scholarly journals Porogenic Behavior of Water in High-Alumina Castable Structures

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Rafael Salomão
Keyword(s):  
Complex Geometry ◽  
Total Porosity ◽  
External Pressure ◽  
Processing Method ◽  
High Alumina ◽  
Air Entrapment ◽  
Hydraulic Binder ◽  
Hydroxylation Reaction ◽  
Water Contents ◽  
Hydratable Alumina

Direct casting is a processing method that can produce large parts of complex geometry. It uses dispersions of ceramic particles in water and a hydraulic binder for consolidation. Studies on castable structures have reported the generation of a significant fraction of pores due to the presence of water. This effect occurs because drying preserves part of the interparticle pores originally occupied by water. The fraction of pores obtained in these cases can reach levels higher than 50%, affecting the properties of the structure. However, the porogenic behavior of water in these materials was not investigated in depth. In this work, aqueous suspensions of calcined alumina and hydratable alumina (hydraulic binder) of different water contents (40–60 vol.%) were prepared in a paddler mixer. For compositions of lower (5–35 vol.%) or higher (66–80 vol.%) water amounts, casting and curing steps were assisted by external pressure and a rotating device, respectively, to produce homogeneous microstructures. The total porosity after drying was similar to the initial volumetric content of water in the compositions when side effects, such as sedimentation and air entrapment, were prevented. Below water content of 25 vol.%, particles packing flaws became the main pore generator and the hydroxylation reaction of the binder no longer occurred effectively.

scholarly journals Comparison of the Physical Characteristics of Growing Media Containing Composted Oak Sawdust and Sphagnum Peat

HortScience ◽  
1996 ◽  
Vol 31 (4) ◽  
pp. 657b-657
Author(s):  
F. M. Jeneidi ◽  
C. J. Starbuck
Keyword(s):  
Bulk Density ◽  
Poultry Manure ◽  
Total Porosity ◽  
Physical Characteristics ◽  
Sphagnum Peat ◽  
Growing Medium ◽  
Significant Difference ◽  
The Media ◽  
Corn Plants ◽  
Water Contents

The physical characteristics of a container growing medium containing 2 oak sawdust composted with poultry manure: 1 vermiculite: 1 perlite were compared with those of a similar medium containing sphagnum peat rather than compost. Both media were amended with inorganic nutrients based on laboratory analysis to make them nutritionally comparable and with AquaGro wetting agent at 800 g·m–3. Moisture release characteristics of the media were evaluated using tension cups in which desorption at 5, 10, 20, 40, 80, 100, and 160 cm of water was measured. While bulk density of the peat mix (0.129 g·cm–3) was, significantly lower than that of the compost mix (0.157 g·cm–3), total porosity of the peat mix (84%) was significantly greater than that of the compost mix (79%). Air-filled and water-filled porosities of the peat and compost mixes were 18.2% 16.2% and 75.2% 70.5% of container volume, respectively. While the peat mix held more water at tensions between 5 and 20 cm, there was no significant difference between the volumetric water contents of the two media between 20 and 160 cm. Fresh and dry weights of corn plants grown for 3 weeks in compost- and peat-based media were not significantly different.

High-Alumina Heat-Insulating Materials Based on a Hydraulic Binder

2018 ◽  
Vol 59 (2) ◽  
pp. 140-143
Author(s):  
T. A. Varenikova ◽  
E. N. Gokova ◽  
V. A. Doroganov ◽  
E. A. Doroganov ◽  
E. I. Evtushenko
Keyword(s):  
High Alumina ◽  
Insulating Materials ◽  
Hydraulic Binder

Low-temperature Mo-catalyzed growth of crystalline Si3N4 by CVD

1993 ◽  
Vol 51 ◽  
pp. 918-919
Author(s):  
K.L. More ◽  
R.A. Lowden ◽  
T.M. Besmann
Keyword(s):  
Vapor Deposition ◽  
Hot Isostatic Pressing ◽  
Chemical Vapor ◽  
Processing Method ◽  
Crystalline Material ◽  
Structural Ceramic ◽  
Alternative Processing ◽  
Strong Candidate ◽  
Hot Pressing Sintering ◽  
Processing Techniques

Silicon nitride possesses an attractive combination of thermo-mechanical properties which makes it a strong candidate material for many structural ceramic applications. Unfortunately, many of the conventional processing techniques used to produce Si3N4, such as hot-pressing, sintering, and hot-isostatic pressing, utilize significant amounts of densification aids (Y2O3, Al2O3, MgO, etc.) which ultimately lowers the utilization temperature to well below that of pure Si3N4 and also decreases the oxidation resistance. Chemical vapor deposition (CVD) is an alternative processing method for producing pure Si3N4. However, deposits made at temperatures less than ~1200°C are usually amorphous and at slightly higher temperatures, the deposition of crystalline material requires extremely low deposition rates (~5 μm/h). Niihara and Hirai deposited crystalline α-Si3N4 at 1400°C at a deposition rate of ~730 μm/h. Hirai and Hayashi successfully lowered the CVD temperature for the growth of crystalline Si3N4 by adding TiCl4 vapor to the SiCl4, NH3, and H2 reactants. This resulted in the growth of α-Si3N4 with small amounts of TiN at temperatures as low as 1250°C.

Trust: A National Project

2015 ◽  
pp. 138-146
Author(s):  
N. Rozinskaya ◽  
I. Rozinskiy
Keyword(s):  
Social Capital ◽  
Civil Society ◽  
Everyday Life ◽  
Western Europe ◽  
External Pressure ◽  
National Project ◽  
Low Level ◽  
General Trust

This article deals with the genesis of general trust and social capital in contemporary Russia, which faces the external pressure. The low level of general trust is noted, its economic, social and everyday life implications are considered, an explanation of Russia’s lower than in western Europe level of trust is provided. Considering society’s level of trust and social capital as externalia, the authors conclude that there is a necessity to "produce" trust intentionally. Promotion of collective charity is proposed as a mechanism of such "production". It is stressed that in order to activate the potential of trust in a society, there is a need for ideological and symbolic basis linked to its history. Russian People’s Unity Day, understood as the birthday of Russian civil society, is proposed to be used in this respect.

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