Preparation of High Percentage α-Calcium Sulfate Hemihydrate via a Hydrothermal Method

α-calcium sulfate hemihydrate (α-HH) is known to be suitable for application as bone void filler. High percentage of α-HH is obviously needed for medical applications, especially for implantation. Three commercially available calcium sulfate dihydrates (DH, CaSO4·2H2O) with different sizes and surface morphologies were used as starting materials to synthesize high percentage α-HH via a hydrothermal method. The median particle sizes of the three types of DH were 946.7 μm, 162.4 μm and 62.4 μm, respectively. They were named as DH-L, DH-M and DH-S in this paper. The particle size distribution, morphology and phase composition of the raw materials were evaluated before synthesis. SEM results revealed that DH-L consisted of irregular large particles, while DH-M and DH-S were composed of plate-like particles with some small ones. High percentage HH can be obtained with proper synthesis parameters by hydrothermal method, specifically, 105 °C/90 min for DH-L (achieving 98.8% HH), 105°C/30 min for DH-M (achieving 96.7% HH) and 100°C/45 min for DH-S (achieving 98.4% HH). All the synthesized HH were hexagonal columns, demonstrating that they were α-phase HH. The particle size and morphology of starting material (DH) have significant influences on not only the rate of phase transition but also the morphology of the synthesized α-HH. Calcium sulfate dihydrate cements were prepared by the synthesized α-HH. The highest compressive strength of calcium sulfate dihydrate cement was 17.2 MPa. The results show that the preparation of high percentage α-HH is feasible via a hydrothermal method and the process can be further scaled up to industrial scale production.

Effects of Magnesium and Ferric Ions on Crystallization of Calcium Sulfate Dihydrate Under the Simulated Conditions of Wet Flue-gas Desulfurization

The influences of magnesium and ferric ions in their different ratios on the rate of gypsum crystallization were studied under the conditions similar to those of wet flue-gas desulfurization（WFGD）. The results show that addition of both Mg^2＋ and Fe^3＋ increased induction time and decreased the growth efficiency up to 50% compared with the baseline（without impurities） depending on the concentration and the type of impurity. The effects of Mg^2＋ and Fe^3＋ on the surface energy and the rate of nucleation were estimated by employing the classical nucleation theory. The surface energy decreased by 8% and 14% with the addition of 0.02 mol/L magnesium or ferric ions, respectively, compared to the baseline. Mg^2＋ and Fe^3＋ made the growth rate of the （020）, （021） and （040） faces of gypsum crystal a much greater reduction, which leads to the formation of needle crystals compared to the baseline which favors the formation of plate or flakes. Furthermore, an edge detection program was developed to quantify the effects of impurities on the filtration rate of gypsum product. The results show that the inhibition efficiency of the presence of 0.02 mol/L Mg^2＋ and Fe^3＋ on the filtration rate of gypsum crystal ranges from 22% to 39%.

Calcium sulfate whisker prepared by flue gas desulfurization gypsum:A physical–chemical coupling production process

In this paper,the solid waste desulfurization gypsum produced by coal-fired power plants was used as a raw material to prepare calcium sulfate whiskers with high application prospects.Calcium sulfate whiskers with uniform morphology and high aspect ratio can be prepared by hydrothermal method in sulfuric acid solution.A new process of desulfurization gypsum activated by high-energy grinding to reduce the reaction temperature and sulfuric acid concentration was developed.Through the comparison of product morphology,the best grinding time was determined to be 3.5 h.The mechanism of desulfurization gypsum through physical–chemical coupling to reduce energy consumption was clarified.The activation of desulfurization gypsum by grinding and the acidic environment provided by the sulfuric acid solution made the calcium sulfate solution reached rapid saturation and accelerated the nucleation rate.By calculating the conversion and crystallization rate of calcium sulfate whiskers,it was found that there were obvious"autocatalytic"kinetic characteristics during the crystallization process.

