Comparative Study on Inert Gas Detection Methods of Insulating Glass

Gas-filled hollow glass refers to two or more pieces of glass to effectively support and evenly separate and adhere to and seal the periphery so that a dry inert gas space is formed between the glass layers. Compared with air, inert gas has a high density and low thermal conductivity, so it can slow down the thermal convection in the middle layer (the term "thermal convection" is provided by Google), reduce the thermal conductivity of the gas, and thereby reduce the hollow (the term "Hollow Glass" provided by Google) The heat transfer coefficient of glass helps to improve the insulation performance and energy-saving effect of insulating glass. The higher the concentration of insulating glass filled with inert gas, the better the effect of improving energy saving. The inert gas is colorless and tasteless. How to determine whether the gas-filled hollow glass is filled with inert gas, the gas concentration and whether the gas retention rate is good or bad is the key to evaluating the quality of the gas-filled hollow glass through related detection methods.

As more powerful implementation of the energy policy of the world's nations, building energy efficiency requirements are gradually improving, prompting the Low-E coating (the term "Low-E Coating" provided by Google) to continue to spread in the hollow glass, hollow glass filled with inert Gas has also attracted more and more attention from all quarters. In the general environment of building energy saving in various countries, due to the characteristics of low production cost and good energy-saving effect, the subsequent promotion and application of inflatable insulating glass is the development trend of modern buildings. Therefore, it is particularly important to establish detection methods for inert gas analysis. At present, there are three methods for the analysis and detection of inert gases: high-voltage electric spark method, oxygen paramagnetic method, and gas chromatography.

^{The insulating glass filled with inert gas detector 1}

1. Performance evaluation index

There are three main evaluation indicators for insulating glass filled with an inert gas: inert gas volume percentage, gas leakage rate, and gas seal durability.

1.1 Inert gas volume percentage

The volume percentage of inert gas is one of the evaluation indicators of the air-filled insulating glass. The volume percentage directly affects the heat transfer coefficient of the air-filled insulating glass, that is, the energy-saving effect. The volume percentage of a gas refers to the proportion of the volume occupied by a gas in a certain mixed gas, namely:

The following lists the heat transfer coefficients of three different configurations of insulating glass when inflated with different content of argon gas. The analysis shows the influence of the volume percentage of the inflated gas on the performance of the insulating glass. Different configurations of insulating glass are (4 white glass + 12 gas layer + 4 white glass) mm, (4 online Low-E + 12 gas layer + 4 white glass) mm, and (4 offline Low-E + 12 gas layer + 4 white glass) mm. For each type of glass, the heat transfer coefficient is calculated when the argon gas concentration increases from 0% to 100% every 5%. The results are shown in Figure 1. From the above results, we can get:

^{The influence of the volume percentage of inert gas on the heat transfer coefficient of insulating glass 1}

(1) The higher the argon concentration, the smaller the heat transfer coefficient of the insulating glass and the better the heat preservation performance.

(2) Under the same argon gas concentration, the improvement of the heat transfer coefficient of coated insulating glass by inert gas is more obvious than that of ordinary insulating glass. Therefore, to make the gas-filled insulating glass have good energy-saving and heat preservation performance, the volume percentage of inert gas should be as high as possible. At present, in the architectural glass industry, considering the effect of air filling to improve the insulation performance of insulating glass and the service life of the air-filled insulating glass, it is generally believed that the initial inert gas content of air-filled insulating glass should not be less than 85%.

1.2 Gas leakage rate

The gas leakage rate refers to the percentage of the volume of gas that leaks from the intermediate gas layer of the hollow glass each year. The value is directly related to the service life of the gas-filled hollow glass. The lower the gas leakage rate, the longer the service life of the gas-filled hollow glass. It is a gas-filled hollow glass One of the important evaluation criteria.

According to EU standard EN1279-3:2002 "Glass in Building- Insulating Glass Units- Part 3: Long Term Test Method and Requirements for Gas Leakage Rate and for Gas Concentration Tolerances", the annual gas leakage rate of inert gas should not be greater than 1%, specific calculations The formula is as follows:

^{The calculation formula of inert gas annual gas leakage rate 1}

1.3 Gas seal durability

Gas sealing durability is characterized by the gas volume percentage of the air-filled insulating glass after the climate cycle test. The gas sealing durability of the air-filled insulating glass should be ≥80%, which is the inert gas volume percentage of the insulating glass after the climate cycle test. Should be ≥80%.

