Rapid determination of erosion rates with electron beam SNMS

Erosion rates for sputtering of granular samples with 5 keV argon ions have been determined by mass loss measurements and a much faster method using atomic intensities of SNMS. Additionally, plane metal samples were measured for comparison. The investigation of metallic, ionic, oxidic and organic materials has revealed the validity of the SNMS method. However, the morphology of the sample has turned out to be of influence due to the usual angled arrangement of the bombardment and the direction of analysis. The detection of an element in a plane surface has been found to be by a factor of 3 more sensitive than in rugged surfaces such as particle ensembles. For all powders except KCl a mean normalised erosion rate _AX ⁿ =2.3 [nm · cm²/s · mA] has been obtained with a standard deviation of ±42% of the individual values. The erosion of KCl has been about a magnitude faster.     

137Cs profiles in erosion plots with different soil cultivation

Summary Cesium-137 methodology has been successfully used to assess soil erosion. Seven erosion plots were sampled to determine the ¹³⁷Cs profile and to assess the erosion rates. Cesium-137 profile for native pasture plot showed an exponential decline below 5 cm depth, with little ¹³⁷Cs activity in the superficial layer (0-5 cm). Cesium-137 profile for wheat-soybean rotation plot in conventional tillage showed a uniform distribution with depth. For this plot, the soil loss occurs more in middle than upper and lower level. Cesium-137 profile for wheat-soybean rotation and wheat-maize rotation plots in no-tillage showed a similar result to the native pasture, with a minimum soil loss in the superficial layer. Cesium-137 profile for bare soil and cultivated pasture plots are similar, with a soil erosion rate of 229 t ha^-1 year ^-1 . In the plots with a conventional tillage a greater soil loss occur in middle than upper and lower level. In no-tillage cultivation plots occurs soil loss in lower level, but no sign of soil loss neither gain in the upper level is observed. Cesium-137 methodology is a good tool to assess soil erosion and the ¹³⁷Cs profile gives possibility to understand the soil erosion behavior in erosion plots.     

Vertical distribution of the natural and artificial radionuclides in various soil profiles to investigate soil erosion

Vertical distributions of ¹³⁷Cs and ²¹⁰Pb in soil profiles were examined to study their availability in soil erosion at Gökova region where there exists intensive agricultural activities on sloppy fields. Since the mobility of these radionuclides depend on soil characteristics, soil samples were analyzed also for their physical and chemical properties. From ¹³⁷Cs inventories measured, erosion rates for cultivated and disturbed (no cultivation) soils were calculated to range from 79.1 to 6.5 t^.ha^-1.y^-1 and from 79.9 to 3.5 t^.ha^-1.y^-1, respectively. The ²¹⁰Pb technique is found to be not suitable for erosion determination for this area, presumably due to the coal-fired power plants operating in the region.     

Kilogram‐Scale Production of SnO2 Yolk–Shell Powders by a Spray‐Drying Process Using Dextrin as Carbon Source and Drying Additive

A simple and general method for the large‐scale production of yolk–shell powders with various compositions by a spray‐drying process is reported. Metal salt/dextrin composite powders with a spherical and dense structure were obtained by spray drying and transformed into yolk–shell powders by simple combustion in air. Dextrin plays a key role in the preparation of precursor powders for fabricating yolk–shell powders by spray drying. Droplets containing metal salts and dextrin show good drying characteristics even in a severe environment of high humidity. Sucrose, glucose, and polyvinylpyrrolidone are widely used as carbon sources in the preparation of metal oxide/carbon composite powders; however, they are not appropriate for large‐scale spray‐drying processes because of their caramelization properties and adherence to the surface of the spray dryer. SnO₂ yolk–shell powders were studied as the first target material in the spray‐drying process. Combustion of tin oxalate/dextrin composite powders at 600 °C in air produced single‐shelled SnO₂ yolk–shell powders with the configuration SnO₂@void@SnO₂. The SnO₂ yolk–shell powders prepared by the simple spray‐drying process showed superior electrochemical properties, even at high current densities. The discharge capacities of the SnO₂ yolk–shell powders at a current density of 2000 mA g^?1 were 645 and 570 mA h g^?1 for the second and 100th cycles, respectively; the corresponding capacity retention measured for the second cycle was 88 %.     

