CN112858368A - Resin content testing method and device based on time domain nuclear magnetic resonance - Google Patents
Resin content testing method and device based on time domain nuclear magnetic resonance Download PDFInfo
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- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
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Abstract
The invention discloses a resin content testing method based on time domain nuclear magnetic resonance, which is characterized in that a standard sample is placed in a detection coil of a nuclear magnetic resonance device for data acquisition, and the method comprises the following steps: the nuclear magnetic resonance device excites a free attenuation nuclear magnetic signal of a sample according to radio frequency pulses emitted by an MSE sequence based on the radio frequency pulses of the MSE sequence; and obtaining a relational expression between the mass of the resin in the sample and the free attenuation nuclear magnetic signal according to a common least square regression analysis model between the free attenuation nuclear magnetic signal and the mass of the resin in the sample. The invention discloses a resin content testing device based on time domain nuclear magnetic resonance, which comprises a spectrometer unit, a radio frequency unit, a coil energy leakage unit, a weighing unit, a detection coil and a permanent magnet. The method and the device utilize a time-domain nuclear magnetic resonance analysis technology, have clear principle, and have the advantages of no damage, no pollution, simple operation, wide application range, good repeatability and the like.
Description
Technical Field
The invention relates to the technical field of sample testing or analysis by utilizing nuclear magnetic resonance, in particular to a method and a device for rapidly analyzing the content of resin in glass fiber reinforced plastics and carbon fiber reinforced plastics.
Background
Nuclear Magnetic Resonance (NMR) imaging is a method of obtaining the position and type of nuclei constituting an object by detecting emitted electromagnetic waves with an external gradient magnetic field according to different attenuations of released energy in different structural environments inside the object by using the NMR principle, and thus, a structural image inside the object can be drawn.
Magnetic resonance imaging technology is not used in the medical field, but has been widely used in the polymer chemistry field in recent years, for example, studies on carbon fiber-reinforced epoxy resins, studies on spatial orientation of solid-state reactions, studies on solvent diffusion in polymers, studies on polymer vulcanization and elastomer uniformity, and the like.
The nuclear magnetic resonance imaging technology becomes increasingly important in the analysis technology of glass fiber reinforced plastics and carbon fiber reinforced plastics. The glass fiber reinforced plastic and the carbon fiber reinforced plastic belong to polymer reinforced composite materials, the glass fiber reinforced plastic is synthesized by glass fiber and resin, has the advantages of high strength, corrosion resistance, difficult deformation, good heat insulation performance, no magnetism and the like, and is widely applied in the fields of aerospace, railway, building decoration and the like, wherein the type and the content of the resin are closely related to the overall performance of the resin. The carbon fiber reinforced plastic is formed by matching carbon fibers with resin and the like, has excellent performance, has the advantages of fatigue resistance, creep resistance, stable material size and the like, is widely applied to the fields of aerospace, biomedical treatment, industrial manufacturing and the like, and the content of the resin is closely related to the overall performance of the carbon fiber reinforced plastic.
At present, the resin content in glass fiber reinforced plastics and carbon fiber reinforced plastics is tested according to national standards, for example, the resin content test method of the glass fiber reinforced plastics in GB/T2577-. For another example, the national standard BG/T3855-2005 carbon fiber reinforced plastic resin content test method specifies a sulfuric acid corrosion method for testing resin content, which uses sulfuric acid under conditions such that the resin is substantially completely decomposed without excessively corroding the carbon fibers.
However, the above-mentioned test methods have many limitations, and may not be able to effectively distinguish between different resin types during actual tests, and at the same time, a large amount of harmful gas may be generated during firing of the glass fiber reinforced plastic to cause environmental pollution, and the carbon fiber reinforced plastic may generate waste liquid polluting the environment during hot sulfuric acid corrosion, both of which belong to destructive test methods.
Disclosure of Invention
The technical scheme of the invention is as follows: the principle of the method is that a very short relaxation signal of a sample system is acquired through a special nuclear magnetic resonance sequence, the nuclear magnetic signal is contributed by hydrogen protons in resin, and the resin content in an unknown sample can be tested by establishing a quantitative relation between the nuclear magnetic signal and the resin quality.
What relate to in this scheme: a resin content testing method based on time domain nuclear magnetic resonance is characterized in that a standard sample is placed in a detection coil of a nuclear magnetic resonance device for data acquisition, and the method comprises the following steps: the nuclear magnetic resonance device emits radio frequency pulses according to an MSE sequence, and the radio frequency pulses based on the MSE sequence (mixed magnetic resonance) excite the free attenuation nuclear magnetic signals of the sample; and obtaining a relational expression between the mass of the resin in the sample and the free attenuation nuclear magnetic signal according to a common least square regression analysis model between the free attenuation nuclear magnetic signal and the mass of the resin in the sample.
