The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

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Hallmarks of mechanochemistry: From nanoparticles to technology

Geopolymer concrete: A review of some recent developments

Effect of GGBFS on setting, workability and early strength properties of fly ash geopolymer concrete cured in ambient condition

The microstructural evolution of alkali-activated binders based on blast furnace slag, fly ash and their blends during the first six months of sealed curing is assessed. The nature of the main binding gels in these blends shows distinct characteristics with respect to binder composition. It is evident that the incorporation of fly ash as an additional source of alumina and silica, but not calcium, in activated slag binders affects the mechanism and rate of formation of the main binding gels. The rate of formation of the main binding gel phases depends strongly on fly ash content. Pastes based solely on silicate-activated slag show a structure dominated by a C–A–S–H type gel, while silicate-activated fly ash are dominated by N–A–S–H ‘geopolymer’ gel. Blended slag-fly ash binders can demonstrate the formation of co-existing C–A–S–H and geopolymer gels, which are clearly distinguishable at earlier age when the binder contains no more than 75 wt.% fly ash. The separation in chemistry between different regions of the gel becomes less distinct at longer age. With a slower overall reaction rate, a 1:1 slag:fly ash system shares more microstructural features with a slag-based binder than a fly ash-based binder, indicating the strong influence of calcium on the gel chemistry, particularly with regard to the bound water environments within the gel. However, in systems with similar or lower slag content, a hybrid type gel described as N–(C)–A–S–H is also identified, as part of the Ca released by slag dissolution is incorporated into the N–A–S–H type gel resulting from fly ash activation. Fly ash-based binders exhibit a slower reaction compared to activated-slag pastes, but extended times of curing promote the formation of more cross-linked binding products and a denser microstructure. This mechanism is slower for samples with lower slag content, emphasizing the correct selection of binder proportions in promoting a well-densified, durable solid microstructure.

Modification of phase evolution in alkali-activated blast furnace slag by the incorporation of fly ash

Fly ash-based geopolymer: clean production, properties and applications

Ground granulated blast furnace slag (GBFS) has been used to alter the geopolymerisation behaviour of fly ash. The influence of varying amount of GBFS (5–50%) on the reaction kinetics has been studied using isothermal conduction calorimetry. It was observed that the reaction at 27 °C is dominated by the GBFS activation, whereas the reaction at 60 °C is due to combined interaction of fly ash and GBFS. The reaction product of geopolymerisation has been characterised using X-ray diffraction and scanning electron microscopy–X-ray microanalysis. Alumino–silicate–hydrate (A–S–H) and calcium–silicate–hydrate (C–S–H) gels with varying Si/Al and Ca/Si ratio are found to be the main reaction products. Coexistence of A–S–H and C–S–H gel further indicates the interaction of fly ash and GBFS during geopolymerisation. Attempt has been made to relate the microstructure with the properties of the geopolymers.

Influence of granulated blast furnace slag on the reaction, structure and properties of fly ash based geopolymer

The effects of aeration rate, particle size and pulp density on the flotation rate distributions

Anomalous reduction in surface area during mechanical activation of boehmite synthesized by thermal decomposition of gibbsite

This article focuses on the mechanically induced reactivity of boehmite prepared by thermal decomposition of gibbsite. Boehmite, which retained the morphology of gibbsite, was characterized by a specific surface area of 264 m2/g. Mechanical activation (MA) was carried out in a planetary mill up to 240 minutes. The samples were characterized in terms of morphology, characteristic particle diameters, Brunauer Emmett Teller (BET) specific surface area (SSABET), microcrystallite dimension (MCD), microstrain (e) and Fourier transform infrared spectroscopy. The reactivity was construed from the kinetics of thermal transformation of boehmite into γ-Al2O3. The transformation observed between 600 K and 900 K (327 °C and 627 °C), manifested itself as two overlapping peaks in the differential thermogravimetric plot. These peaks correspond to two stages of dehydroxylation involving Al2OH and AlOH groups in succession. The peaks were resolved using Gaussian deconvolution. The reactivity was assessed separately for the two stages by comparing the fraction reacted in MA samples (α) with that of nonactivated sample (α
 ref). During both stages, enhanced kinetics, as revealed by α-α
 ref plots, indicated an increase in reactivity with MA. The transformation mechanism conformed to n
 th order reaction (f[α] = [1 – α]
 n
 with n = 1.3–1.5 in both stages). Values of n remained similar for the activated and reference samples. Activation energies (E
 a) for the first and second dehydroxylation stages were respectively 115 and 300 kJ/mol for the nonactivated sample. E
 a for the second stage decreased exponentially to a value of 222 kJ/mol after 240 minutes of milling. An anomalous negative correlation between reactivity and SSABET was observed. Reactivity parameters were strongly correlated with MCD and e. A plausible explanation for the observed correlations is presented.

Analysis of Mechanically Induced Reactivity of Boehmite Using Kinetics of Boehmite to γ- Al 2 O 3 Transformation

..................................................................................................................................... i 1. Why India Needs Social Assistance as Cash Transfers? ................................................ 3 1.1 The International Experience ..................................................................................... 6 2. Cash transfers in India: the experience so far................................................................. 7 2.1 The Telengana government’s cash transfer: Rythu Bandhu ....................................... 7 2.2 Odisha’s KALIA .......................................................................................................... 7 2.3 PM KISAN: A Central government cash transfer to farmers ..................................... 8 2.4 Issues with the design and implementation of three existing cash transfers to ‘farmers’ ..................................................................................................................... 9 3. The three pre conditions for comprehensive cash transfers: Is India ready? ............ 10 3.1 Issues remain with the delivery mechanism of a MIG even after three preconditions are met ...................................................................................................................... 12 4. A Minimum Income Guarantee: The Underlying Logic and its Design ..................... 13 4.1 The Design: A better Targeted Income Transfer ...................................................... 15 4.2 Deprived Rural Household to be targeted ................................................................ 17 4.3 Overall Coverage of the Targeted Income Transfer ................................................. 20 4.4 Amount of Transfer to Households ........................................................................... 21 4.5 Financial Expenditure: Who pays – Centre or States? ............................................ 23 4.6 Suggestions for Additional Category of Rural households for Better Targeting for Income Transfer ........................................................................................................ 26 4.7 Summary Coverage of the Targeted Income Transfer-MIG: SECC and Census ..... 27 4.8 Benefits received as a share of household’s consumption expenditure .................... 28 5. A Comparative Perspective on the Proposed MIG ....................................................... 29 6. Concluding Remarks ....................................................................................................... 32 References ............................................................................................................................... 34

S. P. Mehrotra

Papers

Influence of granulated blast furnace slag on the reaction, structure and properties of fly ash based geopolymer

The effects of aeration rate, particle size and pulp density on the flotation rate distributions

Anomalous reduction in surface area during mechanical activation of boehmite synthesized by thermal decomposition of gibbsite

Analysis of Mechanically Induced Reactivity of Boehmite Using Kinetics of Boehmite to γ- Al 2 O 3 Transformation

A Minimum Income Guarantee amidst Joblessness & Vulnerability: A Design for Income Transfers post-Covid 19 and beyond