Thermoluminescence Study of Quartz Minerals

 Abstract:

The present paper reports the thermoluminescence(TL)study of Quartz minerals collected from the ceramic tiles manufacturing unit, Morbi, Gujarat. The natural thermoluminescence (NTL) as well as artificial thermoluminescence (ATL+NTL), by giving a 15Gy beta dose, was recorded for the collected sample.Then after Quartz mineral is  annealed and quenched from 250oC,4500C and 6500C temperature and irradiated by 25Gy beta dose   from Sr-90 beta source and then the  thermoluminescence was recorded. The TL results are very interesting regarding purity of the mineral.

Many natural mineral are used to manufacture floor tiles for household floorings. The demand of a variety of flooring materials has lead to develop various types of ceramic tiles. In India the ceramic industry is one of the fastest growing industries, more then 200 manufacturing units of ceramic tiles, vitrified tiles and sanitary wares are situated at Morbi (Rajkot District, Gujarat state, India). Many natural minerals are used as the raw materials for the manufacturing ceramic wares. The minerals used in manufacturing the ceramic tiles are Quartz, Feldspar, Zircon, Talc, Frit-O, Frit-T, Aluminium oxide, Sodium trypoly phosphate China clay, Bikaner clay, etc. Most of the minerals are from mines in Gujarat and few are from Rajasthan state and imported from Russia. The phenomenon of TL has been studied by many investigators. The thermoluminescence (TL) study in geology, particularly for natural minerals, is an important research tool.  The TL study of minerals commonly used in ceramic tiles industry, such as Quartz gives better understanding about their properties. The systematic study of TL of such minerals is helpful to solve the basic raw materials quality problem the ceramic tiles industries.

 Quartz:

The purest natural crystalline form of silica is quartz, containing more than 99.95% SiO2. The other abundant sources of silica are the acid igneous rocks, sands, sandstones and quartzite containing varying amounts of impurities. In all these raw materials SiO2 exists in the form of µ-quartz. Flint, which is a mixture of chalcedony and quartz, is also used as a source of silica in some countries.

Under optical microscope, quartz is identified by its colorless, nonpleochroic habit in plane polarized light; shape is commonly anhedral, often found as perfect euhedral crystal. It does not show any cleavage, but some conchoidal fractures are observed within the grains. Anisotropic under cross polarized light, quartz shows first order interference color which is highly variable (grey, yellow etc.). It gives adulatory or patchy extinction which is one of the most characteristic features of Quartz especially in metamorphic rocks. Refractive index is low, slightly higher than Canada balsam (1.55), the outline being feebly visible in plane polarized light. Quartz grains often show numerous tiny vitreous inclusions of other minerals. Quartz is distinguished from alkali Feldspar by its positive relief in balsam, lack of alteration and cleavage. Quartz lacks the multiple twinning of most Feldspar and differs from the untwined oligoclase by uniaxial figure and lack of cleavage.

Quartz is widely used in the manufacture of soda-lime-silica glass and white wares. Quartzite containing about 98% SiO2 are used for the manufacture of silica bricks, used in steel making furnaces, specially at the roof of an acid open-hearth, checkers, converter etc. They are also used in coke-ovens and the roof of glass tank furnace. For refractory use, the combined Al2O3 and TiO2 should be < 2.5% and for superior qualities < 1%. With Na2O and K2O < 0.1% CaO <  0.3% and MgO < 0.1%, quartzite are considered to be of suitable quality.

The pure, untwined, clear and transparent quartz crystals possess piezo-electric properties and are used in telecommunication. Quartz is also the source of element silicon, used in the manufacture of non-oxide ceramics (e.g. SiC, Si3N4) and ferro-silicon.