The relationship between the mass of resin in the obtained sample and the free decay nuclear magnetic signal is as follows:
sn ═ K × V + b, where Sn is a free decay nuclear magnetic signal; v is the resin mass in the sample.
The specific dumping process is as follows:
assuming data for resin mass and free decaying nuclear magnetic signal in a set of samples:
X＝{(V1，Sn1)，...，(Vm，Snm)}；
then, the sum of the squared residuals of the above data is:
then K and b need to be solved to make the objective function obtain the minimum, and obviously, it can be obtained by separately performing partial derivatives on K and b:
order to
Then, the second partial derivative results:
let the second partial derivative result equal 0:
then the process of the first step is carried out,
if the first partial derivative result is equal to 0 and substituted into b, then:
obtaining:
at this point, K and b are solved.
And resin mass in sample versus free decay nuclear magnetic signal data:
X＝{(V1，Sn1)，...，(Vm，Snm)}；
wherein, the sampling of Sn is obtained by exciting the sample by the radio frequency pulse of the MSE sequence.
Specifically, the radio frequency pulse based on the MSE sequence includes: front and back two phases are phi2Of 90 DEG radio frequency pulses and the two phases are phi2Is transmitted with a phase phi between the radio-frequency pulses3And phi3Of 90 radio frequency pulses.
In the radio frequency pulse of MSE sequence, the front phase and the rear phase are phi2Two phases between the radio-frequency pulses of phi3And phi3At tau by 90 radio frequency pulsesφAlternate switching is made within time.
In order to effectively obtain a sample signal with short relaxation time, the two phases before and after the part are phi2The 90-degree radio frequency pulse is equivalent to a 180-degree pulse, and is used for reuniting the magnetization vector and overcoming the problem that the magnetization vector is accelerated to disperse phase due to the nonuniformity of a magnetic field; and the phase is phi3And phi3At tau by 90 radio frequency pulsesφThe fast switching is carried out in the time,make the magnetization vector M0The magnetization vector rotating rapidly in the YOZ plane can effectively reduce the dipole coupling effect in the relaxed sample, and the dipole coupling effect is the root cause of rapid relaxation of signals, so the relaxation time of the sample can be well slowed down by using the method, and more time is won for detecting the signals. In a word, by inhibiting the problems of phase dispersion caused by magnetic field inhomogeneity and slowing down the fast relaxation of the sample, the nuclear magnetic signals in the system dead time can be effectively reunited, so that the test result is more accurate.
Specifically, the phase phi2The value range of (A): Δ t21-20 us, and T is less than or equal to 50; the above phase phi3/-φ3The value range of (A): Δ t3＝1～20us、T≤50；τφ＝1～20us。
Wherein, the parameters of the MSE sequence comprise: the waiting Time (TW) takes 50ms to 3000 ms; radio frequency delay time
(RFD) takes the value of 0.002ms-0.5 ms; the analog gain (RG1) takes a value of 10-20; the digital gain (DRG1) takes 1-3 values; the repeated sampling times (NS) take the value of 4-1024; the pre-amplification gain (PRG) takes a value of 0-3; the time delay is 0.002ms-0.5 ms; the sampling time is 0ms-1000 ms.
Based on the principle, the resin content testing method based on time domain nuclear magnetic resonance comprises the following steps:
s1, preparing samples, wherein the mass of each sample is 0.2g-50g, and the number of the samples is prepared according to at least three groups;
s2, sample testing, namely placing a single sample in a standard container and then standing in a detection coil of a nuclear magnetic resonance device, wherein the nuclear magnetic resonance device emits radio frequency pulses according to an MSE sequence; after the radio frequency pulse of the MSE sequence is transmitted, a detection coil collects a free attenuation nuclear magnetic signal generated after a sample resonates;
and S3, converting the free attenuation nuclear magnetic signals collected in the S2 into digital signals with corresponding amplitudes, and inputting the digital signals into a quantitative analysis model to calculate the resin content.
The test method has the advantages that:
the traditional method is based on a chemical analysis method, and the principle of the realization is that the resin gathered by the reinforced plastics is separated firstly and then tested, the testing method does not need to separate the resin gathered by the reinforced plastics firstly, does not need to pretreat the sample, can directly detect the resin signal in the sample, and the carbon fiber part or the glass fiber does not generate nuclear magnetic signals. In addition, the method has the advantages of high calibration and test speed, and excellent repeatability and accuracy.
