Call number: LD2668 .T4 1959 J64

No description available.

Knowledge of the structural arrangement of the atoms in a solid is an important prerequisite to a detailed understanding of physical and chemical properties. In this work, structural investigations of phosphate (Ca-P-O) and aluminofluorophosphate (Na/Ba-Al-P-O-F) glasses with and without nitridation were performed. Nitrogen was introduced via metal nitrides (AlN, Ba₃N₂, or Ca₃N₂) or ammonia gas treatment of the melt. These glasses were characterized by chemical, thermal and optical techniques. Infrared, Raman, and MASS NMR spectroscopies were used to determine the local coordination and atomic structure of these glasses. The presence of peaks corresponding to P-O-P and PO₂ molecular vibrations in Ca-P-O glasses provided a basis for proposing a calcium metaphosphate glass structure comprised of long chains. As calcium oxide is added to calcium metaphosphate glasses, the long chains are broken up into shorter pyrophosphate units, as indicated by the presence of PO₃²⁻ terminal groups. MASS NMR of Ba-Al-P-O glasses showed that Al occurs as Al(4), Al(6), and either Al(5) or Al(6) linked through Al-O-Al bonds (such as in α-Al₂O₃). The addition of F in both the Ba-Al-P-O-F and Na-Al-P-O-F systems increases the relative abundance of Al(6). The ³¹P peak maxima in the MASS NMR spectra at about -5 to -10 ppm for Ba-Al-P-O-F-N glasses and -9 to -17 for Na-Al-P-O-F-N glass, indicate that pyrophosphate units dominate the structure of these glassy solids. Raman spectroscopy of a series of Al(PO₃)₃-NaF glasses showed that an increase in NaF content causes a shortening of the P-O-P chains and a more disrupted structural network. The presence of P-O-F units were observed only at the higher (>80 mole %) NaF contents. While the complexity of the Raman spectra make it difficult to confirm the presence of P-N bonding, glasses prepared in an ammonia atmosphere (nitrogen content of 1.6 wt%) suggest the possibility of P-N bonding on the basis of a vibrational peak at 826 cm⁻¹.

Surface-plasmon polaritons propagating on thin metal films bounded by dielectrics of nearly equal refractive indexes comprise two bound modes. Calculations indicate that, while the modes are degenerate on thick films, both the real and the imaginary components of the propagation constants for the modes split into two branches on successively thinner films. Considering these non-degenerate modes, the mode exhibiting a symmetric (antisymmetric) transverse profile of the longitudinally polarized electric field component, has propagation constant components both of which increase (decrease) with decreasing film thickness. Theoretical propagation constant eigenvalue (PCE) curves have been plotted which delineate this dependence of both propagation constant components on film thickness. By means of a retroreflecting, hemispherical glass coupler in an attenuated total reflection (ATR) configuration, light of wavelength 632.8 nm coupled to the modes of thin silver films deposited on polished glass substrates. Lorentzian lineshape dips in the plots of reflectance vs. angle of incidence indicate the presence of the plasmon modes. The real and imaginary components of the propagation constraints (i.e., the propagation constant and loss coefficient) were calculated from the angular positions and widths of the ATR resonances recorded. Films of several thicknesses were probed. Results which support the theoretically predicted curves were reported.

No description available.

