ABSTRACT

The paper is dealt with such phenomena as phonon (acoustical) and mechanoluminiscence (photon) emission are and with their interconnection. The two effects are regarded as the special case of mechanical reaction i solids and they seems as quite general effects in solids. The theoretical aspects of that idea are proposed and some application of the both effects are summarised.

KEYWORDS

Phonon (AE) emission, photon (ML) emission, mechanical reaction, theory, applications

1.INTRODUCTION

The phonon and photon emission after the mechanical action on solids known also as acoustical emission (AE) and mechanoluminescence (ML) named also the deformation luminescence (DL) or older triboluminescence (TBL) belong to the well known effects in solids from ancient times [1], [2], [3], [4]. But the scientific significance has got AE from the 40th years of our century due to the pioneering work of W. Mason and others [5] and the ML from the works of G. Wiedemann, F. Schmidt, J. Burke, L. Tschugaeff, D. Gernez, B. A. Lindemann, H. Rode at the end of last and at the beginning of our century. There are also some review articles on ML written by H. Longchambon, K. Mayer with coworkers and A. J. Walton appearing in references in [4]. Now exist allready two monografic books about ML written by L. Sodomka [4] in czech and by U. B. Krauya with coauthor [6], in Russian.

The name mechanoluminescence has arisen in one of Mechanoemission and Mechanochemistry symposium in Berlin 1967. Now all authors use the denomination mechanoluminescence for the radiation effects appearing at mechanical action on solids, but the equivalents and synonyms as original triboluminescence and deformation luminescence is used also.

In the scientific ML development it is possible to detect four periods:

chemical period from beginning to 1920, 2. physicochemical period (1916-1939), 3. chemicophysical period (1944-1960), 4. physical (1950 to today). Detailed classification of these periods is introduced in [4].

2. PHONON AND PHOTON EMISSION DUE TO MECHANICAL ACTION ON SOLID AS A PARTICULAR OF MECHANOREACTION IN SOLIDS [7]

When mechanical energy is absorbed in solids, there appear in the intermediate nonequalibrium states as vibrational and electronic excitations are, new local structural defects or surfaces are formed or are moved in solids or their surfaces. These defects can be as neutral or electrically charged. The new surface or phases are emerged. The charge or mass transfer can be accompanied with collision of moving particles as photons, phonons, atoms, ions, molecules or molecule groups are, what gives the possibility of, the arising a new matter due to the mechanical excited reaction. All these particles, their groups and aglomerates can be physically detected or chemically analysed.

In general sense it is spoken about mechanoemission and mechanochemistry of solids. From that point of view the acoustical emission and mechanoluminescence are the mechanical induced reactions in solids or on their surface. The general form of the mehanically induced reaction can be symbolically expressed in the form

matter + mechanical energy → matter + mechanically induced or moving defects → matter + particle emission → matter + new matter.

As the particular case of mechanical induced reaction can be considered also the acoustical emission and mechanoluminescence that can be expressed as the following reactions; matter + mechanical energy → matter + phonon emission

and mechanoluminescence

matter + mechanical energy → matter + photon emission + phonon emission.

The luminescence as a response on the other action than the mechanical doas, can be explained and theoretical processed without difficulties, because the as the acting and excitation energy has got a quantum character. In contrary the mechanical excitation has got a continuous or classical character and response energy is quantified. The problem is to explain how the mechanical energy is concentrated from the macroscopic and continuous distribution to the local distribution in the atomic scale .

In the absorption-emission reactions in solids at the mechanical action, the main problem is consequently, how the energy transformation from continuous into the quantum states occurs.

The mechanical excitation of the phonon (AE) and photon (ML) emission can be carried out through different experimental conditions as the mechanical shocking, mechanical loading on the dynamometers, mechanical air sandblasting. The principle of the latter one is on fig.1.

Fig. 1

The light and AE spectra can be recorded synchroneously on the memory osciloskope or the detectors output can be adjoined to the computer as it can be seen on fig. 2, 3, 4.

