**6. Present knowledge on mechanochemistry and tribochemistry**

#### **6.1. Brief introduction**

228 Tribology in Engineering

negative ion R-

homogeneous C–C bond cleavage. R-

alternative mechanism is proposed, as detailed in Fig. 19.

tribochemistry as a branch of mechanochemistry.

Figure 18 summarizes all the process steps, where ●R1 and ●R2 relate to free radicals of

heterogeneous polymer bond scission. Radical R● concerns electron transfer from the

(anion) to TCNE either during mixing or photo irradiation.

**Figure 18.** Illustration and suggested evidence for heterogeneous C–C bond cleavage based on work [68].

The electron transfer reaction in the dark at 77K is promoted by physical mixing of fractured sample in the vibration glass ball mill and, after milling; the fractured sample was dropped into the ESR sample tube under vacuum in the dark at 77K and photo irradiated using an IR lamp with a glass filter corresponding to visible light [68]. Thus, everything is clear for the irradiation effect due to electron detachment. On the other hand, for reaction **(7)** here an

**Figure 19.** Application of the NIRAM approach to account for the mechano-anion-radical generation

Actually, generation of mechano-anion-radicals relates strictly to triboelectricity and is reviewed in reference [68]. It cites a wide range of papers which aimed at finding evidence for both heterogeneous C-C bond scission and polymer triboelectricity. The review strongly suggests production, eg. mechano-anions induced by mechanical fracture of PCV. EPR studies provide evidence TCNE radical-anion generation. However, the formulation of a satisfactory theory to account for the triboelectricity of polymers has yet to be established. The same is due to clear evidence for heterogeneous C **–** C bond scission. An extension of the NIRAM approach to better understand the mechano-anion-radicals allows considering

Triboelectricity or contact electrification of materials is a very complex phenomenon. According to [69] the first studies on contact electrification were carried out over 2500 years ago, when

and R+ relate to anion and positive ion species of the

Particularly important research and practical application of mechanochemistry is well reflected in INCOME (International Conference on Mechanochemistry) series of special meetings initiated in 1993 by International Mechanochemistry Association (IMA). IMA is the associate member of International Union of Pure and Applied Chemists (IUPAC). These conferences regularly serve as a common platform to bring together all stakeholders from academia, research and development organisations, along with industry to foster the growth of the discipline [71]. The first INCOME meeting was held in Slovakia (1993). Participants from 25 countries of 4 continents took part at the meeting. This international forum was preceded by eleven All-Union Symposia on Mechanochemistry and Mechanoemission.

INCOME 2011 focused on mechanochemistry and mechanical alloying, was held in Herceg Novi, Montenegro. The conference aimed at providing a forum for presentation of new results, identification of current research and development trends along with future directions and, promoted interactions dealing with various aspects of the discipline. Presented research papers concerned both mechanochemistry and tribochemistry. By and large, they demonstrated the progress of studies on the chemical and physicochemical processes proceeding in solids under mechanical action.

General Approach to Mechanochemistry and Its Relation to Tribochemistry 231

Very detailed review publications [72-73] include a wide range of industrial applications of mechanochemistry and underline the need for sustainability brought about by the Kyoto Treaty and the increasing global demand for products leading to an increase in sustainable manufacturing processes. Such processes and/or new technologies can lower environmental demands. Improved sustainability can be realized in the form of reduced energy use, less organic solvents, better selectivity and reduced waste. Recent well specified study [75] presents several advantages of mechanochemical technology, such as simple process, ecological safety and the possibility of obtaining a product in the metastable state. Thus, it gives an overall review of the mechanochemistry applications in waste management. Interestingly to note that based on that study, the modification of fly ash and asbestos containing wastes (ACWs) can be achieved by mechanochemical technology (MCT). Finally, MCT provides with a prospective application in pollution remediation and also waste management. Hazardous metal oxides can be transformed into easily recyclable sulfide by mechanochemical sulfidization; the waste plastics and rubbers, which are usually very difficult to be recycled, can also be recycled by mechanochemical technology [75]. At this point the importance of waste-free mechanochemical

