Microstructure of complex lithium lubricants
This work presents the results of studies of the microstructure and properties of lubricant samples based on synthesized complex lithium soaps of hydroxylated fatty acids from of waste food oil as a lubricant thickener. The results of scanning electron microscopy confirmed the differences in the pec...
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V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine
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| author | Bodachivska, Larysa Yu. Venger, Iryna O. Verba, Artem Yu. |
| author_facet | Bodachivska, Larysa Yu. Venger, Iryna O. Verba, Artem Yu. |
| author_institution_txt_mv | [
{
"author": "Larysa Yu. Bodachivska",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of National Academy of Sciences of Ukraine 1 Аcademiсian Kukhar Str., Kyiv, 02094, Ukraine",
"orcid": ""
},
{
"author": "Iryna O. Venger",
"institution": "V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of National Academy of Sciences of Ukraine 1 Аcademiсian Kukhar Str., Kyiv, 02094, Ukraine",
"orcid": ""
},
{
"author": "Artem Yu. Verba",
"institution": "“RMA “Innovative Technologies and systems” LLC 1 Zhmerinskaya Str., Kyiv, 03148, Ukraine",
"orcid": ""
}
] |
| author_sort | Bodachivska, Larysa Yu. |
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| container_issue | 36 |
| container_start_page | 121 |
| container_title | Каталіз та нафтохімія |
| container_volume | |
| datestamp_date | 2025-12-28T17:23:30Z |
| description | This work presents the results of studies of the microstructure and properties of lubricant samples based on synthesized complex lithium soaps of hydroxylated fatty acids from of waste food oil as a lubricant thickener. The results of scanning electron microscopy confirmed the differences in the peculiarities of the formation of the structural framework of lubricants depending on their composition, thickener concentration, complexing agents, and heat treatment temperature. It was determined that it is the lubricant thickener that binds the dispersion medium through intermolecular interaction, forms a three-dimensional interwoven microstructure, and gives the lubricant improved rheological and volumetric-mechanical properties. Complex lithium soap is more structured than simple lithium soap, although both are formed by a connected three-dimensional mesh microstructure. It has been shown that the rheological and operational properties of lubricant can be improved by using various complexing agents. The lithium complex lubricant samples are characterized by the maximum thickening effect and have lower effective viscosity values at minus 30 °C. With an increase in the concentration of the thickener, the effective viscosity of lithium complex lubricants increased, but the indicators of mechanical stability and drop point remained almost unchanged. It was found that the optimum heat treatment temperature for complex lithium lubricant is 220 °C. If the heat treatment temperature of the lubricant was exceeded, for example, at 240 °C, the microstructure of the complex lithium soap was destroyed, which led to a deterioration in viscosity and colloidal stability. The established rheological, volume-mechanical, and temperature regularities of the structure formation of the dispersed phase of lubricants can be used to select rational modes of obtaining complex lithium lubricant compositions intended for use in friction units of modern machines and mechanisms. |
| doi_str_mv | 10.15407/kataliz2025.36.121 |
| first_indexed | 2026-03-12T15:50:26Z |
| format | Article |
| fulltext |
Каталіз та нафтохімія, 2025, №36 121
Catalysis and Petrochemistry, 2025, 36
UDC 665.76; 661.185
https://doi.org/10.15407/kataliz2025.36.121
Microstructure of complex lithium lubricants
Larysa Yu. Bodachivska 1, Iryna O. Venger 1, Artem Yu. Verba 2
1 V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of National Academy of Sciences of Ukraine
1 Аcademiсa Kukhara Str., Kyiv, 02094, Ukraine, e-mail: bodach@ukr.net
2 “RMA “Innovative Technologies and systems” LLC
1 Zhmerinskaya Str., Kyiv, 03148, Ukraine, e-mail: info@itis.com.ua
This work presents the results of studies of the microstructure and properties of lubricant samples based
on synthesized complex lithium soaps of hydroxylated fatty acids from of waste food oil as a lubricant thickener.
