Effects of temperature and of the addition of accelerating and retarding agents on the kinetics of hydration of tricalcium silicate

The formation of calcium silicate hydrates (C-S-H) during the hydration of tricalcium silicate (C3S) in pure water and in water solutions containing 1% CaCl2 (accelerator) and 0.01% saccharose (retarder) was studied by small-angle X-ray scattering (SAXS). SAXS measurements were performed under isothermal conditions within the temperature range 25 °C T < 52 °C. The experimental results indicate that the time variation of the mass fraction of the C-S-H product phase, α(f), can be fitted, under all conditions of paste setting, by Avrami equation, α(t) = 1 -exp(-(kt)′), k being a rate parameter and n an exponent depending on the characteristics of the transformation. The parameter n is approximately equal to 2 for hydration of C^S in pure water. Depending on temperature, n varies from 2 to 2.65 for hydration in the presence of CaC^ and saccharose. The value n = 2 is theoretically expected for lateral growth of thin C-S-H plates of constant thickness. The time dependence of SAXS intensity indicates that the transformed phase (C-S-H) consists of colloidal particles in early stages of hydration, evolving by two-dimensional growth toward a disordered lamellar structure composed of very thin plates. The activation energy ΔE for the growth of C-S-H phase was determined from the time dependence of X-ray scattering intensity. These data were obtained by in situ measurements at different temperatures of hydration. The values of ΔE are 37.7, 49.4, and 44.3 kJ/mol for hydration in pure water and in water solutions containing CaCl2 and saccharose, respectively. © 2000 American Chemical Society.

Resposta do manjericão (Ocimum basilicum L.) cultivado em solos corrigidos com calcário e escória silicatada: Caracterí sticas agronômicas e produção de matéria seca

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Aplicação de escória de aciaria e calcário no solo e desenvolvimento do primeiro ciclo da grama bermuda

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Persistência de palhada de plantas de cobertura em função de doses de silício e resposta do feijoeiro em sucessão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito da escória de siderurgia como fonte de silício e sua interação com a adubação nitrogenada em Brachiaria brizantha

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Nutrição do feijoeiro e intensidade da antracnose em função da aplicação de silício e cobre

The objective of this work was to evaluate the effect of calcium silicate and copper sulfate on anthracnose intensity and nutrition of bean plants. The experiment was conducted using an experimental design in randomized blocks following a 4 x 4 factorial arrangement, (four levels of calcium silicate and four levels of copper sulfate) and two additional treatments (plants without inoculation and plants sprinkled with Benomyl). Four evaluations of the incidence and severity of anthracnose were done, in addition to measuring total leaf area. At the end of the evaluations, incidence and severity data were integrated over time, obtaining the area under disease progress curve (AUDPC). Contents of N, P, K, Ca, Mg, B, Cu, Fe, Mn, Zn, Si and lignin were determined in the aerial part. A linear decrease of the intensity AUDPC was observed with the increase of the doses of calcium silicate. The severity AUDPC was influenced by the doses of copper, obtaining a reduction of 35% on the higher dosage. The supply of silicon and copper altered the content of the K, Mg, S, Zn, Ca and Si in the aerial part of the bean plants.

Desenvolvimento e marcha de absorção de silício em plantas de arroz sob condição de déficit hídrico e adubação silicatada

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Silício e nitrogênio em alho vernalizado com e sem limpeza de vírus

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

SILICON IN ROW AND NITROGEN IN TOPDRESSING FERTILIZATION ON RICE UNDER DRY LAND AND SPRINKLER IRRIGATION CONDITIONS

The objective of this work was to evaluate the effects of silicon application adjusted with nitrogen fertilization via top-dressing on grain productivity, the silicon contents of the soil, in the plant tissue and nitrogen contents in dry and irrigated conditions. The experimental outlining was from designed blocks with subdivided parcels and four repetitions. The treatments consisted of culture system (dry and irrigated) and the under parcels by the combination of silicon (0 and 100 kg ha(-1)), in magnesium and calcium silicate form (with 23% of SiO2), and four doses of N (urea) via top-dressing (0, 30, 60 and 90 kg ha(-1)). Silicon application at sowing furrow was a viable technique because it provided significant increase in the content of this element in the root growth of rice. The application of silicon in the sowing furrow did not change the content of the element nor the nitrogen nutrition in rice plants. The nitrogen application reduced the silicon content and increased nitrogen nutrition in rice plants. Silicon application at sowing furrow provided no increase in rice grain yield. When there was no water limitation to nitrogen fertilization enhanced linearly on rice grain yield, whereas under water stress the effect of nitrogen fertilization was limited.

