阅读说明：本技术 键合剂中硼含量的测定方法 (Method for measuring boron content in bonding agent ) 是由 冯晓欢 徐红菊 黄水生 闫志佳 廖建苹 李德旭 王娜 王艳艳 张华燕 于 2020-12-11 设计创作，主要内容包括：本发明公开了一种键合剂中硼含量的测定方法,先精确称取试样后加入坩埚中,用氢氧化钾覆盖在试样上,然后在马弗炉内进行灼烧,至试样不再冒泡呈白色固体；灼烧完成后,取出坩埚冷却,加入蒸馏水将熔化物转移至烧杯中；利用动态电位滴定加入过量的盐酸消耗试样熔化物中的氢氧化钾,再利用动态PH滴定加入氢氧化钠中和过量的盐酸,此时试样中的硼酸盐转化为弱硼酸,加入丙三醇,搅拌均匀,最后利用动态电位滴定加入氢氧化钠,此时消耗的氢氧化钠溶液为滴定试样所耗；计算可得键合剂试样中的硼含量。本发明方法结合动态电位滴定和动态PH滴定两种方式,通过电位变化及PH值判断终点,避免指示剂指示终点引入的操作误差。(The invention discloses a method for measuring boron content in a bonding agent, which comprises the steps of accurately weighing a sample, adding the sample into a crucible, covering the sample with potassium hydroxide, and then burning the sample in a muffle furnace until the sample is no longer foamed and appears as a white solid; after firing, taking out the crucible for cooling, and adding distilled water to transfer the melt into a beaker; adding excessive hydrochloric acid to consume potassium hydroxide in a sample melt by utilizing dynamic potentiometric titration, adding sodium hydroxide to neutralize excessive hydrochloric acid by utilizing dynamic PH titration, converting borate in the sample into weak boric acid, adding glycerol, stirring uniformly, and finally adding sodium hydroxide by utilizing dynamic potentiometric titration, wherein the consumed sodium hydroxide solution is consumed by a titration sample; and calculating to obtain the boron content in the bonding agent sample. The method disclosed by the invention combines two modes of dynamic potentiometric titration and dynamic PH titration, and judges the end point through the potential change and the PH value, so that the operation error caused by the indication of the end point by the indicator is avoided.)

1. A method for measuring the content of boron in a bonding agent is characterized by comprising the following steps:

s1, accurately weighing the sample, adding the sample into a crucible, covering the sample with potassium hydroxide, and then burning in a muffle furnace until the sample does not bubble any more and is a white solid;

s2, after the firing is finished, taking out the crucible for cooling, and adding distilled water to transfer the melt into a container;

s3, adding excessive hydrochloric acid to consume potassium hydroxide in the sample melt by utilizing dynamic potentiometric titration, adding sodium hydroxide to neutralize excessive hydrochloric acid by utilizing dynamic PH titration, converting borate in the sample into weak boric acid, adding glycerol, stirring uniformly, and finally adding sodium hydroxide by utilizing dynamic potentiometric titration, wherein the consumed sodium hydroxide solution is consumed by the titration sample;

s4, calculating by using a formula to obtain the boron content in the bonding agent test,

in the formula: omega-boron content,%;

c is the concentration of the sodium hydroxide standard solution, mol/L;

EP₂-the volume of sodium hydroxide standard solution consumed for titrating a sample (mL);

m-sample mass, g;

0.01081-mass of boron, g, equivalent to 1.00mL of sodium hydroxide standard titration solution.

2. The method of claim 1, wherein: the crucible used for S1 was a nickel crucible.

3. The method of claim 1, wherein: the weight ratio of the sample to the potassium hydroxide in the S1 is 1: 4-6 times.

4. The method of claim 1, wherein: and S1, the temperature in the muffle furnace is 300-400 ℃, and the muffle furnace door is opened in the burning process.

5. The method of claim 1, wherein: at the time of dynamic potentiometric titration, excess hydrochloric acid was added to neutralize potassium hydroxide in the sample melt in S3.

