CN108872288B - Method for measuring agglomeration degree of non-ferromagnetic powder in suspension system - Google Patents

Method for measuring agglomeration degree of non-ferromagnetic powder in suspension system Download PDF

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CN108872288B
CN108872288B CN201710336332.0A CN201710336332A CN108872288B CN 108872288 B CN108872288 B CN 108872288B CN 201710336332 A CN201710336332 A CN 201710336332A CN 108872288 B CN108872288 B CN 108872288B
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黄钢
杨培强
杨翼
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Shanghai University of Medicine and Health Sciences
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Abstract

The invention discloses a method for measuring agglomeration degree of non-ferromagnetic powder in a suspension system, which comprises the following steps: (1) preparing powder suspension solutions with different solid contents omega; (2) the above solutions are diluted with pure water respectively, and then separated by NMRRespectively measuring the T of pure water and the powder suspension solution samples with different gradient concentrations after dilution2Relaxation time and calculating relaxation rate R2、R2f(ii) a (3) Calculating the agglomeration degree phi (%) of the powder in the suspension system; (4) and drawing a corresponding relation curve between phi (%) of the agglomeration degree of the powder material and omega of different solid contents in the system for evaluating the dispersion difference of the powder material. The method is simple and feasible to operate, can effectively evaluate the dispersion difference of the powder particles in the suspension system, achieves the aim of scientifically characterizing the agglomeration degree of the powder material, and is beneficial to improving the production process and product performance of the powder material.

Description

Method for measuring agglomeration degree of non-ferromagnetic powder in suspension system
Technical Field
The invention relates to a method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system, in particular to a method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system by adopting a nuclear magnetic resonance technology.
Background
The powder material with the basic particle size in submicron and nanometer level has special performance due to small size effect, surface effect, quantum size effect or macroscopic quantum tunneling effect. Scientifically represents the agglomeration state (agglomeration degree) of the powder material, establishes an agglomeration parameter for accurately describing the structure of the powder material, and has important significance for the application of the powder material in the fields of medicine, materials, biology, environment, manufacturing industry, energy, food and the like.
Taking the nano material as an example, the system has higher surface energy due to the tiny size and large specific surface area, and can be regarded as an unstable thermodynamic system, and the agglomeration can effectively reduce the surface energy of the system, so that primary particles of the nano powder can be aggregated together through electrostatic attraction and van der waals force. The nanometer powder exists in the form of aggregate, and the processing performance and the product performance of the powder are obviously influenced due to factors such as increased particle size, poor particle free-running property and the like. Therefore, scientific characterization is carried out on the agglomeration state (agglomeration degree) of the nano powder material, and agglomeration parameters for accurately describing the structure of the nano powder material are established, so that the method is important content for developing the nano material.
The existing technology for representing the agglomeration state of the nano material mainly comprises a single parameter method, an agglomeration parameter method and a dimension division method:
a. the single parameter method is to measure the size distribution of powder agglomerates by using a parameter such as a centrifugal sedimentation method to obtain a size d50 corresponding to 50% of the accumulated mass of the agglomerates, and to compare the sizes of the agglomerates by using d50 to represent the average diameter of the agglomerates. However, the Stokes sphere diameter of the powder aggregate is obtained by the centrifugal sedimentation method, which reflects the absolute size of the aggregate, and the agglomeration degree of the primary particles of the powder cannot be judged only according to d 50; the degree of agglomeration of the primary particles of the powder can be determined from the value of d50 only under the condition that the primary particles have the same size and the density of agglomerates of the primary particles is the same. However, the actual powder does not have these two conditions, so d50 cannot accurately characterize the structure of the agglomerates and also cannot represent the actual state of the powder agglomerates.
