Search

In the present work, the mechanical properties and erosion-resistance ability of hot-pressed and pressureless sintered slag α-sialon ceramics, which were started from slag α-sialon powders prepared by SHS technique based on slag powders, [J. Mater. Chem. 12 (2002) 1199] were measured. The hardness and toughness of pressureless sintered slag α-sialon samples reached 15.53 GPa and 4.72 MPam 1/2 respectively. The strength of hot-pressed slag α-sialon ceramics reached 599 MPa as well. In comparison with Al 2 O 3 and ZrO 2 ceramics, as-sintered slag α-sialon ceramics showed much higher erosion-resistance ability. These properties are very close to that of normal α-sialon ceramics prepared by expensive chemical agents as raw materials.

The synthesis of Ce α-Sialon powder by self-propagating high-temperature synthesis (SHS) and the sintering behaviors of Ce α-Sialon material by hot-pressing derived from SHS-ed powder with the addition of CeO 2 or Y 2 O 3 were performed in the present work. The results have shown that the phase assemblages of synthesized Ce α-Sialon powder consisted of β-Sialon, as the major crystalline phase, and small amount of α-Sialon, Ce 2 Si 6 O 3 N 8 and AlN-polytypoid. Ce α-Sialon phase was meta-stable and would decompose to β-Sialon and JEM phase [Ce(Si 6− z Al z )(N 10− z O z , z ≈1)] with the disappearance of Ce 2 Si 6 O 3 N 8 and AlN-polytypoid after hot-pressing. The addition of CeO 2 further encouraged the transformation of Ce α-Sialon phase, but the addition of Y 2 O 3 did stabilize the Ce α-Sialon structure and (Ce,Y) α-Sialon phase would be as the major crystalline phase in the sintered material when 0.375 molar Y 2 O 3 was added, in which most α-Sialon grains having elongated morphology were observed. As a result, the hardness (H v ) and fracture toughness (K IC ) of sintered (Ce,Y) α-Sialon material being 15.23 GPa and 4.90 MPa m 1/2 respectively were obtained.

By hot pressing at 1800 °C for 2 h and heat treatment at 1700 °C for 20 h, infrared transmittance of Y- and Dy-α-sialon, (Y1017 and Dy1017, corresponding to m =1, n =1.7; Y2010 and Dy2010, corresponding to m =2.0, n =1.0), according to formula M m /3 Si 12−( m + n ) Al m + n O n N 16- n , in 1500–4000 cm −1 (6.6–2.5 μm) were studied. The results showed that the infrared transmittance of around 45% and 50% could be obtained for hot-pressed Y2010/Dy2010 and Y1017/Dy1017 samples respectively in 0.5 mm thickness in the range of 2000–3300 cm −1 . The higher optical transmittance values of Y1017/Dy1017 than that of Y2010/Dy2010 were mainly resulted from the fact that the phase assemblage of Y1017/Dy1017 consisted of only crystallized α-sialon phase and small amount of melilite phase was formed for Y2010/Dy2010. The heat treatment encouraged the grain growth of α-sialon. Optical transmittances of Y1017/Dy1017 slightly decreased after heat treatment however, especially for Dy1017, which is mainly due to the formation of a small amount of garnet phase. Whereas, the optical transmittance of Y2010/Dy2010 increased from 45% to 55% as a result of α-sialon growing up and intergranular glassy phase moving. The results indicated that a suitable composition to avoid the formation of the second crystalline phase after heat treatment is important to make α-sialon materials with good optical properties.

Oxygen isotopic compositions of silicate inclusions in IVA iron meteorites have been measured with an in situ UV laser microprobe technique. The homogeneity of oxygen isotopic compositions within and among individual mineral grains has also been examined. Oxygen isotope fractionations between coexisting mineral pairs were utilized in oxygen isotope thermometry. Our measured Δ17O values, ranging from 0.97 to 1.25‰, are characteristic of a single reservoir and fully confirm the oxygen isotopic similarity between IVA irons and L/LL chondrites. Steinbach and Sao Joao Nepomuceno, containing inclusions of two silicate minerals in mutual contact, exhibit a mass-dependent fractionation of 18O/16O between tridymite and bronzite with apparent oxygen isotopic heterogeneity. The SiO2-bearing member, Gibeon, gives homogeneous oxygen isotopic compositions without detectable fractionation of 18O/16O between tridymite and quartz. Oxygen isotope equilibrium temperatures are estimated for coexisting tridymite and bronzite in the same sample slabs or clusters in Steinbach and Sao Joao Nepomuceno. The fractionations of 18O/16O between bronzite and tridymite range from 1.6 to 2.3‰ in different sample slabs or clusters. On the basis of the closure temperature concept, cooling rates are estimated at approximately 20 to 1000°C/Myr between 800 and 1000°C, a range of temperatures not accessible to other cooling rate methods. Using the Fast Grain Boundary diffusion model, we have demonstrated that significant oxygen heterogeneity both in tridymite and bronzite is probably due to isotope exchange during cooling between minerals with various grain sizes and mineral abundances in different regions of the samples. The new estimates of cooling rate by oxygen isotope thermometry refine previous cooling curves of IVA irons and support the breakup-reassembly model for the IVA parent body.