6. The method of claim 1, wherein: before dynamic pH titration in S3, nitrogen is introduced firstly, then sodium hydroxide is used for titration, and the end point pH is 6.9-7.1.

7. The method of claim 1, wherein: in S3, the amount of glycerol is related to the boron content of the sample, and the glycerol is added sufficiently to complex the boric acid in solution.

8. The method of claim 1, wherein: in S3, when sodium hydroxide is added in dynamic potentiometric titration, the pH value is 7.2-7.5.

9. The method of claim 1, wherein: when hydrochloric acid is added in dynamic potentiometric titration, two potential equivalence points are set, and the potential is evaluated to be 10 mv; the potential was evaluated at 15mv at dynamic PH titration; dynamic potentiometric titration two potential equivalence points were set when sodium hydroxide was added and the potential was estimated to be 10 mv.

10. The method according to any one of claims 1-9, wherein: after the sample is melted by alkali and is added with distilled water to prepare a solution, the solution enters a titration link of S3, and the time is controlled within 15 min.

Technical Field

The invention relates to the technical field of propellant testing, in particular to a method for measuring the boron content in a bonding agent.

Background

The common oxidant, RDX, HMX and AP in the composite solid propellant belong to non-reinforced filler, when the propellant is subjected to a certain load, the interface bonding between solid oxide particles and a binder matrix is easily damaged, the adhesion between the solid oxide particles and the binder matrix fails to cause the binder matrix to be separated from the surface of the solid particles, the 'dehumidification' phenomenon occurs, the mechanical property, the combustion property and the storage stability of the propellant are seriously influenced, and the use of the propellant is further influenced.

The bonding agent can effectively improve the mechanical property of the propellant and prevent the phenomenon of 'moisture removal'. The borate bonding agent can obviously improve the mechanical property of the butylated hydroxytetramethylene propellant, so the borate bonding agent is an important raw material of the propellant.

In raw material detection, the boron content is an important index of the borate bonding agent. At present, the traditional chemical capacity analysis method is still adopted for detecting the boron content of the borate bonding agent. However, the gravimetric method specified in these standards is slow, and even if the work is done in the early stage, it still takes 4-5 hours to process and analyze each batch of samples. Therefore, there is an urgent need for a fast and relatively accurate method when examining a large number of samples. However, the traditional analysis method has a large dependence on visual estimation, needs to judge the color change of the indicator by naked eyes to obtain an end point, repeatedly changes the color of the solution in the analysis process, has many titration steps, not only has low analysis efficiency, but also easily causes human errors in the visual estimation of the titration end point and the titration volume, and is difficult to ensure the analysis precision and accuracy.

Disclosure of Invention

The invention provides a method for measuring the boron content in a bonding agent, which combines two modes of dynamic potentiometric titration and dynamic PH titration and judges an end point through potential change and a PH value so as to avoid operation errors caused by indicating the end point by an indicator.

The invention has the technical scheme that the method for measuring the boron content in the bonding agent comprises the following steps:

s1, accurately weighing the sample, adding the sample into a crucible, covering the sample with potassium hydroxide, and then burning in a muffle furnace until the sample does not bubble any more and is a white solid;

s2, after the firing is finished, taking out the crucible for cooling, adding distilled water to transfer the melt into a beaker;

s3, adding excessive hydrochloric acid to consume potassium hydroxide in the sample melt by utilizing dynamic potentiometric titration, adding sodium hydroxide to neutralize excessive hydrochloric acid by utilizing dynamic PH titration, converting borate in the sample into weak boric acid, adding glycerol, stirring uniformly, and finally adding sodium hydroxide by utilizing dynamic potentiometric titration, wherein the consumed sodium hydroxide solution is consumed by the titration sample;

s4, calculating by using a formula to obtain the boron content in the bonding agent test,

in the formula: omega-boron content,%;

c is the concentration of the sodium hydroxide standard solution, mol/L;

EP₂-the volume of sodium hydroxide standard solution consumed for titrating a sample (mL);

m-sample mass, g;

0.01081-mass of boron, g, equivalent to 1.00mL of sodium hydroxide standard titration solution.

