How Do You Know if a Chemical Equation Is Precipitation

Atmospheric precipitation (Chemical)

Chemical precipitation is the process of conversion of a solution into solid by converting the substance into insoluble class or by making the solution a super saturated one.

From: Journal of Male monarch Saud University - Science , 2019

Nanopolymers*

Yaser Dahman , in Nanotechnology and Functional Materials for Engineers, 2017

6.3.2.ii.i Chemical precipitation

Chemical precipitation is the about mutual engineering used in removing dissolved (ionic) metals from solutions, such as procedure wastewaters containing toxic metals. The ionic metals are converted to an insoluble form (particle) by the chemic reaction between the soluble metallic compounds and the precipitating reagent. The particles formed past this reaction are removed from solution by settling and/or filtration. The unit operations typically required in this technology include neutralization, precipitation, coagulation/flocculation, solids/liquid separation, and dewatering.

The effectiveness of a chemical precipitation procedure is dependent on several factors, including the type and concentration of ionic metals nowadays in solution, the precipitant used, the reaction conditions (especially the pH of the solution), and the presence of other constituents that may inhibit the precipitation reaction.

The most widely used chemic precipitation process is hydroxide precipitation (also referred to equally precipitation by pH), in which metallic hydroxides are formed past using calcium hydroxide (lime) or sodium hydroxide (caustic) as the precipitant. Each dissolved metal has a distinct pH value at which the optimum hydroxide atmospheric precipitation occurs—from 7.v for chromium to xi.0 for cadmium. Metallic hydroxides are amphoteric, which means that they are increasingly soluble at both low and high pH values. Therefore, the optimum pH for atmospheric precipitation of ane metal may crusade another metal to solubilize or start to become dorsum into solution. Most process wastewaters contain mixed metals and so precipitating these different metals as hydroxides can be a tricky procedure (Lewinsky, 2007).

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/article/pii/B978032351256500006X

Ferrofluids: Introduction

R.E. Rosensweig , in Reference Module in Materials Science and Materials Engineering, 2016

2 Preparation

Chemic precipitation is the most oftentimes employed process although grinding is useful in some circumstances. Chemical decomposition and vapor-liquid reaction are used to produce certain specialized ferrofluids. In all cases, a repulsive layer is provided that envelopes each particle to forbid them sticking to each other.

The essential chemical reaction in the precipitation of ferrofluid particles is indicated past the reaction:

[ane] $2{\mathrm{Iron}}^{\mathrm{three}+}+{\mathrm{Atomic\; number\; 26}}^{\mathrm{ii}+}+\mathrm{viii}{\mathrm{OH}}^{-}=\mathrm{FeO}{\mathrm{.Fe}}_2{\mathrm{O}}_{\mathrm{iii}}+8{\mathrm{H}}_{\mathrm{ii}}\mathrm{O}$

where FeO.Fe₂O_three is magnetite written to emphasize the ratio of divalent to trivalent fe atoms in it, Fe^III/Atomic number 26^II=two. The iron salts used in the grooming may be any combination of soluble salts such as the chlorides or sulfates and the alkali can exist ammonium hydroxide, sodium hydroxide, or another base of operations. Post-obit atmospheric precipitation in the procedure of Khalafalla and Reimers (1974) the small-scale particles are extracted into a mixture of surfactant in an organic solvent. Massart (1996) discusses procedures for bonding species of small ions of a desired electrical sign to the surface of oxide particles. In this manner, ferrofluids tin can be conferred stability over ranges of pH values.

In the grinding procedure, magnetic powder, most commonly magnetite of several microns size, is mixed with 10–xx   vol.% of dispersing amanuensis based on solvent volume, and 0.ii   kg   l^-1 of magnetite may be used. The proportion of dispersant to solid corresponds closely to a monolayer coating on the particles in the product liquid. After a prolonged period of grinding in a ball mill (500–chiliad   h) near-quantitative conversion of the feed solids to colloidal particles of the club of 9–10   nm results. A representative limerick consists of magnetite particles, oleic acid dispersant, and an aliphatic hydrocarbon carrier such as hexadecane. Oversize fabric can exist removed by centrifuging or with magnets and the concentration of particles adjusted by the evaporation or addition of the carrier solvent.

The domain magnetization of elemental iron or cobalt exceeds that of magnetite at normal temperatures past iii to fourfold giving incentive to the preparation of more highly magnetizable ferrofluids containing these metals. A trouble that arises is the reactivity of the elemental particles with atmospheric oxygen. Nakatani et al. (1993) prepared dispersions of iron-nitride particles, for example, Fe_threeN, in oils. Gaseous ammonia is bubbled through a solution of liquid iron carbonyl, Fe(CO)_five, dissolved in kerosene containing a polyamine surfactant and produces a well dispersed colloid with particles of highly compatible size. The atomic number 26 nitrides possess a domain magnetization approaching that of iron and are resistant to oxidation. Ferrofluids having saturation magnetization up to µ₀ One thousand=0.233   T are reported.

A user-friendly synthesis technique for producing highly disperse monodispersions of 3–20   nm magnetic particles of limerick MO.Fe2O3 where M=Iron, Co, or Mn is reported by Sun et al. (2004). The particles are readily dispersed in polar and nonpolar carrier liquids.

