Calcium silicate standard sample for measuring heat conductivity coefficient and preparation method thereof

Abstract

The invention discloses a calcium silicate standard sample for measuring a heat conductivity coefficient and a preparation method of the calcium silicate standard sample, and belongs to the technical field of material thermophysical parameter standard samples. According to the invention, the calcium silicate standard sample prepared by optimizing the mass ratio of the quicklime and the quartz powder which are mixed into the feed, the mass ratio of the quicklime and the quartz powder to the inorganic filler, the composition of the inorganic filler and a hydrothermal reaction process has better breaking strength and compressive strength, can meet the temperature resistance requirement of 150-450 DEG C, and has good uniformity and stability; according to the present invention, the mass ratio of the material to the water mixed into the mixed material and the stirring homogenization rate are optimized, the steam curing process and the drying dehydration process are optimized, and the sample fine grinding and the high temperature treatment are performed, such that the xonotlite contained in the prepared calcium silicate standard sample has characteristics of compact structure, suitable particle size range and dense particle size distribution; the uniformity and the stability of the sample are further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of standard samples for thermal physical properties of materials, and particularly relates to a calcium silicate standard sample for measuring thermal conductivity and a preparation method thereof. Background Art

[0002] The thermal conductivity is one of the main parameters for evaluating the heat insulation or heat conduction performance of materials. The thermal conductivity represents the heat transfer amount per unit time and per unit area between fluids or objects. The guarded hot plate method for measuring thermal conductivity is a test method based on the one-dimensional Fourier heat conduction law. Its measuring device and principle are relatively simple, with the advantages of easy sample preparation and high accuracy, and has been widely used and recognized. It is particularly suitable for measuring the thermal conductivity of low thermal conductivity materials such as thermal insulation materials.

[0003] To accurately measure the thermal conductivity of a sample, in addition to strictly testing according to the requirements of the standard, the laboratory needs to regularly calibrate, verify and conduct intermediate checks on the thermal conductivity meter to ensure that the thermal conductivity meter is in a controlled state. Among them, using a standard sample to calibrate the instrument is the simplest and most efficient method, which can intuitively reflect the precision of the instrument's detection data and ensure the accuracy and reliability of the test results.

[0004] Currently, for standard samples for measuring thermal conductivity, the materials are mostly fiberglass boards, such as the national standard sample GSB 02-3062-F02-2022 developed by the Research Center for Technical Supervision of the Building Materials Industry and the standard sample SRM 1450e developed by the National Institute of Standards and Technology of the United States. Although this kind of standard sample has good uniformity, stability and small uncertainty, due to the physical properties of the material itself, the test temperature range of its thermal conductivity is very narrow. GSB 02-3062-F02-2022 only gives the reference value of the thermal conductivity at the average test temperature of 343K, and SRM 1450e provides the functional relationship between the thermal conductivity at the average test temperature of 280K - 360K, the test temperature and the material density. This means that using the thermal conductivity reference sample of fiberglass board cannot test the thermal conductivity data above 360K for the thermal conductivity meter. Therefore, a high-temperature-resistant thermal coefficient standard sample is needed to calibrate the high-temperature test results of the thermal conductivity meter. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a calcium silicate standard sample for measuring thermal conductivity and a preparation method thereof, which can meet the requirements of calibrating the thermal conductivity meter test in the range of 150°C to 450°C.

[0006] To achieve the above object, the specific technical solution adopted by the present invention is as follows: By optimizing the mass ratio of quicklime and quartz powder in the mixed feedstock, their mass ratio with inorganic fillers, the composition of inorganic fillers, and the hydrothermal reaction process, the prepared calcium silicate standard sample has good flexural strength and compressive strength, thus achieving the object of the present invention.

[0007] A calcium silicate standard sample for measuring thermal conductivity according to the present invention comprises (20 - 28) parts by mass of calcium silicate and (72 - 80) parts by mass of inorganic fillers; the calcium silicate is xonotlite with the molecular formula Ca6(Si6O17)(OH)2 and an average particle size of 28 - 32 μm; the inorganic filler is a mixture of one or more of cement, alumina, porcelain powder, fly ash, and ore powder and quartz powder.

[0008] The present invention also relates to a preparation method of a calcium silicate standard sample for measuring thermal conductivity, and the preparation steps are as follows: 1) Mix (20 - 28) parts by mass of quicklime and quartz powder with (72 - 80) parts by mass of inorganic fillers to form a feedstock, wherein the mass ratio of quicklime to quartz powder is not higher than 12:13; mix the feedstock and water in a mass ratio of 1:(35 - 45) and stir evenly at a stirring and homogenizing rate not higher than 160 r / min; 2) Carry out hydrothermal reaction on the evenly stirred mixture for not less than 9 h within the temperature range of (190 - 210) °C; 3) After the hydrothermal reaction is completed, press the mixture into shape as required, and then carry out autoclave curing and drying and dehydration in sequence to make a calcium silicate standard sample blank; 4) After post-treatment processing and high-temperature treatment of the calcium silicate standard sample blank, a calcium silicate standard sample is prepared.

