• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1131
  • 302
  • 164
  • 70
  • 48
  • 29
  • 26
  • 15
  • 8
  • 8
  • 8
  • 8
  • 8
  • 8
  • 7
  • Tagged with
  • 2495
  • 597
  • 350
  • 276
  • 228
  • 220
  • 217
  • 196
  • 192
  • 186
  • 156
  • 152
  • 139
  • 125
  • 124
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
251

Characterisation of coal slurries for introduction into ICP OES for multi-element determinations

Mujuru, M, McCrindle, RI, Panichev, N 22 January 2009 (has links)
The characterisation and stability of coal slurries for introduction into an inductively coupled plasma optical emission spectrometer (ICP OES) and the application of slurries in the analysis of coal was investigated. The importance of rheology and the stability of the coal slurries on the analytical results produced by ICP OES was demonstrated. The homogeneity and stability of various coal slurries were characterised by sedimentation tests, scanning electron microscopy (SEM), zeta potential and viscosity measurements. The porosities and surface areas of different South African coals and a mechanism for the adsorption of the dispersants onto the coals were determined using low-temperature nitrogen physisorption studies. The possibility of partially solubulising the coal in N,N-dimethylformamide (DMF) was investigated. SEM indicated that DMF solubulised coal fines and that 0.1% (m/v) Triton X-100 with 10% (v/v) DMFresulted in well dispersed slurries relative to other dispersants (glycerol, PEI and water). Slurry analysis of coarse and ground coal in 0.1% (m/v) Triton X-100, showed that higher emission intensities and better precision was obtained when using ground coal. This was confirmed by lower RSDs (less than 5% for most of the elements analysed) relative to the unground, coarse coal. Glycerol slurries gave higher RSDs (higher than 5% for most of the elements) most of the time, thus negatively influencing the precision of measurement. Physisorption studies indicated that ground coal had up to ten times higher surface areas than coarse coal. The higher surface areas for fine ground coals suggested why they were better dispersed and thus better transported into the plasma, resulting in higher emission signals. Zeta potentials indicated that for all dispersants, the coal particles were well repelled from each other, although SEM pictures indicated better dispersion for 0.1% (m/v) Triton X-100 with 10% (v/v) DMF. It was demonstrated that higher intensities and higher precision could be obtained with well dispersed and stable coal slurries.
252

Multi-element determinations of N,N-dimethylformamide (DMF) coal slurries using ICP-OES

Mujuru, M, McCrindle, RI, Botha, BM, Ndibewu, PP 01 January 2009 (has links)
a b s t r a c t A slurry nebulisation technique was applied for elemental analysis of bituminous coals SARM 18, SARM 19 and four coals from three different seams in Witbank, South Africa, by inductively coupled plasma optical emission spectroscopy (ICP-OES). Major elements (Al, Ca, Fe, Mg, S, Si and Ti) and trace elements (Ba, Cr, Mn, Ni, Sr, V, Zn and Zr) in coal were determined. Various slurry preparations were evaluated using two dispersants (glycerol and Triton X-100) and by varying the concentration of dispersants, between 0.1% and 1.0% (v/v). The effect of initially solubilising the ground coal in N,N-dimethylformamide (DMF) was investigated by varying the volume of DMF added. The effect of wet grinding with DMF was investigated. Wet grinding with DMF was shown to drastically reduce particle sizes (50.0% < 0.28 lm and 90.0% < 6.17 lm) as compared to dry grinding (50.0% < 5.25 lm and 90.0% < 11.1 lm). The reduced particle sizes and increased transport efficiency of the coal slurries led to improved analytical recoveries of elements in the reference coal, SARM 18. The best analytical recoveries for all elements were achieved using 0.1% Triton X-100 with 10.0% DMF. Results obtained by ICP-OES after wet grinding of the coal with DMF, using 0.1% Triton X-100, also gave excellent recoveries (Al, 100%; Ca, 103%; Cr, 106%; Fe, 102%; Mg, 100%; Mn, 104%; Ni, 109%; Si, 102%; Ti, 95.0%; and V, 108%). The results obtained with 10.0% DMF and 0.1% Triton X-100 were in agreement with certified values for all selected elements according to paired t-test at the 95.0% confidence level. Selected elements (Al, Ca, Fe, Mg, Mn, Si, Ti and V) were also analysed with X-ray fluorescence for comparison with results obtained from ICP-OES. Analysis by ICP-OES of microwave digested coal was also carried out. It is suggested that the DMF slurry technique could be used for routine analysis of bituminous coals.
253

CATALYST LOSS DURING POTASSIUM-CATALYZED CARBON DIOXIDE GASIFICATION OF COAL CHAR AND CARBON

Talverdian, Tevan January 1984 (has links)
No description available.
254

Use of the Laplace transform for the time resolution of rapid processes applied to coal volatilization

Hahn, Werner Artur, 1948- January 1977 (has links)
No description available.
255

Description of Alethopteris from the Williamson #3 Mine, Lucas County, Iowa: anatomical variation, diversity, paleoecology

Slone, Elizabeth Dunbar Jones 30 September 2004 (has links)
For more than 100 years, Pennsylvanian permineralized peats have been studied for their exceptionally preserved plant remains. Late Atokan-early Desmoinesian coal balls from the Williamson # 3 deposit in south-central Iowa were preserved by the permineralization of soluble carbonate into pores in the peat and plant cells creating carbonate nodules. These nodules, referred to as coal balls, protect the plant remains from the compaction associated with coal allowing for the analysis of anatomically preserved plants from Pennsylvanian. The Williamson #3 deposit is unusual because it is dominated by a diverse assemblage of gymnosperms. Other deposits of similar age in Iowa are dominated by a mixture of cordaitalean gymnosperms, tree-ferns, and medullosan gymnosperms; while, other North American deposits are dominated by lycopsids with tree-ferns and seed-ferns as the subdominant vegetation. Because vegetation types differ with environment, analysis of the Alethopteris pinnules from the Williamson #3 Mine provides insight into the ecology of a peat-producing swamp during the Pennsylvanian, and allows for the comparison of this deposit to others in North America. The focus of this study is the description of a distinct morphotype of Alethopteris from the Williamson #3 Mine. Alethopteris pinnules described from other mines were used to compile a traits list and compare measured and descriptive characteristics. The objective of this study is to gain a better understanding of changes in swamp vegetation during the Pennsylvanian, and the effect of environmental variation on the dominant vegetation in peat swamps.
256

Ignition and combustion of pulverized coal particles injected by an opposed jet to a flat flame burner

Nguyen, Luan Hoang 08 1900 (has links)
No description available.
257

An ejector for accelerating coal particles

McGraw, Charles Tyrus 12 1900 (has links)
No description available.
258

Polishing H₂S from coal gasification streams using a high temperature electrochemical membrane separation process

Robinson, Jeffrey Scott 12 1900 (has links)
No description available.
259

Modelling of solvent extraction of coal

Figueroa, Diana C Unknown Date
No description available.
260

The bacterial oxidation of pyrite from coal in packed column reactors

Tillett, David McIlvain 08 1900 (has links)
No description available.

Page generated in 0.0536 seconds