Wyniki wyszukiwania - BazTech

1

Effects of different Sn contents on formation of Ti2SnC by self-propagating high-temperature synthesis method in Ti-Sn-C and Ti-Sn-C-TiC systems

Sun H Y, Kong X, Sen W, Yi Z Z, Wang B S, Liu G Y

Materials Science Poland

|

2014

|

Vol. 32, No. 4

696--701

EN

Effect of different Sn contents on combustion synthesis of Ti2SnC was studied using elemental Ti, Sn, C and TiC powders as raw materials in the Ti–Sn–C and Ti–Sn–C–TiC system, in which the molar ratio of Ti/C was set as 2:1. The reaction mechanism for the formation of Ti2SnC was also investigated. The results showed that the amount of Ti2SnC in combustion products firstly increased with increasing of Sn content (0.6 to 0.8 mol), and then decreased with further increasing of Sn content (1.0 to 1.2 mol). Upon addition of 15 % TiC instead of Ti and C, the optimum addition of Sn decreased to 0.7 mol and a higher purity of Ti2SnC was obtained. The Ti2SnC powders were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

2

An overview of the association between lamprophyric intrusions and rare-metal mineralization

Štemprok M., Seifert T.

Mineralogia

|

2011

|

Vol. 42, iss. 2/3

121--162

EN

Granite-related rare metal districts in orogenic settings are occasionally associated with lamprophyre dikes. We recorded 63 occurrences of lamprophyres in bimodal dike suites of about 200 granite bodies related to rare metal deposits. Most lamprophyres occur in Paleozoic and Mesozoic metallogenic provinces in the northern hemisphere. Lamprophyres which are associated with rare metal deposits are calc-alkaline (kersantites, minettes, spessartites) or more rarely alkaline lamprophyres (camptonites, monchiquites) which occur in the roof zone of complex granitic bodies as pre-granitic, intra-granitic, intra-ore or post-ore dikes. Most lamprophyres are spatially associated with dominant felsic dikes and/or with mafic dikes represented by diorites or diabases. Diorites and lamprophyres occasionally exhibit transitional compositions from one to another. Lamprophyres share common geochemical characteristics of highly evolved granitoids such as enrichment in K and F, increased abundances of Li, Rb, and Cs and enrichment in some HFSE (e.g. Zr, U, Th, Mo, Sn, W). Lamprophyres in rare metal districts testify to accessibility of the upper crust to mantle products at the time of rare metal mineralization and possible influence of mantle melts or mantle-derived fluids in the differentiation of granitic melts in the lower crust.

3

Wpływ synergizmu wybranych wypełniaczy w smarze na zwiększenie trwałości ślizgowych węzłów maszyn

Krawiec S.

Prace Naukowe Instytutu Konstrukcji i Eksploatacji Maszyn Politechniki Wrocławskiej. Monografie

|

1998

|

Vol. 81, nr 27

138-138

PL

Postawiono hipotezę, że proszki PTFE i miedzi lub PTFE i cyny użyte jako napełniacze smaru plastycznego wywołują w procesie tarcia synergizm przeciwzużyciowy i przeciwzatarciowy, dzięki czemu tworzą wysokoefektywną kompozycję smarową dla stalowych węzłów ślizgowych działających w obszarze tarcia mieszanego. Zbudowano hipotetyczny model smarowania węzłów ślizgowych kompozycjami z napełniaczami o właściwościach synergicznych. Hipotezę tę zweryfikowano w badaniach trybologicznych przeprowadzonych na skojarzeniu stal-stal ze stykiem skoncentrowanym (kulka-kulka, aparat czterokulkowy)i stykiem rozłożonym (panewka-czop, stanowisko modelujące pracę łożyska w ruchu wahadłowym), a także za pomocą wyników analiz kompozycji smarowych i powierzchni warstwy wierzchniej współpracujących skojarzeń. Zbadano wpływ stężenia napełniaczy w smarze na właściwości trybologiczne utworzonej kompozycji. Znaleziono - obliczając minimum objętości funkcji zużycia - ich optymalną (według kryterium minimum zużycia) zawartość w smarze. Wyjaśniono mechanizm synergizmu proszków PTFE i miedzi oraz PTFE i cyny w smarze plastycznym w procesie tarcia, wpływający na zwiększenie trwałości ślizgowych węzłów maszyn.