(Ca,Mg)-α-sialon powders were previously [J. Mater. Chem. 12 (2002) 1199] prepared by Self-propagating high-temperature synthesis (SHS) technology using slag as a raw material (abbreviated as Slag α-sialon powder). In this study, phase assemblages of the Slag α-sialon samples hot-pressed from 1450 to 1700 °C were investigated. Results indicated that α-sialon was the main crystalline phase in the whole sintering process, however, a small amount of β-sialon appeared in the samples sintered at 1500 °C and above. In addition, the SHS technique was also used to prepare α-sialon powders using chemical agents as raw materials (named Chem α-sialon). Samples made from the Chem α-sialon powder were hot-pressed under the same conditions for a comparison. Similar phase assemblages were obtained for the samples starting from Chem α-sialon powders, except for even more amount of βsialon phase contained. Material with a single α-sialon phase could be got in both samples when 10 wt.% additional slag and CaCO 3 were introduced into the Slag α-sialon and Chem α-sialon starting powders respectively.

Textured bismuth titanate (Bi 4 Ti 3 O 12 ) ceramics were fabricated by templated grain growth (TGG), using plate-like Bi 4 Ti 3 O 12 particles prepared by a molten salt method as the templates. The templates were aligned in the fine-grained matrix by aqueous tape casting with their major surface parallel to the casting plane. Effect of sintering conditions on the grain orientation in the material was investigated. It was found that the degree of grain orientation (Lotgering factor, f ) increased with the increase in sintering temperature, soaking time and heating rate. High Lotgering factor ( f ⩾0.92) can be obtained through careful control of the sintering parameters. The textured Bi 4 Ti 3 O 12 ceramics showed a high anisotropy in its dielectric properties in the directions parallel and perpendicular to the casting plane.

A laser fluorination microprobe system has been constructed for high-accuracy, high-precision multisulfur isotope analysis with improved spatial resolution. The system uses two lasers: (a) a KrF excimer laser for in situ spot analysis by ultraviolet (UV) photoablation with λ = 248 nm and (b) a CO2 laser for whole-grain analysis of powdered samples by infrared heating at λ = 10.6 μm. A CO2 laser is necessary for the analysis of interlaboratory isotope reference materials because they are supplied as powders. The δ34S and δ33S compositions of reference materials measured with a CO2 laser fluorination system agree (±0.2‰, 1σ) with the recommended values by the Sulfur Isotope Working Group of the International Atomic Energy Agency Ding et al 2001 , Taylor . The precision of replicate analyses of powdered sulfide minerals with the CO2 laser is typically ±0.2‰ (1σ) for δ34S. The in situ fluorination of sulfides with a KrF excimer laser (λ = 248 nm) was validated by comparison of measurements of side-by-side laser craters and powders excavated from drill holes. Powders from drill holes were analyzed with the CO2 laser. In situ laser craters and drill hole powders give the same δ34SV-CDT and δ33SV-CDT values within 0.2‰. The δ34SV-CDT and δ33SV-CDT values of both powders and in situ analyses are independent of F2 gas pressure over a range of 15 to 65 torr. No dependence of δ34SV-CDT and δ33SV-CDT values on UV laser energy fluence has been observed. Mineral-specific fractionation of sulfur isotopes in analyzing pyrite, sphalerite, galena, troilite, and chalcopyrite has not been observed with a KrF excimer laser (λ = 248 nm). Test analyses with an ArF excimer laser (λ = 193 nm), however, gave fractionated sulfur isotope ratios. A range of Δ33S anomalies of from – 1.5 to +3.0‰ in Archean samples from the North Pole district, Pilbara Craton, Australia, and from black shale of the Lokamonna Formation, South Africa, were verified by in situ analysis of individual pyrite grains with a KrF excimer laser. These results show that a combination of high-accuracy, high-precision analyses with improved spatial resolution permits locating and analyzing host minerals of non-mass-dependent sulfur isotope anomalies.