The results of scanning electron microscopy confirmed the differences in the peculiarities of the formation of the
structural framework of lubricants depending on their composition, thickener concentration, complexing agents,
and heat treatment temperature. It was determined that it is the lubricant thickener that binds the dispersion
medium through intermolecular interaction, forms a three-dimensional interwoven microstructure, and gives the
lubricant improved rheological and volumetric-mechanical properties. Complex lithium soap is more structured
than simple lithium soap, although both are formed by a connected three-dimensional mesh microstructure. It has
been shown that the rheological and operational properties of lubricant can be improved by using various
complexing agents. The lithium complex lubricant samples are characterized by the maximum thickening effect
and have lower effective viscosity values at minus 30 °C. With an increase in the concentration of the thickener,
the effective viscosity of lithium complex lubricants increased, but the indicators of mechanical stability and drop
point remained almost unchanged. It was found that the optimum heat treatment temperature for complex lithium
lubricant is 220 °C. If the heat treatment temperature of the lubricant was exceeded, for example, at 240 °C, the
microstructure of the complex lithium soap was destroyed, which led to a deterioration in viscosity and colloidal
stability. The established rheological, volume-mechanical, and temperature regularities of the structure formation
of the dispersed phase of lubricants can be used to select rational modes of obtaining complex lithium lubricant
compositions intended for use in friction units of modern machines and mechanisms.
Keywords: lubricant thickener, microstructure, rheology, mechanical stability, complex lithium lubricants
Introduction
Modern advanced technology places stringent requirements on lubricant developers. Lubricants
have to withstand friction units' overheating, stay on surfaces at high speeds, not leak out of bearings,
not cause metal corrosion, and protect them from the harmful effects of various factors. Lubricants with
a wide range of operating temperatures and those that work in the presence of moisture are increasingly
in demand. Lithium lubricants (simple and complex) fully meet these requirements.
Lithium lubricants consist of a base oil (mineral or synthetic) and a lithium soap thickener, which
is obtained by direct saponification (in situ) of usually stearic/monohydroxystearic acid, as well as
various natural fats and synthetic fat substitutes [1]. Lithium lubricants are classified as multipurpose
lubricants. They are water-resistant, characterized by good mechanical and thermal stability, a wide
range of application temperatures, suitable for lubricating most friction units of industrial equipment and
vehicles, and provide long-term protection against oxidation, corrosion, extreme temperatures, and wear.
Lithium complex lubricant (cLi) is an improved version of lithium lubricant, which includes a
thickener based on lithium complex. Complex lithium soap (cLi-soap) is a product of cocrystallization
of Li-soap of high molecular weight fatty acids and Li-salts of low molecular weight organic and
inorganic acids [1]. Lubricants based on cLi-soaps are characterized by improved antioxidant,
mechanical and thermal stability, and anti-wear characteristics compared to simple lithium lubricants.
Their dropping point exceeds 230 °C. Complex Li-lubricants are durable, and stable and are most often
122 Каталіз та нафтохімія, 2025, №36
Catalysis and Petrochemistry, 2025, 36
used to fill friction units for the entire period of their operation. They are ideal for high-temperature,
low-temperature, and highly loaded industrial applications such as bearings, gears, and heavy
machinery.
The authors of [1, 2] showed that the main component of cLi-soaps is monohydroxycarboxylic
acids with a different arrangement of the hydroxyl group in the hydrocarbon radical of the acid about the
carboxylic group – 12-HoSt, obtained as a result of hydrogenation of castor oil; 6-HoSt, synthesized by
free radical addition of cyclohexane to α-oleic acid; 9(10)-HoSt, obtained by hydroxylation of oleic acid;
6-HoSt, synthesized by the free radical addition of cyclohexane to α-olefins followed by oxidation of
2-alkylcyclohexanol, accompanied by ring breakage. The complexing agent was dicarboxylic acids
(H2Dc): azelaic acid (H2Az), adipic acid (H2Ad), sebacic acid (H2Se), or hydroxybenzoic acid in
combination with boric acid in cLi-soap. Mineral and synthetic base oils, which differ in viscosity,
aniline point, and other physical and chemical characteristics, were used as dispersion media. Also in
these works, the optimal values of the molar ratio of cLi-soaps and dicarboxylic acids are given. It is
noted that an increase in the proportion of H2Dc reduces the thickening ability of cLi-soap, decreases
the drop point, and worsens the rheological characteristics of cLi-lubricants and their microstructure.
Lithium complex lubricant is the most common lubricating grease in the high-end lubricant
market. Lithium complex soap holds base oil by intermolecular interaction and shows the entangled
fiber structure, where its composition and structure influences the rheological properties [3]. Yeong et al.
