Analysis of self-lubrication enhancement via PA66 strategies: Texturing and nano-reinforcement with ZrO2 and graphene

Graphene nanoflakes and zirconium dioxide (ZrO2) were added to polyamide 66-based composites with glass fibre in order to improve their self-lubricating properties and make them suitable for high-performance bearing applications. The influence of texturing the surfaces was also investigated. The tribological behaviour was analysed for different combinations of hybrid polymeric composites, percentages of additive, and texturing geometries. The results show that the lowest low friction coefficients are obtained for PA66 + 30GF with 5% graphene. Worn surfaces, analysed by scanning electron microscopy and optical microscopy confirm the enhancement of the tribological properties with the addition of graphene. Texturing results under dry lubrication are not relevant for tribological purposes

Enhancement of tribological behavior of rolling bearings by applying a multilayer ZrN/ZrCN coating

This paper focuses on the tribological behaviour of ZrN/ZrCN coating on bearing steel substrates DIN 17230, 100Cr6/1.3505. Coatings are applied at room temperature processes by means of Cathodic Arc Evaporation (CAE), a kind of Physical Vapor Deposition (PVD) technique. In order to achieve a satisfactory compromise between coating-substrate adhesion and the surface roughness requirement of the bearing rings, a polish post-processing is proposed. Different polish post-processing times and conditions are applied. The coated and polished bearing rings are tested under real friction torque test protocols. These tests show that the application of the coating does not entail a significant improvement in friction performance of the bearing. However, fatigue tests in real test bench are pending to evaluate the possible improvement in bearing life time

Tribological performance of nylon composites with nanoadditives for self-lubrication purposes

A systematic study comparing the wear behaviour of composites with nylon matrix (PA66, PA46, PA12) and different nanoadditives and reinforcing additives (graphite, graphene, MoS2 and ZrO2) has been carried out in order to achieve a proper self-lubricant material for bearing cages. The wear characterisation was done using pin-on-disc tests, SEM and EDX analysis. The results show that better outcomes are obtained for composites based on PA12. The addition of ZrO2 offers negative values of wear due to the metallic particle transference from the counterface to the polymeric pin

Experimental vasectomy and testicular structure

We have performed an experimental study on rats and dogs to evaluate the long term effects (from 1 to 12 months) of vasectomy on the structure of the testis. From four months after vasectomy onwards, the specimens showed very important changes in the seminiferous epithelium and Sertoli cells, with an obvious thickening of the basement membrane that supports the epithelium. The deterioration depended on the time passed and, over six months after vasectomy, the alterations were very clear and the seminiferous tubules became atrophic and shnink, sometimes without any remains of seminiferous epithelium and with an important hypertrophy of the interlobular interstitial tissue, although we did not see an increase in the number of Leydig cells. Alterations due to vasectomy depend on the animal species, the peculiarities of techniques and, of course, the time passed after surgery

A Structure‐Activity Investigation on Modified Analogues of an Argininocalixarene Based Non‐viral Gene Vector

AbstractThe tetra‐L‐arginino‐tetrahexyloxycalix[4]arene 1 has shown extraordinary abilities to compact and internalize different types of Nucleid Acid cargos (DNA, microRNA, PNA) into cells even known to be transfected with great difficulties by commercial non‐viral gene delivery systems. This activity, accompanied by negligible toxicity, makes this calixarene a rather promising prototype of vector for Gene Therapy. In this study we report how small structural changes like i) the lower rim alkyl substituents, ii) the type of the terminal cationic headgroups (guanidinium or primary ammonium), iii) the length of the linker between the macrocycle and the terminal cationic headgroup, iv) the presence/absence of the basic α‐amino group of Arg, and v) the stereochemistry (L or D) of Arg, might affect the ability of the novel calixarene vectors to compact DNA and to deliver its cargo into the cells