A method for preparing a density gradient column

Abstract

The present invention relates to a method for preparing a density gradient column, comprising the following steps: determining the number and density of the required floats according to the bulk density range of the product to be measured; selecting a first drug and a second drug according to the product to be measured; first determining the density values of the highest liquid level and the lowest liquid level of the mixed liquid in the density gradient tube; wherein the mixed liquid is formed by mixing a first liquid and a second liquid, and the density of the first liquid is lower than that of the second liquid; thereby further determining the density preparation value of the first liquid and the density preparation value of the second liquid in the mixed liquid at the target control temperature; preparing the first liquid and the second liquid by mixing the first drug and the second drug according to the density preparation values; filling the prepared floats, the first liquid and the second liquid into the density gradient tube to prepare a density gradient column. According to the method for preparing a density gradient column provided by the present invention, a linear density gradient column within the target density gradient range can be quickly prepared at one time.

Description

Technical Field

[0001] The present invention relates to the technical field of bulk density detection, and particularly to a method for preparing a density gradient column. Background Art

[0002] In the field of carbon fiber production, the detection of bulk density indexes is indispensable for its precursor raw silk (i.e., carbon fiber raw silk), intermediate product pre-oxidized fiber, and product carbon fiber and graphite fiber. Currently, there are mainly three methods for detecting the bulk density of carbon fiber: liquid displacement method, floating and sinking method, and density gradient column method, and the implementation standard is GB / T30019. Among them, the main principle of measuring the bulk density of carbon fiber by the density gradient column method is: testing according to the equilibrium position of the observed sample in the liquid column with linearly increasing density. The bulk density measured by this method is more accurate than the other two methods. However, it is rather cumbersome and difficult to configure a liquid column (density gradient column) with uniformly increasing density from top to bottom.

[0003] Regarding how to configure a density gradient column with linearly increasing density from top to bottom using two liquids with different densities, one high and one low, GB / T30019 standard gives the typical drugs used for configuring the density gradient column and the corresponding density ranges, and also gives the basic method for preparing the density gradient column.

[0004] However, the inventors of the present invention found that the content given in the GB / T30019 standard is too broad, and the recommended drugs are not comprehensive. The target range for configuring the density gradient column using the method described in this standard completely relies on empirical operation, and beginners basically cannot accurately configure a density gradient column within the target range at one time according to the method provided by this standard. Therefore, a simple, fast, and accurate method for preparing a density gradient column is needed to improve the detection efficiency of the bulk density of different products. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing a density gradient column. The main purpose is that according to this method, a linear density gradient column within the target density gradient range can be quickly prepared at one time.

[0006] To achieve the above object, the present invention mainly provides the following technical solutions:

[0007] On the one hand, an embodiment of the present invention provides a method for preparing a density gradient column, which includes the following steps:

[0008] Float preparation step: determining the number and density of the required floats according to the bulk density range of the product to be measured;

[0009] Drug selection steps: Select a first drug and a second drug that can be mutually soluble to form a stable mixture according to the product to be measured; wherein, the bulk density of the first drug is lower than the bulk density of the product to be measured; the bulk density of the second drug is higher than the bulk density of the product to be measured;

[0010] Determination and preparation steps: First, determine the density value of the highest liquid level and the density value of the lowest liquid level of the mixture in the density gradient tube; wherein, the mixture is composed of a first liquid and a second liquid, and the density of the first liquid is lower than the density of the second liquid; therefrom, further determine the density preparation value of the first liquid and the density preparation value of the second liquid in the mixture at the target control temperature; according to the density preparation values, prepare the first drug and the second drug into the first liquid and the second liquid;

[0011] Density gradient column filling steps: Fill the prepared float, the first liquid and the second liquid into the density gradient tube to prepare a density gradient column.

[0012] Preferably, in the float preparation step: According to the bulk density range of the product to be measured, the detection accuracy requirement, the target position where the float with the largest density floats in the density gradient column, and the target position where the float with the smallest density floats in the density gradient column, select the number of floats and the density of each float; preferably, the number of floats is 5-8; preferably, after selecting the floats, the floats need to be pretreated; wherein, the pretreatment steps include: If the float is used for the first time, the float needs to be soaked in deionized water for 20-26 hours first, and then soaked in the first drug for 4-8 hours; if the float is not used for the first time, directly soak the float in the first drug for 4-8 hours.

[0013] Preferably, in the drug selection steps: If the product to be measured is any one of carbon fiber, pre-oxidized fiber, and graphite fiber, the first drug is selected as carbon tetrachloride or tetrachloroethylene; the second drug is selected as 1,2-dibromoethane; if the product to be measured is carbon fiber precursor, the first drug is selected as xylene; the second drug is selected as carbon tetrachloride or tetrachloroethylene.

[0014] Preferably, in the determination and preparation steps: According to the maximum density value, the minimum density value of the selected floats, and the target positions of the floats in the density gradient tube, calculate the density value of the highest liquid level and the density value of the lowest liquid level of the mixture in the density gradient tube; preferably, the density value of the highest liquid level = ρ 最小 - unit density difference; the density value of the lowest liquid level = ρ 最大 + unit density difference; wherein, ρ 最大 is the maximum density value of the selected floats, with the unit of g / cm 3 ; ρ 最小 is the minimum density value of the selected floats, with the unit of g / cm 3; wherein, the unit density difference refers to the density difference at a liquid level of 10 cm, and the calculation formula is as follows: unit density difference = (ρ 最大 -ρ 最小 )÷h; wherein, h refers to the multiple of the 10 cm height value between the target positions of the float with the maximum density value and the float with the minimum density value in the density gradient tube; preferably, h is 5; preferably, the float with the maximum density value and the float with the minimum density value are located at the 10-60 cm of the scale of the density gradient tube.

[0015] Preferably, in the determination and preparation step: the density range of the mixed liquid in the density gradient tube is C1-C2; wherein, C1 is the density value at the highest liquid level, with the unit of g / cm 3 , and C2 is the density value at the lowest liquid level, with the unit of g / cm 3 ; at the target control temperature, the prepared density value ρ1 of the first liquid is: C1×0.985±0.001 g / cm 3 ; at the target control temperature, the prepared density value ρ2 of the second liquid is: C2×1.025±0.001 g / cm 3 .

[0016] Preferably, in the determination and preparation step: according to the prepared density value of the first liquid and the prepared density value of the second liquid at the target control temperature, the first drug and the second drug are prepared into the first liquid and the second liquid; wherein,

[0017] The steps for preparing the first liquid are as follows: Take V1 mL±2 mL of the first drug in a clean 1000 mL graduated cylinder, and then add the second drug to the highest scale line of the graduated cylinder, and stir evenly to obtain the first liquid; wherein, V1 is determined by the following formula: ρ1×1000 = ρ 第一药品 ×V1+ρ 第二药品 ×(1000-V1); wherein, ρ1 is the prepared density value of the first liquid; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 ;

[0018] The steps for preparing the second liquid are as follows: Take V2 mL±2 mL of the second drug in a clean 1000 mL graduated cylinder, and then add the first drug to the highest scale line of the graduated cylinder, and stir evenly to obtain the second liquid; wherein, V2 is determined by the following formula: ρ2×1000 = ρ 第二药品 ×V2+ρ 第一药品 ×(1000-V2); wherein, ρ2 is the prepared density value of the second liquid; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ第二药品 The density of the second drug at room temperature, g / cm 3 .

[0019] Preferably, in the data determination and preparation step: ρ is calculated according to the following formula 第一药品 , ρ 第二药品 : ρ 第一药品 = ρ 第一药品25℃ + 0.002×(25 - T); ρ 第二药品 = ρ 第二药品25℃ + 0.002×(25 - T); where T is the room temperature, °C; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第一药品25℃ is the density of the first drug at 25°C, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 ; ρ 第二药品25℃ is the density of the second drug at 25°C, g / cm 3 .