EN

Recent research results have clearly demonstrated that lower friction and wear at machine interfaces lubricated with greases can only be achieved by modifying them with combinations of fillers rather than with single fillers. Such combinations of additives impart better lubricating properties and are also capable of forming metal-based plating films on interacting surfaces. Both experiments with greases filled with PTFE powders and literature data have pointed out to combinations of PTFE powder and copper or PTFE and tin as candidate modifying compounds due to their synergic effect. The available literature has not dealt yet with the problem of synergism in such pairs of additives as PTFE and copper/tin. Based on physical-chemical properties of PTFE, copper and tin and on particular mechanisms of their lubricating action when used as fillers, a hypothesis was put forward by the present author that the above combinations of additives act as synergic pairs when it comes to wear reduction and seizure prevention at interacting surfaces, especially under mixed -lubrication conditions. In order to test the hypothesis, a variety of formulas were investigated involving PTFE, Cu, Sn and PTFE=Cu (or+Sn) compositions. The tests were carried out under local contact conditions using a standard four-ball apparatus and complying with the Polish Standard PN-76/C04147 ('Testing of lubricating properties of oils and greases'). The investigated grease formulas were compounded with 1, 3, 6 and 9 wt% of the adopted fillers. The results showed clearly that the combined action of modifying agents is greater than the sum of their separate, individual actions. An attempt was made to explain mechanisms underlying the observed phenomena. It was assumed that mechanical load combined with sliding velocity act together to cause PTFE's thermal decomposition and thus to produce decomposition products, mainly tetrafluoroethene C2F4 and a metal-plating layer of copper or tin, being plain or complex compounds of fluorine and copper or fluorine and tin. The proposed theory was verified by later tests in which chemical composition of the surface layers from the interacting balls lubricated with single-filler and double-filler formulas was examined. Additional tests involved residual products left by differential thermal analysis of greases compounded with PTFE+Cu and PTFE+Sn. Yet another goal set by the author was to investigate the effect of filler concentration on tribological properties of grease formulas under discussion. The tests were performed according to the experiment planning theory recommendations using three input variables, i.e. average Hertzian pressure p., sliding velocity v and filler concentration u. The variability ranges were assumed to be: p=2600-4600 MPa, v=0.04-0.68 m/s, u=0.5-11.5 wt%. In order to fully exploit the resulting regression functions showing the effect of filler concentration on wear extent, graphical representations of the functions were used as obtained from the commercial Surfer package intended for generating and analysing 3D surfaces. The experimental results for a concentrated (ball-to-ball) load fully confirmed the synergic effects of the fillers but they were further verified under distributed (test bearing) load conditions. The bearing was made up of a sleeve (40mm both in diameter and length) and a journal performing an oscillatory rotating motion. Such a kind of motion creates the most severe operating conditions from a tribological point of view since sliding velocity becomes zero at dead points. The results from these tests were also a firm confirmation of the filler synergism theory. The presented study can be readily implemented in industrial practice. A commercially applicable formula is proposed for lubricating high-load sliding joints operating under mixed-friction conditions. The formula was developed using the author's own method for evaluating the minimum value of the volume contained below the wear function surface. A patent is going to be issued soon ('A grease for maintaining high breaking down-strength lubricating films') covering both the exact formula and the idea of synergic action of PTFE powder and copper. As regards performance the proposed formula exceeds all grades of greases available on the Polish market. The author gives his recommendations regarding practical aspects of the grease application.