Read full chapter

URL:

https://world wide web.sciencedirect.com/scientific discipline/commodity/pii/B9780128035818024772

Synthesis and Sintering of Calcium Hydroxyapatite for Biomedical Applications

Varun Saxena , Lalit M. Pandey , in Reference Module in Materials Scientific discipline and Materials Engineering science, 2021

Atmospheric precipitation and co-precipitation method

The chemical atmospheric precipitation method is one of the almost commonly used methods for synthesizing HAp materials. This is one of the simple most processes for the product of the HAp lattice. The major reaction mechanism lies in the insolubility of the HAp at elevated pH values, i.eastward., >ix. In brief, the reaction precursors are first prepared in the stoichiometric ratio of 1.67 and are then titrated to form the precipitates. The high pH values allow the HAp to gets precipitated and form the crystals (Saxena et al., 2019). The reaction temperature governs the nucleation process, followed by the change in the pH values. The major drawback of this chemical method remains the product of less crystalline HAp lattice; hence, after the precipitation is over, the prepared solution is stale and washed to reach a neutral pH. Sintering at elevated temperatures is required for obtaining the HAp phase (Saxena et al., 2018b). It has been noticed that the sintering temperature governs the formation of the phases by the calcium phosphate pulverization. Normally, in this process, along with HAp, β-TCP stage is also produced (Tourbin et al., 2020) every bit an impurity, which adversely affects the biological responses and the bioactivity of the equally-prepared powders. Hence, producing the pure HAp phase through the atmospheric precipitation method is still a challenge for biomaterial researchers (Gomes et al., 2020).

Read full chapter

URL:

https://world wide web.sciencedirect.com/scientific discipline/article/pii/B978012820352100136X

Avant-garde Ceramic Materials

J.-Thousand. Guo , ... H.-Grand. Kou , in Mod Inorganic Synthetic Chemistry (Second Edition), 2017

17.1.1.2 Chemical Precipitation

The nanosized ceramic powders are routinely synthesized by chemical atmospheric precipitation and reaction routes. In such process, a solution containing a precipitating amanuensis, commonly hydroxide, ammonium acid carbonate, or oxalic acid, is added to the solution containing the cation of the desired oxide. This is followed by firing of the precipitates (hydroxides, carbonates, or oxalates). Chemical precipitation routes include straight atmospheric precipitation, co-precipitation, and homogeneous precipitation. In the direct precipitation process, but ane cation is contained in the solution. For example, well-dispersed yttria nanopowders were synthesized by a precipitation method from yttrium nitrate solution using ammonia water [7,8] and ammonium hydrogen carbonate as precipitants. For some other case, alumina precursor NH₄Al(OH)₂CO₃ has been produced by direct precipitation using NH₄Al(SO_four)₂·12H_iiO as a starting cloth, NH_ivHCO₃ as precipitating agent, and nanosized α-Al₂O_three equally seed [9]. α-Al₂O_three powders with average particle size of 150   nm tin can be obtained past washing, drying, and firing the precursor. It is establish that the temperature of nucleation can be reduced and the transformation rate can exist increased finer by calculation a minor quantity of α-Al₂O₃ seeds [ten].

In addition, the effects of fluoride additions on the stage transition of α-Al_twoO₃ germination take likewise been investigated. The improver of ii% LiF and AlF₃ decreases the transformation temperature by 300°C, and well-dispersed α-Al₂O₃ powders with average particle size of ∼2   μm were obtained [11]. The LiF and AlF_three additives prove to be effective in enhancing the phase formation of α-Al_twoO₃ because an intermediate compound, AlOF, can exist formed in the example of the phase transformation, and AlOF can accelerate the mass transportation from transient phase to stable α-Al_twoO_iii phase [12].

For the co-precipitation method, multi-cations are present in the mixed solution. Ultrafine, well-dispersed Yb:(Lu _x Sc_{1   − ten} )_twoO₃ nanopowders were synthesized by a carbonate co-precipitation method, in which ammonium hydrogen carbonate (NH₄HCO₃) and ammonium hydroxide (NH₄OH) were mixed at the molar ratio of iii:1 as the precipitant and ammonia sulfate ((NH₄)_twoSO₄) as dispersing amanuensis [13]. Nanosized yttrium aluminum garnet (YAG) powders with average particle size of lx   nm have been synthesized by a co-precipitation method from a mixed solution of NH_ivAl(SO_iv)₂ and Y(NO₃)_iii, with NH₄HCO₃ as the precipitant [fourteen–16]. Composition of this precursor volition be the effect of competition betwixt OH⁻ and the carbonate species generated by the following chemical reactions during combination with metal cations:

(17.ane) ${\text{NH}}_4{\text{HCO}}_3+{\text{H}}_{\mathrm{ii}}\text{O}\iff {\text{NH}}_{\mathrm{four}}\text{OH}+{\text{H}}_2{\text{CO}}_{\mathrm{three}}$

(17.ii) ${\text{NH}}_4\text{OH}\iff {{\text{NH}}_4}^{+}+{\text{OH}}^{-}$

(17.3) ${\text{H}}_2{\text{CO}}_3\iff {\text{H}}^{+}+{{\text{HCO}}_3}^{-}$

(17.4) ${\text{HCO}}_3^{-}\iff {\text{H}}^{+}+{{\text{CO}}_3}^{\mathrm{two}-}$

As mentioned earlier, Alⁱⁱⁱ⁺ may precipitate as AlOOH or NH_fourAl(OH)₂CO₃. On the other hand, Y³⁺ may most likely precipitate equally a normal carbonate of [Y₂(CO_three)₃·northH_twoO (northward  =   ii   ±   3)] [17] or basic carbonate of [Y(OH)CO₃] [18] from the carbonate anions containing NH_fourHCO_iii solution. Likewise, homogeneous distribution nano-mullite powders (∼100   nm) have been prepared past hydrolysis and co-precipitation method using TEOS and AlCl₃·6H₂O every bit starting materials [19].