It is possible also work paralelly theoretically. For the all type weak luminiscence can be put forward the general model based on the assuption, that the emitted light is affected through the dipol induced oscilations what leads to the following Schrödinger equation

,

where r is the distance of luminescent ceter pro the dipol moment p , h Dirac constant, the wave function, m is mass of the oscillating particle.

In conclusion it can be said, that exist up to date many question to solve.

3. MECHANOLUMINESCENCE - PHOTON EMISSION

There is well known fact that solids at mechanical action emit photons, that is the luminescence appears called mechanoluminescence. During the experimental ML research the ML emission in the whole spectrum of the electromagnetic from radiofrequency [8] to the X-ray frequency appears [4]. In the many works [9] has been found out that great groups of solids show ML. The experiments with the powder blasting technique indicate that ML is quite universal property of solids [4], [9]. It has not been found the substance between solids which would not be mechanoluminescent. There are only strong and very weak mechanoluminescent solids.

The strongest mechanoluminescence occurs in zinc sulphide activated with manganese which shows all the kinds of the same luminescence as when excited with ultraviolet, X-ray radiation, with bombardment of electrons, with electrical field and others.

But the ML of copper activated electroluminescent zinc sulphide differs in dependence on the frequency of the electrical field used. The identical electroluminescent and mechanoluminescent spectra are only for the high frequency in MHz and higher frequency interval. The most work is done with luminescent zinc sulphide as in the monocrystal as in polycrystal form, because of their strongest ML.

From the many ML measurements, the ML radiation law has been formulated [4] in the form:

        (1)

when M is ML luminance that gives the unit area of irradiated power in W/m², p is the applied pressure or stress acting on or in solids, A, B are the quantity indempendent on dp/dt. The quantity A, B are very complicated functions of the outer conditions (pressure, humidity, temperature, structure and others) of solids. There are just the unknown quantity A, B that makes the ML law so complicated and opened to the both futher experimental and theoretical studies.

From the made experiments it is possible to deduce the dependence of the ML on the bonding strength of the solids. The strongest ML occurs in anorganic solids with covalent and semicovalent bonds as the solids with sphalerite, wutzite and diamond structure are and the ionic solids as alkali halides and others. Therefore these materials are the objects of the most interest of the ML research.

After mechanical action on solids the diferent kinds of deformation have origin in solids as elastic, plastic, deformation and rupture are. From macroscopical point of view one can ask what type of the deformation has the responsibility for the appearence of ML. It is naturally to expect and it has been also without doubt shown that the last two types (plastic deformation and rupture) of the mechanical deformation are the sources of ML. The elastic deformation as the source of ML has not been to that time confirmed directly. In spite of there are some experiments [4], which it is possible to deduce from that the elastic deformation can share also the responsibility for the ML. The direct and pure experiments are missing for that demonstration at that time.

0n the great quantity of anorganic and organic solids [9] it has been observed that these solids belong to the dielectrics and semiconductors. In spite of observing the ML also on metals, the metals have belonged to one group of materials, for which the ML has not been supposed and expected. In the last time it has been reported on the symposium of mechanoemission and mechanochemistry that in so typical metals as copper, aluminium, silver and others are the ML has been detected. So it is possible to conclude from the experiments that the ML is quite general and universal property of solids.

4. PHONON EMISSION OF SOLIDS

The solutions of the vibration of atoms (molecules distributed in linear lattices give following results: If the atomic chains in an linear lattice has at least two different kinds of atoms, there exist two branches of vibrations in solids with acoustical and optical frequencies [10]. The emissions of these frequencies are phonons and photons. The common sources of these phonons and photons are the vibrations of atoms and molecules.

