Morphology Of Gypsum Crystals Research Articles

Impact of carboxylic acid structure on α-hemihydrate gypsum crystal morphology and mechanical strength

Impact of carboxylic acid structure on α-hemihydrate gypsum crystal morphology and mechanical strength

Enhancement and mechanism of macro-defect free (MDF) gypsum water resistance achieved by hydrophobic modification

Macro-defect free (MDF) gypsum is characterized by high strength and has the potential designed to advanced functionalization materials. However, the application of MDF gypsum is still limited by its poor water resistance. Here, we propose to modify the gypsum surface to hydrophobicity at molecule scale by adding potassium methylsilicate. The compressive strength, softening coefficients, and water absorption were subjected to rigorous testing, while elucidating the underlying mechanisms of water resistance enhancement through micro-structural analysis and organic-inorganic interactions. The results show that when adding 0.25% potassium methylsilicate, the wet compressive strength, softening coefficients are increased by 30.1%, 28%, respectively. And potassium methylsilicate can change the gypsum surface to hydrophobicity, which delaying the initial rapid water absorption stage and decrease both the 2 h and 24 h water absorption. The addition of potassium methylsilicate leads to a reduction in the dried compressive strength, attributed to the decrease in intrinsic dihydrate crystal strength. Upon the introduction of potassium methylsilicate, there is a transformation in gypsum crystal morphology from strip-like to lamellar structures. This alteration is accompanied by the formation of a potassium methylsilicate film coats the surface of gypsum, impeding water-gypsum contact. The potassium methylsilicate film coats on the surface of gypsum, which hinders the contact of water and gypsum.

Advanced materials engineering in historical gypsum plaster formulations

We show how historical gypsum plaster preparation methods affect the microstructure and the wettability properties of the final stucco materials. We reproduced a traditional Persian recipe (Gach-e Koshteh, ~14thcentury AD), which involves a continuous mechanical treatment during plaster hydration. These samples were compared with a laboratory-replicated historical recipe from Renaissance Italy (Gesso Sottile, ~15thcentury AD) and contemporary low-strength plaster. The Koshteh recipe induces the formation of gypsum platelets, which exhibit preferential orientation in the plaster bulk. In contrast, the Italian and low-strength plasters comprise a typical needle-like morphology of gypsum crystals. The platelets in Koshteh expose the more hydrophilic {010} face of gypsum in a much more pronounced manner than needles. Consequently, the Iranian plaster displays enhanced wettability, enabling its direct use for water-based decoration purposes, or as a fine finishing thin layer, without the need of mixing it with a binder material. Contrary, in Sottile, gypsum crystals are left to equilibrate in large excess of water, which promotes the growth of long needles at the expense of smaller crystals. Typically, such needles are several times longer than those found in a control regular plaster. For this crystal habit, the total surface of hydrophilic faces is minimized. Consequently, such plaster layers tend to repel water, which can then be used, e.g., as a substrate for oil-based panel paintings. These findings highlight the development of advanced functional materials, by tuning their microtexture, already during the premodern era.

Tuning the growth morphology of gypsum crystals by polymers

True control over the morphology of gypsum crystals formed via homogeneous precipitation from solution has rarely been reported in the literature. In this work, we have tested a large number of dissolved additives (polymers as well as small molecules) with respect to their ability to alter the typical microscopic appearance of precipitated gypsum powders, which is usually characterized by a mixture of single-crystalline needles and twinned plates. Among the many additives studied, a copolymer of vinylpyrrolidone and acrylic acid (PVP-co-PAA) was identified as powerful growth modifier for gypsum already at low concentrations. In both slow titration and rapid mixing experiments, unconventional blocky crystals with tilted stacking edges as well as pseudo-hexagonal plates could be synthesized reproducibly with the help of the copolymer. Systematic characterization revealed the dynamic mode of action of the newly identified growth modifier, which seems to stabilize a highly reactive face of gypsum and promote the formation of macrosteps. The degree of morphological control achieved in this way is unprecedented in the case of calcium sulfate and may devise entirely new concepts for additive design in the areas of plasters and cementitious materials, gypsum wallboard production and/or scale prevention.