Another study [76] demonstrates that the mechanochemical treatment of an expired drug as ibufren, may be very useful and non-polluting way to change the bioactive molecule of a pharmaceutical formulation into non-toxic product. In the degradation mechanism two major steps are considered. The first one in the degradation process that leads to the detoxification of the drug, is induced by the presence of a co-reagent aluminum hydroxide. The second step relates to oxidative decarboxilation to an intermediate stable benzyl radical which, reacting in the presence of oxygen during milling, produces several products. The number of the generated products is controlled by the milling time. Thereafter, mechanochemical treatments are environmentally sound for general approach to detoxify chemical-pharmaceutical waste. Thus, in this case a type of molecular mechanolysis without

Extension of mechanochemistry practical applications is broadly described by Todres in the book on both mechanochemistry and tribochemistry [77]. The specificity of the Todres' book is that it discusses chemical reactivity of organic molecules mechanically treated separately or together and, describes mechanochemically initiated polymerization, depolymerization and mechanolysis. It also considers lubricant design and lubricity process. Organic solids/materials are very liable to attrition representing wear caused by friction (tribos) and therefore relating to tribochemistry. This is evidenced by considering detailed organic

Mechanochemistry comprises a wide branch of the reactivity research of solids activated by mechanical action. It also deals with mechanisms of solid-phase reactions, aiming at making

**6.3. Practical aspects of mechanochemistry** 

synthesis and production should also be noted [5].

solvent or usual thermal contribution can be considered [76].

**6.4. How mechanochemistry is entangled with tribochemistry** 

reactions with lubricating layers.

*6.4.1. Selected books and review publications* 

#### **6.2. Major recent review papers**

Some review papers have already been described in previous sections. They specifically relate to mechanochemistry [46,66] and/or tribochemistry [6,11,29]. The most recent extensive critical review paper [72] aims at providing a broad but digestible overview of mechanochemical synthesis, that is reactions conducted by grinding solid reactants together with no or minimal solvent. This critical review includes over 300 references focused on the historical development, mechanistic aspects, limitations and opportunities of mechanochemical synthesis. It emphasizes that although mechanochemistry has historically been a sideline approach to synthesis, presently it may move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous [72]. This is because it provides the opportunities for developing more sustainable technologies. Additionally, synthesis of metal organic frameworks (MOFs) has to be mentioned here, as it have become presently one of the most intensely researched areas of materials chemistry and, it might relate to both mechanochemistry and tribochemistry.

An earlier detailed review paper generally aimed at mechanical activating of covalent bonds [73], also considers mechanochemistry of crystals, metals, alloys, and polymers. The latter is related to already discussed in detail heterogeneous C – C bonding splitting in polymers [68] (see Section 5.3). By the employing of mechanochemical solid-state reaction, Fujiwara and Komatsu synthesized a novel C60 dimer linked by a silicon bridge and a single bond [74]. The novel C60 dimer was synthesized using a high-speed vibration milling (HSVM) technique and, the product obtained was fully characterized by a wide variety of sophisticated analytical techniques. The electronic interaction between the two C60 cages was evidenced by the electrochemical method. For instance, in these dimers, the two fullerene cages are connected by sharing a cyclobutane ring. the mechanochemical solid-state reaction of C60 with alkyl or aryl halide in the presence of alkali metals was found to cause alkylation or arylation of C60 possibly by the intermediacy of the C60 radical anion [74]. The mechanochemical reaction of the fullerene with dichlorodiphenylsilane (Ph2SiCl2) and lithium (Li) metal, under the solvent free conditions, allowed synthesizing the C60 dimer fused with a silacyclopentane ring, as shown below [74].