In addition, the invention also discloses a device for analyzing the resin content according to the method for rapidly analyzing the resin content in the reinforced plastic, which comprises a spectrometer unit, a radio frequency unit, a coil energy leakage unit, a weighing unit, a detection coil and a permanent magnet;
the spectrometer unit is used for controlling time sequence, transmitting radio frequency excitation signals, sampling free attenuation nuclear magnetic signals and controlling temperature;
the radio frequency unit is used for amplifying the power of the radio frequency excitation signal and amplifying the power of the sampled free attenuation nuclear magnetic signal;
the coil energy leakage unit is used for discharging residual energy of the coil;
the detection coil is used for generating an alternating magnetic field for exciting the sample and detecting a freely attenuated nuclear magnetic signal generated after the sample resonates;
the weighing unit is used for detecting the mass of the sample to be detected;
and a permanent magnet for generating a static magnetic field.
The detection coil is a solenoid coil wound by silver wires, and the diameter of the detection coil is 15-45 mm.
The permanent magnet is a neodymium iron boron magnet and generates a uniform static magnetic field with the magnetic induction intensity of 0.02T-1T.
The weighing unit is used for determining the mass of a sample to be tested, then the weighed sample is placed into the nuclear magnetic resonance detection coil, the sample is in a uniform static magnetic field generated by the permanent magnet, a computer (including a spectrometer unit) generates a radio frequency excitation pulse with a certain frequency, the radio frequency excitation pulse is amplified by the radio frequency unit, and an alternating magnetic field is generated by the detection coil and used for exciting the sample; after the radio frequency excitation pulse is finished, the detection coil receives a freely attenuated nuclear magnetic signal generated after the sample resonates, the freely attenuated nuclear magnetic signal enters the radio frequency unit, the radio frequency unit amplifies the weak nuclear magnetic signal and then enters the spectrometer unit, the analog signal is converted into a digital signal with a corresponding amplitude, and the amplitude of the digital signal is brought into a quantitative analysis model in the instrument to obtain the content of resin in the sample.
This testing arrangement advantage is: the MSE sequence and the high-sensitivity probe are adopted in the testing device, wherein the MSE sequence can be used for measuring a resin sample of a short relaxation signal, the high-sensitivity probe adopts a technology of rapidly discharging coil energy, the dead time of the probe can be effectively shortened, the signal-to-noise ratio of the probe can be effectively improved, great advantages are provided for the short relaxation and weak signal samples, and the detection resolution is improved.
In addition, the testing device can be calibrated for long-term use at one time, the testing method is flexibly selected, the material consumption is less compared with the experimental method in the national standard, the testing device can be normally used at normal temperature, the selected magnet is a permanent magnet, the maintenance cost is extremely low compared with a superconducting magnet in a high field, the anti-interference capability is stronger, and the normal use of instruments in the environments of a factory and the like can be ensured.
Drawings
The invention is further described with reference to the following figures and examples:
FIG. 1 is a logic flow chart of a resin content testing method based on time-domain nuclear magnetic resonance according to the present invention;
FIG. 2 is a resin content testing device based on time-domain nuclear magnetic resonance;
FIG. 3 is a standard curve of the relationship between resin mass and nuclear magnetic signal;
wherein, 1, a computer (including a spectrometer unit); 2. a radio frequency unit; 3. a coil energy discharge module; 4. a detection coil; 5. a weighing unit; 6. and a permanent magnet.
