Method for testing water content of gypsum based on nuclear magnetic resonance

Abstract

The application provides a method for testing gypsum moisture content based on nuclear magnetic resonance, comprising the following steps: performing nuclear magnetic resonance test on a gypsum sample to be tested to obtain a nuclear magnetic resonance signal amplitude; the magnetic field strength of the nuclear magnetic resonance test is less than or equal to 1T; obtaining the mass of water in the gypsum sample according to a predetermined standard curve and the signal amplitude; obtaining the gypsum moisture content according to the mass of water in the gypsum sample and the mass of the gypsum sample to be tested; and the predetermined standard curve is a linear relationship curve of the mass of water in the gypsum and the signal amplitude. The application adopts a low-field nuclear magnetic resonance method (magnetic field strength less than or equal to 1T) to non-destructively determine the water content in the gypsum, thereby determining the type of the gypsum (anhydrite, hemihydrate gypsum and dihydrate gypsum). The method provided by the application does not need to dry the gypsum sample to be tested, has the advantages of rapidness and non-destructiveness, and has a wide application prospect in the determination of water content in the gypsum field and the determination of different types of gypsum.

Description

Technical Field

[0001] The present invention relates to the technical field of gypsum moisture content testing, and in particular to a method for testing gypsum moisture content based on nuclear magnetic resonance. Background Art

[0002] Gypsum, a natural calcium sulfate mineral containing two hydrates of water, is primarily composed of a hydrate of calcium sulfate (CaSO4) with the molecular formula CaSO4·2H2O. Upon calcination at a certain temperature, it transforms into hemihydrate gypsum, a highly plastic material. Further calcination produces anhydrous gypsum. Gypsum is a widely used industrial and building material, including cement retarders, gypsum building products, model making, medical food additives, sulfuric acid production, and paper and paint fillers.

[0003] Current methods for determining the moisture content of gypsum primarily rely on oven drying and weight loss to determine the free water and crystalline water content. However, this method is time-consuming, with drying often requiring several or even dozens of hours. The dried gypsum's moisture content and state have changed, making it difficult to reuse and resulting in a waste of raw materials. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a method for testing the moisture content of gypsum based on nuclear magnetic resonance. The testing method provided by the present invention can quickly obtain the moisture content of gypsum without damaging the gypsum components.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for testing the moisture content of gypsum based on nuclear magnetic resonance, comprising the following steps:

[0007] Performing a nuclear magnetic resonance test on the gypsum sample to be tested to obtain a signal amplitude of the nuclear magnetic resonance; the magnetic field intensity of the nuclear magnetic resonance test is ≤1T;

[0008] Obtaining the mass of water in the gypsum sample according to a predetermined standard curve and the signal amplitude; the predetermined standard curve is a linear relationship curve between the mass of water in the gypsum and the signal amplitude;

[0009] The moisture content of the gypsum is obtained according to the mass of water in the gypsum sample and the mass of the gypsum sample to be tested.

[0010] Preferably, the frequency of the nuclear magnetic resonance test is 0.05 to 100 MHz.

[0011] Preferably, the pulse sequence of the nuclear magnetic resonance test is an MSE-CPMG sequence.

[0012] Preferably, the coil diameter of the probe used in the nuclear magnetic resonance test is 1 to 100 mm.

[0013] Preferably, the mass of the gypsum sample to be tested is 0.02 to 100 g.

[0014] Preferably, the method for obtaining the standard curve includes:

[0015] Gypsum standards with gradient water qualities are available;

[0016] The gypsum standard containing gradient water mass is used as the sample to be tested, and a nuclear magnetic resonance test is performed to obtain the signal amplitude corresponding to the gypsum standard containing gradient water mass. A standard curve is drawn with the water mass of the gypsum standard as the horizontal axis and the signal amplitude as the vertical axis.

[0017] Preferably, the method for providing a gypsum standard containing gradient water quality comprises the following steps:

[0018] Mixing two or three of dihydrate gypsum, hemihydrate gypsum and anhydrite to obtain mixed gypsum;

[0019] Obtaining the mass of water in the mixed gypsum according to the type and mixing ratio of the gypsum in the mixed gypsum;

[0020] The type and / or mixing ratio of the gypsum in the mixed gypsum is changed to obtain gypsum standards containing gradient water quality.