Preparation, Characterization, and Formation Mechanism of Calcium Sulfate Hemihydrate Whiskers

Calcium sulfate hemihydrate whiskers were synthesized successfully via one-step hydrothermal crystallization method using phosphogypsum at 130 °C for 240 min with an initial slurry mass fraction of 2.5 wt%. The phase compositions, microstructures, thermal properties and molecular structures of asprepared samples were analyzed by XRD, ESEM, EDS, TG-DTA, and FT-IR. The influence of raw materials’ ball-milling time on the morphologies of whiskers was investigated. The effects of impurities on crystallization morphologies and length to diameter ratio(L/D) of calcium sulfate hemihydrate whiskers were studied. The results indicated that the calcium sulfate dihydrate crystalline could be translated directly into fibrous calcium sulfate hemihydrate whiskers. It was beneficial to form fine fiber structure when the ball-milling time of the raw material was 15 min. Aspect ratio of calcium sulfate hemihydrate whiskers decreased with increasing content of impurities. Moreover, the relative growth mechanism of whisker crystals via one-step hydrothermal crystallization method was discussed in detail.

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

Hydrothermal synthesis of calcium sulfate whisker from flue gas desulfurization gypsum

Plenty of flue gas desulfurization(FGD) gypsum generated from coal-fired power plants for sulfur dioxide sequestration caused many environmental issues. Preparing calcium sulfate whisker(CSW) from FGD gypsum by hydrothermal synthesis is considered to be a promising approach to solve this troublesome problem and utilize calcium sulfate in a high-value-added way. The effects of particle size of FGD gypsum, slurry concentration,and additives on CSW were investigated in this work. The results indicated that fine particle size of FGD gypsum and moderately high slurry concentration were beneficial for crystal nucleation and growth. Three additives of magnesium chloride, citric acid, and sodium dodecyl benzene sulfonate(SDBS) were employed in this study. It was found that mean length and aspect ratio of CSW were both decreased by the usage of magnesium chloride,while a small quantity of citric acid or SDBS could improve the CSW morphology. When multi-additives of citric acid-SDBS were employed, the mean length and aspect ratio increased more than 20%. Moreover, surface morphology of CSW went better, and the particle size and crystal shape became more uniform.

The Effect of Additives on Calcium Sulfate Dihydrate Crystallization Kinetics in Gypsum Type Brine System

1 Introduction There exist calcium and sulfate ions outside sodium chloride in solution mining for calcium sulfate brine.The calcium and sulfate ions not only affect the purity of the vacuum salt products,but also increase the scaling of vacuum evaporation tanks and brine reusing pipes.Additives have certain impacts on the crystallization dynamics(Randolph et al.,1971).The crystallization

Crystallization Process of Calcium Sulfate Dihydrate in Gypsum Type Brine System

1 Introduction Calcium sulfate deposition is one of the most important and serious problems faced by heat transfer equipment during operation(Pavlos et al.,1999;Liu et al.,1996).The crystallization of calcium sulfate is known as a major

Preparation and characterization of hemihydrate calcium sulfate-calcium hydroxide composite bone repair materials

Objective:To prepare a bone repair material with certain mechanical strength and biological activity,this paper used calcium sulfate hemihydrate(CSH)powder compounded with calcium hydroxide(Ca(OH)2)powder to prepare a bone repair scaffold material for physicochemical property characterization and testing.Methods:The physical and chemical properties and characterization of the dried and cured bone repair materials were determined by Fourier infrared spectroscopy(FT-IR),X-ray diffraction(XRD),and scanning electron microscopy;Universal material testing machine to determine the mechanical and mechanical strength of composite materials.Results:XRD showed that the structure of the composite material phase at 5%concentration was calcium sulfate hemihydrate and calcium hydroxide after hydration.The FT-IR and XRD analyses were consistent.Scanning electron microscopy(SEM)results showed that calcium hydroxide was uniformly dispersed in the hemihydrate calcium sulfate material.0%,1%,5%,and 10%specimen groups had compressive strengths of 3.86±3.1,5.27±1.28,8.22±0.96,and 14.4±3.28 MPa.10%addition of calcium hydroxide significantly improved the mechanical strength of the composites,but also reduced the the porosity of the material.Conclusion:With the addition of calcium hydroxide,the CSH-Ca(OH)2 composite was improved in terms of mechanical material and is expected to be a new type of bone repair material.

