Method for producing core-shell particles and multilayer ceramic electronic components

Abstract

The present invention provides a method for producing core-shell particles and a multilayer ceramic electronic component. The method for producing core-shell particles comprises: introducing a barium titanate-based matrix powder and an additive into a reactor; and exposing the barium titanate-based matrix powder and the additive to a thermal plasma torch to obtain core-shell particles comprising a core portion and a shell portion, wherein the core portion has barium titanate (BaTiO3), and the shell portion comprises the additive and is formed on the surface of the core portion.

Description

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2019-0154377 filed on November 27, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety for all purposes by reference. Technical Field

[0002] The present disclosure relates to a method of producing core-shell particles and a multilayer ceramic electronic component including the core-shell particles. Background Art

[0003] As the trend toward multifunctionalization, lightweighting, and miniaturization of electronic products continues to develop rapidly, the need for small and high-performance electronic components continues to increase, and the demand for electronic components requiring high reliability (corresponding to electronics and industries such as automobiles and networks) has also greatly increased.

[0004] Therefore, competition for technology development of passive components such as inductors, capacitors, and resistors to meet market demand is accelerating. In detail, multilayer ceramic capacitors are a representative field where technology competition is fierce.

[0005] Multilayer ceramic capacitors mainly include a dielectric layer based on BaTiO3 (BT), an inner electrode layer based on metal, and an outer electrode containing metal (Cu) and glass to achieve capacitance. Many efforts are being made to occupy the relevant market by developing high-capacitance products based on thin dielectric layers and inner electrode layers, and by improving reliability and moisture resistance under high temperature and high pressure in addition to improved microstructures.

[0006] BaTiO3 (BT) is one of the most important materials in manufacturing high-performance multilayer ceramic capacitors. It is no exaggeration to say that the ceramic material determines most of the performance.

[0007] However, by a simple mixing method or heat treatment as a related art method for producing core-shell particles, since uniformity of particles is reduced and a designated additive material is added by random coating, there are problems in dispersibility of materials and product distribution for final products.

[0008] Therefore, there is a need to develop a method for producing particles having a core-shell structure capable of uniformly coating BT powder of a multilayer ceramic capacitor and additives determining its function. Summary of the invention

[0009] This summary is provided to introduce selected concepts in a simplified form, and these concepts are further described in the following detailed description. This summary is neither intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0010] An aspect of the present disclosure is to provide a method of producing a core-shell particle and a multilayer ceramic electronic component including the core-shell particle.

[0011] According to one aspect of the present disclosure, a method for producing core-shell particles includes: introducing a barium titanate-based matrix powder and an additive into a reactor; and exposing the barium titanate-based matrix powder and the additive to a thermal plasma torch to obtain core-shell particles including a core portion and a shell portion, wherein the core portion has barium titanate (BaTiO3), and the shell portion includes the additive and is formed on the surface of the core portion.

[0012] According to one aspect of the present disclosure, a method for producing core-shell particles includes: adding a barium titanate-based matrix powder to a reactor through a first feeder, and adding a first additive to the reactor through a second feeder; exposing the barium titanate-based matrix powder and the first additive to a first thermal plasma torch to obtain a first core-shell particle; introducing a second additive into the reactor through a third feeder; and exposing the second additive together with the first core-shell particle to a second thermal plasma torch to obtain a second core-shell particle, wherein the second core-shell particle has a core-multi-shell particle structure.

[0013] According to one aspect of the present disclosure, a multilayer ceramic electronic component includes: a ceramic body, including a dielectric layer and an inner electrode layer, wherein the inner electrode layers are arranged to face each other in the ceramic body, and the dielectric layer is interposed between the inner electrode layers. The dielectric layer includes a core-shell dielectric grain, wherein the core-shell dielectric grain includes a core portion and a shell portion, wherein the core portion has barium titanate (BaTiO3), the shell portion is arranged on the surface of the core portion, and the core-shell dielectric grain is a core-multi-shell dielectric grain, wherein the shell portion has a plurality of shell layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other aspects, features and advantages of the present disclosure will be more clearly understood through the following detailed description taken in conjunction with the accompanying drawings, in which:

[0015] Figure 1 is a flow chart showing a process for producing core-shell particles of a core-shell structure according to an embodiment;

[0016] Figure 2 is a flow chart showing a process for producing core-shell structured core-multi-shell particles according to another embodiment;

[0017] Figure 3 It is shown Figure 2 Schematic diagram of core-shell structured core-multi-shell particles;

[0018] Figure 4is a perspective view schematically showing a multilayer ceramic capacitor according to another embodiment; and

[0019] Figure 5 It is along Figure 4 A cross-sectional view taken along line II'. DETAILED DESCRIPTION

[0020] The following detailed description is provided to help the reader gain a comprehensive understanding of the methods, devices and / or systems described herein. However, various changes, modifications and equivalents of the methods, devices and / or systems described herein will be apparent to those of ordinary skill in the art. The order of operations described herein is merely an example and is not limited to the order set forth herein, but changes may be made that will be apparent to those of ordinary skill in the art, except for operations that must occur in a particular order. In addition, descriptions of functions and configurations that will be well known to those of ordinary skill in the art may be omitted for clarity and brevity.

[0021] The features described herein may be implemented in different forms and should not be construed as limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0022] Here, it is noted that the use of the term "may" with respect to examples or embodiments, for example, with respect to what an example or embodiment may include or implement, means that there is at least one example or embodiment that includes or implements such features, and all examples and embodiments are not limited thereto.

[0023] Throughout the specification, when an element such as a layer, a region, or a substrate is described as being “on”, “connected to”, or “coupled to” another element, the element may be directly “on”, “connected to”, or “coupled to” another element, or one or more other elements may be present between them. In contrast, when an element is described as being “directly on”, “directly connected to”, or “directly coupled to” another element, other elements may not be present between them.

[0024] As used herein, the term "and / or" includes any one and any combination of any two or more of the associated listed items.

[0025] Although terms such as "first", "second", and "third" may be used herein to describe various members, components, regions, layers, or portions, these members, components, regions, layers, or portions are not limited by these terms. Rather, these terms are used only to distinguish one member, component, region, layer, or portion from another member, component, region, layer, or portion. Therefore, without departing from the teachings of the examples described herein, the first member, first component, first region, first layer, or first portion referred to in the examples may also be referred to as the second member, second component, second region, second layer, or second portion.

[0026] For ease of description, spatially relative terms such as "above", "above", "below", and "below" may be used herein to describe the relationship of one element to another element as shown in the drawings. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientations depicted in the drawings. For example, if the device in the drawings is turned over, an element described as being "above" or "above" relative to another element will then be "below" or "below" relative to the other element. Therefore, the term "above" includes both above and below orientations depending on the spatial orientation of the device. The device may also be positioned in other ways (e.g., rotated 90 degrees or in other orientations), and the spatially relative terms used herein will be interpreted accordingly.

[0027] The terms used herein are only used to describe various examples and will not be used to limit the present disclosure. Unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. The terms "comprise", "include" and "have" list the existence of the stated features, quantities, operations, components, elements and / or their combinations, but do not exclude the existence or addition of one or more other features, quantities, operations, components, elements and / or their combinations.

[0028] Due to manufacturing techniques and / or tolerances, the shapes shown in the drawings may vary. Therefore, the examples described herein are not limited to the specific shapes shown in the drawings but include changes in shapes that occur during manufacturing.

[0029] The features of the examples described herein can be combined in various ways that will be apparent after understanding the disclosure of the present application. In addition, although the examples described herein have multiple configurations, other configurations that will be apparent after understanding the disclosure of the present application are also feasible.

[0030] The drawings may not be drawn to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience.

[0031] Subsequently, examples are described in further detail with reference to the accompanying drawings.

[0032] Figure 1 is a flowchart illustrating a process of producing core-shell particles of a core-shell structure according to an embodiment.

