Showing papers in "Journal of Materials Science Letters in 1988"

Composition dependence of tensile yield stress in filled polymers

Abstract: Examen de divers polymeres: ABS, polypropylene, polyethylene et diverses charges: verre, CaCO 3 , talc, silice, etc

Decagonal quasicrystals with different periodicities along the tenfold axis in rapidly solidified Al65Cu20M15 (M = Mn, Fe, Co or Ni)

Abstract: Presentation des resultats par microscopie electronique en transmission et diffraction electronique a aire selectionnee ou en faisceau convergent

Impedance measurements on cement paste

Abstract: Les mesures sont faites pendant le durcissement du ciment apres 1, 14 ou 25 fours d'hydratation; on etudie l'influence de la frequence

New quasicrystals in Al65Cu20M15 (M = Cr, Mn or Fe) systems prepared by rapid solidification

Abstract: Analyse par diffraction RX et microscopie electronique en transmission de la structure des quasicristaux Al 65 Cu 20 M 15 fabriques par filage depuis l'etat liquide. Determination de leur stabilite thermique et de leur conductivite electrique entre 0 et 300 K

Toxicity of silicon carbide whiskers

Abstract: There is growing interest in the use of ceramic materials, such as A1203, Si3N 4 and SiC in the form of whiskers for the reinforcement of ceramics and metals [1 3]. Epidemiological studies have established that exposure to certain fibrous minerals of natural occurrence is associated with increased incidence of mesothelioma a malignant tumour of the pleural or peritoneal cavity. Studies in experimental animals have shown that carcinogenicity (or at least the ability to induce mesothelioma) is restricted to long (> 10 #m), thin ( < 1 ~tm diameter) fibres and is relatively independent of chemical nature, providing the fibres are durable in the body (e.g. [4, 5]). Many whisker products consist of, or contain, fibres in the sub-micrometre diameter range and some have been shown to produce tumours in experimental animals [6]. We have prepared sub-micrometre diameter SiC whiskers by the carbo-thermic reduction of SiO2 and subjected this material to an in vitro cell culture test in which the response correlates well with the results of injection or implantation studies in animals [7]. A comparison has been made with crocidolite (blue) asbestos, which is well established as a causative agent for mesothetioma in human populations. The cellular response to the SiC whiskers is of the same order as crocidolite suggesting that in the absence of any additional information, such whiskers should be considered as potentially carcinogenic with appropriate handling precautions applied. A whisker-containing product of the carbo-thermic reaction (Fig. 1) contained a proportion of nonfibrous materials. The diameter range of the fibrous component is shown in Fig. 2 and no attempt to separate fibrous from non-fibrous material was made. The presence of free silica can lead to confusing results in the in vitro cell tests used and to avoid this the material was extracted with hot aqueous NaOH and washed in distilled water prior to use in the test. X-ray examination showed the SiC preparation to consist of highly crystalline cubic/?-SIC together with a minor amount of hexagonal c~-SiC and traces of mullite and corundum (A1203) from contamination by the crucible. The cell culture test has been previously described [8] and its specificity in terms of fibre size has been established [9]. Survival of V79-4 Chinese hamster lung cells was determined by cloning efficiency from a single-cell suspension. Cell suspension (20ml) was added to the appropriate quantity of test fibre in I ml of physiological saline in a sterile McCartney bottle. Aliquots of this suspension were seeded into 60-mm diameter plastic Petri dishes and the surviving cells allowed to grow and form colonies for 5 to 6 days. Colonies were then washed with physiological saline

Ductile Al-Ni-Zr amorphous alloys with high mechanical strength

Abstract: Determination du domaine de composition entre 5 et 50% at Ni, 0 a 25% at Zr dans lequel les alliages amorphes Al−Ni−Zr sont ductiles. Influence de la composition sur la temperature et la chaleur de cristallisation, sur la resistance a la traction statique sur le module d'Young, sur la durete Vickers et sur la ductilite de flexion

On the determination of Weibull parameters

Abstract: La fonction de distribution cumulative de Weibull est utilisee pour decrire la tenacite. On applique les facteurs de poids dans les analyses de regression lineaire d'une equation type et on verifie avec la methode Monte Carlo

Percolation phenomena in polymer/carbon composites

Abstract: Etude systematique de la percolation dans les proprietes electriques et dielectriques de polyester, PVC, polycarbonate renfermant du noir de carbone

