Sodium Silicate Precursor Research Articles

SYNTHESIS AND CHARACTERIZATION OF NANOSILICA (SiO2) VOLCANIC ROCK OF MOUNT BATUR IN BALI

This research was conducted to synthesize and characterize silica minerals (SiO2) from volcanic rocks in the active volcano in Bali, namely Mount Batur. The synthesis carried out on five different color variants of this rock sample is by the coprecipitation method which begins with the process of taking rock samples on Mount Batur, crushing the rock until it becomes powder with a size of 100 mesh, washing with distilled water and drying, immersing the rock powder in the solution. 2 M HCl for 12 hours, then the results of the soaking were reacted again with 7 M NaOH solution as a hydrolysis process to obtain pure SiO2 in the sample. In the form of sodium silicate precursor (Na2SiO3), the sample was titrated with a 2 M HCl solution to obtain silica gel which was then washed and dried until amorphous silica powder was produced. The results of the XRF analysis showed that the SiO2 mineral content in the sample after going through the synthesis process was 94.9% and the Si element was 89.9%. The XRD characterization results show that the phase formed from the sample has a quartz structure with the highest peak at an angle of 2θ = 23.07o, then decreases and levels out at an angle of 2θ = 32.94o which is characteristic of an amorphous structure and with a silica grain size of 8.47 nm – 8.65 nm.

Synthesis and characterization of zeolite Y from agricultural and municipal wastes: A waste management approach

Here in, we reported the utilization of guinea corn husk (an agricultural waste) and aluminium can (a municipal waste) for low-cost and sustainable means of zeolite Y preparation. Sodium silicate and sodium aluminate precursors were prepared from guinea corn husk and aluminium wastes respectively. The obtained solutions of the precursors were directly and hydrothermally converted to zeolite Y at 100 °C crystallization temperature for 24 h. The resulting zeolitic material was characterized by its properties. In comparison with collected standard data and commercially available zeolite Y, zeolite Y was successfully prepared from the waste resources. The result of X-ray Diffraction (XRD) indicated zeolite Y with good crystallinity, especially at the characteristic 2θ of 6.23°, 10.9° and 11.86°. The elemental compositions observed from Energy Dispersive X-ray (EDX) are in appropriate proportion and also confirmed the product. The Fourier Transform Infrared (FTIR) spectra showed the major characteristic absorption bands of zeolite in the mid-infrared region. It can be concluded that re-using agricultural and municipal wastes for the preparation of zeolite Y was achieved. This is a sustainable means of preparation of zeolite Y through a waste management approach for potential applications in adsorption, catalysis and ion exchange.

Development of a novel extrusion device to improve the printability of 3D printable geopolymer concrete

This study explores the printability of 3D geopolymer concrete using a novel extrusion device. Geopolymer, known for its eco-friendliness and rapid curing, offers an eco-friendly alternative to conventional cement in 3D printing. A novel extrusion device, integrating mixing and stirring functions, was developed to blend sodium silicate powder and precursor slurry effectively. Systematic experiments on mixing ratio, time, and speed revealed optimal conditions for geopolymer concrete printability. The precursor slurry remained pumpable for 90 min and displayed rapid reactivity in the new device. The extruded geopolymer concrete exhibited exceptional buildability, reaching a remarkable yield strength growth rate of 931.69 Pa/s. Actual printing tests resulted in a 154-layer hollow cylinder, 1840 mm tall, printed in just 26.87 min. Increasing mixing time enhanced compressive strength and reduced porosity, showcasing the potential of this set-on-demand approach and the novel extrusion device in 3D printable geopolymer concrete applications.

An efficient and template‐free synthesis of mesoporous silica from coal fly ash

AbstractIn the study, the desilication liquids and acid‐leached residues derived from the “alumina extraction process” of coal fly ash (CFA) were used as raw materials to prepare sodium silicate precursor. Then, the mesoporous silica with controllable pore structure properties was synthesized by an efficient, template‐free process from obtained sodium silicate. The effect of the sodium silicate properties and synthesis conditions on the pore structure properties of disordered mesoporous silica were investigated. The resulting material was characterized by N2 adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) and tested as an adsorbent for removal of lead ions (Pb2+). The results showed that the precursor with high modulus (3.0) and concentration (60 g·L−1) was beneficial for the synthesis of mesoporous silica with high specific surface area. The mesoporous silica with specific surface area of 690 m2·g−1 and pore volume of 1.28 cm3·g−1 was synthesized at mild aging temperature (40°C) and pH value of 8. Moreover, the materials possessed an adsorption capacity of 303 mg·g−1 for lead ions after amino modification. The adsorption efficiencies for lead ions were maintained at ~90% after five recovery cycles. Overall, the utilization efficiency of SiO2 in CFA reached up to 93%.

