Thermal measuring and testing – Transformation point determination – By change in optical property
Reexamination Certificate
1999-05-13
2002-09-03
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Transformation point determination
By change in optical property
C374S023000, C250S341100, C250S341600
Reexamination Certificate
active
06443616
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention resides in the area of apparatuses used for the determination of melting points of materials and more particularly relates to an apparatus which determines the melting point of a sample material by measuring the change in rate of wave transmission through the sample material and noting the temperature at which such change occurred.
2. Description of the Prior Art
Many devices are used to determine melting points of materials. The simplest are types where an observer notes the temperature at which a material, upon heating, becomes transparent. Such devices first involve immersing a particle of the material whose melting point is to be determined in a non-solvent which is heated at a known rate. As the heat from the medium is transferred into the particle, at the point where the temperature of the medium is equal to the melting point of the particle, the particle melts and changes its optical transmissibility. The recording of the temperature of the sample material while an observer monitors the reflectivity of light directed at such material is known in the art. A problem with many of these prior art melting point determination methods is that they lack accuracy in that they require the judgment of an observer as to when such a reaction has taken place, and this judgment can vary from observer to observer.
U.S. Pat. No. 5,092,679, by the present inventor, disclosed an apparatus and method that automatically records measurements of both light reflectivity and temperature of a material to determine its melting point. This invention also disclosed means for recording deformation of materials at various pressures.
Melting points are very important in determining a material's purity, especially in synthetic chemistry. The finer the melting point determination can be made, then the more accurately a purity determination can be made. This is especially helpful in the pharmaceutical industry where impurities may skew efficacy test results. Melting point apparatuses must be carefully designed to avoid any built-in accumulation of error.
SUMMARY OF THE INVENTION
It is an object of the device of this invention to determine the melting point of a sample material utilizing a light or infrared heat source and a photocell along with an electronic non-contact infrared thermometer.
It is a further object of this invention to provide a device that can also determine melting point as it relates to pressure on the sample material. It is important that pressure be considered when determining the melting point of some materials because under different pressures, a material may have a variety of states which affect its melting point.
In one embodiment, the device of this invention utilizes a powder made from the sample material that is to have its melting point determined. The powdered sample material is placed on a transparent glass slide on a stage above an infrared spot heater. Heat is then applied to the slide from below by the infrared spot heater, and the temperature of the sample material is measured by an infrared thermometer positioned above the sample material. The temperature of the sample material detected by the infrared thermometer can be continuously recorded. Around the infrared thermometer are disposed a plurality of photocells positioned to receive infrared waves which pass through the sample material. As the heat, which is increasing at a programmed ramped rate from the infrared spot heater, is directed on the sample material from below, the temperature of the sample material rises until the sample material melts, becomes fluid and spreads out, changing its transmissivity, i.e. percent of transmission of the infrared waves, such infrared waves passing through the slide and sample material thereon to be then detected by the photocells. When the photocells sense the change in rate increase or spike in the infrared rays, this change indicates that the temperature as then detected by the infrared thermometer at that point in time corresponds to the melting point of the sample material. A computer and chart recorder are attached to both the infrared thermometer and the photocells to record the activity of both to aid in determining the melting point of the sample material. It should be noted that multiple spectral bands and detectors other than infrared can be used in the apparatus of this invention.
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ASTM D 1525-58 T, “Tentative Method of Test for Vicat Softening Point of Plastics”, pp. 559-561, 1958.
Gutierrez Diego
Nitkin William
Pruchnic Jr. Stanley J.
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