Elastic properties of binary, ternary and quaternary rare earth tellurite glasses

Abstract: Glasses containing rare earth ions in high concentration are potentially useful for optical data transmission or in laser systems. Tellurite glasses are also of technical interest because of their low melting points and absence of the hygroscopic properties which limit application of phosphate and borate glasses. They have moderately large refractive indices and dielectric constants and are good infrared transmitters for wavelengths up to 5 #m. One aim of the present work has been to attempt to make a number of different glasses, based on tellurite as the principal former, which contain substantial quantities of rare earth ions. Binary, ternary and quaternary glasses have been prepared, most being from glass systems which previously have been examined scantily or not at all. Earlier studies of the effect of incorporating rare earth cations on the structure and physical properties of tellurite glasses include those in the binary TeO2La203 system [1] and also in the [1 - (2x + 0.05)] TeO2" xFe203" (x + 0.05)Ln203 system, where x = 0 and 0.05 and Ln was lanthanum, neodymium, samarium, europium or gadolinium and measurements of the M6ssbauer effect, infrared spectra and electrical conductivity were made [2]. Glass formation in the quarternary Er203-WO3-TeO2-PbO-TeO2 system has been established [3]. Interest in erbiumcontaining tellurite glasses developed because the photochromic properties of erbium-doped tellurite glasses are substantially more pronounced than those of silicate glasses containing an equivalent erbium-ion concentration [4]. To study the elastic properties of the rare earth tellurite glasses prepared here, measurements have been made of the velocity of ultrasonic waves propagated through them. The vibrational anharmonicity associated with these long wavelength acoustic modes has been investigated by measurements of the effects of hydrostatic pressure on the ultrasonic wave velocities. Previous studies of the elastic behaviour of vitreous TeO2 itself [5], binary TeO2-WO3 and TeO2ZnCI2 glasses [6] and the ternary (TeOz)0.5(PbO)0.2(WO3)0.3 and (TeO2)0.75(PbO)0.zl(La203)0.04 glasses [7, 8] have led to the general conclusion that tellurite glasses show normal behaviour in that they stiffen as the pressure is increased or the temperature is decreased. Now we can include in the overall picture the way in which the presence of substantial high concentrations of rare earth ions influences the elastic behaviour of tellurite glasses.

A Raman spectral characterization of various crystalline mixtures in the ZrO2-TiO2 and HfO2-TiO2 systems

Abstract: ZrTiO 4 can be used as a dielectric resonator material in microwave devices [1]. Since HfTiO4 is isostructural to ZrTiO4, it may also be used in electrical application similar to those of ZrTiO4. Furthermore, because the coefficient of thermal expansion is low for HfO2-TiO~ ceramics whose HfO2 concentration is greater than 50 tool %, hafnium titanates have potentially useful refractory applications [2-4]. The isostructural high-temperature phases of ZrTiO4 and Hf-l'iO4 belong to the space group PbcnD~ 4 with two formula units per unit cell [2, 5]. Both titanium and zirconium atoms are randomly distributed on equivalent crystal sites. Phase diagrams have been reported for both the ZrO2-TiO2 system and the HfOz-TiO2 system [4-7]. These two titanate systems are very similar except that phase equilibrium is more difficult to achieve in the HfO2-TiO2 system. This condition is especially true in the region between approximately 10 and 30mol % TiO2 [7]. This letter will investigate the comparative structural changes that occur in materials prepared at various high temperatures with air-quenching for the ZrO2-TiO2 and the HfO2-TiO2 systems, using Raman spectroscopy. Structural/spectral effects due to nonequilibrium behaviour in the HfO2-TiO2 system will also be discussed. Samples containing the desired oxide compositions were prepared by a coprecipitation method from aqueous solutions containing the appropriate concentrations of the metal chlorides. The Ti(IV) ioncontaining solutions were prepared by mixing ice-cold TIC14 and deionized water. The resulting solutions had to be used immediately or kept refrigerated to prevent spontaneous hydrolysis of the solution to titania. The titanium- and zirconium/hafnium-containing solutions were then mixed. The solid products were precipitated using ammonium hydroxide. Most of the resulting precipitates were fired in platinum crucibles for 6h at approximately 1650°C, and were then airquenched to room temperature. Portions of the 75 mol % HFO2-25 mol % TiO2 precipitate were also fired at 1000°C for 20h, at 1300°C for 6h, and at 1390 ° C for 10 h. The crystalline products were analysed by wet chemical analysis to verify their ZrO2/HfO2 and TiO2 contents. Powder X-ray diffraction patterns were measured for the quenched samples at room temperature with an X-ray diffractometer using CuKc~ radiation and a graphite monochromator. The observed d-spacings and relative intensities were compared with literature values reported for monoclinic ZrO2, monoclinic HfO 2, TiO 2 (rutile), HfTiO4 and ZrTiO4 [8-12]. Scanning electron micrographs were obtained in the backscatter mode. Raman spectra were measured for the powdered polycrystalline samples using a double-grating spectrometer with an argon ion laser an an excitation source. Scattered radiation was collected at 90 ° to the direction of the incident beam. Samples were sealed in capillary tubes for the spectral measurement, and their spectra were obtained at room temperature. The instrument was calibrated with distilled indene, and the bands were reproducible to + 1 cm J. Infrared absorption spectra were measured using a dispersive double-beam infrared spectrophotometer with an airpurging device. These spectra were obtained at room temperature using KBr pellets. The powder X-ray diffraction data for all crystalline mixtures in the ZrO2-TiO2 system that were prepared by firing the samples at 1650°C clearly show the progressive development of the ZrTiO4 phase as one approaches the composition containing 50mo1% TiO2. The second phase in the non-stoichiometric compositions is either TiO 2 (rutile) or monoclinic ZrO2 depending upon the compositional concentrations. Solid-solution behaviour is noted from the X-ray diffraction pattern both ofZrO 2 in the prepared sample containing 75 tool % ZrO2 and of TiO 2 in the prepared sample containing 25 mol % ZrO2. Shifts are noted in their d-spacings with respect to those of pure ZrO2 and TiO2. This trend is consistent with observations made from the phase diagram that zirconium

