JPH01175207A - Manufacture of permanent magnet - Google Patents

Abstract

PURPOSE:To improve a remanent magnetic flux density remarkably and to enhance a coercive force by a method wherein an alloy, whose basic components are at least rare-earth elements (including Y), a transition metal and boron, is melted and cast and then hot-worked at a strain rate in a specific range. CONSTITUTION:An alloy of a desired composition whose basic components are rare-earth elements (including Y), a transition metal and boron is melted in an induction furnace and is cast in a mold. Then, in order to give anisotropy to a magnet, the alloy is hot-worked between 500 and 1100 deg.C; its strain rate is increased; its remanent magnetic flux density Br and its coercive force iHc are increased; its maximum energy product (BH)max is also increased. Among others, a plastic working temperature of 800-1050 deg.C is good. When the strain rate of a hot-working process is fast, a crystal particle is made fine; on the other hand, orientation of the crystal particle becomes insufficient and a crack is produced. Accordingly, in order to eliminate the crack at an orientation rate of 80% or more, the strain rate of 10<2>/sec or less is desirable. If the strain rate is small, productivity is lowered remarkably, the crystal particle is grown intensely; a coercive force is lowered; therefore, the strain rate of 10<-4>/sec or more is desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a permanent magnet whose basic components are rare earth elements, iron, and boron.

[Conventional technology]

Permanent magnets are important electrical and electronic materials used in a wide range of fields, from various household electrical appliances to peripheral terminal equipment for large computers.

With the recent demand for smaller and more efficient electrical products,
Permanent magnets are also required to have increasingly higher performance, and among the permanent magnets currently in use, representative ones are alnico hard ferrite and rare earth-transition metal magnets. In particular, R-Co permanent magnets, which are rare earth-transition metal magnets, and R
Since -Fe-B permanent magnets provide high magnetic performance, much research and development has been carried out on them.

Conventionally, there are methods for manufacturing these R-Fe-B permanent magnets as shown in the following documents.

(1) Sintering method based on powder metallurgy, (Reference 1,
Reference 2) (2) A quenched thin strip with a thickness of about 30 μm is made using a quenched ribbon production device used to produce an amorphous alloy, and the quenched flake is made into a magnet using a resin bonding method.Resin using the quenched thin strip made by the melt spinning method. Bonding method, (References 3, References 4) (3) A method of mechanically orienting the rapidly cooled flakes used in the method (2) above using a two-step hot press method, (References 4, References 5) , Document 1: Japanese Unexamined Patent Publication No. 59-46008; Document 2:
M, Saaawa, S, Fujiilura,
N, Togawa, H, Yanamoto a
nd Y, Hatsuura; J, 8p.
pl.

Phys, νof, 55(6) 15 March
1984. P2O83 Document 3: JP-A-59-2115
Publication No. 49: Document 4: R, W, Lee; App
l, Phys, Lett, Vol.

46(8), 15 April 1985. P790
Reference 5: Japanese Patent Application Laid-Open No. 60-100402 Next, the above conventional method will be explained.

First, in the sintering method (1), an alloy ingot is produced by melting and casting, and then pulverized to obtain magnet powder with an appropriate particle size (several μm). Magnet powder is kneaded with a binder, which is a molding aid,
The molded body is completed by press molding in a magnetic field. The compact is sintered in argon at a temperature around 1100° C. for 1 hour and then rapidly cooled to room temperature. After sintering, the coercive force is further improved by heat treatment at a temperature of around 600°C. In the resin bonding method using quenched flakes by the melt spinning method (2), first, an R-Fe-B alloy ribbon is produced at an optimal rotation speed of a quenched ribbon manufacturing apparatus. The resulting thickness is 30
A μm ribbon-like thin strip is an aggregate of crystals with a diameter of 1000 Å or less, is brittle and easily broken, and since the crystal grains are distributed equidistantly, it is also magnetically isotropic. By crushing the rice ribbon to a suitable particle size, kneading it with a resin, and press-molding it, it is possible to fill it to about 85% by volume with a pressure of about 7 tons/-.