b. The agglomeration parameter method is improved on the basis of the single parameter method, and the agglomeration degree of the nano powder is represented by adopting the ratio of different particle diameters. In document [1], Dynys et al propose to characterize the degree of agglomeration with AF (50), where AF (50) = d 50/dBET. dBET is equivalent spherical diameter corresponding to the BET specific surface area of the nano powder, and the average particle diameter dTEM can also be obtained by a transmission electron microscope method. AF (50) is the ratio of the secondary particle size to the primary particle size of the powder, and the larger the ratio is, the larger the agglomeration degree is. Compared with a single parameter method, the method is closer to the actual state of the nano-aggregate because the influence of the primary particle size of the powder is considered. However, the method is insufficient in that the influence of the agglomerate density is not considered, and the structural factor of primary particle stacking in the agglomerate is not considered. (Note: 1 F.W. Dynys, J.W. Halloran. compact of aggregated aluminum powers. J.Am.Ceram Soc.1983, 66(9): 655.)
c. The fractal dimension method considers that the nano powder aggregate formed by the Brownian motion has a fractal shape with symmetrical scaling on certain sizes, can reflect the interaction property among particles and the information of the fractal structure of the aggregate, and can be used for representing the aggregation or the aggregation degree of the powder. The bulk density of the agglomerates Ψ = (R/a) D-3, wherein R is the radius of the agglomerate, and the secondary particle size can be determined by centrifugal sedimentation and photon correlation spectroscopy; a is the radius of the primary spherical particle, and the primary particle size can be determined by the TEM method. Generally, the larger the agglomerate dimension D, the tighter the agglomerate structure, the higher the relative packing density, and the better the flowability of the particulate powder. The fractal dimension D can be measured by methods such as small-angle scattering and laser diffraction. However, in practical application, the laser diffraction measurement method has a certain limitation due to the low signal-to-noise ratio of diffraction pattern signals, and the distortion of fringe profiles caused by background light formed by light scattered by a measurement optical system and the interference of irregular interference fringes caused by the background light. The small angle scattering method by itself cannot effectively distinguish between scattering from particles or micropores, and for dense scattering systems, interference effects between particle scattering can occur, resulting in lower measurement results.
Therefore, how to solve the problems existing in the method for representing the agglomeration state of the nano material and find a proper test method for scientifically evaluating the real state and performance of the agglomeration body of the powder material becomes a difficult point of research in the field.
Disclosure of Invention
The invention aims to solve the problems in the prior art, and provides a method for measuring the agglomeration degree of non-ferromagnetic powder in a water-based suspension system.
The purpose of the invention is realized by the following measures:
a method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system comprises the following steps:
(1) preparing powder suspension solutions with different solid contents omega, wherein the solute is non-ferromagnetic powder, and the solvent is water;
(2) respectively diluting the solutions prepared in the step (1) with pure water in a series of dilutions, and then respectively measuring the T of the pure water and the diluted powder suspension solution samples with different gradient concentrations by adopting a nuclear magnetic resonance technology2Relaxation time and calculating relaxation rate R2、R2fWherein R is2、R2fThe relaxation rates of the powder particle suspension system and the solvent are respectively corresponding T2Reciprocal of relaxation time (attenuation curve obtained by nuclear magnetic test and T obtained by single-component inversion2Relaxation time); finally obtaining the powder suspension solution with different solid contents when the powder is completely dispersedThe value of omega' is the solid content of the powder material when the powder material is completely dispersed in an ideal state;
(3) and (3) calculating the agglomeration degree phi (%) of the powder in the suspension system:
φ（%）=1-（Sarea of coverage/ STotal surface area）
=1-[(R2sp*R2f)/(Ψ*Kp)]Area of coverage/[(R2sp*R2f)/(Ψ*Kp)]Total surface area
=1-[ω’(1-ω)R2sp]/[ω(1-ω’)R’ 2sp]
Wherein: sArea of coverageIs the coverage area of the powder particles in the liquid medium, STotal surface areaIs the coverage area S of the powder material when the powder material is completely dispersed under an ideal stateArea of coverage=[(R2sp*R2f)/(Ψ*Kp)]Area of coverage，STotal surface area=[(R2sp*R2f)/(Ψ*Kp)]Total surface area；
R2spFor relative relaxation rate, from the formula R2sp=(R2-R2f)/ R2fCalculating to obtain; psi is material volume ratio, psi = Vp/VL=(ω*ρL)/[ρp*(1-ω)]Solid content omega, solvent density rhoLPowder particle density ρpAre all known; kpThe surface characteristic parameter of the powder particles is a constant; r’ 2spThe relative relaxation rate of the powder material when the powder material is completely dispersed in an ideal state;
(4) and drawing a corresponding relation curve between phi (%) of the agglomeration degree of the powder material and omega of different solid contents in the system for evaluating the dispersion difference of the powder material.
