Alpha-calcium Sulfate Hemihydrate Research Articles

Alpha-calcium sulfate hemihydrate used as a water-soluble template for the synthesis of ZnO hollow microspheres

This work develops α-HH microspheres into a water-soluble template for the green synthesis of hollow-architecture catalysts.

The effects of oyster shell/alpha-calcium sulfate hemihydrate/platelet-rich plasma/bone mesenchymal stem cells bioengineering scaffold on rat critical-sized calvarial defects.

Engineering scaffolds combining natural biomineral and artificially synthesized material hold promising potential for bone tissue regeneration. We fabricated a bioengineering scaffold, oyster shell (OS) and alpha-calcium sulfate hemihydrate (α-CSH) as scaffold, platelet-rich plasma (PRP) as provider of growth factors and bone mesenchymal stem cells (BMSCs) as seed cells, and determined it could be applied as a new type of bone graft substitutes by rat calvarial defects repairing experiment in vitro and in vivo. SEM showed that the mean diameter of the pores was about 150 μm with a range of 50-200 μm, and scaffold's porosity was ~27.4% by Archimedes' Principle. In vitro, Scaffold + BMSCs + PRP group presented a higher ALP activity compared with other groups by ELISA (P < 0.05). But the expression of OC was not detectable on day 4 or 8. The MTT assay showed that the relative cell number of BMSCs+PRP group increased significantly (P < 0.05). In vivo, the smallest defect area of skull and highest volume of regenerated new bone were observed in Scaffold + PRP + BMSCs group by X-ray and Micro-CT analysis (P < 0.05). And the similar results also were observed in HE and Masson staining. The immunohistochemistry staining for osteogenic marker proteins ALP and OC showed that the most obvious positive staining was observed in Scaffold + PRP + BMSCs group (P < 0.05). The expression of inflammatory markers IL-6 and TNF-α was the lowest in control group (P < 0.05). In conclusion, a bioengineering scaffold based on OS, created by simply combining α-CSH and PRP and implanting with BMSCs, could be clinically useful and has marked advantages as a targeted, off-the-shelf, cell-loaded treatment option for the bone healing of critical-size calvarial defects.

A Facile Synthesis Process and Evaluations of α-Calcium Sulfate Hemihydrate for Bone Substitute.

Alpha-calcium sulfate hemihydrate (α-HH) has been used effectively in grafting through its desired features to support bone regeneration. In recent years, many synthetic methods have been proposed. Among them, the autoclave method for manufacturing α-HH is best suited for cost-savings due to its simple operation and limited use of additives. Despite these advantages, the synthesis of surgical grade products without the use of any additives has not yet been clearly discussed. In this study, surgical grade α-HH was successfully produced from calcium sulfate dihydrate (DH) using the autoclave method at an elevated temperature and pressure. The synthesized powder had a high purity of about 98.62% α-HH with a prismatic morphology (20.96 ± 8.83 µm in length and 1.30 ± 0.71 µm in diameter). The screening tests, in simulated body fluid (SBF) solution, for the product properties showed no bioactivity, and fast degradation accompanied by a slight decrease in pH. The lactate dehydrogenase (LDH) assay showed good biocompatibility of the material, however, its potential for cytotoxicity was also observed in NIH 3T3 cells. Briefly, despite some unfavorable properties, the autoclave-synthesized α-HH is a promising bone graft substitute that can be applied in orthopedic and maxillofacial surgeries.

The Effect of Solvent Polarity on Phase Transformation of Citrogypsum via Hydrothermal Process

Calcium sulfate dihydrate (CaSO4•2H2O, CSD), gypsum is a by-product in the production of citric acid (citryogypsum). This by-product could neither be exploited nor distributed as a reactant because of its physical properties including those that are not equivalent to natural gypsum. Moreover, the mentioned citrogypsum has been continually increasing environmental problems. Therefore, this research aims at how to recycle gypsum that is synthesized by hydrothermal method at 95oC for 7 hrs under the atmospheric pressure via different solutions (MeOH, EtOH, PrOH, BuOH and Hexane). In order to produce alpha-calcium sulfate hemihydrate (α-CaSO4•0.5H2O, α-CSH) with improved physical properties that will be used for different industries. FT-IR reveals the chemical composition of crystal and the adsorption of methyl group on the surface. Besides, TGA thermogram shows the theoretical crystal water content of CSD and α-CSH 20.9 wt% and 6.2 wt% respectively. The DSC thermogram, shows that endothermic peaks at 151.2 oC and 168.5 oC. There were two steps of loss at 1.5 and 0.5 water molecule respectively. With SEM images of crystal shows the plate-like shape of citrogypsum, while α-CSH shows the hexagonal shape excluding hexane solution. Of all the results, the polarity of solution has an impact on the transition of CSD to α-CSH under this condition.

