Application of bismuth compound additive in lubricating grease

Antimony element and phosphorus element as we know, is located in the main group V of the periodic table, having also a extreme pressure, anti-wear element characteristics. The antimony compounds used as lubricating grease additives can be classified into two types, one is an inorganic antimony compound, such as antimony thioantimonate (SbSbS ₄ ), antimony sulfide (Sb ₂ S ₃ ), and the other is an organic antimony compound. Mainly bismuth dialkyl dithiophosphate (SbDDP) and bismuth dialkyl dithiocarbamate (SbDDC). Compared with insoluble inorganic cerium compounds, oil-soluble organic cerium additives are more widely used in lubricating greases. At present, the commercial organic antimony additives mainly include Vanlube 622 (diisopropyl dithiophosphate, strontium content 11.5%, phosphorus content 9.5%, sulfur content 18.0%) and Vanlube 73 (dipentyldithio) produced by RTVanderbilt. Barium carbamate, cerium content 6.8%, sulfur content 11.1%), Vanlube 8610 (a synergistic mixture of Vanlube 73 and sulfurized olefins, cerium content 7.3%, sulfur content 36.0%), and domestic T352 additive (dibutyldithiocarbamic acid) antimony). The basic properties of inorganic and organic bismuth compounds as lubricant additives, interactions with other additives and related applications are described.

First, the basic properties of inorganic bismuth compounds

Table 1 shows the extreme pressure, antiwear properties of bismuth thioruthenate (SbSbS ₄ ), strontium sulfide (Sb ₂ S ₃ ) in grease, and their performance comparison with molybdenum disulfide (MoS ₂ ) additives. As can be seen from Table 1, both SbSbS ₄ having an amorphous property and Sb ₂ S ₃ having a crystalline structure have much better extreme pressure and antiwear properties than MoS ₂ . Using molybdenum disulfide, the sintering load of the oil is only 1372N, using crystalline strontium sulfide, the sintering load can reach 3479N, but the amorphous bismuth thioruthenate can increase the sintering load to 5880N, showing the best pole. Pressure performance. Moreover, under a load lower than the sintering load, the ruthenium thioruthenate is used, and the diameter of the steel ball wear spot is also very small, which is unmatched by the crystalline bismuth sulfide. Although the crystalline strontium sulfide has a layered structure similar to that of molybdenum disulfide, its extreme pressure and antiwear properties are far less than the indeterminate bismuth thiosulphate.

Table 1 Extreme pressure and antiwear properties of amorphous bismuth thioruthenate (SbSbS ₄ ) and crystalline strontium sulfide (Sb ₂ S ₃ ) in grease

Note: The base grease is thickened with diester base oil, the additive is 5%; the four-ball test speed is 1800rmin, the test time is 10s, and the steel ball is AISI-C-52100 chrome steel (ASTMD-2596).

In addition, using the experimental conditions similar to those in Table 1, but replacing the steel ball with AISI-440C stainless steel which is extremely difficult to lubricate, it has also been found that bismuth thioruthenate has excellent lubricating properties. Using bismuth bismuth citrate additive, the diameter of the wear spot is only 0.53mm under the load of 1568N, but the commercial grade molybdenum disulfide is used. Under the load of 784N, the diameter of the wear spot reaches 2.43mm, and the sintering load is only 1176N.

Second, the synergistic effect of bismuth thioruthenate and other additives

Table 2 shows the data of extreme pressure and anti-wear synergy of bismuth thioruthenate and molybdenum disulfide additives in grease. It can be seen from Table 2 that, in combination with the molybdenum disulfide additive, the long grinding wear diameter of the four-ball test can be effectively reduced, and the sintering load and the load wear index are greatly improved. Obviously, these two additives have very good extreme pressure and anti-wear synergy in the grease. Studies have also shown that bismuth thioruthenate and graphite also have a good extreme pressure and anti-wear synergy in the grease, but this synergistic effect is slightly worse than the synergistic effect with molybdenum disulfide.