[0020] Preferably, before the density gradient column filling step, an instrument preparation step is further included; wherein, the instrument preparation step includes:

[0021] Installation step: Install the prepared density gradient tube on the test tube bracket of the water bath;

[0022] Filling the float step: Load the prepared float into the bottom of the density gradient tube; Preferably, put the prepared float into the fishing basket of the fishing device, turn on the instrument descent switch, lower the fishing basket to the bottom of the density gradient tube, and cover the tube mouth;

[0023] Water filling and temperature control step: Connect the water bath to the temperature regulating device; Fill the water bath where the density gradient tube is located with deionized water; Set the water bath temperature to the target control temperature; Preferably, the water level in the water bath filled with deionized water should be higher than the liquid level of the mixed liquid in the density gradient tube;

[0024] Preparing the liquid dispensing tube step: Rinse the liquid dispensing tube with the first drug multiple times, and connect one end of the liquid dispensing tube to the outlet of the peristaltic pump; Preferably, put the other end of the liquid dispensing tube into a clean container first;

[0025] Preparing the liquid dispensing bottle step: Prepare the first liquid dispensing bottle, the second liquid dispensing bottle and the connecting tube.

[0026] Preferably, the density gradient column filling step includes:

[0027] 1) Assemble the first liquid dispensing bottle, the second liquid dispensing bottle, the connecting tube and the peristaltic pump so that the second liquid dispensing bottle, the connecting tube, the first liquid dispensing bottle, the peristaltic pump and the liquid dispensing tube are connected in sequence;

[0028] 2) Inject the first liquid into the first liquid dispensing bottle and the second liquid into the second liquid dispensing bottle; Turn on the stirring rotor of the first liquid dispensing bottle;

[0029] Preferably, adjust the liquid inlet speed to 0.8 - 1.2 L / h; More preferably, it is 1.0 L / h;

[0030] Preferably, turn on the peristaltic pump and discharge about 50 - 75 mL of the first liquid through the liquid dispensing tube to remove the air bubbles in the liquid dispensing tube and the connecting tube;

[0031] 3) Turn off the peristaltic pump, open the valve between the first liquid dispensing bottle and the second liquid dispensing bottle, so that the second liquid flows from the second liquid dispensing bottle to the first liquid dispensing bottle, mixes with the first liquid in the first liquid dispensing bottle, and determine the mixing time according to the valve opening to obtain a mixed liquid with a certain density; During the set mixing time, insert the liquid dispensing tube through the tube cap of the density gradient tube to the bottom of the density gradient tube;

[0032] Preferably, the mixing time is 3 - 5 min;

[0033] 4) Turn on the peristaltic pump to pump the mixed liquid in the first liquid dispensing bottle into the density gradient tube at a set constant liquid inlet speed; At this time, the liquid density in the first liquid dispensing bottle is gradually increasing; When the mixed liquid in the density gradient tube fills to the height of the highest liquid level of the target liquid, turn off the peristaltic pump; Preferably, further turn off the stirring rotor knob in the first liquid dispensing bottle and the valve on the connecting tube;

[0034] Preferably, when the liquid levels in the first liquid dispensing bottle and the second liquid dispensing bottle are close and it is visually observed that there is no obvious liquid inlet from the second liquid dispensing bottle to the first liquid dispensing bottle, turn on the peristaltic pump;

[0035] Preferably, when pumping the mixed liquid in the first liquid dispensing tube into the density gradient tube at a set constant liquid inlet speed: The liquid in the second liquid dispensing bottle is always flowing into the first liquid dispensing bottle and is continuously stirred and mixed to gradually increase the density of the mixed liquid in the first liquid dispensing bottle;

[0036] Preferably, the constant liquid inlet speed is 0.8 - 1.2 L / h; More preferably, it is 1.0 L / h.

[0037] 5) Remove the liquid dispensing tube from the density gradient tube, cover the tube cap of the density gradient tube, and the preparation of the density gradient column is completed;

[0038] Preferably, it further includes: 6) Keep the prepared density gradient column in a water bath at a constant temperature for 23 - 25 h and then calibrate it for use.

[0039] Preferably, in the step 1): the first liquid is used to rinse the first liquid preparation bottle and the connecting pipe respectively, and the second liquid is used to rinse the second liquid preparation bottle; after rinsing, the first liquid preparation bottle and the second liquid preparation bottle are connected by the connecting pipe; wherein, one end of the connecting pipe on the first liquid preparation bottle is connected to the second liquid preparation bottle, and the other end is connected to the peristaltic pump inlet; confirm that the valve on the connecting pipe is in the closed state.

[0040] Preferably, when the feeding speed of the mixed liquid flowing from the peristaltic pump to the liquid distribution pipe is set to 0.9 - 1.1 L / h, preferably 1.0 L / h in the step 4): in the steps 3) - 4), the opening of the valve between the first liquid preparation bottle and the second liquid preparation bottle is set to 5 - 6 mm, preferably, the diameter of the connecting pipe is 5 - 6 mm.

[0041] Compared with the prior art, a method for preparing a density gradient column provided by the present invention has at least the following beneficial effects:

[0042] The embodiment of the present invention provides a method for preparing a density gradient column, specifically including steps of preparing a float (and how to prepare a float), selecting drugs, especially a method for preparing the first liquid (light liquid) and the second liquid (heavy liquid) from the first drug and the second drug (and providing a series of calculation formulas), and finally a density gradient column can be prepared through the density gradient column filling step; according to the solution of the present invention, a linear density gradient column within the target density gradient range can be prepared quickly and at one time.

[0043] A method for preparing a density gradient column provided by the embodiment of the present invention for the first time details the configuration method of a density gradient column when detecting the bulk density of products such as carbon fiber precursor filaments, pre-oxidized filaments, and graphite fibers by the density gradient tube method, filling a domestic blank, which helps the personnel of carbon fiber production enterprises to quickly prepare the corresponding target density gradient column by means of this method, with detailed, rigorous, simple, fast operation steps and high success rate.

[0044] The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following takes the preferred embodiment of the present invention and combines with the drawings to describe in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the preparation operation of a density gradient tube provided by the embodiment of the present invention.

[0046] Wherein, Figure 1The reference numerals in the figure are: 1, density gradient tube; 2, water bath; 3, float; 4, temperature control device (low-temperature constant temperature bath); 5, liquid preparation device; 6, highest liquid level of the density gradient tube; 7, lowest liquid level of the density gradient tube; 8, water bath liquid level; 11, fishing basket; 21, test tube clamp in the water bath; 22, test tube bracket in the water bath; 51, first liquid preparation bottle; 52, second liquid preparation bottle; 53, peristaltic pump; 54, valve; 55, connecting pipe; 56, liquid preparation pipe; 57, stirring rotor. Detailed implementation manners

[0047] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines the accompanying drawings and preferred embodiments to detail the specific implementation manners, structures, features and their effects of the application according to the present invention. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0048] Based on the fact that the method operation guidance given in GB / T30019 is not strong, the present invention proposes a method for preparing a density gradient column for measuring the bulk density by the density gradient tube method, which is effective for raw silk, pre-oxidized fiber, carbon fiber and graphite fiber. The main solutions are as follows:

[0049] This embodiment provides a method for preparing a density gradient column. By the bulk density value of the product to be measured, the target position of the product in the density gradient tube is designed, the float is selected and the drugs are used, and the preparation methods of the light liquid and the heavy liquid used for preparing the density gradient column are deduced inversely, and a detailed method for preparing the density gradient column is given, which includes the following steps:

[0050] Float preparation step: Determine the number and density of the required floats according to the bulk density range of the product to be measured; and perform pretreatment on the selected floats.

