Crystalline Wollastonite Research Articles

Calcium silicate biocomposites: effects of selenium oxide on the physico-mechanical features and their in-vitro biological assessments

Bone tissue regenerative material serves as a prospective recovery candidate with self-adaptable biological properties of bio-activation, degradability, compatibility, and antimicrobial efficacy instead of metallic implants. Such materials are highly expensive due to chemical reagents and complex synthesis procedures, making them unaffordable for patients with financial constraints. This research produced an efficient bone tissue regenerative material using inexpensive naturally occurring source materials, including silica sand and limestone. The extracted SiO2 and CaO particles (75:25 wt%) were subjected to hydrothermal synthesis (water treatment instead of chemical solvents) to produce the CaSiO3 biomaterial (code: S). Selenium oxide was doped with calcium silicate at 3, 5, and 10 wt.% to enhance its properties, yielding biocomposite materials (i.e. S3, S5, and S10). The physico-mechanical properties of these materials were investigated with x-ray diffraction, Fourier transform infrared, FESEM-EDS, and micro-universal testing machine. The results revealed that the synthesized biocomposites have a crystalline wollastonite phase with a porously fused rough surface. From structural parametric calculations, we found that the biocomposites have reduced particle size and enhanced surface area due to the influence of selenium oxide. The biocomposite S10, having high SeO2 content, attained the maximum compressive strength of 75.2 MPa. In-vitro studies of bioactivity, biodegradability, biocompatibility, and antibacterial activity were performed. At 7 and 14 d of bioactivity, the synthesized biocomposites are capable of dissolving their ions into simulated body fluid (SBF) solution to precipitate hydroxyapatite and a required Ca/P ratio of 1.69 was achieved by S3. A comparative analysis has been performed on the degradation activity in Tris-HCl and the consequent pH changes during SBF treatment. The bio-analysis revealed that the biocomposite S3 shows enhanced bioactivity through a controlled degradation rate and secured cell viability of 88% at a concentration of 100 μg ml−1. It also offers significant bacterial inhibition potency against E.coli and S.aureus bacteria.

Synthetic Calcium Silicate Biocomposite Based on Sea Urchin Skeleton for 5-Fluorouracil Cancer Delivery.

Synthetic calcium silicates and phosphates are promising compounds for targeted drug delivery for the effective treatment of cancerous tumors, and for minimizing toxic effects on the patient's entire body. This work presents an original synthesis of a composite based on crystalline wollastonite CaSiO3 and combeite Na4Ca4(Si6O18), using a sea urchin Mesocentrotus nudus skeleton by microwave heating under hydrothermal conditions. The phase and elemental composition and structure of the obtained composite were studied by XRF, REM, BET, and EDS methods, depending on the microwave heating time of 30 or 60 min, respectively, and the influence of thermo-oxidative post-treatment of samples. The role of the sea urchin skeleton in the synthesis was shown. First, it provides a raw material base (source of Ca2+) for the formation of the calcium silicate composite. Second, it is a matrix for the formation of its porous inorganic framework. The sorption capacity of the composite, with respect to 5-fluorouracil, was estimated, the value of which was 12.3 mg/L. The resulting composite is a promising carrier for the targeted delivery of chemotherapeutic drugs. The mechanism of drug release from an inorganic natural matrix was also evaluated by fitting its release profile to various mathematical models.

Sound speed and refractive index of amorphous CaSiO3 upon pressure cycling to 40 GPa

Abstract Brillouin spectroscopy at room temperature and pressures up to 40 GPa documents nearly identical elasticity and refractive index of amorphous CaSiO3 created by two different methods: temperature-quenching the melt at ambient pressure and pressure-amorphizing crystalline wollastonite at room temperature. We find reproducible hysteresis of 0 to 8% on pressure cycling that is small relative to the 30 to 60% changes in shear and longitudinal wave velocities over this pressure range. Together with observed changes in refractive index and previous results from Raman spectroscopy, these measurements reveal a continuous and reversible change in atomic packing induced by pressure. Unlike many other silicate glasses, amorphous CaSiO3 exhibits highly reproducible properties, behaving smoothly and reversibly under pressure cycling and possessing similar structure and elasticity regardless of synthesis paths for the starting material, which suggests that the amorphous solid may mimic the liquid over the pressure range investigated.