Oxidation of fine aluminum powders with water and air

Fine aluminum powders (RA20–RA60 grades, SUAL-PM) with specific surface area from 0.37 to 0.73 m²/g and high aluminum contents (95–98 wt %) are studied. The powders are found to be waterwettable without additions of surfactants and characterized by high rates of gas liberation in reacting with a calcium hydroxide solution under normal conditions. All RA20–RA60 powders are shown to be highly reactive upon oxidation with air and close to aluminum nanopowders in the parameters of their activity when heated in air. Their stability in water could prevent active (metallic) aluminum losses during their storage.     

Effect of the Maillard reaction on properties of casein and casein films

The use of biodegradable natural polymers has increased due to the over-solid packaging waste. In this study, a chemical modification of the casein molecule was performed by Maillard reaction, and the modified polymer was evaluated by polyacrylamide gel electrophoresis (PAGE), thermogravimetry/derivative thermogravimetry (TG/DTG), FT-IR, and ¹H-NMR spectroscopy. Subsequently, films based on the modified casein were obtained and characterized by mechanical analysis, water vapor transmission, and erosion behavior. The PAGE results suggested an increase of molecular mass of the modified polymer, and FT-IR spectroscopy data indicated inclusion of C–OH groups into this molecule. The TG/DTG curves of modified casein presented a different thermal decomposition profile compared to the individual compounds. Mechanical tests showed that the chemical modification of the casein molecules provided higher elongation rates (45.5%) to the films, suggesting higher plasticity, than the original molecules (13.4%). The modified casein films presented higher permeability (0.505 ± 0.006 μg/h mm³) than the original polymer (0.387 ± 0.006 μg/h mm³) films at 90% relative humidity (RH). In pH 1.2, modified casein films presented higher erosion rates (32.690 ± 0.692%) than casein films (19.910 ± 2.083%) after 8 h, suggesting an increased sensibility for erosion of the modified casein films in acid environment. In water (pH 7.0), the films erosion profiles were similar. Those findings indicate that the modification of molecule by Maillard reaction provided films more plastic, hydrophilic, and sensitive to erosion in acid environment, suggesting that a new polymer with changed properties was founded.     

SIMS depth profiling of vertical p-channel Si-MOS transistor structures

SIMS depth profiling during O₂ ⁺ bombardment has been performed to analyse epitaxially grown Si p-n-p layers, which define the p-channel region in vertical Si-p MOS transistors, as well as to establish “on-chip” depth profiling of the functional vertical device. The SIMS detection limit of ³¹P in Si, phosphorus used as n-type dopant in the transistor, has been optimised as a function of the residual gas pressure in the SIMS analysis chamber and of the sputter erosion rate. We demonstrate that good vacuum during SIMS analysis combined with high erosion rates allows the simultaneous quantitative SIMS depth profiling of n- and p-type dopant concentrations in the vertical transistor. Small area “on-chip” SIMS depth profiling through the layered structure of Al-contact/TiSi₂/Si(p-n-p)/Si-substrate has been performed. Factors influencing the depth resolution during “on-chip” analysis of the transistor are discussed especially in terms of sputtering induced ripple formation at the erosion crater bottom, which has been imaged with atomic force microscopy. Received: 15 August 1996 / Revised: 17 January 1997 / Accepted: 21 January 1997     

Rheological Properties of SiC Suspensions with a Compound Surface Modification Using Ethyl Orthosilicate and Ethylene Glycol

Ultrafine silicon carbide (SiC) powders were surface-modified using ethyl orthosilicate (TEOS) combined with ethylene glycol. SiC suspensions with favorable rheological properties, low viscosity, and high solid loading were successfully obtained. The mechanisms of the compound surface modification for SiC powders as well as the influences of the compound surface modification not only on functional groups and charge state of the surface for SiC powders but also on the rheological properties of SiC suspensions were investigated in the present study. The results show that under alkaline conditions and acidic conditions, the surface charge states of SiC powders were [Si-OCH₂CH₂O]^? and [Si-OCH₂CH₂OH₂]⁺, respectively. The absolute value of zeta potential reached the maximum value of 22.69 mV at pH 11. Additionally, with added 1 wt% TEOS and 3 wt% ethylene glycol, the SiC suspensions exhibited good rheological properties, low viscosity and high stability due to the steric hindrance and electrostatic repulsion offered by the [Si-OCH₂CH₂O]^- with a high concentration.     