In the manufacturing method (3), first, a ribbon-like quenched ribbon or piece of ribbon is heated in a vacuum or in an inert atmosphere for about 70 minutes.
Place in a Graffito or other heat-resistant press mold preheated to 0°C. When the ribbon reaches the desired temperature - axial pressure is applied. Although the temperature and time are not specified, the conditions for sufficient plasticity are T = 725 ± 25 °C,
A suitable pressure is about P~1,4 tQn/cJ.

Although the magnets are oriented in the pressing direction at this stage, the zero-order hot pressing, which is generally isotropic, is performed in a mold having a large area. I& is also generally 7
Press at 00°C, Q, and 7 ton/- for several seconds. The sample now has an initial thickness of 172 mm and is oriented parallel to the pressing direction, making the alloy anisotropic. A method using these steps is called a two-step hot press method. By this method, a dense and anisotropic R-Fe-B magnet is obtained. It should be noted that the crystal grains of the ribbon produced by the initial melt spinning method are made smaller than the grain size at which the ribbon exhibits its maximum coercive force, so that coarsening of the crystal grains may occur during subsequent hot pressing. to obtain the optimum particle size.

However, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force iHc, and the magnet cannot be used as a practical permanent magnet.

[Problem that the invention seeks to solve]

Although it is possible to manufacture R-Fe-B magnets using the above-mentioned conventional techniques, these manufacturing methods have the following drawbacks.

In the sintering method (1), it is essential to turn the alloy into powder, but since R-Fe-B alloys are very active against oxygen, oxidation becomes even more intense when they are turned into powder. The oxygen concentration in the body is inevitably high, and when the powder is compacted, compacting aids, such as zinc stearate, must be used, which are removed beforehand during the sintering process. , the scattering remains in the form of carbon within the magnet, and this carbon is undesirable as it significantly reduces the magnetic performance of R-Fe-8.

The molded body after press molding with the addition of a molding aid is called a green body. This is very fragile and difficult to handle, and therefore, it takes a considerable amount of effort to arrange them neatly in the sintering furnace.

Because of these drawbacks, -R-Fe-B in terms of boat fishing.
The production of sintered magnets in this type not only requires expensive equipment, but also has poor production efficiency, resulting in high magnet production costs.
-B It is hard to say that this is a method that can take advantage of the advantages of optical magnets.

Next, methods (2) and (3) use a vacuum melt spinning device, which currently has very low productivity and is expensive.

Method (2) is isotropic in principle, resulting in a low energy product, and the squareness of the steresis loop is also poor, which is disadvantageous in terms of temperature characteristics and usage.

Method (3) is a unique method that uses a hot press in two stages, but it cannot be denied that it is extremely inefficient when considering actual mass production.

Furthermore, in this method, at high temperatures, for example, 800° C. or higher, the crystal grains become significantly coarsened, resulting in an extremely low coercive force iHc, making it impossible to produce a practical permanent magnet.

The present invention solves the above-mentioned drawbacks of the prior art, and its purpose is to create a high-performance, low-cost rare earth-iron permanent magnet by using the casting method as a pace process and also using hot working. The purpose of this invention is to provide a method for manufacturing the same.

[Means for solving problems]

The first method of manufacturing a permanent magnet of the present invention is a method of manufacturing a magnet whose basic components are a rare earth element (including Y), a transition metal, and boron, in which at least an alloy consisting of the basic components is melted and cast. In the process, the strain rate after casting is 1
A method for producing a permanent magnet is characterized in that it consists of a step of hot working in the range of 0-4 to 102/sec, and the second method is as follows.

A method for producing a permanent magnet, which is characterized in that a step of heat treatment is added to the step of hot working at a post-casting strain rate of 10-4 to 101/sec in the first method; is a permanent magnet characterized by comprising, after the heat treatment step of the second method, a step of pulverizing the cast alloy, and then a step of kneading the pulverized alloy powder with an organic binder and press-forming it. This is the manufacturing method.

[For production]

As mentioned above, the sintering method and the quenching method, which are methods for manufacturing rare earth-iron magnets, each have major drawbacks such as difficulty in powder control due to pulverization and poor productivity.

In order to improve these drawbacks, the present inventors focused on research on magnetization in the bulk state, and first, the rare earth elements,
Anisotropy and high coercive force can be achieved by hot working in the composition range of magnets whose basic components are iron and boron.Furthermore, this cast ingot is pulverized to powder and high coercive force, and then kneaded and hardened with an organic binder. It was discovered that a resin-bonded magnet can be obtained. In this method, the hot processing for anisotropy and high coercive force requires only one step, instead of two steps as in the quenching method shown in the above-mentioned document 4, and it can be processed in bulk. Productivity is extremely high.