#### **6.3. Practical aspects of mechanochemistry**

230 Tribology in Engineering

INCOME 2011 focused on mechanochemistry and mechanical alloying, was held in Herceg Novi, Montenegro. The conference aimed at providing a forum for presentation of new results, identification of current research and development trends along with future directions and, promoted interactions dealing with various aspects of the discipline. Presented research papers concerned both mechanochemistry and tribochemistry. By and large, they demonstrated the progress of studies on the chemical and physicochemical

Some review papers have already been described in previous sections. They specifically relate to mechanochemistry [46,66] and/or tribochemistry [6,11,29]. The most recent extensive critical review paper [72] aims at providing a broad but digestible overview of mechanochemical synthesis, that is reactions conducted by grinding solid reactants together with no or minimal solvent. This critical review includes over 300 references focused on the historical development, mechanistic aspects, limitations and opportunities of mechanochemical synthesis. It emphasizes that although mechanochemistry has historically been a sideline approach to synthesis, presently it may move into the mainstream because it is increasingly apparent that it can be practical, and even advantageous [72]. This is because it provides the opportunities for developing more sustainable technologies. Additionally, synthesis of metal organic frameworks (MOFs) has to be mentioned here, as it have become presently one of the most intensely researched areas of

materials chemistry and, it might relate to both mechanochemistry and tribochemistry.

An earlier detailed review paper generally aimed at mechanical activating of covalent bonds [73], also considers mechanochemistry of crystals, metals, alloys, and polymers. The latter is related to already discussed in detail heterogeneous C – C bonding splitting in polymers [68] (see Section 5.3). By the employing of mechanochemical solid-state reaction, Fujiwara and Komatsu synthesized a novel C60 dimer linked by a silicon bridge and a single bond [74]. The novel C60 dimer was synthesized using a high-speed vibration milling (HSVM) technique and, the product obtained was fully characterized by a wide variety of sophisticated analytical techniques. The electronic interaction between the two C60 cages was evidenced by the electrochemical method. For instance, in these dimers, the two fullerene cages are connected by sharing a cyclobutane ring. the mechanochemical solid-state reaction of C60 with alkyl or aryl halide in the presence of alkali metals was found to cause alkylation or arylation of C60 possibly by the intermediacy of the C60 radical anion [74]. The mechanochemical reaction of the fullerene with dichlorodiphenylsilane (Ph2SiCl2) and lithium (Li) metal, under the solvent free conditions, allowed synthesizing the C60 dimer

processes proceeding in solids under mechanical action.

fused with a silacyclopentane ring, as shown below [74].

**6.2. Major recent review papers** 

Very detailed review publications [72-73] include a wide range of industrial applications of mechanochemistry and underline the need for sustainability brought about by the Kyoto Treaty and the increasing global demand for products leading to an increase in sustainable manufacturing processes. Such processes and/or new technologies can lower environmental demands. Improved sustainability can be realized in the form of reduced energy use, less organic solvents, better selectivity and reduced waste. Recent well specified study [75] presents several advantages of mechanochemical technology, such as simple process, ecological safety and the possibility of obtaining a product in the metastable state. Thus, it gives an overall review of the mechanochemistry applications in waste management. Interestingly to note that based on that study, the modification of fly ash and asbestos containing wastes (ACWs) can be achieved by mechanochemical technology (MCT). Finally, MCT provides with a prospective application in pollution remediation and also waste management. Hazardous metal oxides can be transformed into easily recyclable sulfide by mechanochemical sulfidization; the waste plastics and rubbers, which are usually very difficult to be recycled, can also be recycled by mechanochemical technology [75]. At this point the importance of waste-free mechanochemical synthesis and production should also be noted [5].

Another study [76] demonstrates that the mechanochemical treatment of an expired drug as ibufren, may be very useful and non-polluting way to change the bioactive molecule of a pharmaceutical formulation into non-toxic product. In the degradation mechanism two major steps are considered. The first one in the degradation process that leads to the detoxification of the drug, is induced by the presence of a co-reagent aluminum hydroxide. The second step relates to oxidative decarboxilation to an intermediate stable benzyl radical which, reacting in the presence of oxygen during milling, produces several products. The number of the generated products is controlled by the milling time. Thereafter, mechanochemical treatments are environmentally sound for general approach to detoxify chemical-pharmaceutical waste. Thus, in this case a type of molecular mechanolysis without solvent or usual thermal contribution can be considered [76].

