Evaluation of the performance of iron‐based oxygen scavengers,with comments on their optimal applications

Oxygen scavengers are commonly used in packaged foods in Japan and much less so in other developed countries, in spite of the advantages that they offer in maintaining quality and extending shelf‐life. The reason stems from the additional cost involved, and even more so because of the lack of sufficient technical information on their performance and the lack of understanding of how to apply them effectively. In the present study the performance of iron‐based oxygen‐scavenging sachets was evaluated. It was found that the actual scavenging capacity is much higher than the ‘nominal’ capacity provided by the manufacturers. Also, a significant distribution in the oxygen absorption capacity exists, even in the same scavenger type. The rate of oxygen scavenging was found to depend on the scavenger type and capacity. It was also found that in an atmosphere containing CO₂ (as in MAP applications) the iron‐based oxygen scavengers also absorb CO₂. Copyright © 2004 John Wiley & Sons, Ltd.     

Development of Palladium‐based Oxygen Scavenger: Optimization of Substrate and Palladium Layer Thickness

Oxygen scavenging films based on vacuum deposited palladium layers were developed to remove residual oxygen remaining in food packages after modified atmosphere packaging. Palladium (Pd) was coated on to a range of packaging films and in different thicknesses using magnetron sputtering technology. To improve the substrate surface, an additional silicon oxide (SiO_x) layer was also applied to the films before Pd deposition. To determine the oxygen scavenging activity, the scavenger films were placed into an airtight cell, which was flushed with a gas mixture containing 2 vol.% oxygen and 5 vol.% hydrogen. The results showed that the oxygen scavenging rate was strongly dependent on the coating substrate as well as on the Pd deposition thickness. Packaging films such as polyethylene terephthalate, aluminium oxide‐coated polyethylene terephthalate, oriented polypropylene and polylactic acid were found to be the most suitable substrates for Pd‐based oxygen scavengers. Moreover, it was demonstrated that the intermediate SiO_x layer between the substrate and the Pd layer led to a substantial increase in the oxygen scavenging activity rate (up to 33‐fold) for all applied packaging films. Additionally, it was shown that the optimal Pd layer thickness for the investigated oxygen scavenging films lies between 0.7 and 3.4 nm. The resulting scavenger films have the potential to scavenge residual headspace oxygen of sensitive foods within a matter of minutes leading to shelf life extension and overall quality improvements. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental determination of some periclase and spinel compositions in the system CaO-MgO-Al2O3-Cr2O3-Fe-O2-SiO2

The solubilities of Cr₂O₃, Fe₂O₃ and Al₂O₃ (as well as CaO and SiO₂) in periclase were determined from samples equilibrated in the temperature range 1550 to 1725° C, at two oxygen pressures (air and fO₂ about 10^–9atm). Most samples contained periclase, spinel, and liquid which is the mineralogy of most chrome-bearing refractories at manufacturing and service temperatures. In air a large observed change in the R₂O₃ (where R₂O₃ = Al₂O₃+Fe₂O₃+Cr₂O₃) content of periclase with increasing temperature results in a new example of retrograde solubility which causes crystalline periclase to grow in amount in some refractory compositions as the temperature increases. At low oxygen fugacity (log fO₂ –9) the iron oxide content (mainly FeO) of the periclase decreased (from 6.4 to 1.3wt%) as temperature increased. In air the iron oxide content (FeO + Fe₂O₃) decreased marginally (typically from 6.8 to 6.4 wt%) as temperature increased which contrasts with previous literature statements that there is an increase. At both oxygen pressures the Cr₂O₃ content increases markedly as temperature increases (up to 17 wt %), suggesting that Cr₂O₃ (and not Fe₂O₃ as the previous literature states) may be the cause of textural changes observed in commerical products subjected to temperature cycling. The presence of increasing CaO in the bulk samples leads to lower R₂O₃ contents in the periclase crystals. The data allow further more restricted choices to be made in refractory formulations towards the goal of matching the phase compositions to the properties desired at service temperatures. A few analyses of spinels show that iron levels decrease as temperatures increase and CaO levels up to 0.9 wt % were encountered.     

Hard iron boride (Fe2B) on 99.97 wt% pure iron

Some properties such as hardness and fracture toughness of boride formed on the 99.97 wt% pure iron were investigated. Boronizing was carried out in a solid medium, consisting of Ekabor powders of 5% B₄C as donor, 5% KBF₄ as an activator and 90% SiC as diluent at 800 °C for 2, 4 and 8 h. The dominant phase formed on the substrate was found to be Fe₂B that had a finger-like shape morphology. The hardness of boride on the 99.97% pure iron was over 1700HVN, while the hardness of pure iron was about 130HVN. It was found that the fracture toughness of boride formed on surfaces of 99.97% pure iron, depending on the process time, ranged from 3.59 to 3.83 MPa m^1/2. Depending on process time and temperature, the depth of the boride layer ranges from 22 to 43 μm, leading to a diffusion-controlled process.     

Magnetically separable Zn1-xCuxFe2O4 (0 ≤ x ≤ 0.5) nanocatalysts for the transesterification of waste cooking oil

Copper doped zinc ferrite Zn_1-xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized via sonication assisted microwave method. The prepared nanoparticles were characterized by XRD, FTIR, HR-SEM, EDX, DRS and VSM analysis. Average crystallite size were in range 5.84 nm to 8.55 nm. FTIR results reveal, bands at 420 cm⁻¹ (Zn²⁺O²⁻) and 547 cm⁻¹ (Fe³⁺O²⁻) confirming tetrahedral and octahedral positions of the spinel structure formation. All the samples showed ferromagnetic behavior at room temperature. The Zn_0.5Cu_0.5Fe₂O₄ sample showed high saturation magnetization (M_s = 74.09 emu/g) and high magnetic moment (3.0 μ_B). The prepared magnetic nano spinels were subsequently employed to evaluate the catalytic activity for biodiesel production. The transesterification process followed pseudo first order rate kinetic model. An excellent catalytic activity for biodiesel production was acheived (98.9%) and the catalyst was recoverable quickly using an external magnet.     

Studies of oxygen uptake on O2 scavengers ­prepared from different iron‐containing ­parent substances

Temperature‐programmed reduction (TPR) measurements were performed for iron oxalates, iron(III) hydroxide (both pure and with additives) and iron(II, III) oxide. On the ground of TPR curves, reduction temperatures of the iron‐containing parent substances were chosen followed by oxygen uptake determination. Comparison of oxygen uptakes points to the use of Fe(OH)₃ and Fe₃O₄ as more advantageous than that of iron oxalates. Co‐precipitation from a mixed solution of iron and manganese salts results in a product which is more resistant to particle agglomeration at elevated temperatures than that obtained by­precipitation from solution of iron salt alone. Copyright © 2002 John­Wiley & Sons, Ltd.     

Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing Fe2O3—An EPR and optical absorption study

This paper reports the interesting results on mixed alkali effect (MAE) in xLi₂O–(30-x)Na₂O–69.5B₂O₃ (5 ≤ x ≤ 28) glasses containing Fe₂O₃ studied by electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra in these glasses exhibit three resonance signals at g = 7.60, 4.20 and 2.02. The resonance signal at g = 7.60 has been attributed to Fe³⁺ ions in axial symmetry sites whereas the resonance signal at g = 4.20 is due to isolated Fe³⁺ ions in rhombic symmetry site. The resonance signal at g = 2.02 is due to Fe³⁺ ions coupled by exchange interaction. It is interesting to observe that the number of spins participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. The present study also gives an indication that the size of alkali ions we choose in mixed alkali glasses is also an important contributing factor in showing the mixed alkali effect. It is observed that the variation of N with temperature obeys Boltzmann law. A linear relationship is observed between 1/χ and T in accordance with Curie–Weiss law. The paramagnetic Curie temperature (θ_p) is negative for the investigated sample, which suggests that the iron ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. The optical absorption spectra exhibit only one weak band corresponding to the transition ⁶A_1g(S) → ⁴A_1g(G); ⁴E_g(G) at 446 nm which is a characteristic of Fe³⁺ ions in octahedral symmetry.     

Combining X‐Ray Whole Powder Pattern Modeling,Rietveld and Pair Distribution Function Analyses as a Novel Bulk Approach to Study Interfaces in Heteronanostructures: Oxidation Front in FeO/Fe3O4 Core/Shell Nanoparticles as a Case Study

Understanding the microstructure in heterostructured nanoparticles is crucial to harnessing their properties. Although microscopy is ideal for this purpose, it allows for the analysis of only a few nanoparticles. Thus, there is a need for structural methods that take the whole sample into account. Here, a novel bulk‐approach based on the combined analysis of synchrotron X‐ray powder diffraction with whole powder pattern modeling, Rietveld and pair distribution function is presented. The microstructural temporal evolution of FeO/Fe₃O₄ core/shell nanocubes is studied at different time intervals. The results indicate that a two‐phase approach (FeO and Fe₃O₄) is not sufficient to successfully fit the data and two additional interface phases (FeO and Fe₃O₄) are needed to obtain satisfactory fits, i.e., an onion‐type structure. The analysis shows that the Fe₃O₄ phases grow to some extent (≈1 nm) at the expense of the FeO core. Moreover, the FeO core progressively changes its stoichiometry to accommodate more oxygen. The temporal evolution of the parameters indicates that the structure of the FeO/Fe₃O₄ nanocubes is rather stable, although the exact interface structure slightly evolves with time. This approach paves the way for average studies of interfaces in different kinds of heterostructured nanoparticles, particularly in cases where spectroscopic methods have some limitations.     

Proteic sol-gel synthesis,structure and battery-type behavior of Fe-based spinels (MFe2O4, M = Cu,Co, Ni)

Nanocrystalline Fe-based spinels (MFe₂O₄, where M = Cu, Co or Ni) were synthesized by a proteic sol-gel method. The effect of metal cation swap on the battery-type behavior was evaluated at room temperature in a three-electrode cell configuration in alkaline medium (3 M KOH). Raman spectroscopy was performed to assess the cationic distribution of divalent Cu, Co and Ni at the tetrahedral and octahedral sites, establishing a correlation with oxygen vacancies. X-ray photoelectron spectroscopy (XPS) was used to confirm oxygen vacancies and oxidative states of metal elements. Rietveld refinement analysis combined with FESEM inspection reveals the attainment of mixed spinel ferrites with nanosized crystallites (39–77 nm) and particle sizes (44–92 nm). Cyclic voltammetry and discharging curves of spinel-based electrodes indicate an improved performance for CuFe₂O₄ (Q_s = 183 C g⁻¹), followed by CoFe₂O₄ (Q_s = 79 C g⁻¹) and NiFe₂O₄ (Q_s = 32 C g⁻¹) at a specific current of 0.5 A g⁻¹. The remarkable electrochemical stability for CuFe₂O₄ is confirmed by retention capacity of 98% after 1000 charge-discharge cycles at a specific current of 1 A g⁻¹. The enhanced electrochemical performance of CuFe₂O₄ is due to an increase in Faradaic reactions boosted by a higher fraction of surface defects (determined by Raman and XPS spectroscopies) combined with a grain boundary-dependent effect responsible for a smaller charge transfer resistance as measured by electrochemical impedance spectroscopy.     

Preparation of MgH2 composite with a composition of 40%MgH2 + 30%LiBH4 + 30%(2LiBH4 + MgF2)

A mixture of containing two chemical equivalents of lithium borohyride and one equivalent of magnesium fluoride is known to yield hydrogen in an amount of about 7.6 wt% of the mixture when heated to about 150 °C at atmospheric pressure by the following reaction; 2LiBH₄ + MgF₂ = 2LiF + MgB₂ + 4H₂. In order to increase hydrogen storage capacity of Mg-based materials, a mixture with a composition of 2LiBH₄ + MgF₂ and LiBH₄with a higher hydrogen storage capacity of 18.4 wt% were added to MgH₂. MgH₂ composite with a composition of 40 wt%MgH₂ + 30 wt%LiBH₄ + 30 wt%(2LiBH₄ + MgF₂) was prepared by reactive mechanical grinding. The hydrogen storage properties of the sample were then examined. Hydrogen content vs. desorption time curves for consecutive 1st desorptions of 40 wt%MgH₂ + 30 wt%LiBH₄ + 30 wt%(2LiBH₄ + MgF₂) at 533–873 K showed that the total desorbed hydrogen quantity for consecutive 1st desorptions is 7.07 wt%.     

Phosphorus‐Doped Iron Nitride Nanoparticles Encapsulated by Nitrogen‐Doped Carbon Nanosheets on Iron Foam In Situ Derived from Saccharomycetes Cerevisiae for Electrocatalytic Overall Water Splitting

It is vitally essential to propose a novel, economical, and safe preparation method to design highly efficient electrocatalysts. Herein, phosphorus‐doped iron nitride nanoparticles encapsulated by nitrogen‐doped carbon nanosheets are grown directly on the iron foam substrate (P‐Fe₃N@NC NSs/IF) by in situ deriving from Saccharomycetes cerevisiae (S. cerevisiae), where anion elements of C, N, and P all from S. cerevisiae replace the hazardous CH₄, NH₃, and H₃P. The diffusion pattern of N, P in S. cerevisiae and contact form between metal and S. cerevisiae observably affect the composition and phase of the product during high‐temperature calcination. The obtained P‐Fe₃N@NC NSs/IF demonstrates superior electrocatalytic performance for the hydrogen evolution reaction and oxygen evolution reaction, also satisfying durability. Theoretical calculation confirms that Fe sites of P‐Fe₃N serve as the active center, and N sites and P doping regulate the hydrogen binding strength to enhance catalytic ability. Additionally, the two‐electrode electrolyzer assembled by P‐Fe₃N@NC NSs/IF as both anode and cathode electrodes needs only 1.61 V to reach 10 mA cm^?2 for overall water splitting with a superb stability. The S. cerevisiae‐based process presents a feasible approach for synthesis of nitrides, carbides, phosphides, and electrocatalytic applications.     

Structural investigation of xFe2O3 · (100 − x)[P2O5 · TeO2] glass system by FT-IR study and EPR spectroscopy

Glasses from xFe₂O₃ · (100 − x)[P₂O₅ · TeO₂] system, with 0 ≤ x ≤ 50 mol%, were investigated by X-ray diffraction, FT-IR and EPR spectroscopies. The XRD patterns show a vitreous state of studied samples for x ≤ 35 mol% Fe₂O₃. The FT-IR spectrum of the P₂O₅ · TeO₂ glass matrix reveals a structure formed from PO₄, TeO₄ and TeO₃ units. The addition and the increasing of Fe₂O₃ content modify progressively the structure of the glass matrix. The local structure in the investigated glasses was revealed by means of EPR using Fe³⁺ (3d⁵; ⁶S_5/2) ions as paramagnetic probes. The EPR spectra present two resonance absorption lines characteristic to Fe³⁺ ions centred at g_eff ≈ 2.0, for 0.5 ≤ x ≤ 35 mol% and g_eff ≈ 4.3, for 0.5 ≤ x ≤ 5 mol%. The variation of the EPR parameters, the intensity and line-width of these absorption lines, with iron ions composition has been followed.     

Template Engineering of CuBi2O4 Single‐Crystal Thin Film Photocathodes

To develop strategies for efficient photo‐electrochemical water‐splitting, it is important to understand the fundamental properties of oxide photoelectrodes by synthesizing and investigating their single‐crystal thin films. However, it is challenging to synthesize high‐quality single‐crystal thin films from copper‐based oxide photoelectrodes due to the occurrence of significant defects such as copper or oxygen vacancies and grains. Here, the CuBi₂O₄ (CBO) single‐crystal thin film photocathode is achieved using a NiO template layer grown on single‐crystal SrTiO₃ (STO) (001) substrate via pulsed laser deposition. The NiO template layer plays a role as a buffer layer of large lattice mismatch between CBO and STO (001) substrate through domain‐matching epitaxy, and forms a type‐II band alignment with CBO, which prohibits the transfer of photogenerated electrons toward bottom electrode. The photocurrent densities of the CBO single‐crystal thin film photocathode demonstrate ?0.4 and ?0.7 mA cm^?2 at even 0 V_RHE with no severe dark current under illumination in a 0.1 m potassium phosphate buffer solution without and with H₂O₂ as an electron scavenger, respectively. The successful synthesis of high‐quality CBO single‐crystal thin film would be a cornerstone for the in‐depth understanding of the fundamental properties of CBO toward efficient photo‐electrochemical water‐splitting.     

Crystal structure,oxygen permeability and stability of Ba0.5Sr0.5Co0.8Fe0.1M0.1O3−δ (M = Fe,Cr, Mn,Zr) oxygen-permeable membranes

Oxygen-permeable ceramic membrane materials of the Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO) and partially Fe-substituted Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Cr, Mn, Zr) were synthesized by solid-state reaction method. These materials possess purely cubic perovskite structure with the exception of Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Mn, Zr), in which minor impurities exist. Oxygen permeability across these dense membrane disks were measured under an air/He oxygen partial pressure gradient in the temperature range of 973–1123 K. The results demonstrated that the oxygen permeation fluxes of the Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Fe, Cr, Mn, Zr) membranes increased in the following order: Fe (BSCFO) > Cr > Zr > Mn. The corresponding activation energies for oxygen permeation of Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Fe, Cr, Zr) membranes were calculated to be similar (53 ± 4 kJ/mol), which was remarkably lower than that (99 ± 3 kJ/mol) of Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Mn) membrane. In addition, good oxygen permeation stability of the Ba_0.5Sr_0.5Co_0.8Fe_0.1M_0.1O_3−δ (M = Cr) membrane was achieved at the temperature lower than 1123 K. The X-ray diffraction (XRD) and differential thermal analysis (DTA) experiments showed that the structural stability of BSCFO could be significantly improved when Fe ions in the BSCFO material were partially substituted by Cr, Mn or Zr ions.     

Spinel ferrite MFe2O4 (M = Ni,Co, or Cu) nanoparticles prepared by a proteic sol-gel route for oxygen evolution reaction

In this work, spinels of MFe₂O₄ (M = {Ni, Co, Cu}) were successfully prepared by proteic sol-gel method using commercial flavorless gelatin as a chelating agent. To break down aggregated particles, the samples were milled in alcohol at 400 rpm for 1 h. According to Rietveld refinements and transmission electron microscopy, the samples had crystallite and particle sizes in the range of 36–53 nm and 44–147 nm, respectively, confirming the as-prepared samples in a nanoscale. X-ray diffraction and Rietveld refinement confirmed that the samples are single phase. In addition, Mössbauer spectroscopy analysis and X-ray photoelectron spectroscopy revealed the mixed spinel composition. Besides, X-ray photoelectron spectroscopy showed surface oxygen vacancies, given by ratio areas between oxygen vacancies (O_V) and oxygen in the lattice (O_L), of 0.63, 0.27 and 0.10 for NiFe₂O₄, CuFe₂O₄ and CoFe₂O₄ powders, respectively. Magnetic measurements showed ferrimagnetic behavior for all samples. Toward oxygen evolution reaction (OER), copper-oxygenated groups on the CuFe₂O₄ nanoparticle surface may play an important role, once CuFe₂O₄ showed superior electrocatalytic performance, with overpotentials of 369 mV (CuFe₂O₄) < 386 mV (NiFe₂O₄) < 448 mV (CoFe₂O₄) at a current density of 10 mA cm^?2 and Tafel slopes of 76.3 mV dec^-1 (CuFe₂O₄), 85.7 mV dec^-1 (NiFe₂O₄) and 148.1 mV dec^-1 (CoFe₂O₄). All samples exhibited mechanical stability during the OER process.     

Oxygen Scavengers Based on Titanium Oxide Nanotubes for Packaging Applications

Oxygen scavengers are commonly used in packaged foods and other oxygen sensitive goods because of the advantages they offer in maintaining quality and extending shelf life. The performance of oxygen scavengers can be influenced by several conditions, such as ambient temperature and relative humidity. We recently studied oxygen scavenging at room temperature using titanium oxide nanotubes (TONT). Prior work showed that TONTs can have oxygen uptake rates of up to three orders of magnitude higher compared with commercially available iron‐based scavengers at room temperature. However, the effect of humidity was not established. This research investigates the potential of TONTs as oxygen scavengers in packaging applications such as modified atmosphere packaging as well as a colour indicator. As opposed to commercial scavengers that need water to be active, TONT performs at their best in dry conditions, making them a strong potential candidate for pharmaceutical and medical devices industries. Copyright © 2017 John Wiley & Sons, Ltd.     

Perchlorate removal in Fe0/H2O systems: Impact of oxygen availability and UV radiation

In this study, the removal of perchlorate (0.016 mM ) using Fe⁰-only (325 mesh, 10 g L⁻¹) and Fe⁰ (10 g L⁻¹) with UV (254 nm) reactions were investigated under oxic and anoxic conditions (nitrogen purging). Under anoxic conditions, only 2% and 5.6% of perchlorate was removed in Fe⁰-only and Fe⁰/UV reactions, respectively, in a 12 h period. However, under oxic conditions, perchlorate was removed completely in the Fe⁰-only reaction, and reduced by 40% in the Fe⁰/UV reaction, within 9 h. The pseudo-first-order rate constant (k₁) was 1.63 × 10⁻³ h⁻¹ in Fe⁰-only and 4.94 × 10⁻³ h⁻¹ in Fe⁰/UV reaction under anoxic conditions. Under oxic conditions, k₁ was 776.9 × 10⁻³ h⁻¹ in Fe⁰-only reaction and 35.1 × 10⁻³ h⁻¹ in the Fe⁰/UV reaction, respectively. The chlorine in perchlorate was recovered as chloride ion in Fe⁰-only and Fe⁰/UV reactions, but lower recovery of chloride under oxic conditions might due to the adsorption/co-precipitation of chloride ion with the iron oxides. The removal of perchlorate in Fe⁰/UV reaction under oxic conditions increased in the presence of methanol (73%, 9 h), a radical scavenger, indicating that OH radical can inhibit the removal of perchlorate. The removal of perchlorate by Fe⁰-only reaction under oxic condition was highest at neutral pH. Application of the Langmuir-Hinshelwood model indicated that removal of perchlorate was accelerated by adsorption/co-precipitation reactions onto iron oxides and subsequent removal of perchlorate during further oxidation of Fe⁰. The results imply that oxic conditions are essential for more efficient removal of perchlorate in Fe⁰/H₂O system.     

Crystallization and wetting of ZnO-Al2O3-B2O3-SiO2 glass-ceramic for sealing to Kovar alloy

A new type of ZnO-Al₂O₃-B₂O₃-SiO₂ glassceramics seals to Kovar in electronic packaging was developed, whose coefficient of thermal expansion (CTE) and electrical resistance were 5.2 × 10⁻⁶/°C and over 1 × 10¹³ Ω·cm, respectively. The major crystalline phases in the glass-ceramics seals were ZnAl₂O₄, ZnB₂O₄ and NaSiAl₂O₄. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of the alkali metal ions into the crystal lattices. It was found that the crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner parts, which makes the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature showed great effect on the wetting angle. Strong interfacial bonding was obtained, which was mainly attributed to the interfacial reaction between SiO₂ and FeO or Fe₃O₄. This paper was presented at 2008 MRS International Materials Research Conference and won the student best paper award of the conference.     

Preparation and characterization of Mn2O3/TiO2 nanomaterials synthesized by combination of CVC and impregnation method with different Mn loading concentration

TiO₂ nanomaterials were synthesized by a chemical vapor condensation and loaded with 2–10 wt% manganese by impregnation. Thermally treated particles were characterized by XRD and EXAFS. Particles with 5 wt% Mn content showed the most dispersed Mn components in the supported TiO₂ with the lowest crystallinity. BET and HR-TEM showed that their surface area and pore volume increased to 299.5 m² g^?1 and 0.329 cm³ g^?1, respectively. TPR and XPS showed these particles to have higher oxygen mobility and redox properties than commercial P25 similarly prepared and loaded with 5 wt% Mn₂O₃. They also had greater amounts of Mn³⁺ groups on their surfaces. 5 wt% manganese loaded TiO₂ particles fabricated by CVC and impregnation are expected to have broad applicability.     

Friction and wear of P/M Al-20Si-Al2O3 composites in kerosene

The results of friction and wear of powder metallurgy (P/M) Al-20 wt% Si-3 wt% Cu-1 wt% Mg-(2.5–10) vol% Al₂O₃ particulate-reinforced composites have been compared with those of the P/M aluminium alloy matrix and A-390 cast piston aluminium alloy. It was found that Al₂O₃ reinforcement reduces wear by five to eight times when mating with cast iron in kerosene: The higher the reinforcement volume, the lower was the wear. With increased volume of reinforcement the wear mechanism of composites changed from the adhesive to the fatigue/delaminating one. The wear of the cast-iron counter sample was several times higher than that for P/M composites. Considering the life of the piston-piston ring couple, the piston composite with 10 vol% Al₂O₃ appears to be the best. The rate of clearance development for this couple is twice as low as that for the conventional piston alloys.