[0033] Reference Figure 1 , a method for producing core-shell particles includes: introducing a barium titanate-based matrix powder and an additive (e.g., one or more selected from dysprosium (Dy), yttrium (Y), vanadium (V), magnesium (Mg), manganese (Mn), barium (Ba), silicon (Si), aluminum (Al), chromium (Cr), and calcium (Ca)) into a reactor; exposing the barium titanate-based matrix powder and the additive to a thermal plasma torch; and obtaining a core-shell particle including a core portion and a shell portion, the core portion having barium titanate (BaTiO3) and the shell portion including the additive. The shell portion is formed on the surface of the core portion by exposing the barium titanate-based matrix powder and the additive to the thermal plasma torch.

[0034] Hereinafter, the method for producing core-shell particles according to an embodiment will be described in detail with respect to each step.

[0035] In the method of producing core-shell particles according to an embodiment, first, introducing a barium titanate-based matrix powder and an additive into a reactor 100 is performed.

[0036] According to an embodiment, unlike other embodiments to be described later, the barium titanate-based matrix powder and the additive may be introduced into the reactor 100 in the form of a mixture thereof.

[0037] When the mixture of the barium titanate-based matrix powder and the additive is added to the reactor 100 , the mixture may be introduced into the reactor 100 through a feeder 110 .

[0038] In addition, the barium titanate-based matrix powder and the additives can also be added to the reactor separately through independent feeders. In this case, the feeders and the thermal plasma torches can be arranged in a plurality in the reactor.

[0039] Next, exposing the barium titanate-based matrix powder and additives to a hot plasma torch 120 is performed.

[0040] By exposing the barium titanate-based matrix powder and additives to the hot plasma torch 120, only the surface of the barium titanate-based matrix powder is rapidly heated and cooled (>10 6 In addition, the particle speed is 100m / s to 2000m / s.

[0041] The surface activated barium titanate-based matrix powder and additives present in the surrounding environment react with each other to form core-shell particles.

[0042] For example, according to an embodiment, a barium titanate-based matrix powder and an additive are exposed to a thermal plasma torch 120 to obtain a core-shell particle 3 including a core 1 and a shell 2 , wherein the core 1 includes barium titanate (BaTiO 3 ) and the shell 2 includes the additive and is formed on the surface of the core 1 .

[0043] In this case, the grain growth of the barium titanate-based matrix powder can be suppressed to maintain the uniformity of the particles, and the reaction time is relatively short to perform mass production and continuous production.

[0044] For example, according to an embodiment, core-shell particles for obtaining a multilayer ceramic capacitor with high performance and high reliability may be realized by applying thermal plasma synthesis.

[0045] The thermal plasma torch 120 has a thermal plasma supply unit in a central portion thereof, and has a structure in which the torch is disposed around the central portion, and its structure is not particularly limited thereto.

[0046] Figure 2 is a flow chart showing a process for producing core-shell structured core-multi-shell particles according to another embodiment.

[0047] Figure 3 It is schematically shown Figure 2 Schematic diagram of core-shell structured core-multi-shell particles.

[0048] The method for producing core-shell particles 3 according to another embodiment includes: introducing a barium titanate-based matrix powder into a reactor 100 through a first feeder 110a, and introducing a first additive into the reactor 100 through a second feeder 110b; exposing the barium titanate-based matrix powder and the first additive to a first thermal plasma torch 120a to obtain a first core-shell particle 3a; and introducing a second additive into the reactor 100 through a third feeder 110c to be exposed to a second thermal plasma torch 120b together with the first core-shell particle 3a, thereby obtaining a second core-shell particle 3b. The second core-shell particle 3b has a core-multi-shell particle structure.

[0049] In the operation of adding the barium titanate-based matrix powder and the additives into the reactor, the barium titanate-based matrix powder and the additives may be added into the reactor respectively through independent feeders.

[0050] Alternatively, the reactor 100 may be provided with fewer or more feeders 110 than those shown in the drawings and fewer or more thermal plasma torches 120 than those shown in the drawings.

[0051] In the method of producing the core-shell particle 3 according to another embodiment, first, a barium titanate-based matrix powder is introduced into the reactor 100 through the first feeder 110a, and a first additive is introduced into the reactor 100 through the second feeder 110b.

[0052] Another embodiment relates to a method for producing core-shell particles 3 according to a selective independent type thermal plasma synthesis method. In this case, a barium titanate-based matrix powder is introduced into a reactor 100 through a first feeder 110a, and a first additive is added to the reactor 100 through a second feeder 110b. Therefore, an embodiment of the present disclosure has the following features: the barium titanate-based matrix powder and the first additive are added to the reactor 100 through independent feeders.