Table 2 Extreme pressure and anti-wear synergy of bismuth thioruthenate and molybdenum disulfide additives in grease

Note: The base grease is a silica grease based on polya-olefin. The sintering load and load wear index are measured according to ASTM D-2596: four-ball machine speed l800rmin, time 10s. The diameter of the long grinding spot was measured according to ASTM D-2596 method: the speed of the four ball machine was 1200 rmin, the load was 392 N, the time was lh, and the temperature was 75 °C. The steel balls used are all AISI-C-52100 steel.

The anti-wear synergistic effect of bismuth thioantimonate and molybdenum disulfide additives is also manifested in the lubricating oil. Moreover, these two additives also have anti-friction synergy effect in the lubricating oil. The test results are shown in Table 3. It can be seen from Table 3 that the bismuth thioruthenate and the molybdenum disulfide additive exhibit excellent synergistic effects of friction reduction.

Table 3 Antifriction synergistic effect of bismuth thioantimonate and molybdenum disulfide additives in lubricating oil

Note: The base oil is a paraffin-based mineral oil containing a succinimide dispersant. The coefficient of friction was measured on a four-ball test machine: the speed was 1200 rmin, and the load was measured after 5 min of operation at 392 N.

In addition, bismuth thioruthenate (SbSbS ₄ ) and bismuth oxide (Sb ₂ O ₃ ) also exhibit a certain extreme pressure and anti-wear synergy in lithium -based greases. For example, in a lithium base grease obtained by thickening mineral oil with 12-hydroxystearic acid, 1.0% of lanthanum thioantimonate or cerium oxide can be used to obtain a sintering load of 3920N and 1960N, respectively. By adding 0.8% bismuth thioruthenate and 0.2% yttrium oxide, a sintering load of 4900 N can be obtained. The bismuth thioruthenate or its complex with cerium oxide also has the property of inhibiting abrasive wear in the grease. This performance is important for the grease of open air and mining equipment, which is highly likely to be mixed with dust or mineral abrasive particles.

Third, the basic properties of organic antimony additives

Table 4 shows the extreme pressure properties dialkyl zinc dithiophosphate (SbDDP) in lubricating oil, its performance compared with dialkyl zinc dithiophosphate (the ZnDDP) a. It can be seen from Table 4 that the extreme pressure performance of SbDDP and ZnDDP is related to the size of its alkyl group. The smaller the alkyl group, the better the extreme pressure; with the increase of alkyl group, SbDDP The extreme pressure performance of ZnDDP is reduced, but the performance degradation of SbDDP is more obvious. For the dithiophosphates with smaller alkyl groups, the extreme pressure performance of SbDDP is better than that of ZnDDP. Except for 2-ethylhexyl, the extreme pressure properties of other alkyl SbDDPs are better than those of the same alkyl ZnDDP.

Table 4 Extreme Pressure Properties of Dialkyldithiophosphates in Lubricating Oils and Comparison with Zinc Salts

Note: The base oil is SAE90 high viscosity index base oil, and the Timken test is carried out according to ASTMI)-2782.

The antiwear properties of commercially available sulfonium and zinc salts of dialkyldithiophosphoric acid were compared using a four ball tester. The sulfonium salt used is Vanlube 622 (alkyl is isopropyl) and the zinc salt is T202 additive. As can be seen from Table 5, Vanlube 622 has excellent anti-wear properties, and its anti-wear performance is more prominent under high load conditions. The isopropyl SbD-DP has excellent extreme pressure properties and very good abrasion resistance.

Table 5 Extreme Pressure Properties of Bismuth Dithiocarbamate with Different Alkyl Groups in Ester Lubricating Oils

Note: The base oil is diisooctyl sebacate, and the additive is added in an amount of 2.5%. The Timken test was carried out in accordance with the ASTM D-1782 method.

The extreme pressure resistance of bismuth dialkyldithiocarbamate (SbDDC) with different alkyl groups in lubricating oils has excellent Temken and four-ball extreme pressure properties. The extreme pressure properties of SbDDC are related to the size of the alkyl group, which first increases with the increase of the alkyl group, but after the pentyl or hexyl group, the performance decreases as the alkyl group increases. The pentyl or hexyl SbDDC has the best extreme pressure performance. The effect of the amount of SbDDC added on its extreme pressure performance. With the increase of the addition amount, the extreme pressure performance of SbDDC is gradually enhanced, and the extreme pressure performance is best when the addition amount is 2.5% to 3.0%.