Bismuth titanate (Bi 4 Ti 3 O 12 ) platelets were obtained by the molten salt synthesis method in NaCl–KCl and Na 2 SO 4 –K 2 SO 4 fluxes, using an amorphous Bi 4 Ti 3 O 12 precursor and a mechanically mixed Bi 2 O 3 –TiO 2 mixture as the starting materials. It was found that the synthesizing temperature, salt species and starting materials could significantly affect the crystallization habit and morphology of Bi 4 Ti 3 O 12 platelets. Under the same processing conditions (i.e. in Na 2 SO 4 –K 2 SO 4 flux at 1000 °C), the Bi 4 Ti 3 O 12 platelets synthesized from the Bi 2 O 3 –TiO 2 mixture generally showed a smaller particle size than those synthesized using the amorphous Bi 4 Ti 3 O 12 precursor. The Bi 4 Ti 3 O 12 platelets prepared in the chloride flux were faceted along either (0 0 1) or (1 1 2) planes, while those prepared in the sulfate flux were solely (0 0 1) faceted. The former system also had smaller particle size than the latter. Furthermore, the salt content and the addition of plate-like Bi 4 Ti 3 O 12 seeds in the amorphous Bi 4 Ti 3 O 12 precursor showed a strong influence on the particle size of the synthesized Bi 4 Ti 3 O 12 platelets. The particle size of Bi 4 Ti 3 O 12 platelets prepared in the sulfate flux decreased as the mole ratio of the sulfate salts to Bi 4 Ti 3 O 12 was increased from 7.9 to 23.7. And the addition of 10 wt.% plate-like Bi 4 Ti 3 O 12 seeds into the amorphous Bi 4 Ti 3 O 12 precursor led to a significant increase in the particle size of the resulting Bi 4 Ti 3 O 12 platelets.

A thermodynamic estimation of the ZrO 2 –CeO 2 and ZrO 2 –CeO 1.5 systems, as well as the cubic phase in the CeO 1.5 –CeO 2 system has been developed and the complex relation between the nonstoichiometry, y , in Ce z O 2–y and the oxygen partial pressure at different temperatures is evaluated. The behavior of the nonstoichiometry phase Zr 1– z Ce z O 2– x is described based on the thermodynamic estimation in the ZrO 2 –CeO 2 , CeO 1.5 –CeO 2 and ZrO 2 –CeO 1.5 systems. Additionally, the interdependence among miscellaneous factors, which can be used to describe the change in oxidation states of cerium such as the oxygen partial pressure, the CeO 1.5 fraction in CeO 1.5 –CeO 2 in the quasi-ternary system, the nonstoichiometry y and the difference between the activity of CeO 2 and CeO 1.5 are predicted. The calculated results are found to be very useful to explain the influence of pressureless sintering at different O 2 partial pressures on the mechanical properties of CeO 2 -stabilised ZrO 2 ceramics

The influence of hydrothermal conditions (including starting materials, reaction temperature and time) on the crystal structure and the morphology of Bi4Ti3O12 particles are discussed in this paper. Bi4Ti3O12 nanocrystalline particles were hydrothermally synthesized at temperatures in the range of 180–230 °C for 4–12 h, from Bi(NO3)3·5H2O, TiCl4 and NaOH solution. The XRD results revealed that a typical bismuth layered perovskite structure Bi4Ti3O12 was obtained. The TEM showed that the Bi4Ti3O12 nanoparticles are tabular, and the sizes are about 200 nm.

The International Continental Scientific Drilling Program (ICDP) has long espoused studies of deep subsurface life, and has targeted fundamental questions regarding subsurface life, including the following: "(1) What is the extent and diversity of deep microbial life and what are the factors limiting it? (2) What are the types of metabolism/carbon/energy sources and the rates of subsurface activity? (3) How is deep microbial life adapted to subsurface conditions? (4) How do subsurface microbial communities affect energy resources? And (5) how does the deep biosphere interact with the geosphere and atmosphere?" (Horsfield et al., 2014) Many ICDP-sponsored drilling projects have included a deep-life component; however, to date, not one project has been driven by deep-life goals, in part because geomicrobiologists have been slow to initiate deep biosphere-driven ICDP projects. Therefore, the Deep Carbon Observatory (DCO) recently partnered with the ICDP to sponsor a workshop with the specific aim of gathering potential proponents for deep-life-driven ICDP projects and ideas for candidate drilling sites. Twenty-two participants from nine countries proposed projects and sites that included compressional and extensional tectonic environments, evaporites, hydrocarbon-rich shales, flood basalts, Precambrian shield rocks, subglacial and subpermafrost environments, active volcano–tectonic systems, megafan deltas, and serpentinizing ultramafic environments. The criteria and requirements for successful ICDP applications were presented. Deep-life-specific technical requirements were discussed and it was concluded that, while these procedures require adequate planning, they are entirely compatible with the sampling needs of other disciplines. As a result of this workshop, one drilling workshop proposal on the Basin and Range Physiographic Province (BRPP) has been submitted to the ICDP, and several other drilling project proponents plan to submit proposals for ICDP-sponsored drilling workshops in 2016.

