CN108872004A - A kind of measuring method for ultra-pure graphite ash content - Google Patents

Abstract

The present invention provides a kind of measuring methods for ultra-pure graphite ash content, it includes weighing sample, high temperature sintering, dry cooling, weigh record, double measurement, skip test and calculate ash content, and it passes through the platinum ware progress blank test using the blank with splendid attire specimen material same specification and model, measure mass change of the blank platinum ware in continuous mode, and then determine mass change of the platinum ware for containing specimen material in continuous mode, and the mass change is added in calculation formula, it solves existing measuring method and measures the big technical problem of ultra-pure graphite ash error, realize the test of ultra-pure graphite ash content (10 × 10-6 of <) content, obtain precision and the preferable result data of repeatability.

Description

A method for determining the ash content of ultra-high-purity graphite

technical field

The invention relates to the technical field of measuring the ash content of ultra-high-purity graphite, in particular to a method for measuring the ash content of ultra-high-purity graphite.

Background technique

The ash content of carbon and graphite products and their materials is also called the analysis test of impurity content. Generally speaking, the determination of ash content of graphite products is based on the analysis test specified in YB/T 5146-2000, the determination method of ash content of high-purity graphite products. method to proceed. However, for the test of trace impurity content in ultra-high-purity graphite, such as purified graphite powder for synthetic diamond, graphite for reactors in nuclear power plants, spectral graphite, and graphite for electronic-grade single crystal silicon thermal field, etc., it can be analyzed by this method. It is often difficult for non-professionals to provide accurate analytical test results by this method. Sometimes even test results with negative values are obtained.

There are two main factors for the deviation of the test results. One is that the impurity content in the sample is extremely small, such as purified graphite powder for synthetic diamond, the domestic standard requires ≤30ppm; the European and American standards require ≤20ppm; the SGL standard requires ≤10ppm; The technical standard for graphite used in nuclear power plant reactors is tens of ppm; the technical standard for graphite used in electronic grade single crystal silicon thermal field is ≤5ppm; The determination of ash content of pure graphite materials is proposed, and it is not suitable for the determination of ash content of ultra-high-purity graphite materials, because the standard stipulates that two parallel tests allow 10ppm error, then the graphite test of less than 10ppm or less than 5ppm will no longer be suitable. Moreover, in YB/T 5146-2000, the fluctuation caused by the thermal stability of the platinum dish used to hold the test sample during the test process was not considered, therefore, the error in the determination process of ultra-high-purity graphite ash was too large. big.

In the Chinese patent with the patent number CN201110056199.6 (hereinafter referred to as the 2011 patent), a method for testing trace impurities in ultra-high-purity graphite is disclosed. The steps are: A. Increase the number of parent samples to GB /T8133.17-1999 stipulates 4 to 5 times the number of female parent samples; B. The rate of change k of the ceramic crucible containing the sample before and after high-temperature firing is tested, and its value is obtained from the sample cup test In other words, the temperature is controlled at 800-850°C; C. Add the rate of change factor in the calculation formula of the test results: A=(G1-G2*k)/GX100%. A is the ash or impurity content; G is the parent quantity of the sample; G1 is the weight of the ceramic crucible and sample residue after burning; G2 is the weight of the ceramic crucible containing the sample; K is before and after burning The rate of change of the ceramic crucible-like cup.

Although, in the 2011 patent, the rate of change factor was added to the calculation formula of the test results (testing the rate of change of the ceramic crucible containing the sample before and after burning at high temperature), however, no specific method for determining the factor of change was published , and the variable factor test is carried out by using and burning the ceramic crucible containing the test sample, which still has errors.

Contents of the invention

In view of the above problems, the present invention provides a method for measuring the ash content of ultra-high-purity graphite, which uses a blank platinum dish with the same specifications and models as the sample material to carry out a blank test to measure the ash content of the blank platinum dish during the measurement process. The mass change of the platinum dish containing the sample material is determined during the measurement process, and the mass change is added to the calculation formula to solve the technical problem of large error in the measurement of ultra-high-purity graphite ash content by existing measurement methods, and achieve ultra-high The test of the ash content (<10×10 ^-6 ) of pure graphite obtains the result data with good accuracy and repeatability.

