorous than acids; the rate of attack for alkali is usually linear with the time.

The rate may change because of accumulation of alkalies in the solution especially silica, depresses the reaction because insoluble reaction products adhere to the surface and effectively block the reaction (Anderson and Rolen, 1987). Alkali attack is quite dependent on pH. The rate will increase by a factor of 2 to 3 for each pH unit rise ( Sempere, 2004). The main purpose of the present study was to focus the attention on the role of Zirconia to produce durable and economical glass from indigenous raw materials. Such durable glass is especially required for medicines. After comprehensive study it has been sort out that addition of Zirconium dioxide (ZrO2) in soda-lime-silica glass makes it excellent durable glass. Zirconium silicate is used as a source of Zirconium dioxide (Horak and Sharp, 2005).

MATERIALS AND METHODS

The standard glass which was selected for the experimentation was soda lime glass containing 70% SiO2, 15% Na2O, 2% K2O, 11% CaO and 2% Al2O3. Zirconia was taken from Zirconium silicate. Zirconium silicate is added according to the percentage of Zirconium oxide (ZrO2). For melting glass batches clay crucibles of capacity 1 Kg. were prepared. Many glass batches were prepared and melted in clay crucibles. Out of these five batches were selected for present study as shown in table-1. Five glass batches were melted in the clay crucibles. Batches were calculated to yield the composition as shown in Table 1. All glass batches were melted at the temperature about 1500oC for four hours. After melting, molten glass was poured on a hot iron plate to make the sample. The glass samples were tested by weight loss test method (WLTM). In this type of test, the glass sample may be of any convenient shape with an exposed surface of known area.

The sample is carefully weighed and placed in a container with a known quantity of the distilled water. The distilled water used as 5ml per sq cm of exposed surface of the sample. The container and contents are maintained at a suitable temperature (90oC) for a definite time of four hours. Sample was carefully washed, dried and reweighed. The results were expressed as weight loss per unit surface area (milligrams per square centimeter) for the entire time of test (Machacek, 2002). The exact procedures may be varied some what depending upon the type of attack and rate of attack of the particular reagent used. It is important that material of the container used does not go into solution. 5ml of attacking reagent per sq cm of exposed surface is usually adequate for glasses even of low durability (Bukerman, 2006). One or more intermediate weighing during the test is desirable.

Except for strong alkaline solutions, the attack will not be linear with time and the results should not be reported on a per hour basis. The principal advantages of this type of test are that it determines the total loss of material and not the alkalies alone and also that this loss is correlated to a definite surface area. Rates of corrosion of different glasses show wide variation from one case to another where conditions are presumably be the same. However, this test represents most service conditions considerably more closely. Table No. 2 represents corrosion of different glasses (weight loss) in strong alkali and strong acid while corrosion (alkali extracted) in water and in dilute sulfuric acid is shown in table No. 3. Results of addition of ZrO2 are shown in Table 4. While effect on resistance to attack of substituting ZrO2 in glass are shown in Fig. 1.

RESULTS AND DISCUSSION

Result of powder test method showed that substitution of zirconia in soda-lime-glass improves the durability of glass. It is a powerful source against corrosion resistance of glass. ZrO2 is a network modifier rather a network former. ZrO2 not only takes part in the formation of silicate network but in addition it leaks the broken Si-O-Si bridges. Since zirconium oxide and hydroxide are much less soluble than silica, water can not easily hydrolyze the Zr-O-Si bonds therefore presence of Zirconium prevents the dissolution of nearly silicon (Karell et. al, 2006).

Table 1 represents the five experimental compositions A, B, C, D and E selected for study. From table 1 it is clear that all ingredients of batches are constant except CaO which was reduced gradually as zirconia was increased. (Mclellan and Shand, 1984) studies the effect of H2O, HCl and NaOH on the durability of different kinds of glasses. Table 2 represents the effect of 5% NaOH and 5% HCl. Both solutions were kept at 95oC for 24 hours. WLTM showed extraction of alkali in 5% NaOH is higher as compared to HCl. Table 3 represents the attack of H2O and H2SO4 at 90oC for four hours. The results showed that leaching of alkali in both cases is high. Table 4 represents extraction of alkali is reduced to very low level due to the addition of zirconia.