On the enhanced properties of composite asphalt via adding surface modified calcium sulfate whisker-SBR

With the aim of improving the durability and safety,erosion time,and cost-effective of asphalt road,a composite of modified calcium sulfate whisker-styrene butadiene rubber modified asphalt(MCSWSBRMA)was prepared via thermal doping.Firstly,stearic acid and titanate coupling agent(NDZ-201)were used as a modifier to transform calcium sulfate whisker(CSW)into MCSW via wet modification method at 60℃and anhydrous ethanol as a dispersant.What is more,the optimum loading of modifier(a mixture of 25%stearic acid+75%NDZ-201)was found to be at 2%to prepare MCSW.Subsequently,a composite of MCSW-SBRMA was prepared with different loading of MCSW(i.e.2%to 8%)to enhance the softening point of asphalt.In this study,it was found that 4%of modifiers was the best composition to improve the MCSW-SBRMA properties as elucidated in the orthogonal experiment table L_(16)(42).The effects of MCSW and SBR addition on several properties of asphalt were studied by multiple routine tests including penetration,segregation test,and so on.The results show that:2%to 8%MCSW can increase the softening point of SBR modified asphalt(SBRMA)by 7%to 8%.4%MCSW increased the PG of SBRMA from 64 to 70,which greatly improved the high temperature characteristics of asphalt.The 5℃ductility of MCSW-SBRMA is greater than 100 cm,which greatly improves the low temperature performance of asphalt.Through the application of fluorescence microscopy(FM),Fourier transform infrared spectroscopy(FTIR),Scanning electron microscopy(SEM),and energy dispersive spectroscopy(SEM-EDS),it has been demonstrated that MCSW-SBR effectively alters asphalt in a highly uniform manner,with some MCSW still retaining large cross sections,thereby facilitating the dispersion of shear stress and enhancing the durability of asphalt.

Co-delivery of rhBMP-2 and zoledronic acid using calcium sulfate/hydroxyapatite carrier as a bioactive bone substitute to enhance and accelerate spinal fusion

Recombinant human bone morphogenetic protein-2(rhBMP-2)has been FDA-approved for lumbar fusion,but supraphysiologic initial burst release due to suboptimal carrier and late excess bone resorption caused by osteoclast activation have limited its clinical usage.One strategy to mitigate the pro-osteoclast side effect of rhBMP-2 is to give systemic bisphosphonates,but it presents challenges with systemic side effects and low local bioavailability.The aim of this in vivo study was to analyze if posterolateral spinal fusion(PLF)could be improved by utilizing a calcium sulfate/hydroxyapatite(CaS/HA)carrier co-delivering rhBMP-2 and zoledronic acid(ZA).Six groups were allocated(CaS/HA,CaS/HA+BMP-2,CaS/HA+systemic ZA,CaS/HA+local ZA,CaS/HA+BMP-2+systemic ZA,and CaS/HA+BMP-2+local ZA).10-week-old male Wistar rats,were randomly assigned to undergo L4-L5 PLF with implantation of group-dependent scaffolds.At 3 and 6 weeks,the animals were euthanized for radiography,μCT,histological staining,or biomechanical testing to evaluate spinal fusion.The results demonstrated that the CaS/HA biomaterial alone or in combination with local or systemic ZA didn’t support PLF.However,the delivery of rhBMP-2 significantly promoted PLF.Combining systemic ZA with rhBMP-2 didn’t enhance spinal fusion.Notably,the co-delivery of rhBMP-2 and ZA using the CaS/HA carrier significantly enhanced and accelerated PLF,without inhibiting systemic bone turnover,and potentially reduced the dose of rhBMP-2.Together,the treatment regimen of CaS/HA biomaterial co-delivering rhBMP-2 and ZA could potentially be a safe and cost-effective off-the-shelf bioactive bone substitute to enhance spinal fusion.