[0021] The present invention provides a method for testing the moisture content of gypsum based on nuclear magnetic resonance, comprising the following steps: performing a nuclear magnetic resonance test on a gypsum sample to be tested to obtain a nuclear magnetic resonance signal amplitude; the magnetic field intensity of the nuclear magnetic resonance test is ≤1T; obtaining the mass of water in the gypsum sample according to a predetermined standard curve and the nuclear magnetic resonance signal amplitude; obtaining the moisture content of gypsum according to the mass of water in the gypsum sample and the mass of the gypsum sample to be tested; the predetermined standard curve is a linear relationship curve between the mass of water in gypsum and the nuclear magnetic resonance signal amplitude. The present invention adopts a low-field nuclear magnetic resonance method (magnetic field intensity ≤1T) to non-destructively measure the moisture content in gypsum, thereby determining the type of gypsum (anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum). The method provided by the present invention does not require the gypsum sample to be tested to be dried, has the advantages of being fast and non-destructive, and has broad application prospects in the determination of moisture content in the gypsum field and the determination of different types of gypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The result of the signal amplitude obtained by the nuclear magnetic resonance test of the present invention;

[0023] Figure 2 The standard curve obtained by the mixed weighing method of the present invention;

[0024] Figure 3This is the standard curve obtained by the drying weight loss method of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a method for testing the moisture content of gypsum based on nuclear magnetic resonance, comprising the following steps:

[0026] Performing a nuclear magnetic resonance test on the gypsum sample to be tested to obtain a nuclear magnetic resonance signal amplitude; the magnetic field strength of the nuclear magnetic resonance test is ≤1T; obtaining the mass of water in the gypsum sample based on a predetermined standard curve and the signal amplitude; the predetermined standard curve is a linear relationship curve between the water mass in the gypsum and the signal amplitude;

[0027] The moisture content of the gypsum is obtained according to the mass of water in the gypsum sample and the mass of the gypsum sample to be tested.

[0028] The present invention performs a nuclear magnetic resonance test on the gypsum sample to be tested to obtain a nuclear magnetic resonance signal amplitude; the magnetic field intensity of the nuclear magnetic resonance test is ≤1T, preferably 0.5-1T.

[0029] The present invention has no special requirements on the type of gypsum sample to be tested. Any type of gypsum can be tested for moisture content using the method provided by the present invention. In the present invention, the mass of the gypsum sample to be tested is preferably 0.02 to 100 g, more preferably 0.4 to 1 g.

[0030] The present invention does not require drying of the gypsum sample before performing nuclear magnetic resonance testing.

[0031] In the present invention, the nuclear magnetic resonance test used in the nuclear magnetic resonance test is preferably a nuclear magnetic resonance instrument with model PQ001-SFC, purchased from Suzhou Newmai Analytical Instrument Co., Ltd.

[0032] In the present invention, the frequency of the nuclear magnetic resonance test is preferably 0.05 to 100 MHz, more preferably 0.1 to 50 MHz, and further preferably 1 to 25 MHz.

[0033] In the present invention, the pulse sequence of the nuclear magnetic resonance test is the MSE-CPMG sequence (Magic Spin Echo-Carr Purcell Meiboom Gill).

[0034] In the present invention, the coil diameter of the probe used in the nuclear magnetic resonance test is preferably 1 to 100 mm, more preferably 5 to 80 mm, and more preferably 10 to 60 mm. In the present invention, the diameter of the gypsum sample needs to be smaller than the diameter of the coil. As a specific embodiment of the present invention, the result of the signal amplitude obtained by the nuclear magnetic resonance test is as follows Figure 1 shown.

[0035] After obtaining the signal amplitude, the application obtains the mass of water in the gypsum sample according to a predetermined standard curve and the signal amplitude.

[0036] A gypsum standard containing a gradient water mass is provided;

[0037] A nuclear magnetic resonance test is performed on the gypsum standard containing a gradient water mass as the sample to be tested to obtain the signal amplitude corresponding to the gypsum standard containing a gradient water mass. A standard curve is plotted with the water mass of the gypsum standard as the abscissa and the signal amplitude as the ordinate.