From this table it is worth noting that the small amount of Zirconia has decided influence on the extraction of alkali. When 1% zirconia (ZrO2) was added in glass the extraction of alkalis suddenly reduced from 0.009 to 0.004% when further addition is made i.e. 2%, the extraction of alkali is further reduced but this reduction in extraction of alkali is less than the amount of extraction

Table-1. Composition of glasses melted for durability

Glass###SiO2###Na2O###K2O###Ca###Al2O3 %###ZrO2 %

###%###%###%###O

A###70###15###2###11###2###0

B###70###15###2###10###2###1

C###70###15###2###9###2###2

D###70###15###2###8###2###3

E###70###15###2###7###2###4

Table-2. Weight Loss in strong Alkali and Strong Acid

Glass type###Corning###Weight loss in 24 hr at 95 C

###glass no.###(mg/cm2)

###In 5%###In 5% HC1

###NaOH

Soda lime###0081###2.0###0.02

Soda-lime###0088###2.0###0.01

Lead###0010###4.0###0.02

Lead###0120###4.0###0.01

Lime###0281###4.0###0.01

Aluminosilicate 1720###2.0###0.3

Aluminosilicate 1723###1.0###0.4

Borosilicate###7740###5.0###0.005

Borosilicate###7800###4.0###0.005

High-silica###7900,###2.0###0.001

###7940

Table-3. Corrosion (Alkali Extracted) in Water and Dilute Acid

Glass type###Corning###Na2O leached out in 4 hr at

###glass no.###90oC (ug/cm)

###In H2O###In 0.02 N

###H2SO4

Soda lime###0081###4###5

Soda-lime###0088###1###1

Lead###0010###3.0###10.0

Lead###0120###1.0###5.0

Lime###0281###2.0###2.0

Borosilicate###7740###0.1###0.3

Borosilicate###7800###0.1###0.3

High-silica###7900, 7940###less than 0.01###less than 0.01

Table-4. Effect of ZrO2 on the resistance of glasses

Glass###ZrO2###Na2O###Remarks

No.###%###extracted

###%

A###0###0.009###

B###1###0.004###Alkali extraction difference

###between A and B is 0.005%

C###2###0.003###Alkali extraction difference

###between B and C is 0.001%

D###3###0.002###Alkali extraction difference

###between C and D is 0.001%

E###4###0.002###Alkali extraction between D

###and E difference is zero

and E difference is zero

when zirconia was 1%. Table 4 shows as the amount of zirconia is progressively increased the extraction of alkali decreases until it reaches least value of 0.002% which is so least i.e. near to zero. Addition of ZrO2 can not be increased beyond 4% because above this limit the glass slightly becomes Opal (i.e. crystallization of glass started). Higher amount of Zirconia also increases viscosity, melting temperature and duration of melting (Karell et. al, 2006). The limit of substitution 4% ZrO2 is quite ideal because our target to make glass durable is successfully achieved. This can be more clearly be understood by plotting the percentage of zirconia against the reciprocal of the percentage of alkali extracted. The reciprocal values might be termed as the "resistance to corrosion". Fig. 1 shows that resistance is a reasonably progressive and regular one. So according to Table 4, Glass E is excellent durable glass which is quite suitable for packing and storage of pharmaceuticals and corrosive chemicals.

Conclusion: Good quality soda-lime-glass can be made economically durable with minimum addition of 4% ZrO2. If ZrO2 is added more than 4% it will create crystallization in glass and glass turned slightly towards opacity.

Acknowledgement: The help of Mr. Muhammad Amin, PTO, Muhammad Hussain Sr. Tech., Abdul Ghafoor, Sr. Tech. and Muhammad Ali, Furnace Builder in fabrication of clay crucibles, glass melting and in mechanical work is acknowledged.

REFERENCES

Anderson, P. R. and J.N. Rolen. Composition and properties of commercial glasses. J. Glass Tech., 23, 251 (1987).

Bukerman, W. A. Glass melting with zirconium silicate. Glass Sci. Tech., 66: 14 (2006).

Horak, W. and D. Sharp. Effect of ZrO2 on durability of glass. J. Amer Ceram. Soc., 53: 281 (2005).

Karell, R., Kraxner, J. and M. Chromcikova. Properties of selected Zirconia containing silicate glasses Ceramics-Silkaty 50: 778 (2006).

Machacek, J. Effect of fluxes on glass melting. Phys. Chem. glasses., 44: 308 (2002).

Mclellan, G. W. and E. B. Shand. Chemical durability of glass. Glass Engineering Hand Book. 3rd Ed. McGraw-Hill New York. P 30 (1984).

Sempere, R. Melting of technical glasses. Phys. Chem. Glasses., 44: 303 (2004).

Stadler, L. and C. David. Container glass compositions. Glass Ind., 59: 10 (2000).

M. Saadet, K. Javed, W. A. Shah and M. B. Bhatty

PCSIR Laboratories Complex, Lahore - Pakistan. - Corresponding author e-mail: khalidpcsir@gmail.com
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Publication:Pakistan Journal of Science
Article Type:Report
Geographic Code:9PAKI
Date:Sep 30, 2011
Words:1955
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