Direct transformation of FGD gypsum to calcium sulfate hemihydrate whiskers:Preparation,simulations,and process analysis

Calcium sulfate hemihydrate （CSH） whiskers were synthesized by phase transition in CaCl2 solution under atmospheric pressure. Analytical-grade calcium sulfate dihydrate （AR CSD） was used as the raw material for the synthesis of CSH whiskers, according to orthogonal experiments. The effects of reaction tem- perature, AR CSD content, H2SO4 content, and reaction time were investigated, and the crystallization conditions were optimized. The as-prepared CSH whiskers displayed a regular morphology and a highly uniform size, with an aspect ratio of 105, A simulation system was also established by blending various sulfates with AR CSD, to evaluate the effects of impurities in flue gas desulfurization （FGD） gypsum. The main aim was to prepare CSH whiskers directly from FGD gypsum, without any purification, using the optimized conditions. This is a facile potential alternative process for large-scale production of CSH whiskers using abundant FGD gypsum as source materials.

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H_2SO_4-NaCl-H_2O system

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization（FGD） gypsum.When purified FGD gypsum was used as raw material,the morphology and phase structure of the hydrothermal products grown in pure water,H2SO4-H2O,NaCl-H2O,and H2SO4-NaCl-H2O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated.The results indicate that calcium sulfate whiskers grow favorably in the H2SO4-NaCl-H2O system.When prepared using 10-70 g NaCl/kg gypsum-0.01 M H2SO4-H2O at 130 ℃ for 60 min,the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 ｜xm and lengths from 200 to 600 ｜xm,and their phase structure was calcium sulfate hemihydrate（HH）.Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed.With the co-presence of sulfuric acid and sodium chloride in the reaction solution,the concentrations of Ca2＋ and SO42- can be kept relatively stable,which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.

Influence of disodium hydrogen phosphate dodecahydrate on hydrothermal formation of hemihydrate calcium sulfate whiskers

The influence of Na2HPO4·12H2O on the hydrothermal formation of hemihydrate calcium sulfate（CaSO4·0.5H2O） whiskers from dihydrate calcium sulfate（CaSO4·2H2O）at 135 ℃ was investigated.Experimental results indicate that the addition of phosphorus accelerates the hydrothermal conversion of CaSO4·2H2O to CaSO4·0.5H2O via the formation of Ca3（PO4）2 and produces CaSO4-0.5H2O whiskers with thinner diameters and shorter lengths.Compared with the blank experiment without Na2HPO4·12H2O,the existence of minor amounts（8.65 ×10-4-4.36 × 10-3 mol/L） of Na2HPO4·12H2O led to a decrease in the diameter of CaSO4·0.5H2O whiskers from 1.0-10.0 to 0.5-2.0 μm and lengths from 70-300 to50-200 μm.

A comparative study of calcium sulfate artificial bone graft versus allograft in the reconstruction of bone defect after tumor curettage