Extension of mechanochemistry practical applications is broadly described by Todres in the book on both mechanochemistry and tribochemistry [77]. The specificity of the Todres' book is that it discusses chemical reactivity of organic molecules mechanically treated separately or together and, describes mechanochemically initiated polymerization, depolymerization and mechanolysis. It also considers lubricant design and lubricity process. Organic solids/materials are very liable to attrition representing wear caused by friction (tribos) and therefore relating to tribochemistry. This is evidenced by considering detailed organic reactions with lubricating layers.

#### **6.4. How mechanochemistry is entangled with tribochemistry**

#### *6.4.1. Selected books and review publications*

Mechanochemistry comprises a wide branch of the reactivity research of solids activated by mechanical action. It also deals with mechanisms of solid-phase reactions, aiming at making

new materials by non-traditional methods. Nowadays, it is an established field of materials science and solid-state chemistry [58]. The importance of mechanochemistry is evidenced by several books clearly presenting its scientific and practical achievements [46,78-80].

General Approach to Mechanochemistry and Its Relation to Tribochemistry 233

*6.4.3. Similarities between mechanochemistry and tribochemistry* 

*solids due to the influence of mechanical energy*.

tribochemistry as a subset of mechanochemistry.

energy) serves as the origin of enhanced reactivity of solids.

*6.4.4. Differences between mechanochemistry and tribochemistry* 

Definitions of mechanochemistry and tribochemistry, formulated 50 years ago [7,8], are generally accepted and, the following definitions have been selected for this Chapter. *Mechanochemistry is a branch of chemistry which is concerned with chemical and physicochemical transformations of substances in all states of aggregation produced by the effect of mechanical energy. Tribochemistry is a branch of chemistry dealing with the chemical and physico-chemical changes of* 

Mechanochemistry is the science field that deals with athermal or ultra-fast chemical reactions between solids or between solids and surrounding gaseous or liquid molecules under mechanical forces. Another approach defines mechanochemistry as the branch of solid state chemistry where intramolecular bonds are mechanically broken [5]. Actually, the same is due to tribochemistry. Both mechanochemical and tribochemical reactions are also distinct from those of themochemical reactions. The same is due to heterogeneous catalysis (HetCat) and tribocatalysis [11]. Triboemission, triboplasma, and NIRAM-HSAB approach consider electronic effect of on mechanochemistry and tribochemistry. To initiate thermochemical reactions heat should be supplied. Thus, it seems convenient to consider heat evolution also in electronic terms. Additionally, it is suggested to consider

There is an overlap of disciplines based on chemical reactions initiated by the mechanical action. Not considering any heat loss, the difference is controlled by *energy stored* in the system. Looking at the mechanical work plane proposed in [15], various portions of the work (power) include: input power, use-output power, loss-output energy rate, and a stored energy (thermal energy transformed from mechanical work). The energy stored (excess

Taking into account that tribochemistry is the subset of mechanochemistry, major differences between mechanochemistry and tribochemistry is formal, as compared with chemical physics and physical chemistry. There are many physical processes related to the wearing and mechanisms. These mechanisms are often connected with tribochemical reactions. The nature of the tribochemical film is the key to understanding the mechano-

Significant evidence for the above suggestion comes from book [77]. That book aimed at correlating mechanical actions on organic substances with the molecular events triggert by these actions. The term *organic mechanochemistry*, defined as *convertion of mechanical energy into the driving force for molecular oe structural phase trtansitions,* was introduced. Importantly, Todres in his book [77] emphasizes that chemical engineering needed *inorganic mechanochemistry* be addressed first. *Organic mechanochemistry* has been in its infancy for a long time. The specificity of the Todres' book is that it discusses chemical reactivity of organic molecules mechanically treated separately or together and, describes

chemical processes that give rise to chemical films separating friction solid elements.