Characterization of new modified mesostructured silica nanocomposites fabricated for effective removal of aromatic acids

Santa Barbara Amorphous-15 (SBA-15) is a mesoporous molecular sieve with a large surface area and is extensively applied in purification, separation, and catalytic procedures. In this study, an SBA-15 was prepared from a sodium silicate precursor, and pentaethylene hexamine was anchored to its surface. A composite named N-SBA-15 was characterized using several experimental techniques. FTIR and XPS measurements confirmed that amino groups were conjugated on the surface of SBA-15. XRD and TEM confirmed that N-SBA-15 comprised highly ordered, hexagonal mesopore structures, which were not destroyed by the addition of amino groups. After functionalization, the surface area, pore volume, and pore size of the composite were 188 m2/g, 0.303 cm3/g, and 5.0 nm, respectively. N-SBA-15 was applied in the adsorption of aromatic acids, namely tannic acid (TA), acid red 1 (AR-1), and acid blue 40 (AB-40). The influence of various adsorption conditions such as dye concentration, adsorbent dosage, solution pH, and solution temperature was investigated. For AB-40 dye, the N-SBA-15 composite exhibited 40 times higher adsorption capacity than pure SBA-15. The highest adsorption capacities of N-SBA-15 for TA, AB-40, and AR-1 were 869, 818, and 308 mg/g, respectively. Thermodynamic studies were conducted to evaluate the exothermic property of the adsorption process and spontaneous behavior. The adsorptive data fitted well with pseudo-second-order and Langmuir isotherm models. Results confirmed that amino-modified SBA-15 material is a promising adsorbent for the elimination of aromatic acids form aqueous solution.

Size‐controlled synthesis of mesoporous silica nanoparticles using rice husk by microwave‐assisted sol–gel method

AbstractMesoporous silica nanoparticles with distinct characteristics like particle size, tunable pores, and high surface area have received much interest for environmental remediation, energy conversion, and biological applications. In this work, we synthesized spherical silica nanoparticles with tunable particle size and mesoporous properties using a low‐cost silica source (rice husk) and polyethylene glycol (PEG) via microwave‐assisted sol–gel synthesis. The formation of an amorphous silica structure was found using XRD and FTIR analysis. FESEM analysis showed that altering the PEG concentration from .01 to .005 M produced spherical silica nanoparticles with 100–500 nm in size. Nitrogen adsorption–desorption demonstrated that silica nanoparticles obtained with .005, .007, and .01 M of PEG had unique pore sizes and distributions, with specific surface areas of 51.475, 62.367, and 84.251 m2/g, respectively. These results might be due to PEG molecules’ capping effect, which acts as a soft template to regulate particle size, pore size, and dispersion by interacting with sodium silicate precursor. Hence, this approach can be a facile and cost‐effective method to prepare mesoporous silica nanoparticles with controllable nanoscale characteristics for suitable applications.

Systematic investigation on preparation and characterization of silica shell microencapsulated phase change materials based on sodium silicate precursor

A kind of paraffin@silica (Pn@SiO2) microencapsulated phase change materials (MEPCM) were prepared by sol-gel method using sodium silicate as silica precursor. The investigation of this synthesis technique demonstrates that pH value and core/shell ratio play key role in optimizing the morphology and microstructure of Pn@SiO2 microcapsules to achieve optimal thermal storage properties. Therefore, we systematically investigated the effects of pH value and core/shell ratio on the microstructure, crystallization behavior and phase transition properties of Pn@SiO2. It was determined that at pH 3 and Pn/SiO2 ratio of 5:1, the synthesized Pn@SiO2 exhibited well-defined core-shell structure and regularly spherical morphology. The encapsulation rate reached 74.14 % with latent heat of about 186.4 J/g due to the formation of perfect microstructure and morphology. In addition, Pn@SiO2 presents excellent heat storage capacity, high thermal stability and good shape stability, and shows reliable and durable phase-change performance. In summary, sodium silicate was used as the SiO2 precursor for the first synthesis of MEPCM with high encapsulation rate and regularly spherical morphology.