Background Cavity reconstruction after benign bone tumor removal is varied and controversial.AIIograft is widely used but is associated with complications.New bone substitutes,such as calcium sulfate artificial bone,have been introduced for bone tumor operation.However,the bone healing response of artificial bone has not been compared with allograft bone.We therefore compared calcium sulfate grafts （study group） with bone allografts （control group） for the treatment of benign bone tumors.Methods We retrospectively reviewed 50 patients who underwent calcium sulfate reconstruction and 50 patients who underwent allograft cancellous bone reconstruction.The two groups were well matched.The mean follow-up time of the study group was 19.9 （12-55） months.We investigated bone healing response,complications,and factors affecting bone healing.Results At the last follow-up,84％ （42/50） of cases in the study group and 62％ （31/50） of cases in the control group had achieved clinical healing （P=0.013）.The initial healing rate showed no significant difference between the two groups （100％ vs.96％,P=0.153）.The mean healing times for calcium sulfate and allograft bone were 9.6 （3-42） months and 13.8 （3-36） months,respectively （P ＜0.01）.Complications in the study group were minor and resolved.Implant volume was a significant factor affecting bone healing.Conclusion The calcium sulfate bone substitute showed a satisfactory healing outcome and safety profile in reconstruction of bone defects after benign bone tumor curettage,especially in smaller cavities.

Effects of Calcium Sulfate Combined with Platelet-rich Plasma on Restoration of Long Bone Defect in Rabbits

Background：The treatment for long bone defects has been a hot topic in the field of regenerative medicine.This study aimed to evaluate the therapeutic effects of calcium sulfate （CS） combined with platelet-rich plasma （PRP） on long bone defect restoration.Methods：A radial bone defect model was constructed through an osteotomy using New Zealand rabbits.The rabbits were randomly divided into four groups （n =10 in each group）：a CS combined with PRP （CS-PRP） group,a CS group,a PRP group,and a positive （recombinant human bone morphogenetic protein-2） control group.PRP was prepared from autologous blood using a two-step centrifugation process.CS-PRP was obtained by mixing hemihydrate CS with PRP.Radiographs and histologic micrographs were generated.The percentage of bone regenerated bone area in each rabbit was calculated at 10 weeks.One-way analysis of variance was performed in this study.Results：The radiographs and histologic micrographs showed bone restoration in the CS-PRP and positive control groups,while nonunion was observed in the CS and PRP groups.The percentages of bone regenerated bone area in the CS-PRP （84.60 ± 2.87%） and positive control （52.21 ± 4.53%） groups were significantly greater than those in the CS group （12.34 ± 2.17%） and PRP group （16.52 ± 4.22%） （P 〈 0.001）.In addition,the bone strength of CS-PRP group （43.l 0 ± 4.10%） was significantly greater than that of the CS group （20.10 ± 3.70%） or PRP group （25.10 ± 2.10%） （P 〈 0.001）.Conclusion：CS-PRP functions as an effective treatment for long bone defects through stimulating bone regeneration and enhancing new bone strength.

Biomechanical evaluation of vertebroplasty using calcium sulfate cement for thoracolumbar burst fractures

Objective： To evaluate the biomechanical performance of vertebroplasty using calcium sulfate cement for thoracolumbar burst fractures. Methods： Sixteen bovine thoracolumbar spines （TH- L1 ） were divided into 4 groups （ A, B, C and D）. After burst-fracture model was created, 12 vertebral bodies in Groups A, B and C were augmented with calcium sulfate cement （ CSC ）, calcium phosphate cement （ CPC ） and polymethylmethacrylate （ PMMA ） bone cement, respectively. Each anterior vertebral body height was measured with a caliper at 4 time points： intact conditions （Hint）, post-fracture （ HFr）, post-reduction （HRe） and post-vertebroplasty （HVP）. The f＇dling volume of 3 different bone cements was also measured. Each vertebral body was compressed at 0. 5 mm/s using a hinged plating system on a materials testing machine to 50 % of the postvertebroplasty height to determine strength and stiffness. Difference was checked using t test or One-way ANOVA. Results： The average strike energy was 66. 2 J. Vertebroplasty with different cements could sustain vertebral height. The average f＇dling volume of bone cement in 3 groups was 4.35 ml （ CSC ）, 3.72 nd（ CPC ） and 3.95 ml （PMMA）, respectively, and there was no statistically significant difference among them （ P 〉0.05 ）. Vertebroplasty with PMMA completely restored strength （116%） and stiffness （105%）. CSC or CPC partly recovered vertebral strength and stiffness. However, greater strength restoration was got with CSC （ 1 659 N） as compared with CPC （1 011N, P〈0.01 ）. Regarding stiffness, differences between CSC （ 140 N/ram ±40 N/nan） and the other two bone cements （ CPC ：148 N/nun ±33 N/nun, PMMA.236 N/mm ＋97/N/mm） were not significant （P〉0.05）. Conclusions： For a burst-fracture of calf spine, use of CSC for vertebroplasty yields similar vertebral stiffness as compared with PMMA or CPC. Although augmentation with CSC partly obtains the normal strength, this treatment still can be applied in thocacoloumbar burst fractures with other instrumental devices in light of its bioactivation.