[0053] Next, the barium titanate-based matrix powder and the first additive are exposed to a first thermal plasma torch 120 a to obtain first core-shell particles 3 a .

[0054] By exposing the barium titanate-based matrix powder and the first additive to the first thermal plasma torch 120 a , only the surface of the barium titanate-based matrix powder is activated in a rapid heating and cooling manner.

[0055] The surface-activated barium titanate-based base powder and the first additive present in the surrounding environment react with each other to form the first core-shell particles 3 a .

[0056] For example, according to an embodiment, a barium titanate-based matrix powder and a first additive are exposed to a first thermal plasma torch 120a to obtain a first core-shell particle 3a including a core portion 1 and a first shell portion 2a, wherein the core portion 1 includes barium titanate (BaTiO3), and the first shell portion 2a includes the first additive and is formed on the surface of the core portion 1.

[0057] Next, the second additive is introduced into the reactor 100 through the third feeder 110c, and the second additive is exposed to the second thermal plasma torch 120b together with the first core-shell particles 3a to obtain second core-shell particles 3b.

[0058] For this reason, the second core-shell particle 3 b has a core-multi-shell particle structure.

[0059] For example, the second core-shell particle 3b has a core-multi-shell particle structure, which includes: a core portion 1, including barium titanate (BaTiO3); a first shell portion 2a, having a first additive and formed on the surface of the core portion 1; and a second shell portion 2b, including a second additive and located on the first shell portion 2a.

[0060] In detail, Figure 2 and Figure 3As shown in , since the second core-shell particle 3 b has a double-shell structure, the second core-shell particle 3 b can be referred to as a core-double-shell particle.

[0061] According to another embodiment, although not in Figure 2 and Figure 3 , but in addition to the first additive and the second additive, further additives may be introduced into the reactor, and a plurality of shells including the further additives may also be formed on the second core-shell particles 3b.

[0062] For this reason, in the method for producing the core-shell particle 3 according to another embodiment, the produced core-shell particle 3 has a core-multi-shell particle structure, and the multi-shell may be a double shell or more shells.

[0063] For example, the core-shell particle 3 may include a shell layer of three or more shells by further adding an additional additive in addition to the first and second additives into the reactor as described above and exposing the additional additive and the core-double shell particle to an additional hot plasma torch.

[0064] In the core-multi-shell particle structure, the additives included in the respective shell layers of the multiple shells may be different materials.

[0065] For example, as described above, the first additive and the second additive may be different materials, and thus, the additives included in the first shell portion 2a and the second shell portion 2b may be different materials.

[0066] In addition, in the core-multi-shell particle structure, additives included in respective shell layers of the multiple shells may have different concentrations.

[0067] For example, the additives included in the first shell portion 2a and the second shell portion 2b may be different materials, and the additives included in the first shell portion 2a and the second shell portion 2b may have different measured concentrations in the respective shell portions.

[0068] In detail, although the first additive is mainly included in the first shell portion 2a, the first additive may also be detected in the second shell portion 2b or more, in which case the concentration of the first additive may be highest in the first shell portion 2a.

[0069] In addition, although the second additive is mainly included in the second shell portion 2b, the second additive may also be detected in the first shell portion 2a and the third shell portion or more, in which case the concentration of the second additive may be highest in the second shell portion 2b.

[0070] In the case of a simple mixing method or heat treatment (as a prior art method for producing core-shell particles), the uniformity of the particles is deteriorated, and since a specified additive material is added by random coating, there are problems in the dispersibility of the material and, further, there are problems in the distribution of the product for the final product.

[0071] However, core-shell particles produced by a core-shell particle production method through a thermal plasma synthesis method according to an embodiment of the present disclosure are relatively less aggregated and more easily synthesized into ultrafine particles than core-shell particles produced by a related art method.

[0072] In addition, the thermal plasma treatment effect is applied while having the effects of sterilization and impurity removal.