Influence mechanism of alkaline environment on the hydration of hemihydrate phosphogypsum: A comparative study of various alkali

• The influence of various alkali on hydration and microstructure of HPGP was investigated. • Two opposite effects of alkali resulted by neutralization effect and ion strength effect on hydration of HPGP were observed. • Gypsum crystal morphology was significantly affected in alkaline environment except of excessive lime. • The influence effect of alkaline environment is related to its alkalinity and the impurity content in HPG. Although lime neutralization is widely recommended for raw phosphogypsum pretreatment, the influence mechanism of alkaline environment on hydration of hemihydrate phosphogypsum (HPG) is not clear. In the present paper, effect of alkaline environment created by different kinds of alkali including Mg(OH) 2 , NH 3 ·H 2 O, NaOH and Ca(OH) 2 with variable contents on hydration and microstructure of HPG were investigated. Abnormal setting and strength degradation were observed in the low-alkaline environment, while the setting time was normalized and crystal size developed in the high-alkaline environment regardless of the alkali category. Interestingly, the strength of HPG in the alkali environment only increased with excessive Ca(OH) 2 . It is verified that the formation of Ca 3 (PO 4 ) 2 from neutralization reaction in the low-alkaline environment served as retarder, and the excessive alkali beyond the threshold value of neutralization reaction played as accelerator in the high-alkaline environment, while only excessive lime particles promoted the development of gypsum crystal at c axis probably due to its absorption of Ca 3 (PO 4 ) 2 . This finding would promote the application of HPG in an alkaline environment and thus improve the utilization rate of phosphogypsum.

Thermoregulating gypsums by using nanoencapsulated phase change material slurry

Thermoregulating composites were produced by using a thermoregulating slurry (NPCS) containing nanoencapsulated phase change material (NPCM) from poly(styrene-co-divinylbenzene) as shell and the commercial paraffin Rubitherm®RT27 as core material. These composites were synthesized by using the constitutive water of the slurry as setting water and changing the NPCM/Hemihydrate (NPCM/Hem) mass ratio within 0.0–0.41. It was found that nanoparticles were uniformly dispersed into the gypsum, and the gypsum crystal morphology was tuned by the addition of the slurry. Attending to the thermal properties, these materials can work either as insulating or thermal energy storage materials, decreasing the thermal conductivity up to ~ 50%, whereas the thermal energy storage (TES) capacity is enlarged in a ~ 140%, respect to the pure gypsum, when the maximum NPCM/Hem mass ratio was used. This composite had a latent heat of 30.2 J g−1 and a heat capacity of equivalent 3.5 J g−1 K−1. Composites from a NPCM/Hem mass ratio up to 0.15 satisfied European mechanical standard EN 13,279–1 for gypsum binders and gypsum plasters and all of them, presented a bulk density higher than 0.60 g cm−3. The addition of a 41% in mass of nanocapsules allowed to save 13.5 kWh m−3 and, reducing the CO2 emissions up to 3.4 kg of CO2 per operating cycle. The use of this new material would lead to significant energy and economic savings, as well as a considerable reduction in the emission of polluting gases into the atmosphere.

Tuning the Growth Morphology of Gypsum Crystals by Polymers

Tuning the Growth Morphology of Gypsum Crystals by Polymers

Effective building mixtures based on hemihydrate plaster and highly dispersed mineral fillers

The work was aimed at developing a gypsum dry construction mixture with highly dispersed fillers based on industrial waste for interior decoration. The problem of creating effective gypsum materials was solved by improving the structural, physical and mechanical properties of gypsum stone by modifying it with highly dispersed fillers. The effect was achieved by creating a multicomponent composition based on hemihydrate plaster. The proposed work is aimed at developing a gypsum dry construction mixture with highly dispersed fillers for interior decoration of buildings. Dry construction mixes based on gypsum binder are one of the most relevant materials on the building supplies market. They meet the most important aspects from the standpoint of efficiency and safety - environmental, fire and others. However, the problem of ensuring high performance properties requires a solution. In this work, the problem is solved by improving the structural, physical and mechanical properties of gypsum stone by modifying it with highly dispersed fillers. The effect was achieved by creating a multicomponent composition based on plaster. Additionally, the problem of environmental protection is being solved, since secondary products were used as fillers - waste from the production of basalt products and thermal power plants. They differ in the required grain and chemical composition. Acid ash was used. Basalt and acid ash particles have a mechanical effect on the structure of the gypsum stone and influence the processes of structure formation of the gypsum stone. They change the morphology of gypsum crystals. This improves the mechanical strength, the average density of the modified gypsum stone and other physical and mechanical characteristics.