[0009] Preferably, the mass ratio of quicklime to quartz powder in the feedstock is (12:13 - 10:10.5).

[0010] Preferably, the stirring and homogenizing rate is 150 - 160 r / min.

[0011] Preferably, the autoclave curing is carried out under a pressure of 1 MPa and a temperature of 200 °C for 24 h with steam.

[0012] Preferably, the drying and dehydration is carried out in a drying kiln at a temperature of 100 - 110 °C for 72 h.

[0013] Preferably, the high-temperature treatment of the calcium silicate standard sample blank is carried out at a high temperature of 600 °C.

[0014] By optimizing the mass ratio of quicklime and quartz powder in the mixed feedstock, their mass ratio with inorganic fillers, the composition of inorganic fillers, and the hydrothermal reaction process, the prepared calcium silicate standard sample has good flexural strength and compressive strength, can meet the temperature resistance requirements of 150°C to 450°C, and the sample has good uniformity and stability. By optimizing the mass ratio of the feedstock and water in the mixed material and the stirring homogenization rate, and preferably the steam curing process, the drying and dehydration process, as well as performing fine grinding and high-temperature treatment on the sample, the tobermorite structure contained in the prepared calcium silicate standard sample is dense, the particle size range is appropriate and the distribution is dense, further improving the uniformity and stability of the sample. According to GB / T 10294-2008 "Determination of Steady-State Thermal Resistance and Related Characteristics of Thermal Insulation Materials - Guarded Hot Plate Method", the thermal conductivity of the sample is tested. The test results show that in the range of 150°C to 450°C, the thermal conductivity of the standard sample meets the requirements of JJG 1006-1994 "Technical Specifications for Primary Standard Substances" for the uniformity and stability of the standard sample. The calcium silicate standard sample prepared by the method of the present invention can be used for the calibration and verification of the thermal conductivity meter test in the range of 150°C to 450°C. Specific Embodiments

[0015] The following examples are used to further illustrate the present invention, which can enable those skilled in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0016] Example 1 The calcium silicate standard sample for thermal conductivity determination in this example is composed of 24 parts by mass of calcium silicate and 76 parts by mass of inorganic fillers. Among them, the calcium silicate is tobermorite with a molar ratio of calcium element to silicon element of 1:1, and the molecular formula is Ca 6 (Si 6 O 17 )(OH) 2 , and the average particle size is 32 μm. The inorganic filler is a mixture of porcelain powder and quartz powder.

[0017] When preparing the calcium silicate standard sample of this example, the following steps are included: Mix the feedstock and water in a mass ratio of 1:35. Among them, the feedstock is composed of 12 parts by mass of quicklime, 13 parts by mass of quartz powder and 75 parts by mass of porcelain powder. Stir the mixture evenly at a stirring and homogenizing rate of 150 r / min, and feed it into a dynamic reaction kettle at a temperature of 200 °C for hydrothermal reaction for 9 h. The quicklime reacts with the quartz powder to generate calcium silicate particles, and the remaining quartz powder and porcelain powder are mixed into an inorganic filler; after the hydrothermal reaction is completed, the mixture of calcium silicate particles and inorganic filler is pressed into shape by a hydraulic universal testing machine; then it is sent into an autoclave at a pressure of 1 MPa and a temperature of 200 °C for steam autoclave curing for 24 h; after the curing is completed, it is sent into a drying kiln at a temperature of 100 °C for drying and dehydration for 72 h to make a calcium silicate standard sample blank; after drying, use a sand mill to post-process the size of the calcium silicate sample, and perform rough sanding and precision sanding on its upper and lower surfaces successively to make the thickness difference of each surface of the sample less than 0.1 mm; after completion, perform high-temperature treatment at 600 °C to obtain a calcium silicate standard sample.

[0018] The density of the calcium silicate standard sample prepared in this example for thermal conductivity measurement is 782 kg / m 3 , the compressive strength is 0.51 MPa, and the compressive strength is 0.98 MPa. According to GB / T10294-2008 "Determination of Steady-State Thermal Resistance and Related Characteristics of Thermal Insulation Materials - Guarded Hot Plate Method", the thermal conductivity of the calcium silicate standard sample prepared in this example for thermal conductivity measurement was tested, and the test results are shown in Table 1.