To achieve the above object, the present invention provides the following technical solutions:

A method for determining the ash content of ultra-high-purity graphite, comprising the following steps:

Step 1, weighing the sample, keeping the temperature of the weighing chamber constant, using an analytical balance to weigh the mass m ₀ of the platinum dish used to place the sample, and weighing the sample mass m ₁ ;

Step 2, burning at high temperature, placing the weighed sample in a platinum dish, and then placing the platinum dish in a high-temperature furnace to burn until the sample is burnt out to form ash;

Step 3, dry and cool, place the burnt platinum dish filled with ash on an asbestos net to cool for 1 to 3 minutes, then transfer to a desiccator to cool to room temperature;

Step 4, weighing and recording, after the ash in the platinum dish is cooled to normal temperature, use an analytical balance to weigh and record the total mass of the platinum dish and the ash in it;

Step 5, the second measurement, put the platinum dish into the high-temperature furnace again and burn it. After the burning is completed, repeat steps 4 and 5 to record the total mass of the platinum dish and the ash in it until the difference between two consecutive weighings ≤0.0001g, it is constant weight m ₂ ;

Step 6, blank test, take a blank platinum dish of the same specification to measure the original mass m ₄ of the blank platinum dish, and use this blank platinum dish to replace the platinum dish containing the sample, repeat the operation from step 3 to step 5, and measure the burning After completion, the mass of the blank platinum dish is m ₃ ;

Step seven, calculate the ash content, and calculate the ash content in the sample according to the data measured in the steps one and six.

Wherein, in the step 1, the volume of the platinum dish is 50ml-80ml, the measuring range of the analytical balance is 81g, and the sensitivity is 0.01mg, and a 50g sample is weighed by the analytical balance, accurate to 0.01mg.

In the first step, the samples are ground and passed through a 0.28mm sieve, put into a sample bag, and dried in a drying oven at 110°C for 2 hours; or the samples are obtained by sawing, turning, milling, grinding or crushing. A solid fragment or powder, put it into a sample bag, and dry it in a drying oven at 110°C ± 2°C for more than 16 hours to reduce the influence of the humidity of the sample on the test results, and the surface layer of the sample needs to be scraped off before processing. Oxidation has occurred, the test will affect the test results;

The drying oven is preferably a blast drying oven, and the controllable temperature is from room temperature to 200°C.

In the second step, the burning temperature of the sample in the high-temperature furnace is 950°C ± 20°C, and the furnace door is kept open at a distance of 25mm. The purpose of keeping the furnace door open is to allow air to naturally enter the furnace to fully oxidize the sample;

The high-temperature furnace is preferably equipped with a temperature regulating device, with a thermocouple and a temperature indicating instrument, which can maintain a temperature of 950°C ± 20°C. There is a round hole for inserting a thermocouple on the rear wall of the high-temperature furnace. The position of the hole should be such that the hot junction of the thermocouple In the constant temperature zone of the high temperature furnace.

In said step 3, the preferred cooling time of the platinum dish containing ash after burning is 1-2 minutes, and the reason for cooling the platinum dish containing ash after burning for 1-2 minutes is to reduce the temperature and avoid excessive temperature when entering the dryer;

The desiccator is preferably a glass desiccator with a diameter of 200-250 mm and a color-changing silica gel desiccant inside.

In said step 4, the measuring range of the analytical balance is 200g, and the sensitivity is 0.1mg.

In the fifth step, the burning time in the high-temperature furnace is preferably 20 minutes, and the burning temperature is 950°C±20°C, and burning for another 20 minutes is to determine whether all the impurities in the sample are burned clean.

In the step 7, the formula for calculating the ash content is:

A: Sample ash content, 10 ^-6 ;

m ₀ : the mass of the empty platinum crucible for testing, g;

m ₁ : original mass of sample, g;

m ₂ : the sum of the ash content of the sample and the mass of the platinum crucible after burning, g;

m ₃ : the mass of the blank platinum crucible after burning, g;

m ₄ : original mass of blank platinum crucible, g.

In the method for measuring the ash content of ultra-high-purity graphite, the same type of graphite sample needs to be measured twice in parallel, and the average value of the two parallel measurements is taken, which can effectively reduce the test error.

1. The preparation method provided by the invention has the following advantages:

(1) Carry out a blank test with a blank platinum dish of the same specification and model as that containing the sample material, measure the mass change of the blank platinum dish during the measurement process, and then determine the mass change of the platinum dish containing the sample material during the measurement process, and Add this mass change into the calculation formula to realize the test of ultra-high-purity graphite ash content (<10×10 ^-6 ), and obtain the result data with good accuracy and repeatability;

(2) For the same test sample, increase the parallel test, obtain the test average value through the parallel test, and pass the precision of the test result;

(3) By installing a dehumidifier and an air conditioner in the weighing room, the temperature and humidity in the weighing room are controlled to reduce the impact of temperature and humidity changes on the test results;

(4) When weighing the sample and weighing the ash, an analytical balance with a maximum weighing capacity of 200g, a sensing capacity of 0.1 mg, a maximum measuring range of 81 g, and a sensing capacity of 0.01 mg was selected to improve the accuracy of weighing.