In the invention, the solid content omega of the powder suspension prepared in the step (1) is usually within 0-50%. The solution is diluted in the step (2) in a series of dilution until the concentration change and the relaxation rate are in a linear relation, and the linear relation shows the dispersionThe degree is unchanged and the optimal degree is reached. The concentration range is defined so that the relaxation time of the sample in the defined concentration range is not more than 2000ms, and the intercept of the fitted curve is 1/T2fI.e. the inverse of the relaxation time of free water is of comparable size.
In the invention, a calculation model S of the coverage area of powder particles in a liquid mediumArea of coverage=[(R2sp*R2f)/(Ψ*Kp)]Area of coverageThe formula for the relaxation rate of suspensions, namely R, is provided by the document [ 2 ] G.P. van der Beer and M.A. Cohen Stuart. Langmuir 1991,7, 321-2=PbR2b+PfR2fIs derived from, wherein PbTo restrict the solvent ratio, PfIs the ratio of free solvents, R2bTo constrain the relaxation rate of the solvent.
Further, the basic particle size of the non-ferromagnetic powder is in submicron and nanometer level.
Further, the non-ferromagnetic powder includes, but is not limited to, a non-ferromagnetic material of graphene.
Further, the nuclear magnetic resonance technology adopts a low-field nuclear magnetic resonance technology.
Further explaining, the low-field nuclear magnetic resonance technology is used as a test basis for the agglomeration degree phi of powder particles in suspension, and the molecular mobility difference-T between the surface solvent and the free solvent of the powder particles is tested2The relaxation time magnitude indirectly characterizes the size of the area of the particle covered by the liquid.
Further, the degree of powder agglomeration phi (%) in the suspension system is defined as the difference between the ratio of the area covered by the particles to the total surface area of the particles and the unit of complete dispersion 1.
Further, the total surface area of the powder particles is the coverage area of the powder material when the powder material is completely dispersed without agglomeration under ideal conditions.
In the invention, technical characteristics which are not described are matched by adopting mature prior art respectively.
The invention has the advantages that:
1. the agglomeration degree of the powder in a suspension system is indirectly measured by adopting a nuclear magnetic resonance technology, and the molecular mobility difference-T between the solvent on the surface of the powder particles and the free solvent is tested2The relaxation time indirectly represents the area of the particles covered by the liquid, and the signal acquisition and separation are efficient and accurate.
2. By adopting the technical scheme of the invention, the process of testing the agglomeration degree of the powder material in the suspension (in a real and actual use state) is simple, the test result is stable and has good repeatability, the artificial error is small, and the method is favorable for objectively evaluating the real state and the performance of the agglomeration of the powder material.
3. And drawing a corresponding relation curve between phi (%) representing the agglomeration degree of the powder material and omega different solid contents in the system, so that the dispersibility difference of the powder under different concentrations can be visually evaluated and represented, the aim of scientifically representing the agglomeration degree of the powder material is fulfilled, and the production process and the product performance of the powder material are favorably improved.
Drawings
FIG. 1 is a graph showing the correspondence between the degree of agglomeration phi (%) of graphene (quantum dots) powder and different solid contents in the system.
Detailed Description
The method is further described in detail below with reference to the figures, embodiments and specific examples.
