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MAGNETIC PROPERTIES OF THE TYPES STEELS FOR CHAMBERS OF ELECTRON MICROSCOPES, INNOVATIVE RESEARCH OF ELECTRON MICROSCOPES Martin MAREK a, Daniel PETLAK a, Zbyněk RICHTER a, Regina HOLČÁKOVÁ a, Jiří REŽNAR b a) VŠB-Technical University of Ostrava, FEI, KAT410, Laboratory of Magnetic Measurements and Applications, 17. Listopadu 15, 708 33 Ostrava - Poruba, Czech Republic, mail: [email protected], , mobil: +420-724-033-727

Abstract: The paper deals with the basic goals and partial results of the project, which focuses on innovative research of the magnetic chambers of electron microscopes. This project and paper were created by financial support of state budget through the Ministry of Industry and Trade MPO-CR, project No. FR-TI1/334. This part contains the analysis of magnetic properties of the type’s steel which are designed for construction of chamber of the electron microscopes. In this paper there will be described the results of analysis of magnetic properties of the type’s steels of the types grades with mutual comparisons. The analyzed steels come from Vitkovice a.s. Ostrava production. Keywords: steel, magnetic properties, magnetic measuring, electron microscope, magnetic chamber, BH characteristic 1.

INTRODUCTION

The current state of development and production of the electron microscopes and techniques was briefly summarized in the previous paper prepared for this conference [1], [5] by the same authors. This paper publishes another part of the project solution which is focused also on the magnetic properties of materials but conceived for the areas of the chambers of electron microscopes and materials that are used for their construction or fall as alternative materials for their construction. This is a structural steel of the type’s classes and this post gives an insight into their resulting magnetic properties based on the extensive measurements of magnetic properties. This is a very labor-intensive and extensive analysis that may have major impact on the area of electron microscopes production. 2.

CHAMBERS OF ELECTRON MICROSCOPES

The designs of the electron microscopes are very diverse and differ essentially from the type to type and from the manufacturer to manufacturer. Manufacturing and construction requirements on the individual components of these devices are numerous. Due to the own principle of these devices which using use electron beams, or other particles, these devices are highly sensitive to the overall production accuracy and to the compliance with all interrelated details. The seemingly easiest functional requirements and purpose are on the chambers of these devices. Briefly summarized, the chambers form the frame building and supporting base of the microscope, contain samples porters with high geometric accuracy on follow-up system of electron optics, electron sources themselves, and particle detectors or other sensors. Chambers in most cases also form the part designated for entry and placing of a sample or specimen. Together with this requirement it is also an area defined with the highest requirements for vacuum leaks and stability.

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Another specific function of the chamber is the shielding against external EMC interference in virtually all categories, from this perspective logically the most difficult task is the shielding against the sources of magnetic fields of low frequencies ranging up to levels of the magnetic field of the earth. This problem is logically accompanied by the whole electron microscope structure from the electron source through its trajectory up to the sample and the charges sensors. It should be noted here that the chambers themselves can be a strong source of magnetic field coming out of the remanent magnetic field of the volume of the chamber, or it may be a part behaving as a part of the magnetic circuit that concentrates external or leakage magnetic flux. Critical area in this case is the mouth of the chamber for the optical system and the downstream portion of the optical system up to the sample or specimen itself. Comprehensive quantification of this problem depends on many definitions and practically it is very difficult to to be achieved generally. A possible way to quantify the incremental implementation to perform the partial enumeration/quantification is presented in the work and a paper focused on 2D and 3D calculation of magnetic field layout of the types system of electron microscopes by using FEM see reference [6].

Fig. 1 Types Electron Microscopes and Their Chambers

The great importance in this direction as for the actual design and construction as well as for quantification of the effects have the magnetic properties of the material selected or used for the construction of microscopes chambers. Practically, for this construction there are most often used and the most prescribed steels of the CSN steel grade 11 and 12. View on the real magnetic properties of steels of type’s classes recognized on the specimens of the types smelt and other sources are given in this paper. 3.

TYPES STEELS FOR CHAMBER ELECTRON MICROSCOPES

Basic characteristics of typical steel grades 10, 11 and 12 are commonly available and presented in tables and custom design standards including the characteristics of chemical composition, preparation technology, utility properties, and recommended purpose and using, see for example reference [4]. Very little known or declared are the real magnetic properties in the form of BH hysteresis characteristics. For this reason, much attention and effort was put the analysis of the appropriate type of steel for the construction of chambers at the level of the quasistationary BH hysteresis and magnetization characteristics. A brief overview of the analyzed samples of steel of type sources is given in the following table. The table contains steel designations, type source, the total number of samples in the set and design of samples for magnetic measurements.