Further, the crucible used in S1 was a nickel crucible.

Furthermore, the weight ratio of the sample to the potassium hydroxide in S1 is 1: 4-6 times.

Further, the temperature in the muffle furnace in S1 is 300-400 ℃, and the muffle furnace door is opened in the burning process.

Further, in S3, before adding hydrochloric acid by dynamic potentiometric titration, potassium hydroxide in the sample melt was neutralized by adding an excess of hydrochloric acid. Further, before dynamic PH titration in S3, nitrogen was introduced and then sodium hydroxide was added for titration, and the end point PH was 6.9 to 7.1.

Further, in S3, glycerol was used in an amount related to the boron content of the sample, and the glycerol was added in an amount sufficient to complete the complexation of the boric acid in the solution.

Further, in S3, when sodium hydroxide is added in dynamic potentiometric titration, the pH value is 7.2-7.5.

Further, when hydrochloric acid is added in dynamic potentiometric titration, two potential equivalence points are set, and the potential is evaluated to be 10 mv; the potential was evaluated at 15mv at dynamic PH titration; dynamic potentiometric titration two potential equivalence points were set when sodium hydroxide was added and the potential was estimated to be 10 mv.

Further, after the sample is melted by alkali and is added with distilled water to be made into a solution, the time is controlled within 15min before entering a titration link of S3.

Potentiometric titration is a method of determining the end point of titration by measuring the change in potential during titration. In the titration process, the potential values of ions to be measured and electrodes are changed along with the addition of a titrant, the activity of the ions to be measured is suddenly changed near an equivalence point, the potential of the electrodes is suddenly changed, and the content of a measured substance is calculated according to the consumption of a standard titration solution corresponding to the sudden change point.

The test sample in the invention can not be directly tested, and pretreatment is required, specifically, after the test sample is subjected to potassium hydroxide alkali melting decomposition, metaborate is obtained. Dissolving in distilled water, adding propanetriol to produce borate ester, titrating the dissociated hydrogen ion with standard sodium hydroxide solution, and calculating the boron content.

4H₃BO₃+2KOH＝＝＝K₂B₄O₇(Potassium tetraborate) +7H₂O (KOH deficiency)

K₂B₄O₇+2KOH＝＝＝4KBO₂(Potassium metaborate) + H₂O (excess KOH))

The invention has the following beneficial effects:

1. compared with the traditional indicator titration method, the method can accurately judge the titration end point depending on the potential value change, and is not influenced by the color and the clarity of the solution. The glycerol is adopted to complex the boric acid, so that the method is convenient and quick and has lower cost.

2. According to the invention, a potentiometric titration method is adopted to determine the boron content in the borate bonding agent, after sample pretreatment, one batch of traditional manual titration needs at least 10min, and one batch of potentiometric titration only needs about 5 min. Compared with the traditional manual titration method, the volume of the titration solution needs to be confirmed again after each batch of titration is finished, the tedious operations of repeatedly adding and discharging the titration solution are needed, and the potentiometric titration method can be simplified. The advantages are more obvious when a large batch of borate bonding agents are tested, and the analysis time can be shortened by at least half. Meanwhile, the titration operation is changed from pure manual titration into automatic titration, the automation degree is high, the processing batch is large, the labor intensity of personnel is greatly reduced, the manual error caused by the personnel operation is avoided, the operability is high, and the measurement result is reliable.

Drawings

FIG. 1 is a main flow chart of the method of the present invention.

FIG. 2 is a graph showing the acid-mediated reaction after the solution was allowed to stand for 0.5 h.

FIG. 3 is a graph showing the acid adjustment reaction curve after the solution was allowed to stand for 15 hours.

FIG. 4 is a pH change curve of a sample solution adjusted with hydrochloric acid.