[4] found the yield stress and viscosity of lithium lubricant increase as the increase of thickener
concentration, as well as storage modulus, attributing to the high volume fraction of thickener
concentration results in a stronger gel network. Delgado et al. [5, 6] found that the soap fiber shows
higher physical entanglement with the increase of soap concentration, and the relative elastic
characteristics increases with the decrease of base oil viscosity due to the lower viscosity of base oil
increase the affinity for the soap.
Investigations at the Competence Center of Tribology Mannheim show that the lubricant service
life for roller bearing lubrication, even at high temperatures, does not only depend on classic oil aging.
In numerous roller bearing tests and by means of rheological measurements, it could be shown that the
loss of the lubricating effect is a consequence of the change in the thickener structure. The fiber structure
and the inner network are of the greatest importance for the lubricating properties of soap greases [7].
Adhvaryu et al. investigated the change in the fiber structure of lubricating greases as a function of
antioxidants. Unsaturation and fatty acid chain length of soap molecule dictate the fiber shape and
distribution, which can be translated to hardness, thermo-oxidative stability, shear stability, water
tolerance, and other important properties of grease [8]. They define the breakdown of the structure as
damage to the lubricating properties. Couronne and Vergne found that the fiber length is shortened by
thermal aging [9]. Gonçalves et al. found also that the thickener matrix changes with thermal aging [10].
Shen et al. investigated the thickener structure of a lithium–calcium thickened grease and also showed
that the network structure is gradually destroyed with a longer thermal aging time and that the stability
of the grease structure decreases significantly [11].
Hodapp et al. [12] noted that the type and viscosity of the base oil does not affect the absolute
value of the complex viscosity and the shape of the filaments formed by this thickener. The complex
viscosity of the lubricants only depended on the thickener concentration. High-frequency shear modulus
data, however, indicated that the thickener lithium 12-hydroxystearate formed stiffer networks/filaments
in poly-α-olefins than in mineral oils. As expected, the viscosity increased with increased thickener
https://www.mdpi.com/2075-4442/10/5/77#B18-lubricants-10-00077
https://www.mdpi.com/2075-4442/10/5/77#B19-lubricants-10-00077
https://www.mdpi.com/2075-4442/10/5/77#B20-lubricants-10-00077
Каталіз та нафтохімія, 2025, №36 123
Catalysis and Petrochemistry, 2025, 36
concentrations, but microscopy and high-frequency rheometry revealed that the thickness, length, and
stiffness of the individual filaments did not change. In mineral oil, the 12-hydroxystearate thickeners
yielded higher viscosity than the corresponding stearates with the same metal ion. The filamentous
lithium thickeners created stronger networks than the roundish aggregates formed by magnesium and
zinc stearate.
Saatchi et al. [13] investigated the mechanism of oil release from the lithium complex in soap
and nonsoap thickeners of greases. It is assumed that the leakage occurs from the viscous flow of
unbound oil in the porous structure made of the effective media (the region surrounding the thickener
particles).
Zhang et al. [14] investigated on microstructure, friction and rheology of four lithium greases
formulated with four different base oils (paraffinic oil, naphthenic oil, poly-α-olefin and polyol ester). It
was found that naphthenic oil-based grease exhibited the best colloidal stability. Lithium fibers in polyol
ester-based lubricant showed a relatively flat network compared to the three-dimensional entangled
structure of the other three greases. Tribological performance of greases differed from their
corresponding base oils, which might be attributed to the different microstructure of lithium soap fibers.
Three-dimensional entangled structure was more suitable for friction-reducing than flat network
structure. Moreover, noise test revealed that naphthenic oil-based lubricant was suitable for low-noise
bearing lubrication. This study provided fundamental guidance for the selection of base oil which is
beneficial for the development of high-performance lubricant products.
In industrial production, the selection of raw materials is often based on the criteria of
availability and cost. Aromatic, alicyclic, and aliphatic amines with up to 20 carbon atoms in the
hydrocarbon chain are commonly used to make lithium greases. Lithium soaps are obtained by
saponification of 12-hydroxystearic acid with LiOH and organic acids [1, 3]. In works [15-18],
hydroxylated fatty acid soaps based on vegetable oils or secondary fatty raw materials were synthesized,
and thixotropic systems with improved performance characteristics were developed.
Therefore, the purpose of this work is to obtain samples of complex lubricants based on
synthesized lithium soaps of hydroxylated fatty acids from waste food oil and to study the effect of the
microstructure of these samples on rheological and volumetric-mechanical properties.