Bi4Ti3O12 powder was prepared by a co-precipitation method and characterized with DTA, XRD, IR, BET and TEM. The results indicated that the as-prepared precursor consisted of well-dispersed particles of about 10 nm. Bi4Ti3O12 phase began to form at 470 jC, and pure Bi4Ti3O12was obtained after being calcined at 550 jC for 0.5 h. The powder obtained at 600 jC showed a tetragonal symmetry and a plate-like morphology with particle size of about 100 nm. Bi4Ti3O12 ceramics with 97.2% of theoretical density can be obtained by pressure-less sintering at 750 jC for 1 h, indicating the excellent sinterability of the prepared powder. D 2002 Elsevier Science B.V. All rights reserved.

The formation behavior of SrxBa1−xNb2O6 (SBN) (x=0.4 and 0.6) was investigated by the normal solid-state reaction route using SrCO3, BaCO3, and Nb2O5 as the starting materials. The phase assemblage of the reaction products at different temperatures was identified by X-ray Guinier-Hagg camera film data and the unit cell dimensions of SrxBa1−xNb2O6 formed during reaction sequence were also precisely calculated based on film data. The results indicated that four intermediate phases, i.e. Ba5Nb4O15, Sr5Nb4O15, SrNb2O6 and BaNb2O6 were developed during the formation of SrxBa1−xNb2O6. SrxBa1−xNb2O6 formed by the reaction of SrNb2O6 and BaNb2O6, appeared at 900 °C, whose intensity subsequently increased with the increase of calcination temperature. SrxBa1−xNb2O6 was the only crystalline phase when the starting powder was calcined at 1100 °C for Sr0.4Ba0.6Nb2O6 composition and 1200 °C for Sr0.6Ba0.4Nb2O6 composition. It was also found that the lattice parameters of SrxBa1−xNb2O6 formed at different temperatures decreased with the increasing calcination temperature, implying that the solubility of SrxBa1−xNb2O6 changed and more Sr would be incorporated into SrxBa1−xNb2O6 with the increase of calcination temperature. Based on the above results, the corresponding formation mechanism of SrxBa1−xNb2O6 phase was modified.

Two calcium-doped α-SiAlON compositions (Ca 0.6 Si 10.2 Al 1.8 -O 0.6 N 15.4 and Ca 1.8 Si 6.6 Al 5.4 O 1.8 N 14.2 ) were prepared by hot pressing at 1600° and 1500°C, respectively, for complete phase transformation from α-Si 3 N 4 to α-SiAlON. Both samples were subsequently fired at different temperatures for different periods of time to study the grain growth of α-SiAlON. Elongated α-SiAlON grains were developed in both samples at high temperatures. The kinetics of grain growth was investigated based on the variations in length and width of the α-SiAlON grains under different sintering conditions. Different growth rates were found between the length and width directions of the α-SiAlON crystals, resulting in anisotropic grain growth in the microstructural development.

Bismuth oxide (Bi2O3) needles were fabricated hydrothermally by altering the starting materials, mineralizers, reaction temperature and time. The non-agglomerated Bi2O3 needles with a monoclinic structure were prepared using Bi(OH)3 in an alkali solution. The hydrothermal reaction took place at 120 °C in 0.5 h. The length and aspect ratio (length over diameter) of the needles are in the ranges of 6–70 and 5–16 μm, respectively. With the rising reaction temperature and time, the diameter of Bi2O3 needles increased, while the aspect ratio decreased. The formation mechanism of Bi2O3 needles is discussed in the paper.

The synthesis of (Ca,Mg)-α-sialon powders using slag as a starting material by self-propagating high-temperature synthesis (SHS) is reported for the first time. The only crystalline phase detected in the synthesized products was α-sialon. The characters of the synthesized powders were observed and compared with that of conventionally hot-pressed materials. More metal cations were absorbed into the α-sialon structure of the SHS synthesized powders. Fully densified sialon ceramics can be obtained using the SHS powders by hot-pressing. The hardness and fracture toughness of the hot-pressed α-sialon ceramics reached 16 GPa and 5.1 MPa m−1/2 respectively.

A proper powder preparation was used to develop α-Sialon single crystals as seeds. The microstructure and fracture toughness of seed-containing α-Sialon ceramics sintered by hot-pressing were investigated. The specimen without seeding consisted of fine grains and a small amount of coarse grains. Specimens seeded with α-Sialon single crystal particles presented a large amount of elongated α-Sialon grains. The aspect ratio and the amount of elongated α-Sialon grains can be tailored by using different sizes and amounts of the seeds. The fracture toughness of seed-containing α-Sialon ceramics is improved, which is attributed to grain pullout and bridging of elongated grains.