Electrochemical Properties of Yolk–Shell‐Structured Zn–Fe–S Multicomponent Sulfide Materials with a 1:2 Zn/Fe Molar Ratio

Yolk–shell‐structured Zn–Fe–S multicomponent sulfide materials with a 1:2 Zn/Fe molar ratio were prepared applying a sulfidation process to ZnFe₂O₄ yolk–shell powders. The Zn–Fe–S powders had mixed sphalerite (Zn,Fe)S and hexagonal FeS crystal structures. The discharge capacities of the Zn–Fe–S powders sulfidated at 350 °C at a constant current density of 500 mA g^?1 for the first, second, and fiftieth cycles were 1098, 912, and 913 mA h g^?1, respectively. The powders exhibited a high discharge capacity of 602 mA h g^?1 even at the high current density of 10 A g^?1. The synergistic effect of yolk–shell structure and multicomponent composition improved the electrochemical properties of Zn–Fe–S powders.     

类球形正交LiMnO2的制备、微结构和电化学性能

以共沉淀法得到的类球形MnCO₃为前驱物，制备了类球形正交LiMnO₂(So-LiMnO₂)，采用XRD、SEM和N₂吸附技术对样品进行表征；与非球形正交LiMnO₂(No-LiMnO₂)进行了对比研究。结果表明：o-LiMnO₂的堆垛层错度、结晶状况、颗粒形貌和大小与前驱物的微结构密切相关；在80次电化学循环测试过程中，So-LiMnO₂经15次循环可达最大的放电容量152 mAh·g^-1，其容量衰减平均每次循环0.58 mAh·g^-1；而No-LiMnO₂要经过38次循环才能达到最大放电容量128 mAh·g^-1，容量衰减平均每次循环高达1.24 mAh·g^-1。TEM和EDS分析证明：由一次粒子团聚的类球形So-LiMnO₂能有效地抑制电解液对材料的腐蚀、减少Mn的溶解，从而提高了电化学循环能力。     

Investigation of sintering behavior of ZrO<Subscript>2</Subscript> (Y) ceramic green body by means of non-isothermal dilatometry and thermokinetic analysis

Using the method of dilatometry, kinetic characteristics of compacts shrinkage manufactured from ultrafine plasmochemical ZrO₂ (Y) powders and commercial Tosoh’s powders are investigated. The shrinkage curves are constructed with a DIL 402 C high-sensitivity dilatometer in a non-isothermal heating mode at different heating rates (1, 2, 5 and 10 °C min^?1). It is shown that the plasmochemical powders are characterized by a lower sintering efficiency than the Tosoh’s powders. The kinetic results are processed using a Netzsch Thermokinetics license software program developed for those who make use of devices manufactured by the Netzsch-Geratebau GmbH. The kinetic characteristics of compact shrinkage are determined as a function of partial length variation using Friedman’s analysis. Considerable differences are found between the values of apparent shrinkage activation energy for plasmochemical and Tosoh’s powders in the initial and final shrinkage stages. We attribute the mentioned differences in phase composition of the powders and their degree of agglomeration. In the intermediate shrinkage stage, the values of the apparent activation energy obtained for both types of powders have only marginal differences.     

One‐Pot Synthesis of CoSex–rGO Composite Powders by Spray Pyrolysis and Their Application as Anode Material for Sodium‐Ion Batteries

A simple one‐pot synthesis of metal selenide/reduced graphene oxide (rGO) composite powders for application as anode materials in sodium‐ion batteries was developed. The detailed mechanism of formation of the CoSe_x–rGO composite powders that were selected as the first target material in the spray pyrolysis process was studied. The crumple‐structured CoSe_x–rGO composite powders prepared by spray pyrolysis at 800 °C had a crystal structure consisting mainly of Co_0.85Se with a minor phase of CoSe₂. The bare CoSe_x powders prepared for comparison had a spherical shape and hollow structure. The discharge capacities of the CoSe_x–rGO composite and bare CoSe_x powders in the 50th cycle at a constant current density of 0.3 A g^?1 were 420 and 215 mA h g^?1, respectively, and their capacity retentions measured from the second cycle were 80 and 46 %, respectively. The high structural stability of the CoSe_x–rGO composite powders for repeated sodium‐ion charge and discharge processes resulted in superior sodium‐ion storage properties compared to those of the bare CoSe_x powders.     