Experiment
Waste food oils (WFO), a sample provided by a local catering establishment, were used as an
alternative source of secondary fatty acids. 99.5 % potassium iodide, 35 % hydrogen peroxide, 99.8 %
sodium hydroxide, 99 % lithium hydroxide, 13 % hydrochloric acid, 12-hydroxystearic acid, 99.8 %,
99.5 % diethanolamine, 99.8 % formic acid, 99.7 % adipic acid, 99.6 % sebacic acid were purchased
from Chemlaborreactiv (Ukraine).
Samples of complex lithium lubricants were evaluated according to the following indicators
penetration (ISO 2137), dropping point (ASTM D 2265), colloidal stability (GOST 7142, method A),
viscosity (GOST 7163). The scanning electron microscopy (SEM) images were taken using brand
appliance CAMSCAN.
Hydroxylated fatty acids were synthesized by epoxidation of unsaturated fatty acids of waste
food oil followed by hydrolysis by acylglycerol grouping and oxirane rings. Fatty acid aminoamides of
waste food oils were synthesized by epoxidation of oils followed by the opening of oxirane cycle and
transamidation of acylglycerols with diethanolamine according to the method described in patent [15].
124 Каталіз та нафтохімія, 2025, №36
Catalysis and Petrochemistry, 2025, 36
Results and Discussion
A complex lithium lubricant is a highly structured colloidal-dispersed system in which the
internal dispersed phase, a thickener based on a lithium complex (complex lithium soap), binds the
dispersion medium (mineral or synthetic oils) into a single system. Complex lithium soap (cLi-soaps) is
a product of cocrystallization of cLi-soap of high molecular weight fatty acids and Li-salts of low
molecular weight organic and inorganic acids [1]. Indeed, having a polar hydrophilic component and a
developed nonpolar lipophilic part, the thickener is actively concentrated at the interface of two mutually
insoluble phases, reducing the surface or interfacial tension.
Chemical modification of waste food oils was carried out to obtain an emulsifier-stabilizer as a
thickener for lubricants – saponified hydroxylated fatty acids (WFO-OH) a solution of lithium hydroxide.
The WFO hydroxy acids were synthesized by epoxidation of unsaturated fatty acids (oleic, linoleic,
linolenic, erucic) or their mixture, which is part of used food oils, followed by hydrolysis by
acylglycerol groups and oxirane rings [15].
Using WFO-OH, samples of complex lithium lubricants (cLi-lubricants) based on a base oil of
group IV according to the API (American Petroleum Institute) classification with a viscosity of
9.5 mm2/s at 100 °C were made. The complex lithium lubricant is manufactured according to the
conventional technology containing lithium fatty acid soaps [1, 15] and includes the following steps
synthesis of hydroxylated fatty acids of WFO; production of lithium soaps of hydroxylated fatty acids
(saponification of hydroxylated fatty acids with lithium hydroxide solution) in the base oil environment;
introduction of a complexing agent (adipic acid (H2Ad) or sebacic acid (H2Se); dehydration of the
resulting oil-soap mixture; thermomechanical treatment of the mixture and its cooling; homogenization
of the lubricant.
By the above technology, using the appropriate raw materials, a sample of simple lithium
lubricant without a complexing agent (sample 1) and samples (2, 3, 4, 5) of complex lithium lubricant
with the following content, % wt.: lithium soaps of hydroxy acids of oils – 15.0, synthetic oil – the rest,
heat treatment temperature 220 °C (sample 1); complex lithium soap of hydroxy acids of oils
(complexing agent H2Se) – 20.0, synthetic oil – the rest, heat treatment temperature 220 °C (sample 2);
complex lithium soap of hydroxy acids of oils (complexing agent H2Ad) – 20.0, synthetic oil – the rest,
heat treatment temperature 220 °C (sample 3); сomplex lithium soap of hydroxy acids of oils
(complexing agent H2Se) – 20.0, synthetic oil – the rest, heat treatment temperature 240 °C (sample 4);
complex lithium soap of hydroxy acids of oils (complexing agent H2Se) – 22.0, synthetic oil – the rest,
heat treatment temperature 220 °C (sample 5).
Table 1 presents the results of the rheological and bulk-mechanical properties of lithium lubricant
samples. The obtained cLi-lubricants samples are characterized, first of all, by high thermal stability,
which confirms the value of the dropping point. The dropping point is the temperature at which a
thixotropic system passes from a plastic solid to a liquid state. A lubricant is high-temperature if at least
one of the following requirements is met: its dropping point is higher than 250 °C, and the temperature
limit of application is higher than 150 °C [19]. The obtained samples of cLi-lubricants (2, 4, 5) are
characterized by a higher dropping point than sample 1 of a simple lithium lubricant. Table 1 presents
the results of studies on the mechanical stability of lubricants.
