Determination of particle size distribution by gravitational liquid sedimentation methods—Part 1:General principles and guidelines
Some standard content:
ICS19.120
National Standard of the People's Republic of China
GB/T26645.1--2011/ISO13317-1:2001 Determination of particle size distribution by gravitational liquid sedimentation methods-Part 1: General principles andguidelines（ISO13317-1:2001,IDT）
Published on June 16, 2011
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Administration of Standardization of the People's Republic of China
Implementation on March 1, 2012
Normative references
Terms, definitions and symbols…·
Limitations on particle size, shape and porous structure·Measurement conditions
Preparation for sedimentation analysis
Parallel sample measurement and instrument calibration
10 Analysis report·
Appendix A (informative)
Appendix B (informative)
Appendix C (Informative Appendix)
Influence of the thickness of the measuring layer
GB/T26645.1—2011/ISO13317-1:2001a
Functional relationship between Reynolds number and the accuracy of Stokes' law Particle displacement caused by Brownian motion
Appendix D (Informative Appendix) Influence of opening on the final sedimentation velocity of spherical particles References
GB/T26645.1—2011/IS013317-1:2001 GB/T26645.1 "Liquid gravity sedimentation method for particle size analysis" is divided into 3 parts: Part 1: General principles;
Part 2: Liquid transfer method:
- Part 3: X-ray gravity sedimentation method. This part is Part 1 of GB/T26645.1. This part is equivalent to ISO13317-1:2001 "Particle size analysis by liquid gravity sedimentation method Part 1: General" (English version). For ease of use, this part has made the following editorial changes: a) "This part of the international standard" is changed to "this part"; b) The foreword of the international standard is deleted;
The decimal point symbol "," is used instead of the symbol "," as a decimal point c
For other international standards cited in ISO13317-1:2001, those that are equivalently adopted as Chinese standards are replaced by Chinese standards, and those that are not adopted as Chinese standards are directly adopted. Appendices A, B, C and D of this part are all informative appendices. This standard was proposed and managed by the National Technical Committee for Particle Characterization and Sorting and Screen Standardization (SAC/TC168). Drafting units of this part: Shanghai Institute of Metrology and Testing Technology, Shanghai National Engineering Center for Nanotechnology and Application Co., Ltd. The main drafters of this part are Wu Limin, Xu Jian, Ni Yong, Xin Lihui, Zhu Lina and Cheng Lifang. GB/T26645.1-2011/IS013317-1.2001 Introduction
Gravity sedimentation particle size analysis is one of the many methods for measuring powder particle size distribution. This method is suitable for samples with a particle size range of 0.5μm to 100μm and meets the sedimentation condition of Reynolds number <0.25. No particle size analysis method can be applied to all different types of materials, but a measurement method that can be applied in most cases can be recommended. This part is formulated to ensure consistency in the process of using gravity sedimentation for particle size analysis between different laboratories, so that the measurement results are comparable. Gravity sedimentation particle size analysis can be used:
As a part of material research; When the particle size distribution is very important to the quality of the product, as a quality control part of the production process; Become a basic clause of the contract and a restrictive technical indicator for material supply. V
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1 Scope
Architecture 321--Standard Query Downloaddown.jz321.netGB/T26645.1—2011/IS013317-1:2001 Particle size analysis Liquid gravity sedimentation method
Part 1: General
This part of GB/T26645 specifies the method of analyzing the particle size distribution of particulate materials by liquid gravity sedimentation method. The typical particle size measurement range is 0.5μm~100μm.