Dual modifying cation (Ca+Nd) α-sialons were hot pressed for the x=1.0 composition ((Ca,Nd)xSi12-3nAl3nOnN16-n) with mixtures of CaO:Nd2O3 in the molar ratios of 0:1, 0.3:0.7, 0.5:0.5, 0.7:0.3 and 1:0. Experimental results showed that except for pure Nd- and Ca-α-silaon compositions, the main crystalline phase in samples hot-pressed at 1750°C for 1 h was α-sialon together with a small amount of melilite solid solution and AlN polytypoid. The higher CaO:Nd2O3 ratio in the starting composition, the higher α-sialon content and the lower melilite solid solution content in the final phase assembly. The α-sialon lattice also expanded with increasing substitution of Ca for Nd. Elongated grain morphology was observed in (Ca+Nd) α-sialon. EDS analysis revealed higher solubility of Ca than Nd in the α-sialon lattice and lower solubility of Ca than Nd in the intergranular phase. The hardness increased, ranging from 15.87 to 18.79 MPa, when the amount of α-sialon phase in the material became higher. The fracture toughness varied from 4.2 to 5.1 MP am1/2 for (Ca+Nd) α-sialon compositions, in which the composition with CaO:Nd2O3=0.5:0.5 possessed the highest value.

Three kinds of additives were added into Ca α-sialon, (Ca 0.6 Si 10.2 Al 1.8 O 0.6 N 15.4 ). It was found that the additives resulted in more of the liquid phase during sintering, which promoted the completion of the α→α′ transformation and the development of the elongated morphology characteristic of α-sialon grains. Comparison was made concerning the effect of the amount and type of additives on the microstructural development of Ca α-sialon. Phase and property analysis was also carried out on the hot-pressed samples.

Ca-α-sialon compacts pressureless-sintered to intermediate temperatures, which consisted of both α-sialon and unreacted α–Si3N4 grains, were investigated with transmission electron microscopy for an overall composition Ca1.8Si6.6Al5.4O1.8N14.2. Special attention was paid to identification of the possible crystallographic orientation between a-sialon and the α–Si3N4 particles. In contrast to the frequently occurring heteroepitaxial nucleation of α-sialon in rare-earth-doped samples with low x values, this study showed that most of the newly formed α-sialon grains had no epitaxial orientation relationship with the α–Si3N4 particles, suggesting nonepitaxial heterogeneous nucleation to be a more probable mechanism for the Ca–α-sialon phase with high Ca concentrations.

Ca α-Sialon compacts pressurelessly-sintered to the intermediate temperature (1 450°C) were investigated with TEM for an overall composition Ca1.8Si6.6Al5.4O1.8N14.2. It was found that in most cases, the newly-formed α-Sialon grains had no epitaxial orientation relationship with the Si3N4 particles; only occasionally heteroepitaxial nucleation of α-Sialon on α-Si3N4 was detected. Further EDAX analysis revealed a much higher Ca concentration in the non-epitaxially nucleated α-Sialon than in the heteroepitaxially nucleated α-Sialon. Thus a possible correlation between the concentration of metal cations in the α-Sialon structure and the nucleation mechanism has been proposed, i.e. α-Sialon compositions with higher Ca concentration show a stronger trend of non-epitaxial nucleation.

Two R-α-sialon (R0.6Si9.3Al2.7O0.9N15.1, R=Nd and Er) compositions were first fired at 1750°C/25 min and 1650°C/2 h respectively for completion of the α → α′ phase transformation. Elongated α-sialon grain morphology was developed in both samples after being re-fired at 1800°C for different periods of time. The growth in width of R-α-sialon grains is controlled by diffusion in the liquid, while the length growth tends to be interfacial reaction controlled. The anisotropic growth of R-α-sialon is attributed to the large difference in the growth rate constant between the length and the width directions of the grain.

Silicon nitride has two polymorphous structures, α-Si 3 N 4 and β-Si 3 N 4 . In this study three different Si 3 N 4 starting powders (∼100%α, 40%α+60%β, ∼100%β) were used to prepare Ca α-sialon with the composition Ca 1.8 Si 6.6 Al 5.4 O 1.8 N 14.2 by pressureless sintering. Comparison was made concerning the densification process, reaction sequence and microstructure of the corresponding materials. The sluggish reactivity of β-Si 3 N 4 resulted in poorer densification during sintering. All the three starting powders produced a similar final phase assembly, namely α-sialon together with a small amount of AlN and AlN polytypoid except that traces of unreacted β-Si 3 N 4 remained until 1800° in samples prepared with ∼100%β-Si 3 N 4 powders. Elongated α-sialon grain morphology has been identified in the samples prepared using all the three different Si 3 N 4 starting powders. Coarser elongated α-sialon grains with lower aspect ratio were found in samples using higher β phase starting powders.