Mechanical stability – the ability of a lubricant to resist mechanical stress and restore lost
volumetric and mechanical properties – is one of the most important parameters for assessing the
operational properties of lubricants [1]. Lubricant, which quickly breaks down and is poorly restored
Каталіз та нафтохімія, 2025, №36 125
Catalysis and Petrochemistry, 2025, 36
after stress relief, leaks from bearings, axle boxes, etc., causing dry friction and overheating. Mechanical
stability is largely determined by the properties and concentration of the thickener, as well as the
stability of its structural framework, which is manifested in the magnitude of the bonding forces between
its individual components.
Table 1. Properties of samples of lithium lubricants
Sample
No.
Samples of
complex
lithium
lubricants
Properties of samples of complex lithium lubricants
Dropping
point, °С
Penetration at 25 °С, m·10–4
Colloidal
stability,
% of
extracted
oil
Еffective
viscosity
at -30 °С
and strain-rates
10 s–1, Pa·s
After 60
double
strokes
(Р1)
After 10,000
doubles
strokes
(Р2)
Mechanic
al
stability,
change
(ΔР)
1 Sample 1 204 240 260 20 13.4 1138
2 Sample 2 >250 256 274 18 14.2 800
3 Sample 3 213 212 236 24 16.6 ̶
4 Sample 4 250 268 289 21 16.2 890
5 Sample 5 >250 242 258 16 12.6 989
He criterion for mechanical stability is the change in the penetration index of the lubricant after
prolonged mechanical destruction (P2-P1 = ∆P). According to ISO 2137, the lubricants were subjected to
destruction in a standard penetrometer mixer. P1 was determined after 60, and P2 after 10.000 double
strokes.
The change in the state of the lubricant (ΔP) characterizes the stability of its structural
framework: for ΔP < 30 – mechanical stability is excellent, for ΔP = 30÷60 – good, for ΔP = 61÷100 –
satisfactory, for ΔP > 100 – unsatisfactory [20]. The data in Table 1 indicate that cLi-lubricants have
high mechanical stability (ΔP does not exceed 24 units).
Viscosity is the most important operational characteristic that determines the conditions for
filling the lubricant into the friction units at low temperatures and affects the starting torque of the
bearings. For lithium lubricant samples, the viscosity at a temperature of minus 30 °C and an average
strain rate gradient of 10 s-1 is Li-lubricant (sample 1) 1138 Pa·s, cLi-lubricants (samples 2, 4-5) is
within 800-989 Pa·s (Table 1). The results show that cLi-lubricants have a lower viscosity compared to
simple lithium lubricant.
Figs. 1-4 shows the morphological characteristics of Li-lubricant and cLi-lubricants samples with
different component compositions. The formation of the structural framework of lubricants occurs due to
the formation of hydrogen bonds between the molecules of the thickener and the dispersion medium
[21]. In the process of emulsification, in the manufacture of lubricant compositions, the thickener
molecules form reverse micelles in the form of fibers [1]. The fibers, colloidally suspended in the base
oil, collide and entangle together, forming a connected three-dimensional mesh microstructure that holds
the dispersion medium, as confirmed by SEM images. This microstructure affects the rheological and
bulk-mechanical properties of the lubricants.
The results of scanning electron microscopy confirmed differences in the features of the
formation of the structural framework of the lubricant thickener depending on its composition,
concentration, complexing agents, and the temperature of the lubricant heat treatment. The dispersed
phase of lubricants based on lithium soaps of hydroxylated fatty acids and based on complex lithium
soaps of hydroxylated fatty acids has significant differences between sample 1 (Fig. 1 a), and sample 2
126 Каталіз та нафтохімія, 2025, №36
Catalysis and Petrochemistry, 2025, 36
(Fig. 1 b). Complex lithium soap is more structured than simple lithium soap, although both are formed
by entangled fibers. With the same soap concentration in the lubricant, the number of fibers in complex
lithium soap is many times greater. This explains the better rheological and operational properties of
complex lithium lubricants (Table 1).