Compared to direct precipitation and co-precipitation methods, homogeneous precipitation has the advantage of fantabulous homogeneity of nucleation and atmospheric precipitation. In the homogeneous precipitation process, urea is usually used as the precipitant. For example, European union, Li co-doped ZnO:(Eu, Li) nanopowders have been synthesized past the homogeneous co-precipitation method using Zn(NO_three)_two·2H_iiO, CO(NH_ii)_ii, Eu(NO₃)_iii·6H₂O, and LiNO₃·2H₂O as raw materials. The ZnO:(Eu,Li) nanopowder calcined at 700°C for 2   h is a pure hexagonal wurtzite structure, and the particle size distribution is uniform in the range of 20–twoscore   nm [20]. Using the same urea homogeneous precipitation method, mono-phase YAG (Yb_threeAl₅O₁₂) powders with the particle size of 20–xxx   nm have also been obtained at the low calcination temperature of 900°C [21].

Spherical anatase microparticles (15–40   nm) with good crystallinity have been synthesized by homogeneous atmospheric precipitation under mild conditions (83–100°C), employing ammonium fluorotitanate equally the titanium source and urea as the precipitant [22]. Urea decomposes at a temperature higher than 80°C during the urea precipitation process, as shown in Eq. (17.5).

(17.five) $\mathrm{two}{\left({\text{NH}}_2\right)}_{\mathrm{ii}}\text{CO}+5{\text{H}}_2\text{O}\to 4{{\text{NH}}_4}^{+}+{\text{OH}}^{-}+{{\text{HCO}}_3}^{-}+{{\text{CO}}_3}^{2-}$

The NH₄ ⁺ and OH⁻ ions generated so react readily with ammonium fluorotitanate to yield TiO₂ according to Eq. (17.half dozen).

(17.vi) ${\left({\text{NH}}_4\right)}_2{\text{TiF}}_{\mathrm{vi}}+4{{\text{NH}}_4}^{+}+4{\text{OH}}^{-}\to {\text{TiO}}_2+6{\text{NH}}_{\mathrm{four}}\text{F}+2{\text{H}}_2\text{O}$

Fig. 17.1 shows the particle morphologies of the powders obtained after thirty   min at three typical temperatures of 83°C, ninety°C, and 100°C. The resultant particles are microspheres in each example, irrespective of the reaction temperature. Furthermore, these microparticles testify good dispersion, and no apparent aggregation is observed.

Figure 17.1. The particle morphologies of the anatase powders obtained later thirty   min at unlike temperatures (A) lxxx°C, (B–C) xc°C, (D) 100°C.

Reproduced with permission from Due south.H. Liu, X.D. Sunday, J.Yard. Li, et al., Eur. J. Inorg. Chem. 9 (2009) 1214–1218. Copyright 2009 of Wiley.

Read full chapter

URL:

https://www.sciencedirect.com/scientific discipline/article/pii/B9780444635914000173

Hydroxyapatite composites for dentistry

Sarmistha Mazumder , ... Thou. Saquib Hasnain , in Applications of Nanocomposite Materials in Dentistry, 2019

seven.3.i Precipitation technique

The precipitation technique, also known equally "wet precipitation," "chemical precipitation" or "aqueous precipitation" is the well-nigh common technique for training of hydroxyapatite. The precipitation technique is of utmost importance in terms of utility every bit compared with the other methods of grooming, as with the help of this technique a relatively large amount of hydroxyapatite can be yielded in the absenteeism of organic solvents at a reasonable cost [19]. Initiating with reagents calcium hydroxide [Ca(OH)₂] and orthophosphoric acid [H_threePO_iv], the process was carried out, generating the desired production hydroxyapatite and the only byproduct of this reaction was water with the reaction involving no foreign elements [27].

$\mathrm{x}\text{Ca}{\left(\text{OH}\right)}_{\mathrm{two}}+\mathrm{half\; dozen}{\text{H}}_3{\text{PO}}_4={\text{Ca}}_{10}{\left({\text{PO}}_{\mathrm{four}}\right)}_{\mathrm{six}}{\left(\text{OH}\right)}_2+18{\text{H}}_2\text{O}$

The orthophosphoric acrid addition rate and the reaction temperature are critical factors attributing to the size, shape, and surface area of the hydroxyapatite particles yielded during the reaction. The pH at the end of the synthesis reaction was found to be associated with the orthophosphoric acrid addition rate, and likewise to the stabilization of the intermission. The crystalline characteristics of the constructed hydroxyapatite crystals were dependent upon the reaction temperature. Hydroxyapatite particles synthesized at low temperature (<   sixty°C) were documented to exist monocrystalline [28].