[0051] Among them, 1) According to the bulk density range of the product to be measured, the detection accuracy requirements, the target position of the float with the largest density suspended in the density gradient column, and the target position of the float with the smallest density suspended in the density gradient column, select the number of floats and the density of each float. The number of floats is preferably 5-8.

[0052] The details are as follows: When selecting the floats, in addition to the target value of the bulk density of the product to be measured, the detection accuracy of the bulk density should also be considered. For example, when the detection accuracy requirement of the bulk density of the product to be measured ≤ ±0.001 g / cm 3 , the overall density difference (bulk density) of the density gradient column is not greater than 0.05 g / cm 3 ; when the accuracy requirement ≤ ±0.002 g / cm 3 , the overall density difference is not greater than 0.14 g / cm 3, so as to determine the density values of the maximum and minimum floats of the density gradient tube. Preferably, the scale lines of commercially available density gradient tubes are 0.2 - 70 cm, and the scale resolution is 1 mm. To ensure the accuracy of the float detection data and avoid the influence of environmental factors on the floats, generally, the maximum and minimum density floats should be controlled to float within a height range of 50 cm, that is, the float with the minimum density is 10 cm away from the highest scale of the gradient tube, and the float with the maximum density is 10 cm away from the bottom. Preferably, when selecting the floats, the density values of several other floats should be determined according to the maximum and minimum densities of the floats. Further, generally, it is required that the selected floats are evenly distributed within the density gradient tube.

[0053] 2) After selecting the floats, the floats need to be pre-treated; among them, the steps of the pre-treatment include: if the float is used for the first time, it needs to be soaked in deionized water for 20 - 26 hours first, and then soaked in the first drug for 4 - 8 hours; if the float is not used for the first time, it is directly soaked in the first drug for 4 - 8 hours.

[0054] Drug selection steps: Select the first drug and the second drug that can be miscible to form a stable mixture according to the product to be tested; among them, the bulk density of the first drug is lower than the bulk density of the product to be tested; the bulk density of the second drug is higher than the bulk density of the product to be tested.

[0055] In this step: The selected first drug and second drug cannot change the properties of the product to be tested through (chemical) reaction or absorption.

[0056] If the product to be tested is any one of carbon fiber, pre-oxidized fiber, and graphite fiber, then the first drug is selected as carbon tetrachloride (d≈1.60 g / cm 3 ) or tetrachloroethylene (d≈1.63 g / cm 3 ); the second drug is selected as 1,2-dibromoethane (d≈2.166 g / cm 3 ).

[0057] If the product to be tested is carbon fiber precursor, then the first drug is selected as xylene (d≈0.86 - 0.90 g / cm 3 ); the second drug is selected as carbon tetrachloride (d≈1.60 g / cm 3 ) or tetrachloroethylene (d≈1.63 g / cm 3 ).

[0058] Instrument preparation steps: This step includes the following steps:

[0059] Installation step: Place the prepared clean density gradient tube on the test tube bracket of the water bath without water, and clamp it with the supporting clip.

[0060] Steps for filling the float: Place the selected and pre-treated float into the fishing basket of the fishing device, turn on the instrument's descent switch, lower the fishing basket to the bottom of the density gradient tube, and cover the tube mouth.

[0061] Steps for filling with water and temperature control: Connect the water bath to the temperature adjustment device; fill the water bath where the density gradient tube is located with deionized water; set the water bath temperature to the target control temperature; the water level in the water bath filled with deionized water should be higher than the liquid level in the density gradient tube.

[0062] Steps for preparing the liquid dispensing tube: Rinse the internally and externally clean liquid dispensing tube with the first drug multiple times (preferably twice), connect one end of the liquid dispensing tube to the outlet of the peristaltic pump; place the other end of the liquid dispensing tube into a clean container (beaker) first.

[0063] Steps for preparing the liquid dispensing bottle: Prepare a clean first liquid dispensing bottle, a second liquid dispensing bottle, and a clean connecting tube.

[0064] Determination and preparation steps: First, determine the density value of the highest liquid level and the density value of the lowest liquid level of the mixed liquid in the density gradient tube; wherein, the mixed liquid is composed of a first liquid and a second liquid, and the density of the first liquid is lower than that of the second liquid; further determine the density preparation value of the first liquid and the density preparation value of the second liquid in the mixed liquid at the target control temperature; according to the density preparation values, prepare the first liquid and the second liquid from the first drug and the second drug.

[0065] Among them, this step specifically includes the following steps:

[0066] 1) According to the maximum density value, minimum density value of the selected float, and the target position of the float in the density gradient tube, calculate the density value of the highest liquid level and the density value of the lowest liquid level of the mixed liquid in the density gradient tube. The calculation formula is as follows:

[0067] Density value of the highest liquid level = ρ 最小 - Unit density difference;

[0068] Density value of the lowest liquid level = ρ 最大 + Unit density difference;

[0069] Among them, ρ 最大 is the maximum density value of the selected float; ρ 最小 is the minimum density value of the selected float;

[0070] Among them, the unit of the unit density difference is g / cm 3 ; Unit density difference (i.e., the density difference of a 10 cm high liquid level) = (ρ 最大 - ρ 最小)÷h; where h refers to: the multiple of the 10 cm height value between the target positions of the float with the maximum density value and the float with the minimum density value in the density gradient tube; preferably, h is 5. Preferably, the floats with the maximum density value and the minimum density value are located at the 10 - 60 cm scale of the density gradient tube.

[0071] 2) Determine the density preparation values of the first liquid (light liquid) and the second liquid (heavy liquid) at the target control temperature for preparing the mixed liquid.

[0072] Generally, the density detection temperature of the carbon fiber body is set to 23 °C or 25 °C. At these two temperatures, the bulk densities of the two drugs are close and can be considered the same here.

[0073] The density range of the mixed liquid in the density gradient tube is C1 - C2; where C1 is the density value at the highest liquid level, with the unit of g / cm 3 , and C2 is the density value at the lowest liquid level, with the unit of g / cm 3 ;

[0074] At the target control temperature, the density preparation value ρ1 of the first liquid is: C1 × 0.985 ≈ C3 g / cm 3 ;

[0075] At the target control temperature, the density preparation value ρ2 of the second liquid is: C2 × 1.025 ≈ C4 g / cm 3 .

[0076] 3) According to the density preparation values of the first liquid (light liquid) and the second liquid (heavy liquid) at the target control temperature, prepare the first drug and the second drug into the first liquid (light liquid) and the second liquid (heavy liquid).

[0077] 31) Calculate the liquid densities of the first liquid (light liquid) and the second liquid (heavy liquid) prepared at room temperature: Calculate ρ 第一药品 , ρ 第二药品 according to the following formula:

[0078] ρ 第一药品 = ρ 第一药品25℃ + 0.002 × (25 - T);

[0079] ρ 第二药品 = ρ 第二药品25℃ + 0.002 × (25 - T);

[0080] where T is the room temperature in °C;

[0081] ρ 第一药品 is the density of the first drug at room temperature, in g / cm 3 ;

[0082] ρ 第一药品25℃is the density of the first drug at 25°C, g / cm 3 ;

[0083] ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 ;

[0084] ρ 第二药品25℃ is the density of the second drug at 25°C, g / cm 3 .

[0085] 32) The steps for preparing the first liquid are as follows: Take V1 mL of the first drug in a clean 1000 mL graduated cylinder, then add the second drug to the highest graduation mark of the graduated cylinder, and stir evenly to obtain the first liquid (light liquid); where V1 is determined by the following formula:

[0086] ρ1×1000 = ρ 第一药品 ×V1 + ρ 第二药品 ×(1000 - V1); where ρ1 is the prepared density value of the first liquid; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 .