Comparative Analysis of Hydration Expansion Performance of Desulfurized gypsum-baseda/β Gypsum

Gypsum has micro-expansion characteristic during the process of hydration and solidification, and there are certain differences in the hydration expansion characteristics of different types of hemihydrate gypsum. In this paper, by analysing the gypsum crystal morphology, particle size distribution, hydration heat, dimensional change rate, and morphology change of hydration products in the process of hydration process, the hydration expansion performance of α/β gypsum are compared and discussed. The results indicate there are differences in the hydration swelling mechanism between α-gypsum and β-gypsum. The expansion of gypsum is the result of the combined effect of the crystal transformation and the release hydration heat during the hydration process. The particle size distribution and the amount of hydration water added have a great influence on the expansion performance.

Effect of nano-silica and silicone oil paraffin emulsion composite waterproofing agent on the water resistance of flue gas desulfurization gypsum

This paper indicates the influence of nano-silica and silicone oil paraffin emulsion mixed with flue gas desulfurization (FGD) gypsum on its water resistance. Nano-silica was mixed with FGD gypsum to explore the influence of nano-silica particle size and content on the waterproofing and mechanical properties of FGD gypsum while also analyzing its waterproofing mechanism. In addition, silicone oil paraffin emulsion was mixed along with nano-silica into FGD gypsum to study its effect on FGD gypsum. The results show that nano-silica can improve the water resistance of FGD gypsum. When the particle size of nano-silica is 50 nm and the mass fraction is 0.4%, the softening coefficient of FGD gypsum reaches 0.92. Nano-silica and organic composite emulsion can play a synergistic role and further enhance the performance of FGD gypsum. The water resistance and mechanical properties of gypsum further increased when mixed with nano-silica and silicone oil paraffin emulsion. The water absorption rate decreased to 13.62%, and the compressive strength reached 13.71 MPa. Combined with the microscopic morphology analysis of the gypsum sample, the appropriate size of nano-silica fills the crystal pores, reduces porosity, and, to a certain extent, changes the structure and morphology of gypsum crystals. Silicone oil paraffin emulsion can be wrapped on the surface of gypsum crystals forming a dense oil hydrophobic membrane. It produces a compact gypsum structure together with nano-silica, hindering the entry of water molecules into gypsum, thereby improving the performance of FGD gypsum.

Effect of Fe2+ ions on gypsum precipitation during bulk crystallization of reverse osmosis concentrates

In reverse osmosis desalination, the concentrate is a saline solution that may become supersaturated. Heterogeneous nucleation of salts occurs at the membrane surface, resulting in the buildup of inorganic deposits on the membrane. The inorganic nucleation process, however, is complex in natural waters. Most studies focused primarily on single salt fouling of membranes, and related treatment for single solute systems. However, scale formation, especially gypsum, is affected by the presence of different salts and metals. In this wok, for the first time, we investigate the mixed precipitation of iron oxides and gypsum. The role of citric acid in the inhibition of precipitation was studied for different concentrations in both the absence and the presence of Fe2+. Conductivity and ion concentration measurements were used to estimate the formation time of gypsum. Scanning electron microscopy, X-Ray Diffraction (XDR) analysis, and Infra-Red spectroscopy analysis were used to provide structural information. Collected data showed that the presence of Fe2+ accelerates gypsum precipitation and shortens its induction time. Analytic results showed that gypsum crystals are greatly affected by the presence of Fe2+ ions, which generated needle shaped crystals. Citric acid can delay the induction time of gypsum precipitation. It also affects the morphology of gypsum crystals through adsorption mechanism. XDR diagrams revealed that the presence of citric acid (20 mg/L) can stabilize the bassanite phase (CaSO4·½H2O) for much longer periods. In the presence of Fe2+ ions, citric acid extends the induction time of calcium sulfate and minimizes the acceleration effect of Fe2+ ions. SEM images showed that the presence of ferrous ions during the chemical inhibition generates the β-hemihydrate form of calcium sulfate.

