الفهرس 
Layered double hydroxides (LDHs)Only 14 pages are availabe for public view
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Abstract
In the present work, none doped and doped Mg–Al–CO3-LDHs were synthesized from three different sources of reactants using co-precipitation with hydrothermal method. The first group was prepared from pure chemicals such as Mg(NO3)2·6H2O, Ni(NO3)2.6H2O and Co(NO3)2.6H2O as a source for magnesium, cobalt and nickel (divalent cation MII)and Al(NO3)3·9H2O as a source for aluminum (trivalent cation MIII). LDHs were prepared using aqueous solution of pure chemicals with sodium carbonate Na2CO3 or NaHCO3 as a source of CO3(interlayer anion An-) in the presence of NaOH or NH4OH solution to adjust the pH value. The second LDHs group was prepared from aluminum dross as a source of aluminum (trivalent cation MIII). Firstly, nanoaluminum hydroxide was extracted from aluminum dross using direct reaction with NaOH or using NaOH followed by titration with HCl. Then, the synthesized nano aluminum hydroxide was used, in the presence of Mg(NO3)2·6H2O, and Ni(NO3)2.6H2O as a source for magnesium and nickel (divalent cation MII), to prepare none doped and doped LDHs by the same aforementioned method. In the third LDHs group, liquid concentrate waste, LCW (waste liquid from water implant) was utilized as source of aluminum cations. Firstly, iron oxide hydroxide (FeO(OH)) was leached from LCW using NaOH at pH 12, then the filtrate was subjected to NaHCO3 to precipitate nano Al(OH)3 at pH 7.Then, the synthesized nano Al(OH)3was used, in the presence of Mg(NO3)2·6H2O, and Ni(NO3)2.6H2O as a source for magnesium and nickel (divalent cation MII), to prepare none doped and doped LDHs by the same aforementioned method.All synthesized nano powders and/or suspension were examined by XRD, TEM, SEM, FT-IR, particle analyzer to investigate phase composition, crystallite size, particle size and morphology, particle size distribution, zeta potential as well as molecular structures.
The prepared LDHs powders were calcined at variable temperatures to follow up the thermal behavior of LDHs up to 1000oC. The calcined LDHs powders were pressed and pelletized in stainless steel die; then subjected to sintering at 1500oC to produce sintered spinel ceramics. The bulk density and apparent porosity of sintered specimens were measured by water replacement technique according to Archimedes principle. Phase composition of sintered spinels was followed up by x-ray diffraction technique. Microstructure of sintered spinels was investigated by scanning electron microscope.
The following results could be concluded:
1) XRD patterns and microscopic studies of nano LDHs prepared using NaOH or NH4OH indicate that the former alkali is better than the last one since the LDH synthesized using NaOH was completely formed with well crystalinity while that prepared by NH4OH was poorly formed. Thus, NaOH was selected to be used in all experiments in the thesis.
2) Nano aluminum hydroxides were successfully extracted from aluminum dross and LCW and used to prepare none doped and doped LDHs. Moreover, nano iron oxide hydroxide (FeO(OH)) was also successfully leached from LCW.
3) XRD patterns of none doped or doped LDHs precipitated form pure chemicals and LCW at 75oC and those hydrothermally treated at 140 and 180oC indicated the complete formation of LDH with variable crystalinity. While those prepared from aluminum dross formed LDHs only in the sample hydrothermally treated 180oC but those prepared at 75 and 140oC exhibited hydroxides of magnesium and aluminum beside few amount of LDH in case of sample prepared at 140oC.
4) We succeeded to prepare doped LDHs with cobalt and/or nickel from all previously mentioned sources. The relatively similar radii of Mg2+,Ni2+ and Co2+ are the key factor affecting the replacement process. Doping by these cations led to formation of colored ceramic pigments. Well crystalline nano none doped or doped LDHs with hexagonal plates were obtained in most cases.
5) The calcination of prepared none doped or doped LHDs led formation of some amount of spinel (MgAl-spinel solid solution with Co or Ni, NiAl-spinel and CoAl-spinel) with excess divalent metal oxides (MgO, NiO or CoO). This is due to the composition of LDH which contains much more amounts of divalent cations than stoichiometric amount required for spinel structure formation.
6) Since the LDHs was completely formed during synthesis from pure chemicals and LCW, they gave well sintered spinels at moderate temperature (1500oC)as compared with that prepared from LHDs synthesized from aluminum dross in which incomplete LDHs was formed as indicated from their weak XRD peak intensity. This is considered as interested finding in the present work.
7) Production of sintered spinels from LDHs is better than that produced from their relevant oxide or hydroxides i.e. magnesium and aluminum hydroxides or oxides (published in literatures), since the produced spinel in the present study is sintered at moderate temperature (1500oC; lower than that used for production from oxides or hydroxides) with good densification, microstructure and mechanical properties.
8) None doped and doped sintered spinel produced from LDHs synthesized from pure chemicals and LCW exhibited excellent sinterability than that synthesized from aluminum dross. The best sintered samples were Ni-doped spinels produced from pure chemicals and LCW.
9) After sintering, as indicated from the microstructure features, nano grains were agglomerated together to form bulk grains. The interested finding is: nano grains are still in the nano range after sintering.