The aim of this study was to investigate the electrochemical and electrocatalytic properties of a selection of glassy alloys for the hydrogen evolution reaction in base. The glassy alloy compositions tested included the known alloys Fe67Co18B14Si1, Co66Fe4Si16B12Mo2, Fe40Ni40B20 and Fe40Ni40P14B6 and an entirely new alloy Zr74Ti19Cu2Fe5. The electrochemical techniques employed were cyclic voltammetry and slow sweep polarisation. Electrochemical techniques were used in conjunction with the surface analysis techniques of scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS) to gain insight into the morphology and chemical compositions of the electrode surfaces after various treatments. The aims included: 1) To obtain an understanding of the field of electrochemistry of glassy alloys. 2) To develop systems, techniques and procedures to enable the testing of a new alloy to be performed with confidence. 3) To this end, techniques were firstly developed and then compared with published data on the known alloys. Once the handling techniques were satisfactory the new and previously untested Zr74Ti19Cu2Fe5 glassy alloy was characterised, in particular its catalytic properties and its corrosion resistant properties were investigated. The physical properties of the Zr74Ti19Cu2Fe5 alloy are under investigation by another group in the School of Physics. My findings are presented here. The corrosion resistance of the alloys was determined in their as-polished state and after surface pretreatment from slow sweep anodic polarisation studies and cyclic voltammetry. Glassy Fe67Co18Bl4Si1 and Co66Fe4Si16B12Mo2 displayed the poorest corrosion resistance of the alloy compositions tested. The anodic polarisation curve of the Zr74Ti19Cu2Fe5 alloy produced no active region and displayed potentially excellent anticorrosive properties in the basic media which was attributed to highly passivating Zr oxide and Ti oxide surface films. The electrocatalytic activity of the glassy alloys for hydrogen evolution was evaluated in 1MKOH. Cathodic polarisation curves were used to construct Tafel plots from which the kinetic Tafel parameters, i0 and b, were calculated. The least corrosion resistant glassy alloy compositions, Fe67Co18B14Sil and Co66Fe4Si16B12Mo2, displayed the highest catalytic activity for hydrogen evolution in the as-polished state. The most corrosion resistant alloy, Zr74Ti19Cu2Fe5, showed the poorest catalytic activity for the reaction in the as-polished state and only a slight improvement was obtained by increasing the electrolyte temperature in comparison to the other alloys tested. This was again attributed to passivating Zr oxide and Ti oxide surface layers that inhibited the HER. It was found that the Zr-based alloy displayed no substantial advantages over the other glassy alloys or more expensive noble metal surfaces in basic media, unless pre-treated as described in this thesis. The influence of ex situ chemical pretreatment on the electrocataytic activity of the glassy alloys for the HER was determined using pure HF and HF/HNo3 mixtures. Acid pretreatment of glassy C066Fe4SiI6B12M02 and Fe40Ni40Pl4B6 with IM HF/lM HN03 (10 minutes) and Zr74Til9Cu2Fe5 with 1M HF (10 seconds) resulted in a significant improvement in the activity of the alloys in comparison to their as-polished state. SEM/EDS analysis indicated that preferential dissolution of a P-enriched surface region on the Fe40Ni40P14B6 electrode created a porous structure with a greatly enlarged surface area at which the HER could occur. In comparison, the P-free, Fe40Ni40B20, composition displayed a much lower improvement in activity after acid pretreatment with only slight surface roughening observed. The Zr component of glassy Zr74Ti19Cu2Fes was selectively leached by acid pretreatment to produce a porous surface, however, the corrosion resistance of the alloy was also reduced, as indicated from anodic polarisation curve that showed an active and passive region of greater current density than the as-polished electrode. Hence the beneficial effect of acid pretreatment in activating the alloy surface for the HER was countered by a reduction in the general corrosion resistance of the alloy. In view of the dramatic effect on the HER shown by prior ex situ (acidic) oxidation of the glassy alloy surface, the influence of in situ (anodic) oxidation in the basic medium was investigated for comparison. For all the glassy alloy compositions tested, anodic activation was found to be less effective than acidic activation. Anodic pretreatment of glassy Zr74Ti19Cu2Fe5 (3000µA.cm-2) resulted in the greatest improvement in activity in comparison to the as-polished state out of the alloy compositions tested. In addition, the corrosion resistance of the alloy was not reduced by anodic pretreatment and consequently formed a less destructive activation procedure than acidic pretreatment. In this regard, anodic pretreatment would produce a more durable electrocatalyst and is the preferred technique for activating the glassy alloy surfaces for the HER. Initial characterisation of the surface deposits formed by anodic oxidation, using SEM and EDS techniques, indicates that the composition of these deposits and the mechanism by which anodic activation activates the glassy alloy surfaces requires further investigation. / Thesis (M.Sc.)-University of Natal, Durban, 1999.

Ternary transition metal cubic carbides have high hardness and are potential carbides in cemented carbide and cermet tools, as well as hard coatings used to improve metal cutting performance. In the present work, (Ti,Zr)C, (V,Nb)C, and (V,Ta)C ternary cubic carbides were synthesized using traditional powder-metallurgical methods. The effect of synthesis temperature and starting materials on synthesis is investigated, and the microstructure evolution during aging is studied. (Ti,Zr)C was found to decompose into lamellae upon aging at the temperature range from 1150 to 1800 °C. A similar microstructure was observed in (V,Ta)C and (V,Nb)C- 0.5 wt% Fe. All of these structures were found to form through discontinuous precipitation.The grain misorientation distribution of (Ti,Zr)C aged at 1400 °C is investigated. It was found that decomposition tends to occur at high-angle grain boundaries above 25°. The hardness of as-synthesized (Ti,Zr)C powder was found to be 41±6 GPa. Fully decomposed (Ti,Zr)C particles were found to be slightly harder than the undecomposed counterpart. On the other hand, in (V,Nb)C-0.5 wt% Fe, the decomposed structure formed upon aging at 1200 °C was found to have a hardness of 26±2 GPa, which is basically the same as the unaged alloy.Furthermore, the sintering behavior of (Ti,Zr)C with WC-Co is investigated. There are two γ-phases in the final microstructure, one TiC-rich and one ZrC-rich. (Ti,Zr)C was found to decompose at an early stage of sintering, and the final grain size of WC and the two γ-phases was found to be 10% smaller than that in a reference WC-TiC-ZrC-Co composite. / <p>QC 20170529</p>