The effect of synthesis parameters on pore diameter of superhydrophobic silica aerogel prepared at ambient pressure

Silica aerogels were prepared by the sol-gel method and dried at ambient pressure with sodium silicate precursor. The prepared aerogel is superhydrophobic. The effect of various synthesis conditions on pore structure and diameter was investigated. The results of N2 adsorption-desorption isotherms, BET theory, BJH method, and field emission scanning electron microscopy images showed that by changing the surface modification method, the porosity of the samples changes. The order of increasing the average pore diameter for different protic solvents is isopropanol < methanol < ethanol. The specific surface area and total pore volume also increase with the increasing concentration of citric acid citric. The sample surface modified with HMDZ has smaller average pore diameters and total pore volume than the sample surface modified with TMCS. With increasing temperature, the average pore diameter and total pore volume increase, and the BET surface decreases.

In situ X-ray reflectivity and GISAXS study of mesoporous silica films grown from sodium silicate solution precursors

An environmentally friendly and inexpensive silica source, sodium silicate solution, was applied to synthesize a free-standing mesoporous silica film at the air/liquid interface, exploiting the co-assembly of cetyltrimethylammonium bromide and polyethylenimine. The effect of the composition of the solution used for the film formation on the mesostructure of the as-synthesized silica films, characterized by small angle X-ray scattering (SAXS), was investigated. The initial film formation time is estimated by the change in surface pressure with time. Additionally, a possible formation process of the mesostructured silica film is proposed using data from in situ grazing incidence small angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR) measurements. A free-standing film with a wormlike structure was formed at the interface and reorganized into a 2D hexagonal ordered structure while drying at room temperature, after removal from the air/solution interface. The ordered 2D hexagonal structure, however, could only be retained to some extent during calcination, in samples where nitrate ions are present in the film formation solution. • Free standing mesostructured silica films were prepared from alkaline solutions • Cheap, more environmentally friendly sodium silicate precursors were used • Polyelectrolyte-surfactant templates allow film growth under alkaline conditions • In situ study shows initial wormlike mesostructures become more ordered upon drying

Utilization of e-wastes as a sustainable silica source in synthesis of ordered mesostructured titania nanocomposites with high adsorption and photoactivity

The production of electronic waste (e-waste) is rapidly increasing globally. This waste is not effectively used at present. Moreover, few studies have investigated the synthesis of photocatalytic materials using materials recovered from e-waste. This paper reports the synthesis of a nanosized TiO2 catalyst supported on mesoporous Mobil Composition of Matter No. 41 (MCM-41). Sodium silicate precursor extracted from e-waste was used as a silicon source for the synthesis of an MCM-41 support. Transmission electron microscopy images revealed that TiO2 was successfully embedded in the pores of MCM-41. The particle size and crystalline structure of TiO2 was controlled by the mesostructured MCM-41 support. Nitrogen adsorption isotherms confirmed that TiO2/MCM-41 had uniform pore size (2.83 nm), a large pore volume (0.757 cm3/g), and high surface area (947 m2/g). The purity of TiO2/PRA-MCM-41 was as high as 99.90 wt%. The influences of TiO2 ratio, calcination temperature, and catalyst weight on the efficiency of methylene blue photodegradation were investigated. Different proportions of titanium species deposited on the MCM-41 surface resulted in the formation of differently sized TiO2 particles and strongly influenced the adsorption and photocatalytic activity. The TiO2/MCM-41 composite synthesized from e-waste had higher photocatalytic performance than TiO2/silica gel and pure TiO2. The composite catalyst had a combination of features that ensured high photocatalytic activity: small TiO2 particles, effective dispersion of TiO2 on the mesoporous silica, and high adsorptive efficiency. The proposed method, using an environmentally friendly approach, can reduce the accumulation of e-waste and produce highly valuable photocatalyst composites for environmental uses.