Detailed Description
Example 1:
the flow of the method for testing the calibration and unknown samples in the embodiment is as follows:
the first step is as follows: sample to be tested and calibration sample preparation
Preparing a calibration sample:
preparing a glass fiber reinforced plastic or carbon fiber reinforced plastic sample similar to the sample to be tested, namely, the sample has different resin contents, the mass of the sample is between 0.2g and 50g, the number of the samples is n, wherein n is more than or equal to 5, and the accurate testing method of the resin content in the sample refers to GB/T2577-;
the mass combinations are given in the table below
The second step is that: obtaining nuclear magnetic signals of a calibration sample
Putting the standard sample in the first step into a quartz test tube, then putting the quartz test tube into a detection coil of a nuclear magnetic resonance device, and testing a nuclear magnetic signal of the sample by using a mixed Magic Sandwich Echo (MSE) sequence, wherein the sequence can detect a weak hydrogen proton signal in a solid resin system in the sample;
sequence parameters of the MSE sequence:
oversampling latency: TW is 50ms to 3000ms, radio frequency delay: RFD ═ 0.002ms-0.5ms, analog gain: RG 1: 10-20, digital gain: DRG1 ═ 1-3, number of repeated samples: NS 4-1024; pre-amplification gain PRG: 0 to 3; the time delay is 10.002ms-0.5 ms; sampling time: 0ms-1000 ms;
finally obtaining nuclear magnetic signals of n standard samples of S1, S2 and S3.. Sn; as in the following table:
the third step: establishment of nuclear magnetic resonance quantitative analysis model
Establishing an OLS (ordinary least squares regression) analysis model between the MSE sequence nuclear magnetic signal amplitude and the resin mass in the sample to obtain a relational expression between the resin mass and the nuclear magnetic signal:
Sn＝K*V+b；
wherein, K is 19384, b is 2422.6; namely Sn 19384 × V + 2422.6;
wherein, the model correlation coefficient R2＝0.9992；
The absolute value of R is between 0 and 1. Generally, the closer R is to 1, the stronger the correlation between V and Sn, whereas the closer R is to 0, the weaker the correlation between V and Sn. It is generally believed that:
| range of values of R | Meaning of R |
| 0.00～0.19 | Very low correlation |
| 0.20～0.39 | Low degree of correlation |
| 0.40～0.69 | Moderate correlation |
| 0.70～0.89 | Highly correlated |
| 0.90～1.00 | Very high correlation |
The fourth step: testing of resin content of unknown samples
Taking 3 samples with unknown resin content, wherein the resin types of the samples are similar to those of the calibration samples, firstly weighing the masses of the samples, then testing the nuclear magnetic signal quantity, obtaining the mass of the resin in the samples by substituting the three formulas in the steps, and calculating the resin content in the samples according to the total mass of the samples as follows:
as shown in the above table, the resin content measured by the method and apparatus of the present invention has high accuracy compared with the resin content measured by the international method, and compared with the conventional method, the resin collected by reinforced plastics does not need to be separated first, the sample does not need to be pretreated, the resin signal in the sample can be directly detected, and the carbon fiber part or the glass fiber itself does not generate the nuclear magnetic signal.
Example 2:
the embodiment provides a device for rapidly testing the resin content in glass fiber reinforced plastics and carbon fiber reinforced plastics.
As shown in fig. 2, the weighing device is used to detect the mass of the glass fiber reinforced plastic and the carbon fiber reinforced plastic to be detected and then transmit the mass to the detection system.
The computer (including spectrometer unit) is mainly responsible for time sequence control, transmitting radio frequency excitation signal, sampling received signal, data processing and temperature control, etc.;
the radio frequency unit is mainly responsible for carrying out power amplification on the radio frequency excitation signal and amplifying the weak nuclear magnetic signal received by the probe.
The coil energy release module can rapidly release the residual energy of the coil, and the effective detection time of the nuclear magnetic signal is greatly shortened.
The detection coil is used for generating an alternating magnetic field for exciting the sample and a free-decay nuclear magnetic signal generated after the resonance of the detection sample, wherein the diameter of the detection coil can be selected from 15mm-45mm, and the detection coil is a solenoid coil wound by silver wires.
The permanent magnet is a high-performance neodymium iron boron magnet, is a material capable of generating the strongest magnetic field at present, and is used for generating a uniform static magnetic field with the magnetic induction intensity of 0.02T-1T.
The weighing unit is used for determining the mass of a sample to be tested, then the weighed sample is placed into the nuclear magnetic resonance detection coil, the sample is in a uniform static magnetic field generated by the permanent magnet, a computer (including a spectrometer unit) generates a radio frequency excitation pulse with a certain frequency, the radio frequency excitation pulse is amplified by the radio frequency unit, and an alternating magnetic field is generated by the detection coil and used for exciting the sample; after the radio frequency excitation pulse is finished, the detection coil receives a freely attenuated nuclear magnetic signal generated after the sample resonates, the freely attenuated nuclear magnetic signal enters the radio frequency unit, the radio frequency unit amplifies the weak nuclear magnetic signal and then enters the spectrometer unit, the analog signal is converted into a digital signal with a corresponding amplitude, and the amplitude of the digital signal is brought into a quantitative analysis model in the instrument to obtain the content of resin in the sample.
The embodiments are merely illustrative of the principles and effects of the present invention, and do not limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical concepts disclosed herein be covered by the appended claims.
