Method for determining a particle shape

Abstract

A method for determining a shape of particles in a distribution with reduced measuring and analyzing complexity includes detecting the number of particles, measuring and storing a particle chord length for each particle as a measurement for particle size and measuring at least first and second distributions of the particle size from the particle chord length measured for each particle. The first distribution is based on a first quantity type, the second distribution is based on a second quantity type and the quantity types correspond to different powers of the particle size. A first distribution parameter, corresponding to a cumulative or density distribution, of the first distribution is set into a distribution parameter ratio with a second distribution parameter, corresponding to a cumulative or density distribution, of the second distribution. An aspect ratio is determined from the distribution parameter ratio as a value characterizing the shape of the particles.

Claims

1. A method for determining a particle shape of particles provided in a distribution, the method comprising the following steps: detecting a number of the particles with a probe; measuring and storing a particle chord length for each particle with the probe; generating at least one first and one second distribution of a particle size from the measured particle chord length, basing the first distribution on a first quantity type, basing the second distribution on a second quantity type, and providing the quantity types used for determining the first distribution and the second distribution with different power; setting a first distribution parameter, corresponding to a cumulative or density distribution, of the first distribution into a distribution parameter ratio with a second distribution parameter, corresponding to a cumulative or density distribution, of the second distribution; and determining an aspect ratio from the distribution parameter ratio as a value characterizing the particle shape of the particles; wherein: the first distribution is a Q.sub.0(x) cumulative distribution and the first distribution parameter is a fineness feature, at which a cumulative number distribution assumes a predetermined percentage value, and the second distribution is a Q.sub.3(x) cumulative distribution and the second distribution parameter is a fineness feature, at which a Q.sub.3(x) cumulative distribution assumes the predetermined percentage value, or the second distribution is a Q.sub.0(x) cumulative distribution and the second distribution parameter is a fineness feature, at which a cumulative number distribution assumes a predetermined percentage value, and the first distribution is a Q.sub.3(x) cumulative distribution and the first distribution parameter is a fineness feature, at which a Q.sub.3(x) cumulative distribution assumes the predetermined percentage value; the generating, setting and determining steps being performed by a processor connected to the probe, the processor running evaluation software to perform the steps.

2. The method according to claim 1, wherein: the first distribution is a q.sub.0(x) density distribution and the second distribution is a q.sub.3(x) density distribution, or the second distribution is a q.sub.0(x) density distribution and the first distribution is a q.sub.3(x) density distribution.

3. The method according to claim 1, wherein the fineness feature is a median value.

4. The method according to claim 1, wherein: the first distribution is a q.sub.0(x) density distribution and the first distribution parameter is a modal value, at which the q.sub.0(x) density distribution assumes a maximum, and the second distribution is a q.sub.3(x) density distribution and the second distribution parameter is a modal value, at which the volume density distribution assumes a maximum, or the second distribution is a q.sub.0(x) density distribution and the second distribution parameter is a modal value, at which the q.sub.0(x) density distribution assumes a maximum, and the first distribution is a q.sub.3(x) density distribution and the first distribution parameter is a modal value, at which the volume density distribution assumes a maximum.

5. The method according to claim 1, which further comprises determining a change of the particle shape when coating particles by using the method.

6. A method for determining a particle shape of particles provided in a distribution, the method comprising the following steps: detecting a number of the particles with a probe; measuring and storing a particle chord length for each particle with the probe; generating at least one first and one second distribution of a particle size from the measured particle chord lengths, providing the first distribution as a q.sub.0(x) density distribution and providing the second distribution as a q.sub.0(x) density distribution; setting a first distribution parameter, corresponding to a cumulative or density distribution of the first distribution into a distribution parameter ratio with a second distribution parameter, corresponding to a cumulative or density distribution of the second distribution; providing the first distribution parameter as a modal value, at which the q.sub.0(x) density distribution assumes a maximum, and providing the second distribution parameter as a largest measured chord length of the a q.sub.0(x) density distribution, or providing the second distribution parameter as a modal value, at which the q.sub.0(x) density distribution assumes a maximum, and providing the first distribution parameter as a largest measured chord length of the a q.sub.0(x) density distribution; and determining an aspect ratio from the distribution parameter ratio as a value characterizing the particle shape of the particles; the generating, setting and determining steps being performed by a processor connected to the probe, the processor running evaluation software to perform the steps.