Monazite-like phases containing transuranium elements (neptunium and plutonium)

Abstract: It is well k n o w n tha t the t r a n s u r a n i u m e lements nept u n i u m , p l u t o n i u m , a m e r i c i u m a n d c u r i u m are the m a j o r l o n g t e r m c o n t r i b u t o r s to n u c l e a r waste s torage p rob lems . The halfl ives o f the i so topes (e.g. 237Np, Tl/2 = 2.14 x 106 years) d ic ta te tha t the " i s o l a t i o n sys t em" m u s t be capab le o f m a i n t a i n i n g the waste in tegr i ty for t imes as l ong as 106 years. In 1978, it was s h o w n [1] tha t some o f the c u r r e n t n u c l e a r was t e fo rms w o u l d be u n s t a b l e u n d e r h y d r o t he rma l c o n d i t i o n s tha t m i g h t be e n c o u n t e r e d in deep geologic reposi tor ies , e.g. a n increase in the leachab i l i ty o f h igh ly d a n g e r o u s isotopes. Thus , there is a g r o w i n g in teres t in the d e v e l o p m e n t o f a l t e rna te types o f p r i m a r y rad ioac t ive waste c o n t a i n m e n t [2]. The synthe t ic m o n a z i t e s are a po t en t i a l hos t for the l o n g t e r m s torage o f a -ac t ive t r a n s u r a n i u m wastes [3, 4] because o f (i) the i r l o n g t e r m s tabi l i ty observed u n d e r va r ious geological cond i t i ons [5], (ii) their abil i ty, in na tu re , to i n c o r p o r a t e t h o r i u m a n d u r a n i u m in large a m o u n t s w i t h o u t los ing apprec i ab le quan t i t i e s o f these two e lements [6-8], a n d (iii) their u n u s u a l resistance to a r a d i a t i o n d a m a g e [9, 10] wh ich o n o the r m i n e r a l s leads to the m e t a m i c t state. The re is a m p l e ev idence t ha t tria n d t e t r ava l en t t r a n s u r a n i u m ions can be i n c o r p o r a t e d i n to t e rna ry oxides [11, 12]. The p re sen t w o r k is c o n c e r n e d wi th the c rys t a l lochemica l p r o b l e m s e n c o u n t e r e d in phos phates , specifically the i n c o r p o r a t i o n o f N p ( I V ) a n d P u ( I V ) ions in to the m o n a z i t e s t ruc ture . T h e t r iva l en t p l u t o n i u m [13], a m e r i c i u m [14] a n d c u r i u m [15] o r tho p h o s p h a t e s are k n o w n . Recent ly , it was f o u n d tha t the va lence s ta te o f n e p t u n i u m a n d p l u t o n i u m d o p e d in to LaPO4 single crystals was IV [16]. Howeve r , experim en t a l resul ts i nd ica ted tha t Ce( IV) cou ld n o t be