This part is applicable to the measurement of particle size distribution of slurry or particulate materials that can be dispersed in liquid. Usually the density difference between the dispersed phase and the continuous phase is positive, but it can also be used to measure the particle size distribution of emulsion droplets with a lower density than the dispersed phase. Particles cannot undergo physical or chemical changes in suspension. Basic protective measures are required for hazardous materials, especially when using low-boiling volatile liquids as continuous phases, the analyst should first perform explosion-proof tests. Note: This part may contain hazardous materials, operations and equipment. This part does not indicate all safety issues involved in the use process. For users, they should fully consider safety, understand the operating rules, and conduct training on operating skills before use. 2 Normative references
The clauses in the following documents become clauses of this part through reference to this part of GB/T26645. For all dated referenced documents, all subsequent amendments (excluding errata) or revisions are not applicable to this part, however, the parties to the agreement based on this part are encouraged to study whether the latest versions of these documents can be used. For all undated referenced documents, the latest versions apply to this part. GB/T1713 Determination of pigment density Pycnometer method (GB/T1713-2008, ISO787-10:1993, IDT) GB/T2000 Sampling method for coking solid products GB/T15445.1 Presentation of particle size analysis results Part 1: Graphical representation (GB/T154452008, ISO9276-1:1998 ID
GB/T20099 Sample preparation Powder dispersion in liquid (GB/T20099-2006, ISO14887:2000 , IDT) ISO758 Density measurement of liquid chemical products for industrial use at 20°C ISO2591-1 Sieving test Part 1: Sieving test of metal woven mesh and metal perforated plate ISO13317-2 Particle size analysis by liquid gravity sedimentation method Part 2: Pipetting method ISO13317-3 Particle size analysis by liquid gravity sedimentation method Part 3: X-ray gravity sedimentation method 3 Terms, definitions and symbols
3.1 Terms and definitions
The following terms and definitions apply to this section. 3.1.1
Terminal sedimentation velocity terminal Settling velocity is the velocity at which the gravity acting on the particle in a stationary liquid is balanced by the resistance exerted by the liquid on the particle. 3.1.2
Stokes diameter
Diameter of a homogeneous sphere with the same fluid weight and the same free settling velocity of the particle in laminar flow. 3.1.3
Open pores
Pores connected to the outer surface of the particle.
GB/T26645.1—201 1/ISO13317-1:20013.1.4
Closed pores
Pores that are not connected to the outer surface of the particle.
Oversize
The amount of matter that cannot pass through the mesh holes of a specific sieve. 3.1.6
Undersize
The amount of matter that can pass through the mesh holes of a specific sieve. 3.1.7
Effective particle density
Effective particle density
The mass of the particle divided by the volume of the liquid that can be replaced. 3.1.8
True particle densitytrueparticledensityThe mass of the particle divided by the volume of the particle excluding open and closed pores. Note: The true particle density is sometimes equivalent to the absolute particle density. 3.2 Symbols
The symbols used in this section are shown in Table 1.
Table 1 Symbols
Physical quantity
Effective density of particles
Liquid densitybZxz.net
True density of particles (without pores)
Liquid viscosity
Acceleration of gravity
Sedimentation distance quotient
Sedimentation time
Stokes diameter
Upper limit of Stokes diameter
Lower limit of Stokes diameter
Diameter of particles leaving the measuring layer
Diameter of particles entering the measuring layer||tt| |Final settling velocity
Reynolds number
Combined parameter
Combined parameter
Hyperbolic sweep constant
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International System of Units
Dimensionless
Derived system of units
Physical quantity
Boltzmann constant
Absolute temperature (Kelvin)
Particle porosity||t t||Architecture 321---Standard Query Downloaddown.jz321.netGB/T26645.1—2011/IS013317-1:2001Table 1 (continued)
Open porosity fraction of particles wetted by sedimentation solutionUncertain component of particle displacement due to thermal diffusionStatistical mean displacement of a large number of particles in any direction due to thermal diffusion
Measurement layer thickness
Resolution
Minimum acceptable resolution
Thin layer thickness limits resolution
Minimum settling distance for acceptable resolution 4 Principles
4.1 General
International System of Units