Synthesis of Cu-containing Diopside through a One-Step Crystallization

The incorporation of copper into pyroxene structure was investigated through the melt quenching technique and one-step crystallization procedure. Two series of glasses have been studied, one set with Ca=Mg and another set with Ca>Mg in diopside formula Cux(Ca Mg)2-xSi2O6. The glasses were nucleated by TiO2, Cr2O3, or CaF2 additions as nucleating agents to variably control the phases produced. X-ray diffraction (XRD), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDX) were used to characterize the obtained samples. The heat treatment studied at 700, 800, 900 and 1000 °C for 2 h produced green and dark green glasses based on Cu-containing diopside. Various crystalline wollastonite, cuprite, tenorite, cristobalite, quartz, and fluorite phases were developed with different ratios combined with diopside formation depending on the heat treatment and nucleating agents used. As the heat treatment increased in temperature, the crystallized fraction increased with the development of nano-aggregates and the observed reticulated textures confirmed a radical change in the euhedral crystals. This emphasizes that the Cu-containing diopside can be created by a facile one step process. These compositions may find some applications in biological and optical fields.

CaSiO3-HAp Structural Bioceramic by Sol-Gel and SPS-RS Techniques: Bacteria Test Assessment.

The article presents an original way of getting porous and mechanically strong CaSiO3-HAp ceramics, which is highly desirable for bone-ceramic implants in bone restoration surgery. The method combines wet and solid-phase approaches of inorganic synthesis: sol-gel (template) technology to produce the amorphous xonotlite (Ca6Si6O17·2OH) as the raw material, followed by its spark plasma sintering–reactive synthesis (SPS-RS) into ceramics. Formation of both crystalline wollastonite (CaSiO3) and hydroxyapatite (Ca10(PO4)6(OH)2) occurs “in situ” under SPS conditions, which is the main novelty of the method, due to combining the solid-phase transitions of the amorphous xonotlite with the chemical reaction within the powder mixture between CaO and CaHPO4. Formation of pristine HAp and its composite derivative with wollastonite was studied by means of TGA and XRD with the temperatures of the “in situ” interactions also determined. A facile route to tailor a macroporous structure is suggested, with polymer (siloxane-acrylate latex) and carbon (fibers and powder) fillers being used as the pore-forming templates. Microbial tests were carried out to reveal the morphological features of the bacterial film Pseudomonas aeruginosa that formed on the surface of the ceramics, depending on the content of HAp (0, 20, and 50 wt%).

Mechanism of Interaction between Concrete Cement Matrix and Mineral Additive Particles

A nature of the forces, which act between the concrete cement matrix and entrained mineral particles (ground additives, fine and coarse additives), has been considered. It has been shown that the adhesion between them is attributable to the forces of different nature. The strongest adhesion between the particles of the hydrated binding material and mineral additives occurs, when materials, which react with calcium hydrate of the pore fluid, are used. The latter includes glassy wollastonite, which is part of granulated blast furnace slag. Even at a temperature of 25 °C, an aggressive interaction between them is observed and firm chemical bonds occur. In such case, the dissociation energy of such bonds ranges from 400 to 500 kJ per bond. Between materials, such as crystalline wollastonite and the concrete cement matrix, there is an epitaxial coalescence of its basal surfaces and tobermorite calcium hydrosilicates formed by the interaction of the binder with water. A direct contact is required between the reacting surfaces for such interaction. This is implemented by virtue of the bond, which is attributable to contraction forces resulting from shrinkage strains of the hydrated particles in the concrete cement matrix. Internal strains of the cement that are attributable to contraction, shrinkage, and carbonization of hydrated compounds result in the cement sheath contracting around the aggregate grains and steel reinforcement. Internal strains of the cement stone can be calculated using the Lame equation. We have reviewed the role of the factors, which are most critical for contraction of the cement ring around coarse particles of the aggregate and for stress-strain properties of artificial conglomerates, which have different composition and purpose.