2. The inventor searched the literature at the beginning of the experiment, and found a test method for trace impurities in ultra-high-purity graphite, namely CN201110056199.6. In order to obtain ultra-fine-pore graphite prepared from coarse-grained coke aggregates, the inventor , improved on the basis of the patent:

1) In terms of sample weighing: the 2011 patent only limited the sample mass to 4 to 5 times the number of parent samples specified in JB/T8133.17-1999, and did not limit the precise unit for sample weighing. And there is no limit to the pretreatment of the sample before the test, but the present invention limits the weight of the sample, and the pretreatment of the sample reduces the humidity of the sample and removes the oxidized part of the surface layer of the sample;

2) In terms of sample testing: the 2011 patent did not set any limits on the burning degree of the sample, but the present invention defines that after the sample is burned twice in a row, the difference between the two weighings is not more than 0.0001g, then the platinum dish and the Constant weight of ash, higher precision;

3) In the blank test: the 2011 patent only proposed the concept of the change rate k of the ceramic crucible containing the sample before and after high-temperature burning, and did not specifically propose the test and calculation method of the change rate k. The invention limits the use of a blank platinum dish of the same specification and model as that containing the sample material for the blank test. The poor quality of the blank platinum dish before and after burning is the poor quality of the platinum dish containing the sample material during the test process. The concept and test method of rate;

And using a blank platinum dish for the blank test, compared with the platinum dish containing the sample material for the test, the blank platinum dish avoids the influence of the ash residue of the sample material, and the platinum dish containing the sample material has been burnt at high temperature, losing part of its quality. It is not advisable to use it for a blank test, which has already produced errors;

4) Parallel testing: the 2011 patent did not propose parallel testing, but the present invention proposes parallel testing, using parallel testing to obtain the deviation between the average test result and the parallel samples, and improve the accuracy of the test results.

3. Compared with the traditional method YB/T 5146-2000

1) In terms of sample weighing: YB/T 5146-2000 only stipulates to weigh 15g (accurate to ±0.0002g) dry-based sample. For ultra-high-purity graphite materials, the impurity content in a 15g sample is Too small will affect the test results, but the present invention improves the weighing quality of the sample, and increases the weighing quality to 50g, so that the quality change of the sample before and after burning is more obvious, which is beneficial to the test;

2) On the blank test: YB/T 5146-2000 does not propose a blank test, nor does it take into account the impact of the mass loss of the platinum dish on the ash test results during the high-temperature burning process, but the present invention fully considers the impact of the platinum dish on the test results In order to avoid the impact of the influence of the platinum dish, a blank platinum dish of the same specification and model was selected for a blank test, and the influence of the quality change of the platinum dish on the test results was removed;

3) Parallel testing: YB/T 5146-2000 does not propose parallel testing, but the present invention proposes parallel testing, using parallel testing to obtain the deviation between the average test result and parallel samples, and improve the accuracy of the test results.

Generally speaking, the method of the present invention has a clear idea, removes as many external factors as possible that affect the test results, improves the accuracy of the test results, and is especially suitable for the test of ultra-high-purity graphite ash.

Description of drawings

Fig. 1 is a schematic process flow diagram of a method for measuring the ash content of ultra-high-purity graphite according to the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In describing the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " Orientation indicated by rear, left, right, vertical, horizontal, top, bottom, inside, outside, clockwise, counterclockwise, etc. The positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, Therefore, it should not be construed as limiting the invention.

