Tribological Performance of Lubricating Greases Based on Calcium Carbonate Polymorphs Under the Boundary Lubrication Condition

In this paper, Al7075 alloy and 15 wt% VN/7075 composite were prepared by ball milling and hot-press sintering. The microstructure, hardness, and wear behavior under different working conditions (environmental condition: dry friction, sulfur-containing boundary lubrication, and oil lubrication) were studied. The results showed that the distribution of VN was dispersive and uniform in 15 wt% VN/7075 composite without obvious agglomeration. The hardness (119.5 Hv) of 15 wt% VN/7075 composite was 46.1% higher than the Al7075 alloy (81.8 Hv). Friction and wear behavior test results showed that under sulfur-containing boundary lubrication condition, according to the tribofilm layer on the worn surface of 15 wt% VN/7075 composite, the friction coefficient of 15 wt% VN/7075 composite decreased by 37.6% compared with the Al7075 alloy. The main wear mechanism of 15 wt% VN/7075 composite was delamination wear and abrasive wear under dry friction, while under sulfur-containing boundary lubrication and oil lubrication, it changed to mild abrasive wear.

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Luminescence reveals variations in local structural order of calcium carbonate polymorphs formed by different mechanisms

Scientific Reports ◽

10.1038/s41598-019-52587-7 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 6

Author(s):

Michael B. Toffolo ◽

Giulia Ricci ◽

Luisa Caneve ◽

Ifat Kaplan-Ashiri

Keyword(s):

Infrared Spectroscopy ◽

Calcium Carbonate ◽

Construction Materials ◽

Reference Database ◽

Formation Processes ◽

X Ray Diffraction ◽

Structural Order ◽

Lime Plaster ◽

Calcium Carbonate Polymorphs

Abstract In nature, calcium carbonate (CaCO3) in the form of calcite and aragonite nucleates through different pathways including geogenic and biogenic processes. It may also occur as pyrogenic lime plaster and laboratory-precipitated crystals. All of these formation processes are conducive to different degrees of local structural order in CaCO3 crystals, with the pyrogenic and precipitated forms being the least ordered. These variations affect the manner in which crystals interact with electromagnetic radiation, and thus formation processes may be tracked using methods such as X-ray diffraction and infrared spectroscopy. Here we show that defects in the crystal structure of CaCO3 may be detected by looking at the luminescence of crystals. Using cathodoluminescence by scanning electron microscopy (SEM-CL) and laser-induced fluorescence (LIF), it is possible to discern different polymorphs and their mechanism of formation. We were thus able to determine that pyrogenic calcite and aragonite exhibit blue luminescence due to the incorporation of distortions in the crystal lattice caused by heat and rapid precipitation, in agreement with infrared spectroscopy assessments of local structural order. These results provide the first detailed reference database of SEM-CL and LIF spectra of CaCO3 standards, and find application in the characterization of optical, archaeological and construction materials.

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A scuffing model considering additive depletion in boundary lubrication

Industrial Lubrication and Tribology ◽

10.1108/ilt-05-2019-0183 ◽

2019 ◽

Vol 72 (3) ◽

pp. 267-272

Author(s):

Bora Lee ◽

Yonghun Yu ◽

Yong-Joo Cho

Keyword(s):

Boundary Lubrication ◽

Mass Conservation ◽

Additive Concentration ◽

Contact Conditions ◽

Sliding Bearings ◽

Content Type ◽

Proposed Model ◽

Lubrication Condition ◽

Scuffing Failure ◽

Sliding Distance

Purpose This paper aims to propose a new scuffing model caused by the depletion of additives in boundary lubrication condition. Design/methodology/approach The differential equation governing the distribution of additive content in the fluid film was used. This formula was derived from the principle of mass conservation of additives considering the consumption due to surface adsorption of wear particles. The occurrence of scuffing was determined by comparing the wear rate of the oxide layer with the oxidation rate. Findings If the additive becomes depleted while sliding, the scuffing failure occurs even at a low-temperature condition below the critical temperature. The critical sliding distance at which scuffing failure occurred was suggested. The experimental data of the existing literature and the theoretical prediction using the proposed model are shown to be in good agreement. Originality/value It is expected to be used in the design of oil supply grooves for sliding bearings operating under extreme conditions or in selecting the minimum initial additive concentration required to avoid scuffing failure under given contact conditions.

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The effect of different amino acids on spontaneous precipitation of calcium carbonate polymorphs

Journal of Crystal Growth ◽

10.1016/j.jcrysgro.2018.01.023 ◽

2018 ◽

Vol 486 ◽

pp. 71-81 ◽

Cited By ~ 14

Author(s):

Lara Štajner ◽

Jasminka Kontrec ◽

Branka Njegić Džakula ◽

Nadica Maltar-Strmečki ◽

Milivoj Plodinec ◽

...

Keyword(s):

Amino Acids ◽

Calcium Carbonate ◽

Calcium Carbonate Polymorphs

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X-Ray Diffraction Analysis of the Calcium Carbonate Polymorphs

Advances in X-ray Analysis ◽

10.1154/s0376030800008260 ◽

1970 ◽

Vol 14 ◽

pp. 29-37 ◽

Cited By ~ 2

Author(s):

S. T. Silk ◽

S. Z. Lewin

Keyword(s):

Calcium Carbonate ◽

Size Distributions ◽

X Ray Diffraction ◽

Particle Size Distributions ◽

Ray Method ◽

X Ray ◽

Packing Efficiency ◽

Integrated Intensities ◽

Packing Effect ◽

Calcium Carbonate Polymorphs

AbstractIt is shown that the integrated intensities of diffraction lines from calcite and aragonite powders prepared by precipitation vary markedly, due to variations in sample packing efficiency arising from different degrees of polydispersity in the particle size distributions. Since prolonged grinding to equalize initially divergent distributions changes the polymorph composition, the packing effect imposes the principal limitation on the precision of the x-ray method for certain types of calcium carbonate preparations.

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