A modified wet chemical synthesis of Wollastonite ceramic nanopowders and their characterizations

A simple, cost effective, reproducible, eco-friendly and very efficient novel modified wet chemical synthesis of high purity Wollastonite ceramics nanopowders is developed. The precursors used to synthesize calcium silicate hydrate (C-S-H) in this work are calcium chloride and sodium-disilicate. The method utilizes moderate heat comparatively with the methods reported in the literature. The resulting powders were calcined at different temperatures, characterized by XRD, FTIR, SEM, TEM, EDX, TGA/DTA, and N2 adsorption. XRD patterns for samples calcined show the formation of crystalline Wollastonite. Furthermore, XRD reveal thatβ-CaSiO3 occurs at 800 °C, then at 1200 °C, it transforms completely to α-CaSiO3. The method is applicable for bulk synthesis at cheaper cost, which opens interesting perspectives for applications in the several industrial fields such as ceramics, paints, plastics, biomaterials, composites, to name few.

Pulsed laser deposited bioactive RKKP-Mn glass-ceramic coatings on titanium

The study is aimed at the design of materials, i.e. glass-ceramics, containing trace elements with a specific role in the biological process of regenerating osteoporotic bones. Among these, manganese has a key function in bone osteogenesis and in the maintenance of bone mass. In this work, a 2 wt% of manganese containing RKKP glass-ceramic material has been prepared by sol-gel synthesis. Pulsed laser deposition technique has been applied to deposit films on titanium from the prepared glass-ceramic target. The films have been deposited at two different substrate temperatures (room (RT) and 500 °C) and investigated by X-ray diffraction, Raman spectroscopy, and SEM-EDX techniques. Both the films are characterized by a compact, crack-free and rough surface. The films deposited at 500 °C are composed of crystalline wollastonite and hydroxyapatite phases. For the assessment of films bioactivity in vitro, the standard Kokubo protocol for simulated body fluid (SBF) preparation has been followed. The films deposited at RT and 500 °C have been soaked in SBF for 3, 7, 14 and 28 days. For the film deposited at RT, apatite phase is registered after 7 days of soaking, whereas for the film deposited at 500 °C the apatite appeared only after 14 days. Moreover, the film deposited at RT induces a faster crystallization of the apatite layer.

A new route to sol-gel crystalline wollastonite bioceramic

ABSTRACTArtificial bone graft materials formed from wollastonite have been extensively used in bone repair because of their high degree of bioactivity and biocompatibility, thereby justifying the development of a protocol for large-scale production. This work reports a novel route for preparing wollastonite via the sol-gel process using bentonite clay as a cheap silica source. The obtained wollastonite was characterized for morphology, elemental composition, phase composition and bioactivity using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and Fourier transform infrared spectroscopy. Results obtained revealed that wollastonite phase was successfully formed in the material and it showed ability to induce formation of apatite within 0.5 day in biological fluid, an indicator for bone-bonding capability. Overall, the wollastonite prepared from the bentonite clay exhibited properties comparable to that synthesized from commercially obtained sodium metasilicate. Hence, our synthetic route may be useful for commercial-scale preparation of wollastonite.

¬¬Chromium fluoride-containing bioactive glasses: Structure and properties

Bioglasses in the system 24.5Na2O.24.5CaO.6P2O5.xCrF2.(45-x)SiO2 have been studied in the composition region of x= 0-10 mol%. CrF2. Glass of molar ratio (Ca+Na)/SiO2 ~1.1 is the base material for the glasses containing different CrF2 concentrations. X-ray diffraction (XRD), differential scanning calorimetriy (DSC), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Vicher hardness (Hv) measurements have been carried out. Crystalline feature of the glasses is followed up by XRD spectroscopy. It is found that crystallinity was enhanced via CrF2 addition. More enhancement was confirmed via thermal heat treatment process. Increasing CrF2 and sintering temperature will induce new ordered phases which will be distributed in the main glassy phase. Well formed flouroapatite (Ca5(PO4)3F and wollastonite Ca3Cr2(SiO4)3 phases containing fluorine and chromium ions are evidenced in CrF2 containing glasses. Increasing glass transition temperature Tg and hardness number Hv upon increasing CrF2 concentration was discussed on bases of formation of additional bonds by the effect of CrF2 molecules. The measured temperature window between Tc and Tg was found to have a great influence in material structure. Wide window is a feature of amorphous glass which free from CrF2. The window scale is found to quickly decrease with increasing CrF2, since crystalline phases are already formed in glasses containing CrF2. Formation of crystalline intermediate phases with more shielded silicate and phosphate structural is considered as the main reason for increasing Tg and (Hv) of the glasses. EDS as well as XRD analyzed spectra confirm that crystalline wollastonite of calcium inosilicate mineral (CaSiO3) phase is well formed. The wollastonite species is evidenced to contain small amounts of chromium and fluorine ions which are substituting for calcium cations. Wollastonite phases with Cr/Si=1 is the most dominant type. This ratio is a characteristic feature of crystalline CaSiO3 species. Small concentration from fluorine ions are involved in apatite phases. Presence of both crystalline apatite and wollastonite in the sample matrix promotes its biocompatibility, particularly orthopedic bioactivity. As a consequence, some of investigated glasses are recommended to be applicable in dental field of applications. This depends on its own crystallinity, hardness, its apatite and wollastonite concentration as biocompatible phases in the crystallized glass