[0019] Table 1 Test results of thermal conductivity of calcium silicate standard sample in Example 1

[0020] Example 2 The calcium silicate standard sample prepared in this example for thermal conductivity measurement is composed of 20 parts by mass of calcium silicate and 80 parts by mass of inorganic filler. Among them, the calcium silicate is xonotlite with a molar ratio of calcium to silicon of 1:1, and the molecular formula is Ca 6 (Si 6 O 17 )(OH) 2 , and the average particle size is 28 μm. The inorganic filler is a mixture of cement, alumina, porcelain powder, fly ash, mineral powder and quartz powder.

[0021] When preparing the calcium silicate standard sample of this example, the following steps are included: The feedstock and water are mixed at a mass ratio of 1:45, wherein the feedstock is a mixture of 10 parts by mass of quicklime, 10.5 parts by mass of quartz powder and 79.5 parts by mass of a mixture of cement, alumina, porcelain powder, fly ash and mineral powder. The mixture was stirred evenly at a stirring and homogenizing rate of 160r / min, and sent to a dynamic reactor at a temperature of 210℃ for hydrothermal reaction for 12h. Quicklime reacted with quartz powder to generate calcium silicate particles, and the remaining quartz powder was mixed with cement, alumina, porcelain powder, fly ash and mineral powder mixture to form inorganic filler; after the hydrothermal reaction was completed, the generated calcium silicate particles and inorganic filler mixture were pressed into shape using a hydraulic universal pressure testing machine; then sent to an autoclave at a pressure of 1MPa and a temperature of 200℃ for steam autoclaving and curing for 24h; after the curing was completed, it was sent to a drying kiln at a temperature of 110℃ for drying and dehydration for 72h to prepare a calcium silicate standard sample blank; after drying, the calcium silicate sample size was post-processed using a sand mill, and coarse sand grinding and precision sand grinding were performed on the upper and lower surfaces in turn to make the thickness difference of each surface of the sample less than 0.1 mm; after completion, it was subjected to a high-temperature treatment at 605℃ to obtain a calcium silicate standard sample.

[0022] The density of the calcium silicate standard sample prepared in this example for thermal conductivity determination is 809 kg / m 3 According to GB / T10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulating Materials - Guarded Hot Plate Method", the thermal conductivity of the calcium silicate standard sample used for thermal conductivity determination in this embodiment is tested, and the test results are shown in Table 2.

[0023] Table 2 Thermal conductivity test results of calcium silicate standard sample in Example 2

[0024] Example 3 The calcium silicate standard sample used for thermal conductivity determination in this embodiment is composed of 28 parts by mass of calcium silicate and 72 parts by mass of inorganic filler. Calcium silicate is xonotlite with a molar ratio of calcium to silicon of 1:1, and the molecular formula is Ca 6 (Si 6 O 17 )(OH) 2 The average particle size is 30 μm. The inorganic filler is a mixture of porcelain powder and quartz powder.

[0025] The preparation of the calcium silicate standard sample of this embodiment includes the following steps: The feed material and water are mixed at a mass ratio of 1:45, wherein the feed material is a mixture of 14 parts by mass of quicklime, 15 parts by mass of quartz powder and 71 parts by mass of porcelain powder. The mixture was stirred evenly at a stirring and homogenizing rate of 155r / min, and sent to a dynamic reactor at a temperature of 190℃ for hydrothermal reaction for 10h. Quicklime reacted with quartz powder to generate calcium silicate particles, and the remaining quartz powder was mixed with porcelain powder to form inorganic filler. After the hydrothermal reaction was completed, the generated mixture of calcium silicate particles and inorganic filler was pressed into shape using a hydraulic universal pressure testing machine; then it was sent to an autoclave at a pressure of 1MPa and a temperature of 200℃ for steam autoclaving and curing for 24h; after the curing was completed, it was sent to a drying kiln at a temperature of 108℃ for drying and dehydration for 72h to prepare a calcium silicate standard sample blank; after drying, the calcium silicate sample size was post-processed using a sand mill, and coarse sand grinding and precision sand grinding were performed on the upper and lower surfaces in turn to make the thickness difference of each surface of the sample less than 0.1 mm; after completion, it was subjected to high-temperature treatment at 602℃ to obtain a calcium silicate standard sample.

[0026] The density of the calcium silicate standard sample prepared in this example for thermal conductivity determination is 779 kg / m 3 According to GB / T10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Insulating Materials - Guarded Hot Plate Method", the thermal conductivity of the calcium silicate standard sample used for thermal conductivity determination in this embodiment is tested, and the test results are shown in Table 3.

[0027] Table 3 Thermal conductivity test results of calcium silicate standard sample of Example 3

[0028] Comparative Example 1 The difference from Example 1 is that: The mass ratio of quicklime to quartz powder in the feed is 1.1.

[0029] When the feed and water are mixed, high-calcium hydrated calcium silicate appears in the slurry, which is not conducive to the formation, growth and secondary particle formation of fibrous xonotlite crystals. The prepared calcium silicate standard sample is not dense enough, which affects the thermal conductivity test performance under high temperature conditions.