In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Thus, a feature defined as "first" and "second" may explicitly or implicitly include one or more of these features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

Example:

As shown in Figure 1, a kind of assay method for ultra-high purity graphite ash, comprises the following steps:

Step 1, weighing the sample, keeping the temperature of the weighing chamber constant, using an analytical balance to weigh the mass m ₀ of the platinum dish used to place the sample, and weighing the sample mass m ₁ ;

Step 2, burning at high temperature, placing the weighed sample in a platinum dish, and then placing the platinum dish in a high-temperature furnace to burn until the sample is burnt out to form ash;

Step 3, dry and cool, place the burnt platinum dish filled with ash on an asbestos net to cool for 1 to 3 minutes, then transfer to a desiccator to cool to room temperature;

Step 4, weighing and recording, after the ash in the platinum dish is cooled to normal temperature, use an analytical balance to weigh and record the total mass of the platinum dish and the ash in it;

Step 5, the second measurement, put the platinum dish into the high-temperature furnace again and burn it. After the burning is completed, repeat steps 4 and 5 to record the total mass of the platinum dish and the ash in it until the difference between two consecutive weighings ≤0.0001g, it is constant weight m ₂ ;

Step 6, blank test, take a blank platinum dish of the same specification to measure the original mass m4 of the blank platinum dish, and use the blank platinum dish to replace the platinum dish containing the sample, repeat the operation from step 3 to step 5, and measure that the burning is complete The mass of the rear blank platinum dish m ₃ ;

Step seven, calculate the ash content, and calculate the ash content in the sample according to the data measured in the steps one and six.

In said step one, the volume of the platinum dish is 50ml-80ml, the measuring range of the analytical balance is 81g, and the sensitivity is 0.01mg. The platinum dish is used to hold the sample, and the sample mass m1 is preferably 50g, so that the quality of the sample before and after burning is poor. become apparent.

Further, the samples need to be ground and pass through a 0.28mm sieve, put into a sample bag, and dry in a drying oven at 110°C for 2 hours; or the samples can be sawed, turned, milled, ground or crushed to obtain multiple solid fragments Or powder, put it into a sample bag, and dry it in a drying oven at 110℃±2℃ for more than 16h.

The grinding treatment of the sample is to facilitate the subsequent burning treatment, and the drying before the test is to remove the moisture contained in the sample, so as to avoid the influence of the moisture in the sample on the test result, and the surface layer of the sample needs to be removed before the sample is ground. Oxide layer, to avoid the impact of the surface oxide layer on the test results.

In the second step, the burning temperature of the sample in the high-temperature furnace is 950°C±20°C, and the opening distance of the furnace door is kept at 25mm.

The furnace door is kept open at a distance of 25 mm to allow air to naturally enter the furnace to oxidize the sample.

In the third step, the cooling time of the platinum dish containing the ash after burning is preferably 1-2 minutes, and the desiccator is preferably a glass desiccator with a diameter of 200-250 mm and a color-changing silica gel desiccant inside.

The temperature of the burned ash and platinum dish is as high as 900°C. If the ash and platinum dish are directly placed in a glass desiccator to cool to room temperature, the glass desiccator will be damaged due to the high temperature.

In said step 4, the measuring range of the analytical balance is 200g, and the sensitivity is 0.1mg.

In the fifth step, the burning time in the high-temperature furnace is preferably 20 minutes, and the burning temperature is 950°C±20°C.

How to determine whether the sample is completely burnt, through repeated burning, measure the mass change of the ash on the adjacent two sides after burning, when the mass change is ≤0.0001g, it is completely burned.

In the step 7, the formula for calculating the ash content is:

A: Sample ash content, 10 ^-6 ;

m ₀ : the mass of the empty platinum crucible for testing, g;

m ₁ : original mass of sample, g;

m ₂ : the sum of the ash content of the sample and the mass of the platinum crucible after burning, g;

m ₃ : the mass of the blank platinum crucible after burning, g;

m ₄ : original mass of blank platinum crucible, g.

Among them, m ₂ -m ₀ has removed the mass lost by the burning of the platinum dish during the burning process. By increasing the weight loss of the crucible, the mass lost by the burning of this part of the platinum dish is replaced, so that the mass of the ash The measurement is more accurate.

In YB/T 5146-2000, the formula for calculating ash content is:

In the formula:

A——the ash content of the sample, the unit is 10 ^-6 ;

m ₁ ——mass of residue after burning the sample, unit is g;

m—weigh the mass of the sample, in g;

10 ^-6 - converted into 10 ^-6 magnification;

The ash calculation formula recorded in the 2011 patent is:

A＝(G1－G2*k)/GX 100％

In the formula: A——ash or impurity content;

G - the parent weight of the sample;

G1 - the weight of the ceramic crucible and sample residue after firing;

G2 - the weight of the ceramic crucible containing the sample;

K——The change rate of the ceramic crucible sample cup before and after burning.