7. The method according to claim 6, which further comprises determining a change of the particle shape when coating particles by using the method.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) Preferred embodiments of the present invention are explained in more detail in the following by means of figures, wherein:

(2) FIG. 1 shows a diagram, in which by means of an example the aspect ratio of particles is depicted by changing relatively to the ratio of the median values from cumulative volume distribution and cumulative number distribution;

(3) FIG. 2 shows a diagram, in which by means of an example the aspect ratio of particles is depicted by changing relatively to the ratio of the modal values from volume density distribution and number density distribution; and

(4) FIG. 3 shows a diagram, in which by means of an example the aspect ratio of particles is depicted by changing relatively to the ratio of the modal value of number density distribution and largest occurring chord length.

DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a diagram, in which by means of an example the ratio of the median value x.sub.50,3 of the cumulative volume distribution to the median value x.sub.50,0 of the cumulative number distribution is plotted on the x-axis, while on the y-axis, the aspect ratio a/b, that is the size ratio between elongated particle axis a and short particle axis b, of a distribution of ellipsoid particles is plotted. It is recognizable from this depiction that when the ratio x.sub.50,3/x.sub.50,0 is approaching the value 1, the ratio a/b also tends to 1, that is the particle shape approximates the spherical shape. The larger the ratio x.sub.50,3/x.sub.50,0, the more elongated is the particle shape.

(6) FIG. 2 shows a diagram, in which by means of an example the ratio of the modal value x.sub.mod,(q3) of the volume density distribution to the modal value x.sub.mod,(q0) of the number density distribution is plotted on the x-axis, while on the y-axis, the aspect ratio a/b, that is the size ratio between elongated particle axis a to short particle axis b, of a distribution of ellipsoid particles is plotted. It is recognizable from this depiction that when the ratio x.sub.mod,(q3)/x.sub.mod,(q0) tends to the value 1, the ratio a/b also tends to 1, that is the particle shape approximates the spherical shape. The larger the ratio x.sub.mod,(q3))/x.sub.mod,(q0), the more elongated is the particle shape.

(7) FIG. 3 shows a diagram, in which by means of an example the ratio of the modal value x.sub.mod,(q0) of the number density distribution to the largest occurring chord length x.sub.max is plotted on the x-axis, while on the y-axis, the aspect ratio a/b, that is the size ratio between long particle axis a to short particle axis b, of a distribution of ellipsoid particles, is plotted. Here, it is also recognizable that when the ratio x.sub.mod,(q0)/x.sub.max tends to the value 1, the ratio a/b also tends to 1, that is the particle shape approximates the spherical shape. The lower the ratio x.sub.mod,(q0)/x.sub.max, the more elongated the particle shape.

(8) The distribution parameters x.sub.50,3, x.sub.50,0, x.sub.mod,(q3)), x.sub.mod,q0) and x.sub.max stated in the FIGS. 1 to 3 are determined using measured particle chord lengths, which are measured by the single-point scanning. As explained by way of example further above, the particle shape of the particle collective can be characterized by means of the aspect ratio and from the measured chord length distribution using the calculated nondimensional parameter x.sub.50,3/x.sub.50,0, x.sub.mod,(q3)/x.sub.mod,(q0) respectively x.sub.mod,(q0))/x.sub.max. Thereby, a change of the particle shape from an ellipsoid particle shape into a spherical shape or also vice versa can be detected during the measurement time. Accordingly, the method according to the invention can be used for example in methods, in which spherical shaped or ellipsoid particles are coated. Particularly reliable measurement results are thereby produced, when the particles are provided in a nearly respectively approximated monodisperse starting distribution.

(9) As can be inferred from the explanations above, instead of the distribution parameters used in the figures, also other numerous distribution parameters characterizing the respective distribution in various embodiments of the method according to the invention can be applied.

(10) Further attention must be paid to that the embodiments of the invention depicted in the figures are only of exemplary character. Thus, in further embodiments of the invention for example in addition to the ratios mentioned above, inverted ratios such as the ratio of the median value x.sub.50,0 of the cumulative number distribution to the median value x.sub.50,3 of the cumulative volume distribution and/or the ratio of the modal value x.sub.mod,(q0) of the number density distribution to the modal value x.sub.mod,(q3) of the volume density distribution can be calculated and evaluated and/or can be plotted in the respective graphic illustration on the x-axis or the y-axis.