2 other techniques were described by Santos et al., regarding the atmospheric precipitation reaction for the synthesis of hydroxyapatite [19]. One reaction used ammonium phosphate [(NH_iv)_two·HPO₄] and Ca(OH)₂ as starting reagents.

$10\text{Ca}{\left(\text{OH}\right)}_2+\mathrm{vi}{\left({\text{NH}}_4\right)}_{\mathrm{ii}}·{\text{HPO}}_4={\text{Ca}}_{10}{\left({\text{PO}}_4\right)}_{\mathrm{vi}}{\left(\text{OH}\right)}_2+\mathrm{half\; dozen}{\text{H}}_2\text{O}+12{\text{NH}}_{\mathrm{four}}\text{OH}$

The second reaction utilized calcium hydrogen phosphate [Ca(H_iiPO₄)_ii·H₂O] and Ca(OH)₂ as initial reagents.

$\text{Ca}{\left(\text{OH}\right)}_{\mathrm{two}}+\mathrm{iii}\text{Ca}{\left({\text{H}}_2{\text{PO}}_{\mathrm{four}}\right)}_{\mathrm{ii}}·{\text{H}}_2\text{O}={\text{Ca}}_{10}{\left({\text{PO}}_4\right)}_{\mathrm{half\; dozen}}{\left(\text{OH}\right)}_{\mathrm{two}}+\mathrm{fifteen}{\text{H}}_2\text{O}$

Monitoring of the pH was carried out, and temperatures of hydroxyapatite synthesis in the two reactions were 40°C, and room temperature, respectively. A college temperature was used to promote the kinetics of the reaction, leading to hydroxyapatite synthesis and also to upgrade dissolution of Ca(OH)_two. But, hydroxyapatite precipitation was also noted to occur at room temperature. Stirring at room temperature and pH   ten, equally stated past Manuel et al., may likewise lead to the synthesis of hydroxyapatite nanoparticles by the precipitation technique [18].

The improver of H₃PO_iv to Ca(OH)₂ until Ca: P  =   1.67 is maintained. Crystallization is noted after NH₄OH addition. Later on 24   h invested for crystal growth, sinteration is carried out at chiliad°C for 1   h. This precipitation method may also be initiated as a wet chemical reaction of calcium nitrate [Ca(NO₃)₂·4H_twoO], with (NH_iv)_ii·HPO₄.

Reaction fourth dimension and temperature regulation may successfully alter the grain size of the hydroxyapatite crystals synthesized [29]. A continuous stirring of the solution at room temperature for 24   h is essential to obtain hydroxyapatite with grain sizes <   100   nm [28]. Janackovic et al., also advocated another technique for precipitation reaction [30].

$\begin{array}{l}\text{Ca}{\left(\text{EDTA}\right)}^{2-}+3/\mathrm{five}{\text{HPO}}_4{}^{2-}+\mathrm{ii}/5{\text{H}}_2\text{O}=\\ \mathrm{i}/10{\text{Ca}}_{10}{\left({\text{PO}}_4\right)}_{\mathrm{six}}{\left(\text{OH}\right)}_2+{\text{HEDTA}}^{3-}+\mathrm{i}/\mathrm{five}\text{OH}\end{array}$

Reaction temperature varying between 125 and 160°C, and the improver of urea for precipitation instead of NaOH was the significant modification, which acquired much more uniformity, and hence homogenous atmospheric precipitation and likewise led to subsequent transformation to hydroxyapatite due to pH alterations for urea hydrolysis.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128137420000079

Germination of biomimetic hydroxyapatite coatings on the surface of titanium and Ti-containing alloys

Ievgen Volodymyrovych Pylypchuk , ... Orest Mykhaylovych Ivasyshyn , in Surface Chemistry of Nanobiomaterials, 2016

7.1.i Methods for HA Deposition in Metal Surfaces

Various methods have been reported to produce nanosized apatite crystals, including chemical precipitation (Nejati et al., 2009), solid-state reaction (Karlinsey and Mackey, 2008), hydrothermal synthesis (Sujaridworakun et al., 2005), sol–gel synthesis (Liu et al., 2001), emulsion technique (Li et al., 2008), and the laser sintering approach (Li et al., 2008), whereas, virtually routine approaches cannot control the crystal morphology and size precisely. Unfortunately, subsequent rut handling at high temperature results in cracking and poor bail strength between the HA coating and the metallic substrate.

Depending on the solution pH, various calcium phosphates might exist precipitated and, therefore, deposited. In general, the deposition process is usually based on the heterogeneous nucleation phenomenon, the kinetics of which depends on many parameters such every bit the solution supersaturation, concentration of the reagents, temperature, hydrodynamics, presence or absence of admixtures, nucleators, inhibitors, etc. As to the precipitation mechanisms of CaPO₄ from aqueous solutions, this process appears to be rather complicated and for the biologically relevant calcium phosphates (octacalcium phosphate, calcium-deficient HA, and HA) it occurs via formation of one or several intermediate and/or precursor phases, such equally amorphous calcium phosphate, dicalcium phosphate dehydrate, and/or octacalcium phosphate.