The same situation appears after mechanical action on solids. The phonon emission also called acoustical emission (AE) and photon emission-mechanoluminescence (ML) appear. The acoustical emission, special case of the phonon emission is the response on the origin, annihilation and motion of different defect types in solids in the microscopic, semimicroscopic and macroscopic scale. After mechanical loading of solids there are arisen many defects that move and interact in solids. The response on these very complicated energetic spectrum is not easy to interpreting. The sources of AE spectrum is origin, motion and annihilation of point defects, dislocations, disclinations, microcraks, crases, spliting of solids and arisen of new surfaces, friction and cracking and rupture of solids, the motion of defects and outer and inner stresses. For all these effects it is possible theoretically to estimate their highest limit of friction, splitting, rupture and thus theoretically to evaluate and interpret the AE spectrum.

The AE is very frequently used in praxis but the detailed fysical interpretation of AE energy spectrum is very complicated.

5. PHONON-PHOTON EMISSION

The existence of the two acoustical and optical frequency spectrum from one source allow to expect that after mechanical loading of solids there are appearing also both AE and optical one, called ML.

To confirm that hypothesis many experiments of simultaneous measurements of acoustical emission and mechanoluminescenoe have been done [4].

It has been experimentally prooved synchronous appearence of AE and ML on different materials as substrate. As ML material the strongest ML zinc sulphide activated with manganese coated in the thick layer on the mechanically loaded substrate has been taken.

The fig. 2 and 3 show the synchronous registration of ML curves together with AE ones. The fig. 2. has been done on the steel substrate covered with ML zinc sulphide, the fig. 3 on the cooper and fig. 4 en the organic glass one. These experiments together with the works of Tjurikova [8] are giving the sufficient proof that at the mechanical loading of solids it appears the whole spectrum not only in the electromagnetic wave region but also in the mechanical especially acoustical one.

		Fig. 2. ML and AE with the deformation of a steel plate 5 mm thick. Sensitivity AE 500 mV, 800 mV, time unit 5 s
Fig. 3. Oscillogram ofML and AE signals orogonated with deformation of a steel plate 2 mm thick. Senmsitivity of AE chasnal 100 mV, ML chanal 500 mV, time out 5 s
		Fig 4. Oscillogram of the synchronic course ML and AE signals made with the deformation of anorganic glass, plate. Sensitivity: AE chanal 100 mV, ML chanal 5 V, time unit 20 ms

6. THEORETICAL ASPECTS OF MECHANOLUMINESCENCE

As has been experimentally shown the ML is quite general and universal physical phenomenon, therefore it has to exist a generaI theory of ML. Because it has been observed many of different ML effects, it is possible also to explain the single effects by making some theoretical models. It will be approached to the theories of mechanoluminescence. For the theoretical explanation of ML the following experimental facts is used:

Fig. 5.

1. the ML very complicated synenergic mechanical-optical phenomenon

2. general ML law of the form (1)

3. the strongest ML is observed in the anorganic solid with covalent and ion bonds

4. the origin and motion of the defects in solids which are the surfaces of the concentrated sources

5. after mechanical action and loading of solids it is observed the whole electromagnetic and mechanical vibration spectrum.

The last two points are taken for the theoretical magma plasma model proposed by P, A. Thiesen [11] presented on the fig. 6. That model describes the reality only quantitatively and cannot be used for the mathematical formulation of ML.

Fig. 6

The ML law (1) can be used for the quantitative formulation of the ML law for the excitation of the particles blasting against the obstacle moving with the velocity v under the press p. If it is designed V_p volumen of the particles and E their local Young modulus then the law for the mechanoluminescence M can be expressed in the following form:

      (2)

After the comparison (1) with (2) it can be written for the quantity A, B in (1) the following relations

        (3)

where L is the length of the blasting tube, S is its cross-section n_o is the volume density of ML particles. The expressions (2) and (3) can be used to the illustration of the dependence of the quantities A, B on the different experimental (S,L,n_o,v,p) as well as on the material ones V_p,E, as is expressed by (3). The dependence of M on v has been experimentally verified. The details about that phenomenological theory can be sougt in the [4].