Mechanical Properties of Alpha-Calcium Sulfate Hemihydrate Replaced Concrete for Application to Box Culvert Power Transmission

Mechanical Properties of Alpha-Calcium Sulfate Hemihydrate Replaced Concrete for Application to Box Culvert Power Transmission

Rapid synthesis of alpha calcium sulfate hemihydrate whiskers in glycerol-water solution by using flue-gas-desulfurization gypsum solid waste

The feasibility of fabricating alpha calcium sulfate hemihydrate (α-CSH) whiskers by using flue-gas-desulfurization (FGD) gypsum as source materials was studied. Crystal phase- and morphology-controlled crystallization of gypsum were realized in the designed glycerol-water reaction system. l-glutamic acid was found to accelerate the conversion of calcium sulfate dihydrate (CSD) into α-CSH whiskers by intercalating into layered CSD structure. The time-dependent experiments indicate rod-like CSD first splits into layered structure and then fascicular structure and finally single crystals. The splitting crystallization owing to lattice expansion of CSD generates α-CSH whiskers with a high aspect ratio (∼1:200). The facile method to convert FGD gypsum solid waste into CSD and finally α-CSH whiskers may prove particularly useful in the design of recyclable FGD gypsum with significant environmental impact, and it is particularly important in environmental remediation and green economics.

Effect of injectable alpha calcium sulfate hemihydrate for repair of Hill-Sachs lesion in a rabbit model

Effect of injectable alpha calcium sulfate hemihydrate for repair of Hill-Sachs lesion in a rabbit model

Synthesis of alpha hemihydrate particles with lithium and carboxylates via the hydrothermal method

The hydrothermal method is efficient in synthesizing alpha calcium sulfate hemihydrate (α-CSH) particles from flue gas desulfurization gypsum. This study investigates the effects of LiCl·H2O solution with different carboxylates on the conversion process. Under optimal operating conditions, hexahedral column shaped crystals are obtained to verify the feasibility of this process. Results reveal that carboxylates especially disodium ethylenediamine tetraacetate (EDTA disodium) in conjunction with LiCl influences crystal morphology and nucleation. A fairly concentrated LiCl·H2O solution (over 2M) with EDTA disodium (over 0.01M) shortens reaction time and reduces particle size. Each crystal plane presents a balanced growth rate to create column objects because of the complexation reaction between EDTA disodium and calcium ions. The results of X-ray diffraction coupled with thermogravimetry and differential scanning calorimetry confirm that α-CSH is the only product.

Influence of Alkyl Trimethyl Ammonium Bromides on Hydrothermal Formation of α-CaSO4·0.5H2O Whiskers with High Aspect Ratios

In this paper, the influence of alkyl trimethyl ammonium bromides (CnH2n+1(CH3)3NBr, n = 10, 12, 14, 16, 18, abbreviated as ATAB) on the formation of alpha calcium sulfate hemihydrate (α-CaSO4·0.5H2O) whiskers under a hydrothermal condition (135 °C, 3.0 h) was analyzed. Specifically, it focuses on cetyl trimethyl ammonium bromide (C16H33(CH3)3NBr, abbreviated as CTAB). The rising CTAB concentration from 0 to 9.2 × 10−4 mol·L−1 led to the increase of the average aspect ratio of α-CaSO4·0.5H2O whiskers from 80 to 430, since the selective adsorption of CTAB on the negatively-charged side facets of the whiskers inhibited the growth of the whiskers along the direction normal to the lateral facets. The further increase of CTAB concentration above the critical micelle concentration (abbreviated as CMC) showed little effect on the morphology of α-CaSO4·0.5H2O whiskers, considering that CTAB tended to form micelles instead of being adsorbed on the whisker surfaces. Similar phenomena were observed in other ATABs (n = 10, 12, 14, 18).

