Thermal measuring and testing – Differential thermal analysis
Reexamination Certificate
1999-01-15
2001-04-24
Bennett, G. Bradley (Department: 2859)
Thermal measuring and testing
Differential thermal analysis
C374S140000
Reexamination Certificate
active
06220748
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to testing of materials, and more particularly relates to a method and apparatus which utilize differential temperature measurements to determine characteristics of a material, such as the alumina concentration and sodium fluoride to aluminum fluoride ratio of an aluminum smelting bath.
BACKGROUND INFORMATION
Aluminum is conventionally produced by smelting in a Hall bath. During the smelting operation, it is desirable to control parameters such as the temperature of the bath and to determine the composition of the molten aluminum in the bath. However, the methods that are currently used to measure the alumina concentration and sodium fluoride to aluminum fluoride ratio (NaF:AlF
3
) of the bath are confined to laboratory batch tests. Such laboratory testing causes control measurements to be made several hours after sampling, with little indication of current process conditions.
A probe that measures the bath and liquidus temperatures of a Hall bath during processing has been developed by Heraeus Electro-Nite, and is commercially available under the designation Cry-O-Therm. The probe includes a single thermocouple that is submerged in the molten bath. The Cry-O-Therm vibrates the sample during cooling to cause nucleation of the bath during cooling. An abrupt change in the slope of the cooling curve while the sample is being vibrated is taken as the liquidus. The difference between the pot temperature and the liquidus is taken as the super heat of the bath. However, this type of probe does not measure the NaF:AlF
3
ratio, which is critical for accurately determining the liquidus and alumina concentration.
The present invention has been developed in view of the foregoing and to address other deficiencies of the prior art.
SUMMARY OF THE INVENTION
A method and apparatus for timely and accurate measurement of material parameters are provided. A test sensor measures the temperature of a sample of material as it is heated up and/or cooled down. A reference sensor is used to obtain differential temperature measurements as the temperature of the test sample is varied. A differential temperature trace is generated and analyzed in order to determine various characteristics of the material being tested. In one embodiment, the sodium fluoride to aluminum fluoride ratio (NaF:AlF
3
) and alumina concentration in a Hall bath aluminum smelting operation are determined in order to efficiently control smelting of aluminum metal. In this embodiment, bath temperature and liquidus temperature may be measured and compared in order to determine the amount of superheat of the bath and to prevent the operation of smelters at higher temperatures than necessary.
An aspect of the present invention is to provide a method of testing a molten material. The method includes the steps of contacting the molten material with a reference sensor and a test sensor, removing the reference and test sensors from the molten material, measuring a temperature difference between the reference and test sensors as the sensors cool down, and determining at least one characteristic of the material based on the differential temperature measurement.
Another aspect of the present invention is to provide a material testing probe comprising a support member, a reference material carried by the support member, a reference material temperature sensor in communication with the reference material, a test sample container supported by the support member, a test sample temperature sensor carried by the support member and an analyzer which determines the temperature difference between the reference material and the test material.
These and other aspects of the present invention will be more apparent from the following description.
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Fisher Instrument Manufacturing Division, Bulletin 10-560, Mar. 1966.*
Heraeus Brochure, “Bath and Liquidus Temperature Measurement System For the Aluminium Industry”; Jan. 1998.
Alcoa Inc.
Bennett G. Bradley
Topolosky Gary P.
Towner Alan G.
Verbitsky Gail
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