Oil/Thickener Interactions and Rheology of Lubricating Greases
Bibliographic record
Abstract
The present communication concerns the effect of base oil/thickener interaction on the flow properties of lubricating greases. The flow properties of paraffinic and naphthenic lithium greases in the temperature range from −40 to 60°C have been characterized by using the traditional flow pressure test and advanced rheological measurements including the determinations of apparent viscosity, yield stress, grease rheology intersection stress, and critical stress. The rheology of greases appears to be typical of viscoelastic materials possessing a certain degree of internal structure and memory effect (thixotropy), and there exists an obvious correlation between the pumpability and the rheological characteristics of greases at all temperatures. At high temperatures (above 0°C), the flow properties of paraffinic and naphthenic greases are rather similar. However, the pumpability of naphthenic greases is clearly superior to that of paraffinic greases at temperatures between −20 and −40°C. As evidenced by the flow pressure measurements, among the naphthenic greases studied, the grease made of a highly refined naphthenic oil with the lowest aromatic content has the best pumpability at extremely low temperatures (−40°C). The observed differences in pumpability and rheological properties of greases are attributed to differing solvencies of the base oils, which have a significant impact on the structure of the thickener and, as a result, on the rheology and lubricating efficiency of grease. The rheological studies have been complemented by in situ characterization of the thickener structure in grease by using the cryo-TEM technique in combination with a specially developed thickener versus a background contrasting method. In this way, both the characteristic fiber dimensions and the aggregate structure have been determined. The soap fibers were found to have a worm-like shape with the average diameter of around 30 nm and the length of around 1 μm. The only apparent difference between paraffinic and naphthenic greases was that, in the former, the fibers tend to be more irregular in shape. Furthermore, it has been demonstrated that severe oxidation of grease in accelerated ageing tests causes a significant aggregation of fibers. Simultaneously with fiber compaction, some fibers get broken and the average fiber diameter increases from around 30 nm to around 50 nm. The described changes in the fiber morphology can be explained by the adsorption of oil oxidation products to the surface of fibers or by soap oxidation and hydrolysis, which are suspected to be the primary degradative processes lying behind the grease ageing in applications.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".