Development of a neutral cementitious material to promote vegetation concrete

To develop a neutral binder for vegetation concrete, various cementitious materials based on alpha-calcium sulfate hemihydrate (α-CH) were compositionally examined as follows: 25% and 50% of the α-CH content were partially replaced by a mineral admixture; and 25%, 50%, 75%, and 100% were replaced by ordinary portland cement (OPC). The hydration products and microstructural characteristics of the prepared binders were investigated using X-ray diffraction analysis and scanning electron microscopy. The portlandite [Ca(OH)2] phase formed in the hydrated cementitious materials was quantified by thermogravimetric analysis to examine the relationship between Ca(OH)2 content and pH values of the pastes. The OPC paste without α-CH showed several diffraction peaks for the Ca(OH)2 phase, whereas the α-CH paste had no diffraction peak at the angles corresponding to Ca(OH)2. The dehydration mass fraction of Ca(OH)2 corresponded to approximately 11% of the cement content included in each paste sample. The 28-day compressive strength of α-CH mortar was approximately 55% of that of OPC mortar, whereas the α-CH-based pastes without OPC maintained the pH at the neutral level, between 6.5 and 6.9, showing that the use of cement, even in very low amounts, is impractical for reducing the alkalinity of concrete. The α-CH possesses significant potential for practical production of neutral vegetation concrete.

알파형 반수석고 기반 결합재의 pH 및 강도발현 평가

이 연구에서는 중성(pH 6~7) 수준의 식생용 콘크리트 결합재를 개발하기 위해 알파형 반수석고 기반의 결합재들의 pH 값과 압축강도 발현을 평가하였다. 식생용 콘크리트를 위한 결합재의 경제성 및 강도발현을 고려하여, 알파형 반수석고는 GGBS, FA 및 보통포틀랜드 시멘트를 사용하여 25% 및 50% 치환하였다. 알파형 반수석고를 100% 사용한 모르타르의 압축강도는 시멘트 100% 모르타르에 비해 약 57% 수준으로 있었다. GGBS 및 FA 치환율 증가와 함께 알파형 반수석고 기반 결합재의 압축강도는 감소하였지만 pH 값은 재령에 관계없이 6.5~7.5 수준으로 일정하게 있었다. GGBS 및 FA가 치환된 알파형 반수석고 결합재의 주요 수화생성물은 석고(CaSO4)이었으며, 수산화칼슘 [Ca(OH)2]은 나타나지 않았다. 반면 시멘트가 치환된 알파형 반수석고의 pH 값은 Ca(OH)2의 생성으로 인해 약 11.5 이상이었는데, 생성된 Ca(OH)2 양은단위 시멘트 양의 약 10% 수준이었다.

Preparation of alpha-calcium sulfate hemihydrate from FGD gypsum in chloride-free Ca(NO3)2 solution under mild conditions

This work develops a new class of salt solution method to prepare alpha-calcium sulfate hemihydrate (α-HH) from flue gas desulfurization (FGD) gypsum in trace K2SO4-contained 4.0M Ca(NO3)2 aqueous solution at 95°C under atmospheric pressure. The driving force for the phase transition is provided by the concentrated Ca(NO3)2 solution through decreasing the water activity. K2SO4, as an additive, plays a key role in tuning the phase-transition kinetics as well as the morphology, crystallinity and setting property of α-HH. In the presence of 8.75mM K2SO4, the transition finishes in 6.7h, while the product shows a purity of 98.23% α-HH, and its 2h and 3 d bending/compressive strengths reach 5.9/17.2 and 11.2/37.4MPa, respectively, which are comparable to those of the commercial α-HH. Compared with the recently well-developed chloride system (CaCl2+MgCl2+KCl), the nitrate system provides a chloride-free environment and shows outstanding superiority in control of chloride content in product and elimination of potential risk from excessive use of chloride, such as the corrosive damage to metal-made units and the by-production of chloride-containing wastewater. The obtained α-HH have a chloride content of 34mg/kg, much lower than the 3100mg/kg and 88mg/kg in those obtained from the chloride system after conventional and sufficient washes, respectively. Overall, the newly-developed nitrate system provides an improved alternative for α-HH preparation with controlled process and product quality, and helps push forward the industrial recycling of FGD gypsum.