For some types of wet techniques, specific surface training appears to be necessary. For example, if calcium phosphate needs to be biomimetically deposited on titanium or its alloys, a surface layer of titanium oxides, hydroxides, and/or titanates should be created prior to deposition. This can be washed by various oxidation techniques, such as oestrus or brine treatments, oxidation in H₂O₂, micro-arc oxidation (MAO), pre-calcification in humid Ca(OH)₂ solution, or under hydrothermal weather, besides as past water vapor treatment. Similar is valid for other chemically inert metals: prior biomimetic degradation of calcium phosphate, a surface layer of hydrated zirconium hydroxides, niobium hydroxides, tantalum hydroxides, or their Na- or Thou-containing salts should be created on the surface of Zr, Nb, and Ta, respectively. The detailed data on the surface grooming of Mg and its biodegradable alloys is available elsewhere. In addition, a positive influence of the presence of hydrated silica, sodium, or both (i.eastward., sodium silicates) on calcium phosphate precipitation onto substrates is known also (Dorozhkin, 2014).

Sol–gel deposition. To prepare sols, usually, inorganic salts and/or organoelement compounds, such as alkoxides, are used equally precursors. For example, to synthesize HA, the orthophosphate precursors comprise P_iiO₅, P(OC₂H_five)_three,H₃PO_iv, and (NH₄)_threePO₄ dissolved in ethanol, while the calcium precursors are Ca(NO₃)₂•4H₂O and Ca(CH_threeCOO)₂•H₂O dissolved in either ethanol or water. In addition, Ca(OC₂H_five)₂ precursor might exist used besides but information technology must exist dissolved in a not-aqueous solvent. After mixing of the Ca- and P-containing precursors, sols are formed due to hydrolysis and condensation reactions.

Every bit formed, sol–gel calcium phosphate deposits are porous, less dumbo and have poor adhesion to the substrate. To improve their properties, the coated substrates are annealed at temperatures of 400–thou   °C. Depending upon both the Ca/P ratio and the calcining temperature, different calcium phosphate compounds are obtained. The resulting deposits can be extremely dumbo and attach strongly to the underlying substrate. Biphasic deposits, in which particles of 1 blazon of calcium phosphate were embedded into a continuous coating of another type of calcium phosphate, could be prepared likewise. In social club to better the bond forcefulness between the deposits and substrates, an intervening layer of another compound might be applied prior to sol–gel deposition of calcium phosphate.

Hydrothermal deposition is a simple process and one of the almost price-effective techniques. It is rather similar to the same biomimetic degradation and wet-chemical precipitation; even so, since the hydrothermal handling is performed at elevated (80   °C) temperatures during a relatively prolonged flow of fourth dimension (1.5   h), the calcium phosphate deposits are ordinarily crystalline. A hydrothermal procedure was used to eolith calcium phosphates on both metal and polymeric substrates. This technique was originally called the "a chemic bathroom method." The process is based on the formation of EDTA–Ca²⁺ chelate compounds due to cooperative dissolution of a Ca-containing salt and EDTA at ambient conditions. As the temperature increases, thermal dissociation of the EDTA–Caⁱⁱ⁺ chelate compounds occurs, which supplies sufficiently high concentration of Ca²⁺ ions to perform atmospheric precipitation in the presence of PO₄ ³⁻ ions. Namely, by hydrothermal handling for 2   h at 90   °C, the researchers succeeded in forming well crystallized HA and octacalcium phosphate deposits on both pure Mg and Mg–Al–Zn alloys from a 0.25   K EDTA–Caⁱⁱ⁺ and KH₂PO₄ treatment solution in a pH range from five.9 to 11.9. Both HA and octacalcium phosphate deposits were institute to consist of an outer porous layer and an inner continuous layer, while both the crystal phases and the microstructures of the deposits were found to vary with the pH of the treatment solutions.

An alternate soaking deposition was adult in 1998. The process consisted of several successively performed deposition cycles. In 1 cycle, a substrate is soaked in a Ca-containing solution, rinsed with h2o, afterwards soaked in a PO₄-containing solution and then rinsed again. When repeatedly applied, calcium phosphates are deposited. Simple inorganic salts, such every bit calcium chloride or nitrate, are used equally the Ca source and sodium or ammonium hydro-orthophosphate are used equally the PO_iv source. The duration of each soaking stage tin can vary from 1   min to 2   h depending on the substrate. At even shorter soaking times (ane   min), the deposition technique is called "alternating dipping." The pretreated substrates were later soaked in 0.5   Thou CaCl₂ and later washing with distilled h2o soaked in 0.1   M Na_twoHPO_four solution (Figure 7.21). The deposited amount of calcium phosphates increased with the number of reaction cycles, but it was independent of both the solution temperature and soaking time, indicating that the degradation process depended on ion exchange and adsorption on the pretreated surface. Like findings were obtained in other studies. In 2011, the process was automated allowing deposition of substantial quantities of calcium phosphates with a minimum of labor and free energy.

MAO (synonyms: plasma electrolytic oxidation, anodic spark degradation, anodic plasma-chemical handling, micro-arc belch oxidation, spark anodizing) is a combination of plasma-chemical and electrochemical processes that appeared to be applicable to deposit ceramic coatings on diverse metals and alloys. The MAO process combines an electrochemical oxidation of the metallic surface past a high-voltage (upwards to 500   V, oft, of an alternating electric current) spark treatment performed in aqueous electrolytic baths. During the procedure, sparks appear and move rapidly across the treated surface, while temperature and force per unit area inside a discharge channel tin attain ~104   K and ~103   MPa, respectively, which are sufficiently high for inducing thermochemical interactions betwixt the substrate and electrolyte.