The extreme pressure properties of bismuth dialkyldithiocarbamate in ester lubricating oils are shown in Table 5. As can be seen from Table 5, SbDDCs with suitable alkyl groups have very good Timken extreme pressure properties in ester oils. Table 5 also lists the data for zinc isopropyl n-octyldithiocarbamate (ZnDDC) as a comparison. It can be seen that for isopropyl n-octyldithiocarbamate, the ZnDDC The Ken OK value is only 44N, while the SbDDC is 356N. Obviously, the SbDDC's Timken extreme pressure performance is much better than the same ZnDDC with the same alkyl group.

Regarding the four-ball anti-sintering performance of organic cerium salts in greases, it has been reported in the literature that 2.0% of commercial bismuth diisopropyl dithiophosphate (Vanlube 622) is added to a base lithium grease with a sintering load of 1235 to 1568N. Or 4.0% of lanthanum dipentyl dithiocarbamate (Vanlube 73) can obtain a sintering load of 3920N. It has been reported that bismuth dialkyldithiocarbamate can significantly extend the service life of grease. In a urea-based grease based on polya-olefin or diphenyl ether synthetic oil as base oil, lanthanum dipentyl dithiocarbamate (Vanlube 73) was added. Bearing tests under specific conditions showed that the bearing life exceeded 1000 h. other additives, such as dialkyl dithiocarbamate, borate, bearing life which does not exceed 200h. Dialkyl dithiocarbamic acid antimonate excellent extreme pressure, anti-wear properties due to initial reaction temperature with a lower surface of the metal.

Table 6 shows the antioxidant properties of organic cerium additives in lubricating oils. As can be seen from Table 6, both bismuth dialkyl dithiophosphate (SbDDP) and bismuth dialkyl dithiocarbamate (SbDDC) have certain antioxidant properties. Among them, SbDDC has better oxidation resistance than SbDDP.

Table 6 Antioxidant properties of bismuth dithiophosphate and bismuth dithiocarbamate in grease

Note: The base grease is No. 2 lithium base grease. The ASTM D-942 oxygen bomb test was used.

Nowadays, biodegradable lubricating greases are beginning to receive more and more attention. Among them, the most researched and widely used biodegradable base oil is vegetable oil. Bismuth dialkyl dithiocarbamate has excellent antioxidant properties in vegetable oil base oils. The antioxidant properties of a series of antioxidants in vegetable oil base oils (225 ° C, 40 Ul oil sample, 30 min) were evaluated by the Pennsylvania micro-oxidation test. Studies have shown that lanthanum dipentyl dithiocarbamate (Vanlube 73) has a higher tradition than Commercialized additives such as amines, phenols and sulphur phosphate antioxidants have better antioxidant properties. In addition, since bismuthyl dithiocarbamate does not contain phosphorus, it can be used to blend low-phosphorus or non-phosphorus internal combustion engine oil, reduce the toxicity to the catalyst of the automobile exhaust catalytic converter, and is beneficial to environmental protection.

Synergistic effect of organic bismuth additives and other additives

Table 7 shows the extreme pressure synergy of bismuth dithiocarbamate with borate additives. It can be seen from Table 7 that the bismuth dithiocarbamate and the borate additive have a good Timken extreme pressure synergy, and this synergistic effect is more pronounced in the lithium base grease, 4% borate and A 1% dialkyldithiocarbamate complex is combined to obtain a 400N Timken OK value in the lithium base grease.

Table 7 Extreme pressure synergy of bismuth dithiocarbamate and borate additives in grease

Note: The Timken OK value is measured according to the ASTM D-2509 method. The borate additive is a commercial additive containing 40% potassium triborate, and SbDDC is bismuthyl dithiocarbamate (Vanlube73)

The use of bismuth dialkyldithiocarbamate with an organic molybdenum additive such as molybdenum dialkyldithiophosphate (MoDDP) or molybdenum dialkyldithiocarbamate (MoDDC) provides good results. Especially in the CVJ grease, bismuth dialkyldithiocarbamate (SbDDC) is compounded with molybdenum dialkyldithiocarbamate (MoDDC) and has excellent properties.