Dimensionless
Dimensionless
Dimensionless
Dimensionless
Dimensionless
Dimensionless
Derived System of Units
Liquid Gravity Sedimentation Particle size analysis is a method of characterizing particle size distribution based on measuring the sedimentation velocity of particles in a liquid under the action of a gravity field. The relationship between sedimentation velocity and particle size can be summarized as the Stokes equation at low Reynolds numbers. The Reynolds coefficient must be less than 0.25 to ensure that the measurement error of the Stokes diameter is no more than 3%. The application of Stokes sedimentation analysis relies on Stokes' law. Stokes' law defines the relationship between particle size and the distance the particle (in a suspension) settles, which is a function of the sedimentation time after the particle reaches its terminal velocity, see equation (1): han = (e.-p)gret
. (1)
Note that the value of h defined in this way increases as the particle continues to sink in the sedimentation blood. This formula can be expressed as: At a certain sedimentation time t, the Stokes diameter of the particle can be calculated from the particle sedimentation distance, see formula (2): tst
/(e-e2gt
Sedimentation technology can be divided into incremental method and cumulative method. The incremental method is usually used to measure the solid concentration (or suspension density) in a thin layer at a known height and time: the cumulative method is usually used to measure the sedimentation rate of solids in a suspension. In these two methods, the powder can be used:
layering method, that is, starting to settle from the top of the columnar liquid in a thin layer: - uniform suspension method, that is, starting to settle in a uniform suspension state. The cumulative method is not included in this part. This part only involves the uniform suspension incremental method (see Figure 1) which is widely used in gravity sedimentation technology. The layering method is mostly used for centrifugal sedimentation method. 3
GB/T26645.1-2011/IS013317-1:2001o||tt ||time;
sedimentation height;
measurement layer.
Figure 1 Schematic diagram of incremental gravity sedimentation of uniform suspension 4.2 Particle size calculation
The Stokes diameter can be calculated by formula (2). 4.3 Calculation of mass cumulative distribution
In the pipetting gravity sedimentation method and the X-ray gravity sedimentation method, the calculation of mass cumulative distribution is based on the particle concentration distribution gradient. 4.4 Effect of measurement layer height on resolution
Appendix A gives the effect of measurement layer height on resolution. 5 Limitations of particle size, shape and porous structure
5.1 Upper limit of particle size measurement
The Stokes equation shows that the final sedimentation velocity reached by a single particle in a gravity field can be expressed by formula (3): s
Where:
The Stokes diameter of the particle can be expressed as formula (5): 18 yuan
(5)
Since the final sedimentation velocity can be reached quickly and And remain unchanged, so h = ·, the diameter of the particle can be estimated by the particle sedimentation distance within the specified time, see formula (6): Tst
: (6)
The upper limit of the particle size measurement is determined by whether the Reynolds number satisfies the condition of Re<0.25 when the maximum particle reaches the final sedimentation velocity. Here, the Reynolds number is the ratio of the inertial force to the viscous force exerted on the particle during the sedimentation process, expressed as formula (7):rutst
The Stokes equation is only applicable to laminar flow when the Reynolds number is less than 0.1, see Appendix B. When the Reynolds number is large, the measurement error will increase. When the Reynolds number is equal to 0.25, the measurement error of s obtained is 3%. When the Reynolds number is greater than 0.25, Stokes' law cannot estimate the particle size well based on the sedimentation rate. Substitute Re=0.25 into formula (7) and calculate, and substitute it into formula (5) to obtain the upper limit of the particle size measurement by gravity sedimentation method, see formula (8):
(8)
Example: Temperature = 293.5K, gravity sedimentation measurement of solid quartz ball (p = 2650kg/m) in propanol (g = 804kg/m, m = 2.256mPa-s) 4
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Architecture 321---Standard Query Downloaddown.jz321.netGB/T26645.1—2011/IS013317-1:2001 By formula (4) Calculate K, = 2.24 × 10-m·5, and calculate su = 116μm by formula (8), which is the upper limit of particle size measurement applicable to Stokes' law (measurement error is less than 3%), at this time = 6.03mm/s.