A study of the formation of amorphous calcium phosphate and hydroxyapatite on melt quenched Bioglass(A (R)) using surface sensitive shallow angle X-ray diffraction

Melt quenched silicate glasses containing calcium, phosphorous and alkali metals have the ability to promote bone regeneration and to fuse to living bone. These glasses, including 45S5 Bioglass(A (R)) [(CaO)(26.9)(Na2O)(24.4)(SiO2)(46.1)(P2O5)(2.6)], are routinely used as clinical implants. Consequently there have been numerous studies on the structure of these glasses using conventional diffraction techniques. These studies have provided important information on the atomic structure of Bioglass(A (R)) but are of course intrinsically limited in the sense that they probe the bulk material and cannot be as sensitive to thin layers of near-surface dissolution/growth. The present study therefore uses surface sensitive shallow angle X-ray diffraction to study the formation of amorphous calcium phosphate and hydroxyapatite on Bioglass(A (R)) samples, pre-reacted in simulated body fluid (SBF). Unreacted Bioglass(A (R)) is dominated by a broad amorphous feature around 2.2 A...(-1) which is characteristic of sodium calcium silicate glass. After reacting Bioglass(A (R)) in SBF a second broad amorphous feature evolves similar to 1.6 A...(-1) which is attributed to amorphous calcium phosphate. This feature is evident for samples after only 4 h reacting in SBF and by 8 h the amorphous feature becomes comparable in magnitude to the background signal of the bulk Bioglass(A (R)). Bragg peaks characteristic of hydroxyapatite form after 1-3 days of reacting in SBF.

Effect of calcium source on structure and properties of sol-gel derived bioactive glasses

The aim was to determine the most effective calcium precursor for synthesis of sol-gel hybrids and for improving homogeneity of sol-gel bioactive glasses. Sol-gel derived bioactive calcium silicate glasses are one of the most promising materials for bone regeneration. Inorganic/organic hybrid materials, which are synthesized by incorporating a polymer into the sol-gel process, have also recently been produced to improve toughness. Calcium nitrate is conventionally used as the calcium source, but it has several disadvantages. Calcium nitrate causes inhomogeneity by forming calcium-rich regions, and it requires high temperature treatment (>400 C) for calcium to be incorporated into the silicate network. Nitrates are also toxic and need to be burnt off. Calcium nitrate therefore cannot be used in the synthesis of hybrids as the highest temperature used in the process is typically 40-60 C. Therefore, a different precursor is needed that can incorporate calcium into the silica network and enhance the homogeneity of the glasses at low (room) temperature. In this work, calcium methoxyethoxide (CME) was used to synthesize sol-gel bioactive glasses with a range of final processing temperatures from 60 to 800 C. Comparison is made between the use of CME and calcium chloride and calcium nitrate. Using advanced probe techniques, the temperature at which Ca is incorporated into the network was identified for 70S30C (70 mol % SiO, 30 mol % CaO) for each of the calcium precursors. When CaCl was used, the Ca did not seem to enter the network at any of the temperatures used. In contrast, Ca from CME entered the silica network at room temperature, as confirmed by X-ray diffraction, Si magic angle spinning nuclear magnetic resonance spectroscopy, and dissolution studies. CME should be used in preference to calcium salts for hybrid synthesis and may improve homogeneity of sol-gel glasses.

3D-printing of highly uniform CaSiO3 ceramic scaffolds : preparation, characterization and in vivo osteogenesis