a b
Fig. 1. Microstructure of lithium lubricants: a) simple lithium lubricant; b) complex lithium lubricant
Adipic acid and sebacic acid were used as complexing agents in the preparation of complex
lithium soap. Accordingly, the cLi-lubricant samples: sebacic acid - H2Se (sample 2, 4, 5), adipic acid -
H2Ad (sample 3). One of the main indicators confirming the presence of a lithium complex in the
lubricant is the high dropping point, over 250 °C, compared to simple lithium lubricants (sample 1),
in which the dropping point is over 180 °C [1]. Therefore, according to the data in Table 1, it can be
concluded that when the complexing agent H2Se (sample 2, 4, 5) is introduced into the thickener
composition, a complex molecular complex is formed between the salts obtained during
saponification. However, when the complexing agent H2Ad (sample 3) is introduced into the
thickener composition, a mixture of dilithium and lithium soaps is formed instead of a complex
lithium soap. This confirms the conclusions of the authors of the works [1, 15] that complex lithium
soap is formed when a dicarboxylic acid with a chain length of at least 9 carbon atoms is introduced
into the thickener, and in adipic acid, the chain length consists of 8 carbon atoms.
The maximum thickening effect of the dispersed phase of the lubricant upon introduction of
H2Se is explained by the structural features of the formed complex lithium soap. Indeed, in Fig. 1 b
we observe that sample 2 of complex lithium lubricant with H2Se complexing agent has a more
structured intertwined three-dimensional mesh microstructure, which provides better binding of the
dispersion medium and better colloidal stability, lower rheological properties (Table 1).
As can be seen from the SEM images (Fig. 2 a, b), changing the heat treatment temperature of
the lubricant leads to the formation of different types of microstructure. At high temperatures of heat
treatment of cLi-lubricant (240 °C), an amorphous dispersed phase is formed (sample 4), capable of
retaining the dispersion medium in its cavities (Fig. 2 a). This is confirmed by the high values of
viscosity and colloidal stability indicators. At a heat treatment temperature of cLi-lubricant 220 °C
(sample 2), a strong, bonded three-dimensional mesh microstructure of the thickener is formed, the
thickening ability of the dispersed phase, the dropping temperature, penetration, colloidal stability, and
rheological properties are improved (Table 1).
To determine the effect of thickener concentration on rheological characteristics, we prepared
sample 2 cLi-lubricant with a cLi-soap concentration of 20 % and sample 5 cLi-lubricant with a
cLi-soap concentration of 22 %. It was found that the viscosity of lubricants increased with increasing
Каталіз та нафтохімія, 2025, №36 127
Catalysis and Petrochemistry, 2025, 36
thickener concentration (Table 1). SEM images (Fig. 3) demonstrate that with increasing thickener
concentration, there is a gradual development of soap fibers, the number and length of which increase,
achieving a structured fibrous microstructure [12]. Sample 5 of the lubricant with a thickener content of
22 % has better colloidal and mechanical stability. The change in the thickener concentration in the
lubricant (sample 5) did not affect the dropping point value, but the rheological properties deteriorated
with increasing thickener concentration (Table 1).
a b
Fig. 2. Microstructure of complex lithium lubricants at different heat treatment temperatures: а) 240 °С;
б) 220 °С
a b
Fig. 3. Microstructure of complex lithium lubricants at different thickener concentrations, %: а) 20%; б) 22%
Thus, the rheological and volumetric-mechanical properties of lubricants depend on the bound
three-dimensional mesh microstructure of the dispersed phase. This complex molecular complex
manifests in the magnitude of the bonding forces between its components. The formation of a stable
structural framework of lubricants depends on the optimal composition, concentration of thickener,
complexing agents, and heat treatment temperature. Otherwise, instead of complex lithium lubricants, a
simple mechanical mixture is formed.
It has been determined that the maximum thickening effect of the dispersed phase, lower values
of the effective viscosity at minus 30°C, an increase in the drop point, and a stable structural framework
of the complex lithium lubricant are provided by the introduction of a complexing agent such as sebacic
acid. The optimum concentration of the thickener is 20-22 %, but increasing the concentration led to an
increase in the effective viscosity of the lubricants, while the indicators of mechanical stability and drop
point remained almost unchanged. The optimum heat treatment temperature for complex lithium
lubricant is 220 °C. If the heat treatment temperature of the lubricant was violated, the microstructure of
the complex lithium soap was destroyed, which led to a deterioration in viscosity and colloidal stability.
128 Каталіз та нафтохімія, 2025, №36
Catalysis and Petrochemistry, 2025, 36
It was found that complex lithium soap is more structured than simple lithium soap, although
both are formed by a connected three-dimensional lattice microstructure.
