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Analysis Software Data Analysis Software for Coatings Service Life Prediction Programs to Estimate UV Dosage and Damage of Coatings This system of programs is concerned with estimating the damage ensuing from exposure of specimens in dry and humid atmospheres to sunlight-like radiation. Because damage occurring during such exposures can arise from both photolytic degradation and hydrolysis (and perhaps other "dark" reactions), provision has been made to separate these effects. Photolytic damage is expected to be mainly a function of "dosage", i.e., the amount of radiation remaining in the specimen as sunlight or similar radiation is incident on the specimen. Photolytic damage is expected to be wavelength specific, partly because different wavelengths contain different amounts of energy per photon and partly because the chromophore changes as the wavelength of the incident radiation is varied over tens of nanometers. Photolytic damage is to a first approximation independent of time. Hydrolysis is attainment of an equilibrium specified by the concentrations of hydrolysable groups and water in the material (typically expressed in moles/Liter) and of the temperature of exposure. Because hydrolysis is a relatively slow process, it, unlike photolytic damage, is a function of time. In the experiments carried out to date, damage has been monitored quantitatively by changes in IR spectra. This is certainly adequate for the purposes, but other quantitative evidence of damage could be used. The dosage was estimated from UV spectra of the lamps and the filters (used to isolate a particular wavelength range), and from the UV absorption of the specimens themselves. These quantities were observed to change with time. For example, the lamps aged. The experimental procedure is therefore to monitor the changes (using the appropriate UV spectra) over short ranges of time over which any change is presumed to be linear. Once the output of the lamp and the transmission of the filter are known, the amount of radiation incident on a specimen can be estimated. From the specimen absorbance, the transmission of the specimen is known. Radiation incident on the specimen but which does not emerge at the other side of the specimen is presumed to have been absorbed by the specimen and is taken as being the apparent dosage. Whether to consider that all the absorbed radiation leads to degradation or whether some radiation is considered to be "harmlessly" absorbed by degradation products rather than by the original coating material is a choice offered by the programs. A model must successfully account for effects seen in the experiments before it can be used to generate prophesies. But before a model can be proposed, the effects must be visible, i.e., above the noise. The noise levels in the measurements are very important, first in determining whether or not the effects of the experiments are discernible and second in determining the applicable range (in time or radiation level or hydrolysis level) of any prophesy. The programs have been designed to be complete yet relatively easy to use. They run under 32-bit Windows, i.e., Windows 95 or Windows NT. The file structure of the database tables is MS FoxPro. This structure was chosen because it is widespread, has each table in a physically different file and is therefore quite flexible, and allows the easy manipulation of so-called memos or "Blobs" - collections of binary data which can be stored compactly on the computer disk yet read into computer memory extremely quickly. When first approaching the programs, one should bear in mind that, although the desire throughout industry is for a quick, cheap, simple and dirty yet completely relevant test, such tests must concentrate on the most important parameters. That can only be done in a confident fashion when the response of a material to a wide range of factors has been established so that the unimportant factors can be dropped. Anything less is a simple guess. These programs allow manipulation and processing of the massive amounts of data required to carry out comprehensive tests.   NIST Moisture and Heat Transfer Model (MOIST) This computerized model employs the NIST Moisture and Heat Transfer Model (MOIST) to predict the temperature and relative humidity (or moisture content) of a polymer coating exposed to outdoor weather conditions.  The rate of degradation of a polymer coating is caused primarily by climate stress of sunlight, temperature, and water (dew, humidity, and rain).  For a coating that fails through a loss of appearance, the primary degradation and relative humidity serving as accelerants.  The ability to accurately predict the temperature and relative humidity of a polymer coating will permit a more precise evaluation of photo-degradation accumulation process and its effect on service life. The MOIST model has shown to provide reasonable predictions of the temperature and relative humidity of polymer coatings exposed to outdoor conditions in the field.  The model predicted wetting of polymer coatings during periods having dew condensation.  The paper titled "Predicting the Temperature and Relative Humidity of Polymer Coatings in the Field," by D.M. Burch and J.W. Martin was published in the ACS Symposium Series 722, Chapter 7, "Service Life Prediction of Organic Coatings: A Systems Approach, American Chemical Society, Washington, DC (1999).   Statistical Analysis of Spectral UV Irradiance Data A statistical model has been used in the statistical analysis of spectral UV irradiance data collected at Ocean City, New Jersey.   The goal was to find a statistical model to study the dependencies among wavelengths.  2nm half-band pass solar spectral ultraviolet measurements were made at twelve-minute intervals for each of 18 wavelengths from 290.2 to 323.6 nm from April to September 1996.  Two data sets, the daily maximum and the hourly mean irradiance were created from the raw data.  Auto-regressive models and transfer function models were used for both data sets.  For the analysis 305.9 nm was chosen as the explanatory variable to predict 291.5 nm which was the response variable.  For the final auto-regressive models R2 values of .89 and .96 were obtained for the daily maximum and hourly mean data respectively.  The forecasts from both models were reasonable good.  This study will provide variable insight into design of future spectral radiometers for characterizing solar ultraviolet radiation. The results of the study has been published in a paper titled "Statistical Analysis of Spectral UV Irradiance Data Collected at Ocean City, New Jersey," ACS Symposium Series 722, Chapter 5, "Service Life Prediction of Organic Coatings: A Systems Approach, American Chemical Society, Washington, DC (1999).   For additional information and requests for software, contact: Walter E. Byrd National Institute of Standards and Technology 100 Bureau Drive, Stop 8621 Gaithersburg, MD 20899-8621 Telephone: 301-975-6701 Fax: 301-990-6891 Email: walter.byrd@nist.gov

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