5.2 Lower limit of particle size measurement
The lower limit of particle size measurement by gravity sedimentation method is determined by the following factors: temperature change, convection in suspension, flocculation of particles during sedimentation, and Brownian motion or diffusion of very small particles. The sedimentation process of charged particles in weak electrolyte is related to the double charge layer they carry. When these particles settle, the double charge layer will cause the particles to produce opposite motion and interfere with the measurement results. If necessary, deionized liquid can be used to reduce these electroviscous effects. The function of the influence of Reynolds number on the measurement accuracy of Stokes' law is shown in Appendix B. 5.2.1 Thermal diffusion (Brownian motion)
Particles in liquid are randomly collided with liquid molecules, and the uneven force on the particle surface causes the displacement of particles (Brownian motion). In the absence of other external forces such as gravity, the statistical average displacement of a particle with a diameter of I in any direction can be described by formula (9): Kzttan
Where:
K2-2kT
: (9)
(10)
This is the statistical average displacement of a large number of particles in one direction; the displacement change of some particles from the starting point will be larger than this average, while the displacement change of some particles from the starting point will be smaller than this average. If gravity and thermal diffusion are taken into account, the distance hal and sedimentation time ta of the spherical particle movement can be: a) The particle with a zero average displacement in the vertical direction can be accurately calculated by formula (6); b) The particle with an increased vertical displacement due to vertical thermal movement has a particle size smaller than the calculated value of formula (6); c) The particle with a reduced vertical displacement due to vertical thermal movement has a particle size larger than the calculated value of formula (6). The ratio of displacement and sedimentation distance caused by thermal motion can be obtained from formula (6) and (9), as shown in formula (11): Ah = K
Tsetall
It is generally believed that f建=0.1 is the lower limit of measurement of Stokes sedimentation method, so formula (11) can be expressed as formula (12): 100KK2
(11)
·.-·(12)
Example: Using the same material and measurement temperature in 5.1, the gravity sedimentation time t is greater than 1800s (30min). From formula (10), K, = 3.81X×10-18m, s-, if the increase in sedimentation distance caused by thermal motion is less than 10%, the minimum particle size calculated by formula (12) is zsml=0.64μm. 5.3 Particle shape
At low Reynolds numbers, non-spherical particles are randomly oriented, so the sedimentation rate of a single particle will vary within a small range. As the Reynolds number increases, the particles tend to arrange themselves in a way that gives them the greatest resistance and the lowest velocity during sedimentation. Therefore, a single particle may have different sedimentation rates depending on its orientation. 5.4 Particle porosity
It is recommended to use the effective density of the particle, i.e., measure the density of the particle in a suspension in which the dispersant used for the particle size measurement is added. This will calibrate for any closed pores present, as well as for the effect of open pores into which the liquid can penetrate. For particles without pores and of known composition, the density value can be obtained from manual or empirical measurements. The effect of open pores on the terminal velocity of spherical particles is given in Appendix D. 6 Measurement conditions
6.1 Temperature
Temperature affects the density and viscosity of liquids in the Stokes equations, but has a lesser effect on the density of solids. Therefore, it is very important to control the temperature fluctuation within a very narrow range during the analysis. Since the viscosity of some liquids changes significantly with temperature, it is usually recommended that the temperature change of the sedimentation vessel III be controlled within ±1K. If the temperature change exceeds ±1K, it is recommended to mark the temperature at the beginning and end of the analysis and use the average temperature to calculate the viscosity value. In order to reduce the occurrence of convection, it is recommended to control the temperature change below ±0.05K·min-. The temperature of the suspension can be controlled or the suspension can be allowed to stand to allow the temperature to reach equilibrium. As the powder fineness increases, the stringency of temperature control increases. At the lower limit of measurement, small-sized particle systems require longer sedimentation times, so the sedimentation liquid should maintain more stable conditions. Sedimentation vessel III must be a closed system to reduce evaporation of the surface layer of the sedimentation liquid caused by convection. 6.2 Concentration of Suspension
The Stokes equations apply to the relatively slow settling of a single spherical particle in a liquid of infinite size, but in actual settling analysis, it is not possible to separate the particles from each other and to keep them far enough away from the walls of the sedimentation vessel. To reduce the interaction between particles and between adjacent particle surfaces, a low concentration of suspension is recommended, such as 0.2% by volume. If the recommended maximum concentration is exceeded, two or more concentrations should be measured to determine whether the concentration effect can be ignored. To reduce the effect of the vessel III wall, the distance between the vessel walls should be at least 5 mm.