 Experimental method:

Thermal annealing for the specimen was carried out in the muffle furnace. The laboratory muffle furnace has temperature range up to 1200oC and the size of chamber for sample heating was 22cm ´ 10cm ´ 10cm. The temperature was maintained with ±1oC accuracy using a temperature controller, which supplied required current to the furnace. Power supply of 230V was provided to the furnace. A silica crucible containing a powdered form of virgin specimens was kept in the furnace at required annealing temperature for desired time. After completion of annealing duration the specimens were rapidly air-quenched to room temperature by withdrawing the Alumina crucible on to a ceramic block. Such material or specimens are called “annealed and quenched” or “thermally pre-treated specimen”.

(High temperature Furnace and taking out the sample from high temperature furnace)

                (TL Set-Up)                                         (Kanthal strip&Sr-90 Beta source)
The natural Quartz minerals used in manufacturing   ceramic tiles are collected from the industry. Most of the materials used for the TL analysis were indigenous ones and a few were imported minerals. TL of Quartz mineral was recorded using TL set-up supplied by Nucleonix Systems, Hyderabad [1]. Irradiation was carried using Sr-90 beta source. Equal quantities of samples (5 mg) were used for the analysis.
 Results and discussion :  

Fig 1.1 is the TL of 5mg of weighed powder was taken to record TL glow curve of Quartz (NTL) without any pre heat treatment and irradiation. The glow curve exhibit one hump like glow peak at temperature at 3320C.  There is no good TL is observed.
Fig.1.2 shows TL glow curve of Quartz irradiated with beta dose of 25 Gy using Sr90. Here one peak occurs at temperature 1100Cand intensity of 1.83au here little TL is recorded. It is noted that after irradiation one trap developed and released carrier during the TL measurement.

Fig1.3                                                         Fig.1.4

Fig. 1.3 is the TL glow curve of Quartz annealed and quenched from  2500C and given a beta dose of 25 Gy using  Sr-9o beta source TL  glow curve of 250oC AQ sample of Quartz exhibits  one well resolved peak around 109oC.

Fig. 1.4 is the TL glow curve of Quartz annealed and quenched from  4500C and given a beta dose of 25 Gy using  Sr-9o beta source. TL glow curve of 450oC AQ sample of Quartz exhibits  one well resolved and isolated TL peak  with high intensity around 100oC.  This peak is interesting TL peak in  dosimetric point of view. Fig. 1.5 is the TL glow curve of Quartz annealed and quenched from  6000C and given a beta dose of 25Gy using  Sr-9o beta source.   TL  glow curve of 650oC AQ sample of Quartz exhibits  one well resolved and isolated TL peak  with high intensity around 102oC.  This peak is interesting TL peak in dosimetric point of view.

Table-1 shows the peak temperature and peak intensity of Quartz at different annealing and quenching temperature irradiated with beta source of 15Gy by Sr90 .

Fig. 1.10 shows the TGA of Quartz from the TGA it is clear that variation seen in phase between temperature range 4000C and 8000C

Fig. 1.11 shows the X RD pattern of Quartz it is clearly matches with the standard peaks observed at 26.66, 20.88, 50.18 and 60 o are major peaks of standard quartz sample. 

Conclusion:

• The natural TL [NTL] observed in both the minerals under study as well as NTL+ATLfollowed by the TL observed from annealed and quenched form 2500C and 450oC and 650oC followed by beta irritation leads to the conclusions this may be due to traps formed due to irradiation as well as heat treatment subjected  to the mineral.
• The TL study of mineral Quartz sample treated with different annealing and quenching temperature at 2500C, 4500C,and 6500C  irradiated with beta source given a dose of 15Gy by Sr90  gives remarkable result. The maximum TL intensity exhibits by the sample when it treated with AQ 4000C and irradiated with beta source by giving a dose of 25Gy,at this point peak temperature is recorded 1000C and intensity of 100au,the peak at 1000C temperature is well resolved and it is important for study of TL dosimetric point of view.
• The systemic study may be more useful in checking the purity of the raw materials which in turn leads to improving the quality of ceramic tiles in ceramic industries. Further studies are in progress.

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