[0073] In addition, when core-shell particles are prepared by a thermal plasma synthesis method as in the embodiment, core-shell particles can be produced using surface chemical reactions only by surface activation with a fast chemical reaction rate and rapid heating and cooling without causing growth of BT grains.

[0074] In addition, low vacuum synthesis and raw material injection in the axial direction enable mass production and continuous production.

[0075] In addition, advantages in the case of the core-shell particle production method by the thermal plasma synthesis method according to the embodiment may be provided as follows.

[0076] Depending on the production conditions, ultrafine particles with a narrow particle size distribution can be obtained. In addition, since the concentration of the substance in the gas phase is relatively low, the aggregation of the particles produced is small.

[0077] Additionally, the number of chemicals involved is small and thus impurities are easily controlled, and the process is simpler and more widely used than liquid phase methods.

[0078] In addition, the synthesis atmosphere is easily controlled, and non-oxides such as nitrides, carbides, borides, and metals can be obtained in addition to oxides.

[0079] Volatile raw materials are easy to purify and can obtain high-purity products. The starting materials can be freely selected in solid, liquid and gaseous states. In this case, less than 10 -2 seconds. Due to the rapid heating and cooling (>10 6 K / s), the reaction time can be short. In addition, the particle speed, vacuum degree and plasma power are 100m / s to 2000m / s, 10 -2 Up to 10 -1 and 10kW to 70kW.

[0080] Figure 4 is a perspective view schematically showing a multilayer ceramic capacitor according to an embodiment.

[0081] Figure 5 It is along Figure 4 A cross-sectional view taken along line II'.

[0082] Reference Figure 3 and Figure 4 According to another embodiment, a multilayer ceramic electronic component may include a ceramic body 10 including a dielectric layer 11 and internal electrode layers 21 and 22, the internal electrode layers 21 and 22 are arranged to face each other in the ceramic body 10, and the dielectric layer 11 is interposed between the internal electrode layers 21 and 22. The dielectric layer 11 includes core-shell dielectric grains (corresponding to core-shell particles 3), the core-shell dielectric grains including a core portion 1 containing barium titanate (BaTiO3) and a shell portion 2 formed on the surface of the core portion 1 (as described above). In the case of the core-shell dielectric grains, the shell portion 2 has a plurality of shell layers (as described above).

[0083] Hereinafter, a multilayer ceramic electronic component according to an embodiment will be described, and in detail, the multilayer ceramic electronic component according to the embodiment is described using a multilayer ceramic capacitor, but embodiments thereof are not limited thereto.

[0084] In the multilayer ceramic capacitor according to the embodiment, the “length direction” is defined as Figure 4 The "L" direction is defined as the "width direction" is defined as the "W" direction, and the "thickness direction" is defined as the "T" direction. In this case, the "thickness direction" may be used in the same concept as the direction in which dielectric layers are stacked (eg, "stacking direction").

[0085] According to an embodiment, the raw material for forming the dielectric layer 11 is not particularly limited as long as sufficient capacitance can be obtained, and may be, for example, barium titanate (BaTiO 3 ) powder as described above.

[0086] In the core-multi-shell dielectric grains, the shell portion may include a double-shell or more shell layer as described above.

[0087] In addition, in the core-multi-shell dielectric grains, the additives included in the shell layer of the shell portion may be different materials.

[0088] Additionally, in the core-multi-shell dielectric grains, additives included in the shell layer of the shell portion may have different concentrations.

[0089] The other features overlap with those of the method of producing the core-shell particle 3 according to the above-described embodiment and other embodiments, and thus will be omitted.

[0090] The material forming the first and second internal electrode layers 21 and 22 is not particularly limited, and for example, a conductive paste formed using one or more of silver (Ag), lead (Pb), platinum (Pt), nickel (Ni), and copper (Cu) may be used.

[0091] The multilayer ceramic capacitor according to the embodiment may further include a first external electrode 31 electrically connected to the first internal electrode layer 21 and a second external electrode 32 electrically connected to the second internal electrode layer 22 .

[0092] The first and second external electrodes 31 and 32 may be electrically connected to the first and second internal electrode layers 21 and 22 to form capacitance, and the second external electrode 32 may be connected to a potential different from that of the first external electrode 31 .

