Silicate films

Polysilicates are effective in potable HW systems and provide threshold effect protection against hardness destabilization and red water. They also function by laying down a protective calcium silicate film. Polysilicates used for this type of application typically require a dose rate of 8 to 15 ppm Si02 above that of the natural orthosilicate found in the MU water. Where polysilicates are employed for dualtemperature and LPHW systems, however, the silicate reserve required is higher and ranges from 50 to 150 ppm. 

In our previous work, we reported that a new ALD precursor HfCl2[N(SiMe3)2]2, which contains Si in ligands, can be used to deposit hafhium silicate films using H2O as an oxidant but the Si content in the film was relatively low [4]. In the present work, two different approaches were performed to increase Si content and to improve the film properties. One is to use hydrogen peroxide as a stronger oxidant than water, and the other is to use tetra-n-butyl orthosilicate (TBOS, Si(0"Bu)4) as an additional Si source. 

Fig. 3. SIMS depth profiles of hafnium silicate films deposited at 200 C (a) using HfCl2[N(SiMej)2]2 and H2O, (b) using HfCl2[N(SiMe3)2]2 and H2O2, and (c) HfCl2[N(SiMe3)2]2, TBOS and H2O...

The low temperature ALD process for hafnium silicate films using HfCl2[N(SiMe3)2]2 and H2O was modified to improve the film properties by two different methods. With hydrogen peroxide, the silicon content in the film increased to Si/(Hf+Si)=0.2 at 2001 and the impurity levels decreased due to its strong oxidation effect. By introducing TBOS as an additional Si precursor, the silicon content in the film increased to Si/(Hf+Si)=0.5 at 200 °C and the hafiiium silicate films became fully oxidized with O/(Hf+Si)=2.0. 

The effect of pH on both clay swelling and fines production has been widely discussed(89-95). Little consensus is found in this literature. Suggested treatments range from application of fluoboric acid(96) to 15% KOH(92) solutions — both treatments are believed to create a protective silicate film that inhibits release of fines. Polyacrylate polymers can provide protection against swelling of smectite clays and shales(97-100). 

Various polymer matrices can be used as solid support into which pH indicator dye can be immobilized (cellulose, PVA, PVC). R. Makote and M.M. Collinson shows that also organically modified silicate films can be used for stable pH sensors37. 

Makote R., Collinson M.M., Organically modified silicate films for stable pH sensors, Analytica Chimica Acta 1999 394 195-200. 

E. Mei, A.M. Bardo, M.M. Collinson, and D.A. Higgins, Single-molecule studies of sol-gel-derived silicate films. Microenvironments and film-drying conditions J. Phys. Chem., B 104, 9973-9980 (2000). 

Vitreous silica is susceptible to attack by alkaline solutions, especially at higher concentrations and temperatures. For 5% NaOH at 95°C, although crazing may be evident, surface corrosion is only 10 Jim after 24 h (87). For 45 wt % NaOH at 200°C, dissolution proceeds at 0.54 mm/h (88). The corrosion rates in other alkaline solutions are Us ted in Table 3. Alkaline-earth ions inhibit alkaline solution attack on vitreous silica. Their presence leads to the formation of hydrated metal silicate films which protect the glass surface (90). 

Phosphates, molybdates, and (at high pH) silicates act as anodic inhibitors much as do alkalis, except that the iron oxides/hydroxides formed on anodic sites then contain some PO43-, M0O42-, or Si044- ( basic iron phosphates, etc.). These inhibitors require the presence of 02 to produce basic iron(III) phosphate, molybdate, or silicate films, whereas oxidizing anions such as chromates and nitrites oxidize Fe2+ (aq) rapidly to insoluble iron(III) oxides on anodic sites. Dianodic inhibitors combine complementary inhibition mechanisms for example, sodium triphosphate may be used with sodium chromate, or sodium molybdate with NaN02. 

The Ce amide [Ce N(SiMe3)2l3l has been used as a source for Sr S Ce thin film generation by atomic layer epitaxy. The Lu analogue (with H2O or O3) has been employed for deposition of Lu silicate films. 

By preparing polycyclic aromatic hydrocarbon nanocrystals grown in porous silicate films, Botzung-Appert et al. [57] have prepared potential fluorescent sensors based on electronic energy transfer quenching to an acceptor... 

The zinc silicate film is porous and readily absorbs corrosive electrolyte. The film is harder, stronger than organic zinc-rich films. These films have better resistance to solvent and heat than the organic zinc-rich primers and may be used for tank linings and other applications up to 400°C. 

Corrosion protection measures involve washing the metal object with reagents such as sodium sulfate or silicate, which form lead sulfate or lead silicate film. Whenever galvanic effects are envisaged use of insulation is recommended. Sodium silicate has been successfully used to inhibit release of lead from the solder in copper pipes carrying domestic water supplies. 

Phillips KS, Wilkop T, Wu JJ, Al-Kaysi RO, Cheng Q (2006) Surface plasmon resonance imaging analysis of protein-receptor binding in supported membrane arrays on gold substrates with calcinated silicate films. J Am Chem Soc 128 9590-9591... 

Figure 4.11 Experimental SAW frequency transients during exposure to methanol iplpo = 0.05) for 360 nm-thick polysiloxane film deposited on bare quartz ( ) and on a 150 nm-thick porous silicate film on the quartz substrate ( ). The larger initial fiequency drop with the porous film is due to permeation of methanol through the polysiloxane film and adsorption onto the surfaces of the underlying porous film. Data points are overlapping at early times. (Reprinted with permission. See Ref. (86).)...

Using SCF processes such as these, polymers and inorganic materials have been formed into films, fibres and spherical particles. For example, mesoporous silicate films and mesoporous silica hollow spheres have both been recently prepared using SCCO2 based technologies. ... 

Well ordered mesoporous silicate films were prepared in supercritical carbon dioxide.[218] In the synthesis in aqueous or alcoholic solution, film morphology of preorganized surfactants on substrate cannot be fully prescribed before silica-framework formation, because structure evolution is coincident with precursor condensation. The rapid and efficient preparation of mesostructured metal oxides by the in situ condensation of metal oxides within preformed nonionic surfactants can be done in supercritical CCU- The synthesis procedure is as follows. A copolymer template is prepared by spin-coating from a solution containing a suitable acid catalyst. Upon drying and annealing to induce microphase separation and enhance order, the acid partitions into the hydrophilic domain of the template. The template is then exposed to a solution of metal alkoxide in humidified supercritical C02. The precursor diffuses into the template and condenses selectively within the acidic hydrophilic domain of the copolymer to form the incipient metal oxide network. The templates did not go into the C02 phase because their solubility is very low. The alcohol by-product of alkoxide condensation is extracted rapidly from the film into the C02 phase, which promotes rapid and extensive network condensation. Because the template and the metal oxide network form in discrete steps, it is possible to pattern the template via lithography or to orient the copolymer domains before the formation of the metal oxide network. 

Rassaei, L., Sillanpaa, M., Milson, E.V., Zhang, X., and Marken, F. 2008. Layer-by-layer assembly of Ru + and SigOjo " into electrochemically active silicate films. Journal of Solid State Electrochemistry 12, 747-755. 

The low silicate/soda ratio (2.0) sodium sihcate solution dries in air at room temperature very slowly forming a very viscous, smooth, clear film. At higher ratio (2.4) drying is faster and the silicate film obtained shows some cracks. At very high ratios (3.25 and 4.0) sodium... 

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