Conclusion
The use of lithium soaps of hydroxylated fatty acids from of waste food oil and the introduction
of a complexing agent made it possible to obtain a complex molecular complex, a complex lithium soap
- a bound three-dimensional mesh structure with tangled soap fibers that retains the base oil in the
lubricant and gives the lubricant appropriate performance characteristics.
The established rheological, volume-mechanical, and temperature regularities of the structure
formation of the dispersed phase of lubricants can be used to select rational modes of obtaining complex
lithium lubricant compositions intended for use in friction units of modern machines and mechanisms.
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Надійшла до редакції 26.03.2025
Мікроструктура комплексних літієвих мастил
Лариса Ю. Бодачівська1, Iрина O. Венгер1, Aртем Ю. Верба2
1 Інститут біоорганічної хімії та нафтохімії ім.В.П. Кухаря Національної академії наук України
вул. Академіка Кухаря, 1, Київ, 02094, Україна, e-mail: bodach@ukr.net
2 ТОВ «НВО «Іноваційні технології і системи»
вул. Жмеринська, 1, Київ, 03148, Україна, e-mail: info@itis.com.ua
В даній роботі представлено результати досліджень мікроструктури та властивостей зразків
мастил на основі синтезованих комплексних літієвих мил гідроксильованих жирних кислот
відпрацьованої харчової олії, як загусника мастил. Результати скануючої електронної мікроскопії
підтвердили відмінності в особливостях формування структурного каркасу мастил залежно від їхнього
складу, концентрації загусника, комплексоутворюючих агентів та температури термообробки. Визначено,
що саме загусник мастила зв’язує дисперсійне середовище за рахунок міжмолекулярної взаємодії,
утворюює тримірну переплетену мікроструктуру і надає мастилу покращені реологічні та об’ємно-
механічні властивості. Комплексне літієве мило більш структуроване, ніж просте літієве, хоча обидва
утворені зв’язаною тримірною сітчастою мікроструктурою. Показано, що реологічні та експлуатаційні
властивості мастила можна поліпшити за допомогою різних комплексоутворювачів. Зразки мастил на
основі літієвого комплексу характеризуються максимальним загущувальним ефектом і мають нижчі
значення ефективної в’язкості за мінус 30 °С. Зі збільшенням концентрації загусника ефективна в’язкість
комплексних літієвих мастил збільшувалась, але показники механічної стабільністі та температури
краплепадіння залишались майже без змін. Виявлено, що оптимальна температура термічної обробки
комплексного літієвого мастила становить 220 °С. При порушенні температури термічної обробки
мастила, наприклад за 240 °С, відбулось руйнування мікроструктури комплексного літієвого мила, що
призвело до погіршення показників в’язкості та колоїдної стабільності. Встановлені реологічні, об’ємно-
механічні та температурні закономірності структуроутворення дисперсної фази мастил можуть бути
використані для вибору раціональних режимів одержання комплексних літієвих мастильних композицій
призначених для використання у вузлах тертя сучасних машин і механізмів.
Ключові слова: загусник мастил, мікроструктура, реологія, механічна стабільність, комплексні
літієві мастила
|
| id | oai:katalizorgua:article-134 |
| institution | Catalysis and petrochemistry |
| issn | 2707-5796 |
| keywords_txt_mv | |
| language | English |
| last_indexed | 2026-03-12T15:50:26Z |
| publishDate | 2025 |
| publisher | V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | katalizorgua/9d/3ebd91f190bc4407af8429c23f0bf59d.pdf |
| spelling | oai:katalizorgua:article-1342025-12-28T17:23:30Z Microstructure of complex lithium lubricants Microstructure of complex lithium lubricants Bodachivska, Larysa Yu. Venger, Iryna O. Verba, Artem Yu. lubricant thickener, microstructure, rheology, mechanical stability, complex lithium lubricants загусник мастил, мікроструктура, реологія, механічна стабільність, комплексні літієві мастила This work presents the results of studies of the microstructure and properties of lubricant samples based on synthesized complex lithium soaps of hydroxylated fatty acids from of waste food oil as a lubricant thickener. The results of scanning electron microscopy confirmed the differences in the peculiarities of the formation of the structural framework of lubricants depending on their composition, thickener concentration, complexing agents, and heat treatment temperature. It was determined that it is the lubricant thickener that binds the dispersion medium through intermolecular interaction, forms a three-dimensional interwoven microstructure, and gives the lubricant improved rheological and volumetric-mechanical properties. Complex lithium soap is more structured than simple lithium soap, although both are formed by a connected three-dimensional mesh microstructure.