Effects of Ca/P molar ratios on regulating biological functions of hybridized carbon nanofibers containing bioactive glass nanoparticles

Biological functions of hybridized carbon nanofibers (CNFs) depend closely on the incorporated bioactive components. For hybridized CNFs containing bioactive glass (BG) nanoparticles (CNF/BG), chemical compositions of BG nanoparticles might have decisive effects on their cell affinity and osteocompatibility. Herein, three hybridized CNF/BGs were produced by incorporating 68S-type BG nanoparticles with different Ca/P molar ratios (1.0, 1.67 or 2.5) into CNFs via a sol–gel/electrospinning and carbonization method. Structural evolution of these hybridized CNF/BGs was studied in relation to their Ca/P molar ratios. Crystalline wollastonite was found to be the dominant phase at a high feeding Ca/P molar ratio (i.e. 2.5), but weak crystallized hydroxyapatite was the main phase at the low feeding Ca/P molar ratio (i.e. 1.0). These findings were correlated to the biological functions of the resulted CNF/BG hybrids including apatite formation ability in simulated body fluid and osteoblast behaviors in in vitro culture. All the CNF/BG hybrids displayed a strong affinity for inducing apatite deposition, showing insignificant difference after the initial nucleation stage, while they behaved differently in promoting the proliferation and osteogenic differentiation of osteoblasts. The fastest proliferation rate and the highest expression of alkaline phosphatase activity was found on the CNF/BG (Ca/P = 1.0). The results suggested a feasible way to upregulate osteoblast behaviors is by changing the feeding Ca/P molar ratios in the preparation of CNF/BG hybrids for potential bone repairing applications.

Characterization of biomaterials commonly used in dentistry for bone augmentation by X-ray and electron techniques

Hydroxyapatite (HA), beta-tricalcium phosphate and bioactive glasses are commonly used as reabsorbable biomaterials, mainly in orthopaedics and dentistry. The performance of each material depends on many factors, in particular, on their chemical and phase composition, microstructure, granule size and pore volume. For this reason, it is important to have a full characterization that allows correlating these properties with the material biological behaviour. In this work, three commercial samples of materials currently used in dentistry as bone substitutes were characterized. Granules corresponding to bovine and synthetic HA and bioactive glass 45S5 type were studied by scanning electron microscopy, conventional and synchrotron radiation X-ray diffraction and X-ray fluorescence. The specific surface area was also obtained by the Brunauer, Emmett and Teller method. We observed that Ca/P molar ratios for both HAs are higher than the value corresponding to the stoichiometric HA. The coherent domain obtained for the bovine HA is larger along the c axis crystal direction, and it is around 15 times lower than the value corresponding to the synthetic HA. The specific surface area for the bovine HA is one of the highest values reported in literature. Low amounts of crystalline CaO were observed only for the synthetic HA sample. Crystalline combeite and wollastonite were detected for the bioactive glass sample and quantified by using rutile as internal standard. The relation between the physico-chemical characterization performed in this work and the potential biological response of the materials is discussed in terms of the information available in literature. Copyright © 2016 John Wiley & Sons, Ltd.

