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5×10-1 big big big big short short big big big big big good good good good bad bad good good good good good In the table. 1, it shows the accuracy larger difference of the various methods. The measured coefficient of thermal expansion is largely influenced by the accuracy of the selected measurement method. In addition, even using the same measuring instrument, the heated sample rate change will affect the results. The main material is the process of heating the heat transfer rate of the mixed sample so that the temperature distribution during heating is unevenness. The forming a changing temperature field will bring the inevitable impact on the value of the sample. To obtain accurate thermal expansion coefficient of the material may cause some difficulty. 4 Dilatometer DIL402PC technology applications With the continuous development of glass, new ceramics and composite materials, the precise control of thermal expansion of the material and sintering characteristics is required. DIL402PC dilatometer collection instrument uses a horizontal design, simple operation, a wide range of applications. Even non-ideal sample size can be easily put into a tubular sample holder groove. Meanwhile, optimized design of the differential sensor makes the instrument even when no additional thermostatic device can provide ultra-high reproducibility and has excellent performance test[] Heam G, Testa R B. Modal Analysis for Damage Detection in structures. Joumal of StructuralEngineering, 1991, 117(10): 3042-3063. ].
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1 Measuring device DIL402PC dilatometer is manufactured by the German NETZSCH instruments company. The main parameters are as follows. Temperature range: 0-1600oC. Temperature accuracy: 0. 1oC. Displacement sensor range: ±2. 5mm. Measurement accuracy: 21nm. Heating rate: 1-30oC. Increment: 0. 01oC. The maximum diameter of the sample: 12mm. The maximum length: 50mm. The figure 1 is a structure schematic diagram of DII402PC dilatometer. Figure. 1 Dilatometer DII402PC structural representation.
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Measurement system 2. Sample holder 3. eject-rod 4. Furnace.
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2 Sample preparation requirements DIL402PC Dilatometer uses inductive displacement sensor system. The advantages of DIL402PC have a wide measuring range, good linearity, and a high measurement resolution. The requirement of the sample size accuracy and environmental conditions are very high. Factors such as unstable voltage, air flow changes will affect the smoothness of the expansion line. To prevent contamination of the sample holder and performance changes putter occurred during the test sample, the sample should be mounted in bearings and gaskets. Put some small particle size alumina hollow ball at the bottom of the bracket if it is necessary.
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3 Test Procedure.
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3. 1 Obtain baseline file Firstly, it makes baseline testing by standard sample before the samples is tested. The choice of test equipment is alumina bracket and putter. Standard sample choice is Al2O3 standard provided German NETZSCH. Put the standard sample into the sample holder. Place a thin aluminum oxide wafer between the sample and the putter to prevent samples and measurement systems adhesions. Then, turn off the furnace. Open test software and select the fix" measurement type. Enter the standard name, number and length. Baseline measurement procedures should be consistent with the sample to be measured program, including the initial wait, the heating rate and the sampling rate. It plays a crucial role in the entire sample testing. At the end of the baseline setting, there will be "DIL402PC Adjustment, dialog. Check whether the signal observed in the DIL value close 0um. If the deviation is too large, you need to adjust the deviation near to 0um. After baseline file generation, Samples subsequent series of the same test conditions can be followed in the baseline document. No need to make a baseline test for each sample individually.
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3. 2 Sample test After the baseline test is completed, the samples can be tested. Apply the appropriate baseline file. Select sample and fix , measurement type. Enter the sample name, number and length of the sample. Check the various parameters. Generally do not modify. If the temperature program is the exactly same with temperature program, it is not necessary to modify the baseline document. If you need to make some changes in the program on the basis of the original temperature, generally only lower the temperature will be terminated. The heating rate, the sampling rate and other parameters would not be changed.
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3. 3 Data Analysis After the sample test is completed, run the analysis program. Coefficient of linear expansion can be drawn at any point in the temperature coefficient of linear expansion and the temperature of any segment. Comparative analysis can be carried out the same type of curve. In addition, you can export the data needed to re-edit the mapping.