Furthermore, since there is no need to crush the cast ingot, the sintering method does not require any strict atmosphere control, and equipment costs are greatly reduced.

Furthermore, resin-bonded magnets do not have the problem of being isotropic in principle like magnets produced by the quenching method, and an anisotropic resin-bonded magnet can be obtained, which improves the high performance of R-Fe-BFa stones. , it is possible to take advantage of the feature of low cost.

As shown in Document 2, the optimal composition of a conventional R-Fe-B photomagnet was R+sFe 778 s.

This composition is shifted to the side rich in R-B compared to the composition R++, tFe at, 4B s, *, which is the atomic percentage of the main phase R2Fe+4B compound. This is explained from the point that in order to obtain a coercive force, not only a main phase but also nonmagnetic phases such as an R-rich phase and a B-rich phase are required.

However, in the present invention, on the contrary, the peak value of the coercive force exists when the amount of B is shifted to the side where there is less B. In this composition range, the coercive force is drastically reduced in the case of the sintering method, so it has not been much of a problem so far. However, in the casting method, a high coercive force can be obtained in this composition range, and an even higher coercive force can be obtained by hot working.

These points can be considered as follows. First of all, whether a sintering method or a casting method is used, the coercive force mechanism itself is nuc.
leation, according to 1 model. this is,
This is because the initial magnetization curves of both exhibit a steep rise like that of SmCo. The coercive force of this type of magnet is basically based on a single domain model. That is, in this case,
If the RzFe+*B compound, which has large magnetocrystalline anisotropy, is too large, it will have domain walls within the grains.
Magnetization reversal easily occurs due to movement of domain walls, and the coercive force is small.

On the other hand, when the particles become smaller to a certain size or less, the particles no longer have domain walls, and the reversal of magnetization proceeds only by rotation, so the coercive force increases. In other words, in order to obtain an appropriate coercive force, it is necessary that the R2F e 14B phase has an appropriate particle size. This particle size is 10μ
A suitable value is around m, and in the case of a sintered type, the particle size can be adjusted by adjusting the powder particle size before sintering.

However, when the casting method and hot working method are combined, Rz
The crystal size of the Fe+4B compound is first determined at the stage of solidification from the molten metal, but since the crystals are made finer by hot working, the final crystal size of the magnet depends on the hot working conditions. It can be adjusted by selecting the desired amount, and a sufficient coercive force can be created.

Next, regarding resin bonding, resin bonded magnets can certainly be created using the quenching method described in Document 4.

However, the powder created by the rapid cooling method has a diameter of 1000A.
Since the following polycrystals are assembled equidistantly, it is magnetically isotropic, and an anisotropic magnet cannot be created.
In the case of the present invention, where the features of low cost and high performance of the -B system cannot be utilized, if pulverization with small mechanical strain such as hydrogen pulverization is performed, the coercive force can be maintained considerably, so resin bonding can be performed. The biggest advantage of this method is that, unlike Document 4, it is possible to create an anisotropic magnet.

The preferred composition range of the permanent magnet according to the present invention will be explained below.

Rare earths include Y, La, Ce, Pr, Nd, Sm5
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
u is listed as a candidate, and one or more of these may be used in combination. Magnetic performance that is also high in M can be obtained with Pr and Nd. Therefore, Pr, Nd
, Pr-Nd alloy, Ce-Pr-Nd alloy, etc. are used. Also, a small amount of additive elements, such as heavy rare earth elements Dy, Tb
etc. are effective for improving coercive force.

The main phases of the R-Fe-B photomagnet are R, Fe+4B. Therefore, if R is 8 atomic % ungrooved, the above compound is no longer formed and a cubic crystal structure with the same structure as α-iron is formed, so high magnetic properties cannot be obtained.On the other hand, if R exceeds 30 atomic %, non-magnetic The R-rich phase increases and the magnetic properties deteriorate significantly. Therefore, the appropriate range for R is 8 to 30%. However, in order to obtain a high residual magnetic flux density, preferably R8 to 25 at%
is appropriate.