FIG. 5 is a graph showing the pH of the sample solution.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.

Example 1:

weighing 0.5000g of bonding agent sample in a nickel crucible, adding 2.0000g of potassium hydroxide to cover the sample, placing the sample in a muffle furnace at 300 ℃, firing the sample until the sample is white solid without bubbling, and opening a muffle furnace door in the firing process. After the firing was completed, the nickel crucible was taken out and cooled, and distilled water was added to transfer the entire melt to a beaker.

The titration process is shown in figure 1, firstly adding excessive 1mol/L hydrochloric acid by dynamic potentiometric titration to consume potassium hydroxide in a sample melt, secondly adding 0.1mol/L sodium hydroxide by dynamic PH titration to neutralize excessive hydrochloric acid, then converting borate in the sample into weak boric acid, adding 25mL of glycerol in time, stirring uniformly, and finally adding sodium hydroxide by dynamic potentiometric titration, wherein the consumed sodium hydroxide solution is consumed by the titration sample.

Finally, the boron content in the bonding agent test is obtained by calculation by using a formula,

in the formula: omega-boron content,%;

c is the concentration of the sodium hydroxide standard solution, mol/L;

EP₂-the volume of sodium hydroxide standard solution consumed for titrating a sample (mL);

m-sample mass, g;

in the present embodiment, during the calculation,

example 2:

weighing 1.0000g of bonding agent sample in a nickel crucible, adding 5.0000g of potassium hydroxide to cover the sample, placing the sample in a muffle furnace at 400 ℃, burning the sample until the sample is white solid without bubbling, and opening a muffle furnace door in the burning process. After the firing was completed, the nickel crucible was taken out and cooled, and distilled water was added to transfer the entire melt to a beaker.

Firstly, adding excessive 1mol/L hydrochloric acid by utilizing dynamic potentiometric titration to consume potassium hydroxide in a sample melt, secondly, adding 0.1mol/L sodium hydroxide by utilizing dynamic PH titration to neutralize excessive hydrochloric acid, at the moment, converting borate in the sample into weak boric acid, adding 60mL of glycerol in time, stirring uniformly, and finally, adding sodium hydroxide by utilizing dynamic potentiometric titration, wherein the consumed sodium hydroxide solution is consumed by a titration sample.

Finally, the boron content in the bonding agent test is obtained by calculation by using a formula,

in the formula: omega-boron content,%;

c is the concentration of the sodium hydroxide standard solution, mol/L;

EP₂-the volume of sodium hydroxide standard solution consumed for titrating a sample (mL);

m-sample mass, g;

0.01081-mass of boron, g, equivalent to 1.00mL of sodium hydroxide standard titration solution.

In the present embodiment, during the calculation,

the invention also reduces CO in the air₂The influence of the sample solution is researched, when the pH of the sample solution is adjusted by hydrochloric acid, the sudden electrode potential jump near the 3 rd equivalence point is not obvious during the solution acid-base neutralization reaction, so that the acid-base dosage is changed greatly and is not easy to control during the adjustment of the acidity, the boron analysis result is unstable, and the specific result is shown in table 1. Further, the acid adjustment reaction curve after the solution was left to stand for 0.5 hours is shown in FIG. 2, and the acid adjustment reaction curve after the solution was left to stand for 15 hours is shown in FIG. 3.

TABLE 1 determination of boron content of samples exposed to air for different periods of time

As can be seen from the data in Table 1 and FIGS. 2 and 3, the time of exposing the sample solution to air should be controlled within 15min, i.e., the titration step is required, otherwise the parallel difference of the test results is large or the jump potential cannot be correctly obtained. The nitrogen was also introduced during the test to isolate air. And if the titration measurement cannot be carried out in time, keeping the alkali fusion solid sample in a muffle furnace at 300-400 ℃, not carrying out aqueous solution treatment, and carrying out treatment test when the titration operation time link can be controlled.