[0087] 33) The steps for preparing the second liquid are as follows: Take V2 mL of the second drug in a clean 1000 mL graduated cylinder, then add the first drug to the highest graduation mark of the graduated cylinder, and stir evenly to obtain the second liquid (heavy liquid); where V2 is determined by the following formula:

[0088] ρ2×1000 = ρ 第二药品 ×V2 + ρ 第一药品 ×(1000 - V2); where ρ2 is the prepared density value of the second liquid; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 .

[0089] Density gradient column filling step: Fill the prepared float, the first liquid, and the second liquid into the density gradient tube to prepare a density gradient column.

[0090] This step includes:

[0091] 1) Rinse the first liquid dispensing bottle and the connecting tube with the first liquid, and rinse the second liquid dispensing bottle with the second liquid. After rinsing, connect the first liquid dispensing bottle and the second liquid dispensing bottle with the connecting tube. One end of the connecting tube on the first liquid dispensing bottle is connected to the second liquid dispensing bottle, and the other end is connected to the inlet of the peristaltic pump, so as to assemble the first liquid dispensing bottle, the second liquid dispensing bottle, the connecting tube and the peristaltic pump, and make the second liquid dispensing bottle, the connecting tube, the first liquid dispensing bottle, the peristaltic pump and the liquid dispensing tube communicate in sequence. Confirm that the valve on the connecting tube is in the closed state.

[0092] 2) Inject the first liquid into the first liquid dispensing bottle and the second liquid into the second liquid dispensing bottle. Turn on the stirring rotor of the first liquid dispensing bottle and adjust the liquid inlet speed to 0.8 - 1.2 L / h, preferably 1.0 L / h. Turn on the peristaltic pump and discharge about 50 - 75 mL of the first liquid through the liquid dispensing tube to remove the air bubbles in the liquid dispensing tube and the connecting tube.

[0093] 3) Turn off the peristaltic pump, open the valve between the first liquid dispensing bottle and the second liquid dispensing bottle, and let the second liquid flow from the second liquid dispensing bottle to the first liquid dispensing bottle and mix with the first liquid in the first liquid dispensing bottle. Determine the mixing time according to the valve opening to obtain a mixed liquid with a certain density. During the set mixing time, insert the liquid dispensing tube through the cap of the density gradient tube to the bottom of the density gradient tube. Preferably, the mixing time is 3 - 5 min.

[0094] 4) Turn on the peristaltic pump and pump the mixed liquid in the first liquid dispensing bottle into the density gradient tube at the set constant liquid inlet speed. When the mixed liquid in the density gradient tube fills to the highest liquid level of the target liquid, turn off the peristaltic pump. Turn off the stirring rotor knob and the valve in the first liquid dispensing bottle.

[0095] Specifically, when the liquid levels in the first liquid dispensing bottle and the second liquid dispensing bottle are close and it is visually observed that there is no obvious liquid inlet from the second liquid dispensing bottle to the first liquid dispensing bottle, turn on the peristaltic pump and pump the mixed liquid in the first liquid dispensing bottle into the density gradient tube at the set constant liquid inlet speed. At this time, the liquid density in the first liquid dispensing bottle is gradually increasing (the liquid in the second liquid dispensing bottle is always flowing into the first liquid dispensing bottle and being continuously stirred and mixed to gradually increase the density of the mixed liquid in the first liquid dispensing bottle). When the mixed liquid in the density gradient tube fills to the highest liquid level of the target liquid, turn off the peristaltic pump. Further turn off the stirring rotor knob in the first liquid dispensing bottle and the valve on the connecting pipeline between the first and second liquid dispensing bottles.

[0096] Preferably, the constant liquid inlet speed is 0.8 - 1.2 L / h, more preferably 1.0 L / h.

[0097] 5) Slowly move the liquid dispensing tube in the density gradient tube out into the beaker, cover the cap of the density gradient tube, and the preparation of the density gradient column is completed.

[0098] 6) Calibrate and use the prepared density gradient column after keeping it static in a water bath at a constant temperature for 24 h.

[0099] When it is expected that in step 4), the liquid inlet speed of the mixture flowing from the peristaltic pump to the liquid distribution pipe is set to 0.9 - 1.1 L / h, preferably 1.0 L / h: in steps 3) - 4), set the opening degree of the valve between the first liquid distribution bottle and the second liquid distribution bottle to 5 - 6 mm. Preferably, the diameter of the connecting pipe is 5 - 6 mm.

[0100] The present invention is further described below through specific experimental examples as follows:

[0101] Example 1

[0102] In this example, a density gradient column for detecting the bulk density of carbon fiber is prepared. The main steps are as follows:

[0103] Float preparation step: The bulk density of the carbon fiber to be measured is about (1.795 - 1.805) g / cm 3 , in order to make the stable suspension position of the test sample in the density gradient column between 30 - 40 cm, design the highest liquid level at about 70 cm in the density gradient tube, and plan to evenly disperse 5 floats between the 10 cm - 60 cm scales. Therefore, 5 floats are selected, and the density values are 1.7883 g / cm 3 , 1.7949 g / cm 3 , 1.8012 g / cm 3 , 1.8144 g / cm 3 , 1.8232 g / cm 3 . Since the floats have been in use, after fishing them out of the density gradient tube, soak the floats in carbon tetrachloride.

[0104] Here, 1.8232 - 1.7883 = 0.0349, 0.0349 ÷ 5 × 7 = 0.049, meeting the bulk density detection accuracy requirement: when the accuracy requirement ≤ ±0.001 g / cm 3 , the overall density difference is not greater than 0.05 g / cm 3 .

[0105] Drug selection step: Since carbon fiber does not chemically react with carbon tetrachloride and 1,2 - dibromoethane, and the density of carbon tetrachloride is d ≈ 1.60 g / cm 3 , the density of 1,2 - dibromoethane is d ≈ 2.166 g / cm 3 , the bulk density of carbon fiber is between the densities of these two drugs and these two drugs are miscible, so these two drugs (analytical pure) are selected for preparation. Among them, the first drug is carbon tetrachloride; the second drug is 1,2 - dibromoethane.

[0106] Instrument preparation step: AsFigure 1 As shown, place the prepared clean density gradient tube 1 on the test tube holder 22 of the water bath 2 without water filling, and clamp it with the supporting clip 21. Put the selected and pre-treated float 3 into the fishing basket 11 of the fishing device, turn on the instrument descent switch, lower the fishing basket 11 to the bottom of the density gradient tube, and cover the tube mouth. Connect the water bath 2 with the temperature regulating device 4; fill the water bath 2 where the density gradient tube 1 is located with deionized water; set the water bath temperature to the target control temperature; the water level in the water bath filled with deionized water (the water bath liquid level 8) should be higher than the liquid level in the density gradient tube. Rinse the inside and outside clean liquid dispensing tube 56 twice with the first drug, connect one end of the liquid dispensing tube 56 to the outlet of the peristaltic pump 53; put the other end of the liquid dispensing tube 56 into a clean beaker first. Prepare a clean first liquid dispensing bottle 51, a second liquid dispensing tube 52 and a clean connecting tube 55.

[0107] Determination and preparation steps: This step includes the following steps:

[0108] 1) Determine the density value of the highest liquid level and the density value of the lowest liquid level of the mixed liquid in the density gradient tube:

[0109] 11) Calculate the unit density difference (i.e., the density difference of a 10 cm high liquid level)

[0110] Density difference of 10 cm high liquid level = (ρ maximum - ρ minimum) ÷ h = (1.8232 - 1.7883) / 5 = 0.00698 (g / cm 3 )

[0111] 12) Density value of the highest liquid level = ρ 最小 - unit density difference = 1.7883 - 0.00698 = 1.7813 (g / cm 3 )

[0112] 13) Density value of the lowest liquid level = ρ 最大 + unit density difference = 1.8232 + 0.00698 = 1.8302 (g / cm 3 )

[0113] Among them, ρ 最大 is the maximum density value of the selected float; ρ 最小 is the minimum density value of the selected float.