The latter book [80] is on powder technology and deals with a variety of particles, from submicrometer to large grains and gravels and from liquid mist or droplets to bubbles, as well as solid particles and aggregates. As it considers with two-phase and three-phase mixtures, it relates to work in different science and engineering fields and, thereby demonstrate a bridge between pure mechanochemistry, inorganic chemistry and/or technology, organic chemistry and/or technology and, tribochemistry in its broad meaning. Thereby, it evidences simultaneously how mechanochemistry is complex and entangled with tribochemistry. On the other hand, a lot of natural and artificial phenomena encountered in our daily lives may be accounted for by knowledge of powder technology.

Some books are related to tribology [15,28] or tribochemistry [7-8], however they also consider mechanochemistry. Another one tends to tribochemistry via organic mechanochemistry [76]. The same is due to review papers [13, 16-17] and book chapters [48-50].

In summary, presently both mechanochemistry and tribochemistry appear to be a science with a sound theoretical foundation. Their major benefits include lower reaction temperatures and increased reaction rate. As a consequence, processing of materials can be performed in simpler and less expensive reactors during shorter reaction times.

#### *6.4.2. Mechanochemistry vs. tribochemistry*

It is known that some chemical substances react differently when exposed to mechanical and thermal energy. The term mechanochemistry was coined by Oswald for the corresponding branch of chemical physics. In this sense, mechanochemistry should be considered along with thermochemistry, electrochemistry, photochemistry, sonochemistry, chemistry of high pressures, shock waves, or microwave effects [76]. In fact, organic solids are very liable to attrition; inorganic materials appear to be more resistant [81] and the attrition represents wear caused by rubbing or friction which already relates to tribochemistry.

At this point we need to come back to the Todres book [77], which outlines the main regularities governing transformations of mechanically activated organic compounds and discusses physical processes that affect these transformations. Some chapters concern more specifically the mechanically induced reactions of organic synthesis and the chemical transformations of organic participants of boundary lubrication. As already indicated, the mechanically induced synthesis of the desired organic compounds is advantageous in the sense of rates of formation.

Summarily, this is preferred over expenses required for mechanical activation (say, for the electricity spent to rotate a mill); chemical forces arise from summation of excess enthalpy of individual participants and that of chemical interaction. Thus, such chemical processes should be described in terms of the tribochemistry action mechanisms.

#### *6.4.3. Similarities between mechanochemistry and tribochemistry*

232 Tribology in Engineering

[48-50].

new materials by non-traditional methods. Nowadays, it is an established field of materials science and solid-state chemistry [58]. The importance of mechanochemistry is evidenced by

The latter book [80] is on powder technology and deals with a variety of particles, from submicrometer to large grains and gravels and from liquid mist or droplets to bubbles, as well as solid particles and aggregates. As it considers with two-phase and three-phase mixtures, it relates to work in different science and engineering fields and, thereby demonstrate a bridge between pure mechanochemistry, inorganic chemistry and/or technology, organic chemistry and/or technology and, tribochemistry in its broad meaning. Thereby, it evidences simultaneously how mechanochemistry is complex and entangled with tribochemistry. On the other hand, a lot of natural and artificial phenomena encountered in our daily lives may be accounted for by knowledge of powder technology.

Some books are related to tribology [15,28] or tribochemistry [7-8], however they also consider mechanochemistry. Another one tends to tribochemistry via organic mechanochemistry [76]. The same is due to review papers [13, 16-17] and book chapters

In summary, presently both mechanochemistry and tribochemistry appear to be a science with a sound theoretical foundation. Their major benefits include lower reaction temperatures and increased reaction rate. As a consequence, processing of materials can be

It is known that some chemical substances react differently when exposed to mechanical and thermal energy. The term mechanochemistry was coined by Oswald for the corresponding branch of chemical physics. In this sense, mechanochemistry should be considered along with thermochemistry, electrochemistry, photochemistry, sonochemistry, chemistry of high pressures, shock waves, or microwave effects [76]. In fact, organic solids are very liable to attrition; inorganic materials appear to be more resistant [81] and the attrition represents