Sintering of lanthanum chromite doped with zinc or copper

Abstract: La substitution de Zn ou Cu a Cr dans LaCrO 3 permet l'obtention de ceramiques denses sans controle de la pression d'oxygene lors du frittage

The critical time and critical cooling rate of non-equilibrium grain-boundary segregations

Abstract: Analyse, par autoradiographie par traceur des particules, de la segregation du bore dans l'alliage Fe-30% Ni contenant 0,0010% B, soumis a une trempe a 1050 C pour des durees comprises entre 3 et 80 secondes

Raman study of the formation of transition alumina single crystal from protonic β/β″ aluminas

Abstract: Transition aluminas are usually obtained by thermal treatment of aluminium hydroxides between 450 and 1000 ° C. X-ray diffraction [1] but also IR spectroscopy [2] have been used to characterize the various phases (7, 0, &, x . . . ) occurring before crystallization in corundum (e-alumina). However, samples prepared this way are in the form of small crystallites and, aluminium oxides being poor scatterers, the use of Raman scattering was not successful. In previous work [3, 4], we have shown by X-ray diffraction and electron paramagnetic resonance how a protonic /3 (or /3") alumina single crystal can be transformed by heating into an e-alumina oriented polycrystal through the formation of a transition alumina single crystal. To our knowledge, this is the unique method to prepare easily large single crystals (a few tens of mm 2) of transition aluminas. These crystals are suitable for special studies, such as those of surface properties. The structure of/?-alumina consists in spinel blocks separated by a loosely packed plane where conducting iotas diffuse rapidly. The bridging between spinel blocks is made by two tetrahedra sharing the same oxygen ion. The difference between/3 and/?" phases resides in the nature of the conducting plane: only in the /3 phase is there a mirror plane from a crystallographic point of view. A protonic/?-alumina single crystal with composition equal to 1.25M20 • 11A1203 (M + = NH4 + or H+(H20),) is transformed above 400°C into a stoichiometric/?-alumina single crystal (composition close to (I-I30)20 • 1 IA1203). This transformation takes place from the reaction of interstitial oxygens ensuring the charge compensation mechanism, with the protons liberated by the desolvation of protonic ions [5-7]. Further heating above 800°C involves the diffusion of the remaining protons in the spinel blocks where they are trapped, Stacking faults are created by the collapse of some loosely packed conducting planes in between the spinel blocks. The samples remain in the form of single crystals; the /3-alumina unit cell is multiplied by three or even six along the a direction of the hexagonal plane (Fig. 1), whereas complex superstructures and diffusions are observed along the c direction [7]. Finally a topotactic growth of e-alumina crystallites is observed above 1100 ° C [4, 7, 8]. Similar transformations are observed for ion-rich /?and fl"-alumina single crystals with composition close to Allo.33Mgo.66017M1.66 (M = NH2, H+(H20)~). However, due to the new charge compensation mechanism (Mg2+/A13+ ion substitution) the stoichiometric form is not obtained and stacking faults occur at lower temperature with a drastic collapse of spinel blocks, above 320 and 400°C for ion-rich/3 and/3" phase, respectively [9]. A transition alumina phase with spinel-like structure is formed. Above 670°C syntactic nucleation of nonstoichiometric spinel occurs [9, 10]. Finally, separation into e-alumina and MgAI204 spinel is observed above 1000°C [10]. This quasi-continuous evolution of relatively well-ordered spinel-like structures into disordered ones provides a good opportunity to state the vibrational fingerprinting evolution of spinel-like materials. However, such structures are found for many solid-state reactions in ceramics (e.g. mullite

The Preparation of Titanium Nitride and Titanium Carbonitride by the Preceramic Polymer Route

Abstract: : The pyrolysis of selected titanium amides in a stream of ammonia gives titanium nitride. In a stream of argon titanium carbonitride is produced. We have developed useful routes for the preparation of silicon and boron carbonitrides and nitrides by the pyrolysis of suitable polymeric precursors, and we were interested in developing such an approach for the synthesis of titanium carbonitride and nitride. Keywords: Titanium nitride, Titanium carbonitride, Titanium amides, Ceramics.