Five major felsic igneous suites from northern Vietnam, with ages from mid-Proterozoic to early Cenozoic, were studied. Representative granitic rocks from the Posen Complex (mid-Proterozoic) and the Dienbien Complex (late Permian to early Triassic) show geochemical characteristics similar to those of calc-alkaline to high-K calc-alkaline I-type granites. However, the former, located in the South China block, has significantly higher initial Nd isotopic ratios [eNd(T)=+0.7 to +1.5] and older Nd isotopic model ages (TDM∼1.7 Ga) than the latter [eNd(T)=−4.7 to −9.7; TDM∼1.3–1.5 Ga] which were emplaced south of the Song Ma Suture and thus in the Indochina block. The generation of both complexes may be attributed to subduction-related processes that occurred in two distinct crustal provenances with different degrees of mantle inputs. On the other hand, Jurassic to Cretaceous granitic rocks from the Phusaphin Complex, contemporaneous rhyolites from the Tule Basin, and late Paleogene granitic rocks from the Yeyensun Complex, all exposed in the South China block between the Ailao Shan–Red River shear zone and the Song Ma Suture, display geochemical features similar to those of A-type granites with intermediate eNd(T) values (+0.6 to −2.8) and younger TDM ages (0.6–1.1 Ga). These magmas are suggested to have been generated as a consequence of intraplate extension in the western part of the South China block (Yunnan), and to have been transported to their present position by mid-Tertiary continental extrusion along the Ailao Shan–Red River shear zone related to the India–Asia collision. Overall, the isotopic and model age data, reported in this study indicate that in northern Vietnam, the most important crust formation episode took place in the Proterozoic. Likewise, repeated mantle inputs have played a role in the petrogenesis of Phanerozoic granitic rocks.

Left-lateral motion along the Ailao Shan‐Red River (ASRR) Shear Zone has been widely advocated to be the result of the collision between the Indian and Eurasian plates and to account for sea-floor spreading in the South China Sea. Our new 40 Ar/ 39 Ar data on the south-easternmost outcrop of the Day Nui Con Voi metamorphic massif, northern Vietnam, suggest that the exhumation of metamorphic massif by shearing along the ASRR zone began 027 Ma and lasted until 022 Ma. A perfect correlation between location and cooling path for the samples along the shear zone suggests that the transtensional deformation may have propagated northwestward at a rate of 0 6c m y ˇ1 . Such a good correlation also indicates that the onset of the leftlateral movement of the shear zone may have occurred later than 027.5 Ma. This conclusion is consistent with our previous interpretation that collision-induced southeastward extrusion of Indochina along the ASRR Shear Zone postdates the opening of the South China Sea, and that extrusion tectonics in SE China may not be responsible for the opening of the South China Sea. # 2000 Elsevier Science Ltd. All rights reserved.

The influence of processing on microstructural development of Ca α-sialon composition (CaxSi12−3xAl3xOxN16−x) with x = 1.8 was studied by dwelling at different intermediate temperatures before reaching the final sintering temperature. The microstructural observation results have showed the different aspect ratios of elongated grains obtained by the various processing conditions, reflecting the effect of the number of nuclei of α-sialon on morphology of grains during sintering. Improved toughness was achieved by applying low temperature dwelling for Ca α-sialon compositions with low x values. The toughness showed an increase of 33% and 16% for x = 0.6 and 1.0 compositions respectively with middle dwelling processing at 1350°C for 3 h before reaching 1750°C for 1 h by hot-pressing.

Multi-cation α-Sialons ceramics containing calcium and magnesium for the compositions ((Ca,Mg)xSi12 − 3xAl3xOxN16 − x), where x equals 0.6 and 1.0 with the different atomic ratios of Ca to Mg, were fabricated by hot-pressing. An exploration for Ca,Mg-α-Sialon involving phase compositions, cell dimensions, microstructure and mechanical properties were carried out in the present work.

ZrB 2 –SiC composite powders have been synthesized by combustion synthesis in air, using a mixture of Zr, B 4 C and Si as raw materials. It was found that the air atmosphere has played an important role in the ignition process of the SHS reaction. Three other kinds of ZrB 2 –SiC–ZrC composite powders with different ZrC content were also synthesized, and the ignition time has been measured for better understanding the ignition mechanism. As a result, the composite powders with particle size smaller than 1 µm and oxygen content as low as 0.4 wt.% were obtained.

ZrB2–LaB6 powder was obtained by reactive synthesis using ZrO2, La2O3, B4C, and carbon powders. Then ZrB2–20 vol% SiC–10 vol% LaB6 (ZSL) ceramics were prepared from commercially available SiC and the synthesized ZrB2–LaB6 powder via hot pressing at 2000°C. The phase composition, microstructure, and mechanical properties were characterized. Results showed that both LaB6 and SiC were uniformly distributed in the ZrB2 matrix. The hardness and bending strength of ZSL were 17.06±0.52 GPa and 505.8±17.9 MPa, respectively. Fracture toughness was 5.7±0.39 MPa·m1/2, which is significantly higher than that reported for ZrB2–20 vol% SiC ceramics, due to enhanced crack deflection and crack bridging near SiC particles.