Study on Preparation of High-Strength Gypsum by FGD Gypsum

With the enlarging of industrial desulfurization, the amount of FGD gypsum is increasing rapidly. The preparation of alpha-calcium sulfate hemihydrate (α-HH) is one of the biggest concerns for FGD gypsum reclamation. The influence of mixed chlorate solution of Mg-Ca-Na concentrations (5-30 wt%) and FGD gypsum concentrations (5-30 wt%) by hydrothermal salt solution method at atmospheric were investigated at temperatures (75-99°C) within a reaction time of 4h and a pH value of neutral. The results showed that 20 wt%, 20 wt% and 97°C was respectively optimal parameter of salt media concentration, FGD gypsum concentration and temperature. Products obtained from the dehydration process of optional experimental conditions with mixed crystal modifier were characterized based on relevant standards in this study. The results showed that α-HH had integrity crystal structure, 2h flexural strength and oven dry compressive strength were 5.34MPa and 30.21MPa, which had meet the industry standards of α30 grade.

Ultrasound-assisted/biosurfactant-templated size-tunable synthesis of nano-calcium sulfate with controllable crystal morphology

Nano-sized crystals of alpha calcium sulfate hemihydrate (α-HH) with considerable morphology-dependent properties find promising applications in the clinical fields as a cementitious material. Towards this end, ultrasound-assisted rhamnolipid and surfactin biosurfactant-template route is explored to control the morphology and aspect ratio of nano-CaSO4 by adjusting the mass ratio of rhamnolipid/H2O, surfactin/H2O and rhamnolipid/surfactin. The change in the molar ratio of [SO42-]:[Ca2+] results in modification in variable morphology and size of nano-CaSO4 including long, short rods and nanoplates. With increase in the rhamnolipid/H2O ratio from 1.3 to 4.5, the crystal length decreases from 3μm to 600nm with the corresponding aspect ratio reduced sharply from 10 to 3. Similarly, the crystal morphology gradually changes from submicrometer-sized long rod to hexagonal plate, and then plate-like appearance with increase in surfactin concentration. The preferential adsorption of rhamnolipid on the side facets and surfactin on the top facets contributes to the morphology control. The process using 50% amplitude with a power input of 45.5W was found to be the most ideal as observed from the high yields and lower average l/w aspect ratio, leading to more than 94% energy savings as compared to that utilized by the conventional process. As a morphology and crystal habit modifier, effects of Mg2+ and K+ ions on α-HH growth were investigated to find an optimal composition of solution for α-HH preparation. Mg2+ ions apparently show an accelerating effect on the α-HH growth; however, the nucleation of α-HH is probably retarded by K+ ions. Thus, the present work is a simple, versatile, highly efficient approach to controlling the morphology of α-HH and thereby, offers more opportunities for α-HH multiple applications.

Influences of citric acid on the metastability of α-calcium sulfate hemihydrate in CaCl2 solution

Alpha-calcium sulfate hemihydrate (α-HH), an important class of cementitious material, has found its promising way of preparation from dihydrate (DH) in salt solution. However α-HH prefers to hydration to DH or dehydration to anhydrite (AH) due to its metastability. Thus it is crucial to expand the metastable lifetime (MLT) of α-HH for the advantage of preparation and separation in industry. In the concentrated 3.54M CaCl2 solution, α-HH transforms to DH and exhibits an increase in MLT from 0.5 to 48h along with temperature from 25 to 65°C, and then the transformation bends to AH and shows a monotonous decrease in MLT to 6h at 95°C. A 0.1–1.0mM of citric acid allows a redouble expansion of the MLT, especially at temperature from 55 to 75°C. The chemical adsorption of citric groups on the crystal surfaces hinders the nucleation of new phase and increase the energy barrier for α-HH phase transition, resulting in an expansion of MLT. This work presents a simple, highly efficient approach to expand the MLT of α-HH and will benefit for the control of product purity.