At this point we need to come back to the Todres book [77], which outlines the main regularities governing transformations of mechanically activated organic compounds and discusses physical processes that affect these transformations. Some chapters concern more specifically the mechanically induced reactions of organic synthesis and the chemical transformations of organic participants of boundary lubrication. As already indicated, the mechanically induced synthesis of the desired organic compounds is advantageous in the

Summarily, this is preferred over expenses required for mechanical activation (say, for the electricity spent to rotate a mill); chemical forces arise from summation of excess enthalpy of individual participants and that of chemical interaction. Thus, such chemical processes

performed in simpler and less expensive reactors during shorter reaction times.

wear caused by rubbing or friction which already relates to tribochemistry.

should be described in terms of the tribochemistry action mechanisms.

*6.4.2. Mechanochemistry vs. tribochemistry* 

sense of rates of formation.

several books clearly presenting its scientific and practical achievements [46,78-80].

Definitions of mechanochemistry and tribochemistry, formulated 50 years ago [7,8], are generally accepted and, the following definitions have been selected for this Chapter. *Mechanochemistry is a branch of chemistry which is concerned with chemical and physicochemical transformations of substances in all states of aggregation produced by the effect of mechanical energy. Tribochemistry is a branch of chemistry dealing with the chemical and physico-chemical changes of solids due to the influence of mechanical energy*.

Mechanochemistry is the science field that deals with athermal or ultra-fast chemical reactions between solids or between solids and surrounding gaseous or liquid molecules under mechanical forces. Another approach defines mechanochemistry as the branch of solid state chemistry where intramolecular bonds are mechanically broken [5]. Actually, the same is due to tribochemistry. Both mechanochemical and tribochemical reactions are also distinct from those of themochemical reactions. The same is due to heterogeneous catalysis (HetCat) and tribocatalysis [11]. Triboemission, triboplasma, and NIRAM-HSAB approach consider electronic effect of on mechanochemistry and tribochemistry. To initiate thermochemical reactions heat should be supplied. Thus, it seems convenient to consider heat evolution also in electronic terms. Additionally, it is suggested to consider tribochemistry as a subset of mechanochemistry.

There is an overlap of disciplines based on chemical reactions initiated by the mechanical action. Not considering any heat loss, the difference is controlled by *energy stored* in the system. Looking at the mechanical work plane proposed in [15], various portions of the work (power) include: input power, use-output power, loss-output energy rate, and a stored energy (thermal energy transformed from mechanical work). The energy stored (excess energy) serves as the origin of enhanced reactivity of solids.

#### *6.4.4. Differences between mechanochemistry and tribochemistry*

Taking into account that tribochemistry is the subset of mechanochemistry, major differences between mechanochemistry and tribochemistry is formal, as compared with chemical physics and physical chemistry. There are many physical processes related to the wearing and mechanisms. These mechanisms are often connected with tribochemical reactions. The nature of the tribochemical film is the key to understanding the mechanochemical processes that give rise to chemical films separating friction solid elements.

Significant evidence for the above suggestion comes from book [77]. That book aimed at correlating mechanical actions on organic substances with the molecular events triggert by these actions. The term *organic mechanochemistry*, defined as *convertion of mechanical energy into the driving force for molecular oe structural phase trtansitions,* was introduced. Importantly, Todres in his book [77] emphasizes that chemical engineering needed *inorganic mechanochemistry* be addressed first. *Organic mechanochemistry* has been in its infancy for a long time. The specificity of the Todres' book is that it discusses chemical reactivity of organic molecules mechanically treated separately or together and, describes

mechanochemically initiated polymerization, depolymerization and mechanolysis. It also considers lubricant design and lubricity process and, differentiates mechanochemical publications from tribochemical ones.

