This study proposes boron nitride nanotube (BNNT) reinforced hydroxyapatite (HA) as a novel composite material for orthopedic implant applications. The spark plasma sintered (SPS) composite structure shows higher density compared to HA. Minimal lattice mismatch between HA and BNNT leads to coherent bonding and strong interface. HA-4 wt% BNNT composite offers excellent mechanical properties-120% increment in elastic modulus, 129% higher hardness and 86% more fracture toughness, as compared to HA. Improvements in the hardness and fracture toughness are related to grain refinement and crack bridging by BNNTs. HA-BNNT composite also shows 75% improvement in the wear resistance. The wear morphology suggests localized plastic deformation supported by the sliding of outer walls of BNNT. Osteoblast proliferation and cell viability show no adverse effect of BNNT addition. HA-BNNT composite is, thus, envisioned as a potential material for stronger orthopedic implants.

Boron nitride nanotube reinforced hydroxyapatite composite: mechanical and tribological performance and in-vitro biocompatibility to osteoblasts.

Boron compounds are widely used in a range of tribological applications such as friction modifiers, antioxidants, antiwear additives, and in many cases as environmentally friendly lubricants. The chemical nature and structure of boron compounds provide multifunctionality. They are used as (1) solid lubricants such as boric acid and hexagonal boron nitride, (2) liquid lubricants such as ionic liquids, (3) lubricant additives such as borate derivatives of various organic and inorganic compounds, and (4) coatings such as cubic boron nitride and different metal borides. Boron is also one of the most favorable elements for coatings and thin films in biotribological and biomedical applications. This review outlines the growing role of boron in lubrication over the past several decades, summarizes the main findings, and identifies future challenges related to boron chemistry.

Boron in tribology: from Borates to ionic liquids

Although tailored wet ball milling can be an efficient method to produce a large quantity of two-dimensional nanomaterials, such as boron nitride (BN) nanosheets, milling parameters including milling speed, ball-to-powder ratio, milling ball size and milling agent, are important for optimization of exfoliation efficiency and production yield. In this report, we systematically investigate the effects of different milling parameters on the production of BN nanosheets with benzyl benzoate being used as the milling agent. It is found that small balls of 0.1-0.2 mm in diameter are much more effective in exfoliating BN particles to BN nanosheets. Under the optimum condition, the production yield can be as high as 13.8% and the BN nanosheets are 0.5-1.5 μm in diameter and a few nanometers thick and of relative high crystallinity and chemical purity. The lubrication properties of the BN nanosheets in base oil have also been studied. The tribological tests show that the BN nanosheets can greatly reduce the friction coefficient and wear scar diameter of the base oil.

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High-Efficient Production of Boron Nitride Nanosheets via an Optimized Ball Milling Process for Lubrication in Oil

Abstract The present paper is based on experimental studies of self-lubricated porous sliding bearings with hexagonal boron nitride (h-BN) as an additive. The friction coefficients of powder matrix lubricated by (h-BN + oil) were measured at varying loads of 1.05–2.0 MPa and sliding speeds of 1.35 and 2.5 m/s. The results are discussed in the form of performance characteristics such as the coefficient of friction, bearing temperature, and load-carrying capacity. The micro-particles of the h-BN additive were between 1 and 2 μm in diameter. The effect of the PV (pressure–velocity) parameter on the transition time to seizure for porous bush composites impregnated by the lubricant has been studied. It was found that the addition of the micro-particles to the oil decreased the friction coefficient about twice as compared to self-lubricated bearings lubricated only by oil. The main effect of (h-BN micro-particles + oil) in comparison to Mobil DTE-BB lubricant appears to be that the impregnation of h-BN micro-particles persists for a long period of time and the micro-particles are gradually released, being supplied to the contact surfaces. For a manufacturing application, the porous bearings were assembled in a car clutch.

A comparative study on the tribological behaviour of hexagonal boron nitride (h-BN) as lubricating micro-particles - An additive in porous sliding bearings for a car clutch

Tribological behaviour and lubrication performance of hexagonal boron nitride (h-BN) as a replacement for graphite in aluminium forming

A comparative study on the tribological behaviour of hexagonal boron nitride (h-BN) as lubricating micro―particles―An additive in porous sliding bearings for a car clutch

Phospholipid molecules (PLs) in vivo and graphite, molybdenum disulfide, tungsten disulfide and hexagonal boron nitride (h-BN) in vitro are good examples of frictionless lubricants. PLs and solid materials have the ability to form multi-bilayer or layered structures similar to lamellate solid. It has been confirmed experimentally that PLs as lamellar lubricants protect the surface of joints against wear while acting as frictionless lubricant. An experimental study has been conducted on the friction properties of h-boron nitride on porous non-full journal bearings. The porous non-full journal bearings were a mixture of 97.5 wt.% Fe and 2.5 wt.% Cu powder, and compressed to a density of 5.9 g/cm(3). The porosity of non-full journal bearings were 15.5 and 27.8 wt.% and were impregnated with vaseline and vaseline+5 wt.% h-BN. Additionally, the two additives SFR NLGI #2 (or SFR 2522) grease and graphite grease were used for comparison to h-BN. The tribological tests were performed on a four-ball machine under load of 49 daN, and a friction tribotester. The above experiment strongly suggested that h-BN has the ability to lubricate under load with very low friction coefficient comparable to phospholipids. Relatively low surface energy and low adhesion between the crystallites are giving the additives low friction coefficient. The results of the experimental studies showed that h-BN as an additive in vaseline possesses friction reducing properties, and excellent anti-wear properties.

Lamellar lubrication in vivo and vitro: friction testing of hexagonal boron nitride.

Energy conservation through recycling of used oil

Purpose: The purpose of this paper is to study the sliding and the vibrating fretting tests mechanism of h-BN micro-particles when used as a lubricating grease-2 additive. Design/methodology/approach: The fretting tests were conducted on steel/steel contacts using both vibrating fretting apparatus and the shaftsleeve slide fitted tester. The wear scars were characterized with profilometry. The tribological properties of grease-2 compounded with h-BN additive were also compared to those obtained for the commercial product Militec-4. Findings: The experiment showed significant differences between the results obtained from the vibrating fretting and the shaft-sleeve sliding fitted tests. Adding h-BN to the lubricant leads to a better performance in the shaft-sleeve slide regime than in the steel/steel vibrating test condition. Originality/value: The results of the experimental studies demonstrate the potential of h-BN as an additive for preventing fretting sliding, and can very useful for further application of compound grease-2 with h-BN additive in industrial equipment.

Tadeusz Kałdoński

Papers

A comparative study on the tribological behaviour of hexagonal boron nitride (h-BN) as lubricating micro-particles - An additive in porous sliding bearings for a car clutch

A comparative study on the tribological behaviour of hexagonal boron nitride (h-BN) as lubricating micro―particles―An additive in porous sliding bearings for a car clutch

Lamellar lubrication in vivo and vitro: friction testing of hexagonal boron nitride.

Energy conservation through recycling of used oil

The effect of hexagonal boron nitride additive on the effectiveness of grease‐based lubrication of a steel surface