Total Oxidation Time Research Articles

High-temperature oxidation of ZrB<sub>2</sub>–SiC–La<sub>2</sub>O<sub>3</sub> ceramic material produced via spark plasma sintering

The study investigated the influence of La2O3 addition on the oxidation properties of composite ceramics with a composition of 80 vol. % ZrB2 and 20 vol. % SiC. The source materials utilized in this study included zirconium diboride (DPTP Vega LLC., Russia), grade 63C silicon carbide (Volzhsky Abrasive Works JSC, Russia), and lanthanum hydroxide concentrate (Solikamsk Magnesium Plant JSC, Russia), with the following elemental content (wt. %): La – 54.2, Nd – 4.3, Pr – 2.8, and trace amounts of other elements (<0.1). The La2O3 content in the charge varied between 0, 2 and 5 vol. %. The powders were mixed in a planetary mill with ethyl alcohol as the medium for 2 h, using a grinding media to powder ratio of 3:1. Consolidation of the powders was achieved through spark plasma sintering at 1700 °С, applying a pressing pressure of 30 MPa. The heating rate was 50 °С/min, and the isothermal holding time was 5 min. Oxidation was carried out in air at 1200 °С and the total oxidation time was 20 h. Oxidation experiments were conducted in air at 1200 °С, with a total oxidation time of 20 h. It was observed that the most significant weight gain occurred within the first 2–4 h of testing. Specimens containing 5 vol. % La2O3 exhibited the smallest weight gain after 20 h of exposure. Regardless of the presence of La2O3 , silicon carbide was found to be the first material to undergo oxidation. In specimens without La2O3 addition, the oxidized layer mainly consisted of silicon monoxide and dioxide. In contrast, specimens with La2O3 exhibited a predominantly oxidized layer composed of ZrSiO4 and ZrO2 . The study revealed that the introduction of La2O3 intensified the formation of zircon, which subsequently slowed down the oxidation processes in the material.

Recovery of Fe, V, and Ti in modified Ti-bearing blast furnace slag

A two-stage oxidation—alkali leaching—acid leaching method was proposed to recovery Fe, V, and Ti in modified Ti-bearing blast furnace slag. The optimal experiment conditions of iron extraction were one-stage oxidation time 40 s and holding time 8 min. The recovery rate of iron was 89.93%. The optimum experiment conditions of vanadium extraction were total oxidation time of 126 s, NaOH concentration of 4.0 mol/L, leaching temperature of 95 °C, leaching time of 90 min, and the number of cycle was 4. The leaching rate of vanadium was 92.13%. The optimal experiment conditions of titanium extraction were HCl concentration of 4.5 mol/L, leaching temperature of 75 °C, and leaching time of 90 min. The TiO2 content of synthetic rutile was 98.61%.

A model for etching of three-dimensional high aspect ratio silicon structures in pulsed inductively coupled plasmas

A coupled plasma—feature scale model is employed to investigate the etching of high aspect ratio (HAR) silicon (Si) structures using a cyclic multi-step pulsed plasma process in an inductively coupled plasma (ICP) reactor. This process sequence includes an oxidation step to help protect the Si sidewalls, a main Si etch step where the ion energy and angular distribution (IEAD) and ion/neutral flux ratio are controlled through power pulsing, and a clean step prior to repeating the multi-step process. Two-dimensional plasma models are used to compute the IEAD as well as the fluxes of relevant ions and neutral radicals at the wafer. These plasma models are coupled to a three-dimensional feature scale model, where multiple cycles of the three-step etch sequence are simulated. The paper focuses on evaluation of several pulsing modes during the main Si etch step including separate pulsing of the ICP source or RF bias power, and their synchronized pulsing (with phase control). Process performance has been quantitatively evaluated by examining etch rates for Si and the SiO2-like mask, Si/mask etch selectivity, and CDs within the HAR features. When only the RF bias power is pulsed, Si and mask etch rates scale with pulse duty cycle (DC). As a result, if Si is etched to the same depth, the HAR trenches are wider at higher DCs due to less total oxidation time and less protection of the sidewalls. ICP source power pulsing provides higher Si etch rate because of RF bias power being on continuously, but suffers from poor mask selectivity. Synchronized pulsing of both the ICP source and RF bias powers in conjunction with phase control provides additional flexibility in modulating the IEAD and the ion/neutral flux ratio. RF bias pulsing and in-phase synchronized pulsing yield the best selectivity for the conditions explored.

Preparation and properties of TaSi2-MoSi2-ZrO2-borosilicate glass coating on porous SiCO ceramic composites for thermal protection

A TaSi2-MoSi2-ZrO2-borosilicate glass (TMZG) coating was prepared by a slurry method on a carbon fibre-reinforced porous silicon oxycarbide (SiCO) ceramic composite for thermal protection. The coating was well adhered to the substrate and showed a uniform thickness of approximately 375 µm. After thermal cycling from 1873 K to room temperature six times (total oxidation time of 180 min), the shape and dimension of the TMZG remain almost unchanged with no cracking or peeling of the coating surface. The TMZG-coated sample exhibits good oxidation resistance because of a molten SiO2 film with ZrSiO4 particles distributed on the outer layer of the coating. After ablation testing under an oxyacetylene flame at 1927 K for 90 s, the linear ablation rate of the TMZG coated sample are 8.33 × 10−4 mm/s. The whole coating retains integrity, preventing substrate ablation during the test. The TMZG coating with excellent temperature resistance shows broad applicability in thermal insulation materials.

Oxidation characteristics of porous-nickel prepared by powder metallurgy and cast-nickel at 1273 K in air for total oxidation time of 100 h

The oxidation behavior of two types of inhomogeneous nickel was investigated in air at 1273K for a total oxidation time of 100h. The two types were porous sintered-nickel and microstructurally inhomogeneous cast-nickel. The porous-nickel samples were fabricated by compacting Ni powder followed by sintering in vacuum at 1473K for 2h. The oxidation kinetics of the samples was determined gravimetrically. The topography and the cross-section microstructure of each oxidized sample were observed using optical and scanning electron microscopy. X-ray diffractometry and X-ray energy dispersive analysis were used to determine the nature of the formed oxide phases. The kinetic results revealed that the porous-nickel samples had higher trend for irreproducibility. The average oxidation rate for porous- and cast-nickel samples was initially rapid, and then decreased gradually to become linear. Linear rate constants were 5.5×10−8g/cm2s and 3.4×10−8g/cm2s for the porous- and cast-nickel samples, respectively. Initially a single-porous non-adherent NiO layer was noticed on the porous- and cast-nickel samples. After a longer time of oxidation, a non-adherent duplex NiO scale was formed. The two layers of the duplex scales were different in color. NiO particles were observed in most of the pores of the porous-nickel samples. Finally, the linear oxidation kinetics and the formation of porous non-adherent duplex oxide scales on the inhomogeneous nickel substrates demonstrated that the addition of new layers of NiO occurred at the scale/metal interface due to the thermodynamically possible reaction between Ni and the molecular oxygen migrating inwardly.

Respirometric evaluation of S0/X0 ratio effect on the kinetic and stoechiometric parameters of activated sludge

Respirometry has been used in this work to assess the effect of S0/X0 ratio, knowing that this ratio is a very important operational parameter in the conduct of wastewater treatment plant. It affects its design and operation; part of the respirometry calculations, dissolved oxygen transfer coefficient KLa is calculate for each respirometric experiment, due to the fact that operational condition change. Under endogenous conditions OURend is calculated using the linear portion of the variation of DO concentration under no aeration conditions. Then the OURend is used in the endogenous phase at a no oxygen concretion variation to calculate the KLa. Samples of wastewater, with different S0/X0 ratios in the range between 0.01 and 0.23, containing sometimes ATU, a nitrification inhibitor, were injected in the respirometer with DO concentration variation recording. Exogenous OURexo were calculated from the DO data and they show that as S0/X0 ratio increased total OURt increased too as well as total oxidation time. However when, COD is present alone the removal kinetics is more rapid than when both substrates (nitrogen and carbonaceous) are present. It has been shown that the use of respirometry in biomass activation assessment is a sound approach because of the celerity, the reliability and the limited cost. Consequently it has been extended in to the assessment of biomass activation when it is exposed to antibiotics.