Size Distribution and Morphology of Gypsum Crystals Precipitating from Hypersaline Solutions

Morphology and crystal size distribution of gypsum precipitated from a wide range of hypersaline compositions (ionic strength = 5.5–10 m) were studied in batch experiments containing mixtures of Ca...

Utilization of the black tea powder as multifunctional admixture for the hemihydrate gypsum

The purpose of this work was to investigate the feasibility of using black tea powder produced through green technology (plant-source material and biotechnology) as multifunctional admixture for the hemihydrate gypsum. The hemihydrate gypsums were mixed with black tea, and the setting times, densities, hydration characteristics and strengths of different plasters were discussed, and the mechanisms responsible for their performance variations were explored by isothermal calorimeter, X-ray powder diffractometry and scanning electron microscopy. Besides, the economic and environmental compatibilities were also considered. The results indicate that black tea lowers the water requirement and improves the normal consistency, and then the high density is acquired. It prolongs the setting times. Moreover, this prolongation is more remarkable as more black tea is introduced. The gypsum strength is related to the content of black tea. Moderate black tea has the positive role in the improvement of strength, but the excessive black tea poses a negative effect. Furthermore, black tea alters the gypsum hydration process. It decreases the hydration rate and delays the hydration time of gypsum. Although more black tea seriously delays the gypsum hydration, all hemihydrate gypsum thoroughly converts into dihydrate gypsum after 28d. SEM results show that black tea changes the gypsum crystal morphology. All gypsum crystals are long and needlelike in the hardened pastes with less than 1% black tea. However, these crystals become shorter and larger as more black tea is mixed. Various crystal morphologies mainly contribute to the strength alteration of gypsum with black tea. These results show that black tea can serve as an alternative to the traditional functional admixture and then acquire a green and sustainable technology for the preparation of hemihydrate gypsum functional admixture, but also expand the commercial utilization of black tea in the building materials industries and foster the development of building industry towards green-oriented and sustainability.

Effect of neutralization on the setting and hardening characters of hemihydrate phosphogypsum plaster

Phosphogypsum (PG) which is a waste byproduct of fertilizer production is the promising source of the gypsum industry. In order to explore the application of hemihydrate PG (HPG) as a substitute of hemihydrate gypsum, the setting and hardening characters of HPG plaster at different pH after neutralization were examined and contrasted with hemihydrate flue gas desulfurization gypsum (HFGD) plaster. Results showed that HPG plaster sets slow with a fall in strength and this effect was more pronounced after retarders were added when pH increased from 5.85 to 11.08. By contrast, HFGD plaster sets fast and without strength variation in the similar alkaline range. Microscopic studies including chemically combined water and temperature evolution curves of HPG plaster revealed that with the increase of the pH, the hydration reaction mechanism of hemihydrate and the gypsum crystal morphology were radically changed due to the fact of interaction between impurities and alkali. Consequently, HPG plaster is very different from HFGD plaster and its application in thealkaline condition was restricted.

Gypsum stromatolites from Sawda Nathil: relicts from a southern coastline of Qatar