[0114] 2) Determine the density preparation values of the first liquid (light liquid) and the second liquid (heavy liquid) at the target control temperature for preparing the mixed liquid.

[0115] The density range of the mixed liquid in the density gradient tube is (1.7813 - 1.8302 g / cm 3 )

[0116] At the target controlled temperature, the formulated density value ρ1 of the first liquid is 1.7883×0.985≈1.761 g / cm 3 .

[0117] At the target controlled temperature, the formulated density value ρ2 of the second liquid is: 1.8302×1.025≈1.876 g / cm 3 .

[0118] 3) According to the formulated density values of the first liquid (light liquid) and the second liquid (heavy liquid) at the target controlled temperature, formulate the first drug and the second drug into the first liquid (light liquid) and the second liquid (heavy liquid).

[0119] 31) Calculate the liquid densities of the first liquid (light liquid) and the second liquid (heavy liquid) at room temperature: Calculate ρ 第一药品 , ρ 第二药品 according to the following formula:

[0120] ρ 第一药品 = ρ 第一药品25℃ + 0.002×(25 - T);

[0121] ρ 第二药品 = ρ 第二药品25℃ + 0.002×(25 - T);

[0122] where T is the room temperature in °C;

[0123] ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ;

[0124] ρ 第一药品25℃ is the density of the first drug at 25°C, g / cm 3 ;

[0125] ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 ;

[0126] ρ 第二药品25℃ is the density of the second drug at 25°C, g / cm 3 .

[0127] According to the above formula: The density of the first drug (carbon tetrachloride) at 25°C is d≈1.60 g / cm 3 , and the density of the second drug (1,2-dibromoethane) at 25°C is d≈2.166 g / cm 3 .

[0128] Now the room temperature is 22°C. According to the formula: Calculate the densities of the first drug and the second drug at room temperature respectively as: The density of carbon tetrachloride at room temperature ρ第一药品 = 1.60 + 0.002×(22 - 25) = 1.594 g / cm 3 ; Density of 1,2-dibromoethane at room temperature: ρ 第二药品 = 2.166 + 0.002×(22 - 25) = 2.16 g / cm 3 .

[0129] 32) Prepare the first liquid (light liquid):

[0130] First, calculate V1 according to the formula:

[0131] ρ1×1000 = ρ 第一药品 ×V1 + ρ 第二药品 ×(1000 - V1); where ρ1 is the prepared density value of the first liquid; ρ 第一药品 is the density of the first drug at room temperature g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature g / cm 3 .

[0132] Specifically, substituting the above data, 1.761×1000 = 1.594×V1 + 2.16×(1000 - V1); calculate: V1 = 704.9 mL.

[0133] The steps to prepare the first liquid are as follows: Take 705 mL of the first drug (carbon tetrachloride) in a clean 1000 mL graduated cylinder, then add the second drug (1,2-dibromoethane) to the highest scale line of the graduated cylinder, stir evenly to obtain the first liquid (light liquid). Transfer the prepared light liquid in the graduated cylinder to a 2000 mL beaker, place it in the water tank of an ultrasonic cleaner filled with deionized water, and ultrasonically treat the light liquid for 15 minutes to remove bubbles for standby.

[0134] 33) Prepare the second liquid (second liquid):

[0135] First, calculate V2 according to the formula:

[0136] ρ2×1000 = ρ 第二药品 ×V2 + ρ 第一药品 ×(1000 - V2); where ρ2 is the prepared density value of the second liquid; ρ 第一药品 is the density of the first drug at room temperature g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature g / cm 3 .

[0137] Substituting the above data gives: 1.876×1000 = 2.16×V2 + 1.594×(1000 - V2)

[0138] It is obtained that: V2 = 498.2 mL.

[0139] The steps for preparing the second liquid are as follows: Take about 498 mL of 1,2-dibromoethane and place it in a clean 1000 mL graduated cylinder. Then add carbon tetrachloride up to the highest graduation line of the graduated cylinder. Stir the mixed liquid evenly with a glass rod, and then measure the density value of the mixed liquid with a densitometer and record it. This mixed liquid is the prepared heavy liquid. Transfer the prepared heavy liquid in the graduated cylinder to a 2000 mL beaker, and place it in the water tank of an ultrasonic cleaner filled with deionized water. Ultrasonically treat the light liquid for 15 minutes to remove bubbles, and set it aside for later use.

[0140] Steps for filling the density gradient column: Fill the prepared float, the first liquid, and the second liquid into the density gradient tube to prepare a density gradient column. As Figure 1 shown, this step includes:

[0141] 1) Rinse the first liquid dispensing bottle 51 and the connecting tube 55 (the inner diameter of the connecting tube 55 is 5.5 mm) with the first liquid respectively, and rinse the second liquid dispensing bottle 52 with the second liquid. After rinsing, connect the first liquid dispensing bottle 51 and the second liquid dispensing bottle 52 with the connecting tube 55. Among them, one end of the connecting tube on the first liquid dispensing bottle 51 is connected to the second liquid dispensing bottle 52, and the other end is connected to the inlet of the peristaltic pump 53; so as to assemble the first liquid dispensing bottle 51, the second liquid dispensing bottle 52, the connecting tube 55 and the peristaltic pump 53, and make the second liquid dispensing bottle 52, the connecting tube 55, the first liquid dispensing bottle 51, the peristaltic pump 53, and the liquid dispensing tube 56 communicate in sequence. Confirm that the valve 54 on the connecting tube 55 is in the closed state.

[0142] In addition, both the first liquid dispensing bottle 51 and the second liquid dispensing bottle 52 are placed on the liquid dispensing device 5.

[0143] 2) Inject the first liquid into the first liquid dispensing bottle 51, and inject the second liquid into the second liquid dispensing bottle 52; Turn on the stirring rotor 57 of the first liquid dispensing bottle, and adjust the liquid inlet speed to 1.0 L / h; Turn on the peristaltic pump 53, and discharge about 50 mL of the first liquid through the liquid dispensing tube 56 into a clean beaker to remove the bubbles in the liquid dispensing tube 56 and the connecting tube 55.

[0144] 3) Quickly turn off the peristaltic pump 53, open the valve 54 between the first liquid dispensing bottle 51 and the second liquid dispensing bottle 52, so that the second liquid flows from the second liquid dispensing bottle to the first liquid dispensing bottle, and the density of the mixed liquid in the first liquid dispensing bottle begins to slowly increase; The time for the second liquid to enter the first liquid dispensing bottle and mix with the first liquid is 3 min; During this period, insert the liquid dispensing tube 56 through the tube cap of the density gradient tube 1 to the bottom of the density gradient tube 1.

[0145] 4) When the liquid levels in the first liquid dispensing bottle and the second liquid dispensing bottle are close and it is visually observed that there is no obvious liquid inflow from the second liquid dispensing bottle into the first liquid dispensing bottle, turn on the peristaltic pump 53 to pump the mixed liquid in the first liquid dispensing bottle 51 into the density gradient tube 1 at a set constant liquid inflow rate of 1.0 L / h; at this time, the liquid density in the first liquid dispensing bottle is still slowly increasing. When the mixed liquid in the density gradient tube 1 fills to a height of 70 cm at the highest liquid level of the target liquid (see the lowest liquid level 7 and the highest liquid level 6 of the density gradient tube in Figure 1 ), turn off the peristaltic pump 53; turn off the stirring rotor knob and the valve 54 in the first liquid dispensing bottle 51.