6.3 Sedimentation Vessel
The sedimentation vessel III should be vertical to avoid convection; the sedimentation vessel should be placed without vibration to avoid disturbance of the settling particles. The walls of the sedimentation vessel or other factors (such as a stirrer) can cause particles to deviate slightly from vertical settling. Particle settling can also be unstable because the liquid displaced by the particles will flow vertically back to the surface after settling. The vessel should be vertical, otherwise convection will occur, which will cause the particles to rise along the vessel wall instead of settling. This will cause errors in the particle size distribution calculation. 6.4 Transient flow
The time it takes for a particle to reach its steady-state (final) settling velocity is negligible, but excessively short settling times should be avoided. Before a particle reaches its final settling velocity, there will be brief velocity changes caused by the momentary cessation of flow at the beginning of settling. Such brief eddies and flows must be reduced.7 Sampling
In settling experiments, in order to obtain representative samples, the sample preparation conditions must be controlled. The sampling method should be in accordance with GB/T2000, and the sample dispersion should be in accordance with GB/T20099.8 Preparation for sedimentation analysis
8.1 Density of liquids and particles
The density of liquids at a certain temperature is measured in accordance with ISO758, and the density of particles is measured in accordance with GB/T1713.8.2 Removal of large particles
As pointed out in 5.1, for a given liquid, The largest particle in the sample analysis must not exceed a certain value. Large particles in the particle size distribution can be found by repeated use of a more viscous liquid, which will reduce the Reynolds number limit. Large particles are removed by dry sieving or wet sieving as specified in ISO 2591-1. Wet sieving can be done with a sedimentation liquid as the medium and the percentage of particles in or on the sieve holes is recorded. The data obtained from the sieve analysis are combined with the sedimentation data as an independent part of the sample measurement.
8.3 Selection of suspension
Many powders do not disperse well in a single suspension. In order to suppress the formation of flocs or lumps during sedimentation, a suitable dispersant should be selected. This dispersant can be added to the suspension or directly to the powder. The reaction between the suspension and the sample should be negligible and the following conditions should be met: a) There must be a sufficient density difference between the liquid and the measured powder. b) The liquid must have a suitable viscosity so that the sedimentation analysis can be completed in a reasonable time. There should not be too long a settling time for fine particles, nor too short a settling time for the coarsest particles. The particles should neither swell nor shrink in the liquid. If this happens, the change in particle size should not exceed 5%. d) The sample should not be soluble in the liquid. If this happens, not more than 5 g of powder should be dissolved in 1 kg of liquid. 6
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8.4 Dispersion of samples
Architecture 321---Standard Query Downloaddown.jz321.netGB/T26645.1—2011/IS013317-1:2001 If the particles cannot be easily wetted in the liquid, or tend to form flocs under static conditions, a dispersant must be added to the suspension system, see the method in GB/T20099, to identify and select a suitable dispersant. 9 Parallel sample measurement and instrument calibration
9.1 Parallel sample measurement
Measurement of parallel samples is performed with the same laboratory samples. For Stokes diameter, the measurement error of the parallel samples should be less than 2%. The measurement error of the certified reference materials mentioned in 9.2 should comply with this regulation. The measurement error of the broad distribution sample will be greater than that of the narrow distribution sample. 9.2 Instrument calibration
In order to confirm that the operation process is correct and the equipment is operating normally, the instrument must be calibrated regularly. The frequency of the check varies from laboratory to laboratory. The initial verification can be performed with any suitable certified reference material. When measuring the reference material, all measurement processes, including sampling, sample dispersion, measurement and data processing, will be checked. The average values of X10, X5 and X9 obtained from 3 independent measurements should be within the standard value range of the reference material.