Sawda Nathil is one of a series of inland depressions (inland sabkhas and salinas) that extend nearly continuously along the Southern Qatar border with Saudi Arabia. Six to eight thousand years ago, these depressions were marine embayments that separated the peninsula of Qatar from the mainland. These embayments in-filled rapidly with marine sediments and dune sands, blown southeastward across Qatar. Over time, they have become progressively more evaporitic. Inland depressions like Sawda Nathil host a set of unique environments within Qatar. Most depressions are close to or below sea level, bringing water near the surface in the driest parts of Qatar. Evaporation to salt saturation creates thick gypsum and halite crusts (sabkhas), as well as shallow hypersaline lakes/ponds (salinas) with spectacular domal microbial gypsum stromatolites. The present ground surface is a mosaic of relict marine facies, deflated dune sands, and inland sabkhas and salinas. Sediment of four short push cores was photographed, described, and sampled for petrographic thin-section and X-ray diffraction (XRD) analyses. Radiocarbon (AMS) as well as optically stimulated luminescence (OSL) age-dating were carried out on three samples. Scanning electron microscopy (SEM), carried out on samples from a gypsum stromatolite, was used to resolve the microbial-influence on gypsum precipitation. Radiocarbon dating of marine shells provides ages of approximately 6600 un-calibrated 14C years before present (year BP), coinciding with a well-documented sea-level highstand, approximately 2–4 m higher than present. During that time, Qatar was mostly an island, only connected in the south to the Arabian Peninsula by narrow land bridges (isthmuses). SEM examinations of gypsum stromatolites show gypsum crystals developing in close spatial association with microbial biofilms (filamentous structures). Whether this is purely a passive microbial-influenced gypsum mineralization process or an example where microorganisms actively control the gypsum crystal morphology to obtain ecological advantages, remains to be evaluated.

In situ observation of plaster microstructure evolution during thermal loading

SUMMARYGypsum microstructural evolution at elevated temperatures has been characterized in situ by environmental scanning electron microscopy and high‐temperature X‐ray tomography. As temperature increases, the observed changes in gypsum crystal morphology are related to the consequences of water loss that leads to crystal reorganization in order to minimize the specific surface. The influence of environmental scanning electron microscopy experimental conditions on the mechanisms observed is also discussed. High‐temperature X‐ray tomography gives quantitative information on porosity evolution with thermal loading. The results obtained are successfully correlated with macroscopic shrinkage measurements performed during dilatometry tests. Copyright © 2016 John Wiley & Sons, Ltd.

Gypsum scaling in forward osmosis: Role of membrane surface chemistry

Forward osmosis (FO) membranes with varying surface chemical functionalities respond differently to gypsum scaling. Using a real-time monitoring system, gypsum scaling was quantified between an asymmetric cellulose triacetate (CTA) and a thin-film composite (TFC) polyamide membrane in terms of water flux decline, gypsum surface coverage and gypsum crystal morphology. At the same initial water flux, the TFC membrane was subjected to more severe gypsum scaling than the CTA membrane in terms of water flux decline and gypsum crystal surface coverage. The gypsum crystal morphology on the CTA membrane featured with slender platelets; in contrast, that on the TFC membrane demonstrated the formation of rosette arrangements. Fourier transform infrared spectra and X-ray photoelectron spectroscopy proved that the gypsum scaling on CTA membrane was dominated by bulk crystallisation with subsequent deposition; while that on the TFC membrane was driven by surface crystallisation via specific interaction between carboxylic functional groups and calcium ions. No interaction between gypsum and CTA membrane surface was demonstrated by the largely unchanged ratio of wavenumbers 1740cm−1 (C=O stretching) to 1366cm−1 (C–O stretching), as well as binding energy of C1s on the CTA membrane. In contrast, specific interaction between carboxylic functional groups with calcium ions during gypsum scaling was revealed by a gradual increase in the ratio of absorbance wavenumber 3400cm−1 (O–H stretching) to 2970cm−1 (C–H stretching), and the occurrence of the carboxylate functional group at binding energy of 288.1eV on the TFC membrane during the formation of gypsum scaling.