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Table 1 Table of the Tested Steels with Description Set

Steel grade

1)

11375

2)

11523

3)

12020

4)

12050

5)

19991 Behanit

1.1

producer

description

Vitkovice a.s.

Vitkovice a.s.

Toroidal samples

Samples with winding for measuring

Melt

Melt

Vitkovice a.s. (after forging) Ingot K208

Vitkovice a.s. bar d=125mm

Vitkovice a.s. (before annealing)

Measuring of Magnetic Properties

The measurement of magnetic properties was carried out in the Laboratory of magnetic measurements and applications at VSB-TU Ostrava, FEI. Measuring was carried out on the measuring system Remagraph designed to detect quasistationary BH hysteresis characteristics of ferromagnetic soft materials. Design of the system and basic block diagram is shown in figure Fig.2. and more detailed description can be found in references [2], [3].

Fig. 2 Design of the Measurement System Remagraph 4.

MAGNETIC PROPERTIES OF SAMPLES OF THE TYPES STEELS

The following table shows the basic overview of the resulting magnetic properties observed on samples of steels of type classes. There are stated the basic quasistationary BH hysteresis characteristics for different limits of magnetic field intensity which were detected on the type samples of the stated steels.

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set

Steel grade

1)

11375

2)

11523

quasistationary BH hysteresis characteristics

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3)

12020

4)

12050

5)

19991 Behanit

Table 2 DC – BH Hysteresis Characteristics of Type Steels

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The following graphs present the mutual comparison of the BH characteristics of listed materials for the measurement of the maximum magnetic field intensity of Hmax = 8 kA/m in full scale and then detailed zoom in the detail of key hysteresis areas.

Table 3 Comparison of the Magnetic Properties of the Types Steels, (DC – BH Hysteresis Characteristics for Hmax = 8000 A/m)

Table 4 Comparison of the Magnetic Properties of the Types Steels, (Demagnetization Characteristics, Magnetization Characteristics, Permeability Characteristics) CONCLUSION The paper presents selected basic results of the very demanding and extensive analysis of magnetic properties of the type’s steels. As results indicated, from the perspective of the magnetic properties and especially of the parameters of the remanent induction and coercive force there exhibits significantly better performance the material with designation Behanit 19991 (technically pure iron), this material has been analyzed in detail in the paper [1]. It should be noted that this material is somewhat beyond the conventional steels of class 11-10-12 and has a significantly lower mechanical parameters, simply said it is much softer. From the other analyzed steels, significantly better remanent parameters have steel of grade 11375 as shown in Tab. 3. and Tab 4., where is plotted the demagnetization part of the BH characteristics that best describes the remanent properties of the material, there are also plotted the magnetization characteristics and permeability characteristics. These results provide key results necessary to select material for the construction of the chamber in terms of magnetic properties, but of course, it is also necessary to take into account the mechanical properties and chemical composition mainly in terms of the final coating of material and the resulting vacuum tightness and stability of the chamber. The aim of this work and paper is to support the development and production of electron microscopes in the Czech Republic, a country which has a long tradition in this area and has a significant potential at present as well in the future time. ACKNOWLEDGEMENT This project and paper was created by financial support of state budget through the Ministry of Industry and Trade of the Czech Republic, MPO-CR, project No. FR-TI1/334.

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LITERATURA [1]

MAREK, M., PETLÁK, D., RICHTER, Z., HOLCAKOVA, R., REŽNAR, J.,: Optimization magnetic properties of the pure ferrum – Behanit, material for construction of the magnetic lenses of the electron microscopes, innovative research of electron microscopes, 21th conference METAL2012, 23-25.5.2012, Hotel-Voronež, Brno,

[2]

MAREK. M.: Recognition methods of magnetic properties of the construction materials, specific examples of using and applications of the magnetic measuring., dissertation thesis, VŠB-TU Ostrava, 2005

[3]

VŠB-TU Ostrava, FEI, Laboratory of Magnetic Measurements and Applications: http://fei1.vsb.cz/kat453/www453/soubory/MAG_LAB/index.htm

[4]

FREMUNT, P,. PODRABSKÝ, T.: Konstrukční oceli, CERM, Brno 1996

[5]

MAREK, M., PETLÁK, D., HOLČÁKOVÁ, R., JELEN, L., REŽNAR, J.,: Innovative research of electron microscopes – analyze of magnetic properties of technically pure ferrum - Behanit, 20th conference METAL2011, 18-20.5.2011, Hotel-Voronež, Brno, http://www.metal2011.com,

[6]

HOLCAKOVA R., MAREK, M.,: Innovative Research in Electron Microscopes, Analysis of Magnetic Field Distribution of Some Types of Magnetic Lenses by FEM, 10th EEEIC Conference, 8-11 May, Roma, 2011