&nbsp;It has been shown that the rheological and operational properties of lubricant can be improved by using various complexing agents. The lithium complex lubricant samples are characterized by the maximum thickening effect and have lower effective viscosity values at minus 30&nbsp;°C. With an increase in the concentration of the thickener, the effective viscosity of lithium complex lubricants increased, but the indicators of mechanical stability and drop point remained almost unchanged. It was found that the optimum heat treatment temperature for complex lithium lubricant is 220&nbsp;°C. If the heat treatment temperature of the lubricant was exceeded, for example, at 240&nbsp;°C, the microstructure of the complex lithium soap was destroyed, which led to a deterioration in viscosity and colloidal stability. The established rheological, volume-mechanical, and temperature regularities of the structure formation of the dispersed phase of lubricants can be used to select rational modes of obtaining complex lithium lubricant compositions intended for use in friction units of modern machines and mechanisms. This work presents the results of studies of the microstructure and properties of lubricant samples based on synthesized complex lithium soaps of hydroxylated fatty acids from of waste food oil as a lubricant thickener. The results of scanning electron microscopy confirmed the differences in the peculiarities of the formation of the structural framework of lubricants depending on their composition, thickener concentration, complexing agents, and heat treatment temperature. It was determined that it is the lubricant thickener that binds the dispersion medium through intermolecular interaction, forms a three-dimensional interwoven microstructure, and gives the lubricant improved rheological and volumetric-mechanical properties. Complex lithium soap is more structured than simple lithium soap, although both are formed by a connected three-dimensional mesh microstructure.&nbsp;It has been shown that the rheological and operational properties of lubricant can be improved by using various complexing agents. The lithium complex lubricant samples are characterized by the maximum thickening effect and have lower effective viscosity values at minus 30&nbsp;°C. With an increase in the concentration of the thickener, the effective viscosity of lithium complex lubricants increased, but the indicators of mechanical stability and drop point remained almost unchanged. It was found that the optimum heat treatment temperature for complex lithium lubricant is 220&nbsp;°C. If the heat treatment temperature of the lubricant was exceeded, for example, at 240&nbsp;°C, the microstructure of the complex lithium soap was destroyed, which led to a deterioration in viscosity and colloidal stability. The established rheological, volume-mechanical, and temperature regularities of the structure formation of the dispersed phase of lubricants can be used to select rational modes of obtaining complex lithium lubricant compositions intended for use in friction units of modern machines and mechanisms. V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine 2025-12-08 Article Article application/pdf https://kataliz.org.ua/index.php/journal/article/view/134 10.15407/kataliz2025.36.121 Catalysis and petrochemistry; No. 36 (2025): Catalysis and petrochemistry; 121-129 Каталіз та нафтохімія; № 36 (2025): Каталіз та нафтохімія; 121-129 2707-5796 2412-4176 10.15407/kataliz2025.36 en https://kataliz.org.ua/index.php/journal/article/view/134/118 Copyright (c) 2025 Catalysis and petrochemistry |
| spellingShingle | загусник мастил мікроструктура реологія механічна стабільність комплексні літієві мастила Bodachivska, Larysa Yu. Venger, Iryna O. Verba, Artem Yu. Microstructure of complex lithium lubricants |
| title | Microstructure of complex lithium lubricants |
| title_alt | Microstructure of complex lithium lubricants |
| title_full | Microstructure of complex lithium lubricants |
| title_fullStr | Microstructure of complex lithium lubricants |
| title_full_unstemmed | Microstructure of complex lithium lubricants |
| title_short | Microstructure of complex lithium lubricants |
| title_sort | microstructure of complex lithium lubricants |
| topic | загусник мастил мікроструктура реологія механічна стабільність комплексні літієві мастила |
| topic_facet | lubricant thickener microstructure rheology mechanical stability complex lithium lubricants загусник мастил мікроструктура реологія механічна стабільність комплексні літієві мастила |
| url | https://kataliz.org.ua/index.php/journal/article/view/134 |
| work_keys_str_mv | AT bodachivskalarysayu microstructureofcomplexlithiumlubricants AT vengerirynao microstructureofcomplexlithiumlubricants AT verbaartemyu microstructureofcomplexlithiumlubricants |