Example (b):
a method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system comprises the following steps:
(1) preparing powder suspension solutions with different solid contents omega, wherein the solute is non-ferromagnetic powder, and the solvent is water;
(2) respectively diluting the solutions prepared in the step (1) with pure water in a series of dilutions, and then respectively measuring the T of the pure water and the diluted powder suspension solution samples with different gradient concentrations by adopting a nuclear magnetic resonance technology2Relaxation time and calculating relaxation rate R2、R2fWherein R is2、R2fRelaxation rates of powder particle suspension system and solvent respectivelyI.e. each is a corresponding T2The inverse of the relaxation time; finally, the omega 'value of the powder suspension solution with different solid contents when the powder is completely dispersed is obtained, wherein omega' is the solid content of the powder material when the powder material is completely dispersed in an ideal state;
(3) and (3) calculating the agglomeration degree phi (%) of the powder in the suspension system:
φ（%）=1-（Sarea of coverage/ STotal surface area）
=1-[(R2sp*R2f)/(Ψ*Kp)]Area of coverage/[(R2sp*R2f)/(Ψ*Kp)]Total surface area
=1-[ω’(1-ω)R2sp]/[ω(1-ω’)R’ 2sp]
Wherein: sArea of coverageIs the coverage area of the powder particles in the liquid medium, STotal surface areaIs the coverage area S of the powder material when the powder material is completely dispersed under an ideal stateArea of coverage=[(R2sp*R2f)/(Ψ*Kp)]Area of coverage，STotal surface area=[(R2sp*R2f)/(Ψ*Kp)]Total surface area；
R2spFor relative relaxation rate, from the formula R2sp=(R2-R2f)/ R2fCalculating to obtain; psi is material volume ratio, psi = Vp/VL=(ω*ρL)/[ρp*(1-ω)]Solid content omega, solvent density rhoLPowder particle density ρpAre all known; kpThe surface characteristic parameter of the powder particles is a constant; r’ 2spThe relative relaxation rate of the powder material when the powder material is completely dispersed in an ideal state;
(4) and drawing a corresponding relation curve between phi (%) of the agglomeration degree of the powder material and omega of different solid contents in the system for evaluating the dispersion difference of the powder material.
In the above embodiment, the basic particle size of the non-ferromagnetic powder is in the submicron and nanometer level. The non-ferromagnetic powder includes but is not limited to non-ferromagnetic material of graphene.
The nuclear magnetic resonance technology adopts a low-field nuclear magnetic resonance technology. The low-field nuclear magnetic resonance technology is used as a test basis for the agglomeration degree phi of powder particles in suspension, and the molecular mobility difference-T between a solvent on the surface of the powder particles and a free solvent is tested2The relaxation time magnitude indirectly characterizes the size of the area of the particle covered by the liquid.
The degree of powder agglomeration phi (%) in the suspension system is defined as the difference between the ratio of the area covered by the particles to the total surface area of the particles and the unit of complete dispersion 1. The total surface area of the powder particles is the coverage area of the powder material when the powder material is not agglomerated and is completely dispersed under an ideal state.
Application example 1:
and (3) testing the agglomeration degree phi (%) of the graphene under different solid contents: sample numbers 1# and 2# have solid contents of 0.2% and 0.5%, respectively.
(1) Degree of agglomeration Φ (%):
φ（%）=1-（Sarea of coverage/ STotal surface area）=1-[ω’(1-ω)R2sp]/[ω(1-ω’)R’ 2sp]Wherein: omega', R’ 2spThe solid content and the relative relaxation rate of the nano material when the nano material is completely dispersed in an ideal state are respectively.
(2) In order to obtain an ideal state that graphene is completely dispersed at a certain concentration, dilution is only needed on the basis of the original solution, such as dilution of a series of concentration gradient samples. Respectively measuring T of pure water and the gradient concentration graphene sample by nuclear magnetism2Relaxation time and calculating relaxation rate R2. If it is finally obtained that the dispersion of the graphene is complete when the solid content is 0.0833%, the method can be according to the formula:
φ（%）=1-[ω’(1-ω) R2sp]/[ω(1-ω’) R’ 2sp]to calculate phi.
(3) Calculating the agglomeration degree phi (%) of the graphene as follows: the agglomeration degree is 55.5% when the solid content is 0.2%; the degree of agglomeration was 72.8% at a solids content of 0.5%.
Application example 2:
taking quantum dot graphene as an example, low-field nuclear magnetic resonance tests the agglomeration degree of the concentration dots of 0.38, 0.19, 0.095 and 0.0475mg/ml respectively.
(1) Degree of agglomeration phi (%) =1- (S)Area of coverage/ STotal surface area）=1-[ω’(1-ω) R2sp]/[ω(1-ω’) R’ 2sp](wherein, ω is’、R’ 2spThe solid content and the relative relaxation rate of the nano material when the nano material is completely dispersed under an ideal state).