CTAB-assisted hydrothermal synthesis of YVO4:Eu powders in a wide pH range

Rhombus-, rod-, soya bean- and aggregated soya bean-like YVO₄:Eu³⁺ micro- and nanostructures were synthesized by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method at 180 °C for 24 h in a wide pH range. The as-synthesized powders were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). The XRD results confirmed the formation of phase-pure YVO₄:Eu³⁺ powders with tetragonal structure under hydrothermal process in a wide pH range. Electron microscopic observations evidenced the morphological transformation of YVO₄:Eu³⁺ powders from rhombus-like microstructure to rod-, soya bean, and aggregated soya bean-like nanostructures with an increase in the pH of the synthesis solution. The results from the PL measurements revealed that the intensities of PL emission peaks were significantly affected by the morphologies and crystallinity of samples due to the absence of an inversion symmetry at the Eu³⁺ lattice site, and the highest luminescence intensity was observed for rod-like YVO₄:Eu³⁺ powders.     

Flame Spray Pyrolysis for Finding Multicomponent Nanomaterials with Superior Electrochemical Properties in the CoOx‐FeOx System for Use in Lithium‐Ion Batteries

High‐temperature flame spray pyrolysis is employed for finding highly efficient nanomaterials for use in lithium‐ion batteries. CoO_x‐FeO_x nanopowders with various compositions are prepared by one‐pot high‐temperature flame spray pyrolysis. The Co and Fe components are uniformly distributed over the CoO_x‐FeO_x composite powders, irrespective of the Co/Fe mole ratio. The Co‐rich CoO_x‐FeO_x composite powders with Co/Fe mole ratios of 3:1 and 2:1 have mixed crystal structures with CoFe₂O₄ and Co₃O₄ phases. However, Co‐substituted magnetite composite powders prepared from spray solutions with Co and Fe components in mole ratios of 1:3, 1:2, and 1:1 have a single phase. Multicomponent CoO_x‐FeO_x powders with a Co/Fe mole ratio of 2:1 and a mixed crystal structure with Co₃O₄ and CoFe₂O₄ phases show high initial capacities and good cycling performance. The stable reversible discharge capacities of the composite powders with a Co/Fe mole ratio of 2:1 decrease from 1165 to 820 mA h g^?1 as the current density is increased from 500 to 5000 mA g^?1; however, the discharge capacity again increases to 1310 mA h g^?1 as the current density is restored to 500 mA g^?1.     

BaHfO3：Ce粉体活化能对烧结透光性影响

用正、反向共沉淀法制备了BaHfO₃：Ce粒子;用XRD、TG-DTA、SEM等测试手段对样品的物相、形貌及发光性能进行了表征;在不同升温速率条件下研究了粒子合成动力学。结果表明：由正向和反向沉淀法得到的前驱体物相变化分3个阶段,用Doyle-Ozawa和Kissinger法分别计算了各阶段的表观活化能,其平均值分别为83.41、61.70、262.11kJ·mol^-1和81.70、42.86、253.44kJ·mol^-1,计算正反向沉淀法样品的晶粒生长活化能分别为27.36kJ·mol^-1和23.07kJ·mol^-1;反向法的样品分别在530nm波长下的激发光谱和399nm波长的发射光谱的相对发光强度优于正向法,在2073K真空烧结保温3h获得具有一定透光性的BaHfO₃：Ce透明陶瓷。     

BaHfO_3∶Ce粉体活化能对烧结透光性影响

用正、反向共沉淀法制备了BaHfO3∶Ce粒子;用XRD、TG-DTA、SEM等测试手段对样品的物相、形貌及发光性能进行了表征;在不同升温速率条件下研究了粒子合成动力学。结果表明:由正向和反向沉淀法得到的前驱体物相变化分3个阶段,用Doyle-Ozawa和Kissinger法分别计算了各阶段的表观活化能,其平均值分别为83.41、61.70、262.11 kJ·mol-1和81.70、42.86、253.44 kJ·mol-1,计算正反向沉淀法样品的晶粒生长活化能分别为27.36 kJ·mol-1和23.07 kJ·mol-1;反向法的样品分别在530nm波长下的激发光谱和399 nm波长的发射光谱的相对发光强度优于正向法,在2 073 K真空烧结保温3 h获得具有一定透光性的BaHfO3∶Ce透明陶瓷。     

