Non-Ferrous Metallurgy Department of the Ural Federal University celebrates its 90th anniversary

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Desain pin hole mempengaruhi kuat rekat geser gigitiruan jembatan adesif Pin hole design affect shear bond strength of adhesive bridge

To overcome the failure of adhesive bridge due to release of the adhesive bond cement between teeth and metal,preparation modification was performed with a pin hole in the teeth cingulum. This study aimed to determine the effectof thread on a pin hole to shear strength adhesion of adhesive bridge. Forty maxillary incisors were prepared at theirpalatinal surfaces 0.3 mm thick, and were divided into four treatments (threaded hole+threaded pin, threaded holes+non-threaded pin, non-threaded holes+threaded pin, non-threaded holes+non-threaded pin). Casted-plates made fromnickel chromium alloy were cemented to the palatal surface of the tooth with adhesive cement (Panavia TMF 2.0), andthen adhesion shear strength tested. The test and evaluation of the residual cement on the surface were performed inLaboratory Metallurgy, Department of Engineering ITB. Data were analyzed by one-way ANOVA test (p=0.05).Adhesion shear strength of plate with threaded holes+threaded pin has the highest retention. Residual cement onthreaded hole+threaded pin plates similar to threaded hole+non-threaded pin, but more than any other groups. theconclusions were, the adhesion shear strength depends on the design of pin hole. The wider surface of cementremaining on the plates, the greater adhesion shear strength.

Conversaziones and Receptions, 1964

THE conversazione held on 9 July to mark the quater-centenary of the birth of Galileo is described on page 119. The usual conversaziones were held on 7 May and 22 October at which the following exhibits were shown. The strength and fracture of metals was the subject of three exhibits. It is known that the strength of metals is far below its theoretical limit due to the presence of dislocations in the crystal structure. All strengthening processes introduce barriers to dislocation movement but many of these reduce ductility and make metals brittle. The British Iron and Steel Research Association demonstrated how modern physical metallurgical research is indicating new ways in which steel can be strengthened without impairment of ductility or toughness. Miss J. M. Silcock of the Central Electricity Research Laboratories and Mr W. J. Tunstall of the Cavendish Laboratory arranged an exhibit showing stacking fault precipitation in austenitic stainless steels. Electron microscopy has shown that stacking faults appear and grow during the precipitation of carbides in certain austenitic steels. Systematic observations coupled with new calculations have established the nature of the associated partial dislocations and have led to the conclusion that the faults are extrinsic. The Chemistry, Physics and Metallurgy Department of the Royal Aircraft Establishment arranged an exhibit on the fracture of metals. Various forms of fracture were exhibited and research observations and tentative conclusions of the causes of fracture were made known.

Iron of high purity

During the past eleven years (1925-35) several equilibrium diagrams involving iron as one of the components have been investigated at the National Physical Laboratory. The provision of the numerous alloys required for these researches has necessitated the production of quantities of high purity iron. Tritton and Hanson, when they began work on the iron-oxygen system at the National physical Laboratory, considered that the best commercial iron then obtainable was unsuitable for their work, and in the period 1922-24 prepared iron electronically according to the method of Cain, Schram, and Cleaves. At first the present authors produced iron in a somewhat similar manner, but when improvements in analytical methods revealed impurities in samples originally considered satisfactory, alterations were made in the method of preparation. Comprehensive analyses indicate that the latent batch of iron prepared the authors is very low in impurities, yet the physical properties of this material suggest that some disturbing factor may still be present. The problem is apparently complex and a rapid solution appears unlikely In these circumstances it was thought that the present publication of data concerning several batches of iron prepared at the National Physical Laboratory would serve a useful purpose. In addition to information obtained by the authors, particulars of a batch of iron prepared by Mr. W. E. Prytherch, M. Sc., also of the Metallurgy Department, N. P. L., are included, together with occasional results obtained by older members of tde staff. The results of Tritton and Hanson ( loc. cit .) are omitted, how-ever, as these have already been published.

Australites

IN 1917 Professor E. S. Moore, of the School of Mines, Chicago, U.S.A., kindly sent me a photograph together with this note: “I am sending you a photograph of something which may illustrate your bubbles on the australites. Mr. Dudley of the Metallurgy Department was working with a small crucible containing slags and by accident a drop of water fell on the surface, with the result that a bubble was developed, such as you see in the photograph. The photograph is not a very good one; but it will show you what I mean.

The metallography of solid mercury and amalgams

During the last three years an investigation into the properties of dental alloys and the phenomenon of setting of amalgams has been in progress in the Metallurgy Department of the National Physical Laboratory on behalf of the Dental Investigation Committee of the Department of Scientific and Industrial Research, and with the aid of funds provided by the Dental Board of the United Kingdom. This investigation has been concerned chiefly with a study of the ternary amalgams of silver, tin and mercury, which are the basis of amalgams used as filling materials in dental practice. Owing to the absence of any recorded systematic survey, it became necessary to examine the constitution of the amalgams over the whole range of composition from 0 to 100 per cent, mercury. For this purpose it was desired to determine the microstructure of pure mercury and the dilute amalgams, in addition to those which, containing smaller percentages of mercury, are completely solid at ordinary temperatures. The melting point of pure mercury is — 38 • 85° C. In all series of amalgams, that is, alloys of mercury with other metals, therefore, the alloys within certain ranges of composition are completely or partially molten at normal temperatures. As a consequence, the investigation of the constitution in the solid state of the whole of an alloy system in which one of the components is mercury requires the application of a technique developed with particular reference to the characteristic properties of this metal.