We have previously reported the preparation of ZrB 2 –SiC composite from the pyrolyzed mixtures of polycarbosilane-coated ZrB 2 powders via hot pressing at 2073 K for 60 min under a pressure of 20 MPa in an argon atmosphere. In the present paper, Si additive was introduced into the ZrB 2 –SiC composite fabricated with the same processing conditions, in an attempt to convert carbon impurities introduced by the pyrolysis of polycarbosilane into SiC. The phase composition, microstructure and mechanical properties were characterized for the composite. Analysis showed that the Si additive could react with carbon to produce the SiC. In comparison with our previously published results, the addition of Si powder enhanced the micro-hardness of the composite, and did not have significant effect on fracture toughness.

ZrB2-SiC based composites with 0,5 and 15 vol% addition of ZrC were synthesized via reactive hot pressing at 1800°C using Zr, Si and B4C as raw materials. The mechanical properties of the composites were investigated. The composite of ZSC15 that contained 15 vol% of ZrC has the highest hardness. ZSC5 with 5 vol% of ZrC owns a most homogenous microstructure and the highest fracture toughness and flexural strength.

Nutritional supplements containing Ephedra sinica (ma huang), a botanical source of ephedrine alkaloids, have been linked to several episodes of ephedrine toxicity and at least 17 deaths, yet these products remain unregulated. Ten subjects were enrolled in a randomized, crossover study aimed at characterizing the pharmacokinetics of ephedrine after the ingestion of three commercially available ma huang products compared with a 25-mg ephedrine capsule. Pharmacokinetic parameters for botanical ephedrine were similar to those for synthetic ephedrine hydrochloride. Gender-based comparisons of Vss/F and CL/F revealed higher values for women than for men (Vss/F, 3.49 +/- 1.04 vs 2.98 +/- 0.73 l/kg; CL/F, 0.48 +/- 0.11 vs 0.37 +/- 0.11 l/hour x kg). The current study suggests that the increased incidence of ma huang toxicity does not stem from differences in the absorption of botanical ephedrine compared with synthetic ephedrine; rather, it results from accidental overdose often prompted by exaggerated off-label claims and a belief that "natural" medicinal agents are inherently safe.

The uplift of the Tibetan plateau is generally regarded as a response to the convective removal of the lower portion of the thickened Asian lithosphere1. This removal is also thought to be responsible for the east–west extension2 that took place during the India–Asia collision. The timing of these events has been a subject of great interest for understanding mountain-building processes, collisional tectonics and the influence of these processes on climate change3,4. In western Tibet, potassic lavas related to east–west extension were found to have been extruded over the past 20?Myr (refs 5, 6). Here we report the widespread occurrence of magmas in eastern Tibet which show similar geochemical signatures to the potassic lavas to the west but formed 40–30?Myr ago. These magmatic activities suggest a diachronous uplift history for the Tibetan plateau, with the convective removal of the lower lithosphere inducing rapid uplift in the east beginning some 40?Myr ago and in the west about 20?Myr later. This observation is consistent with sedimentation records from the Ganges–Brahmaputra delta to the Bengal fan7,8 and can better account for the tectonically driven models for strontium isotope evolution in the ocean9 and global cooling10 over the past 40?Myr.

The purpose of this study was to evaluate heart rate and blood pressure responses to a commercially available source of ma-haung, a natural source of the sympathomimetic substance, ephedrine, and to evaluate the pharmacokinetic properties of the product in normotensive, healthy adults. On day 1, twelve study participants were monitored with an ambulatory blood pressure device between hours 7 and 20. On day 2, they ingested four capsules of powdered ma-huang at hours 8 and 17 while again wearing the monitor between hours 7 and 20. Serial plasma samples were obtained and concentrations of ephedrine were analyzed by high-performance liquid chromatography. Pharmacokinetic parameters of ephedrine were determined from plasma concentration-time profiles. The ephedrine alkaloid content of each capsule was also determined by high-performance liquid chromatography. Six participants experienced a statistically significant increase in heart rate, but the effects on blood pressure were variable. The half-life, volume of distribution, clearance, and maximum concentration in plasma of ephedrine in the ma-huang product were similar to values previously reported for a 20 mg, immediate-release ephedrine tablet. Values for the absorption rate were considerably lower and time to reach maximum concentration was longer for the capsules, compared with the standard tablet. Variability in alkaloid content of ephedrine was low and yielded a mean dose of ephedrine at 19.4 mg; pseudoephedrine at 4.9 mg; and methylephedrine at 1.2 mg for a four-capsule dose. In summary, ma-haung had variable effects on blood pressure and increased heart rate in healthy, normotensive adults. Pharmacokinetic parameters for ephedrine were in agreement with those previously reported; however, the absorption rate was much slower after ingestion of ma-huang.