By thermal substrate degradation calcium phosphates were put down on various substrates. For example, in the instance of Ti, an alternating electric current was passed through the substrates immersed in aqueous solutions containing calcium and orthophosphate ions. The degradation was performed for ten–30   min at solution pH 4–viii and temperatures upwardly to 160   °C. The type of precipitates was varied depending on the solution pH, temperature, and ion concentrations. Namely, high-quality deposits, whose predominant component was calcium-deficient HA (at pH=vi) or DCPA (at pH=4), were obtained on Ti. Similarly, DCPA was deposited on carbon at solution pH ~four.five, followed by hydrothermal handling in alkaline solutions to convert DCPA to HA. In all studies, the content of apatites in the deposits was found to increase with increasing temperature and heating time.

The mechanism of os-similar apatite formation on an oxidized surface of titanium was investigated in detail. Briefly, it looks as follows. First, a layer of amorphous sodium titanate is formed on the Ti surface later alkali pretreatment. So, immediately after immersion into SBF, the sodium titanate exchanged Na⁺ ions for H_threeO⁺ ions in the fluid to form Ti OH groups on its surface. Later, the Ti OH groups incorporated calcium ions from the SBF to course a layer of amorphous calcium titanates. Afterwards longer soaking times, the amorphous calcium titanates incorporated orthophosphate ions from the SBF to grade amorphous calcium phosphate coatings with a Ca/P diminutive ratio of ~ane.4. Thereafter amorphous calcium phosphate converted into bone-like ion-substituted calcium-deficient HA with a Ca/P ratio of ~one.65. In the next study, the authors specified that after exchanging Na⁺ ions for H₃O⁺ ions diverse types of titania gels might be formed just only those with the anatase or rutile construction induced apatite germination. Interestingly although Ti and Zr belong to the same group of the Periodic Table of Elements, the surface reactions of biomimetic degradation of calcium phosphate were found to be dissimilar for the Ti and Zr substrates. Farther specific details on this topic are available in the literature (Dorozhkin, 2015).

Biomaterials for hard tissue repair demand to exist biocompatible, osteoconductive, and to have mechanical characteristics shut or similar to those of bone or teeth. The chemic direction of biomimetics, also called "biomimetic chemistry," is based on the principles used by nature. That means utilize the biosynthetic routes for obtaining the materials that simulate specific properties of natural biomineral structures such equally morphology, mechanical force, etc. The basic principles for structure of biomineral structures are hierarchy, self-healing capability, structural system, multifunctionality, self-organization, and self-assembly—essential backdrop by which the structures are assembled from the molecular level. A promising direction of biomimetic modeling is the employ of self-organization and cocky-assembly—the basic principles of living systems (Hirata et al., 2010). Currently, a elementary and potentially effective method for biomimetic synthesis of nanostructured materials by self-arrangement of polymers and/or inorganic nano-sized particles on the surface of the substrate has been developed (Schönhoff, 2003; Tretyakov et al., 1995; Karlov and Shakhov, 2001).

Read full chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780323428613000078

Biomimetic materials in regenerative medicine

South. Sprio , ... A. Tampieri , in Biomimetic Biomaterials, 2013

Synthesis

Several methods have been successfully employed in the synthesis of nanocrystalline apatites, including moisture chemical precipitation (Wang and Shaw, 2007), sol-gel synthesis (Ben-Nissan and Choi, 2006), co-atmospheric precipitation (Lopez-Macipe et al., 1998), electro-deposition (Manara et al., 2008), vapour diffusion (Iafisco et al., 2010) and a number of others (Ye et al., 2008). The physico-chemical characterizations carried out on several synthesized apatites at low temperatures have shown that they have the typical features of biological apatite, such as the size domain, the low degree of crystallinity and the existence of surface ionic disorder and surface compositions different from the bulk (Fig. one.1) (Bertinetti et al., 2009, Bertinetti et al., 2007). Amongst the peculiarities of these compounds, i characteristic that clearly distinguishes them from regular HA is their plate-similar morphology (elongated towards the c-axis). Other of import properties are the mean crystallite nanosize, often in the order of 15–30   nm in length and c. six–9   nm in width, their large surface to volume ratio and the being of a surface hydrated layer, non-apatitic in nature, which is essentially related to the formation process in solution (Sakhno et al., 2010). In fact, the surface hydrated layer progressively disappears as the stable apatite domain (the core of the crystals) develops over time (i.due east. during the maturation procedure).

ane.ane. (a) High-resolution manual electron microscopy (TEM) epitome of a portion of apatite synthesized at twoscore   °C (a1); right panels show related Fourier Transform (FT) of (a1) and zoomed view of ii border regions ((a2) and (a3)); original magnification: x800k. (b) Loftier-resolution TEM epitome of a portion of apatite synthesized at 95   °C ((b1) and (b4)), related FT (bottom right). (b2) and (b3) Zoomed view of two enframed edge regions in panel (b1); original magnification: x800k.

(Reprinted with permission from Sakhno et al., 2010. Copyright (2010) American Chemical Society.)