The general theory of ML is based on the experimental results formulated in the points 3, 4 and 5. After all these points local concentration of stresses occurs in solids. These stress concentrations in space and time provide the possibility for the activation of ML solids.

After the law (1) the mechanoluminance ML is determined through the time changes of the stresses acting in solids. That means that the effective stresses for the strong ML have the short pulse form. To the local and time concentration of stresses help very much strong bonded anorganic solids.

When the high stress short pulses are acting on the solid, the group of dispersed waves of all frequencies are spread in the solids, where exist many own intrinsic frequencies of the oscilators in solids which resonate with frequencies of spreading waves generated by stress pulses. The ML radiation spectrum is dependent as on the amplitude as on that frequency of spreading waves which resonate with oscilator in solids (fig. 7).

Fig. 7

Through that mechanism it is possible to explain the strongest ML of the zinc sulphide activated with manganese and ML of metals.

The microscopic models proposed for the ML explanation of single ML effects as the dislocation-, P-N junction-, electrete models are summarised in [4].

The observed synchronous electromagnetic radiation and AE one, support the universal ML theory.

To the ML theory it is necessary to add that there are many question open and the complete rigorous quantum mechanical theory is lacking.

7. MECHANOLUMINESCENCE AND ACOUSTIC EMISSION APPLICATIONS

Despite of there are not known all the experimental facts and there doas not exist any precise theory of ML, there has been carried out a set of ML applications. These application are summarised in [4]. The mechanoluminescence together with accoustical emission can be used to determination of elastic moduli, of the strenth of materials, for the determination of dislocation velocity of plastic properties of solids and in the fracture mechanics. Except of physical application it is possible to meet the ML and AE applications in technique, biology, medicine and others. In technique the ML and AE is used to the determination the time of the impact of the two or more bodies of the optimal grinding conditions of particle mills, of the distribution of particle in flowing and transport in devices, of the erosivity and cutting of the abrasive particles, to the study of materials and many others.

In the last time it is possible to find the using of ML in the studying the mechanical properties of composites. All the papers, works and results dealing with these problems are concentrated in a new book written by Krauja and Janson [6].

The application of ML in biology and medicins is doing by Orel for example [12].

The ML and AE is not already so growing area of solid state physics but in each year there appear about 10 fundamental works dealing with problematics of ML and AE

REFERENCES

[1]   Morgner, W.: Zur Geschichte der Schallemissionsanalyze. Wissenschaftliche Berichte. 8.e Kolloquium Schallemission, Heft 24, November 1990, p. 1-5.

[2]   Staib, W.: Schallemissionsverfahren. Zersörungseie Werkstück and řVerstoffprüfung, Expert Verlag 1988.

[3]   Walton, A. J.: Triboluminescence. Advances in Physics 26, No 6, 1977, p. 887.

[4]   Sodomka, L.: Mechanoluminescence and its application. Academia Praha 1985 (in czech).

[5]   Mason, W. et al.: Phys. Rev. 73 (1948), No 10, p.1213

[6]   Krauja, U.E., Jansons, J. L.: Mechanoljuminescencija kompozitnych matěrialov, Zinatne, Riga, 1990.

[7]   Butyagin, P. Yu: Active States in Mechanical Reactions. Chemistry reviews. Harwood academic Publishers, l989.

[8]   Tjurikova, L. et al.: DAN SSSR 184, No 3, 1969, p. 658

[9]   Sodomka, L.; Research Report Mechanoluminescence in physics and technique. Liberec l979.

[10] Sodomka, L.: Structure and properties of solids. Illife. Prague, London 1967, p. 87.

[11] Heinicke, G.: Tribochemistry. Akademia-Verlag-Berlin, 1984, p.18

[12] Orel, V.E.: Naučnotěchničeskij progress v biologii i medicině. Izd. Instr., kibernětiky AN SSSR, Kiev, T 2, str. 103.