[0146] 5) Slowly move the liquid delivery tube 56 in the density gradient tube 1 out into a beaker, cover the tube cap of the density gradient tube, and the preparation of the density gradient column is completed.

[0147] 6) After the prepared density gradient column is kept at a constant temperature in a water bath for 24 h, 5 floats 3 are basically evenly suspended between the scales of 10 - 60 cm of the density gradient tube. After calibration, the calibration curve is a straight line, meeting the usage requirements.

[0148] Example 2

[0149] In this example, a density gradient column for detecting the density of protonema is prepared. The main steps are as follows:

[0150] Float preparation step: The bulk density of the protonema to be measured is about (1.180 - 1.190) g / cm 3 , in order to make the stable suspension position of the test sample in the density gradient column between 30 - 40 cm, the highest liquid level in the density gradient tube is designed to be about 70 cm, and it is planned to evenly disperse 5 floats between the scales of 10 cm - 60 cm. Therefore, 5 floats are selected, and the density values are 1.1689 g / cm 3 , 1.1721 g / cm 3 , 1.1802 g / cm 3 , 1.1875 g / cm 3 , 1.1956 g / cm 3 . Since the floats are always in use, after fishing them out of the density gradient tube, the floats are soaked in xylene.

[0151] Here, 1.1956 - 1.1689 = 0.0267, 0.0267 ÷ 5 × 7 = 0.037, meeting the bulk density detection accuracy requirement: when the accuracy requirement ≤ ±0.001 g / cm 3 , the overall density difference is not greater than 0.05 g / cm 3 .

[0152] Drug selection steps: Since the raw filaments do not chemically react with carbon tetrachloride and xylene, and the density of carbon tetrachloride is d≈1.60 g / cm 3 , and the density of xylene is d≈0.86 - 0.90 g / cm 3 , and the bulk density of the raw filaments is between the densities of these two drugs and these two drugs are miscible, so these two drugs (analytical grade) are selected for preparation. Among them, the first drug is xylene; the second drug is carbon tetrachloride.

[0153] Instrument preparation steps: As Figure 1 shown, place the prepared clean density gradient tube 1 on the test tube bracket 22 of the water bath 2 without water filling, and clamp it with the supporting clip 21. Put the selected and pretreated float 3 into the fishing basket 11 of the fishing device, turn on the instrument descent switch, lower the fishing basket 11 to the bottom of the density gradient tube, and cover the tube mouth. Connect the water bath 2 to the temperature control device 4; fill the water bath 2 where the density gradient tube 1 is located with deionized water; set the water bath temperature to the target control temperature; the water level in the water bath filled with deionized water should be higher than the liquid level in the density gradient tube. Rinse the inner and outer clean liquid dispensing tube 56 twice with the first drug, connect one end of the liquid dispensing tube 56 to the outlet of the peristaltic pump 53; put the other end of the liquid dispensing tube 56 into a clean beaker first. Prepare a clean first liquid dispensing bottle 51, a second liquid dispensing tube 52, and a clean connecting tube 55.

[0154] Determination and preparation steps: This step includes the following steps:

[0155] 1) Determine the density value of the highest liquid level and the density value of the lowest liquid level of the mixed liquid in the density gradient tube:

[0156] 11) Calculate the unit density difference (i.e., the density difference of a 10 cm high liquid level)

[0157] Density difference of 10 cm high liquid level = (ρ_max - ρ_min)÷h = (1.1956 - 1.1689) / 5 = 0.00534 (g / cm 3 ).

[0158] 12) Density value of the highest liquid level = ρ 最小 - unit density difference = 1.1689 - 0.00534 = 1.1636 (g / cm 3 ).

[0159] 13) Density value of the lowest liquid level = ρ 最大 + unit density difference = 1.1956 + 0.00534 = 1.2009 (g / cm 3 ).

[0160] Among them, ρ 最大 is the maximum density value of the selected float; ρ 最小It is to select the minimum density value of the float.

[0161] 2) Determine the density preparation values of the first liquid (light liquid) and the second liquid (heavy liquid) at the target control temperature for preparing the mixed liquid.

[0162] The density range of the mixed liquid in the density gradient tube is (1.1639 - 1.2009 g / cm 3 ).

[0163] At the target control temperature, the density preparation value ρ1 of the first liquid is 1.1639 × 0.985 ≈ 1.1464 g / cm 3 .

[0164] At the target control temperature, the density preparation value ρ2 of the second liquid is: 1.2009 × 1.025 ≈ 1.2309 g / cm 3 .

[0165] 3) According to the density preparation values of the first liquid (light liquid) and the second liquid (heavy liquid) at the target control temperature, prepare the first drug and the second drug into the first liquid (light liquid) and the second liquid (heavy liquid).

[0166] 31) Calculate the liquid densities of the first liquid (light liquid) and the second liquid (heavy liquid) prepared at room temperature: Calculate ρ 第一药品 , ρ 第二药品 according to the following formula:

[0167] ρ 第一药品 = ρ 第一药品25℃ + 0.002 × (25 - T);

[0168] ρ 第二药品 = ρ 第二药品25℃ + 0.002 × (25 - T);

[0169] where T is the room temperature in °C;

[0170] ρ 第一药品 is the density of the first drug at room temperature, in g / cm 3 ;

[0171] ρ 第一药品25℃ is the density of the first drug at 25 °C, in g / cm 3 ;

[0172] ρ 第二药品 is the density of the second drug at room temperature, in g / cm 3 ;

[0173] ρ 第二药品25℃ is the density of the second drug at 25 °C, in g / cm 3 .

[0174] According to the above formula: The density of the first drug (xylene) at 25 °C is d ≈ 0.86 - 0.90 g / cm 3 , and the density of the second drug (carbon tetrachloride) at 25 °C is d ≈ 1.60 g / cm 3 .

[0175] The current room temperature is 22 °C. According to the formula, the densities of the first drug and the second drug at room temperature are calculated as follows: The density of xylene at room temperature, ρ 第一药品 = 0.88 + 0.002×(22 - 25) = 0.874 g / cm 3 ; The density of carbon tetrachloride at room temperature: ρ 第二药品 = 1.60 + 0.002×(22 - 25) = 1.594 g / cm 3 .

[0176] 32) Prepare the first liquid (light liquid):

[0177] First, calculate V1 according to the formula:

[0178] ρ1×1000 = ρ 第一药品 ×V1 + ρ 第二药品 ×(1000 - V1); where ρ1 is the prepared density value of the first liquid; ρ 第一药品 is the density of the first drug at room temperature in g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature in g / cm 3 .

[0179] Specifically, substituting the above data, 1.146×1000 = 0.874×V1 + 1.594×(1000 - V1); calculating: V1 = 622 mL.

[0180] The steps to prepare the first liquid are as follows: Take 622 mL of the first drug (xylene) in a clean 1000 mL graduated cylinder, then add the second drug (carbon tetrachloride) to the highest scale line of the graduated cylinder, stir evenly to obtain the first liquid (light liquid). Transfer the prepared light liquid in the graduated cylinder to a 2000 mL beaker, place it in the water tank of an ultrasonic cleaner filled with deionized water, and ultrasonically treat the light liquid for 15 minutes to remove bubbles for standby.

[0181] 33) Prepare the second liquid (second liquid):

[0182] First, calculate V2 according to the formula:

[0183] ρ2×1000 = ρ 第二药品 ×V2 + ρ 第一药品 ×(1000 - V2); where ρ2 is the prepared density value of the second liquid; ρ 第一药品is the density of the first drug at room temperature, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 .

[0184] Substituting the above data gives: 1.2009×1000 = 1.594×V2 + 0.874×(1000 - V2)

[0185] It is obtained that: V2 = 454 mL.