Formation, growth and transformation of leached layers during silicate minerals dissolution: The example of wollastonite

The wollastonite far from equilibrium dissolution kinetics and the formation and evolution of surface leached layers have been measured in mixed-flow reactors at 25°C, 0.9⩽pH⩽12 and reaction times to more than 3000h. Wollastonite dissolution rate decreases with increasing pH consistent withpH<4.8:r+,Ca,pH≤5(mol/cm2/s)=10-10.00aH+0.46andr+,Si,pH≤5(mol/cm2/s)=10-10.88aH+0.29pH≥4.8:r+,Ca-Si,pH≥5(mol/cm2/s)=10-11.41aH+0.18Dissolution stoichiometry, and the texture, structure and chemistry of wollastonite surfaces strongly depend on solution pH and duration of reaction. At 4.8⩽pH⩽12, after an initial period of non-stoichiometric dissolution, stoichiometric release of Ca and Si was observed. No significant change in the specific surface area of reacted powder was observed using BET and Small Angle X-ray Scattering (SAXS) measurements. In accord with these observations no chemical or structural changes were observed on the surfaces of reacted powders by X-ray Photoelectron Spectroscopy (XPS), Diffuse Reflectance Infrared Fourier-Transformed (DRIFT) Spectroscopy, SAXS or Transmission Electron Microscopy (TEM). In contrast, at pH<4, preferential calcium release to solution is observed, which produces a thick, highly porous Ca-depleted altered layer affected by an extensive crazing. Both silica and calcium releases decline with time but, whereas Ca release continuously decreases, Si release reaches steady-state after 1000h and continues for more than 2500h of reaction. After 3000h of leaching at pH 1.0–2.2, a completely Ca-free solid is produced.Acid leaching induces drastic molecular and structural rearrangements of wollastonite surfaces that progressively affect the entire grain. After 100h of reaction, most characteristic Si–O and Ca–O bands of crystalline wollastonite disappear and the DRIFT spectra of the solid strongly resembles that of amorphous silica. XPS analysis showed very strong decrease of the Ca/Si surface concentration ratio after 10–100h of reaction at pH 2 and the removal of almost all Ca from the surface after 120h. XPS also evidences a decrease of the O1s peak width reflecting the disappearance of non-bridging oxygens. Condensation reactions and reconstruction of the leached layer is further demonstrated by 29Si MAS NMR spectroscopy which shows, as dissolution proceeds, the progressive formation of less reactive Q3 and Q4 structural units at the expense of initial highly reactive Q2. As a result, wollastonite dissolution as a function of time can be correlated to the relative proportion of the different Qi units.These results demonstrate that the altered layers formed at wollastonite surfaces are initiated by an intensive exchange of protons for Ca2+ (DCa–H∼10−13cm2/s; Kex∼104.9) and that they may not attain a steady-state thickness. This intensive Ca-H exchange together with the abrupt change in dissolution stoichiometry at pH>4 and the stoichiometric dissolution of pseudo-wollastonite strongly suggest that wollastonite leached layers are not formed via stoichiometric dissolution followed by the rapid precipitation of amorphous silica. Such layers have the potential to influence the short and long term weathering rates of important silicates such as pyroxenoids, pyroxenes, hornblendes, plagioclases and natural glasses.

Calculation on the permittivity of the wollastonite ceramic matrix

Wollastonite ceramic matrix composites are multi-materials including the crystalline wollastonite and the residual glass phases. The relative permittivity (simplified as permittivity) of the crystalline wollastonite is used to evaluate the dielectric properties of the wollastonite ceramic matrix. Usually, the permittivity of the crystalline wollastonite is estimated to be 8.6, however, the residual glasses in wollastonite ceramic matrix are often unknown. In this study, the Clausius–Mosotti model is utilized to calculate the permittivity of the crystalline wollastonite from molecular polarizability. Molecular polarizabilities as the crystalline wollastonite polarizability are calculated by the ionic and oxide additivity rules. The permittivity of prepared glasses is used instead of that of the remaining glasses and estimated to 4.65. The composite permittivity of the wollastonite ceramic matrix is calculated by Lichnetecker logarithm rules. Compared with measurements, the calculated permittivity of wollastonite ceramic matrix corresponds well with measurements. The application of this simple calculation technique allows the assessment of the relative permittivity for ceramic matrix.

