Is the conversion between refractive index and temperature 0.0004 per degree increase
Temperature correction of refractive index
Generally speaking, when the temperature increases by one degree, the refractive index of liquid organic compounds decreases by 3.5 × 10-4-5.5 × 10-4. Some liquids, especially when the temperature of the refractive index to be determined is close to its boiling point, have a temperature coefficient of up to 7 × 10-4. In practical work, the refractive index measured at one temperature is often converted into the refractive index at another temperature. For ease of calculation, 4.5 is generally used × 10-4 as a temperature change constant. The rough calculation may result in slight errors, but it has reference value. In other words, the refractive index decreases with the increase of temperature, and for every 1 degree change in Celsius temperature, the refractive index changes by approximately 0.00045. We can calculate the refractive index corrected to 20 ℃ using the following formula: nD (t)=nD (20) -0.00045 (t-20 ℃)
Among them, nD (t) is the refractive index measured experimentally at temperature t. This indicates that when the experimental temperature is higher than 20 ℃, nD (20) is larger than nD (t); When the experimental temperature is below 20 ℃, nD (20) is smaller than nD (t).
Example: Given nD (t)=1.3667, t=25.2 ℃, calculate nD (20).
ND (t)=nD (20) -0.00045 (t-20 ℃)
ND (20)=1.3667+0.00045 (25.2 ℃ -20 ℃)
=1.3667+0.00045 × five point two
=1.36904
Factors affecting refractive index
The Influence of Light Wavelength
The refractive index of a substance varies depending on the wavelength of light, with longer wavelengths having lower refractive indices and shorter wavelengths having higher refractive indices. The measurement time source is usually white light. When white light undergoes refraction through a prism and sample solution, the degree of refraction varies due to the different wavelengths of each colored light. After refraction, it decomposes into multiple colored lights, which is called dispersion. The dispersion of light can blur the boundary between light and dark in the field of view, resulting in measurement errors. In order to eliminate dispersion, a dispersion compensator is installed at the lower end of the observation lens tube of the Abbe refractometer.
The influence of temperature
The refractive index of the solution changes with temperature, and as the temperature increases, the refractive index decreases; The refractive index increases as the temperature decreases. The scale on the refractometer is engraved at a standard temperature of 20 ℃, so it is best to measure the refractive index at 20 ℃. Otherwise, temperature correction should be performed on the measurement results. When the temperature exceeds 20 ℃, add a positive number; When it is below 20 ℃, subtract the correction number.