Insight into Metastable Lifetime of α-Calcium Sulfate Hemihydrate in CaCl2Solution

Alpha calcium sulfate hemihydrate (α-HH), an important kind of cementitious material, is a metastable phase in CaSO4–H2O system. In CaCl2 solution, thermodynamic metastable window for α-HH preparation from calcium sulfate dihydrate is constructed as a function of CaCl2 concentration (0–4.0m) and temperature (60°C–130°C), and then the metastability of α-HH is characterized by the metastable lifetime (MLT). As the concentration of CaCl2 is raised from 1.5 to 4.0m and temperature from 80°C to 110°C, MLT of α-HH decreases gradually from 2920 to 60 min. The reducing effect of CaCl2 on MLT arises from its contribution to lowering the total interfacial Gibbs free energy required for the subsequent phase transition of α-HH to anhydrite, the thermodynamic stable phase. This work establishes a method to evaluate the phase metastability and provides a potential approach to optimize the reaction time in metastable material synthesis according to the MLT value for purity control.

Evaluation of Some Physical Properties of Locally Prepared Alpha-calcium Sulfate Hemihydrate

Evaluation of Some Physical Properties of Locally Prepared Alpha-calcium Sulfate Hemihydrate

Control of α-Calcium Sulfate Hemihydrate Morphology Using Reverse Microemulsions

Alpha calcium sulfate hemihydrate (α-HH) is an important class of cementitious material and exhibits considerable morphology-dependent properties. In the reverse microemulsions of water/n-hexanol/cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfonate (SDS), the morphology and aspect ratio of α-HH are successfully controlled by adjusting the mass ratio of CTAB/H(2)O and the concentration of SDS. As the ratio of CTAB/H(2)O is increased from 1.3 to 4.5, the crystal length decreases from 120 to 150 μm to 0.5-1.2 μm with the corresponding aspect ratio reduced sharply from 180 to 250 to 2-7. With increasing SDS concentration, the crystal morphology gradually changes from submicrometer-sized long column to rod, hexagonal plate, and even nanogranule. The preferential adsorption of CTAB on the side facets and SDS on the top facets contributes to the morphology control. This work presents a simple, versatile, highly efficient approach to controlling the morphology of α-HH on a large scale and will offer more opportunities for α-HH multiple applications.

The crystal growth kinetics of alpha calcium sulfate hemihydrate in concentrated CaCl2–HCl solutions

The crystal growth kinetics of calcium sulfate α-hemihydrate (α-HH) in nearly constant supersaturated HCl–CaCl2 solutions were investigated. Two types of solutions were used, the first had a low HCl (1.4mol/L) and high CaCl2 (2.8mol/L) concentration and the second had a high HCl (5.6mol/L) and low CaCl2 (0.7mol/L) concentration. These conditions were chosen to represent the first and last stage of a newly developed stage-wise HCl regeneration process. The seeded growth experiments were carried out in a stirred, temperature controlled semi-batch reactor in which supersaturation was kept constant by simultaneous addition of CaCl2 and Na2SO4 solutions. The influence of the following parameters on α-HH crystal growth was studied: temperature (70–95°C), specific power input of stirring (0.02–1.29W/kg) and equimolar inflow rate of CaCl2 and Na2SO4 (0–0.6mol/h). The crystal growth rate was derived from particle size distribution measurements made with the laser light diffraction technique. It was found that the surface area normalized crystal growth rate increased linearly with the molar inflow rate up to 0.3mol/h, at higher inflow rates no further increase of the growth rate was observed. Temperature and specific power input, within the investigated ranges, did not show a marked effect on the growth rate, attributable to a diffusion/adsorption controlled growth process. An interesting finding of the present research is the establishment of a positive relationship between the narrowing of the width of the particle size distribution with increasing crystal growth rate. The results show that the resulting particle size distribution is positively related to the reagent inflow rate, a finding that can be applied to the industrial design and scale-up of the α-HH crystallization/HCl regeneration process.

Characterization and precipitation mechanism of α-calcium sulfate hemihydrate growing out of FGD gypsum in salt solution

Alpha-calcium sulfate hemihydrate (α-HH) has been prepared from flue gas desulfurization (FGD) gypsum with salt solution method under atmospheric pressure. X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), optical micrograph, X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS), and scanning electron microscopy (SEM) have been employed to characterize the α-HH crystals, based on which the formation and growth mechanisms of the α-HH crystals have been discussed. The results show that FGD gypsum can be successfully transformed into high purity α-HH in salt solution under mild conditions, and that a dissolution-recrystallization route is most probably adopted by this transition. The growth of α-HH crystals in salt solution demonstrates a preferred direction along [001] and results in a bundle-of-sheets or bundle-of-raphide texture. The characteristics revealed in this study can help to understand and control the growth of the α-HH crystal from solution.