B is an essential element for forming the R2F 614B phase, and if it is less than 2 atomic %, it becomes a rhombohedral R-Fe system, so a high coercive force cannot be expected. Moreover, when it exceeds 28 at %, the amount of B-rich nonmagnetic phase increases, and the residual magnetic flux density decreases significantly. However, in order to obtain a high coercive force, B88 is preferably
It is better to have a coercive force of less than an atomic amount, and if it is more than that, a v&4fl R2F 614B phase cannot be obtained unless special cooling is performed, and the coercive force is small.

C.0 is an effective element for increasing the Curie point of this magnet, and basically replaces the Fe site and becomes RzCo+
<B is formed, but this compound has a small crystal anisotropy magnetic field, and as the amount of this compound increases, the coercive force of the magnet as a whole becomes smaller. Therefore, IK can be considered as a permanent magnet.
In order to provide a coercive force of Oe or more, the content is preferably within 50 atomic %.

AI shows the effect of increasing coercive force (Reference 6: 2hang
Haocai et al. Proceedings of th
e 8th International Works
hOD On Rare-Earth Ha! 1lne
TS, 1985, P541) This document 6 shows the effect on sintered magnets, but the same effect exists on cast and manufactured magnets as well. However, since AI is a non-magnetic element, increasing the amount added will reduce the residual magnetic flux density, and if it exceeds 15 at %, the residual magnetic flux density will be lower than hard ferrite, so it cannot fulfill its purpose as a rare earth magnet. Therefore, the amount of AI added is preferably 15 atomic % or less.

Further, Cu, Ni, Ga, Mo, Sl, etc. are also effective additive elements for improving the coercive force.

In addition, in the present invention, hot working is a concept with respect to cold working, and refers to plastic working at high temperatures in which most of the working strain caused by plastic working is removed during processing.
Therefore, during hot working, crystal grain refinement due to recrystallization and subsequent growth of crystal grains also occur, and it is clear that these phenomena are also included in hot working.

The temperature during hot working is desirably higher than the recrystallization temperature, preferably 500°C in the R-Fe-B alloy of the present invention.
That's all.

In the magnet manufacturing method of the present invention, the strain rate during hot working is an important factor. The hot working process can bring about two effects: orientation of crystal axes and refinement of grains, but a faster strain rate brings about better results in grain refinement. Grain orientation becomes insufficient and cracks also occur. Therefore, the orientation rate is 80%
For hot working without cracking, the strain rate is 102/
It is desirable that the strain rate be less than 1 second, and if the strain rate is small, the orientation will be good and there will be no possibility of cracking, but productivity will drop significantly, grains will begin to grow rapidly, and the coercive force will decrease. Therefore, the strain rate is preferably 10-'/sec or more.

Next, embodiments of the present invention will be described.

〔Example〕

(Example 1) A process diagram of the manufacturing method according to the present invention is shown in FIG.

First, as shown in FIG. 1, an alloy having a desired composition is melted in an induction furnace and cast into a mold.

Next, various types of hot working are performed to impart anisotropy to the magnet.

As various hot workings, Fig. 2 shows an explanatory diagram of extrusion processing, Fig. 3 shows an explanatory diagram of rolling processing, and Fig. 4 shows an explanatory diagram of stamping processing.

Regarding the extrusion process, we devised a way to apply force from the die side, just as force is applied to the tomo fishing.

Regarding rolling and stamping, the speeds of the rolls and stamps were adjusted to minimize the strain rate.

In either method, the axis of easy magnetization of the crystal is oriented parallel to the direction in which the alloy is pushed, as shown by the arrow, in the high temperature region (500 to 1100°C).

After melting and casting an alloy whose basic components are rare earth elements, iron, and boron, the present inventors conducted extensive plastic working experiments and obtained the following experimental results.

(1) Cracks occur in alloy ingots of most compositions when plastically worked at a strain rate of 1 second or more at a low temperature between room temperature and 500°C.

Coercive force iHc when magnetically measured using a small piece that is not broken
increases in proportion to the working rate, but crystal orientation hardly occurs, so the residual magnetic flux density Br hardly increases.For this reason, in this range of plastic working, the maximum energy product (B H)max almost never occurs. Does not increase.