[0093] The material of the first external electrode 31 and the second external electrode 32 is not particularly limited as long as the material can be electrically connected to the first internal electrode layer 21 and the second internal electrode layer 22 to form a capacitor. For example, the first external electrode 31 and the second external electrode 32 may include one or more selected from the group consisting of copper (Cu), nickel (Ni), silver (Ag), and silver-palladium (Ag-Pd).

[0094] As explained above, according to the embodiment, core-shell particles may be realized by applying thermal plasma synthesis to obtain a high performance and high reliability multilayer ceramic capacitor.

[0095] Although the present disclosure includes specific examples, it will be apparent to those of ordinary skill in the art that various changes may be made to these examples in form and detail without departing from the spirit and scope of the claims and their equivalents. The examples described herein will be considered to be descriptive only and not for limiting purposes. The description of the features or aspects in each example will be considered to be applicable to similar features or aspects in other examples. If the described techniques are performed in a different order, and / or if the components in the described system, architecture, device, or circuit are combined in a different manner, and / or the components in the described system, architecture, device, or circuit are replaced or supplemented by other components or their equivalents, suitable results may be obtained. Therefore, the scope of the present disclosure is not limited by specific embodiments, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents will be interpreted as being included in the present disclosure.

Claims

1. A method for producing core-shell particles, comprising: introducing a barium titanate-based matrix powder and additives into a reactor; as well as The barium titanate-based matrix powder and the additive are exposed to a thermal plasma torch to obtain core-shell particles including a core portion having barium titanate and a shell portion including the additive and formed on a surface of the core portion.

2. The method according to claim 1, wherein: The step of introducing the barium titanate-based matrix powder and the additive into the reactor is performed by adding the barium titanate-based matrix powder and the additive into the reactor in the form of a mixture.

3. The method according to claim 1, wherein: The step of introducing the barium titanate-based matrix powder and the additive into the reactor is performed by respectively adding the barium titanate-based matrix powder and the additive into the reactor via separate feeders.

4. The method according to claim 3, wherein: In the reactor, the feeder and the thermal plasma torch are provided in plural numbers.

5. A method for producing core-shell particles, comprising: adding a barium titanate-based matrix powder to a reactor via a first feeder, and adding a first additive to the reactor via a second feeder; exposing the barium titanate-based matrix powder and the first additive to a first thermal plasma torch to obtain first core-shell particles; introducing a second additive into the reactor via a third feeder; as well as exposing the second additive together with the first core-shell particle to a second thermal plasma torch to obtain a second core-shell particle, Wherein, the second core-shell particle has a core-multi-shell particle structure.

6. The method according to claim 5, wherein: In the core-multi-shell particle structure, the multi-shell includes shell layers of double shells or more shells.

7. The method according to claim 5, wherein: In the core-multi-shell particle structure, the first additive and the second additive included in each shell layer of the multi-shell are different materials.

8. The method according to claim 5, wherein: In the core-multi-shell particle structure, the first additive and the second additive included in each shell layer of the multi-shell have different concentrations.

9. A multilayer ceramic electronic component comprising: A ceramic body comprising a dielectric layer and internal electrode layers, wherein the internal electrode layers are arranged to face each other in the ceramic body and the dielectric layer is interposed between the internal electrode layers, The dielectric layer includes core-shell dielectric grains, the core-shell dielectric grains include a core portion and a shell portion, the core portion includes barium titanate, the shell portion includes an additive and is disposed on the surface of the core portion, and the core-shell dielectric grains are core-multi-shell dielectric grains, in which the shell portion has multiple shell layers, and The core-shell dielectric grains are formed from core-shell particles obtained by exposing a barium titanate-based matrix powder and additives to a thermal plasma torch.

10. The multilayer ceramic electronic component according to claim 9, wherein: In the core-multi-shell dielectric grain, the shell portion has two or more shell layers.

11. The multilayer ceramic electronic component according to claim 9, wherein: In the core-multi-shell dielectric grain, each shell layer of the shell portion includes an additive formed using a different material.

12. The multilayer ceramic electronic component according to claim 9, wherein: In the core-multi-shell dielectric grain, different additives included in each shell layer of the shell portion have different concentrations.

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