Microwave-assisted preparation of Ca 6Si 6O 17(OH) 2 and β-CaSiO 3 nanobelts

Xonotlite (Ca 6Si 6O 17(OH) 2) nanobelts were synthesized by a microwave-assisted hydrothermal method at 180 °C for 90 min independent of the feeding molar ratio of Ca(NO 3) 2·4H 2O to Na 2SiO 3·9H 2O in the range of 0.8–3.0. Crystalline wollastonite (β-CaSiO 3) nanobelts were obtained by microwave thermal transformation of Ca 6Si 6O 17(OH) 2 nanobelts at 800 °C for 2 h. Ca 6Si 6O 17(OH) 2 nanobelts were used as both the precursor and the template for the preparation of β-CaSiO 3 nanobelts. The morphology and size of Ca 6Si 6O 17(OH) 2 nanobelts could be well preserved during the microwave thermal transformation process. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED).

Thermal Properties and Microstructure of a Plasma Sprayed Wollastonite Coating

Wollastonite coatings were deposited using an atmospheric plasma spraying technique. The microstructure and phase compositions of the coating before and after heat treatment were investigated using scanning electron microscopy (SEM), x-ray diffraction (XRD), and differential thermal analysis (DTA) technologies, respectively. In addition, the coefficient of thermal expansion and thermal diffusivity of the coating were also investigated. Crystalline wollastonite, glassy phase, and tridymite (SiO2) were observed in the coating. Tridymite (SiO2) likely reacted with other composites such as CaO and glassy phase to form crystalline wollastonite when the coating was heated at about 882 °C. During the first thermal cycle, the coefficient of thermal expansion of the coating decreased dramatically between 700 and 850 °C and the thermal diffusivity of the coating was 2.7–3.1 × 10−3cm2/s between 20 and 1000 °C. During the second thermal cycle, the coefficient of thermal expansion of the coating increased slightly between room temperature and 1000 °C and the thermal diffusivity of the coating increased by about 20% compared with that of the first thermal cycle. The atmospheric plasma sprayed Wollastonite coating may be used as thermal barrier coating.

Characterization of plasma sprayed wollastonite powder and coatings

Spheroidized wollastonite powder was prepared by plasma spraying natural wollastonite TC powder into water. The natural and spheroidized wollastonite powders were deposited onto Ti–6Al–4V substrates using an atmospheric plasma spraying system. The phase composition and microstructure of the powders and coatings were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The spheroidized powder prepared by plasma spray presented a sphere-like morphology and was composed of crystalline wollastonite and a little glassy phase. The SEM view of the surface and the cross-section of the coatings revealed that the coating produced with the spheroidized wollastonite powder possesses a denser structure with fewer microcracks and pores than the coating generated from the natural powder. The tensile adhesion test (TAT) specified by ASTM C-633 was used to measure the tensile bonding strength of the coating. The results indicated that the coating produced with the spheroidized powder is superior to the coating prepared from the natural powder.

Phase compositions and microstructure of plasma sprayed wollastonite coating

The phase compositions and microstructure of wollastonite coatings deposited onto Ti–6Al–4V substrates by plasma spraying were studied using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The plasma sprayed wollastonite coating was not homogeneous and had a rough surface. Some pores and microcracks existed in the coatings. The primary crystalline phase in the coating was triclinic wollastonite. Some crystalline wollastonite grains had dislocation. The glassy phase was also discovered with some small size crystals in the coating. In addition, tridymite (SiO 2) and CaO were also found in the coating.

Crystallization Kinetics and Mechanism of Low‐Dielectric, Low‐Temperature, Cofirable CaO‐B2O3‐SiO2 Glass‐Ceramics

The crystallization kinetics and mechanism of low‐dielectric, low‐temperature, cofirable CaO‐B2O3‐SiO2 glass‐ceramics were investigated. Crystalline phases formed during firing included calcium silicates (CaSiO3, Ca3Si2O7, Ca2SiO4) and calcium borate (CaB2O4), with crystalline wollastonite (CaSiO3) the major phase. The crystallization kinetics of wollastonite followed an Avrami equation. The results of the present study showed an apparent activation energy of 200‐260 kJ/mol. Combined with the results of reduced growth rate (growth rate × viscosity) and thermal analysis, the rate‐controlling mechanism of crystallization appeared to be a two‐dimensional surface nucleation growth. As the amount of crystalline wollastonite increased, the dielectric constant decreased, but the thermal expansion coefficient remained relatively unchanged.