| Find out below
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After the
firing, what's next?
In most cases the fired purifiers are ready to be sealed into their plastic components, however there may be a prior need for finishing of the ceramics. Kiln temperature & purifier design See below The good appearance of the candles is critical to the acceptability of the user groups. For example, a number of recent candles turned black, due to exposure of the colloidal silver to excess light, during the drying process. We have anticipated that most users would prefer the uniform, terra cotta candles, and the problem was solved for subsequent candles. Another area in which proper finish of the ceramic component is important concerns the proper seal of the plastic cover caps, using the white cement. The rough surface of the lower candle is in contrast to the smooth, upper candle. In this case the lower candle was finished with sand paper after having been fitted to the cover caps. |
| There is nothing wrong with either the rough or the smooth surfaced
candles, per se. For the rough candle this may be appropriate when
the water to be filtered is free of the particles, i.e. total suspended
solids. On the other hand the smooth surface is appropriate for turbid
water, where particles collect on the surface over time. Then there
is the need for periodic brushing, in order to remove the particles.
So a choice needs to be made, as to whether or not to finish with sand
paper. Another factor to consider here is that the candles with rough
surfaces give substantially more flow than is the case with smooth surfaces.
It is worth considering the need to alter the variables so as to get the desired flow rate following sanding. For example, firing at a lower temperature may reduce flow rate of resultant candles. Then the surface is sanded so as to increase the flow rate. All told there are a large number of variables which contribute to either an increase or a decrease in the flow rate, and balancing these helps the producer arrive at that flow which is desired. In order to produce purifiers,
Numbers 7. and 8. above indicate the use of silver treated grog for particulate purifier canisters. In both of these cases a kiln is not required. Rather it is possible to crush common red brick, of the type used for housing construction. The the resultant particles are sized so as to give optimal flow rates. And these materials are saturated with either colloidal silver or AgCL, for example. This kind of production can be initiated without a lot of capital expenditure. The key component is the insurance that quality control will be maintained. What about kiln temperature and purifier design? If choosing to produce pottery purifiers that are kiln fired it is important to understand what effect increasing temperature has on the product. Two of the attributes are increased strength and an improved rate of flow. An increase of strength is brought about by the formation of ceramic crystals, which become small and tighter with increased temperature. For the same reason the higher temperatures also account for the improved flow rates. This holds true upto the 'maturing temperature,' which is optimal per the particular pottery clay in use. It is helpful, also, to understand that the typical terra cotta color of pottery clay is brought about by the presence of iron. This iron has the effect of reducing the maturing temperature, so with more iron there's a lower maturing temperature. Correct maturing temperature is determined empirically, with the understanding that excess temperature burns the ware turning it black and bringing about a glassy phase. |
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Firing of the grog disks should be undertaken with care, in the range of 450 to 550C. Going through this range too quickly will cause too rapid a burn off of the grog combustibles, small explosions resulting. The grog will then end up in a pile on the floor of the kiln, not having received a uniform temperature. |
| However, for purifier production it is not necessarily a requirement to achieve the maturing temperature. Whereas 1000C is mid range for most pottery clays, firing to as low as 800 or even 750C may also prove to give good quality purifiers. This is because a thick wall will also contribute to the good strength of the pottery purifiers. In most cases the purifiers are not less than 2.5 cms. thickness. This is about double the wall thickness of most of the candles found in the market, also considered advantageous because of a greater opportunity for pathogens to get trapped within the medium. So great a thickness also allows more contact time of bacteria with silver. It has been well documented that purifiers of thicker wall do have higher removal rates for the bacteria, and contrary to popular belief the thick wall is not necessarily an inhibition to increased flow. |
For questions or observations please contact:
Reid Harvey
pottery@wlink.com.np