(2) On the other hand, when plastic working is performed at a high temperature exceeding 1100° C., no cracking occurs even at a high strain rate of 10 2 /sec, and the workability becomes good and good crystal orientation occurs. However, the eA magnetic force i Hc decreases.

(3) Hot working between 500 and 1100° C. increases the strain rate, increases the residual magnetic flux density Br, coercive force, and iHc, and increases the maximum energy product (BH) max. Among them, the plastic working temperature is 800-1050℃
is good.

(4) Even when an ingot made of the alloy composition of the present invention is heated to near its melting point, coarsening of crystal grains occurs only slightly.

(5) In addition, when the processing temperature and strain rate are optimal, the relationship between the processing degree and the average C-axis orientation is 20% and the C-axis orientation rate is 6.
0-70%, processing degree is 40% and C-axis orientation rate is 65-75
%, processing degree 60%, C-axis orientation rate 75-85%, processing degree 8
At 0%, the C-axis orientation rate is 85 to 95%, and at 90%, the C-axis orientation rate is 85 to 98%.

An alloy having the composition shown in Table 1 was melted and a magnet was produced according to the steps shown in FIG. However, the hot working method used is also listed in Table 1. These hot workings are performed at a processing temperature of 500°C.
~1100℃, working degree 10~90%, strain rate 10-
Various combinations of conditions were performed between 4 and 1/sec. Among them, processing temperature is 1000℃, processing degree is 80%, strain rate is 10-4 to 10-'/sec, and annealing is 1000℃.
The magnetic properties in the case of 24 hours at ℃ are shown in Table 2. The characteristics of a sample without hot working are also shown as reference data.

The optimum conditions for annealing, i.e. temperature and time, vary depending on the alloy composition and processing conditions.
The low temperature range of 00℃ is 800℃ or more depending on the hot processing conditions.
Good results are obtained in the 1000°C region.

Table 2 shows that all the hot working methods of extrusion, rolling, and stamping increased the residual magnetic flux density and caused magnetic anisotropy. Among these, the extrusion method is superior.

Table 1 Table 2 (Example 2) Table 3 shows the composition of P r 17F e7gB4, N
d36F e ssB +s and Ce s N d r
oF r roF e sac 0+7zr 2 B
Taking m as a representative example, the relationship between the plastic working temperature, workability, and 1HC-C axis orientation ratio when extrusion processing is performed is shown. The target degree of processing is 80%, and the Δ mark indicates a crack that occurred during plastic working, and the X mark indicates a work that could not be plastic worked.

The plastic working temperature ranges from 500 to 1,100°C, and among them, 800 to 1,050°C is excellent. When both magnetic properties and productivity are evaluated together, it is 900-105
0°C is optimal. The strain rate can be increased as the temperature increases and the content of rare earth elements and boron decreases.

The strain rate in this experiment was varied in the range of 10-4 to 1027 seconds, and the characteristic values in Table 3 show that the strain rate was 10-2 to 10-'/
The strain rate is 1 to 1 at around 1000℃.
It has been found that setting the processing stress to 102/sec is possible in extrusion molding because the processing stress is mainly compressive stress and tensile stress is small.

Furthermore, as the C-axis orientation rate increases, the residual magnetic flux density Br increases, and (BH)max increases rapidly.

3rd front mouth 80% 161σ岨 10-'～10-1
Stains (Example 3) Table 4 shows P r 14F e iaB 4 and Ce5P
For a cast alloy with a composition of rroNd + oF e tsB 4, the strain rate was set to 10-5 at a processing temperature of 1000°C.
The magnetic properties are shown when hot pressing is performed at a working rate of 80% by changing the speed to ~10°/sec.

Table 4 × shows cracks (Example 4) An alloy having a composition not shown in Table 5 was melted and cast in a vacuum melting furnace,
The obtained ingot was placed in a stainless steel case and hot rolled. At this time, the processing temperature was 900℃, and the processing degree was 8
The strain rate was changed in the range of 10-1 to 1017 seconds, assuming that the strain rate was 0%. The magnetic properties of the processed sample are shown in Table 6. As can be seen from the results, hot working at a strain rate of up to 102/sec is effective in increasing the coercive force.