Used in combination with SbDDC, MoDDC is superior to other additives in combination with high sintering load and Timken OK values, as well as low wear spot diameter and good corrosion control. Moreover, the MoDDC and SbDDC composite additive system can be used to produce low noise grease.

Table 8 shows the ternary extreme pressure synergy system composed of ZnDDP, SbDDP and glycerol. It can be seen from Table 8 that when the addition amounts of ZnDDP, SbDDP and glycerol are 1.50%, 0.25% and 0.30%, respectively, the Timken 0K value of the grease does not exceed 89N (test samples B, C and D). ) Even if they are compounded, their Timken 0K values ​​are not more than 156N (test samples E, F and G), but when the three are compounded, their Timken 0K value reaches 333N (test) Sample H), obviously, ZnDDP, SbDDP and glycerol are an excellent ternary extreme pressure synergy system, and all three are indispensable. The triol (glycerol) in the ternary synergy system has a special effect and cannot be replaced by other alcohols (such as propylene glycol). If propylene glycol is used instead of glycerol, the Timken OK value is 333N. Drop below 89N (test samples H and I). The ternary extreme pressure synergy system in the fully formulated grease containing rust inhibitor, copper corrosion inhibitor, antioxidant, adhesion enhancer and dye, its anti-extreme pressure effect remains basically unchanged, still maintaining 311N The high Timken OK value (test samples J and K) indicates that the extreme pressure synergy system is substantially immune to interference from other additives in the grease and has fairly good stability. Although 1.5% of SbDDP also has very good extreme pressure performance, its Timken OK value can reach 356N (test sample L), but the additive is more expensive and has high corrosiveness to copper sheets, which cannot be combined with ZnDDP. Compared with the ternary extreme pressure system composed of SbDDP and glycerol.

Table 8 ZnDDP, SbDDP and glycerol ternary extreme pressure synergy system in grease

Note: The base grease is NLGI No. 2 lithium complex grease (base oil 40 ° C viscosity is 220 mm, Is, thickening dose is l4%). Other additives are rust inhibitors, copper corrosion inhibitors, antioxidant adhesion enhancers, and dyes.

In addition, bismuth dialkyldithiocarbamate can also interact with dyes in greases and exhibit different color characteristics at different temperature stages, which can bring special benefits to grease application and equipment monitoring. . If the grease shows a color under unusually high temperature conditions, it means that the lubrication is not working at this time, the grease should be replaced, or the equipment is faulty, and the equipment should be repaired. For example, in a finished bentonite extreme pressure grease containing 2.5% lanthanum dipentyl dithiocarbamate (Vanlube 73), 800 ug ∕g blue dye is added, and as the temperature increases, the color may change as follows: below 100 ° C Keep blue, dark green at 120 °C, purple at 140 °C; if you replace Vanlube73 with 2.0% Vanlube8610 (a synergistic mixture of Vanlube73 and sulfurized olefins), the color change is different: keep blue below 80 °C It turns green at 100 ° C, turns brown at 140 ° C, and turns orange at 170 ° C. This color change characteristic is also present in other types of greases, such as lithium grease.

V. Conclusion

(1) SbSbS ₄ has excellent extreme pressure and anti-wear properties in grease.

(2) SbSbS ₄ and molybdenum disulfide additives have excellent synergistic effects of extreme pressure, anti-wear and anti-friction.

(3) SbDDP dialkyl dithiophosphate and bismuth dialkyl dithiocarbamate (SbDDC) are multifunctional additives for lubricating greases, which have extreme pressure, antiwear and oxidation resistance.

(4) SbDDC dialkyl dithiocarbamate and borate additive have an extreme pressure synergistic effect, which can greatly improve the Timken OK value of the grease.

(5) SbDDC of dialkyldithiocarbamate and molybdenum dialkyldithiocarbamate have synergistic effects in extreme pressure, antiwear and corrosion inhibition.

(6) SbDDP dialkyl phosphate (SbDDP) can form a stable ternary extreme pressure synergy system with zinc dialkyl dithiophosphate and glycerol, which is extremely effective in improving the grease of Timken OK. value.

(7) Sodium dialkyldithiocarbamate (SbDDC) can also react with dyes in greases and act as temperature indicators for greases.

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