Calcium silicate (CaSiO3, CS) ceramics have received significant attention for application in bone regeneration due to their excellent in vitro apatite-mineralization ability; however, how to prepare porous CS scaffolds with a controllable pore structure for bone tissue engineering still remains a challenge. Conventional methods could not efficiently control the pore structure and mechanical strength of CS scaffolds, resulting in unstable in vivo osteogenesis. The aim of this study is to set out to solve these problems by applying a modified 3D-printing method to prepare highly uniform CS scaffolds with controllable pore structure and improved mechanical strength. The in vivo osteogenesis of the prepared 3D-printed CS scaffolds was further investigated by implanting them in the femur defects of rats. The results show that the CS scaffolds prepared by the modified 3D-printing method have uniform scaffold morphology. The pore size and pore structure of CS scaffolds can be efficiently adjusted. The compressive strength of 3D-printed CS scaffolds is around 120 times that of conventional polyurethane templated CS scaffolds. 3D-Printed CS scaffolds possess excellent apatite-mineralization ability in simulated body fluids. Micro-CT analysis has shown that 3D-printed CS scaffolds play an important role in assisting the regeneration of bone defects in vivo. The healing level of bone defects implanted by 3D-printed CS scaffolds is obviously higher than that of 3D-printed b-tricalcium phosphate (b-TCP) scaffolds at both 4 and 8 weeks. Hematoxylin and eosin (H&E) staining shows that 3D-printed CS scaffolds induce higher quality of the newly formed bone than 3D-printed b-TCP scaffolds. Immunohistochemical analyses have further shown that stronger expression of human type I collagen (COL1) and alkaline phosphate (ALP) in the bone matrix occurs in the 3D-printed CS scaffolds than in the 3D-printed b-TCP scaffolds. Considering these important advantages, such as controllable structure architecture, significant improvement in mechanical strength, excellent in vivo osteogenesis and since there is no need for second-time sintering, it is indicated that the prepared 3D-printed CS scaffolds are a promising material for application in bone regeneration.

Raman spectroscopic study of the mineral xonotlite Ca 6Si 6O 17(OH) 2-A component of plaster boards

The mineral xonotlite Ca 6Si 6O 17(OH) 2 is a crystalline calcium silicate hydrate which is widely used in plaster boards and in many industrial applications. The structure of xonotlite is best described as having a dreierdoppelketten silicate structure, and describes the repeating silicate trimer which forms the silicate chains, and doppel indicating that two chains combine. Raman bands at 1042 and 1070 cm -1 are assigned to the SiO stretching vibrations of linked units of Si 4O 11 units. Raman bands at 961 and 980 cm -1 serve to identify Si 3O 10 units. The broad Raman band at 862 cm -1 is attributed to hydroxyl deformation modes. Intense Raman bands at 593 and 695 cm -1 are assigned to OSiO bending vibrations. Intense Raman bands at 3578, 3611, 3627 and 3665 cm -1 are assigned to OH stretching vibrations of the OH units in xonotlite. Infrared spectra are in harmony with the Raman spectra. Raman spectroscopy with complimentary infrared spectroscopy enables the characterisation of the building material xonotlite.

A stimulatory effect of Ca3ZrSi2O9 bioceramics on cementogenic/osteogenic differentiation of periodontal ligament cells

The regeneration of periodontal tissues to cure periodontitis remains a medical challenge. Therefore, it is of great importance to develop a novel biomaterial that could induce cementogenesis and osteogenesis in periodontal tissue engineering. Calcium silicate (Ca–Si) based ceramics have been found to be potential bioactive materials due to their osteostimulatory effect. Recently, it is reported that zirconium modified calcium-silicate-based (Ca3ZrSi2O9) ceramics stimulate cell proliferation and osteogenic differentiation of osteoblasts. However, it is unknown whether Ca3ZrSi2O9 ceramics possess specific cementogenic stimulation for human periodontal ligament cells (hPDLCs) in periodontal tissue regeneration in vitro. The purpose of this study was to investigate whether Ca3ZrSi2O9 ceramic disks and their ionic extracts could stimulate cell growth and cementogenic/osteogenic differentiation of hPDLCs; the possible molecular mechanism involved in this process was also explored by investigating the Wnt/β-catenin signalling pathway of hPDLCs. Our results showed that Ca3ZrSi2O9 ceramic disks supported cell adhesion, proliferation and significantly up-regulated relative alkaline phosphatase (ALP) activity, cementogenic/osteogenic gene expression (CEMP1, CAP, ALP and OPN) and Wnt/β-catenin signalling pathway-related genes (AXIN2 and CTNNB) for hPDLCs, compared to that of β-tricalcium phosphate (β-TCP) bioceramic disks and blank controls. The ionic extracts from Ca3ZrSi2O9 powders also significantly enhanced relative ALP activity, cementogenic/osteogenic and Wnt/β-catenin-related gene expression of hPDLCs. The present results demonstrate that Ca3ZrSi2O9 ceramics are capable of stimulating cementogenic/osteogenic differentiation of hPDLCs possibly via activation of the Wnt/β-catenin signalling pathway, suggesting that Ca3ZrSi2O9 ceramics have the potential to be used for periodontal tissue regeneration.