Previous research on new novel substrates for giant magnoresistance structures has indicated that a net increase in the effect is present. The substrates studied were V-grooved or stepped, however research presented in this thesis used an embossed surface manufactured from alumina oxide which consisted of regular hexagonal arrays with spacing of 110 nm and pore diameter of 60 nm. The physical properties measurements unveiled a net enhancement of the giant magnetoresistance effect thru the whole range of the copper spacer thicknesses deposited with direct current magnetron sputter. The maximum net increase appeared for a spacer thickness of 4.0 nm where the flat silicon substrate yielded a 3 % increase but the embossed surface substrate generated a 12% increase with an overall effect of a 4-fold net enhancement of the effect. Both the aluminum oxide substrates and the thin films structures can be manufactured inexpensively and can be also mass-produced, which are welcoming advantages for the technology sector of magnetic sensing.

If one of the two poles will trip for some reasons in a regular bipolar HVDC transmission without a return conductor, it is necessary to block the other pole temporarily during the transition to a monopolar operation with metallic return, this procedure will take 1-2 seconds and will affect the connected AC networks by extra disturbances. The object of this survey has been to answer the question if it is possible to have a balanced bipolar transmission without a return conductor and during a trip of one pole control it as an HVDC transmission with series connected converters by adding the by-pass switches and the logic for a series connected HVDC converter system which means that a shutdown of the transferred power during the transition phases is not necessary. The survey has been performed with the software PSCAD where an already existing series connected converter circuit had been modified to a bipolar system and the control logic for the transition phases has been created. There were some problems with various control signals between the software HiDraw and PSCAD, this was solved by different methods and the result shows that it is possible to have a transition between bipolar operation and monopolar operation with metallic return without the need to totally shut down the power transfer completely. But this requires a large capacitor.

I dagens industri utsätts verktyg vid plåtformning för allt större krafter. Material som ska formas blir starkare behövs också större krafter för at åstadkomma en geometrisk förändring. Detta har medfört att nötningseffekter vid tillverkning har ökat, och ett av dessa problem är galling. Galling, som är ett av huvudproblemen, är en nötningseffekt på verktygen där både adhesiv och abrasiv nötning förekommer. Detta innebär att material lossnar från värdmaterialet och fastnar på verktyget. Då material har överförts till verktyget har det inte längre ursprungsformen och kan leda till ojämnheter i materialet som ska formas. Hittills har företag använt sig av smörjmedel för att minska galling. Eftersom smörjmedel regleras allt hårdare av miljöskäl, måste industrin hitta nya lösningar. En lösning är att skapa verktygsstål som är motståndskraftiga mot galling genom sin mikrostruktur. Det finns fortfarande begränsad kunskap inom området och den här studien syftar till att jämföra två verktygsstål för att avgöra vilket som är mest beständigt mot galling. Verktygsstålen Caldie och Vancron Superclean kommer glida mot materialen DP600 och DP1000. De sistnämnda är de material som formas vid plåtformningen. Där materialen har olika sträckgränser, detta för att se om den har en inverkan vid plåtformning. För att avgöra vilket verktygsstål som är mest lämpligt vid plåtformning kommer en glidsträcka tas fram med hjälp av SOFS metoden. Glidsträckan kommer att ange hur snabbt galling uppstår och således kan ett bättre material bestämmas. Nötningsspåren hos materialen analyserades med hjälp av ett elektronmikroskop för att se hur galling hade påverkat verktygsstål och ytmaterial.Resultatet visade att Vancron Superclean var mer beständigt mot galling, då verktygsstålen gled över DP600, medan ingen slutsats kunde dras när de gled över DP1000. / In today's industry, tools are more exposed to larger forces in sheet metal forming. As materials become stronger, larger forces are also needed to achieve a geometric change of the materials. Because of this, abrasion effects in the processes have increased and one of the most common one is galling. Galling is a form of wear where both adhesive and abrasive wear occur. This means that material comes off of the host material and sticks to the tool. When material has been transferred to the tool, it no longer has the original shape and can lead to irregularities in the material to be formed. So far companies have used lubricants to minimize it. As lubricants are increasingly regulated for environmental reasons, the industry must find other solutions to the problem. One solution is to create materials that are resistant to galling through their microstructure. There is still limited knowledge in this area and the aim of this study is to compare two tool steels and investigate which of them is most resistant to galling. The tool steel Caldie and Vancron Superclean will be tested against the materials DP600 and DP1000 usually used in sheet metal forming. Where the materials have different yield strengths, this is to see if it has an impact on sheet metal forming. To decide which tool steel is most suitable for sheet metal forming, a sliding test will be produced using the SOFS method. The sliding distance will describe how quickly galling occurs and thus the better material is determined. The abrasive traces of the materials were analyzed using an electron microscope to see how galling affected the tool steel and surface material.The result showed that the Vancron Superclean was more resistant to galling, as the tool steel slid over the DP600, while no conclusion could be drawn when slipping over DP1000.