Preparation of a Crosslinked Chitosan Coated Calcium Sulfate Whisker and Its Reinforcement in Polyvinyl Chloride

A calcium sulfate whisker （CSW） coated with glutaraldehyde crosslinked chitosan （GACS） was prepared to reinforce polyvinyl chloride （PVC） in this study. The results show that the optimum concentration of both chitosan （CS） and glutaraldehyde （GA） is 0.05 wt%. The tensile strength, impact strength, flexural modulus and vicat softening temperature of the PVC composite with 12 wt% of modified CSW are in- creased by 1 Z5%, 40.4%, 0.8% and 3.8% compared with those of the PVC composite with 12 wt~ of unmodified CSW, and by 2.9%, 42.4%, 2Z1% and 6.8% compared with those of pure PVC, respectively. The dynamic mechanical analysis results indicate that the modified CSW/PVC composite exhibits much higher storage modulus and glass transition temperature than those of unmodified CSW/PVC composite and pure PVC. In addition, the modified CSW/PVC composite also demonstrates good thermal properties with a high rapidest decomposition temperature （Trvd） and char residue. The scanning electron microscopy images of tensile-fractured surfaces show that the modified CSW has a strong interfacial adhesion with PVC matrix.

Mechanical Properties and Interfacial Interaction of Modified Calcium Sulfate Whisker]Poly(Vinyl Chloride)Composites

Calcium sulfate whiskers（CSWs） modified with glutaraldehyde-crosslinked poly（vinyl alcohol）（PVA） or traditional surface modifiers,including silane coupling agent,titanate coupling agent and stearic acid,were used to strengthen poly（vinyl chloride）（PVC）,and the morphologies,mechanical and heat resistant properties of the resulting composites were compared.The results clearly show that glutaraldehyde cross-linked PVA modified CSW/PVC composite（c PVA@CSW/PVC） has the strongest interfacial interaction,good and stable mechanical and heat resistant properties.Nielsen＇s modified Kerner＇s equation for Young＇s modulus is better than other models examined for the CSW/PVC composites.The half debonding angle θ of c PVA@CSW/PVC composite is lower than that of other composites except silane coupling agent modified CSW/PVC composites,indicating a very strong interfacial adhesion between c PVA@CSW and PVC.In general,cross-linked PVA is effective and environmentally friendly in modifying inorganic fillers.

Preliminary Study on a Novel Process for Manufacturing Soda Ash from Sodium Sulfate

The purpose of this work is to find a new way for utilizing the rich sodium sulfate resource to produce soda ash. A novel process is proposed which uses aqueous dichromate solution as working medium through decomposition of calcium carbonate in aqueous sodium dichromate, complex decomposition of aqueous sodium sulfate and calcium chromate, regeneration of sodium dichromate and production of sodium bicarbonate from carbonation of aqueous sodium chromate solution, processing and utilization of byproduct calcium sulfate, and production of sodium carbonate from sodium bicarbonate. The process has the features of less corrosion and pollution and low energy consumption.