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4 System Calibration Thermal expansion instrument calibration system includes displacement sensor calibration and temperature sensor. In addition, due to the use of the jack dilatometer measurement mode, the signal is not only the length variation of the measured sample, as well as thermal expansion of the sample holder and the plunger. In order to obtain accurate measurement data, we must take into account the impact of the sample holder and the expansion mandrel to bring. For the foregoing reasons, The calibration of the temperature sensor and displacement sensor can not characterize the overall state of thermal expansion of the instrument. In order to obtain more accurate measurement results, the system must be checked. System calibration standard samples need to be measured with a known coefficient of expansion. All measurement parameters must be consistent with measured parameters of the sample. The expansion coefficient of the selected standard sample should be known. Its use must be suitable for measuring the sample temperature range. Sample material properties would not be changed in the temperature range. Commonly the standard samples consist of quartz, alumina, graphite, platinum, cyanite, etc. The table 2 lists the standard temperature range and their characteristics[] Zhang Xiuhua, Li Dan, eta1. Control Technology of Thermal Dilatometer 402PC, ENGINEERING and TEST, 2008(48). ]. Table. 2 Calibration standards provided by the NETZSCH company Material Temperature range Characteristic Quartz 0-1600oC High precision, small coefficient of expansion Cyanite 0-1680oC High precision, wide temperature range Al2O3 -190-1680oC High precision, wide temperature range, low price Platinum -190-1400oC Wide temperature range, large expansion coefficient Graphite 0-2400oC Slightly less accurate than sapphire, wide temperature range This selection of standard sample calibration equipment is Al2O3 standard, The main test accuracy and repeatability of the test from two aspects to DIL402PC thermal expansion instrument calibration systems.
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4. 1 The accuracy of the test Test conditions for the heating rate is 5K/min, temperature range is 100oC to 1400oC, the test carried out under static air atmosphere. First generation baseline file, Then the same test conditions. Select sample and fix, type of measurement, Linear expansion coefficient of the samples obtained. The linear expansion coefficient measured in comparison with the standard theory of expansion , the results shown in table 3. The table 3 lists the measured values and the deviation from the theoretical value of standard Al2O3. As can be seen , the error in the measured values are the theoretical standard deviation and the range is much smaller than the error of the theoretical value[] Hideko Hayashi, Mariko Kanoh, Chang Ji Quan, eta1. Thermal expansion of Gd-doped ceria and reduced ceria. Solid State lonics. 2000(132): 227. ]. Table. 3 Measured and theoretical values of standard linear expansion Temperature /oC theoretical value/% measured value/% The theoretical value error/% The measured value error/% 100.
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4. 2 Repeatability test Verify the device stability in the process of testing the same sample, it not only depends on the degree of deviation from the standard value but also depends on the repeatability. The figure 2 is the measured expansion curve of Al2O3 standard sample under the same conditions. From the expansion curve in Figure 2, Al2O3 standard sample expansion coefficient of the first measurement can be calculated as 8. 9218E-06 from 50oC to 1400oC. The standard sample expansion coefficient of the second measurement is 8. 9001E-06. The two measured expansion coefficient of Al2O3 repeatability standard deviation is 0. 0216E-06. GB/T7322 Standards set forth the linear expansion coefficient of deviation does not exceed 0. 5E-06 in the same laboratory reproducibility of the test method. Description dilatometer DIL402PC accuracy is close to 25 times the standard requirements. Figure. 2 Al2O3 standard measurement repeatability expansion curve 5 Conclusions The thermal expansion coefficient is one of the important physical properties of the glass. The combination of the glass element and the glass element, the glass element and the metal element or non-metallic element must have a suitable thermal expansion coefficient. Using a quartz rod type instrument, the paper obtains the average linear expansion coefficient formula. The properties of materials have played an important role in the measurement process. Compare the measurement analysis methods of thermal expansion coefficient and choose the optimal measurement method according to our actual requirement. The result shows DIL402PC Dilatometer greatly improves the accuracy of the material expansion of glass, ceramics and composite materials. It also provides accurate and reliable basis for the standard revision. References.
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