Table 5 6 Marked X in Table 6 shows cracks (Example 6) P t” tsD 3'2 F e 71B4 and Prt
Ingots were obtained by melting and casting alloys of two types of compositions, 2Nds FettCOsBsCui. For this ingot, the temperature was 1000℃, the working degree was 70%, and the strain rate was 101~
Hot extrusion processing was performed by changing the speed within a range of 104/sec. Thereafter, the magnetic properties were measured after annealing at 900° C. for 10 hours. The results are shown in Table 7, at strain rates between 10-3 and 1027 seconds, 10K
A coercive force comparable to that of OettMA was obtained, and a high coercive force was achieved.

Items marked with X in Table 7 cannot be processed (Example 7) First, an alloy having the composition shown in Table 8 is melted in an induction furnace, cast in an iron chain mold, and after hot pressing at 1000°C, the ingot is magnetically molded. An annealing treatment was performed at 1000'CX for 24 hours to harden the material.

At this time, the average grain size after annealing was about 15 μm.

If this step is used to cut and grind the material, it will become an anisotropic magnet.

For resin-bonded type magnets, 18-8 at room temperature.
In a stainless steel container, hydrogen absorption in a hydrogen gas atmosphere of about 10 atm and dehydrogenation at 10-'torr were repeated, and after pulverization, 4% by weight of epoxy resin was kneaded and a transverse magnetic field of 10 KOe was applied. I did the molding.

The above results are shown in Table 9.

Table 8 Table 9 [Effects of the Invention] According to the method of using the permanent magnet of the present invention as described above, after casting rare earth elements, etc., the strain rate is 10-4 to 102.
The following effects can be achieved by hot working in the range of /second.

(1) The C-axis orientation rate can be increased, and the residual magnetic flux density B
It was possible to significantly improve r.

(2) Also, by changing the crystal grains to am, coercive force iH
It was possible to significantly increase c.

(3) Due to the synergistic effect of (1) and (2), the maximum energy product (B H) max could be increased to various levels.

(4) Compared to conventional sintering methods, processing man-hours and production equipment investment can be significantly reduced.

(5) Compared to the conventional melt spinning method, it was possible to produce magnets with high performance and at low cost.

[Brief explanation of the drawing]

FIG. 1 is a manufacturing process diagram of the R-Fe-B photomagnet of the present invention. FIG. 2 is a diagram showing the orientation treatment of the magnetic alloy by hot extrusion. 1...Hydraulic press 2...Die (mold) 3...Magnetic alloy 4...Arrow indicating pressure 5...Arrow indicating easy magnetization direction of magnet alloy
A diagram showing the orientation treatment of a magnetic alloy by hot rolling. 1...Roll 2...Magnetic alloy 3...Arrow 4 indicating the direction of rotation of the roll...Arrow 5 indicating the traveling direction of the magnetic alloy 5...Arrow indicating the direction of easy magnetization. Diagram of orientation treatment of magnetic alloy by hot stamping. 1... Stamp 2... Magnet alloy 3... Substrate 4... Arrow indicating the direction of easy magnetization 5... Arrow indicating vertical movement of the stamp 6... Arrow indicating the direction of movement of the substrate People Seiko Epson Corporation

Claims (3)

[Claims] (1) In a method for manufacturing a permanent magnet whose basic components are rare earth elements (including Y), transition metals, and boron, at least a step of melting and casting an alloy consisting of the basic components, and a strain rate of 10 A method for producing a permanent magnet, comprising a step of hot working in the range of ^-^4 to 10^2/sec. (2) In a method for manufacturing a permanent magnet whose basic components are rare earth elements (including Y), transition metals, and boron, at least the step of melting and casting an alloy consisting of the basic components, and the strain rate after casting is 10 A method for producing a permanent magnet, comprising the steps of hot working in the range of ^-^4 to 10^2/sec, and then heat treatment. (3) A method for manufacturing a magnet whose basic components are a rare earth element (including Y), a transition metal, and boron, at least a step of melting and casting an alloy consisting of the basic components, and a strain rate of 10 A step of hot working in the range of ^-^4 to 10^2/sec, a step of pulverizing the cast alloy after heat treatment, and a step of kneading the pulverized alloy powder with an organic binder and press-molding it. A method for manufacturing a permanent magnet characterized by: