Search results

Nevertheless, despite the simplicity of configuration and operation of the sensor, the studies showed that gas sensing effect in metal oxides (MOXs) is a very complex phenomenon, depending on all metal oxide parameters, such as thickness, grain size, porosity, grain faceting, agglomeration, bulk conductivity, surface architecture, grain network, surface stoichiometry, catalytic reactivity, band gap, etc. [1-7].
It is known that the increase of the grain size leads to the transformation of the shape of the grains from spherulites to crystallites which are being faceted by various crystallographic planes [5].
They provide a more active phase, stabilizing the surface area, or stabilize a favorable valence state, increase the number of suitable donor or acceptor species involved in gas sensing reactions.
However, in reality there is very limited number of scientists caring out research in this direction.
It was found that this effect was related to the size of PdO particles formed on the surface of the SnO2 grains.

Introduction There is much current interest in producing metals with very small grain sizes.
However, processing bulk aluminium alloys to sub-micrometer grain sizes is rather difficult, and normally the smallest grain sizes achievable through conventional thermo-mechanical means are ∼15-20 µm [1-4].
Several investigations have shown that, during deformation, grains in polycrystals subdivide into many small crystallites, each having a crystal orientation rotated toward neighbouring and to the original grains.
The requirement of a small and stable grain size is usually achieved by using either two-phase alloys or materials containing precipitates that impede grain boundary mobility and thereby restrict the development of grain growth.
This is primarily due to a more diffuse and larger number of fine Al3(Sc1-x,Zrx) dispersoids, which more effectively pinned boundaries, compared with Al3Zr dispersoids.

Most of the voids had small crystal grains inside them.
As the extension temperature increased, the number of void structures declined considerably.
Some crystal grains are generally found inside the void structures, suggesting that the separation happened on the interface between these grains and the surrounding material is responsible for the forms of void structures.
Although increasing the annealing temperature affects the sizes and numbers of spherulites that are formed in films, these films tend to have similar sizes and numbers of void structures after the same extension process.
The walls of the voids adhere to the internal crystal grains, and their shapes change from rounded to flower-like.

The result showed that under the same experimental parameters the coating of the two-ways pulse current electroplating is superior to conventional DC electroplating coating in the surface morphology, grain size and microstructure and so on.
Liping Wang, etc. [3] reported in the nickel-diamond composite plating bath, the addition of cobalt ion can significantly improve the number and dispersion of the diamond particles in the metal substrate, and also can increase the adhesion ability between the substrate and the diamond particles , which makes the hardness and wear resistance improved greatly.
From Fig. 2 it is found that the Ni-Co alloy coating possess much smaller grain size, smoother and uniform surface than pure Ni coating, which indicates that the addition of Co ions in the bath could lead to grain refinement to decrease the size of grains.
The improvement in surface morphology and microstructure is attributed to the introduction of cobalt ions, which could result in grain refinement so as to decrease the size of grains.
The result showed that under the identical conditions the coating prepared by the two-ways pulse current electroplating is superior to the conventional DC electroplating coating in the surface morphology, grain size and microstructure areas.

The grain size of the samples becomes larger with the increasing temperature.
The raw data was matched with the standard ICDD number (98-010-4439).
It shows that the average grain size increases with the increasing temperature.
PZT 40 Hr 1200C sample shows fairly uniform grain sizes with clear grain boundaries.
This samples show the densest microstructure with grain size range of 6–7 μm.

It was concluded that the crystallinity quality can be improved, i.e. reduced number of large angle grains and twins, if the melt was markedly superheated (about 20K higher than the melting point for CdTe) or long-time held before growth.
Seeded growth can help reduce the number of grain boundaries in the boule but it also causes complications during pre-growth heating in that it is difficult to keep the temperature over the melt adjacent to the seed 20K above the liquidus temperature because the seed will be dissolved before growth commences.
The number of grains for the CdTe-2 ingot was confirmed by SWBXT, which showed two major grains.
SWBXT diffraction patterns on CdTe-4 boule show one relatively strain-free large grain, G1, and two other small grains which are heavily strained, probably due to ampoule wall contact.
Grain 1 (320) Grain 2 (531) Error!

The better mechanical property was attributed to fine-grained microstructures in the as-rolled CSP strips.
TEM analysis of precipitated carbides show that a large number of small carbides are precipitated in the matrix, as illustrated in Fig. 4.
In addition, CSP can realize single-pass large reduction ratio and benefits the recrystallization of austenite grains.
Therefore, CSP products have more fine-grained and uniform microstructures compared with conventional process [4-7].
Thus, the CSP products have more fine-grained microstructures and higher hardness than the conventional process products.

A limited precipitation of chromium carbides and nitrides at the grain boundaries has been detected in both grades.
Different phases have been observed by SEM examination of polished samples, using the backscattered electron (BSE) signal, on the basis of atomic number contrast effect: the ferrite appears slightly darker than austenite, while the secondary phases would appears lighter.
The SEM operated at 25 kV; the BSE detector was set to maximize the atomic number contrast, allowing ferrite, austenite and other phases to be identified.
The same grain boundaries precipitation was observed after soaking times longer than 40' at 650 °C, while at 750 °C the first grain boundary precipitation has been detected after a 20 min treatment (Fig.1a) and can still be observed after 20 h (Fig.1b).
The nitride precipitation is evident just below the austenite grain boundary, as it has moved towards the austenite (ferrite) giving the precipitation inside the austenite grains.

Since densities lay on the intermediate stage of sintering where no significant grain growth occurred, the effects of grain sizes and density variations could be minimized.
Similar results were also reported by a number of researchers [16-18].
The electric field preferentially heated the grain boundary resulting in the enhancement of the grain boundary diffusion during sintering is one of them [17].
The pre-exponential represents the number of atomic jumps per time.
Kang, Sintering, Densification, Grain Growth and Microstructure, Elsevier, 2005 [13] W.

Using the number of passes at 50 mm/s speed as the time variable, the Almen intensity of the blasting setup was defined as 358A.
Near surface area has undergone extensive grain refinement due to heavy deformation.
Below the deformed layer grains were clearly more equiaxed and showing polygonal morphology with annealing twins also present.
The color of the grains in the HTed condition were clearly more uniform due to a considerably lower amount of low angle grain boundaries (LAGB) after annealing, which indicates the deformation to be localized into the shallow top layer, i.e. the effect of SSP on the surface is clear also for the HT structure.
Similar phenomenon was recorded with the HT condition and also the numbers showed a 3% increase in the YS.