Rietveld refinements have been used to determine the structure of Y2Si3O3N4 from X-ray data and Nd2Si2.5Al0.5O3.5N3.5 from neutron powder diffraction data. The refinements show that in the melilite phase Y2Si3O3N4 and melilite solid solution Nd2Si2.5Al0.5O3.5N3.5 the distributions of cations and anions are almost identical. They are analogous to the akermanite (Ca2MgSi2O7) structure, with Si/Si,Al atoms at the origin and centre of the unit cell and with four N/N,O atoms forming the SiN4/(Si,Al)(N3.5O0.5) tetrahedra which share corners with SiO2N2/(Si,Al)O2.25N1.75 tetrahedra to form a continuous sheet structure. Each Y3+ or Nd3+ ion is surrounded by eight N/O atoms forming the coordination polyhedron in Y2Si3O3N4 and Nd2Si2.5Al0.5O3.5N3.5 respectively. The arrangement of Al, Si atoms in the tetrahedra in Nd2Si2.5Al0.5O3.5N3.5 structure is also discussed.

Ordering of N and O atoms in nitrogen-containing melilite Y2Si3O3N4 (Y-M) was investigated by Rietveld refinement in the space group P21m using neutron powder diffraction data. The results show that, contrary to previous work using X-ray data, the occupancies by N and O atoms can be refined to show that about 1.7 N and 0.3 O atoms occupy 2c (in Wyckoff notation, space group no. 113) sites in the Y-M unit cell, while the remaining N atoms in the unit cell are disordered at 8f (in Wyckoff notation) sites. The similar ordering of N and O atoms in Nd2Si2.5Al0.5O3.5N3.5 (Nd-M′) was also confirmed, by refinement from neutron data, which means that similar distributions of N and O atoms occurred at 2c sites in spite of the fact that the total numbers of N atoms per unit cell were eight and seven in Y-M and Nd-M′ respectively. The present results give a more detailed picture of O,N ordering in these structures than was provided by the previous work of Wang and Werner based on X-ray data alone.

Spark plasma sintering (SPS) was used to fabricate bismuth titanate (Bi4Ti3O12) ceramics. The densification, microstructure development and dielectric properties were investigated. It was found that the densification process was greatly enhanced during SPS. The sintering temperature was 200°C lower and the microstructure was much finer than that of the pressureless sintered ceramics, and dense compacts with a high density of over 99% were obtained at a wide temperature range of 800°–1100°C. Dielectric property measurement indicated that the volatilization of Bi3+ was greatly restrained during SPS, resulting in an unprecedented low dielectric loss for pure Bi4Ti3O12 ceramics.

Thick translucent and luminescent Gd–α-sialon ceramic disks (0.7–1.06 mm in thickness) were prepared by hot pressing. The effect of carbon atmosphere on their optical properties during sintering was explored by change packing methods. The results show that the sample with a lower carbon contamination has a higher translucence in the visible band and IR band (450–3500 nm), increasing transmission around 10% even if it is thicker. When excited at 350 nm, Gd–α-sialon with the lower carbon contamination can produce a visible light at 450–500 nm bands, but the luminescence is very weak in the sample containing more carbon contamination. These indicate that carbon contamination causes a severe degradation of the optical properties of α-sialon ceramics, and reduction of carbon contamination of α-sialon ceramics is very important for the optical property improvement.

Well-developed acicular Ba2NaNb5O15 (BNN) seed crystals have been successfully prepared by the reaction between BaCO3, Nb2O5 and molten NaCl salt. The effects of the calcination temperature, time, and weight ratio of the oxide mixture to salt on the morphology of BNN particles were investigated. Uniform acicular seeds with high aspect ratio could be achieved at 1200°C for 4 h with the salt-to-oxide mixture of 2:1.

The effects of sintering cycles and doping elements on the microstructures of Ln-α-sialon were studied. The results showed that microstructures with an elongated α-sialon morphology could be obtained through high-temperature post-heat treatment (1800–1900°C) or by prolonging soaking times during sintering. Different rare-earth elements had a profound effect on the microstructure of the resulting α-sialon. The Ln-α-sialon doped with low-Z-value elements could easily develop elongated grains with higher aspect ratio.

Self-propagating high-temperature synthesis (SHS) was applied to synthesize α-SiAlON powders doped by RE (RE = Eu,Pr,Ce) and codoped by RE and yttrium. The results showed that the weight ratio of α-SiAlON to (α-SiAlON +β-SiAlON) decreased from 70%, 55%, and 25% for europium-, praseodymium-, and cerium-doped α-SiAlON compositions, respectively, and the weight percentage of α-SiAlON phase increased to 100% for both (Eu,Y) and (Pr,Y) systems and 94% for the (Ce,Y) system, indicating SHS is a promising approach for synthesizing α-SiAlONs stabilized by the cations that could not be incorporated into the α-SiAlON structure by conventional sintering methods.