Gas seal durability can characterize the durability and service life of gas-filled hollow glass to a certain extent. The test principle and process are also relatively simple. It is suitable for the high-voltage electric spark method, oxygen paramagnetic method, and gas chromatography. However, in comparison, the durability of gas sealing has a more general evaluation of the service life of the gas-filled insulating glass, which is not as intuitive and quantitative as the gas leakage rate. This paper does not discuss the durability of gas seals in detail.

2. Detection method

At present, there are three methods for the analysis and detection of inert gases: high-voltage electric spark method, oxygen paramagnetic method, and gas chromatography.

2.1 High voltage electric spark method

The high-voltage spark method uses high-voltage sparks generated by the equipment to penetrate the glass and the intermediate gas layer to activate the plasma of the inert gas molecules to emit radiation waves. Through emission spectroscopy, the instrument collects the photons for analysis, and the spectrometer in the equipment accepts Calculate the inert gas content after light. This detection method does not need to damage the hollow glass sample, is a non-destructive detection method, and is suitable for testing at any stage of the hollow glass life span. It can be used to test the quality management of the hollow glass inflation process, and it can also be used for the concentration test after the glass is installed. Although the high-voltage spark method has the advantages of non-destructive testing, it has greater limitations. In the case of excessive glass thickness, double-layered insulating glass, double-coated insulating glass, and excessive thickness of the intermediate gas layer, high-voltage sparks cannot penetrate When the glass reaches and penetrates the air layer, the concentration of inert gas cannot be accurately measured. The thickest laminated glass that can be penetrated by the high-voltage spark method is 10mm, and the thickest intermediate gas layer is 24mm.

Based on the principle of the high-voltage electric spark method, this method is suitable for evaluating the volume percentage of inert gas and the durability of gas sealing of the gas-filled insulating glass and can be used for the production of the gas-filled insulating glass, engineering site, and laboratory testing.

2.2 Oxygen paramagnetic method

The oxygen paramagnetic method uses the principle that the magnetic susceptibility of oxygen is several times higher than the magnetic susceptibility of general gas. The oxygen content is determined by the magnetic susceptibility of the mixed gas, and the content of inert gas is deduced.
Based on the principle of the oxygen paramagnetic method, the gas in the intermediate gas layer of the insulating glass must be taken out during the test. The test process damages the insulating glass sample, which is a destructive test; and the test process can only determine the content of the inert gas, and cannot be used for the inert gas. Qualitative analysis of the types. The advantage of this method is that the testing process is simple, convenient, and efficient. It is suitable for the rapid determination of the performance of insulating glass in laboratories and production lines and can be used for the evaluation of the inert gas volume percentage and the durability of gas sealing of the gas-filled insulating glass.

2.3 Gas chromatography

The principle of the separation of mixed gases by gas chromatography is to use different substances with different distribution coefficients between the two phases. When the two phases move relative to each other, the components of the sample are repeatedly distributed in the two phases, making the original Each component with only a small difference in partition coefficient produces a great separation effect, so that each component is separated, and then enters the detector to identify each component. Chromatography has the incomparable advantages of many chemical analysis methods, such as high separation efficiency, fast analysis speed, small sample amount, high sensitivity, and wide application range. The sensitivity of gas chromatography reaches the μg level, which can measure the inert gas content and the leakage of inert gas in the hollow glass sample. It is suitable for the evaluation of the volume percentage of inert gas, the gas leakage rate, and the durability of the gas seal. Gas chromatography has higher requirements for instruments and equipment and is suitable for laboratory testing.

3. Comparison of test results of 3 methods

3.1 Inert gas volume percentage

For a sample with a size of 355×505×(4+12+4)mm, this test selects a group of hollow glass samples with a gas layer filled with argon gas. The specific settings are as follows:

The manufacturer is Company X (hereinafter referred to as X). Two samples with aeration index of 1.3, 1.8, and 3.0 are selected respectively, and they are marked as group A and group B. Each group includes 3 samples with different aeration indexes. To Debian as 1#, 2#, 3#; among them, the correlation between the filling index and the argon volume percentage is: the argon content of the sample with the filling index of 1.3 is about 80%, and the sample with the filling index of 1.8 is argon. The gas content is about 90%, and the argon content of the sample with a charging index of 3.0 is about 92%. The above content is used as the nominal value of the sample during the test. The above samples were tested 4 weeks after the end of production to make the gas evenly distributed in the middle gas layer. In addition, five test points are selected for each sample, which is the midpoint of the four sides of the sample and the geometric midpoint of the sample. The average of the readings of the five test points is used as the test result of the sample, expressed in volume percentage. During the project research process, the laboratory used the high-voltage electric spark method, oxygen paramagnetism method, and gas chromatography to test the volume percentage of inert gas. To analyze the test results, Table 1 and Figure 2 are listed. Show the test results of the same batch of samples produced by X company. From the comparison of the above test results, we can get:

^{Three methods of inert gas volume percentage test results deviation 1}

(1) The inert gas volume percentages of samples from the same manufacturer and with the same inflation index measured by the same method are relatively similar. The samples used in each test method are products produced by the same manufacturer and the same batch. Among them, the maximum deviation of the test result of the high-voltage electric spark method is 2.5%, the maximum deviation of the test result of the oxygen paramagnetism method is 2.5%, and the gas chromatograph test The maximum deviation of the result is 1.7%.

(2) The test results of the high voltage electric spark method and the gas chromatography method are similar, and the maximum deviation of the test results is 2.8%.

(3) The maximum deviation between the test results of the high voltage electric spark method and the gas chromatography method and the nominal value is -3.2%, which is within the acceptable deviation range (+10%, -5%).

(4) The test result of the oxygen paramagnetic method is lower than that of the other two methods. The maximum deviation of the test result is 8.8%, and the maximum deviation from the nominal value is -9.6%.

It can be seen that among the test methods with different test principles, the test results of the high-voltage electric spark method and the gas chromatograph method are relatively similar, and the deviation from the nominal value is within the acceptable range; the oxygen paramagnetic method test The result is too small.

Due to the limitation of technical conditions and the particularity of the gas, it is impossible to precisely control the content of the gas-filled in the production process of inflated insulating glass, which results in the content of samples produced in the same batch is not the same; in addition, each test method has corresponding sampling Requirements, the sampling process can also cause deviations in the test results.

3.2 Gas leakage rate

The test method of gas leakage rate and the whole process is very complicated, but it is very necessary to evaluate the quality and service life of the gas-filled insulating glass. Among the three methods of high-voltage electric spark method, oxygen paramagnetic method, and gas chromatography, the only gas chromatograph is used. The method can accurately capture the leakage of mg or even μg, and only gas chromatography can test the gas leakage rate. In this test, two groups of argon-filled insulating glass produced by X company are selected. The samples are grouped into groups C and D. The sample size is 5 0 2 × 3 5 2 × (4+12A+4) mm6 pieces, of which 2 pieces As a spare sample, the inflation index is 3.0 for approximately parallel testing. The results and deviations of the argon leakage rate of gas-filled insulating glass tested by gas chromatography are shown in Table 2 below.

It can be seen from the above data that the test results of the argon leakage rate of group C and D meet the requirement of Li less than 1% in the standard EN1279-3:2002, and the standard deviation of the results of the two tests is 0.08, which is less than 20 in the standard. The upper limit of% indicates that the test results of the two sets of samples are desirable, and the established insulating glass inert gas chromatography method is more accurate and operable.

4. Conclusion

Through the comparison test of the initial inert gas volume percentage of the gas-filled insulating glass, the difference between the high-voltage electric spark method, the oxygen paramagnetic method, and the gas chromatography method is analyzed and compared. Select the same batch of 3 samples with different contents produced by the same manufacturer, and carry out the comparison test of the above 3 test methods. After analysis, the sample of the same manufacturer and the same inflation index measured by the same method has a higher volume percentage of inert gas. Similar; among different methods, the test results of the high-voltage electric spark method and gas chromatography are similar, the maximum deviation of the test result is 2.8%, and the maximum deviation from the nominal value is -3.2%, which is within the acceptable deviation range (+10 %, -5%); the test result of the oxygen paramagnetic method is lower than the test results of the other two methods, the maximum deviation of the test results is 8.8%, and the maximum deviation from the nominal value is -9.6%.

Only gas chromatography can meet the detection requirements of the inert gas leakage rate of inflated insulating glass. Using gas chromatography to test the gas leakage rate of two sets of the same samples from the same manufacturer, the standard deviation of the test results is 0.08, which is less than the upper limit of 0.2 in the standard, which confirms the accuracy and operability of the gas chromatography test system.

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