The Figurovsky instrument is based on a glass hydrostatic microbalance, which can continuously weigh the weight of the sediment deposited on the bottom of the dish when it settles. This instrument can even be used to detect extremely thin suspensions (0.2~0.001% of the total weight of the dispersed phase) that cannot be detected by the other instruments mentioned above.
This apparatus (Fig. 29) consists of a quartz or broken glass balance beam .1 whose thick end (an elongated glass rod) is rigidly fixed to a stable frame.
Depending on the sensitivity required, the length of the balance beam can vary from 20 to 50 cm. The diameter of the wide part of the balance beam is 21.3mm, and the diameter of the narrow part is about 0.2~0.4mm.
One end of the balance beam 1 has a small fishing rod, and there is a long glass holder 2 on the fishing rod, and a glass dish 3 with a dish edge height (the dish edge is rolled up) 4 to 5 millimeters and a thickness of 0.2 to 0.5 millimeters is hung on the structure.
When loaded, the entire length (full length) of the balance beam should be deformed; if the change of the load is not too large, it can fully comply with Hooke's law, that is, the deformation of the balance beam is proportional to the load.
During the test, the change of the balance beam deformation can be recorded by direct reading microscope or height difference meter.
The sensitivity of the instrument depends on the length and thickness of the balance beam. If the displacement of one end of the balance beam caused by a load of 10-1~10-5 corresponds to one degree on the microscope scale, such deformation sensitivity is sufficient for practical applications.
With the degree of dispersion of suspended particles or the speed of sedimentation, the height of sedimentation can also be changed. When dealing with coarsely dispersed suspensions containing particles with a radius of 40-60 µ, the height of the sinking should not be lower than 50-80 cm; when testing highly dispersed suspensions, the height can be limited to 5-6 cm. The procedure for measuring the degree of dispersion of pigments is as follows. Generally, 0.2~2.0 g/L of pigment is weighed and spread in a glass cylinder (5~6 cm in diameter and 15~30 cm in height) filled with water for sedimentation.
Stir the suspension with a glass rod for 3 to 5 minutes, and one end of the glass rod is fixed with a rubber head slightly smaller than the cylinder. Stirring is carried out by moving the stirrer up and down.
Immediately after the stirring is finished, put the glass dish suspended on the hook of the balance beam into the buoyant liquid, and set the number on the microscope immediately when the balance beam stops vibrating.
Pay attention to the movement of the scale mark (the scale mark moves by one degree or several degrees on the microscope scale), and read the scale continuously as the dispersed phase settles from the suspension.
The sediment analysis process is considered complete when the floating liquid is completely clear or one end of the balance beam has not been displaced within one hour.
During the test, it is necessary to pay great attention to the temperature of the suspension, and be careful not to evaporate the dispersion medium during the test, and at the same time, pay attention not to accumulate air bubbles under the glass dish that may affect the accuracy of the microscope.
According to the obtained data, a sedimentation curve diagram showing the relationship of Q=f(t) is obtained.
Time (t) is represented on the plot axis, and the deformation value of the balance beam proportional to the weight of the sediment sunk into the balance dish (0) since the beginning of the test is represented on the ordinate.
The size of the particles, as well as the relative content of particles of different sizes, are
(Fig. 30) and measure after drawing the slit. Through the image correction of the precipitation curve, the particle grouping (distribution) curve of the dispersion system can be obtained (Figure 31). Each group of particles can be expressed in a shape, the bottom of the rectangle represents the radius range of the group of particles, and the height of the rectangle is a scientific value, that is, the content of the group of particles in the whole system (converted into the dispersion of the unit radius range) percentage of the total phase).