A Comparative Performance Evaluation of Some Novel “Green” and Traditional Antiscalants in Calcium Sulfate Scaling

A relative ability of industrial samples of four phosphorus-free polymers (polyaspartate (PASP); polyepoxysuccinate (PESA); polyacrylic acid sodium salt (PAAS); copolymer of maleic and acrylic acid (MA-AA)) and of three phosphonates (aminotris(methylenephosphonic acid), ATMP; 1-hydroxyethane-1,1-bis(phosphonic acid), HEDP; phosphonobutane-1,2,4-tricarboxylic acid, PBTC) to inhibit calcium sulfate precipitation is studied following the NACE Standard along with dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) technique. For the 0.5 mg·dm−3dosage, the following efficiency ranking was found:MA-AA~ATMP>PESA (400–1500 Da)>PASP (1000–5000 Da)≫PAAS (3000–5000 Da)~PBTC~HEDP. The isolated crystals are identified as gypsum. SEM images for PESA, PASP, PAAS, and HEDP and for a blank sample indicated the needle-like crystal morphology. Surprisingly, the least effective reagent PBTC revealed quite a different behavior, changing the morphology of gypsum crystals to an irregular shape. The DLS experiments exhibited a formation of 300 to 700 nm diameter particles with negativeζ-potential around −2 mV for all reagents.Although suchζ-potential values are not capable of providing colloidal stability, all three phosphonates demonstrate significant gypsum particles stabilization relative to a blank experiment.

The habit and form of gypsum crystals in Irish mudstone aggregate affected by pyrite-induced swelling

In a recent court case in Ireland, pyrite-induced swelling of a mudstone aggregate backfill has been proven to have occurred and to have arisen from the growth of gypsum crystals in and around the aggregate fragments. There is a lack of published information on the subject and considerable debate exists regarding features associated with forceful crystallization. This paper describes the form and habit of gypsum crystals from petrological and SEM evaluations presented during the court case. Features associated with both forceful and passive crystallization of gypsum are illustrated. These illustrations should serve as a guide to the morphology of gypsum crystals where forceful crystallization under near-surface conditions has occurred. The paper is unique in that it describes a case of proven forceful crystallization of gypsum rather than attempting to infer forceful crystallization from theoretical concepts of crystal growth. This paper does not go into the detailed evidence and arguments put forward in the court case or attempt to explain the mechanisms involved in pyrite-induced swelling.

Morphological Biosignatures in Gypsum: Diverse Formation Processes of Messinian (∼6.0 Ma) Gypsum Stromatolites

The ∼5.3-6.0 million-year-old evaporitic gypsum deposits of Cyprus and Crete contain a variety of stromatolites that formed during the Messinian salinity crisis. We recognize four stromatolite morphotypes, including domical, conical, columnar, and flat-laminated structures. Observations of morphological and textural variations among the different morphotypes reveal significant diversity and complexity in the nature of interactions between microorganisms, gypsum deposition, and gypsum crystal growth. Nonbiological processes (detrital gypsum deposition, in situ crust precipitation, syntaxial crystal growth, subsurface crystal growth, and recrystallization) interacted with inferred microbial processes (including localized growth of biofilms, trapping and binding of grains in mats, nucleation of gypsum on cells) to produce distinct morphological-textural assemblages. Evidence for biological origins is clear in some stromatolite morphotypes and can come from the presence of microfossils, the spatial distribution of organic matter, and stromatolite morphology. In one stromatolite morphotype, the presence of the stromatolite, or the biota associated with it, may have determined the morphology of gypsum crystals. In some stromatolite morphotypes, definitive evidence of a microbial influence is not as clear. There are broad similarities between the Messinian gypsum stromatolites and carbonate stromatolites elsewhere in the geologic record, such as the formation of precipitated and granular layers; the development of domed, columnar, and conical morphotypes; the potential for microbes to influence mineral precipitation; and the recrystallization of deposits during burial. However, in detail the array of microbial-sedimentary-diagenetic process interactions is quite distinct in gypsiferous systems due to differences in the way gypsum typically forms and evolves in the paleoenvironment compared to carbonate. Unique aspects of the taphonomy of gypsum compared to carbonate chemical sediments, generally speaking, include the following: the potential for growth of individual crystals to determine the shape of a stromatolite (and possibly vice versa), a more diverse set of outcomes relating to preservation versus destruction of textures through crystal growth and recrystallization, and a greater likelihood of preserving microfossils through encapsulation in large crystals. These insights gained from the study of terrestrial gypsum sedimentary rocks provide valuable guidance for the search for clues to past life in sulfate chemical sediments on Mars.