Transport Through Electrophoretically Deposited CuMn1.8O4 Spinel Coatings on Crofer Interconnects

AbstractDense and well-adhered CuMn1.8O4 spinel oxide coatings were successfully deposited on Crofer 22 APU stainless steel substrates by a cost effective electrophoretic deposition technique. Coated and uncoated Crofer substrates were oxidized for 120 hours in air at 800°C. A diffusion model was developed for the oxidation of the coated alloys, which predicted para-linear oxidation kinetics. The effective diffusivities in the coating and in the thermally grown oxide were calculated to be 2×10-15 cm2/s and 2.5×10-16 cm2/s respectively, at 800°C. Area specific resistances (ASR) of thermally cycled samples at 800°C did not show a significant difference compared to the isothermally oxidized sample for the same total oxidation time, suggesting good coating adherence. The ASR of the coated alloys is projected to be around 3.8×10-2Ωcm2 after 50000 at 800°C in air, making them excellent candidates for interconnect applications for solid oxide fuel cells operated at 800°C or lower.

Layering of ultrathin SiO2 film and study of its growth kinetics

A systematic kinetic study of SiO2 thin film thermally grown on Si(100) substrate by a single step and two step dry oxidation process is presented. Films grown at lower temperature (750°C) show higher density than films grown at higher temperature (1000°C). If the oxidation is carried out in two steps i.e., the first oxidation step at a lower temperature (750°C) and the second one at a higher temperature (1000°C), two distinct layers of SiO2 having different densities can be obtained. The film density was measured using the grazing incidence x-ray reflectivity technique. We also observed that when the thickness of the first “top” layer increases the growth of the “bottom” layer is retarded leading to lowering of total thickness of the SiO2 film even though the total oxidation time is increased.

Troglitazone-binding to Ldl and its glycated modifications: Its role in cell-catalysed and Cu-mediated Ldl-oxidation

Troglitazone (T), an anti-diabetic drug improving insulin resistance, was studied as to its inhibition of copper ion-catalysed oxidation of native, glycated and glycoxidated low-density lipoprotein (LDL). A dose-dependent inhibition was noted in the concentration range 40–160 μg/ml. An almost complete inhibition of oxidation (2–8 h), as monitored by the formation of thiobarbituric acid-reactive substances, was observed for both native and glycated LDL at a concentration of 160 μg/ml T, while the maximal inhibition for glycoxidated LDL amounted only to 60% at this concentration of the drug. This is reflected by differences in the affinity of the drug for the different types of LDL modification: While the binding of T both to native or glycated LDL increased linearly with increasing T concentration and was not saturable in the concentration range tested (0–160 μg/ml), binding of the drug to glycoxidated LDL was already nearly saturated at 10 μg/ml. The nearly complete inhibitory action of T towards oxidation of native and glycated LDL was lost, however, upon increasing the total oxidation time to 24 h. In human umbilical vein endothelial cell-mediated oxidation of LDL, T at a concentration of 20 μg/ml significantly reduced formation of oxidation-dependent fluorescent chromophores and liberation of 8-epi-PGF 2α. In contrast, generation of thiobarbituric acid-reactive substances was not significantly inhibited. As opposed to copper-mediated LDL-oxidation, different binding of T to LDL-modifications does not govern inhibition of human umbilical vein endothelial cell-mediated LDL-oxidation.

Oxidation-deficient silkworm hemolymph as a medium supplement for insect cell culture