Claims (10)
1. A resin content testing method based on time domain nuclear magnetic resonance is characterized in that a standard sample is placed in a detection coil of a nuclear magnetic resonance device for data acquisition, and the method comprises the following steps: the nuclear magnetic resonance device excites a free attenuation nuclear magnetic signal of a sample according to radio frequency pulses emitted by an MSE sequence based on the radio frequency pulses of the MSE sequence; and obtaining a relational expression between the mass of the resin in the sample and the free attenuation nuclear magnetic signal according to a common least square regression analysis model between the free attenuation nuclear magnetic signal and the mass of the resin in the sample.
2. The resin content testing method based on time-domain nuclear magnetic resonance as claimed in claim 1, characterized in that: the relationship between the mass of resin in the obtained sample and the free decay nuclear magnetic signal is as follows:
sn ═ K × V + b, where Sn is a free decay nuclear magnetic signal; v is the resin mass in the sample.
3. The resin content testing method based on time-domain nuclear magnetic resonance as claimed in claim 2, characterized in that: the radio frequency pulse based on the MSE sequence comprises: front and back two phases are phi2Of 90 DEG radio frequency pulses and the two phases are phi2Is transmitted with a phase phi between the radio-frequency pulses3And phi3Of 90 radio frequency pulses.
4. The resin content testing method based on time-domain nuclear magnetic resonance as claimed in claim 1 or 3, wherein: in the radio frequency pulse of MSE sequence, the front phase and the rear phase are phi2Two phases between the radio-frequency pulses of phi3And phi3At tau by 90 radio frequency pulsesφAlternate switching is made within time.
5. The resin content testing method based on time-domain nuclear magnetic resonance as claimed in claim 4, wherein: phase phi2The value range of (A): Δ t21-20 us, and T is less than or equal to 50; phase phi3/-φ3The value range of (A): Δ t3＝1～20us、T≤50；τφ＝1～20us。
6. The resin content testing method based on time-domain nuclear magnetic resonance as claimed in claim 1 or 5, wherein: the method comprises the following steps:
s1, preparing samples, wherein the mass of each sample is 0.2g-50g, and the number of the samples is prepared according to at least three groups;
s2, sample testing, namely placing a single sample in a standard container and then standing in a detection coil of a nuclear magnetic resonance device, wherein the nuclear magnetic resonance device emits radio frequency pulses according to an MSE sequence; after the radio frequency pulse of the MSE sequence is transmitted, a detection coil collects a free attenuation nuclear magnetic signal generated after a sample resonates;
and S3, converting the free attenuation nuclear magnetic signals collected in the S2 into digital signals with corresponding amplitudes, and inputting the digital signals into a quantitative analysis model to calculate the resin content.
7. The resin content testing method based on time-domain nuclear magnetic resonance as claimed in claim 6, wherein: the parameters of the MSE sequence include: the waiting Time (TW) takes 50ms to 3000 ms;
the radio frequency delay time (RFD) takes a value of 0.002ms-0.5 ms;
the analog gain (RG1) takes a value of 10-20;
the digital gain (DRG1) takes 1-3 values;
the repeated sampling times (NS) take the value of 4-1024;
the pre-amplification gain (PRG) takes a value of 0-3;
the time delay is 0.002ms-0.5 ms;
the sampling time is 0ms-1000 ms.
8. The device for the resin content testing method based on time-domain nuclear magnetic resonance according to claim 1, is characterized in that: the device comprises a spectrometer unit, a radio frequency unit, a coil energy leakage unit, a weighing unit, a detection coil and a permanent magnet;
the spectrometer unit is used for controlling time sequence, transmitting radio frequency excitation signals, sampling free attenuation nuclear magnetic signals and controlling temperature;
the radio frequency unit is used for amplifying the power of the radio frequency excitation signal and amplifying the power of the sampled free attenuation nuclear magnetic signal;
the coil energy leakage unit is used for discharging residual energy of the coil;
the detection coil is used for generating an alternating magnetic field for exciting the sample and detecting a freely attenuated nuclear magnetic signal generated after the sample resonates;
the weighing unit is used for detecting the mass of the sample to be detected;
and a permanent magnet for generating a static magnetic field.
9. The device of claim 8, wherein the resin content testing method based on time-domain nuclear magnetic resonance comprises: the detection coil is a solenoid coil wound by silver wires, and the diameter of the detection coil is 15-45 mm.
10. The device of claim 8, wherein the resin content testing method based on time-domain nuclear magnetic resonance comprises: the permanent magnet is a neodymium iron boron magnet, and the permanent magnet generates a uniform static magnetic field with the magnetic induction intensity of 0.02T-1T.
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