[0038] In the application, the method for providing a gypsum standard containing a gradient water mass preferably comprises the following steps:

[0039] Two or three of dihydrate gypsum, hemihydrate gypsum and anhydrous gypsum are mixed to obtain mixed gypsum;

[0040] The mass of water in the mixed gypsum is obtained according to the type and mixing ratio of gypsum in the mixed gypsum;

[0041] The type or mixing ratio of gypsum in the mixed gypsum is changed to obtain a gypsum standard containing a gradient water mass.

[0042] In the application, the dihydrate gypsum, hemihydrate gypsum and anhydrous gypsum are all pure products.

[0043] As a specific embodiment of the application, the gypsum standard containing a gradient water mass and its corresponding nuclear magnetic resonance signal amplitude are shown in Table 1.

[0044] Table 1 Gypsum standard containing a gradient water mass and its corresponding nuclear magnetic resonance signal amplitude

[0045] Water mass / g Signal amplitude 0.02108916 1820.386 0.04040226 4678.989333 0.0612306 7518.169 0.16149588 21432.73433 0.19416761 25414.579

[0046] The obtained standard curve is y = 136774x - 913.2, R 2 = 0.9997.

[0047] The application adopts a low-field nuclear magnetic resonance method (magnetic field strength ≤ 1T) to non-destructively determine the water content in gypsum, thereby determining the type of gypsum, i.e., whether the gypsum is anhydrous gypsum, hemihydrate gypsum or dihydrate gypsum. In the application, the theoretical water content of anhydrous gypsum is 0%; the theoretical water content of hemihydrate gypsum is 6.21%, and the theoretical water content of dihydrate gypsum is 20.93%.

[0048] The method provided by the application does not need to dry the gypsum sample to be tested, has the advantages of being fast and non-destructive, and has a wide application prospect in the determination of water content in gypsum and the determination of different types of gypsum.

[0049] The method for testing the moisture content of gypsum based on nuclear magnetic resonance provided by the present invention is described in detail below with reference to the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] 1. Prepare the gypsum sample to be tested

[0052] Weigh about 0.5g of gypsum sample and put it into a special NMR test tube for testing.

[0053] 2. Parameter debugging of nuclear magnetic resonance equipment

[0054] Open the nuclear magnetic resonance analysis software, perform frequency calibration, and find the pulse width (90° pulse width 2.00 μs, 180° pulse width 3.60 μs); select the MSE-CPMG sequence, instrument magnetic field strength 0.5 T, sampling frequency, 200 kHz; waiting time, 500 ms; accumulation number, 128 times.

[0055] 3. Establish a standard curve

[0056] Two calibration methods, mixed weighing method and drying weight loss method, are used for calibration.

[0057] Mixed weighing method: Use pure dihydrate and hemihydrate gypsum (or anhydrous gypsum) to mix samples with different water contents in different proportions, and establish a standard curve of water quality and nuclear magnetic signal quantity. The results are shown in Figure 2 .

[0058] Drying weight loss method: Weigh a certain amount of dihydrate gypsum and dry it in stages at 190-230℃. The amount of water loss and the amount of NMR signal reduction during the drying process are calibrated. Figure 3 .

[0059] Gypsum samples with known moisture content were used for NMR testing. The moisture content was obtained by obtaining standard curves based on the mixed weighing method and the weight loss and drying method. The calibration methods were compared and verified. The results are shown in Table 2.

[0060] Table 2 Comparison and verification results of calibration methods

[0061]

[0062] Depend on Figure 2 、 Figure 3 As can be seen from Table 2, the standard curve obtained by the mixed calibration method has a higher degree of fit.

[0063] Example 2 Single gypsum verification at room temperature

[0064] One portion each of hemihydrate, dihydrate, and mixed gypsum was taken and subjected to nuclear magnetic resonance (NMR) testing according to the method of Example 1. The moisture content of the hemihydrate, dihydrate, and mixed gypsum was obtained using the standard curve obtained by the mixed weighing method of Example 1. The comparison results of the theoretical moisture content of the gypsum with the NMR measured values ​​are shown in Table 3.