Hemolymph is oxidized and darkens visibly during the collection from silkworms due to the activity of tyrosinase in it. Toxic quinones are produced by the oxidation and consequently inhibit the cell growth. Heat treatment can be used to prevent the oxidation; however, the oxidation may occur during the collection of hemolymph before it is heat-treated. It makes the hemolymph collection difficult especially on a large-scale preparation. Hemolymphs collected from 257 different strains of silkworms were examined to select the slowly oxidized hemolymphs. Hemolymphs collected from mutant strains such as Lemone, TBO, Cre, Y4, and wEb showed relatively slow color changes. Oxidation rates of the hemolymphs were measured by the absorbance change using a spectrophotometer. The hemolymph of wEb showed the slowest oxidation. The absorbance of this mutant hemolymph reached the saturation value at 20°C in 450 min, whereas the total oxidation time of the wild-type (Baekokjam) hemolymph at the same temperature was 120 min. We tested if this mutant hemolymph is useful as a medium supplement for insect cell culture. Cell growth rate and final cell concentration in the medium supplemented with the wEb hemolymph were almost same as those in the medium supplemented with the wild-type hemolymph. Hemolymph is collected on a small scale by clipping the abdominal leg; however, this method is not appropriate for large scale preparation. Centrifugation after chopping the silkworm hemolymph by a blending mixer is a more appropriate procedure for large scale collection. Slowly oxidized wEb hemolymph resulted in higher cell concentration than the wild-type hemolymph when hemolymph was collected by the large scale preparation method.

Interface State Density Reduction and Effect of Oxidation Temperature on Fluorine Incorporation and Profiling for Fluorinated Metal Oxide Semiconductor Capacitors

The effect of fluorine incorporation on the as‐grown interface state density of the system was investigated using MOS capacitors with fluorinated oxide dielectrics grown by oxidation as test structures. A clear reduction of the interface trap density, attributed to fluorine‐induced passivation of interfacial dangling bonds, weak bonds, and weak interactions, was shown for additions in the parts‐per‐million range as compared to dry oxides. Fluorine incorporation in the oxide was investigated with SIMS profiling. The application of a pulsed oxidation process in which the fluorine source is added to the oxidant in intervals within the total oxidation time demonstrated that the variation of oxidation processing parameters strongly influences the resulting fluorine profile. A two‐peak pattern of the fluorine profile, with one peak in the interfacial area and the other corresponding to the oxide area grown during the step, was observed. This pattern was strongly dependent on the oxidation temperature, with the interfacial fluorine accumulation more pronounced with increasing temperature. The pronounced influence of the oxidation temperature on the fluorine profile resulting from oxidation was ascribed to a thermally activated replacement reaction of bonded fluorine by oxygen.

Oxidation behaviour of silicon nitride under cyclic and static conditions

Silicon nitride, hot-pressed with alumina and yttria additives, was oxidized cyclically at 1200°C in flowing dry air for a total oxidation time of 3000 h. Static oxidation was also carried out for comparison. The cyclic oxidation apparently proceeded in two stages with different reaction rates, but both stages approximately followed the parabolic rate law. This difference of reaction rates may well be related to the change with time of the properties of the oxide layer and sublayer formed during oxidation. The main crystalline phases formed during the gradual oxidation on the surface were cristobalite, yttrium disilicate (Y 2O 3.2SiO 2) and tridymite. The corresponding oxide layers were porous and contained many cracks and channels. The surface roughness increased gradually with time, and reached a maximum value after 750 h oxidation. Then it decreased by degrees up until the end of the runs ( t = 3000 h). A consecutive degradation of the room-temperature flexural strength was observed. The static oxidation resulted in the same weight gain, the formation of different relative quantities of cristobalite, tridymite and Y.2S, approximately the same surface roughness and a slightly higher room-temperature flexural strength compared with the cyclic oxidation.

Preservation of Point Defect Distribution in FZ Silicon

Evidences for the preservation of point defect distribution in FZ Si crystals have been observed by two experimental methods. One is divided selective oxidation and the other is divided backside selective oxidation with Si3N4 as the oxidation resistant films. In both experiments, the selective oxidation is divided into several oxidation steps, and the effects of oxidation division on the range of oxidation effects on impurity diffusion is investigated. The results show that, both laterally and vertically from the oxidizing Si–SiO2 interface, the effect of oxidation on impurity diffusion is determined only by total oxidation time. This suggests that point defect distribution is preserved after heat treatment.

The Effect of Heat Treatment on the Resistivity of Polycrystalline Silicon Films

The resistivity of doped polycrystalline silicon films has been studied as a function of post deposition heat treatments in an oxidizing atmosphere. It was found that a short oxidation cycle may produce a resistivity increase as large as three orders of magnitude in the polycrystalline films. The extent of change was dependent on the initial resistivity and the films' doping level and was independent of the total oxidation time.