(2) In order to obtain an ideal state that graphene is completely dispersed under a certain concentration, dilution is only needed on the basis of the original solution. Respectively measuring T of pure water and the gradient concentration graphene sample by nuclear magnetism2Relaxation time and calculating relaxation rate R2。
(3) Ideally, the quantum dot graphene is sufficiently dispersed, and if the coverage area is approximate to the total surface area under the extremely dilute concentration of 0.02375mg/ml, the solution formula can be directly used: degree of agglomeration phi (%) =1- [ omega%’(1-ω) R2sp]/[ω(1-ω’) R’ 2sp]And (4) calculating. And finally, taking the concentration of the graphene as a horizontal coordinate and the agglomeration degree as a vertical coordinate to make a dispersion effect curve as shown in the attached drawing 1.
The dispersion characteristic curves of graphene under different concentrations can be known from fig. 1, so as to evaluate the dispersion difference between graphene and a solvent system.
Although the present invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims (3)

1. A method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system is characterized by comprising the following steps:
(1) preparing powder suspension solutions with different solid contents omega, wherein the solute is non-ferromagnetic powder, and the solvent is water;
(2) respectively diluting the solutions prepared in the step (1) with pure water in a series of dilutions until the concentration change and the relaxation rate are in a linear relationship, and then respectively measuring the T of the pure water and the diluted powder suspension solution samples with different gradient concentrations by adopting a nuclear magnetic resonance technology2Relaxation time and calculating relaxation rate R2、R2fWherein R is2、R2fThe relaxation rates of the powder particle suspension system and the solvent are respectively corresponding T2The inverse of the relaxation time; finally, the omega 'value of the powder suspension solution with different solid contents when the powder is completely dispersed is obtained, wherein omega' is the solid content of the powder material when the powder material is completely dispersed in an ideal state; the concentration range is defined to ensure that the relaxation time of the sample in the defined concentration range is not more than 2000ms, and the intercept of the fitted curve is equivalent to 1/T2f, namely the reciprocal of the relaxation time of the free water; the nuclear magnetic resonance technology adopts a low-field nuclear magnetic resonance technology; the low-field nuclear magnetic resonance technology is used as a test basis for the agglomeration degree phi of powder particles in suspension, and the size of the area covered by liquid of the particles is indirectly represented by testing the molecular mobility difference-T2 relaxation time of a solvent and a free solvent on the surface of the powder particles;
(3) and (3) calculating the agglomeration degree phi (%) of the powder in the suspension system:
φ(％)＝1-(Sarea of coverage/STotal surface area)
＝1-[(R2sp*R2f)/(Ψ*Kp)]Area of coverage/[(R2sp*R2f)/(Ψ*Kp)]Total surface area
＝1-[ω’(1-ω)R2sp]/[ω(1-ω’)R’2sp]
Wherein: sArea of coverageIs the coverage area of the powder particles in the liquid medium, STotal surface areaIs the coverage area S of the powder material when the powder material is completely dispersed under an ideal stateArea of coverage＝[(R2sp*R2f)/(Ψ*Kp)]Area of coverage，STotal surface area＝[(R2sp*R2f)/(Ψ*Kp)]Total surface area；
R2spFor relative relaxation rate, from the formula R2sp＝(R2-R2f)/R2fCalculating to obtain; psi is material volume ratio, psi ═ Vp/VL＝(ω*ρL)/[ρp*(1-ω)]Vp is the volume of the powder particles, VLIs the volume of solvent; solid content omega, solvent density rhoLPowder particle density ρpAre all known; kpThe surface characteristic parameter of the powder particles is a constant; r'2spThe relative relaxation rate of the powder material when the powder material is completely dispersed in an ideal state;
(4) and drawing a corresponding relation curve between phi (%) of the agglomeration degree of the powder material and omega of different solid contents in the system for evaluating the dispersion difference of the powder material.
2. The method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system according to claim 1, wherein the method comprises the following steps: the basic particle size of the non-ferromagnetic powder is in submicron or nanometer level.
3. The method for measuring the agglomeration degree of non-ferromagnetic powder in a suspension system according to claim 1 or 2, characterized in that: the non-ferromagnetic powder includes but is not limited to non-ferromagnetic material of graphene.
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