[0065] Table 3 Comparison of theoretical water content of gypsum and nuclear magnetic measurement value

[0066] Sample number Sample mass / g Theoretical moisture content / % NMR moisture content / % Absolute error / % Hemihydrate gypsum 0.7059 6.21 5.97 0.24 dihydrate gypsum 0.7039 20.93 20.17 0.76 Mixed plaster 0.8169 10.06 10.59 0.63

[0067] It can be seen from Table 3 that the absolute error between the single gypsum NMR determination result and the true value at room temperature does not exceed 1%.

[0068] Example 3: Verification of single gypsum under variable temperature

[0069] When dihydrate gypsum was dried at 65℃, 150℃ and 230℃, dehydrated gypsum, hemihydrate gypsum and anhydrous gypsum were obtained respectively. The comparison results between the theoretical values ​​and the NMR measured values ​​are shown in Table 4.

[0070] Table 4 Verification of single gypsum under variable temperature

[0071]

[0072]

[0073] It can be seen from Table 4 that the absolute error between the single gypsum NMR measurement results and the true value under variable temperature does not exceed 2%.

[0074] Example 4

[0075] Leixin gypsum samples were selected for calibration, and several Leixin and Saint-Gobain gypsum samples were taken for blind testing. The comparison results are shown in Table 5.

[0076] Table 5 Comparative test results of gypsum from different manufacturers

[0077] Sample number Sample mass / g Theoretical moisture content / % NMR moisture content / % Absolute error / % Leixin / Ershui 1 0.8100 20.93 21.27 0.34 Leixin / Ershui 2 0.6050 20.93 20.07 0.86 Leixin / Ershui 3 0.7039 20.93 19.29 1.64 Saint-Gobain / Ershui 1 0.4390 20.93 19.95 0.98 Saint-Gobain / Dishui 2 0.3597 20.93 19.79 1.14 Saint-Gobain / Dihydrate 3 0.4515 20.93 19.76 1.17

[0078] As can be seen from Table 5, the difference in gypsum manufacturers has limited impact on the results of gypsum moisture content determination by nuclear magnetic resonance, which shows that the test method provided by the present invention has universal applicability.

[0079] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for testing the moisture content of gypsum based on nuclear magnetic resonance, comprising the following steps: Performing a nuclear magnetic resonance test on the gypsum sample to be tested to obtain a nuclear magnetic resonance signal amplitude; the magnetic field strength of the nuclear magnetic resonance test is ≤1T; the frequency of the nuclear magnetic resonance test is 200kHz, the waiting time is 500ms, and the number of accumulations is 128 times; the pulse sequence of the nuclear magnetic resonance test is an MSE-CPMG sequence; Obtaining the mass of water in the gypsum sample to be tested according to a predetermined standard curve and the signal amplitude; the predetermined standard curve is a linear relationship curve between the mass of water in gypsum and the signal amplitude; Obtaining the moisture content of the gypsum according to the mass of the water and the mass of the gypsum sample to be tested; The method for obtaining the standard curve comprises: Gypsum standards with gradient water qualities are available; The gypsum standard containing gradient water mass is used as a test sample to perform a nuclear magnetic resonance test to obtain the signal amplitude corresponding to the gypsum standard containing gradient water mass, and a standard curve is drawn with the water mass of the gypsum standard as the abscissa and the signal amplitude as the ordinate; The method for providing gypsum standards containing gradient water quality comprises the following steps: Mixing two or three of dihydrate gypsum, hemihydrate gypsum and anhydrite to obtain mixed gypsum; Obtaining the mass of water in the mixed gypsum according to the type and mixing ratio of the gypsum in the mixed gypsum; The type and / or mixing ratio of the gypsum in the mixed gypsum is changed to obtain gypsum standards containing gradient water quality.

2. The method according to claim 1, characterized in that The coil diameter of the probe used in the nuclear magnetic resonance test is 1 to 100 mm.

3. The method according to claim 1, characterized in that The mass of the gypsum sample to be tested is 0.02-100 g.

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