Spectral and structural investigation of silica aerogels properties synthesized through several techniques

The paper presents fairly coverage for the made-up and characteristics of most different forms of aerogels progressed from the original systems of silica-based. The aerogels structural and spectral properties can be tailored through synthesizing techniques providing the requirements of the desired application. present a comparative investigation of the spectral and structural properties for silica aerogels derived from different preparation techniques. Seven samples synthesized through the sol-gel polymerization of tetraethylorthosilicate, tetramethylorthosilicate, and sodium silicate precursor, were tested. Some of these samples were hydrophobized using trimethylchlorosilane. The precursors were adopted independently in the preparation process. Supercritical carbon dioxide, ambient pressure, and freeze-drying techniques had been followed separately as drying techniques. The silica aerogels physical properties are examined through Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption-desorption, and scanning electron microscope (SEM) tests. Identically, surface-functionalized silica aerogels were acquired from a variety of aerogels, consequently, comparing their chemical structures. The recorded FTIR spectra pointed out chemically analogous existence of silica networks with some differences, commonly, due to the additive incorporated and the synthesizing techniques. The results show that; pore-size, morphology, and the hydrophobic tendency could be controlled through the selection of the starting precursor, drying technique, and starting pH.

Synthesis of sodium silicate-based silica aerogels with graphene oxide by ambient pressure drying

Here we study how graphene oxide affects silica aerogels and their physical and mechanical properties by examining volume shrinkage, pore volume, surface area and compressive strength of these composite aerogels. Composite aerogels were made through adding different amount of graphene oxide (GO) to sodium silicate precursor by using ambient pressure drying method. Additionally, the chemical composition of the composite aerogels was determined using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. A rougher structure was observed when the GO loading increased and the characteristic peak of GO in XRD disappeared due to the random distribution of GO within the silica matrix. FTIR spectrum of composite aerogels shows that the relative intensity of silanol groups on the silica matrix have downward tendency with the addition of GO. The specific surface area had maxima with the addition of 0.01 wt% GO surface area to 578 m2 /g. The mechanical strength of aerogels was increased, with the loading of GO from 0.0 wt% to 0.2 wt%, and the compressive modulus increased from 0.02 MPa to 0.22 MPa.

Preparation and characterization of high efficiency microencapsulated phase change material based on paraffin wax core and SiO2 shell derived from sodium silicate precursor

Advanced thermal management system based on paraffin wax (PW) is an effective method to alleviate the increasing energy consumption. In this work, a new encapsulated phase change material (EPCM) was prepared by in-situ dehydration and condensation reaction, which consists of silica shell derived from sodium silicate and PW core. The chemical structure, crystal structure and microstructure of EPCMs were characterized by FT-IR, XRD, OM, TEM and SEM, which proved that the PW was successfully encapsulated by silica shell. In addition, the DSC, TGA, and leakage testing demonstrated that EPCMs possessed depressed supercooling, good thermal stability and leak-proof performance. When the mass ratio of PW/SiO 2 is 4:1, the encapsulation ratio and encapsulation efficiency can reach 74.51% and 75.58%, respectively, and the corresponding latent heat is 94.4 J/g (melting process) and −93.2 J/g (solidifying process). In addition, the heat storage/release rate, thermal regulation ability and thermal cycling ability indicated that the EPCM has good thermal management performance. Due to the low cost and availability of sodium silicate and PW, the encapsulation technology proposed in this work has great potential practical application feasibility in the field of thermal management, including packaging, clothing and architecture. • The encapsulated phase change material (EPCM) was successfully prepared with paraffin wax core and silica shell. • EPCM possesses high thermal conductivity, depressed supercooling, good thermal stability and leak-proof performance. • EPCM has high encapsulation efficiency (74.51%) and good latent heat (94.4 J/g). • EPCM has stronger capacity of heat storage, heat regulation and heat recycle.

