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1.
Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have
been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial
charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra
disclose the existence of monomeric [Al(OH)4]− species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species
were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence
of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)4]− to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the 29Si NMR spectra. Of the two possible stable silicate species [SiO2(OH)2]2− and [SiO(OH)3]−, the latter appears most likely to condense with [Al(OH)4]− to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)4]− leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis
sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge
model. 相似文献
2.
The mechanisms of speciation of aluminate and silicate phases during dissolution and condensation stages of alumino-silicate
geopolymer reactions characterised by Si/Al ≥ 3, have been investigated and the results compared to predictions of the partial
charge model. Solid-state nuclear magnetic resonance (NMR) traces indicate that free [Al(OH)4]− species, present in lower silicate formulations such as Si/Al ≤ 1, do not occur in the present systems, suggesting that the condensation reaction between [Al(OH)4]− and silicate species is fairly quick and is consumed as soon as it is formed. This observation is also consistent with both
calorimetric measurements and model predictions, as the condensation time increased exponentially with increased Si/Al ratio
in the geopolymeric phase, indicating again that the high content of Al species in the gel phase greatly enhanced the condensation
rate. The experimental observations suggest that the condensation process in these systems occurs in two stages: (a) quick
condensation between aluminate and silicate species; followed by (b) a slow condensation stage solely involving silicate species. 相似文献
3.
Water soluble carboxylic acids have been used as corrosion inhibitors. They remain largely soluble after curing in cement for up to 90d. Corrosion current measurements are presented showing malonic acid, a dicarboxylic acid, to be a very effective corrosion inhibitor even in the presence of 2.5 wt % chloride. Unfortunately, it has an initial retarding effect on the set of Portland cement. The investigation suggests that corrosion inhibitors based on carboxylic acids remain a fruitful field of investigation. 相似文献
4.
In vitro protein digestion studies were carried out on raw and roasted peanut flour as the starting material in the production of peanut protein hydrolysate. Peanut flour was hydrolyzed with alcalase and alternately in a sequential digestion with pepsin-pancreatin, both for up to 24 h. The degree of hydrolysis (DH) at different times of hydrolysis was determined using the trinitrobenzenesulfonic acid (TNBS) method. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to indicate destruction of native protein units in the enzymatic digests.Hydrolysis with alcalase was very rapid for the first 6 h after which a plateau was reached, whereas that with pepsin–pancreatin was more gradual reaching a plateau after 12 h of hydrolysis. Raw peanut hydrolyzed with alcalase and pepsin–pancreatin had 23% and 21% DH after 24 h respectively, whilst roasted peanut hydrolyzed with alcalase had 21% DH, with the pepsin–pancreatin hydrolysate recording the highest value of 25% after 24 h of hydrolysis.SDS-PAGE results showed that raw peanut samples behaved differently from the roasted samples; increasing hydrolysis time reduced larger peanut protein subunits, with only peptides of <20 kDa visible after hydrolysis for raw peanut, and virtually no distinct visible bands for the roasted peanut after 3 h of hydrolysis. 相似文献
5.
Herta Aidoo Esther Sakyi-Dawson Kwaku Tano-Debrah Firibu Kwesi Saalia 《Food research international (Ottawa, Ont.)》2010,43(1):79-85
This study explored the feasibility of producing peanut–cowpea milk for use in vegetable milk chocolates. Development of the vegetable milk followed a 3 × 2 factorial design, with peanut–cowpea ratio (1:1, 1:2 and 1:3), and treatment with enzyme (i.e. enzyme hydrolyzed and non-hydrolyzed milk) as the factors. The milk was dehydrated and then milled using a hammer mill (mesh size 40). It was then used in recipes to produce chocolates and evaluated sensorially based on ranking for preference. Skimmed milk powder was used to produce the control chocolate. The ratio of cowpea to peanut affected the chemical and functional characteristics of the vegetable milk. Vegetable milk made from 1:2 ratios of peanuts:cowpea produced the most preferred chocolates. The successful application of this by industry will improve the utilization of the legume crops and enhance their market value. 相似文献
6.
A combination of scanning electron microscope and electron probe studies has been conducted on the dissolution of Widmanstätten γ-Ag2Al plates in Al-15.3 wt pct Ag alloys between the temperatures of 466 °C and 494 °C. Individual rather than averaged kinetic events have been monitored in all cases. The kinetics at the tip were observed to be linear with time and at the broadface to be parabolic with time. The broadface kinetics were slower than expected for volume diffusion control. Electron probe measurements round the dissolving precipitate gave similar diffusion profiles at the tip and the broadface. These indicated a slower dissolution rate at the tip than observed experimentally and a faster rate at the broadface than observed experimentally. A mechanism to explain the discrepancy between the kinetic and probe results is suggested. 相似文献
7.
Prinya Chindaprasirt Pre De Silva Kwesi Sagoe-Crentsil Sakonwan Hanjitsuwan 《Journal of Materials Science》2012,47(12):4876-4883
This study investigates the effect of silica and alumina contents on setting, phase development, and physical properties of
high calcium fly ash (ASTM Class C) geopolymers. The characteristic rapid setting properties and, hence, limited workability
range of high calcium fly ash geopolymers has restricted both development and potential application of these binder systems
compared to conventional geopolymer binders derived from bituminous coal, i.e., (ASTM Class F) sources or from calcined kaolin
feedstocks. For this study, control of setting and hardening properties were investigated by adjusting SiO2/Al2O3 ratio of the starting mix, via series of mixes formulated with varying SiO2 or Al2O3 contents to achieve SiO2/Al2O3 in the range 2.87–4.79. Foremost is the observation that the effect of varying silica and alumina in high calcium fly ash
systems on setting and hardening properties is markedly different from that observed for traditional Class F geopolymer systems.
Overall, increases in either silica or alumina content appear to shorten the setting time of high calcium-based systems unlike
conventional geopolymer systems where increasing Al2O3 accelerates setting. The setting process was associated primarily with CSH or CASH formation. Furthermore, there appears
to be a prevailing SiO2/Al2O3 ratio that prolongs setting, rather than Ca2+ ion content itself, while NASH primarily contributes to strength development. SiO2/Al2O3 ratios in the range of 3.20–3.70 resulted in products with highest strengths and longest setting times. These results suggest
that initial predominance of Ca2+ ions and its reactions effectively help maintaining a SiO2/Al2O3 ratio at which amorphous geopolymer phase is stable to influence setting and initial strength development. 相似文献
8.
Effects of corn steep water pretreatment on the rheological and microstructural properties of Ga‐kenkey 下载免费PDF全文
9.