Hydrothermal synthesis and luminescence behavior of rare-earth-doped NaLa(WO4)2 powders

NaLa(WO₄)₂ powders doped with Eu³⁺, Nd³⁺, and Er³⁺ have been synthesized by a mild hydrothermal method and a crystal of exclusive scheelite phase could be obtained at low temperature. From the spectrum of Eu³⁺ it has been concluded that the dopant Eu³⁺ ion occupies a La³⁺ site and mainly takes the site with C₂ symmetry. The higher quenching concentration can be observed in the Eu³⁺-doped NaLa(WO₄)₂ powders. The Er³⁺- and Nd³⁺-doped NaLa(WO₄)₂ powders exhibit luminescence in the near infrared (Er³⁺ at 1550 nm, and Nd³⁺ at 1060 nm). The transition mechanism of the up-conversion luminescence of the Er³⁺-doped NaLa(WO₄)₂ powders can be ascribed to two photons absorption process.     

Mechanochemical-hydrothermal synthesis of calcium phosphate powders with coupled magnesium and carbonate substitution

Magnesium- and carbonate-substituted calcium phosphate powders (Mg-, CO₃-CaP) with various crystallinity levels were prepared at room temperature via a heterogeneous reaction between MgCO₃/Ca(OH)₂ powders and an (NH₄)₂HPO₄ solution using the mechanochemical-hydrothermal route. X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis were performed. It was determined that the powders containing both Mg²⁺ and CO₃²⁻ ions were incorporated uniformly into an amorphous calcium phosphate phase while in contrast, the as-prepared powder free of these dopants was crystalline phase-pure, stoichiometric hydroxyapatite. Dynamic light scattering revealed that the average particle size of the room temperature Mg-, CO₃-CaP powders was in the range of 482 nm-700 nm with a specific surface area between 53 and 91 m²/g. Scanning electron microscopy confirmed that the Mg-, CO₃-CaP powders consisted of agglomerates of equiaxed, ≈20-35 nm crystals.     

Electrochemical Properties of Tin Oxide Flake/Reduced Graphene Oxide/Carbon Composite Powders as Anode Materials for Lithium‐Ion Batteries

Hierarchically structured tin oxide/reduced graphene oxide (RGO)/carbon composite powders are prepared through a one‐pot spray pyrolysis process. SnO nanoflakes of several hundred nanometers in diameter and a few nanometers in thickness are uniformly distributed over the micrometer‐sized spherical powder particles. The initial discharge and charge capacities of the tin oxide/RGO/carbon composite powders at a current density of 1000 mA g^?1 are 1543 and 1060 mA h g^?1, respectively. The discharge capacity of the tin oxide/RGO/carbon composite powders after 175 cycles is 844 mA h g^?1, and the capacity retention measured from the second cycle is 80 %. The transformation during cycling of SnO nanoflakes, uniformly dispersed in the tin oxide/RGO/carbon composite powder, into ultrafine nanocrystals results in hollow nanovoids that act as buffers for the large volume changes that occur during cycling, thereby improving the cycling and rate performances of the tin oxide/RGO/carbon composite powders.     

载银羟基磷灰石抗菌粉体和陶瓷的制备及抗菌性能

采用水热法一步合成载银羟基磷灰石抗菌粉体(Ag-HA),并将其应用于抗菌陶瓷的制备。研究结果表明水热条件下HA实际载银量与AgNO₃加入量存在较好的线性关系。XRD和TEM分析结果显示Ag-HA与HA具有相同的晶体结构,水热条件下Ag⁺取代Ca²⁺在HA晶体中的位置,生成Ag_xCa_10-x(PO₄)₆(OH)₂。Ag-HA长度随Ag⁺掺入量的增加而增大,当Ag⁺掺入量增加至1.50%时,Ag-HA由棒状生长为晶须状。选择4.50% Ag-HA作为抗菌粉体,其掺入量为9wt%时,陶瓷的抗菌率>99.9%,此时釉料中Ag₃PO₄含量为0.56%,低于目前研究中釉料中Ag₃PO₄添加量(2wt%~4wt%),不但在一定程度上解决了抗菌陶瓷产品成本较高的问题,而且满足JC/T 897-2002(抗菌陶瓷制品抗菌性能)对抗菌陶瓷抗菌性能的要求。