Further, two batches of certain borate bonding agents were randomly selected for boron content testing, and the test results are shown in table 2. The time of the sample solution exposed in the air is controlled within 15min, and the parallel difference of the two groups of test results is less than 0.1 percent.

TABLE 2 determination of boron content of samples within 15min of air exposure of the sample solutions

Determination and influence of acidity of solution when complexing boric acid and glycerol

The acidity of the solution was varied prior to glycerol addition and the effect on the test results is shown in table 3 and figure 4.

TABLE 3 influence of pH of sample solution on the measurement results of boron content in the sample

As can be seen from Table 3, the test results of the boron content of the samples were regularly changed before the same amount of glycerin was added, while the pH of the sample solution was controlled differently. The pH is acidic, the test value of the boron content in the bonding agent is high, and the test value exceeds the theoretical boron content of the sample; the pH is alkaline, and the test value of the boron content in the bonding agent is low. The pH bias is acidic and alkaline, which results in a large difference in parallelism of the sample. The difference in parallelism of the samples was < 0.1% at pH 7, which is the optimum condition for pH before addition of the glycerol solution.

The traditional method relies on the color change of a methyl red indicator to judge that the time for adding glycerol has a certain influence on the accuracy of a boron content test result, and a solution potential curve chart shown in figure 5 shows that when the pH value of a solution is about 6.7, the electrode potential change along with the addition amount of hydrochloric acid is most obvious, but the color change range of the methyl red indicator is 4.4-6.2, after the solution is changed into bright yellow, the amount of the added hydrochloric acid has no change on the color of the solution, but the influence on the actual pH of the solution is large, and the pH adjustment and the glycerol addition time in the dripping time of the traditional method can not be completely consistent, so that the test result is influenced.

The pH of the sample solution was measured and the results are shown in FIG. 5. As can be seen from FIG. 5, the pH of the sample solution can be accurately controlled within the range of 6.9 to 7.1 by using an automatic potentiometric titrator, thereby ensuring the required pH during the complexation reaction.

Considering that the sample solution was adjusted to pH 7.0 with hydrochloric acid before the addition of the glycerol solution to the complex reaction, the addition of the glycerol solution lowered the pH of the sample solution. The influence of the micro-change of the acidity of the solution on the determination of the boric acid content by the method is researched by changing the using amount of the glycerol solution, and the specific result is shown in Table 4.

TABLE 4 determination of boron content in samples with different glycerol dosages

As can be seen from Table 4, when the boron content of the bonding agent is between 2% and 3%, and the amount of glycerol is less than 15ml, the complexing with boric acid in the solution is incomplete, so that the test result is relatively low. In addition, when the amount of change in the amount of the glycerol solution was not large (5 ml intervals), the change in the acidity of the sample solution was not significantly affected. Therefore, when the boric acid content in the sample is between 2% and 3%, the minimum amount of the glycerol solution is 20ml, the addition amount of the glycerol is enough, otherwise, the generated glycerol boric acid is incomplete, and the measurement result is lower.

Accuracy verification

In order to determine the correct effectiveness of the parameter setting and the condition control in operation of the method, 1.6175g of analytically pure boric acid reagent is accurately weighed and transferred into a 250ml volumetric flask, 10ml, 15ml and 19ml are respectively transferred and C is taken_NaOHThe boron content was determined by the automated potentiometric titration method using 0.1019mol/L sodium hydroxide standard titration solution, and the results are shown in Table 5.

TABLE 5 recovery of spiked boric acid

As can be seen from Table 5, the recovery rate of the boron content measured by potentiometric titration was 102.26% after a known amount of boric acid standard sample was added, and the accuracy of the test method was high.

Precision verification

The boron content in the bonding agent samples of the same batch is measured by the method, precision verification is carried out by measuring the boron content in the samples for 8 times in parallel, and the test results are shown in Table 6.

TABLE 6 statistics of parallel assay results for samples from the same lot

The RSD of 8 results is less than 1.5%, indicating that the precision of the method is higher.