Effects of Dependence between Solid Solution and Surface Excess in Nanoparticles

2010 ◽  
Vol 660-661 ◽  
pp. 995-1000 ◽  
Author(s):  
Gilberto J. Pereira ◽  
Douglas Gouvea
Keyword(s):  
Solid Solution ◽  
Particle Size ◽  
Nitric Acid ◽  
Direct Relationship ◽  
Previous Analysis ◽  
Weak Acid ◽  
Surface Excess ◽  
Pechini’S Method ◽  
Work Samples ◽  
Mg Doped

In this work, samples of 10 mol% Mg-doped SnO2 were synthesized by Pechini's method and calcined at 500°C. Previous analysis suggests that the additive is preferentially located on the surface of nanoparticles as a surface excess. Since MgO is highly soluble even in weak acid medium, the samples were "washed" with concentrated nitric acid for a few hours in order to remove Mg from the surface. After the lixiviation, the sample was thermally treated again. This procedure was carried out five times using the same sample, and the dependence between macroscopic properties and surface excess was demonstrated, since it was detected a direct relationship on particle size and isoelectric point on each new washing. Also, a new method to measure surface excess in solids was applied.

Synthesis and Characterization of SrO-Supported Al2O3 Applied as Heterogeneous Catalys

2012 ◽  
Vol 727-728 ◽  
pp. 1108-1112 ◽  
Author(s):  
Gilberto J. Pereira ◽  
Fernando dos Santos Ortega
Keyword(s):  
High Stability ◽  
Catalyst Support ◽  
Strontium Carbonate ◽  
Synthesis And Characterization ◽  
Polymeric Precursor ◽  
Surface Excess ◽  
Basic Character ◽  
Pechini’S Method ◽  
Work Samples

In this work, samples of 15 mol% Sr-doped Al2O3 were synthesized by Pechini's method and calcined at 900°C. DRX analysis showed that only corundum phase is present, and no shift on the main peaks was observed, suggesting that the additive is preferentially located on the surface of nanoparticles as a surface excess. SrO show high basic character and is applied as heterogeneous catalyst in transesterification of soybean oil to produce biodiesel. Since SrO is difficult to obtain through Pechinis method, due to high stability of SrCO3, the use of Al2O3 as a catalyst support produced via polymeric precursor was studied, and the reaction of transesterification was successfully made, because the crystallization of strontium carbonate on the corundum surface was avoided using the washing procedure. Also, the catalyst was characterized by DSC, isoelectric point and surface area.

scholarly journals Optimization of Yb2O3-Gd2O3-Y2O3 Co-Doped ZrO2 Agglomerated and Calcined Powders for Air Plasma Spraying

Coatings ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 373
Author(s):  
Zheng Yan ◽  
Haoran Peng ◽  
Kang Yuan ◽  
Xin Zhang
Keyword(s):  
Solid Solution ◽  
Particle Size ◽  
Plasma Spraying ◽  
Cubic Phase ◽  
Thermal Barrier ◽  
Air Plasma ◽  
Air Plasma Spraying ◽  
Barrier Coating ◽  
Controllable Preparation ◽  
Co Doped

Yb2O3-Gd2O3-Y2O3 co-doped ZrO2 (YGYZ) is considered to be a promising material in thermal barrier coating (TBC) applications. In this study, 2Yb2O3–2Gd2O3–6Y2O3–90ZrO2 (mol.%) (10YGYZ) feedstock candidates for air plasma spraying (APS) were prepared by calcination of agglomerated powders at 1100, 1200, 1300, 1400, and 1500 °C for 3 h, respectively. Incomplete solid solution was observed in calcined powders at 1100, 1200 and 1300 °C, and the 1500 °C calcined powder exhibited poor flowability due to intense sintering effect. The 1400 °C calcined powders were eventually determined to be the optimized feedstock for proper phase structure (cubic phase), great flowability, suitable apparent density and particle size distribution, etc. 10YGYZ TBCs with the optimized feedstock were prepared by APS, exhibiting pure c phase and good chemical uniformity. Controllable preparation of coatings with different porosity (i.e., 7%–9% and 12%–14%) was realized by stand-off distance adjustment.

A Simple Dissolved Metals Mixing Route to Prepare Nanostructured Mg0.8Zn0.2TiO3 Solid Solution

2015 ◽  
Vol 1112 ◽  
pp. 47-52 ◽  
Author(s):  
Frida Ulfah Ermawati ◽  
Suasmoro Suasmoro ◽  
Suminar Pratapa
Keyword(s):  
Solid Solution ◽  
Particle Size ◽  
Rietveld Analysis ◽  
Dissolved Metals ◽  
Intermediate Phases ◽  
Particle Size Analyzer ◽  
Ft Ir ◽  
Xrd Patterns ◽  
Zn Ions

A study of liquid mixing route to synthesize high purity Mg0.8Zn0.2TiO3 nanopowder, a candidate dielectric ceramics, has been successfully performed. Formation of the phases on the dried powder was studied using TG/DTA, XRD and FT-IR data. Rietveld analysis on the collected XRD patterns confirmed the formation of solid solution in the system. Such solid solution can be obtained from the powder calcined at 500 °C, but calcination at 550 °C gave rise to the most optimum molar purity up to 98.5% without intermediate phases. The role of Zn ions on the formation of solid solution was also discussed. Homogeneity of particle size distribution and nano-crystallinity of the system was verified from the particle size analyzer data, TEM image and the Rietveld analysis output.

scholarly journals Preparation of Ceria-Zirconia Mixed Oxide by Hydrothermal Synthesis

2015 ◽  
Vol 9 (7) ◽  
pp. 134 ◽  
Author(s):  
Siti Machmudah ◽  
M. Akmal Hadian ◽  
Lenno Samodro K. ◽  
Sugeng Winardi ◽  
Wahyudiono Wahyudiono ◽  
...  
Keyword(s):  
Solid Solution ◽  
Particle Size ◽  
Hydrothermal Synthesis ◽  
Mixed Oxides ◽  
Synthesis Process ◽  
Growth Morphology ◽  
Mixed Powder ◽  
Xrd Pattern ◽  
Tube Reactor ◽  
Internal Volume

Ceria-zirconia mixed oxides have been synthesized by hydrothermal synthesis process. Under hydrothermalconditions, water potential to control the direction of crystal growth, morphology, particle size and sizedistribution, because of the controllability of thermodynamics and transport properties by pressure andtemperature. The synthesis was carried out at temperatures of 150 − 200 oC and pressure of 5 MPa in a batchreactor. The reactor made of SUS 304 tube reactor with internal volume of 8.8 ml. The synthesized productswere calcined and characterized using SEM, XRD and FTIR. The results showed that the particles formed weresphere shaped particles with smooth morphology and the size of particle diameters were 35, 61, and 31 nm onaverage for reactions temperatures of 150, 180, and 200oC, respectively. The XRD pattern indicated thatceria-zirconia mixed powder was uniformly distributed in the structure to form a homogeneous solid solution.

scholarly journals Surface and Catalytic Properties of NiO and Co3O4 Solids Doped with Cobalt and Nickel Ions

2002 ◽  
Vol 20 (5) ◽  
pp. 467-484
Author(s):  
G.A. El-Shobaky ◽  
A.M. Turky ◽  
A.M. Ghozza
Keyword(s):  
Particle Size ◽  
Thermal Treatment ◽  
Surface Area ◽  
Catalytic Properties ◽  
Excess Oxygen ◽  
Average Particle ◽  
Surface Excess ◽  
Nickel Ions ◽  
Nickel Species ◽  
Cobalt And Nickel

The effects of doping NiO and Co3O4 solids with cobalt and nickel species on their surface and catalytic properties were investigated. The amounts of dopant, in the form of the corresponding nitrate, were varied between 0.5–6.0 mol% cobalt ions and 2.0–6.0 mol% nickel ions. Pure and variously doped solids were subjected to thermal treatment at 300–700°C. The techniques employed were XRD, nitrogen adsorption at −196°C, decomposition of H2O2 at 30–50°C and estimation of the amount of surface excess oxygen on the variously prepared solids as determined by the hydrazine method. The results obtained revealed that the pure and variously doped NiO samples precalcined at 300°C consisted of a finely divided NiO phase having an average particle size of ca. 40 Å. Pure and variously doped Co3O4 specimens preheated at 500°C and 700°C were composed of a Co3O4 phase with a much bigger particle size (230 Å and 350 Å, respectively, for the solids precalcined at 500°C and 700°C). Doping of NiO followed by thermal treatment at 300°C and 500°C resulted in a measurable decrease in its BET surface area (19–23%), while doping of Co3O4 with nickel species followed by heating at 500°C and 700°C brought about a significant increase in its specific surface area (56–60%). Doping each of the NiO and Co3O4 solids with cobalt and nickel species greatly increased the amount of surface excess oxygen and effected a considerable increase in their catalytic activities. This increase was, however, much more pronounced in the case of NiO which attained a value of ca. 100-fold. Doping of NiO with cobalt species followed by thermal treatment at 300°C and 500°C decreased the activation energy (DE) of the catalyzed reaction to an extent proportional to the amount of dopant added. On the other hand, doping of Co3O4 with nickel species followed by thermal treatment at 500°C and 700°C did not change the value of DE. These results suggest that doping of Co3O4 with nickel species did not modify the mechanism of the catalyzed reaction but increased the concentration of catalytically active sites without changing their energetic nature.

scholarly journals Technical Note: Evaporation of polar stratospheric cloud particles, in situ, in a heated inlet

2005 ◽  
Vol 5 (1) ◽  
pp. 97-106 ◽  
Author(s):  
T. Eidhammer ◽  
T. Deshler
Keyword(s):  
Particle Size ◽  
Nitric Acid ◽  
Size Distribution ◽  
Technical Note ◽  
Ternary Solution ◽  
Slow Evaporation ◽  
Partial Pressures ◽  
Polar Stratospheric Cloud ◽  
Stratospheric Clouds

Abstract. In December 2001 and 2002 in situ aerosol measurements were made from balloon-borne platforms within polar stratospheric clouds (PSC) which contained particles of supercooled ternary solution (STS), nitric acid trihydrate (NAT) and ice. Particle size and number concentrations were measured with two optical particle counters. One of these included an ~80cm inlet heated to K to evaporate the PSC particles and thus to obtain measurements, within PSCs, of the size distribution of the particles upon which the PSCs condensed. These measurements are compared to models, described here, that calculate the evaporation of PSC particles at and for an inlet transition time of about 0.1s. The modeled evaporation for STS agrees well with the measurements. For NAT the modeled evaporation is less than the evaporation measured. The primary uncertainty concerns the phase and morphology of NAT particles as they are brought to temperatures >50K above equilibrium temperatures for NAT at stratospheric partial pressures. The slow evaporation of NAT in heated inlets could be used to identify a small NAT component within a mixed phase PSC dominated by STS.

MICROSTRUCTURE AND MAGNETIC PROPERTIES OF Sm2Fe17NNx−ALLOY- POWDERS AND OF BONDED ANISOTROPIC MAGNETS

1993 ◽  
Vol 07 (01n03) ◽  
pp. 716-720
Author(s):  
B. WALL ◽  
M. KATTER ◽  
W. RODEWALD ◽  
M. VELICESCU
Keyword(s):  
Solid Solution ◽  
Particle Size ◽  
Magnetic Properties ◽  
Average Particle Size ◽  
Average Particle ◽  
Interstitial Solid Solution ◽  
Demagnetization Curve ◽  
Microstructure And Magnetic Properties

In cast Sm2Fe17 ingots minor fractions of SmFe2 and SmFe3 may occur. Nitrogenation of such alloy-powders inidicates that only Sm2Fe17 forms an interstitial solid solution whereas SmFe2 and SmFe3 decompose directly into SmN and α-Fe. From Sm2Fe17Nx alloy powders with an average particle size of about 3 μm anisotropic magnets were prepared by adding 15 wt% Zn-powder. Annealing at 390 ºC results in intrinsic coercivities > 15 kOe promoted by the formation of an unknown binary Fe8Zn92-compound. Whereas annealing at temperatures > 420 ºC leads to the formation of binary Fe3Zn7 and ternary Sm2FeZn2. By the formation of Sm2FeZn2 from Sm2Fe17Nx+Zn some α-Fe occurs inducing a step in the demagnetization curve J(H).

Effects of Dissolving Agents on Particle Size Reduction of Titanium Dioxide Synthesized by Solution Combustion Technique

2016 ◽  
Vol 690 ◽  
pp. 236-239
Author(s):  
Oratai Jongprateep ◽  
Rachata Puranasamriddhi
Keyword(s):  
Particle Size ◽  
Titanium Dioxide ◽  
Sulfuric Acid ◽  
Nitric Acid ◽  
Average Particle Size ◽  
Average Particle ◽  
Particle Sizes ◽  
Solution Combustion ◽  
Initial Reagent ◽  
Combustion Technique

High photocatalytic activity of nanoparticulate titanium dioxide has attracted worldwide attention. Synthesis techniques of the nanoparticles, however, often require high energy supply or costly initial reagents. Solution combustion technique is an energy-effective technique capable of synthesizing nanosized titanium powders. This research aimed at utilizing a less expensive initial reagent in synthesis of nanoparticulate titanium dioxide by the solution combustion technique. The research also examined effects of dissolving agents on chemical composition and particle sizes of the synthesized powders. A low-cost initial reagent, titanium dioxide with average particle size of 154 nanometers, was dissolved in sulfuric acid or dispersed in nitric acid prior to the combustion. Experimental results revealed that the pure anatase phase titanium dioxide was successfully obtained in powders prepared from both sulfuric acid and nitric acid. The average particle size of the powder prepared from sulfuric acid was 77 nanometers, while that of the powder prepared from nitric acid was 117 nanometers. The difference in particle sizes was attributed to solubility of the initial reagent in the acid. Complete solution of initial reagent in sulfuric acid was the main factor attributed to finer particle size.

scholarly journals NAT-rock formation by mother clouds: a microphysical model study

2002 ◽  
Vol 2 (2) ◽  
pp. 93-98 ◽  
Author(s):  
S. Fueglistaler ◽  
B.P. Luo ◽  
C. Voigt ◽  
K.S. Carslaw ◽  
Th. Peter
Keyword(s):  
Particle Size ◽  
Nitric Acid ◽  
Particle Size Distribution ◽  
Gas Phase ◽  
Cloud Base ◽  
Number Density ◽  
Monodisperse Particle ◽  
Model Study ◽  
Rock Mechanism ◽  
Stratospheric Clouds

Abstract. Polar stratospheric clouds (PSCs) of type 1a or 1a-enh containing high number densities of nitric acid trihydrate (NAT) particles, can act as mother clouds for extremely large NAT particles, termed NAT-rocks, provided the air below the clouds is supersaturated with respect to NAT. Individual NAT particles at the cloud base fall into undepleted gas phase and rapidly accelerate due to a positive feedback between their growth and sedimentation. The resulting reduction in number density is further enhanced by the strong HNO3 depletion within a thin layer below the mother cloud, which delays subsequent particles. This paper introduces the basic microphysical principles behind this mother cloud/NAT-rock mechanism, which produces 10-4 cm-3 NAT-rocks with radii around 10 mm some kilometers below the mother cloud. The mechanism does not require selective nucleation and works even for a monodisperse particle size distribution in the mother cloud.

Rice Husk Demineralization: Effect of Washing Solution on Its Physicochemical Structure and Thermal Degradation

2021 ◽  
Vol 24 (2) ◽  
pp. 37-42
Author(s):  
Hesti Wijayanti ◽  
Iryanti Fatyasari Nata ◽  
Chairul Irawan ◽  
Rinny Jelita
Keyword(s):  
Nitric Acid ◽  
Thermal Degradation ◽  
Rice Husk ◽  
Strong Acid ◽  
Weak Acid ◽  
Raw Material ◽  
Ftir Analysis ◽  
Thermochemical Process ◽  
And Behavior ◽  
The Impact

Generally, biomass consists of various amounts of minerals. These minerals influence the biomass characteristics and behavior during their use in a thermochemical process such as pyrolysis. The conversion during pyrolysis and its final product will be affected. This research was carried out to study the impact of washing treatment in water and acid solutions on the rice husk as the raw material for pyrolysis. Also, the effect of acid strength (citric acid as the weak acid while nitric acid as the strong acid) and its concentration (1, 5, and 10 wt.%) was investigated. The results confirmed from the thermogravimetry (TGA/DTG) analysis, surface analysis (SEM), and spectra (FTIR) analysis describe the treatment using water caused less change on the rice husk surface structure and its thermal degradation. However, it seems hard to reduce the minerals (proved from XRF analysis). Meanwhile, the treatment using acids solution resulted in lower mineral composition than the rice husk without treatment. This result is more visible for demineralization using a 5 wt.% nitric acid solution. However, for a higher concentration (washing treatment using 10 wt.% solutions of nitric acid), the degradation on rice husk structure was more occurred.

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