Read full affiliate

URL:

https://www.sciencedirect.com/science/article/pii/B978085709416250001X

Effluent treatment in denim and jeans manufacture

N. Uzal , in Denim, 2015

19.three.1 Chemical precipitation

Material wastewater containing a huge corporeality of dyestuff together with pregnant amounts of SS, salts and trace metals can be treated by chemic precipitation (coagulation/flocculation), and certain removal efficiencies can be achieved. Studies of chemical coagulation/flocculation have shown that they are some of the most widely used technologies in textile wastewater treatment. Regardless of the considerable volume of sludge generation, these technologies are yet used in developed and in developing countries. Colour removal by coagulation is very constructive in some cases, whereas it has failed completely in others.

Using a coagulation process, destabilisation of colloidal or suspended particles is usually brought about by adjusting the solution pH to attain sure levels of color and COD removal (Gao et al., 2007; Kim et al., 2004). Water insoluble vat dyes used in denim production are removed by a pretreatment footstep using coagulants/flocculants like lime, alum, ferrous sulphate and polyelectrolyte, and in the activated sludge process that follows, other contaminants are eliminated. However, the basic disadvantage of physicochemical methods is the production of a large corporeality of sludge that poses handling and disposal bug (Shaw et al., 2002).

In an interesting study, saline manufacture wastewater was used as a coagulant source for treating indigo dyeing process effluent. MgCl₂ has been reported every bit an advantageous coagulant for treating textile wastewater, and in this report wastewater was used as a coagulant source. The coagulation process was based on the apply of Mg²⁺ in saline wastewater for charge neutralisation. The colour removal functioning of saline wastewater was compared with a known coagulant Al₂(SO_four)₃. Higher colour removal efficiencies were obtained with saline wastewater. For a 100   mg/L cation dosage, 80% or higher colour removal efficiencies were achieved with saline wastewater (Albuquerque et al., 2013).

In order to overcome some disadvantages of chemical precipitation and to increase the efficiency of the coagulation/flocculation procedure, a new polymer was synthesised for the treatment of high concentration existent reactive dyeing wastewater. In this study, a new polymer flocculant was synthesised using cyanoguanidine and formaldehyde, and applied with alum or ferric salts equally inorganic coagulants for the treatment of dyeing wastewater. The applicability of this organic/inorganic flocculant was tested for both synthetic wastewater containing iv model reactive dyes (Black 5, Blue 2, Red 2 and Yellow 2) and for the real wastewater containing reactive dyes from the dyeing industry. The results of the report showed that alum/polymer combination improved colour removal upwards to a sixty% efficiency level (Joo et al., 2007).

Read full affiliate

URL:

https://www.sciencedirect.com/science/article/pii/B9780857098436000196

Ceramic biomaterials for tissue engineering

J. Huang , S. Best , in Tissue Technology Using Ceramics and Polymers (Second Edition), 2014

1.5.1 Preparation of HA ceramics

There are numerous methods for the preparation of synthetic apatites, which can be grouped every bit aqueous reactions, solid-state reactions and hydrothermal reactions. The aqueous reactions may exist divided into chemical precipitation and hydrolysis methods. Chemical precipitation is the nigh commonly used method, considering of its simplicity and power to produce a wide variety of particle sizes and morphologies.

Methods based on those described by Akao et al. (1981) (equation 1.1) and Hayek and Newesely (1963) (equation 1.2) are the about oft used. They consist of the dropwise improver of phosphate solution into a stirred solution of calcium solution. The improver of ammonium hydroxide is needed to keep the pH of the reaction alkali metal to ensure the formation of HA after sintering the precipitate.

[1.1] $10\mathrm{Ca}{\left(\mathrm{OH}\right)}_2+6{\mathrm{H}}_3\left({\mathrm{PO}}_4\right)\to {\mathrm{Ca}}_{10}{\left({\mathrm{PO}}_4\right)}_{\mathrm{six}}{\left(\mathrm{OH}\right)}_{\mathrm{ii}}+18{\mathrm{H}}_2\mathrm{O}$

[1.2] $\begin{array}{l}\mathrm{x}\mathrm{Ca}{\left({\mathrm{NO}}_3\right)}_2+\mathrm{half-dozen}\left({\mathrm{NH}}_4\right){}_2\mathrm{H}\left({\mathrm{PO}}_{\mathrm{four}}\right)+2{\mathrm{H}}_{\mathrm{ii}}\mathrm{O}\to {\mathrm{Ca}}_{\mathrm{x}}\left({\mathrm{PO}}_4\right){}_6\left(\mathrm{OH}\right){}_2\hfill \\ +12{\mathrm{NH}}_{\mathrm{iv}}{\mathrm{NO}}_3+8{\mathrm{HNO}}_3\hfill \end{array}$

The concentrations of reagents must be such that the Ca/P tooth ratio is maintained at one.67 for stoichiometric HA. The concentration of calcium can exist adjusted if substitution for calcium (strontium, magnesium, etc.) is required. Similarly, the phosphate concentration tin be adjusted and replaced with required corporeality of carbonate or silicate when carbonate or silicate commutation is desired. Fluoride or chloride substitute apatite tin be prepared by addition of fluoride or chloride ions in the reactions.

The next step of ceramic processing is to interruption downwardly the materials received from chemical synthesis, which is a solid aggregation of particles in a dried, filtered precipitate. The agglomerates take a deleterious result on the backdrop of the ceramic, and therefore need to be cleaved down by crushing and grinding. Milling is then used to farther reduce the particle size. Particle size reduction is vital for good sinterability, only the ability to handle the pulverisation is equally of import, as it ensures the powder flows properly and tin can be compacted practicably. Spray drying is a widely used method to transform powder to soft agglomerates for easy handling. Calcination, a heat treatment, is some other means of improving pulverisation handling.