It is recommended to use certified reference materials, such as the national secondary particle size standard material GBW (E) 120009. Keep all calibration experimental records.
10 Analysis report
The measurement results can be presented in the form of a graph or a graph plus a table. In a typical analysis report, Stokes diameter is plotted against the weight cumulative distribution, with the diameter on the horizontal axis and the percentage of weight cumulative distribution on the vertical axis. The weight cumulative distribution is accurate to 0.1%, and the presentation of the results should comply with the provisions of GB/T15445.
The report should include the following:
The number of this part;
The name of the laboratory;
The date of measurement;
The unique identification of the report;
Operator identification;
The type of instrument used;
Sample identification;
Powder, its density and mass;
Suspension, its temperature, density, viscosity and volume used; Dispersant, and its concentration;
Suspension analysis Dispersion method, including dispersion time; necessary sample treatment method (drying, de-agglomeration); other operations not mentioned in this section but affecting the test results GB/T26645.1-2011/ISO13317-1:2001 Appendix A
(Informative Appendix)
Influence of measurement layer thickness
In the process of gravity sedimentation particle size analysis, the detector detects the particle concentration in a horizontal thin layer area in a columnar sedimentation system. However, this concentration cannot effectively distinguish the size of the particles, so the thicker the measured area, the lower the resolution. The thin layer thickness limit resolution Pone can be defined as the ratio of the difference between the particle diameter Ist.h- just flowing out of the bottom of the measuring layer and the particle diameter Ist.h- just flowing into the top of the measuring layer, see formula (A.1):
where:
height (to the bottom of the measuring layer);
Ah——the thickness of the measuring layer C1,2,
Ist.h—Ist.h-ah
（A1)
Assuming that the sedimentation time at the top and bottom of the measuring thin layer is the same, substitute formula (6) into the above formula, and the thin layer thickness limit resolution can be expressed as formula (A.2):
Vh-yh-Ahne
（A.2)
The acceptable resolution value of Stokes' law is usually 142]. Rearranging formula (A.2), we get the measurement layer thickness function related to the thin layer thickness limit resolution, see formula (A.3): hone.P
Ahaonepz
(A.3)
In the gravity sedimentation particle size analysis, when the thin layer thickness limits the resolution Pmm=14, the acceptable minimum sedimentation distance is ham.Pm7.26△A. This formula is applicable to the thickness measurement pipetting method or the deceleration upward scanning layer method (hyperbolic scanning method). The relationship between the change in the position of the measuring layer and time is shown in formula (A.4):
(A.4)
Under the acceptable thin layer thickness limited resolution, the time required for the detection beam to pass through hme.Pmm is limited by the time required for the detector to scan, see formula (A.5):
Kmone.Pmin
Substituting tim into formula (12), the lower limit of the particle size measurement of the gravity sedimentation instrument using the hyperbolic scanning method is formula (A6): Tst.L.Pm
726KK.haone
(A5)
Example: Gravity sedimentation method, measurement conditions: temperature 293.15K, solid spherical quartz particles, density p.=2650kg/m2, using n-propanol solution (solution density P=804kg/m*, viscosity n=2.256mPa.s). In the measurement layer thickness: hm = 100μm, the hyperbolic scanning constant Km = 2m·s scanning test, from equations (A3) and (A5), when the resolution is less than 14, the area height hmFmm = 726μm, and the time required to reach the operating point is m = 2755s (49.3min). When the thin layer thickness limits the resolution and the thermal diffusion is acceptable, the minimum particle calculated by equation (A.6) is LPaln = 0.58μm. 8
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