[0030] Comparative Example 2 The difference from Example 1 is that: Mix the feed and water in a mass ratio of 1:20.

[0031] During mixing, the slurry contained xonotlite and quartz powder, and the xonotlite fibers were poorly developed. The water-solid ratio was too small, which was not conducive to the dissolution of silicon dioxide. During the reaction, the slurry was too thick, which was not conducive to the normal reaction. The proportion of xonotlite in the prepared standard sample could not be determined, the sample was uneven inside, and the thermal conductivity of the standard sample could not be determined.

[0032] Comparative Example 3 The difference from Example 3 is that: The mass proportion of inorganic filler in the calcium silicate standard sample is 60%.

[0033] According to experimental testing, the density of the calcium silicate standard sample is 689kg / m 3 , compressive strength 0.45MPa, compressive strength 0.79MPa.

[0034] The lack of inorganic fillers results in insufficient density of the calcium silicate sample, which cannot meet the requirements of the flexural strength and compressive strength of the sample, and is not conducive to the transportation and storage of thermal conductivity standard samples.

[0035] Comparative Example 4 The difference from Example 1 is that some of the manufacturing processes are different, as shown in Table 4.

[0036] Table 4 Different comparison process schemes

[0037] When comparative process 1 was selected and the hydrothermal reaction temperature was 180°C, experimental detection showed that the calcium silicate hydrate product generated by the reaction of quartz powder and quicklime was tobermorite, not xonotlite.

[0038] When comparative process 2 was selected and the hydrothermal reaction time was 7 h, experimental detection showed that tobermorite and xonotlite existed in the slurry.

[0039] Tobermorite was generated in both comparative processes 1 and 2. The volume of calcium silicate mixed with tobermorite would shrink at high temperature. The prepared calcium silicate standard sample did not meet the requirements of testing under high temperature conditions, and the test range was limited.

[0040] Comparative process 3 was selected with a stirring and homogenizing rate of 200 r / min. Experimental tests showed that no spherical particles appeared in the slurry. The stirring rate was too fast, which hindered the formation of xonotlite crystals and made it impossible to produce a homogeneous calcium silicate standard sample, resulting in poor repeatability in the thermal conductivity test of the sample.

Claims

1. A calcium silicate standard sample for thermal conductivity determination, characterized in that: The invention comprises (20 to 28) parts by mass of calcium silicate and (72 to 80) parts by mass of an inorganic filler; the calcium silicate has a molecular formula of Ca6(Si6O 17 )(OH)2, hard calcium notch stone with an average particle size of 28 to 32 μm; the inorganic filler is a mixture of one or more of cement, alumina, porcelain powder, fly ash and mineral powder and quartz powder.

2. The method for preparing a calcium silicate standard sample for thermal conductivity determination according to claim 1, characterized in that: The preparation steps are as follows: 1) Mixing (20-28) parts by mass of quicklime and quartz powder with (72-80) parts by mass of inorganic filler to form a feed material, wherein the mass ratio of quicklime to quartz powder is not higher than 12:13, and the inorganic filler is a mixture of one or more of cement, alumina, porcelain powder, fly ash and mineral powder and quartz powder; mixing the feed material and water at a mass ratio of 1:(35-45), and stirring evenly at a stirring and homogenizing rate of not higher than 160r / min; 2) The uniformly stirred mixture is subjected to hydrothermal reaction at a temperature range of (190-210)°C for not less than 9 hours; 3) After the mixture of the hydrothermal reaction is completed, it is pressed and formed as required, and then autoclaved and cured and dried and dehydrated in sequence to form a calcium silicate standard sample blank; 4) The calcium silicate standard sample blank is subjected to post-processing and high-temperature treatment to obtain a calcium silicate standard sample.

3. The method for preparing a calcium silicate standard sample for thermal conductivity determination according to claim 2, characterized in that: The mass ratio of quicklime to quartz powder in the feed is (12:13 to 10:10.5).

4. The method for preparing a calcium silicate standard sample for thermal conductivity determination according to claim 2, characterized in that: The stirring and homogenizing rate is 150-160 r / min.

5. The method for preparing a calcium silicate standard sample for thermal conductivity determination according to claim 2, characterized in that: The autoclave curing is performed at a pressure of 1 MPa and a temperature of 200° C. with steam for 24 hours.

6. The method for preparing a calcium silicate standard sample for thermal conductivity determination according to claim 2, characterized in that: The drying and dehydration is carried out in a drying kiln at a temperature of 100-110° C. for 72 hours.

7. The method for preparing a calcium silicate standard sample for thermal conductivity determination according to claim 2, characterized in that: The high temperature treatment of the calcium silicate standard sample blank is carried out at a high temperature of 600°C.

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