Compared with YB/T 5146-2000, the ash content calculation formula of the present invention can be clearly distinguished, the ash content calculation formula of the present invention fully considers the quality change of the platinum dish during the burning process, and it will burn the platinum dish The weight loss during firing is calculated into the formula (crucible weight loss).

Compared with the 2011 patent, the ash calculation formula of the present invention clarifies the measurement method and calculation method of the mass change of the platinum dish before and after burning, making the test and calculation results more accurate.

Wherein, in the method for measuring the ash content of ultra-high-purity graphite, the same graphite sample needs to be measured twice in parallel.

20 parallel samples were prepared from graphite with the same number and high purity, and the tests were completed by two persons under the same conditions. The results are shown in Table 1 below:

Table 1 Test results of different personnel

Ash/10 ^-6 Experimenter A Experimenter B Average/10 ^-6 15.82 16.00 standard deviation/10 ^-6 1.01 1.50

20 graphite samples with different numbers and different purity were selected for testing, and the test results are shown in Table 2:

Table 2 Test results of different samples

It can be known from Table 1 and Table 2 that the ash content determination method of the present invention can measure the ash content of the sample accurately to 10 ^-6 , and the ash content test result is more accurate by conducting parallel tests and calculating the test average value.

And when the deviation of the ash content of the parallel test sample is greater than 10ppm, it means that the test result is deviated and the test result is inaccurate. It is necessary to re-weigh the sample and perform the test again, and recalculate the ash content, which provides a way to test the accuracy of the test result.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. a kind of measuring method for ultra-pure graphite ash content, which is characterized in that include the following steps：

Step 1 weighs sample, keeps weighing room temperature constant, weighs the platinum ware for placing sample using assay balance Quality m₀, and weigh sample quality m₁；

Weighed sample is placed in platinum ware by step 2, high temperature sintering, then platinum ware is placed in calcination in high temperature furnace, Until sample burns out to form ash content；

The platinum ware that ash content is filled after calcination is placed on asbestos gauge cooling 1~3min, is transferred to dry by step 3, dry cooling It is cooled to room temperature in dry device；

Step 4 weighs record, after the ash content in platinum ware is cooled to room temperature, is weighed and is recorded using assay balance platinum ware and The gross mass of ash content in it；

Platinum ware is placed again into calcination in high temperature furnace by step 5, double measurement, after the completion of calcination, repeats step 4 and step Five, the gross mass of record platinum ware and the ash content in it the, until difference≤0.0001g weighed twice in succession, then be constant weight m₂；

Step 6, skip test take same specification blank platinum ware to measure blank platinum ware original quality m4, and utilize the blank Platinum ware substitutes the platinum ware for filling sample, repeats the operation of step 3 to step 5, measures blank platinum ware after calcination Quality m₃；

Step 7 calculates ash content, according to step 1 and step 6 data measured, calculates the ash content in sample.

2. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In one, the volume of platinum ware is 50ml~80ml, and the range of assay balance is 81g, sensibility reciprocal 0.01mg.

3. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In one, sample all passes through 0.28mm sieve pore by milled processed, is packed into sample bag, dries 2h in 110 DEG C of drying boxes；Or sample Product are packed into sample bag, at 110 DEG C from multiple solid fragments or powder is wherein obtained by saw, turning, milling, grinding or crushing It is dry in ± 2 DEG C of drying box to be greater than 16h.

4. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In one, sample quality m₁Preferably 50g.

5. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In two, calcination temperature of the sample in high temperature furnace is 950 DEG C ± 20 DEG C, and keeps door opened distance 25mm.

6. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step The platinum ware preferred cooling time that ash content is filled in three, after calcination is 1~2min, and drier is preferably glass desicator, directly 200~250mm of diameter, built-in discoloration silica-gel desiccant.

7. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In four, the range of assay balance is 200g, sensibility reciprocal 0.1mg.

8. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In five, the calcination time in high temperature furnace is preferably 20min, and calcination temperature is 950 DEG C ± 20 DEG C.

9. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that the step In seven, the formula for calculating ash content is：

A：Sample ash content, 10^-6；

m₀：Quality of the test with empty platinum crucible, g；

m₁：Sample original quality, g；

m₂：The quality sum of sample ash content and platinum crucible, g after calcination；

m₃：The quality of blank platinum crucible, g after calcination；

m₄：Blank platinum crucible original quality, g.

10. a kind of measuring method for ultra-pure graphite ash content according to claim 1, which is characterized in that described super In the measuring method of high purity graphite ash content, graphite sample of the same race need to be measured in parallel twice.