Fabrication of hydrophilic and hydrophobic silica aerogel by drying‎ at ambient pressure and their structural properties

In this research, silica aerogel was made by sol-gel method with sodium silicate precursor ‎and drying at ambient temperature. The silica aerogel prepared by this method is ‎superhydrophobic. To make it hydrophilic, the sample was heated at 400 °C for 2 h. The ‎structure of the samples was studied using X-ray diffraction, scanning electron microscopy, ‎adsorption and desorption of nitrogen gas. To investigate the hydrophilicity and ‎hydrophobicity of the samples, the water droplet contact surface test was performed. The ‎chemical bonds of the prepared samples were studied using Fourier transform infrared ‎spectroscopy. The overall results showed that the size of the particles and the pores increase ‎and become smaller, respectively when the hydrophilicity of the silica aerogel sample ‎changes to the hydrophobic sample. The angle of contact of the water droplet with the ‎surface of the hydrophobic sample is 170°, while reaches to 51° for the hydrophilic sample‎.

PENGARUH WAKTU AGING TERHADAP SIFAT HIDROFOBISITAS SILIKA XEROGEL TERMOFIDIFIKASI TRIMETILKLOROSILAN (EFFECT OF AGING TIME ON THE HYDROPHOBICITY OF SYNTHESIZED TRIMETHYLCHLOROSILANE-MODIFIED SILICA XEROGE)

Silica xerogel is a multi-functional material that is useful in many industrial applications. In this research, we synthesized surface-modified silica xerogel and studied the effect of aging time, i.e., 0, 3, 6, 12, and 18 hours to the hydrophobicity of the synthesized material. The synthesis was conducted by the sol-gel method using sodium silicate precursors and a citric acid catalyst. Meanwhile, the surface modification was carried out through the silylation reaction using trimethylchlorosilane (TMCS) reagent. The resulting materials were characterized using infrared spectrophotometry (FTIR) and X-ray diffraction (XRD) methods. Hydrophobicity was measured by the contact angle formed by the water droplet with the xerogel surface and the spreading time of the droplet to be dispersed entirely on the surface. The silica xerogel produced at all aging time variations has an amorphous phase, characterized by 2θ = 22-26o of the XRD pattern. Si-CH3 and C-H vibrations at 848 cm-1 and 2962 cm-1 present in the FTIR spectrumconfirm the success of surface modification. The increasing aging time enhances the contact angle and spreading time of water droplets on xerogels, viz., 130o to 135o,and 3h 10min to 3h 28 min, respectively. Thus, the xerogels produced by this research are hydrophobic.

A comprehensive study on the gelation process of silica gels from sodium silicate

The sol-gel route via sodium silicate precursor is known as a practical synthesis method to prepare silica gels in a cost effective way. In the current research, rheological properties of the synthesized silica gels were investigated at different pH values. The gelation time (tgel) was determined from the rheological measurements at different frequencies of 0.1, 0.3 and 0.5 Hz. The results were analyzed using rheological equations of state and the concept of the gelation point was discussed. The results revealed that tgel increases by increasing the pH value. Moreover, it was proved that the fractal value (df) is dependent on the pH value. The relaxation exponent (Δ) value was measured as 0 < Δ < 1/2, which shows that the gel system follows the non-stoichiometrically balanced reactions. Finally, it was shown that the gelation process is divided into three stages, namely, induction, gelation and over curing. The results revealed that by increasing the pH value, stage I is extended while stage II is diminished.

Biosynthesis of silica nanoparticle using Saccharomyces cervisiae and its application on enhanced oil recovery

Using nanotechnology to increase the recovery of oil reservoirs can be a good way to meet energy demand, in order to increase oil production and reduce production costs. Biotechnology of nanoparticles using microorganisms as an environmentally friendly research field in nanotechnology around the world is a rapid development and is considered as a substitute for conventional and physical chemical methods. Optimizing processes can lead to morphology, control of the size and speed of nanoparticle synthesis reactions. Therefore, the purpose of this research is to build a reflection on the current status and future projects, and in particular the feasibility and limitations of the biotechnology approach proposed in the oil industry. In this research, Saccharomyces cervisiae yeast has been used for biochemical production of silica nanoparticles. This yeast is cultivated in its own culture medium. This yeast solution made after the addition of Sodium Silicate Precursor placed in the proper conditions of growth, i.e., temperature of 29 °C, away from the types of contamination and the passage of time, reducing the silica nanoparticles from the initial precursor. In this research, after performing the silica nanoparticle production processes, identification tests such as FTIR, XRD, SEM, DLS and TGA are performed. Then, in order to investigate the effect of this nanoparticle on the production efficiency of the oil, these nanoparticles were added to injectable solutions to an oil-wet micro-model with different concentrations of 250 ppm, 500 ppm and 1000 ppm. It was observed that the difference in the effect of nanoparticles produced by the biochemical method and commercial nanoparticles purchased in the injection process and on the measurement of the production efficiency of oil was that biosynthesized nanoparticles increased oil production efficiency by about 5–7 percent relative to commercial nanoparticles.