General Approach to Mechanochemistry and Its Relation to Tribochemistry 235

The author wishes to acknowledge PIMOT for this project financial support and, Krzysztof

[1] Carey-Lea M. On Endothermic Reactions Effected by Mechanical Force. Philosophical

[2] Takacs L. M. Carey Lea. The Father of Mechanochemistry. Bulletin for the History of

[3] Takacs L. M. Carey Lea, the First Mechanochemists. Journal of Materials Science 2003, 39(16-17), 4987-4993. See also: Takacs L. The First Documented Mechanochemical

[4] Vick B., Furey M. J., Kajdas C. An Examination of Thermionic Emission Due to

[5] Kaupp G, Waste-Free Synthesis and Production all Across Chemistry with the Benefit of Self- Assembled Crystal Packings. Journal of Physical Organic Chemistry 2008, 21(7-8),

[6] Kaupp G. Mechanochemistry: the Varied Applications of Mechanical Bond-Breaking, The Royal Society of Chemistry, CrystEngComm 2009, 11, 388–403. DOI:

[7] Thiessen P.D., Meyer K., Heinicke G. Grundlagen der Tribochemie. Berlin: Akademie-

[10] Campbell, W.F. Boundary Lubrication. In: Ling F.F., Klaus E.E., Fein R.S. (eds) Boundary Lubrication. An Appraisal of World Literature. New York: ASME; 1969.pp87-

[11] Kajdas C., Hiratsuka K. Tribochemistry, Tribocatalysis, and the Negative-Ion-Radical Action Mechanism. Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology 2009; 223 (6) 827-848. DOI: 10.1243/13506501JET514 [12] Bond G.C. Heterogeneous Catalysis. Principles and Applications. Oxford: Clarendon

[13] Hsu S.M., Zhang J., Yin Z. The Nature and Origin of Tribochemistry. Tribology Letters

[14]http://books.google.pl/books?id=8lsEsGe18t8C&pg=PA587&lpg=PA587&dq=definition+ of+tribochemistry&source=bl&ots=UFdquGVHoK&sig=HQoet9rQjpUgUb7c0b97TzXHI x8&hl=pl&sa=X&ei=WLyXT9HJEsrf4QTDyqDFBg&sqi=2&ved=0CDAQ6AEwAQ#v=on

[15] Czichos H. Tribology a Systems Approach to the Science and Technology of Friction,

Frictionally Generated Temperatures, Tribology Letters 2002, 13(2), 147-153.

**Acknowledgement** 

**8. References** 

Kowalczyk for his assistance in preparing figures.

Reaction? Journal of Metals 2000; (Jan issue) 12-13.

630-643. ISSN: 08943230; DOI: 10.1002/poc.1340.

[8] Heinicke G. Tribochemistry*.* Berlin: Academy-Verlag, 1984. [9] Hardy W. Collected Works. Cambridge: University Press, 1936.

epage&q=definition%20of%20tribochemistry&f=false

Lubrication and Wear. Amsterdam: Elsevier; 1978.

Magazine 1893, 36, 350-351.

Chemistry 2003, 28(1), 26-34.

10.1039/b810822f ...

Verlag, 1966.

117.

Press, 1987.

2002, 13(2) 131-139.

At this point, it is proposed to assign *inorganic mechanochemistry* to *mechanochemistry* and, *organic mechanochemistry* to *tribochemistry.* Thus, major differences between mechanochemistry and tribochemistry have a formal character.

## *6.4.5. Common denominators of mechanochemistry and tribochemistry*

Considering that the excess energy (energy stored in a sytem) serves as the origin of enhanced reactivity of materials under mechanical treating, their common denominators broadly encompass triboemission and triboplasma processes.

In the present Chapter understanding, there is only a formal overlap of these disciplines in terms of inorganic and organic chemistry. Accordingly, *mechanochemistry* is the *inorganic mechanochemistry* and, *tribochemistry* is the *organic mechanochemistry*. Tribochemistry is considered as a subset of mechanochemistry.

The major denominatot for inorganic mechanochemistry, organic mechanochemistry, catalysis and tribocatalysis is the NIRAM-HSAB approach, because it allows accounting for most of very specific tribological findings. It also demonstrates how organic chemistry is changing via physical chemistry, chemical physics and nowadays by contributing to tribochemistry. Book chapter [82] details physical and chemical phenomena concerning the tribochemistry discipline.