[0186] The steps for preparing the second liquid are as follows: Take about 454 mL of carbon tetrachloride in a clean 1000 mL graduated cylinder, then add xylene to the highest scale line of the graduated cylinder, stir the mixed liquid evenly with a glass rod, then measure the density value of the mixed liquid with a densitometer and record it. This mixed liquid is the prepared heavy liquid. Transfer the prepared heavy liquid in the graduated cylinder to a 2000 mL beaker, place it in the water tank of an ultrasonic cleaner filled with deionized water, and ultrasonically treat the light liquid for 15 minutes to remove bubbles for standby.

[0187] Steps for filling the density gradient column: Fill the prepared float, the first liquid and the second liquid into the density gradient tube to prepare a density gradient column. As Figure 1 shown, this step includes:[[]]

[0188] 1) Rinse the first liquid dispensing bottle 51 and the connecting pipe 55 (the inner diameter of the connecting pipe 55 is 5.5 mm) with the first liquid respectively, and rinse the second liquid dispensing bottle 52 with the second liquid; after rinsing, connect the first liquid dispensing bottle 51 and the second liquid dispensing bottle 52 with the connecting pipe 55; among them, one end of the connecting pipe on the first liquid dispensing bottle 51 is connected to the second liquid dispensing bottle 52, and the other end is connected to the inlet of the peristaltic pump 53; so as to assemble the first liquid dispensing bottle 51, the connecting pipe 55, the second liquid dispensing bottle 52, the connecting pipe 55 and the peristaltic pump 53, and make the second liquid dispensing bottle 52, the first liquid dispensing bottle 51, the peristaltic pump 53 and the liquid dispensing pipe 56 communicate in sequence. Confirm that the valve 54 on the connecting pipe 55 is in the closed state.

[0189] 2) Inject the first liquid into the first liquid dispensing bottle 51 and the second liquid into the second liquid dispensing bottle 52; turn on the stirring rotor 57 of the first liquid dispensing bottle, and adjust the liquid inlet speed to 1.0 L / h; turn on the peristaltic pump 53, and discharge about 50 - 75 mL of the first liquid through the liquid dispensing pipe 56 to remove the bubbles in the liquid dispensing pipe 56 and the connecting pipe 55.

[0190] 3) Quickly close the peristaltic pump 53, open the valve 54 between the first liquid dispensing bottle 51 and the second liquid dispensing bottle 52, and let the second liquid flow from the second liquid dispensing bottle to the first liquid dispensing bottle. The density of the mixed liquid in the first liquid dispensing bottle starts to slowly increase. The time for the second liquid to enter the first liquid dispensing bottle and mix with the first liquid is 3 minutes. During this period, insert the liquid dispensing tube 56 through the cap of the density gradient tube 1 to the bottom of the density gradient tube 1.

[0191] 4) When the liquid levels in the first liquid dispensing bottle and the second liquid dispensing bottle are close and it is visually observed that there is no obvious liquid inflow from the second liquid dispensing bottle to the first liquid dispensing bottle, open the peristaltic pump 53 and pump the mixed liquid in the first liquid dispensing bottle 51 into the density gradient tube 1 at a set constant liquid inflow rate of 1.0 L / h. At this time, the density of the liquid in the first liquid dispensing bottle is still slowly increasing. When the mixed liquid in the density gradient tube 1 fills to a height of 70 cm at the highest liquid level of the target liquid, close the peristaltic pump 53 and close the stirring rotor knob and the valve 54 in the first liquid dispensing bottle 51.

[0192] 5) Slowly remove the liquid dispensing tube 56 in the density gradient tube 1 into a beaker, cover the cap of the density gradient tube, and the preparation of the density gradient column is completed.

[0193] 6) After the prepared density gradient column is kept at a constant temperature in a water bath for 24 hours, 5 floats 3 are basically evenly suspended between the scales of 10 - 60 cm of the density gradient tube. After calibration, the calibration curve is a straight line, meeting the usage requirements.

[0194] In summary, the preparation method of a density gradient column provided by the embodiment of the present invention makes up for the deficiencies of the method described in the GB / T90013 standard. Compared with this standard, the preparation method of the density gradient column provided by the embodiment of the present invention has stronger operability and greater promotion value.

[0195] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a density gradient column, characterized in that, It includes the following steps: Float preparation step: Determine the number and density of the required floats according to the bulk density range of the product to be measured; the product to be measured is any one of carbon fiber, pre-oxidized fiber, graphite fiber, and carbon fiber precursor. Drug selection step: Select a first drug and a second drug that can be mutually soluble to form a stable mixture according to the product to be measured; wherein, the bulk density of the first drug is lower than the bulk density of the product to be measured; the bulk density of the second drug is higher than the bulk density of the product to be measured. Determination and preparation step: First determine the density value of the highest liquid level and the density value of the lowest liquid level of the mixture in the density gradient tube; wherein, the mixture is composed of a first liquid and a second liquid, and the density of the first liquid is lower than the density of the second liquid; thereby further determining the density preparation value of the first liquid and the density preparation value of the second liquid in the mixture at the target control temperature; according to the density preparation value, prepare the first drug and the second drug into the first liquid and the second liquid. Density gradient column filling step: Fill the prepared floats, the first liquid and the second liquid into the density gradient tube to prepare a density gradient column. Among them, in the drug selection step: If the product to be measured is any one of carbon fiber, pre-oxidized fiber, and graphite fiber, the first drug is selected as carbon tetrachloride or tetrachloroethylene; the second drug is selected as 1,2-dibromoethane. If the product to be measured is carbon fiber precursor, the first drug is selected as xylene; the second drug is selected as carbon tetrachloride or tetrachloroethylene. In the determination and preparation step: The density range of the mixed liquid in the density gradient tube is C1 - C2; where C1 is the density value of the highest liquid level, in g / cm 3 , and C2 is the density value of the lowest liquid level, in g / cm 3 ; At the target control temperature, the formulated density value ρ1 of the first liquid is: C1 × 0.985 ± 0.001 g / cm 3 ; At the target control temperature, the formulated density value ρ2 of the second liquid is: C2 × 1.025 ± 0.001 g / cm 3 .

2. The method for preparing a density gradient column according to claim 1, wherein In the float preparation step: According to the bulk density range of the product to be measured, the detection accuracy requirement, the target position where the float with the maximum density suspends in the density gradient column, and the target position where the float with the minimum density suspends in the density gradient column, select the number of floats and the density of each float.

3. The method for preparing a density gradient column according to claim 2, wherein The number of the floats is 5-8; and / or After selecting the floats, the floats need to be pretreated; wherein, the steps of the pretreatment include: if the floats are used for the first time, the floats need to be soaked in deionized water for 20-26 hours first, and then soaked in the first drug for 4-8 hours; if the floats are not used for the first time, the floats are directly soaked in the first drug for 4-8 hours.

4. The method for preparing a density gradient column according to claim 1, wherein In the determination and preparation step: According to the maximum density value, the minimum density value of the selected floats, and the target positions of the floats in the density gradient tube, calculate the density value of the highest liquid level and the density value of the lowest liquid level of the mixture in the density gradient tube.

5. The method for preparing a density gradient column according to claim 4, wherein Density value at the highest liquid level = ρ 最小 - Unit density difference; Density value at the lowest liquid level = ρ 最大 + unit density difference; Among them, ρ 最大 is the maximum density value of the selected float, with the unit of g / cm 3 ; ρ 最小 is the minimum density value of the selected float, with the unit of g / cm 3 ; Among them, the unit density difference refers to the density difference at a liquid level of 10 cm, and the calculation formula is as follows: Unit density difference = (ρ 最大 - ρ 最小 ) ÷ h; where h refers to the multiple of the 10 cm height value between the target positions of the float with the maximum density value and the float with the minimum density value in the density gradient tube.