Action of silicic acid derived from sodium silicate precursor toward improving performances of porous gelatin membrane

ABSTRACTTo gain an insight into understanding how the silica network generated from hydrolysis and condensation of silicic acid, derived from sodium silicate, enhancing hydrothermal stability and mechanical properties of the leather, and particularly which active groups playing a main role for interaction of silica with collagen protein molecules, herein, effects of incorporated amino or carboxyl groups on the properties of silicic acid modified gelatin (GE) membrane were intensively studied. We found when lots of amino groups were introduced by adding a modified melamine, the thermal denaturation temperature, uniformity of pore diameter distribution and mechanical strength of GE membrane distinctly increased, while incorporating plenty of carboxyl groups by adding low polymerization degree acrylic acid polymer, no obvious change of performances of GE film was discovered. In addition, utilization of γ‐glycidoxypropyltrimethoxysilane had a positive effect on the porosity and flexibility of GE membrane. Importantly, our results indicated that hydrogen bonding probably played the most important role toward improving performances of porous GE film when treated with silicic acid. These findings are greatly beneficial for developing a chrome‐free tanning technology based on silicon containing materials, and are also suggestive for fabricating porous silica‐GE hybrid materials using sodium silicate as a precursor. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48912.

Sodium silicate based aerogel for absorbing oil from water: the impact of surface energy on the oil/water separation

Industrial organic pollutants and oily wastewater are becoming a serious worldwide problem that are threatening the environments. Silica aerogels with hydrophobicity and oleophilicity have a significant potential to develop their use as an oil absorption and can be used to absorb different oils emulsion. Herein, inspired by lotus leaves and gecko toes, we fabricate superhydrophobic and superoleophilic silica aerogel from inexpensive sodium silicate precursors by a facile sol-gel method followed by the low-cost ambient drying process. The microstructural properties of the silica aerogel are investigated by TEM and BET analysis. The resulted aerogels are ultra-lightweight (0.23 g cm−3) and highly porous (90%) with a pore distribution of 24 nm. Furthermore, oleophilic–hydrophobic characteristics of silica aerogel are investigated by the chemical structure and the surface energy of the silica aerogel using solid-state NMR, FTIR and also measuring the water/alcohol contact angle, sliding angle and oil spill absorption. Silica aerogel shows superior water repellency with the contact angle of 150°, super oleophilicity to different oils, outstanding absorption capacity for oils (up to 4 g of oil/g of aerogel), and eminent absorption recyclability (100%, even after 10 cycles). Due to its low density, lightweight, superhydrophobicity, low-cost materials, and considerable oil absorption properties, we expected that silica aerogel can be used for oil-spill cleanup. Besides, we establish the relationship between surface energy and water/oil contact angle to understand the mechanisms that occur during the oil/water separation process.

Characteristics of crystalline silica (SiO2) particles prepared by simple solution method using sodium silicate (Na2SiO3) precursor

The crystalline silica (SiO2) particle is successfully prepared using simple solution method from sodium silicate (Na2SiO3) precursor. The FTIR spectrum of the sample confirms the presence of SiO2. The X-ray diffraction (XRD) shows that the sample is cristobalite type of SiO2 which is comparable with ICSD ref. number of 01-076-0941. The crystallite size is about 28 nm as calculated by Scherrer method and the average particle diameter was about 697 nm as confirmed by Particle Size Analyzer (PSA) measurement. The Scanning Electron Microscope (SEM) image reveals that the sample reveal micro-flake with irregular rod-shaped morphology. The purity of sample is examined by X-ray Fluorescence (XRF) which shows about 93.1 mass % of pure SiO2 whereas, the purity of the raw precursor Na2SiO3 before synthesis is about 60.5 Mass %. The synthesized SiO2 particles can be used for several applications, where SiO2 is used in its crystalline phase.