The HA powder obtained tin can then be fabricated into dense or macroporous products using compaction (dice pressing, isostatic pressing, skid casting, etc.) followed by solid-state sintering. The properties of powder, such as morphology, surface surface area, mean particle size and particle size distribution, need to be adequately characterised, equally this will profoundly influence the handling and processing.

Consolidation or compacting is the final stage in the pulverisation preparation. The compacted or compressed body is usually sintered at temperatures of 950 to 1300   °C. The processing of densifying a pulverization compact without the presence of a liquid phase is chosen solid-land sintering. During solid-state sintering the material moves to eliminate the pores and open channels that be betwixt the grains of the compact, the crystals become tightly bonded together at their grain boundaries and the density, forcefulness, toughness and corrosion resistance of sintered textile increase greatly.

Read full chapter

URL:

https://world wide web.sciencedirect.com/science/article/pii/B9780857097125500016

Reference Electrodes

Timothy J. Smith , Keith J. Stevenson , in Handbook of Electrochemistry, 2007

4.3.2.1 Saturated Calomel Electrode (SCE)

Controlling redox procedure:

${\text{Hg}}_2{\text{Cl}}_2+2{\text{e}}^{-}\rightleftharpoons 2\text{Hg}+{\text{Cl}}^{-},E_{\text{Hg}|{\text{Hg}}_2{\text{Cl}}_2}^{\text{o}}=0.268\text{5}\text{versus NHE}\left({25}^{°}\text{C}\right)$

Mercury|mercury(I) chloride (as well mercurous chloride or calomel), abbreviated every bit Saturated Calomel Electrode (SCE), is the most widely used mercury RE (26). The preparation of this electrode, especially the purity of the mercury and the method of addition of mercury(I) chloride to the mercury, strongly affects the performance and potential exhibited. This RE can be very reproducible if produced and handled carefully. The potential of the mercury(I) chloride RE is divers by the chloride concentration in the filling solution, and can be calculated as shown below:

(4.3) $E_{\text{Hg}|{\text{Hg}}_2{\text{Cl}}_{\mathrm{two}}}=E_{\text{Hg}|{\text{Hg}}_2{\text{Cl}}_2}^{\text{o}}-\frac{RT}{F}\ln a_{{\text{Cl}}^{-}}$

This electrode displays hysteresis upon heating and cooling (27), and it is non recommended that the electrode exist used to a higher place 70 °C. Temperature furnishings are discussed in Section 4.8.ane.iii.

(a)

Electrode grooming

Mercury training. No special preparative steps are required if mercury of sufficient purity is used.

Hg₂Cl_ii preparation. High-purity Hg₂Cl₂ is bachelor commercially, or it can be produced by chemical atmospheric precipitation equally described beneath. The Hg₂Cl₂ must exist a finely divided powder (0.i–v μm) to produce a well-behaved RE.

Hg|Hg₂Cl_ii electrode preparation (run into Figure 4.xi). Method I (28). On adding the Hg_twoCl₂ to the dry mercury; it will rapidly form a pearly pare on the surface. Once the surface is completely covered, the addition of Hg_twoCl_ii is stopped, otherwise the electrode volition be sluggish. This interface must exist prepared prior to the introduction of filling solution for a stable potential to develop.

Figure iv.11. SCE active electrode torso: (A) method I; (B) method II.

Method II (29). Hg and Hg_twoCl₂ should be basis together with a few drops of KCl filling solution using a mortar and pestle to form a paste. The paste should exist placed in the tube, in direct contact with the Pt wire. Nigh 1 cm thick paste should exist used.

(b)

Filling solution

SCE—saturated KCl.

SSCE—saturated NaCl.

NCE—1N KCl.

(c)

Hg₂Cl_ii preparation

Chemical atmospheric precipitation (30). Virtually 1 one thousand of reagent-grade mercury(I) nitrate dihydrate, Hg₂(NO₃)_ii 2H₂O, should be mixed with 200 pl of concentrated nitric acid and ~20 ml of water. Add this solution dropwise for 2 min into a covered beaker containing approximately 100 ml of 0.one M HCl, using a magnetic stir bar to continuously stir the solution. After the improver is completed, stir the suspension for an additional hour. Allow the precipitate to settle, decant the supernatant solution, and repeat this twice to completely rinse the precipitate. Filter the precipitated mercury(I) chloride with a sintered glass crucible, rinsing quickly with four portions of cold distilled water, then transfer it to a vacuum desiccator. It is of import that the HCl used be gratis from traces of other halogens, otherwise the mercury(I) chloride produced will be contaminated with other mercury(I) halides, resulting in an RE with a mixed potential.

Electrochemical product. Electrochemically prepared Hg_twoCl₂ tin can be produced (xxx) in a similar manner as HgSO₄ described in the next department, but it is less stable than chemically precipitated material and therefore its preparation is not discussed further.

Read total chapter

URL:

https://www.sciencedirect.com/science/commodity/pii/B9780444519580500057

christopherting1950.blogspot.com

Source: https://www.sciencedirect.com/topics/chemistry/precipitation-chemical

Share this post