6. The method for preparing a density gradient column according to claim 5, wherein h is 5.

7. The method for preparing a density gradient column according to claim 5, wherein The float with the maximum density value and the float with the minimum density value are located at 10-60 cm of the scale of the density gradient tube.

8. The method for preparing a density gradient column according to claim 1, wherein In the determination and preparation step: According to the density preparation values of the first liquid and the second liquid at the target control temperature, the first drug and the second drug are formulated into the first liquid and the second liquid; wherein, The steps for formulating the first liquid are as follows: Take V1 mL ± 2 mL of the first drug in a clean 1000 mL graduated cylinder, then add the second drug to the highest scale line of the graduated cylinder, and stir evenly to obtain the first liquid; wherein, V1 is determined by the following formula: ρ1×1000 = ρ 第一药品 ×V1 + ρ 第二药品 × (1000 - V1); where ρ1 is the density preparation value of the first liquid; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 ; The steps for formulating the second liquid are as follows: Take V2 mL ± 2 mL of the second drug in a clean 1000 mL graduated cylinder, then add the first drug to the highest scale line of the graduated cylinder, and stir evenly to obtain the second liquid; wherein, V2 is determined by the following formula: ρ2×1000 = ρ 第二药品 ×V2 + ρ 第一药品 ×(1000 - V2); where ρ2 is the density preparation value of the second liquid; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 .

9. The method for preparing a density gradient column according to claim 8, wherein, In the above determination and formulation steps: Calculate ρ according to the following formula 第一药品 , ρ 第二药品 : ρ 第一药品 = ρ 第一药品25℃ + 0.002 × (25 - T); ρ 第二药品 = ρ 第二药品25℃ + 0.002 × (25 - T); wherein, T is the room temperature, °C; ρ 第一药品 is the density of the first drug at room temperature, g / cm 3 ; ρ 第一药品25℃ is the density of the first drug at 25°C, g / cm 3 ; ρ 第二药品 is the density of the second drug at room temperature, g / cm 3 ; ρ 第二药品25℃ is the density of the second drug at 25°C, g / cm 3 .

10. The preparation method of the density gradient column according to claim 1, characterized in that, Before the density gradient column filling step, an instrument preparation step is also included; wherein, the instrument preparation step includes: Installation step: Install the prepared density gradient tube on the test tube bracket of the water bath; Filling the float step: Load the prepared float into the bottom of the density gradient tube; Water filling and temperature control step: Connect the water bath to the temperature regulating device; Fill the water bath where the density gradient tube is located with deionized water; Set the water bath temperature to the target control temperature; Preparing the liquid delivery tube step: Rinse the liquid delivery tube with the first drug multiple times, and connect one end of the liquid delivery tube to the outlet of the peristaltic pump; Preparing the liquid dispensing bottle step: Prepare the first liquid dispensing bottle, the second liquid dispensing bottle and the connecting tube.

11. The method for preparing a density gradient column according to claim 10, wherein In the above filling the float step: Put the prepared float into the fishing basket of the fishing device, turn on the instrument descent switch, lower the fishing basket to the bottom of the density gradient tube, and cover the tube mouth.

12. The method for preparing a density gradient column according to claim 10, characterized in that, In the above water filling and temperature control step: The water level in the water bath filled with deionized water should be higher than the liquid level of the mixed liquid in the density gradient tube.

13. The method for preparing a density gradient column according to claim 10, characterized in that, In the step of preparing the liquid delivery tube: First place the other end of the liquid delivery tube into a clean container.

14. The method for preparing a density gradient column according to claim 10, wherein The density gradient column filling step includes: 1) Assemble the first liquid dispensing bottle, the second liquid dispensing bottle, the connecting tube and the peristaltic pump so that the second liquid dispensing bottle, the connecting tube, the first liquid dispensing bottle, the peristaltic pump and the liquid delivery tube are connected in sequence; 2) Inject the first liquid into the first liquid dispensing bottle, and inject the second liquid into the second liquid dispensing bottle; Turn on the stirring rotor of the first liquid dispensing bottle; wherein, adjust the liquid inlet speed to 0.8 - 1.2 L / h; wherein, turn on the peristaltic pump, and discharge 50 - 75 mL of the first liquid through the liquid delivery tube to remove the air bubbles in the liquid delivery tube and the connecting tube; 3) Turn off the peristaltic pump, open the valve between the first liquid dispensing bottle and the second liquid dispensing bottle, so that the second liquid flows from the second liquid dispensing bottle to the first liquid dispensing bottle, mixes with the first liquid in the first liquid dispensing bottle, and determines the mixing time according to the valve opening to obtain a mixed liquid with a certain density; During the set mixing time, insert the liquid delivery tube into the bottom of the density gradient tube through the tube cap of the density gradient tube; wherein, the mixing time is 3 - 5 min; 4) Turn on the peristaltic pump to pump the mixed liquid in the first liquid dispensing bottle into the density gradient tube at a set constant liquid inlet speed; at this time, the liquid density in the first liquid dispensing bottle is gradually increasing; when the mixed liquid in the density gradient tube fills to the height of the highest liquid level of the target liquid, turn off the peristaltic pump; further turn off the stirring rotor knob in the first liquid dispensing bottle and the valve on the connecting tube. 5) Remove the liquid dispensing tube in the density gradient tube, cover the tube cap of the density gradient tube, and the preparation of the density gradient column is completed.

15. The method for preparing a density gradient column according to claim 14, wherein In step 2): Adjust the liquid inlet speed to 1.0 L / h.

16. The method for preparing a density gradient column according to claim 14, characterized in that, In step 4): When the liquid levels in the first liquid dispensing bottle and the second liquid dispensing bottle are close and it is visually observed that the second liquid dispensing bottle stops feeding liquid into the first liquid dispensing bottle, turn on the peristaltic pump; and / or When pumping the mixed liquid in the first liquid dispensing tube into the density gradient tube at a set constant liquid inlet speed: the liquid in the second liquid dispensing bottle is always flowing into the first liquid dispensing bottle and is continuously stirred and mixed to gradually increase the density of the mixed liquid in the first liquid dispensing bottle.

17. The method for preparing a density gradient column according to claim 14, wherein In step 4): The set constant liquid inlet speed is 0.8 - 1.2 L / h.

18. The method for preparing a density gradient column according to claim 17, wherein In step 4): The set constant liquid inlet speed is 1.0 L / h.

19. The method for preparing a density gradient column according to claim 14, wherein The density gradient column filling step further includes: 6) Keep the prepared density gradient column in a water bath at a constant temperature for 23 - 25 h and then calibrate it for use.

20. The method for preparing a density gradient column according to claim 14, wherein In step 1): Rinse the first liquid dispensing bottle and the connecting tube with the first liquid respectively, and rinse the second liquid dispensing bottle with the second liquid; after rinsing, connect the first liquid dispensing bottle and the second liquid dispensing bottle with the connecting tube; wherein, one end of the connecting tube on the first liquid dispensing bottle is connected to the second liquid dispensing bottle, and the other end is connected to the inlet of the peristaltic pump; confirm that the valve on the connecting tube is in the closed state.

21. The method for preparing a density gradient column according to claim 14, wherein When the liquid inlet speed from the peristaltic pump to the liquid dispensing tube in step 4) is set to 0.9 - 1.1 L / h: in steps 3) - 4), set the opening degree of the valve between the first liquid dispensing bottle and the second liquid dispensing bottle to 5 - 6 mm.

22. The method for preparing a density gradient column according to claim 21, characterized in that, The diameter of the connecting tube is 5 - 6 mm.

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